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I. Tamir, A. Benyamini, E. J. Telford, F. Gorniaczyk, A. Doron, T. Levinson, D. Wang, F. Gay, B. Sacépé, J. Hone, [K. Watanabe](https://orcid.org/0000-0003-3701-8119), [T. Taniguchi](https://orcid.org/0000-0002-1467-3105), C. R. Dean, A. N. Pasupathy, D. Shahar

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[Sensitivity of the superconducting state in thin films](https://mdr.nims.go.jp/datasets/a68c9649-18b1-44ba-93f0-4ee20dfd551f)

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Science Journals — AAASSC I ENCE ADVANCES | R E S EARCH ART I C L ECONDENSED MATTER PHYS I CS1Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot76100, Israel. 2Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany.3Department of Mechanical Engineering, Columbia University, New York, NY10027, USA. 4Department of Physics, Columbia University, New York, NY 10027,USA. 5University Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, Grenoble38000, France. 6National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.*Corresponding author. Email: idan.tamir@fu-berlin.deTamir et al., Sci. Adv. 2019;5 : eaau3826 15 March 2019Copyright © 2019The Authors, somerights reserved;exclusive licenseeAmerican Associationfor the Advancementof Science. No claim tooriginalU.S. GovernmentWorks. Distributedunder a CreativeCommons AttributionNonCommercialLicense 4.0 (CC BY-NC).Sensitivity of the superconducting state in thin filmsI. Tamir1,2*, A. Benyamini3, E. J. Telford4, F. Gorniaczyk1, A. Doron1, T. Levinson1, D. Wang4,F. Gay5, B. Sacépé5, J. Hone3, K. Watanabe6, T. Taniguchi6, C. R. Dean4,A. N. Pasupathy4, D. Shahar1,4For more than two decades, there have been reports on an unexpected metallic state separating the establishedsuperconducting and insulating phases of thin-film superconductors. To date, no theoretical explanation hasbeen able to fully capture the existence of such a state for the large variety of superconductors exhibiting it.Here, we show that for two very different thin-film superconductors, amorphous indium oxide and a singlecrystal of 2H-NbSe2, this metallic state can be eliminated by adequately filtering external radiation. Our resultsshow that the appearance of temperature-independent, metallic-like transport at low temperatures is sufficient-ly described by the extreme sensitivity of these superconducting films to external perturbations. We relate thissensitivity to the theoretical observation that, in two dimensions, superconductivity is only marginally stable. on March 30, 2019http://advances.sciencemag.org/Downloaded from INTRODUCTIONAll noninteracting two-dimensional (2D) electronic systems in thethermodynamic limit are expected to exhibit an insulating groundstate (1). This prevailing notion has been challenged only in the casewhere strong interactions dominate the electronic state notably in low-disorder, strongly interacting semiconductors, where an apparenttransition to metallic conduction at low temperatures (T’s) has beenobserved (2, 3).The physics gets more complex in the case where electronic cor-relations can lead to superconductivity. It is theoretically acceptedthat, in realistic 2D systems, with the unavoidable disorder and at afinite T, superconductivity exists only marginally and finite resistiv-ity is always expected (4, 5). The value of this residual resistance issensitive to the state of the system, and it usually depends exponen-tially on experimental variables such as T, magnetic field (B), measure-ment current (I), and the level of microscopic disorder. An exceptionis the case of exactly zero B, which can effectively be attained inexperiments, where true superconductivity, with zero resistance at afinite T, is expected.For these thin-film systems, the superconducting state can bemarkedly terminated with a transition to an insulating phase (6, 7).In this superconductor-insulator transition (SIT), metallic behavioris expected to be restricted to an unstable point at the transition (8).This point of view is often supported by experiments using a variety ofways to drive the SIT including thickness variation, disorder, B, andcarrier concentration [for a review, see (9)].There is, however, a growing number of independent studies(10–17) where the observation of an unexpected metallic state, in-tervening between the superconducting and insulating phases, hasbeen reported. The unique characteristic