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S Hubmann, G Di Battista, I A Dmitriev, [K Watanabe](https://orcid.org/0000-0003-3701-8119), [T Taniguchi](https://orcid.org/0000-0002-1467-3105), D K Efetov, S D Ganichev

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[Infrared photoresistance as a sensitive probe of electronic transport in twisted bilayer graphene](https://mdr.nims.go.jp/datasets/125b85bf-ff20-4428-bbe3-3f2655bce27a)

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Infrared photoresistance as a sensitive probe of electronic transport in twisted bilayer graphene2D MaterialsPAPER • OPEN ACCESSInfrared photoresistance as a sensitive probe ofelectronic transport in twisted bilayer grapheneTo cite this article: S Hubmann et al 2023 2D Mater. 10 015005 View the article online for updates and enhancements.You may also likeMapping global hotspots and trends ofwater quality (1992-2010): a data drivenapproachSébastien Desbureaux, Frédéric Mortier,Esha Zaveri et al.-Developing magnetorelaxometry imagingfor human applicationsSoudabeh Arsalani, Patricia Radon, PeterPhilipp Schier et al.-Honeybees modify flight trajectories inturbulent windBardia Hejazi, Christian Küchler,Gholamhossein Bagheri et al.-This content was downloaded from IP address 144.213.253.16 on 04/11/2022 at 08:22https://doi.org/10.1088/2053-1583/ac9b70/article/10.1088/1748-9326/ac9cf6/article/10.1088/1748-9326/ac9cf6/article/10.1088/1748-9326/ac9cf6/article/10.1088/1361-6560/ac9c41/article/10.1088/1361-6560/ac9c41/article/10.1088/1367-2630/ac9cc4/article/10.1088/1367-2630/ac9cc42D Mater. 10 (2023) 015005 https://doi.org/10.1088/2053-1583/ac9b70OPEN ACCESSRECEIVED28 July 2022REVISED7 October 2022ACCEPTED FOR PUBLICATION17 October 2022PUBLISHED3 November 2022Original 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.PAPERInfrared photoresistance as a sensitive probe of electronictransport in twisted bilayer grapheneS Hubmann1, G Di Battista2,3, I A Dmitriev1, K Watanabe4, T Taniguchi5, D K Efetov2,3,6and S D Ganichev1,7,∗1 Terahertz Center, University of Regensburg, 93040 Regensburg, Germany2 ICFO—Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Castelldefels, Barcelona 08860, Spain3 Fakultät für Physik, Munich Quantum Center, and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität München,Geschwister-Scholl-Platz 1, 80539 München, Germany4 Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan5 International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan6 Munich Center for Quantum Science and Technology (MCQST), Schellingstraße 4, 80799 München, Germany7 CENTERA Laboratories, Institute of High Pressure Physics, Polish Academy of Sciences, PL-01-142 Warsaw, Poland∗ Author to whom any correspondence should be addressed.E-mail: sergey.ganichev@ur.deKeywords: photoresistance, twisted bilayer graphene, infrared, temperature, bolometric, heatingAbstractWe report on observation of the infrared photoresistance of twisted bilayer graphene (tBLG) undercontinuous quantum cascade laser illumination at a frequency of 57.1 THz. The photoresistanceshows an intricate sign-alternating behavior under variations of temperature and back gate voltage,and exhibits giant resonance-like enhancements at certain gate voltages. The structure of thephotoresponse correlates with weaker features in the dark dc resistance reflecting the complex bandstructure of tBLG. It is shown that the observed photoresistance is well captured by a bolometricmodel describing the electron and hole gas heating, which implies an ultrafast thermalization ofthe photoexcited electron–hole pairs in the whole range of studied temperatures and back gatevoltages. We establish that photoresistance can serve a highly sensitive probe of the temperaturevariations of electronic transport in tBLG.1. IntroductionIn a breakthrough discovery in 2018 it was experi-mentally shown that when two graphene layers arestacked vertically, while being twisted by a magicangle of 1.1◦, the inter-layer hybridization leads tothe emergence of ultra-flat electronic bands [1–3].Strikingly, these bands were found to host a pleth-ora of exotic electronic phases including uncon-ventional superconductivity, correlated insulators,as