# Fileset

[Merino_2023_2D_Mater._10_021001.pdf](https://mdr.nims.go.jp/filesets/9765ee9b-8f97-402f-9824-8acd8345ddcb/download)

## Creator

Rafael Luque Merino, Paul Seifert, José Durán Retamal, Roop K Mech, [Takashi Taniguchi](https://orcid.org/0000-0002-1467-3105), [Kenji Watanabe](https://orcid.org/0000-0003-3701-8119), Kazuo Kadowaki, Robert H Hadfield, Dmitri K Efetov

## Rights

[Creative Commons BY Attribution 4.0 International](https://creativecommons.org/licenses/by/4.0/)

## Other metadata

[Two-dimensional cuprate nanodetector with single telecom photon sensitivity at T = 20 K](https://mdr.nims.go.jp/datasets/85f94b05-69eb-465a-9713-4f62720014b5)

## Fulltext

Two-dimensional cuprate nanodetector with single telecom photon sensitivity at T = 20 K   2D MaterialsLETTER • OPEN ACCESSTwo-dimensional cuprate nanodetector with singletelecom photon sensitivity at T = 20 KTo cite this article: Rafael Luque Merino et al 2023 2D Mater. 10 021001 View the article online for updates and enhancements.You may also likeTelecom wavelength single photonsourcesXin Cao, Michael Zopf and Fei Ding-An integral gated mode single photondetector at telecom wavelengthsZhengjun Wei, Peng Zhou, Jindong Wanget al.-Superconducting nanowire single-photondetectors: physics and applicationsChandra M Natarajan, Michael G Tannerand Robert H Hadfield-This content was downloaded from IP address 144.213.253.16 on 25/03/2023 at 07:07https://doi.org/10.1088/2053-1583/acb4a8/article/10.1088/1674-4926/40/7/071901/article/10.1088/1674-4926/40/7/071901/article/10.1088/0022-3727/40/22/011/article/10.1088/0022-3727/40/22/011/article/10.1088/0953-2048/25/6/063001/article/10.1088/0953-2048/25/6/0630012D Mater. 10 (2023) 021001 https://doi.org/10.1088/2053-1583/acb4a8OPEN ACCESSRECEIVED26 October 2022REVISED11 January 2023ACCEPTED FOR PUBLICATION19 January 2023PUBLISHED9 February 2023Original content fromthis work may be usedunder the terms of theCreative CommonsAttribution 4.0 licence.Any further distributionof this work mustmaintain attribution tothe author(s) and the titleof the work, journalcitation and DOI.LETTERTwo-dimensional cuprate nanodetector with single telecomphoton sensitivity at T = 20 KRafael Luque Merino1,8,9,∗, Paul Seifert1,2, José Durán Retamal1,3, Roop KMech1,8,9, Takashi Taniguchi4,Kenji Watanabe5, Kazuo Kadowaki6, Robert H Hadfield7 and Dmitri K Efetov1,8,9,∗1 ICFO—Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Castelldefels, Barcelona 08860, Spain2 Institute of Physics, Faculty of Electrical Engineering and Information Technology (EIT 2), Universität der Bundeswehr München,Neubiberg 85577, Germany3 Catalan Institute of Nanoscience and Nanotechnology (ICN2), BIST & CSIC, Barcelona 08193, Spain4 International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan5 Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan6 University of Tsukuba, 1-1-1 Tennodai, Tsukuba-shi 305-8572, Japan7 James Watt School of Engineering, University of Glasgow, Glasgow, United Kingdom8 Fakultät für Physik, Ludwig-Maximilians-Universität, Schellingstrasse 4, 80799 München, Germany9 Munich Center for Quantum Science and Technology (MCQST), München, Germany∗ Authors to whom any correspondence should be addressed.E-mail: rafael.luque@icfo.eu and dmitri.efetov@lmu.deKeywords: 2D, cuprate, nanodetector, telecom, photon, nanowire, He-FIBSupplementary material for this article is available onlineAbstractDetecting light at the single-photon level is one of the pillars of emergent photonic technologies.This is realized through state-of-the-art superconducting detectors that offer efficient, broadbandand fast response. However, the use of low TC superconducting thin films limits their operationtemperature to approximately 4 K and below. Here, we demonstrate proof-of-conceptnanodetectors based on exfoliated, two-dimensional cuprate superconductor Bi2Sr2CaCu2O8-δthat exhibit single-photon sensitivity at telecom wavelength at a record temperature of T = 20 K.These non-optimized devices exhibit a slow (∼ms) reset time and a low detection efficiency(∼10−4). We realize the elusive prospect of single-photon sensitivity on a high-TC nanodetectorthanks to a novel approach, combining van der Waals fabrication techniques and a non-invasivenanopatterning based on light ion irradiation. This result paves the way for broader application ofsingle-photon technologies, relaxing the cryogenic constraints for single-photon detection attelecom wavelength.Superconducting nanowire single-photon detectors(SNSPD’s) constitute an established technology forbroadband, sensitive and fast detection of faint opticalsignals [1–3]. These detectors, based on low Tcsuperconducting thin films such as NbN or WSi,provide high efficiency [4], fast response (∼ ns)[2, 3] and excellent timing resolution (∼ ps) [5].SNSPD’s can be integrated in free-space and fiber-coupled architectures [1, 2], aswell as planar photoniccircuits [6, 7]. However, their operating temper-ature is usually limited to T ≤ 4 K by the Tcof the thin films. To date, the highest operatingtemperature for an SNSPD is 11 K, demonstratedin a MgB2 nanostrip [8]. Expanding single-photondetection to higher operating temperatures, longerwavelengths and faster response motivates the searchfor new material platforms [9–11]. In particular, vander Waals (vdW) heterostructures of 2D materials[12–15] and high-Tc superconductors [9, 16–24]have received interest as candidates for the devel-opment of next-generation SNSPD’s with increasedcapabilities.Cuprate superconductors are natural candidatesto push SNSPD technology to higher temperatures[9]. A cuprate-based SNSPD could operate aboveliquid nitrogen temperatures (77 K) offering acritical technological advantage. Fabrication ofcuprate detectors has proven to be very challen-ging, as cuprates degrade rapidly under ambientconditions. Despite extensive research efforts, mostcuprate nanostructures exhibit flux-flow behaviourcharacterized by smooth current–voltage (I–V)© 2023 The Author(s). Published by IOP Publishing Ltdhttps://doi.org/10.1088/2053-1583/acb4a8https://crossmark.crossref.org/dialog/?doi=10.1088/2053-1583/acb4a8&domain=pdf&date_stamp=2023-2-9https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/https://orcid.org/0000-0003-3701-8119https://orcid.org/0000-0002-8084-4187https://orcid.org/0000-0001-5862-0462mailto:rafael.luque@icfo.eumailto:dmitri.efetov@lmu.dehttp://doi.org/10.1088/2053-1583/acb4a82D Mater. 