attributed to this “anom-alous metal” is that the superconducting transition, signaled by anexponential decrease below a well-defined critical T, TC, of the sheetresistance (R) from its normal state value, RN, is terminated, upon fur-ther cooling, with a crossover to a T-independent R that persists downto the lowest T ’s. This behavior, seen in thin films for which RN is sub-stantially lower than the quantum of resistance RQ≡ h/e2 ≃ 25.8kW, isobserved over a wide range of experimental parameters and extends torelatively high T ’s (18). Unlike ordinary metals, this state exhibits avanishing Hall effect that was associated with a new particle-hole sym-metric ground state (19, 20), its microwave response shows no cyclotronresonance, and it reveals the existence of short-range superconductingcorrelations (21).The physical origin of this anomalous metallic state remains con-troversial, with experimental measurements variously interpreted asevidence of a Bose-metal phase (16) or dissipation arising from collec-tive vortex tunneling (10, 15). Although several theoretical groupshave addressed this state (19, 22–31), its robustness and ubiquitousnature pose difficulties in the development of a comprehensive model(18). The purpose of this article is to show that the apparent metallicbehavior can result from an unforeseen sensitivity of these marginalsuperconductors to external perturbations.RESULTSOur data were obtained from two very different superconductingsystems. The first is amorphous indium oxide (a:InO) thin film(Fig. 1, A and B), known for its high level of disorder reflected by highRN (≲ h4e2 ≃ 6:4 kilohms). The second system we investigated is madeof sheets exfoliated from a single crystal of 2H-NbSe2 (Fig. 1, C andD), which are of high purity and are characterized by low RN (<100ohms) (32). Within the field of thin-film superconductors, these twosystems represent opposite limits with respect to structure and dis-order. Moreover, while 2H-NbSe2 is a purely 2D superconductor hav-ing a thickness d ≪ x, x being the superconducting coherence length,d of the a:InO films is approximately five times larger than its x (33).We begin by showing that the superconducting phase into whichour samples transition at TC, and which is interrupted as saturationsets in at lower T ’s, is completely restored by introducing external low-pass filters into the measurement setup (see fig. S1). This is illustrated byplotting R as a function of T −1 obtained from an a:InO film (Fig. 1E)and a 2H-NbSe2 film (Fig. 1F). In both samples, R obtained from theunfiltered measurements (i.e., measured without additional externallow-pass filters, red traces) initially decreased exponentially with an ap-proximate activated behavior R(T) º exp(−U(B)/kBT), where U(B) isthe activation energy and kB is the Boltzmann constant. The exponen-tial decrease then terminated with a transition to a saturated regime1 of 6http://advances.sciencemag.org/SC I ENCE ADVANCES | R E S EARCH ART I C L E on March 30, 2019http://advances.sciencemag.org/Downloaded from that persisted down to our lowest T ’s. It is this saturated behaviorof R that was previously interpreted as indicating the novel metallicstate (10, 15, 16, 18).When we repeated the measurements, this time with additionallow-pass filters installed (blue traces), we found that R continued tofollow the activated trend down to much lower T ’s, and as T was fur-ther lowered, R continued to decrease to our noise level without satu-rating. The external low-pass filters effectively reduce the bandwidth ofour measurements from 1 to 30 MHz (set by the twisted pairs of re-sistive measurement wires acting as low-pass resistor–capacitor filters)down to 200 to 300 kHz, depending on the specific setup (see, e.g.,fig. S2).The lowest R we now measure can exceed two orders of mag-nitude below the corresponding saturated values of the unfilteredmeasurements. We note that even with filtering, we continue to ob-serve deviation from activated behavior in the lowest T rangesmeasured. However, we believe that this results from imperfect filters.Additional measurements of a:InO film in a second fridge with im-proved low-T filters show no deviation from activated behavior overthe full range of achievable T ’s (Fig. 2). We conclude that our data donot support the existence of quantum corrections (10, 15, 34) to thewell-known transport due to thermally activated vortices (5).Although the effect the