well as magnetic and topological phases [2–6].These discoveries, demonstrating that the twist anglecan be used to control the state of 2D materialsand for manipulation of strong electronic correla-tions, produced a remarkable excitement and multi-disciplinary research (see, e.g. [7–25] and referencestherein). In particular, optoelectronic studies providea way to access the unique and rich physics of twis-ted bilayer graphene (tBLG) and open a potentialfor a novel kind of devices, such as detectors ofterahertz and infrared radiation [26, 27]. So far,these studies have been limited to investigation ofphotocurrents excited in unbiased tBLG structures[22, 28–39].Here we report on observation and study of theinfrared photoresistance in tBLG with small twistangle of ∼1◦. The photoresistance exhibits a com-plex sign-alternating behavior upon variation of theback gate voltage and the sample’s temperature. Inparticular, at low temperatures it exhibits sharp neg-ative spikes at several gate voltages. We show that theinfrared photoresistance is caused by the bolomet-ric effect—change of the dc resistivity due to electronand hole gas heating. This conclusion is supported bythe fact that the photoresistance closely follows thefirst derivative of the dark dc resistance with respectto the temperature: the shape of the gate-voltagedependence of the photoresistivity at all temperaturespractically coincides with the difference of resistancetraces obtained at two neighboring temperatures.This property enables us to estimate the heating effectand to demonstrate its weak sensitivity both to the© 2022 The Author(s). Published by IOP Publishing Ltdhttps://doi.org/10.1088/2053-1583/ac9b70https://crossmark.crossref.org/dialog/?doi=10.1088/2053-1583/ac9b70&domain=pdf&date_stamp=2022-11-3https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/https://orcid.org/0000-0003-0789-6391https://orcid.org/0000-0003-2643-0773https://orcid.org/0000-0003-1370-6355https://orcid.org/0000-0003-3701-8119https://orcid.org/0000-0001-6423-4509mailto:sergey.ganichev@ur.de2D Mater. 10 (2023) 015005 S Hubmann et almeasurement temperature and to the gate voltage,controlling the low-energy moiré band structure andposition of the chemical potential in tBLG. We thusestablish that, despite high energy of electron–holepairs excited by the infrared radiation, the rich struc-ture and sharp negative spikes in the gate voltage ofobserved photoresistance are completely determinedby the temperature variations of low-energy trans-port, which is strongly affected by the moiré poten-tial of small angle tBLG. Our study demonstrates thatphotoresistance can serve as a sensitive probe of thelow-energy transport characteristics, even those thatare hardly detectable using the standard transportmeasurements.2. Samples andmethodsThe heterostructure consisting of the tBLG layersandwiched between hexagonal boron nitride (hBN)was prepared using a ‘cut and stack’ technique, wherea single flake of monolayer graphene is cut in twopieces using an AFM tip, and these two pieces arestacked together via substrate rotation yielding a con-trolled twist between the two graphene layers, fordetails see [40]. Bottom and top layers of hBN hada thickness of 16 and 10 nm, respectively. The twographene sheets were stacked one on top to theother at a target angle of 1◦. A graphite layer onthe bottom of the hBN/tBLG/hBN was used as alocal back gate electrode. The stack was etched intoa Hall bar geometry 17× 2µm2. A CHF3/O2 mix-ture was used to expose the graphene edges, with sub-sequent evaporation of Cr/Au (5/50 nm) providingohmic contacts for transport and photoresistancemeasurements.The sample was placed in a temperature-variableHe exchange gas optical cryostat with ZnSe win-dows. To capacitively tune the carrier density in thetBLG structure, back gate voltage UG in the rangeof ±3 V was applied to the graphite back gate ofthe device. The sample resistance, R, was measuredin two-terminal geometry using the standard low-frequency lock-in technique, with excitation currentof 100 nA.Figure 1 shows the sample resistance as a func-tion of the applied gate voltage measured at dif-ferent temperatures in the range from T= 3.6 to170K. At low