10 (2023) 021001characteristics that preclude SNSPD operation [16,22, 23]. Sharp and hysteretic transport character-istics, as those of conventional SNSPD thin films,were reported for high-quality YBa2Cu3O7-δ (YBCO)nanowires along with the observation of dark counts[18, 19, 21]. To date, conventional fabricationapproaches based on lift-off methods or heavy ionmilling have not realized the prospect of a cuprateSNSPD.We explore an alternative approach based on exfo-liated, 2D cuprate Bi2Sr2CaCu2O8-δ (BSCCO). Novelfabrication methods allow us to harness the pristinesuperconducting properties of few-layer BSCCO[24–26]. We report multiple nanostructures withsharp, hysteretic I–V characteristics combined withhigh Tc (70–80 K). Optoelectronic measurementsof the BSCCO nanostructures reveal single-photonsensitivity up to a record temperature of T = 20 K.The detection speed and efficiency remain low forthese proof-of-concept cuprate nanodetectors.1. Results and discussion1.1. Device fabrication and transportcharacterizationFigure 1(a) summarizes the detector concept and fab-rication. We fabricate vdW heterostructures of few-layer BSCCO encapsulated with a top hBN insidean Ar-filled glovebox [27]. We use a bottom con-tact approach with thin metallic electrodes to bypasslift-off methods, which lead to oxidation of few-layerBSCCO. In order to preserve superconductivity inBSCCO nanostructures, we use a helium focusedion beam (He-FIB) to pattern our BSCCO/hBNheterostructures [28]. The doping level (and elec-tronic properties) of few-layer BSCCO can be locallymodified by light He-ion irradiation [29–31]. Dir-ect patterning of insulating BSCCO areas can restrictthe supercurrent to flow exclusively along channels ofcrystalline, non-irradiated BSCCO that preserve highTc. Importantly, for low ion doses the He-FIB irradi-ation does not etch through the encapsulating hBNlayer (see figure S4). This non-invasive patterningtechnique allows us to produce high-quality nano-structures based on 2D BSCCO flakes that remainprotected by the encapsulating hBN. This methodalso provides very high lateral resolution, allowing thewriting of complex patterns with ∼ nm resolution.The left inset in figure 1(a) shows an scanning elec-tron microscopy (SEM) image of a He-FIB definednanostructure in our BSCCO/hBN stacks. This deviceis 250 nm wide and 2.7 µm long. See Methods andsections S1 and S2 of the SI for further details on thedevice fabrication.We study the transport properties of the fab-ricated BSCCO nanostructures and compare themto pristine BSCCO flakes. In figure 1(b) we presenttemperature dependent measurements of the two-terminal resistance R, normalized to its value at 120 K(R120K) for three BSCCO/hBN nanopatterned detect-ors and an exfoliated, unpatterned BSCCO flake (ref-erence sample). All the curves show clear supercon-ducting transitions, where R/R120K drops to close to0 resistance, with a residual resistance value stem-ming from the contact resistance in this two-terminaldevice. The critical temperature of the BSCCO nano-structures Tc, defined from the mid-point of thesuperconducting transition, ranges between 60 and80 K. The lowered Tc and broadened SC transitionof the patterned flakes likely derive frommicroscopicdisorder and/or He-ion implantation [30, 31]. Still,the critical temperatures remain close to their nom-inal value and near liquid nitrogen temperatures.The upturn of the resistance below Tc stems fromcontact resistance at the BSCCO/Au interface form-ing a Schottky barrier. For two-terminal measure-ments with low excitation current (10–100 nA inthis measurement) the contact resistance contribu-tion becomes sizable. When applying a DC offset cur-rent, as done below, this Schottky barrier is greatlylowered.Figure 1(c) shows the I–V characteristics of theBSCCO nanostructures for different temperatures,and the inset shows the corresponding colour plot forthe full temperature range. The I–V curve atT = 10 Kfeatures an abrupt transition to the resistive state ata critical current. The combination of high Tc andlow critical current Ic proves that the nano-patterningconfines the supercurrent into a narrow, pristineBSCCO channel, as the intrinsic Ic for an unpatternedBSCCO flake is several orders of magnitude larger.The critical current density of the nano-constrictionis JC ∼ 7x106A cm−1, comparable to previous reportson high-quality nanowires based on YBCO thin films[18, 19]. The appearance of a single, well-definedvoltage jump at Ic reflects a robust superconduct-ing state of the undamaged channel in the BSCCOnanoconstriction. As T increases, the I–V character-istics become flux-flow like. However remarkably, thesharply transition at Ic persists up to T = 30 K.Strikingly we observe a strong hysteresis in the I–V curves with respect to the sweeping direction of thebias current Ib, as shown in figure 1(d) at T = 20 K.As I is decreased below Ic, the superconducting statein the nanostructure is not recovered. Instead, thenanowire switches back into its superconducting stateat a lower retrapping current Ir. The occurrence of thehysteresis is a linked to the sharp I–V characteristics atIc and the high normal state resistance in the BSCCOnanostructure [18–21]. It also intricately depends onthe thermal properties of the superconducting devices[20]. In our nano-structured BSCCO constrictions,the thermal conductance is reduced both in-plane,across the disordered irradiated BSCCO regions [30],22D Mater. 