filters have on both systems is qualitativelysimilar, it is important to point out that, while for a:InO it is only seenwell below TC, for 2H-NbSe2 filtering has a measurable effect rightfrom TC and at B = 0. In Fig. 3A, we show the thermodynamic super-conducting-normal transitions of 2H-NbSe2, at B = 0 in the left panel,and near HC2 (the upper critical field terminating superconductivity)for several T ’s in the right. The common theme in these figures is that asignificant effect of the filters is measured very close to the transitioninto superconductivity. In contrast, for a:InO, initial differences betweenfiltered and unfiltered measurements are only seen much below TC. Thisis summarized in Fig. 3B, where we present the B − T phase diagram forTamir et al., Sci. Adv. 2019;5 : eaau3826 15 March 2019our samples. For 2H-NbSe2, the initial effect of the filters, indicated bygreen triangles, overlaps within error with the superconductor-normalphase boundary (defined by R = 0.9 ⋅ RN), while for a:InO the filterssignificantly influence the results only well within the superconductingphase, indicated by blue and red triangles.While filtering external radiation effectively eliminates the appar-ent metallic behavior, we found that saturation can be reintroduced byincreasing the current used in our four-terminal measurements. Forthis purpose, we used both DC and AC currents (IDC and IAC; seeMaterials and Methods) with similar results. The saturation inducedFig. 1. Eliminating saturation. (A and C) System structure and (B and D) microscope image of a:InO (AD12a) and 2H-NbSe2 (024) films, respectively. (E and F) R versusT−1 obtained from an a:InO film at B = 7 and 8 T, and a quad-layer 2H-NbSe2 at B = 2.3 and 3.5 T, respectively. Blue traces are measured with, and red traces without,filters. The top axis indicates the corresponding T’s. The black dashed lines in (E) are guides to the eye, indicating activated behavior. The data were measured byapplying a standard four-terminal lock-in technique with I0 = 1 (a:InO) and 100 (2H-NbSe2) nA.Fig. 2. Fully recovered activated behavior. R versus T −1 obtained from IT1b20,an a:InO film, measured with better filtration (see Materials and Methods for de-tails) at different B values. Activated behavior (straight line in an Arrhenius plot) isapparent down to our noise floor or lowest measurement T ’s (see, e.g., dashedblack lines at B = 10.75 and 12.3 T).2 of 6http://advances.sciencemag.org/SC I ENCE ADVANCES | R E S EARCH ART I C L E on March 30, 2019http://advances.sciencemag.org/Downloaded from by increasing IAC is demonstrated in Fig. 4A, where we present dataobtained from an a:InO film measured with filters at B = 10 T, usingincreasing levels of I0 (the amplitude of IAC). While at I0 = 1 nA, themeasured V/I, where V is the voltage drop along the sample, followedan activated behavior with deviations that are barely noticeable overour noise level, for I0 ≥ 50 nA the data significantly deviated from itslow-I0 value and saturation set-in at low T ’s, with the saturated valueincreasing with I0. For reference, we include one trace (red) measuredwithout filters and at I0 = 1 nA, which exhibits the low-T saturation.We note that, because R is an equilibrium value defined by limI→0V/I,the data presented in Fig. 4A strictly equal R only in the ohmic regime(I0 ≲ 1 nA). Similar results are obtained while increasing IDC (see Fig.4B, where we present data obtained from a 2H-NbSe2 film).When superconductors are subjected to strong enough B, theirtransport properties are dominated by vortex physics (5). ExcessiveI can dislodge vortices, which are otherwise pinned at low T’s, in-ducing voltage and dissipation. The saturation induced in our exper-iment by increasing I can therefore be attributed to heating. Under theapplication of a higher power (P = I⋅V) by the measurement circuit,the electronic system is unable to equilibrate with its low-T environ-ment. This leads to an out-of-equilibrium steady state where the elec-trons are held at an elevated T, Teff, higher than the surrounding T (35).The I-induced deviations from activated behavior, as well as the satu-ration regions, can therefore be attributed to Teff > T. We can self-consistently extract these Teff ’s by fitting the R(T) data, obtained fromthe filtered measurements in the ohmic regime, with an activated formand then using this fit as our thermometry calibration curve: For eachvalue of V/I, in