temperatures the resistance exhibitsclear sharp peaks at certain gate voltages characteristicfor tBLG: The charge neutrality point (CNP)-peakat UG,eff = 0 V is flanked by highly-resistive peaksat ±2.5V with strongly insulating behavior. Fromthe position of these peaks which mark the edgesof the moiré bands, the twist angle was estimatedto be ∼1◦, using the thickness of the bottom hBNlayer to calculate the gate capacitance. The resistancetraces also show less pronounced peaks at±1 V. Thissuggests that the area between the source and draincontacts B and C (see figure 2) acquires some twistFigure 1. Two-point dc resistance Rmeasured betweencontacts B and C (see inset in figure 2) as a function of theeffective gate voltage at temperatures T ranging from 3.6 to170K. The upper axis shows the corresponding carrierdensity calculated using the gate capacitance asn= UG,eff · 9.62× 1011V−1 cm−2.Figure 2. Normalized photoresistance∆R/R as a functionof the effective gate voltage at a temperature T= 3.6K. Thecorresponding resistance without illumination is illustratedby blue line. The inset shows a sketch of the Hall barstructure, contacts B and C used for the two-pointmeasurements, and the linear polarization angle withrespect to the short side of the Hall bar (the azimuth angleα= 75◦).angle inhomogeneity, i.e. that the measured area isdominated by a twist angle of ∼1◦ but also containsfractions with lower twist angles of ∼0.6◦. Recentstudies with STM or SQUID-on-tip techniques [19]provide a direct experimental evidence of such twistangle inhomogeneity. The inhomogeneity can alsobe responsible for the double-peak structure of R at±2.5V. Note that the gate voltage corresponding tothe CNP, UCNP, was varying slightly between differ-ent sample cooldowns due to different charge trap-ping in the gate insulator [41, 42]. Correspondingly,in the presented data we use the effective gate voltageUg,eff = UG −UCNP.22D Mater. 10 (2023) 015005 S Hubmann et alIn order tomeasure the photoresistance we used acontinuous wave (cw) quantum cascade laser (QCL)which operated at a radiation frequency of 57.1 THz(photon energy of 236 meV) and provided an max-imum output power of 130 mW. The normally incid-ent radiationwas focused onto the tBLG sample usinga parabolic mirror, which resulted in a laser spotwith diameter of about 0.5 mm as checked by apyroelectric camera [43, 44]. This spot diameter wasan order of magnitude larger than the Hall bar sizeensuring a uniform illumination of the sample. Thepolarization state of the incoming radiation was con-trolled using a quarter-wave plate and linear polar-izers. The photoresistance was measured as the dif-ference between the two-point dc resistance in thepresence and absence of cw QCL illumination,∆R=Rill −R. In all figures apart from figures 5 and 6, wepresent the results for the normalized photoresistance∆R/R.3. ResultsApplying the infrared radiation to the tBLG structurewe observed a photoinduced change∆Rof the sampleresistance [45]. Figure 2 shows a typical exampleof recorded ∆R, normalized to the dark resistanceR, as a function of the applied gate voltage UG,eff.These data were obtained at the lowest T= 3.6 K.Besides a primary narrow negative spike at the CNP,the photoresistance ∆R/R exhibits several spikes atlarge negative and positive gate voltage, namely, atUG,eff =−2.46,Ug,eff = 2.14, and 2.38V. Comparisonof these data with the dark resistance, see blue line infigure 2, shows that positions of the negative spikesin ∆R/R coincide with the peak positions in R. Wethus observe that, despite the huge photoexcitationenergy of 236 meV, the major sharp features in theUG,eff-dependence of∆R/R correspond to the abruptchanges of dc transport properties when the chemicalpotential is passing the edges of the low-energy moirébands at ∼10 meV from the CNP, see discussionbelow. This establishes that the infrared photoresist-ance can indeed serve a sensitive probe of the low-energy dc transport of tBLG. In this connection, it isworth mentioning that variations of the photoresist-ance∆R withUG,eff are orders of magnitude strongerthan those in the dark resistance R (not exceeding50%), and thus remain equally strong if the photores-istance∆R is not normalized