10 (2023) 021001Figure 1. Two-dimensional superconducting cuprate nanowires for photodetection. (a) Illustration of the detector concept. Ahigh-Tc superconducting BSCCO flake is encapsulated with hBN and then nanopatterned using a focused He-ion beam. Theresulting nanostructure is current-biased (Ib) in a two-terminal configuration. Left inset shows an SEM image of the nanowire inDevice A, scale bar has 1 µm length. Right inset depicts a schematic cross-section of the vdW heterostructure. (b) Two-terminalresistance vs. temperature of the BSCCO nanostructures. All curves have been normalized to the resistance value at 120 K, beforethe superconducting transition. Black curve shows the four-terminal resistance for a reference, unpatterned BSCCO flake. For allnanostructures, Tc ranges between 60–80 K. (c) I–V characteristics of device A for increasing temperature. The abrupt voltagejump at 10 K evolves towards a smooth transition at 40 K. Inset depicts the superconducting phase diagram for this device.Overlayed plot indicates the extracted Ic (T) dependence. Beyond 50 K, the smooth I–V characteristics preclude a reliableextraction of Ic. (d) I–V characteristic for device A at T = 20 K, exhibiting a sharp voltage jump along with a well-definedhysteresis loop. Vertical offset between red and blue traces is due to Joule heating effects in the DC measurement. Inset shows Ic(T) and Ir (T). Hysteresis loop remains finite up to T = 30 K.and out-of-plane, as the 2D flake lies on the substratewithout any lattice matching [32]. Figure S5 in the SIdemonstrates the ubiquity of hysteretic behaviour inthese nanostructures.Such hysteretic behaviour is a key requirementfor SNSPD. The nucleation of a self-sustaining resist-ive region after photo-absorption induces Joule heat-ing, precluding the recovery of the superconduct-ing state when approaching Ic from above. Super-conducting nanowire detectors are kept well belowTc and biased close to their critical current Ib ∼ Ic.Photo-induced hotspots are nucleated and grow dueto Joule heating leading to a thermal runaway ofthe detector, which latches into the resistive stateuntil the bias current is shunted [33]. Thus, a voltagedrop takes place in the shunting circuit due to theresistive switching of the nanodetector. Remarkably,the observed hysteretic behaviour of the BSCCOnano-constrictions persists up to T = 30 K (seefigure 1(d)) highlighting their potential as supercon-ducting nanodetectors with single photon sensitivityand high operating temperature.1.2. Photo-induced switching events in the BSCCOnanostructureWe now characterize the optoelectronic response ofthe BSCCO nano-constriction at a temperature ofT = 20 K, where figure 2(c) shows a sketch of thereadout circuit and section 5 of the SI illustrates thecomplete optoelectronic setup. The BSCCO nano-constriction is current-biased close to its switchingcurrent Ib∼ 0.97 Ic and connected in parallel to a loadresistor RLoad. The load resistor shunts the currentonce the nanostructure turns resistive, and enablesfree-running detection as the device self-resets aftera time τ . We illuminate the biased BSCCO nanode-tector using a CW laser at a telecom wavelength ofλ = 1550 nm, and monitor the voltage drop across32D Mater. 10 (2023) 021001Figure 2. Photo-induced voltage signal in Bi2212 nanowires. (a) Photo-induced voltage drop at the load resistor over time for50 pW optical power (black) and under no illumination (grey). Black trace is offset by 0.2 mV for clarity. Traces recorded at T =10.8 K, Ib = 0.98 Ic. (b) Oscilloscope trace of the voltage trace generated by a switching event. The obtained decay timeis τ = 712 µs. Switching rate of the detector along the red dashed line in (a). Optoelectronic measurement schematic and spatialphotovoltage map, overlayed with SEM image of the nanowire. The nanowire is biased close to its critical current Ib ∼ Ic.(d) Switching rate of the detector along the red dashed line in (c).RLoad over time. We observe clear photo-inducedclicks that appear only at elevated photon fluxesare absent in dark conditions. Figure 2(a) illustratesthe appearance of these switching events under laserillumination.Using an oscilloscope we measure the time-domain traces of the photo-induced clicks. We findthat each click (figure 2(b)) features a fast rise time(few µs) and a slow decay time τ = 712 µs, obtainedfitting the falling edge of the pulse. The full recov-ery time of the device lasts about 2 milliseconds.The observed τ is much slower than the resettime of conventional SNSPD’s(∼ ns) [2, 3] andthe reported intrinsic photoresponse time of cupratesuperconductors [26, 34]. This slow relaxation time isconsistent across all devices (figure S7).We believe the observed timescale to be anextrinsic effect, as the hotspot dynamics in a BSCCOnanostructure are expected to be orders of mag-nitude faster. In previous work, we found the intrinsicthermal relaxation time of BSCCO bolometers to bein the order of nanoseconds [24]. These limitationslikely stem from a non-optimized electrical circuit,which does not include a Bias Tee to isolate the bias(DC) and readout (AC) paths. It is worth noting thatthe contact resistance in these devices also sets somelimitations on the choice for parallel load resistors, aswell as energy dissipation and capacitance in the con-tact interfaces that may affect the shunting dynamics.We identify the photo-active area by scanning thelaser beam across the device and measuring with theAC Lock-in technique. As expected, peaks at the nar-rowest area of the device where the superconduct-ing state is closest to its transition. In figure 2(c), weoverlay the photo-voltage mapping Vph with a SEMimage of the device. Having located the detector’s act-ive area, we now measure its switching rate using aZurich UHLFI as a fast voltmeter. Figure 2(d) showsthe measured switching rate of the detector in a scanacross the nano-constriction (indicated by the reddashed line in figure 2(c)). As the laser spot illu-minates the ‘wings’ of the nanostructure, the switch-ing rate is constant and increases five-fold at thenanostructure’s narrowest, most sensitive area. Thehigh spatial sensitivity of the switching rate indicatesthat the clicks do not originate from a heating,42D Mater. 