the elevated I measurements, we associate a Teffcorresponding to V/I = R in the calibration curve. Using this procedure,we conveniently define Tsat as Teff in the R saturation regime.We now wish to suggest that the R saturation observed in ourunfiltered experiments, and which bears a notable resemblance to theI-driven saturation (see Fig. 4A), can also be associated with heating.While in this case the source of heating is less obvious, the fact thatfiltering the electrical lines connected to the sample effectively elimi-nates the saturation suggests that the culprit is ambient noise currentsthat propagate down the lines and couple directly to the low-T electronicsystem. We can estimate the power density (p) delivered to the elec-tronic system by these noise currents (pr) by comparing Tsat obtainedTamir et al., Sci. Adv. 2019;5 : eaau3826 15 March 2019during the application of known p in our filtered, elevated Imeasurements(TIsat) to theTsat obtained in the unfiltered, ohmicmeasurements (Trsat). Todo this, we plot, in Fig. 4C, the p dependence ofTIsat for two of our samplesanduse it as our pmeter. Reddiamonds indicateTrsat values correspondingto the unfiltered curves of each sample. We find pr = 1.8W/cm3 for thea:InO sample and 8.2 × 104 W/cm3 for the 2H-NbSe2 sample.Although our results show that our a:InO and 2H-NbSe2 filmsdo not exhibit an intermediate metallic phase, we cannot rule outthe existence of such a phase in other superconducting systems forwhich a metallic state was previously reported (10, 15). We can,however, naively extend our effective-temperature analysis to thesesystems. In Fig. 4D, we present Tsat versus B obtained from ourdata (blue and green symbols), together with Tsat values that weextracted from published data (black symbols). Whenever compar-isons between results obtained from filtered and unfiltered measure-ments are not available (empty symbols), we fitted the data measuredat higher T ’s with activated behavior and used these fits as our ther-mometry calibration curves. This procedure, introduced in this con-text in (10), only provides a lower bound for Tsat because the filteredmeasurements can also exhibit higher U(B) (see fig. S3). While thedata in Fig. 4D represent several very different systems, measured overa wide range of T ’s, they all share a similar B dependence: We foundthat TsatelogðHC2=aBÞ, where a is a fit parameter of order 1, worksreasonably well.Before we proceed to discuss the implication of this simple elevatedeffective-temperature scenario, we wish to point out that there are otherpossible mechanisms that would lead to I-dependent transport in thin-film superconductor such as ours. Nonlinear vortex–related responsemay be relevant at finite B’s, and Berezinskii–Kosterlitz–Thouless vortex-antivortex unbindingmay be at work at B = 0. At this stage, we are unableto rule out that these mechanisms play a notable role in the I responseof the system andmay even lead to saturated, T-independent R as T→ 0.Weare not aware of amodel that accounts for the stark difference betweenthe results of the filtered and unfiltered measurements.DISCUSSIONThe data we present here show that the metallic behavior, often ob-served in thin-film superconductors, results from the exposure of theFig. 3. Resistive transition. (A) Measurements of the T-driven (left) and B-driven (right) superconducting-normal phase transition in a 2H-NbSe2 film (024). Bluetraces are measured with, and red traces without, filters. (B) B−T phase diagram. The black line separating the superconducting and normal phases, defined by R =0.9 · RN, is obtained from the 2H-NbSe2 sample and includes data that were left out from (A) for visibility. The T and B values, where DR/RF = (RUnfiltered − RFiltered)/RFiltered = 3%, are marked in both (A) and (B) by green triangles. Both TC andHC2 are defined at R = 0.9 ·RN. For our a:InO films, blue and red triangles, we used TC =2.5 K (Ad12a) and 3 K (IT1b5).3 of 6http://advances.sciencemag.org/SC I ENCE ADVANCES | R E S EARCH ART I C L E on March 30, 2019http://advances.sciencemag.org/Downloaded from superconducting phase to unwanted radiation or high I’s. While thesecan, in many cases, be eliminated, it is still worthwhile to consider whythese superconductors so readily respond to excitations that leave othersystems, under similar conditions (see the Supplementary Materials forfurther discussion), unaffected. We point out that Tsat is