to the dark resistance R,see figure 5.As the temperature of measurements increases,the behavior of the photoresistance changes substan-tially, see figure 3. While the photoresistance dips atpositions of the peaks in dark resistance remain pro-nounced up to 70K, their magnitude is significantlyreduced with increasing T. These changes are againconsistent with evolution of the dc resistance R infigure 1, where all peaks become progressively weakerFigure 3. Normalized photoresistance∆R/R as a functionof the effective gate voltage at different temperatures from10 to 70K.Figure 4. Temperature evolution of normalizedphotoresistance∆R/R (red), resistance R (blue), and thederivative of the resistance with respect to the temperature∂R/∂T (green) at an effective gate voltage of UG,eff = 0 Vcorresponding to the CNP.and broader at elevated T (for T≲ 30K). Moreover,one observes that the sign of ∆R at a fixed UG,eff fol-lows the sign of temperature variation ofR at the sameUG,eff, for a detailed comparison see figures 4–6. Athigher T, the side peaks become very weak in R whilethe corresponding features are still well resolved in∆R, whereas the broad CNP peak in R continues tobroaden and starts to grow. Consistently, at T> 70Kthe photoresistance becomes positive in the wholerange of gate voltages (see figure 6(d)). Finally, fortemperatures above 140K the photoresistance signalbecomes vanishingly small.We now turn to a quantitative comparisonof the temperature evolution of the dc resistanceand photoresistance. Figure 4 shows the temperat-ure dependence of the normalized photoresistance∆R/R (red line) together with that of the resist-ance R without illumination (blue) at UG,eff = 0corresponding to the CNP. It is clearly seen that32D Mater. 10 (2023) 015005 S Hubmann et alFigure 5. Photoresistance∆R as a function of the effectivegate voltage measured at a temperature of T= 3.6K plottedtogether with the scaled difference between the darkresistances measured at T= 10K and T= 3.6K.the photoresistance changes its sign with increasingtemperature. Apart from that, comparing the tem-perature dependence of the photoresistance withthe dark resistance we find that the photoresist-ance closely follows the temperature derivative of thedark resistance, ∂R/∂T, see green line in figure 4.As discussed below, this provides a strong evid-ence that the observed photoresistance is caused bythe radiation-induced electron and hole gas heat-ing. Another justification comes from the ana-lysis in figure 5. Here we directly compare thenon-normalized photoresistance ∆R measured atT= 3.6 K (red line) with the difference of the darkresistance traces measured at temperatures of 10 and3.6 K and observe that, up to a constant scaling factorof 1.07, these curves nearly coincide, see figure 5.Similar precise coincidence is observed at higher T,see figure 6.4. DiscussionThe results presented above demonstrate that, des-pite a complex moiré band structure of tBLG, thephotoresistance of this material in the studied fre-quency range is pretty well captured by a rathercommon and well-established mechanism relatedto electron heating [46]. Within this mechanism,the stationary non-equilibrium energy distribu-tion of electrons under continuous illumination isapproximately given by the equilibrium Fermi–Diracdistribution, but with the measurement temperat-ure T replaced by an elevated electron temperatureTe > T. The value of the electron temperature Teshould be found self-consistently from the energybalance equation. This equation expresses the sta-tionary condition that, for certain Te > T, theenergy absorbed by electrons is fully compensatedby the energy flow from hot electrons to the lat-tice (usually assumed to remain at the measurementtemperature T). Provided Te −T≪ T, the photores-istance due to electron heating is given by:∆R=∂R∂Te(Te −T), (1)in full accordance with our findings, presented infigures 4–6 and discussed in more details below. Thisdescription of electron heating and of the corres-ponding photoresistance is generally valid when equi-libration of the absorbed energy within the electronsystem is faster than its transfer to the thermal bath ofphonons but, in practice, is also frequently applicablewhen