10 (2023) 021001Figure 3. Single photon sensitivity at T = 20 K. (a) Switching rate and dark count rate of device A at 20 K for increasing biascurrent. Vertical segments indicate the bias points examined in (c). (b) Distribution of the photo-induced switching events indevice A for increasing optical power at 20 K,Ib = 0.97Ic. The switching event distribution is consistent with Poissonian statisticsof few-photon events. Dashed lines illustrate the best-fitting Poissonian distribution. Each bin is a 60 millisecond time window.(c) Normalized switching rate versus normalized optical power for two different bias conditions. Each magnitude is normalized toits maximum value. The switching statistics for Ib = 0.97Ic follow a linear dependence, indicating single-photon sensitivity of thenanodetector. For Ib = 0.85Ic, the switching rate follows a power law of exponentm≈ 3, indicating multi-photon sensitivity ofdevice A at lower bias currents. Switching events recorded at 20 K. The maximum switching rate for Ib = 0.97Ic and Ib = 0.85Icare 450 Hz and 38 Hz, respectively. Maximum optical power is 100 pW.bolometric effect. Instead, this observation pointstowards Cooper pair breaking and a subsequent ava-lanche effect leading to nanowire switching.1.3. Statistics of the switching events andsingle-photon sensitivityWe characterize the sensitivity of our BSCCO nan-odetectors by studying the switching rate as a func-tion of applied bias current Ib and incident opticalpower P. All following measurements are performedat T = 20 K. In order to reliably discern switch-ing events from the noise floor, we define a voltagethreshold based on the detector’s switching statist-ics under no illumination at each Ib. The followingdiscussion is consistent for different choices of thisthreshold. The protocol to define the threshold is fur-ther detailed in section S7 of the SI.First, we fix the optical power on the detectorand vary the applied bias current Ib. For SNSPD-type detectors, the sensitivity and detection efficiencystrongly depend on Ib, increasing as Ib approaches Ic.These detectors reach single-photon sensitivity for IbIc, at the cost of increased false counts due to thermalfluctuations and/or stray photons. Figure 3(a) showsthe switching rate of the detector for increasing Ibunder P = 60 pW illumination and in dark condi-tions. We find that the switching rate of our BSCCOnanowire rapidly grows for Ib ⩾ 0.9 Ic. A full sat-uration of the detector’s switching rate, indicative offull internal quantum efficiency, was not observed.The growth of the switching rate slows down signi-ficantly for Ib ⩾ 0.97 Ic, suggesting that a full satura-tion could be achieved. The non-saturating switchingrate is common in nanoconstriction detectors wherethe device geometry leads to a position-dependent Ic.Thus, as Ib is increased the effective active area of thenanodetector changes and the switching rate does notfully saturate [35, 36].The bias current dependence of the dark switch-ing events resembles that of the total switching rate.This suggests that the dark count rate stems from theabsorption of stray photons, likely coming from thethermal emission from the room-temperature object-ive. As the bias current is increased, the switching rategrows surpasses the dark switching rate as the detectorbecomes more sensitive to the high flux of 1550 nmphotons.We analyze the statistics of the observed switch-ing events fixed temperature of T = 20 K and forvarying optical powers and bias current configura-tions. We record switching events in 5 min windows.The distribution of few-photon detection events inSNSPD’s can be described through Poissonian stat-istics, as the switching events are rare and uncorrel-ated. In figure 3(b), we illustrate the distribution ofswitching events at Ib = 0.97 Ic for increasing opticalpower. At low optical power (1 pW), very few clicksare observed and the switching events exhibit a highlyskewed Poissonian-like distribution. As the opticalpower is increased, the switching rate of the detectorincreases and the distribution evolves towards highermean values µ and variances σ2. The distribution ofthe observed clicks is compatiblewith Poissonian stat-istics arising from few-photon absorption events inthe BSCCOnanodetector. The bins in figure 3(b) cor-respond to 60 millisecond time windows.Lastly, we present the power dependence of theswitching rate of our BSCCO superconducting nan-odetectors. As the sensitivity of SNSPD-type detect-ors depends strongly on the applied bias current[36, 37], we study the sensitivity of our devices attwo different bias conditions, highlighted by the ver-tical colored segments in figure 3(a). The low-bias52D Mater. 