routinelyaround a few kelvin, where it is unlikely that the cryogenic environmentwill limit the sample’s ability to cool. Because the external power couplesonly to the electronic system, which exhibits an exponential T depen-dence, it is reasonable to conclude that the observed sensitivity is a resultof a bottleneck in the heat-transfer process that is between the electronsand the host phonons (35). This is not unexpected because in supercon-ductors the electron condensate is decoupled from the heat-carryingphonons. If such a limiting mechanism is at play, a much more thor-ough theoretical analysis is necessary before we can go any further withquantitative tests.In this study, we were able to compare two very different systemsunder virtually identical measurement conditions. It is reasonable toTamir et al., Sci. Adv. 2019;5 : eaau3826 15 March 2019assume that, without filters, the radiation delivered to both types ofsamples would be the same. Unexpectedly, we find very different pr’s.Similarly, their Tsat values are different: <0.4 K for a:InO and ~2 K for2H-NbSe2. If the effective-temperature picture is correct, we need to un-derstand why two samples under similar external radiation end up re-sponding in such a differentmanner. The reason,we believe, is rooted inthe energy balance maintained by the electrons. Even if the radiation isthe same, it is very likely that different systemswill absorb this energy indifferent ways, reflecting the specific details of their electronic state.Compounding this are possible differences between the strength ofthe coupling to the phonon system to which the electrons can transferthe energy absorbed from the radiation. A detailed understanding ofthis scenario awaits further theoretical developments.In summary, we showed that two very different thin-film super-conductors are extremely sensitive to external perturbations and, inresponse to such perturbations, exhibitmetallic-like, saturatedT depen-dence. We suggested two possible mechanisms: The first is based onFig. 4. Induced saturation and saturation T. (A) V/I versus T −1 obtained from an a:InO film, measured at B = 10 T with increasing I0’s. (B) dV/dI versus T−1 obtainedfrom a 2H-NbSe2 film, measured at B = 2.3 T with an increasing level of IDC (see Materials and Methods). In both (A) and (B), we include one trace (red) measured, at ourlowest I, without filters. (C) T Isat versus p extracted from the a:InO data presented in (A) (circles), and the 2H-NbSe2 data presented in (B) (triangles), adopting the samecolor scale for the different I’s. The red symbols represent Trsat extracted from the unfiltered measurements. The a:InO data include IAC’s left out of (A) for visibility. Thesecurves are used as p meters to estimate pr = 1.8 and 8.2 × 104 W/cm3 for the a:InO and 2H-NbSe2 samples, respectively. (D) Tsat versus B evaluated for several samples.Our data are plotted in blue (a:InO) and green (2H-NbSe2). The MoGe (10), Ta (11), and ZrNCl (15) data (black symbols) were extracted from the cited references. Fullsymbols represent data that were calculated using filtered measurements as a thermometer, while data plotted with empty symbols were estimated following theprocedure in (10). All samples exhibit similar logarithmic B dependence (see dashed black lines).4 of 6http://advances.sciencemag.org/SC I ENCE ADVANCES | R E S EARCH ART I C L Evortex depinning, and in the other, we assume that an overheated stateexists, where the electronic system is unable to equilibrate with itssurroundings. In the latter case, one should theoretically address notonly the external power dissipated but also the heat flow away fromthe electronic system.http:/Downloaded from MATERIALS AND METHODSIn this work, we studied several different a:InO and 2H-NbSe2samples. Their relevant parameters are presented in table S1. Detailsof the growth and fabrication were previously published [see (32) for2H-NbSe2 and (36) for a:InO].The data presented in Fig. 2 were measured in a dilution refrigera-tor equipped with heavily filtered DC lines comprising feedthrough pifilters at room temperature, low-resistance twisted pairs (~8 ohms)from 300 to 4 K to reduce Johnson noise, lossy shielded twisted-pairs(~500 ohms) from 4 K to the mixing chamber (MC) stage, copper-powder filter (37) on the MC stage, and cryogenic-compatible 47-nFcapacitor-to-ground on the sample holder. Furthermore, as thermo-metry below 0.1 K is delicate, a RuO2 