this condition is violated.In our case, the photon energy, ℏω = 236 meV,strongly exceeds all other involved energy scales—the temperature, Fermi energy, and moiré minibandswidths—all being of the order of 1 to 10 meV [2].It follows that a typical optical absorption processtakes place between occupied initial electron stateswell (∼120 meV) below the Fermi energy EF andempty states well above EF, as illustrated in the insetin figure 6(d). At such high energies the states are onlyweakly influenced by the moiré superlattice [27] andcan be considered as a continuumwithout significantmodulations of the density of states. Thus, a changeof the gate voltage, which strongly modifies the moiréelectron spectrum and resistance in the vicinity ofFermi energy and CNP, should only weakly affect theamount of absorbed energy governed by such dis-tant states. Similarly, the relaxation of hot electronsshould also possess a weak sensitivity toUG. The pho-toexcited electrons and holes are expected to rapidlythermalize via electron-electron collisions simultan-eously transferring the excess energy to the lattice viathe acoustic phonon emission [47]. All these pro-cesses involve huge number of possible intermediatestates with typical energies comparable to ℏω ≫ EFand, thus, may also possess a weak sensitivity to thelow-energy spectrum of tBLG and the exact positionof EF, controlled by the gate voltage UG.As a result, the electron temperature Te, express-ing the balance between absorption and energy relax-ation, is expected to be largely insensitive to UG.In sharp contrast to Te, the temperature derivative∂R/∂Te of the dark resistance should be highly sens-itive to bothUG and temperature, in particular in thevicinity of the moiré band edges where the transportcontributions of different states in the temperaturewindow around the Fermi energy can be essentiallydifferent.The above conclusions are well supported by ourexperimental findings, which confirm that the signof the photoresistance correlates with the temperat-ure dependence of R, see figure 4 [48]. Moreover, theanalysis presented in figure 5 confirms that the UG-dependence of ∆R coincides with that of ∂R/∂Te,while the electron heating factor ∆T≡ Te −T inequation (1) turns out to be insensitive to UG. This42D Mater. 10 (2023) 015005 S Hubmann et alFigure 6. Photoresistance∆R as a function of the effective gate voltage measured at temperatures of 10K (a), 17 K (b), 30 K(c), and 70K (d) plotted together with the scaled difference between the dark resistances measured at neighboring temperatures(provided in the legends together with the scaling factors). The inset in panel (a) shows the relative radiation-induced heating∆T/T estimated from the scaling factors using equation (1). The inset in panel (d) shows a sketch of the optical excitation andrelaxation processes leading to electron heating at energies in the vicinity of the flat bands.implies a surprisingly low sensitivity of the high-frequency heating to the low-energy spectrum oftBLG. As discussed above, such a weak sensitivity isexpected for the photoexcitation process, as well asthe initial stages of thermalization and energy transferto lattice. However, at a later stage, when the energyof nonequilibrium carriers reduces to ∼10 meV,one would rather expect that the relaxation processbecomes sensitive to details of the band structure andposition of the chemical potential. Nevertheless, ourobservations suggest that in the studied device thethermalization remains ultimately fast under all con-ditions, resulting in Te independent of UG.This result is further confirmed by the analysis infigure 6: At all temperatures the shape of the photores-istance can be well reproduced by the difference ofthe dark resistance traces measured at two neighbor-ing temperatures. Only in close vicinity of the strongnegative spikes some small and not systematic devi-ations are noticeable (see horizontal bars in figures 5and 6). These can be attributed by a limited accur-acy of estimated ∂R/∂T obtained from comparisonof resistance traces at two different temperatures. Thescaling coefficients, obtained from such comparison(see legends in figures 5 and 6) provide an estimate forthe electron