10 (2023) 021001condition (orange) corresponds to Ib = 0.85 Ic andthe high-bias condition (blue) is Ib = 0.97 Ic.Figure 3(c) shows the power dependence ofthe switching rate in the high and low-bias condi-tions. The few-photon sensitivity of an SNSPD-typedetector can be inferred from the power depend-ence of its switching rate. The probability to detectk photons (switching event caused by simultan-eous absorption of k photons) is given by P [k]∝e−λλk/k!, where λ is the mean (absorbed) photonnumber in the detector per unit time. For a single-photon detector the switching rate should increaselinearly with incident power P [k= 1]∝ λ. Weobserve a linear (m= 0.95≈ 1) power dependenceof the switching rate in the high-bias condition(Ib ∼ 0.97 Ic). When the bias current is lowered,the switching rate of the BSCCO detector is stronglyreduced and exhibits a markedly different depend-ence. For low bias (Ib ∼ 0.85 Ic), the dependencefalls closer to a power law of exponent m= 2.93≈ 3,indicative of multi-photon (two and three-photon)events dominating the detector’s response. Exten-ded data supporting this observation is presented insection 8 of the SI.This behaviour is consistent with a single-photonsensitivity of the BSCCO nano-constrictions at T =20 K for telecom photons, where the observation ofmulti-photon sensitivity at lower bias current fur-ther supports the SNSPD-like characteristics of theBSCCO nanodetectors [36, 37]. As discussed before,far from the superconducting transition, the energydeposited by a single absorbed photon is not enoughto trigger a switching event and multiple simultan-eous photons need to be absorbed. Multi-photonsensitivity is rarely observed in commercial SNSPD’s,as large fill factor designs make simultaneous absorp-tion of multiple photons in the same area extremelyunlikely. Instead, for detectors featuring constric-tions, these events are more prominent and theirphoton sensitivity is strongly bias-dependent [36]. Inour case, the CW nature of the illumination also pro-motes multi-photon contributions to the switchingrate.The detection efficiency can be roughly estimatedusing the incident power, number of switching eventsand the optical cross-section of the detector. Fur-ther details on the efficiency estimation are providedin section S11 of the SI. In the high-bias condi-tion where single-photon sensitivity is observed, weestimate a lower bound for the detector efficiencyof η ≈ 3.3× 10−4. Several factors may contribute tothis low figure-of-merit: (a) due to the large super-conducting gap of BSCCO, the energy of a singletelecom photon would only break around a dozenCooper pairs. The resulting quasiparticle generationprocess that leads to a resistive switching may there-fore not be efficient [38]. (b) the effective (elec-tronic) width of the active regionmay be smaller thanestimated, as the microscopic details of the irradi-ation are unknown. (c) Another plausible scenario isthe existence of a highly efficient, nanometric regioninside the detector where photodetection takes place.Assuming an absorption coefficient of 17% [39] andfull quantum efficiency, we can estimate the area ofsuch a region to be∼ 80 nm2. This scenario is remin-iscent of switching events around local microscopicdefects and cannot be ruled out.The microscopic details of the physical processesoccurring after photo-absorption in the BSCCOnanostructures remain an open question. Eventhough our experiment does not probe the detectionmechanism of this system, our results are consist-ent with an agnostic hotspot model. In this scenariothe photon energy is absorbed by the superconduct-ing condensate, locally breaking Cooper pairs. TheCooper pair density is suppressed in the hotspot,precluding the supercurrent from flowing across thefull width of the nanostructure. The hotspot growsthrough avalanche effect due to Joule heating, even-tually causing the entire nanowire width to becomeresistive. This avalanche effect can give rise to macro-scopic voltage signals from a microscopic perturba-tion (single-photon absorption).The observation of strong hysteresis in the I–Vcharacteristics of our nanodetectors supports thenucleation of a self-sustaining hotspot. We observecomplete latching of the nanodetector after photo-absorption in the absence of a shunting circuit, prov-ing that the avalanche effect can be triggered optically.In literature, hotspots in cuprate thin films have beenobserved directly through thermal imaging [40] andindirectly through transport measurements [41, 42].The large thermal conductivity κ of cuprates has lim-ited cuprate nanostructures to the flux-flow regime,where an avalanche effect does not take place and ulti-mate sensitivity cannot be achieved. Suppression ofthe thermal conductance in these 2D vdWnanostruc-tures could explain the existence of a self-sustaininghotspot. This behaviour is not expected for Au-capped thin films studied in other reports [16, 18].We believe that tailoring of thermal and electronicproperties will be key for developing next-generationquantum sensors based on cuprate nanostructures.Achieving this while preserving the superconduct-ing properties of the material may prove challen-ging. Possible advances of the device fabrication arediscussed in section 4 of the SI. Other avenues toenhance detector performance include the designof optical gratings and nanoantennas to boost theabsorption in the material. The integration in planarphotonic architectures, highly compatible with 2Dmaterials, could also boost the device’s efficiency[6, 7, 24]. Lastly, the material properties of BSCCOalso show promise for detection of single-photonsat shorter wavelengths, as well as its application forphotodetectors resilient to high magnetic fields [43].62D Mater. 