thermometer calibrated by60Co nuclear orientation thermometry has been installed on the sam-ple holder close to the sample; thus, it was subjected to the samecooling power from the wiring. This additional on-chip thermometrysuppresses the very last deviations from activated transport at thelowest T ’s./advances.sciencemag.orgSUPPLEMENTARY MATERIALSSupplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/3/eaau3826/DC1Fig. S1. Schematics of the measurement circuit.Fig. S2. Probe transmission.Fig. S3. Activation energy.Table S1. Sample parameters.References (38–40) on March 30, 2019/REFERENCES AND NOTES1. E. Abrahams, P. W. Anderson, D. C. Licciardello, T. V. Ramakrishnan, Scaling theory oflocalization: Absence of quantum diffusion in two dimensions. Phys. Rev. Lett. 42,673–676 (1979).2. S. V. Kravchenko, G. V. Kravchenko, J. E. Furneaux, V. M. Pudalov, M. 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Wellstood, C. Urbina, J. Clarke, Hot-electron effects in metals. Phys. Rev. B 49,5942–5955 (1994).Acknowledgments: We are grateful to I. Aleiner, B. Altshuler, M. Feigelman, D. Kennes,S. A. Kivelson, K. Michaeli, A. Millis, P. W. Phillips, and B. Spivak for fruitful discussions.Funding: This research was supported by The Israel Science Foundation (ISF grant no. 556/17),the Minerva Foundation, Federal German Ministry for Education and Research, GrantNo. 712942, the Horizon 2020 European Research Council (ERC) grant QUEST no. 637815, theNSF MRSEC program through Columbia in the Center for Precision Assembly of Superstraticand Superatomic Solids (DMR-1420634), the Global Research Laboratory (GRL) Program5 of 6http://advances.sciencemag.org/cgi/content/full/5/3/eaau3826/DC1http://advances.sciencemag.org/cgi/content/full/5/3/eaau3826/DC1https://arxiv.org/abs/1712.07215http://advances.sciencemag.org/SC I ENCE ADVANCES | R E S EARCH ART I C L E(2016K1A1A2912707) funded by the Ministry of Science, ICT and Future Planning via theNational Research Foundation of Korea (NRF), and Honda Research Institute USA Inc. A portionof this work was performed at the National High Magnetic Field Laboratory, which issupported by National Science Foundation Cooperative Agreement Nos. DMR-1157490 andDMR-1644779 and the State of Florida. We also acknowledge the support provided byThe Leona M. and Harry B. Helmsley Charitable Trust. Author contributions: I.T., A.B., E.J.T.,F. Gorniaczyk, A.D., T.L., K.W., and T.T. prepared the samples. I.T., A.B., E.J.T., F. Gorniaczyk, A.D.,T.L., D.W., F. Gay, and B.S. performed the experiments. I.T. and A.B. carried out the analysisand interpretation of the results. I.T. wrote the manuscript with the input of all co-authors.B.S., J.H., C.R.D., A.N.P., and D.S. supervised the project. Competing interests: The authors declarethat they have no competing interests. Data and materials availability: All data needed toTamir et al., Sci. Adv. 2019;5 : eaau3826 15 March 2019evaluate the conclusions in the paper are present in the paper and/or the SupplementaryMaterials. Additional data related to this paper may be requested from the authors.Submitted 5 June 2018Accepted 30 January 2019Published 15 March 201910.1126/sciadv.aau3826Citation: I. Tamir, A. Benyamini, E. J. Telford, F. Gorniaczyk, A. Doron, T. Levinson, D. Wang,F. Gay, B. Sacépé, J. Hone, K. Watanabe, T. Taniguchi, C. R. Dean, A. N. Pasupathy, D. Shahar,Sensitivity of the superconducting state in thin films. Sci. Adv. 5, eaau3826 (2019).6 of 6 on March 30, 2019http://advances.sciencemag.org/Downloaded from http://advances.sciencemag.org/Sensitivity of the superconducting state in thin filmsWatanabe, T. Taniguchi, C. R. Dean, A. N. Pasupathy and D. ShaharI. Tamir, A. Benyamini, E. J. Telford, F. Gorniaczyk, A. Doron, T. Levinson, D. Wang, F. Gay, B. Sacépé, J. Hone, K.DOI: 10.1126/sciadv.aau3826 (3), eaau3826.5Sci Adv ARTICLE TOOLS http://advances.sciencemag.org/content/5/3/eaau3826MATERIALSSUPPLEMENTARY http://advances.sciencemag.org/content/suppl/2019/03/11/5.3.eaau3826.DC1REFERENCEShttp://advances.sciencemag.org/content/5/3/eaau3826#BIBLThis article cites 37 articles, 4 of which you can access for freePERMISSIONS http://www.sciencemag.org/help/reprints-and-permissionsTerms of ServiceUse of this article is subject to the registered trademark of AAAS.is aScience Advances Association for the Advancement of Science. No claim to original U.S. Government Works. 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