heating ∆T, which remains at the levelof 5 K in the whole studied interval of temperatures.From this estimate, we also establish that the relativeheating ∆T/T (see inset in figure 6) remains smallfor all T except the lowest T= 3.6K (figure 5). Inthe latter case equation (1), valid for the linear heat-ing regime, is only marginally applicable, and theobtained value of∆T can be inaccurate.5. SummarySummarizing, we show that, despite high energy ofelectron–hole pairs excited by the infrared radiation,the rich structure and sharp negative spikes in thegate voltage dependence of observed photoresistanceare fully determined by the temperature variationsof low-energy transport and, therefore, are stronglyaffected by the moiré potential of small angle tBLG.Ourmain observations and analysis demonstrate thatphotoresistance provides an alternative highly sensit-ive method for characterization of low-energy trans-port properties of tBLG which, despite its intrinsiccomplexity, permits a reliable treatment and clearunderstanding. In addition, the analysis of resist-ance detected in the presence and absence of radi-ation at varying T yields a direct access and measureof electron heating in illuminated tBLG, which may52D Mater. 10 (2023) 015005 S Hubmann et alprovide an important quantitative check to futuretheories describing optical excitation and relaxationprocesses in this intriguing and rapidly developingclass of 2D electronic systems.Data availability statementThe data that support the findings of this study areavailable upon reasonable request from the authors.AcknowledgmentsThe support from the Deutsche Forschungsge-meinschaft (DFG, German Research Foundation) viaProject SPP 2244 (GA501/17-1) and Project DM1-5/1(I A D), and from the Volkswagen Stiftung Program(97738) are gratefully acknowledged. S D G thanksthe support from the IRAP program of the Found-ation for Polish Science (Grant No. MAB/2018/9,Project CENTERA). D K E acknowledges supportfrom the Ministry of Economy and Competitivenessof Spain through the ‘Severo Ochoa’ programme forCentres of Excellence in R and D (SE5-0522), Fun-dacio Privada Cellex, Fundacio Privada Mir-Puig,the Generalitat de Catalunya throughthe CERCAprogramme, funding from the European ResearchCouncil (ERC) under the European Union’s Horizon2020 research and innovation programme (GrantAgreement No. 852927). G D B acknowledges sup-port from the ‘Presidencia de la Agencia Estatal deInvestigación’ (Ref. PRE2019-088487). K W and T Tacknowledge support from JSPS KAKENHI (GrantNos. 19H05790, 20H00354 and 21H05233).Appendix. Infrared radiation-inducedphotocurrentsApart from the photoresistance studied in a biasedtBLG, in the absence of external bias we observedpolarization-dependent photocurrents. Exemplaryresults, obtained at low T= 3.6K, are shown infigures 8–10. For the photocurrent measurements thecontinuous infrared 57.1 THz radiation produced byQCL was electronically modulated at a frequency offQCW = 160 Hz. The photocurrent along and acrossthe Hall bar was measured using standard lock-intechnique as a voltage drop between different pairs ofcontacts BC and BD, see figure 7.In the case of linear polarization and low intensityI, the photocurrent j∝ I can be generally representedas [22]:j= j0 − j1 cos(2α)− j2 sin(2α), (2)where the components j0, j1, and j2 are coefficients infront of the first three Stokes parameters, and the azi-muth angle α is defined as the angle of linear polariz-ation with respect to y-direction across the Hall bar,Figure 7. Sketch of the sample structure. The azimuthangle α is defined between the vector of the radiationelectric field E and the short side of the Hall bar.Photosignals and transport were measured using thecontacts marked in blue.Figure 8. The gate voltage dependencies of polarization-independent component j0 of the photocurrent, seeequation (2), measured using contact pairs BC and BD.Blue line: dark resistance measured between the contacts Band C.see figure 7. The last linearly independent compon-ent of the photocurrent jC, proportional to the forthStokes parameter, requires application of the circu-larly polarized radiation, inwhich case the second andthird Stokes parameters vanish, and:j= j0 + jCη . (3)The helicity-dependent photocurrent contributionjCη, proportional to the radiation helicity η =±1, hasopposite signs for the right- and left-handed circu-larly polarized radiation.Figure 8 shows the extracted polarization-independent contribution of the photocurrent j0as a function of the applied gate voltage for bothmeasurement directions BC and BD. It is seen thatthe photocurrent behaves similarly for both meas-urement directions. Similar to the photoresistancepresented in the main text, the photocurrent showspronounced features corresponding to peaks in thesample resistance (blue line in figure 8). However,in contrast to the photoresistance, at the CNP thephotocurrent changes sign, together with the changeof the charge of the majority carriers. Empirically,62D Mater. 10 (2023) 015005 S Hubmann et alFigure 9. The gate voltage dependencies of polarization-sensitive photocurrent components j1, j2, and jC, seeequations (2) and (3), measured between contacts B and D.Blue line: dark resistance measured between the contacts Band C.this behavior resembles a derivative of the resistiv-ity with respect to the gate voltage, the density, orthe Fermi energy. A similar differential line shapeof the photocurrent in systems with a CNP-like fea-ture has been reported and understood in previousworks where a wide range of effects like plasmonicresonances in a Dyakonov-Shur configuration [49],thermoelectric effects [50, 51], ratchet effects [52],and edge photocurrents [42, 53] were studied.The differential line shape has already beenobserved also in tBLG in the terahertz range of radi-ation frequencies [22, 33], where, however, it wasrather linked to asymmetric scattering and the changeof the carriers type at the CNP. We believe that in ourdevice the origin is similar to that identified in [22]and is rooted in asymmetric elastic scattering of car-riers. At the same time, the theory developed in [22]describes photocurrents induced via the intrabandterahertz absorption, and thus is not directly applic-able to the present case of direct interband transitionsinduced by the infrared illumination. Investigationof the corresponding mechanisms of sign-alternatingtBLG photocurrents due to the interband absorptionremains an interesting subject for future work. Thefocus of our present work is rather on photoresist-ance which, unlike photocurrent, does not requireany spatial asymmetry, as the direction of current isdefined by the external bias, absent in the photocur-rent studies. The model that we successfully imple-mented for interpretation of results in the main textis not applicable to the photocurrents, as it does notinclude any asymmetry and thus results in vanishingphotocurrent.Figures 9 and 10 show the gate voltage depend-ences of the extracted photocurrent componentsj1 and j2, sensitive to the direction of the linearpolarization, as well as the helicity-ensitive con-tribution jC, separately for the transverse (con-tacts BD, figure 9) and longitudinal (contacts BC,Figure 10. The gate voltage dependencies of polarization-sensitive photocurrent components j1, j2, and jC, seeequations (2) and (3), measured between contacts B and C.Blue line: dark resistance measured between the contacts Band C.figure 10) photocurrents. Similar to the polarization-independent component j0, the polarization-sensitivecomponents possess similar features for both meas-urement directions correlated with the peaks in thesample resistance (blue lines). In contrast to the pho-tocurrents detected in previous studies in the tera-hertz frequency range [22, 33], in the infrared rangethe polarization-sensitive components are found tobe much smaller than the polarization-independentphotocurrent, see figure 8.ORCID iDsS Hubmann https://orcid.org/0000-0003-0789-6391G Di Battista https://orcid.org/0000-0003-2643-0773I A Dmitriev https://orcid.org/0000-0003-1370-6355K Watanabe https://orcid.org/0000-0003-3701-8119S D Ganichev https://orcid.org/0000-0001-6423-4509References[1] Bistritzer R and MacDonald A H 2011 Proc. Natl Acad. 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Introduction 2. Samples and methods 3. Results 4. Discussion 5. Summary Appendix. Infrared radiation-induced photocurrents References