10 (2023) 021001In summary, we report single-photon sensitivityat T = 20 K for telecom photons in nanostruc-tures based on exfoliated 2D cuprate superconductorBSCCO. This proof-of-concept nanodetector sets thehighest operation temperature reported to date foran SNSPD-type detector, establishing BSCCO-basedvdW nanostructures as a promising platform fornext-generation quantum sensors.2. NoteDuring the elaboration of this text, we becameaware of a similar work published in arXiv afterours. This complementary work by Charaev et alemploys similar fabrication methods, highlightingthe potential for next-generation SNSPD’s based onhigh-temperature superconductors. The reference isCharaev et al arXiv:2208.05674 (2022).3. Methods3.1. Device fabricationWe fabricate our samples through the dry-transfertechnique inside an Ar-filled glovebox (H2O,O2 < 0.8 ppm). Few-layer flakes of optimallydoped BSCCO (10–20 nm) are exfoliated usingpolydimethylsiloxane (PDMS) stamps, then trans-ferred onto pre-patterned metallic electrodes (Ti/Au,2/20 nm). BSCCO flakes are then encapsulated usingpre-selected thin hBN flakes (∼ 20 nm). We probethe two-terminal resistance of our devices using aprobe-station inside the glovebox. The entire processis performed in less than 20min to avoid degradationof few-layer BSCCO flakes. The entire vdW assemblyprocess is done at room temperature.The chip is then pasted onto a stub for He-FIBusing silver paste and the contacts of the device arebonded onto the metallic stub, so the entire deviceremains grounded during patterning. Outside theglovebox, the devices are always in vacuum using acommercial vacuum container. Therefore, the deviceis only exposed momentarily, for example duringbonding.In the He-FIB we work with 30 KeV accelerationvoltage for the Helium beam, and typical emissioncurrents between 2–5 pA. For each sample, we cal-ibrate the optimal He ion dose in order to locallyturn BSCCO insulating. This process is discussed insection 2 of the SI, as well as in [22]. Typical ion dosesrange between 20–90 pC µm−2. Crucially, for low iondoses, theHelium ion beamdoes not etch through theencapsulating hBN layer so the BSCCO flakes remainprotected. We fabricate simple nanowires as well ascomplex structures (see section 1 of the SI). Lastly, weremove the sample from the metallic stub and bondthe chip to a pre-grounded PCB. The PCB is thenloaded into our optical cryostat.Our devices are typically kept in the cryostat for2–4 week measurement runs. Careful thermal cyc-ling can preserve the detector’s SC properties. Pro-longed exposure to air leads to oxidation due to oxy-gen out-diffusion and water creep through the SiO2roughness.3.2. Transport and optoelectronic setupWe characterize the optoelectronic properties of thevdW BSCCO nanowires using an Attodry800 opticalcryostat with a base temperature of 8 K. We maintaina temperature of 20 K on the sample using a stand-ard calibrated microheater + Cernox thermometercombination.We ensure proper thermalization of thesample with the cryostat’s cold finger.For transport characterization, we perform bothAC Lock-in measurements and DC measurements.For the AC Lock-In measurements, we use a 10 nAAC excitation current at a reference frequency of126 Hz. An SRS860x Lock-In amplifier is usedboth for sourcing and sensing. DC measurementsare performed using a combination of DC sources(Yokogawa GS200, Keithley 2450) and a multimeter(Keithley 2700). It is worth noting that for Device C,the normal state resistance is very large (∼100 KΩ),making a voltage bias circuit favourable over a cur-rent bias circuit.Laser excitation is provided by a telecom CWdiode laser (Thorlabs SFL1550P), driven by aDC cur-rent source (Keithley 2400). The laser beam is firstattenuated using neutral density filters. Then, it isaligned and focused onto the sample using a com-bination of room-temperature galvanic mirrors anda cryogenic three-axis piezo stage for the sample.At optimal focus, the laser has a beam width ofw0 ∼ 2 µm. The optical power is measured using apower meter. We calibrate the laser excitation powerin the range between 10 nWand 1µW.Thenwe intro-duce a neutral density filter of density D = 4 in theoptical path, which attenuates the optical power byfour orders of magnitude.The detector is current-biased, connected in par-allel to a load resistor. The voltage drop at the load res-istor generated by the detector’s resistive switching isrecorded using a ZurichUHFLI (10MΩ input imped-ance, 600 MHz bandwidth, 1.8 GSa s−1 samplingrate). A low-noise amplifier with 45 dB gain andbandwidth between 100 Hz and 100 KHz is used topre-amplify the voltage spikes. The Zurich UHLFIrecords switching events for 5 min at each opticalpower and bias current setting. Time—domain tracesof the switching events are recorded using the oscillo-scope function of the Zurich UHFLI with a samplingrate of 175 MHz. Alternatively, we study the photo-voltage signal of the device using an optical chop-per and a Lock-In amplifier (SRS860x) referenced atthe chopper frequency. Optimizing the optical coup-ling to the detector becomes easier in this ‘slower’7https://arxiv.org/abs/2208.056742D Mater. 10 (2023) 021001configuration (see figure 2(c)). A schematic of theoptoelectronic setup for single-photon detection isshown in figure S6.Data availability statementThe data that support the findings of this study areavailable upon reasonable request from the authors.AcknowledgmentsR L M acknowledges fruitful discussions with Gior-gio di Battista and support with the He-FIB byHananHerzig Sheinfux, Johann Osmond and Helena Loz-ano. D K E acknowledges support from the Min-istry of Economy and Competitiveness of Spainthrough the ‘Severo Ochoa’ program for Centres ofExcellence in R&D (SE5-0522), Fundació PrivadaCellex, Fundació PrivadaMir-Puig, theGeneralitat deCatalunya through the CERCA program, the H2020Programme under Grant Agreement No. 820378,Project: 2D × SIPC and the La Caixa Foundation. KW and T T acknowledge support from the ElementalStrategy Initiative conducted by the MEXT, Japan,Grant No. JPMXP0112101001, JSPS KAKENHIGrantNo. JP20H00354 and the CREST (JPMJCR15F3),JST P S acknowledges support from the Alexander-von-Humboldt Foundation and the German Fed-eral Ministry for Education and Research throughthe Feodor-Lynen program. R L M acknowledgesthat this Project has received funding from the “Sec-retaria d’Universitats I Recerca de la Generalitat deCatalunya, as well as the European Social Fund (L’FSEinverteix en el teu futur)—FEDER.Author contributionsD K E, P S and R L M conceived and designed theexperiments; R L M and P S performed the experi-ments; R L M, J R D and P S fabricated the devices;R L M and D K E analyzed the data; K K, T T, K Wcontributed materials; R M and D K E supported theexperiments: R L M and D K E wrote the paper withinsight from R H H.ORCID iDsKenji Watanabe https://orcid.org/0000-0003-3701-8119Robert H Hadfield https://orcid.org/0000-0002-8084-4187Dmitri K Efetov https://orcid.org/0000-0001-5862-0462References[1] Morozov D V, Casaburi A and Hadfield R H 2021Superconducting photon detectors Contemp. Phys. 62 69–91[2] Holzman I and Ivry Y 2019 Superconducting nanowires forsingle-photon detection: progress, challenges, andopportunities Adv. Quantum Technol. 2 1800058[3] Gol’tsmann G N, Okunev O, Chulkova G, Lipatov A,Semenov A, Smirnov K, Voronov B, Dzardanov A,Williams C and Sobolewski R 2001 Picosecondsuperconducting single-photon optical detector Appl. Phys.Lett. 79 705–7[4] Marsili F et al 2013 Detecting single infrared photons with93% system efficiency Nat. Photon. 7 210–4[5] Korzh B et al 2020 Demonstration of sub-3 ps temporalresolution with a superconducting nanowire single-photondetector Nat. Photon. 14 250–5[6] Pernice W H P, Schuck C, Minaeva O, Li M, Goltsmann G N,Sergienko A V and Tang H X 2012 High-speed andhigh-efficiency travelling wave single-photon detectorsembedded in nanophotonic circuits Nat. Commun. 3 1325[7] Münzberg J, Vetter A, Beutel F, Hartmann W, Ferrari S,Pernice W H P and Rockstuhl C 2018 Superconductingnanowire single-photon detector implemented in a 2Dphotonic crystal cavity Optica 5 658[8] Shibata H, Takesue H, Honjo T, Akazaki T and Tokura Y2010 Single-photon detection using magnesium diboridesuperconducting nanowires Appl. Phys. Lett. 97 212504[9] Santavicca D F 2018 Prospects for faster, higher-temperaturesuperconducting nanowire single-photon detectorsSupercond. Sci. Technol. 31 040502[10] Parlato L et al 2017 Investigation of dark counts in innovativematerials for superconducting nanostripe single-photondetector applications Photon Count. Appl. 10229 1022901[11] Lian S J, Cheng B, Cui X and Miao F 2019 Van der Waalsheterostructures for high-performance device applications:challenges and opportunities Adv. Mater. 32 1903800[12] Lee G-H et al 2019 Graphene-based Josephson junctionmicrowave bolometer Nature 586 42–46[13] Walsh E D et al 2021 Josephson junction infraredsingle-photon detector Science 372 409–12[14] Di Battista G, Seifert P, Watanabe K, Taniguchi T, Fong K C,Principi A and Efetov D K 2022 Revealing the thermalproperties of superconducting magic-angle twisted bilayergraphene Nano Lett. 22 6465–70[15] Orchin G J et al 2019 Niobium diselenide superconductingphotodetectors Appl. Phys. Lett. 114 251103[16] Arpaia R, Ejrnaes M, Parlato L, Tafuri F, Cristiano R,Golubev D, Sobolewski R, Bauch T, Lombardi F andPepe G P 2015 High-temperature nanowires for photondetection Physica C 509 16–21[17] Xing X, Balasubramanian K, Bouscher S, Zohar O, Nitzav Y,Kanigel A and Hayat A 2020 Photoresponse above 85 K ofselective epitaxy grown high-Tc superconducting microwiresAppl. Phys. Lett. 117 032602[18] Arpaia R, Golubev D, Baghdadi R, Ciancio R, Drazic G,Orgiani P, Montemurro D, Bauch T and Lombardi F 2017Transport properties of ultrathin YBaCuO nanowires: aroute to single-photon detection Phys. Rev. B 96 064525[19] Andersson E, Arpaia R, Trabaldo E, Bauch T and Lombardi F2020 Fabrication and electrical transport characterization ofhigh quality underdoped YBa2Cu3O7-δ nanowiresSupercond. Sci. Technol. 33 064002[20] Skocpol W J, Beasley M R and TinkhamM 1974 Self-heatinghotspots in superconducting thin-film microbridges J. Appl.Phys. 45 4054[21] Ejrnaes M, Parlato L, Arpaia R, Bauch T, Lombardi F,Cristiano R, Tafuri F and Pepe G P 2017 Observation of darkpulses in 10 nm thick YBCO nanostrips presenting hystereticcurrent voltage characteristics Supercond. Sci. Technol.30 12LT02[22] Lyatti M, Savenko A and Poppe U 2016 UltrathinYBa2Cu3O7-δ films with high critical current densitySupercond. Sci. Technol. 29 065017[23] Li M, Winkler D and Yurgens A 2015 Single-crystallineBi2Sr2CaCu2O8+x detectors for direct detection ofmicrowave radiation Appl. Phys.Lett. 106 152601[24] Ghosh S, Jangade D A and Deshmukh MM 2022 Nanowirebolometer using a 2D high-temperature superconductorNanotechnology 34 0153048https://orcid.org/0000-0003-3701-8119https://orcid.org/0000-0003-3701-8119https://orcid.org/0000-0003-3701-8119https://orcid.org/0000-0002-8084-4187https://orcid.org/0000-0002-8084-4187https://orcid.org/0000-0002-8084-4187https://orcid.org/0000-0001-5862-0462https://orcid.org/0000-0001-5862-0462https://orcid.org/0000-0001-5862-0462https://doi.org/10.1080/00107514.2022.2043596https://doi.org/10.1080/00107514.2022.2043596https://doi.org/10.1002/qute.201800058https://doi.org/10.1002/qute.201800058https://doi.org/10.1063/1.1388868https://doi.org/10.1063/1.1388868https://doi.org/10.1038/nphoton.2013.13https://doi.org/10.1038/nphoton.2013.13https://doi.org/10.1038/s41566-020-0589-xhttps://doi.org/10.1038/s41566-020-0589-xhttps://doi.org/10.1038/ncomms2307https://doi.org/10.1038/ncomms2307https://doi.org/10.1364/OPTICA.5.000658https://doi.org/10.1364/OPTICA.5.000658https://doi.org/10.1063/1.3518723https://doi.org/10.1063/1.3518723https://doi.org/10.1088/1361-6668/aaaed9https://doi.org/10.1088/1361-6668/aaaed9https://doi.org/10.1117/12.2267647https://doi.org/10.1117/12.2267647https://doi.org/10.1002/adma.201903800https://doi.org/10.1002/adma.201903800https://doi.org/10.1038/s41586-020-2752-4https://doi.org/10.1038/s41586-020-2752-4https://doi.org/10.1126/science.abf5539https://doi.org/10.1126/science.abf5539https://doi.org/10.1021/acs.nanolett.1c04512https://doi.org/10.1021/acs.nanolett.1c04512https://doi.org/10.1063/1.5097389https://doi.org/10.1063/1.5097389https://doi.org/10.1016/j.physc.2014.09.017https://doi.org/10.1016/j.physc.2014.09.017https://doi.org/10.1063/5.0006584https://doi.org/10.1063/5.0006584https://doi.org/10.1103/PhysRevB.96.064525https://doi.org/10.1103/PhysRevB.96.064525https://doi.org/10.1088/1361-6668/ab807ehttps://doi.org/10.1088/1361-6668/ab807ehttps://doi.org/10.1063/1.1663912https://doi.org/10.1063/1.1663912https://doi.org/10.1088/1361-6668/aa94b9https://doi.org/10.1088/1361-6668/aa94b9https://doi.org/10.1088/0953-2048/29/6/065017https://doi.org/10.1088/0953-2048/29/6/065017https://doi.org/10.1063/1.4918788https://doi.org/10.1063/1.4918788https://doi.org/10.1088/1361-6528/ac9684https://doi.org/10.1088/1361-6528/ac96842D Mater. 10 (2023) 021001[25] Yu Y, Ma L, Cai P, Zhong R, Ye C, Shen J, Gu G D, Chen X Hand Zhang Y 2019 High-temperature superconductivity inmonolayer Bi2Sr2CaCu2O8+δ Nature 575 156–63[26] Seifert P et al 2021 A high-Tc van der Waals superconductorbased photodetector with ultra-high responsivity andnanosecond relaxation time 2D Mater. 8 035053[27] Cao Y et al 2015 Quality heterostructures fromtwo-dimensional crystals unstable in air by their assembly ininert atmosphere Nano Lett. 15 4914–21[28] Ward B, Notte J A and Economou N 2006 Helium ionmicroscope: a new tool for nanoscale microscopy andmetrology J. Vac. Sci. Technol. B 24 2871–4[29] Cybart S A, Cho E Y, Wong T J, Wehlin B H, Ma M K,Huynh C and Dynes R C 2015 Nano Josephsonsuperconducting tunnel junctions in YBa2Cu3O7-δ directlypatterned with a focused helium ion beam Nat. Nanotech.10 598–602[30] Müller B, Karrer M, Limberger F, Becker M, Schröppel B,Burkhardt C J, Kleiner R, Goldobin E and Koelle D 2019Josephson junctions and SQUIDs created by focused heliumion beam irradiation of YBa2Cu3O7 Phys. Rev. Appl.11 044082[31] Cho E Y, Ma M K, Huynh C, Pratt K, Paulson D N,Glyantsev V N, Dynes R C and Cybart S A 2015YBa2Cu3O7-δ superconducting quantum interferencedevices with metallic to insulating barriers written with afocused helium ion beam Appl. Phys. Lett.106 252601[32] Chen X K, Zeng Y J and Chen K Q 2020 Thermal transportin two-dimensional heterostructures Front. Mater. 7 578791[33] Engel A, Renema J J, Il’in K and Semenov A 2015 Detectionmechanism of superconducting nanowire single-photondetectors Supercond. Sci. Technol. 28 114003[34] Jukna A and Sobolewski R 2003 Time-resolvedphotoresponse in the resistive flux-flow state in Y-Ba-Cu-Osuperconducting microbridges Supercond. Sci. Technol.16 911–5[35] Zhang L et al 2014 Characterization of superconductingnanowire single-photon detector with artificial constrictionsAIP Adv. 4 067114[36] Bitauld D, Marsili F, Gaggero A, Mattioli F, Leoni R,Nejad S J, Lévy F and Fiore A 2010 Nanoscale opticaldetector with single-photon and multiphoton sensitivityNano Lett. 10 2977–81[37] Sobolewski R, Verevkin A, Gol’tsman G N, Lipatov A andWilsher K 2003 Ultrafast superconducting single-photonoptical detectors and their applications IEEE Trans. Appl.Supercond. 13 1151–7[38] Zhao Y G et al 2001 Optical Cooper pair breakingspectroscopy of cuprate superconductors Phys. Rev. B63 132507[39] Sandilands L J, Reijnders A A, Su A H, Baydina V, Xu Z,Yang A, Gu G, Pedersen T, Borondics F and Burch K S 2014Origin of the insulating state in exfoliated high-TCtwo-dimensional atomic crystals Phys. Rev. B 90 081402[40] Niratisairak S, Johansen T H, Katouda S and Ishibashi T2011 Evolution of a hotspot in a thin BSCCO structured filmPhysica C 471 222–5[41] Xiao Z L, Andrei E Y and Ziemann P 1998 Coexistence of thehot-spot effect and flux-flow instability in high-TCsuperconducting films Phys. Rev. B 58 11185[42] Lyatti M, Wolff M A, Savenko A, Kruth M, Ferrari S,Poppe U, Pernice W, Dunin-Borkowski R E and Schuck C2018 Experimental evidence for hotspot and phase-slipmechanisms of voltage switching in ultra-thin YBa2Cu3O7-δnanowires Phys. Rev. B 98 054505[43] Polakovic T, Armstrong W, Karapetrov G, Meziani Z E andNovosad V 2020 Unconventional applications ofsuperconducting nanowire single photon detectorsNanomaterials 10 11989https://doi.org/10.1038/s41586-019-1718-xhttps://doi.org/10.1038/s41586-019-1718-xhttps://doi.org/10.1088/2053-1583/ac072fhttps://doi.org/10.1088/2053-1583/ac072fhttps://doi.org/10.1021/acs.nanolett.5b00648https://doi.org/10.1021/acs.nanolett.5b00648https://doi.org/10.1116/1.2357967https://doi.org/10.1116/1.2357967https://doi.org/10.1038/nnano.2015.76https://doi.org/10.1038/nnano.2015.76https://doi.org/10.1103/PhysRevApplied.11.044082https://doi.org/10.1103/PhysRevApplied.11.044082https://doi.org/10.1063/1.4922640https://doi.org/10.1063/1.4922640https://doi.org/10.3389/fmats.2020.578791https://doi.org/10.3389/fmats.2020.578791https://doi.org/10.1088/0953-2048/28/11/114003https://doi.org/10.1088/0953-2048/28/11/114003https://doi.org/10.1088/0953-2048/16/8/314https://doi.org/10.1088/0953-2048/16/8/314https://doi.org/10.1063/1.4881981https://doi.org/10.1063/1.4881981https://doi.org/10.1021/nl101411hhttps://doi.org/10.1021/nl101411hhttps://doi.org/10.1109/TASC.2003.814178https://doi.org/10.1109/TASC.2003.814178https://doi.org/10.1103/PhysRevB.63.132507https://doi.org/10.1103/PhysRevB.63.132507https://doi.org/10.1103/PhysRevB.90.081402https://doi.org/10.1103/PhysRevB.90.081402https://doi.org/10.1016/j.physc.2011.01.009https://doi.org/10.1016/j.physc.2011.01.009https://doi.org/10.1103/PhysRevB.58.11185https://doi.org/10.1103/PhysRevB.58.11185https://doi.org/10.1103/PhysRevB.98.054505https://doi.org/10.1103/PhysRevB.98.054505https://doi.org/10.3390/nano10061198https://doi.org/10.3390/nano10061198 Two-dimensional cuprate nanodetector with single telecom photon sensitivity at T = 20 K    1. Results and discussion 1.1. Device fabrication and transport characterization 1.2. Photo-induced switching events in the BSCCO nanostructure 1.3. Statistics of the switching events and single-photon sensitivity 2. Note 3. Methods 3.1. Device fabrication 3.2. Transport and optoelectronic setup References