2D Materials LETTER • OPEN ACCESS You may also like - Telecom wavelength single photon Two-dimensional cuprate nanodetector with single sources Xin Cao, Michael Zopf and Fei Ding telecom photon sensitivity at T = 20 K - An integral gated mode single photon detector at telecom wavelengths Zhengjun Wei, Peng Zhou, Jindong Wang To cite this article: Rafael Luque Merino et al 2023 2D Mater. 10 021001 et al. - Superconducting nanowire single-photon detectors: physics and applications Chandra M Natarajan, Michael G Tanner and Robert H Hadfield View the article online for updates and enhancements. This content was downloaded from IP address 158.109.49.35 on 08/11/2023 at 14:40 2D Mater. 10 (2023) 021001 https://doi.org/10.1088/2053-1583/acb4a8 LETTER Two-dimensional cuprate nanodetector with single telecom OPEN ACCESS photon sensitivity at T = 20 K RECEIVED 26 October 2022 Rafael Luque Merino1,8,9,∗, Paul Seifert1,2, José Durán Retamal1,3, Roop K Mech1,8,9, Takashi Taniguchi4, REVISED Kenji Watanabe5, Kazuo Kadowaki6, Robert H Hadfield7 and Dmitri K Efetov1,8,9,∗ 11 January 2023 1 ICFO—Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Castelldefels, Barcelona 08860, Spain ACCEPTED FOR PUBLICATION 2 19 January 2023 Institute of Physics, Faculty of Electrical Engineering and Information Technology (EIT 2), Universität der Bundeswehr München, Neubiberg 85577, Germany PUBLISHED 3 9 February 2023 Catalan Institute of Nanoscience and Nanotechnology (ICN2), BIST & CSIC, Barcelona 08193, Spain 4 International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan 5 Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan Original content from 6 University of Tsukuba, 1-1-1 Tennodai, Tsukuba-shi 305-8572, Japan this work may be used 7 under the terms of the James Watt School of Engineering, University of Glasgow, Glasgow, United Kingdom 8 Creative Commons Fakultät für Physik, Ludwig-Maximilians-Universität, Schellingstrasse 4, 80799 München, Germany 9 Attribution 4.0 licence. Munich Center for Quantum Science and Technology (MCQST), München, Germany ∗ Any further distribution Authors to whom any correspondence should be addressed. of this work must maintain attribution to E-mail: rafael.luque@icfo.eu and dmitri.efetov@lmu.de the author(s) and the title of the work, journal Keywords: 2D, cuprate, nanodetector, telecom, photon, nanowire, He-FIB citation and DOI. Supplementary material for this article is available online Abstract Detecting 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, broadband and fast response. However, the use of low T C superconducting thin films limits their operation temperature to approximately 4 K and below. Here, we demonstrate proof-of-concept nanodetectors based on exfoliated, two-dimensional cuprate superconductor Bi2 Sr2 CaCu2 O8-δ that 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-T C nanodetector thanks to a novel approach, combining van der Waals fabrication techniques and a non-invasive nanopatterning based on light ion irradiation. This result paves the way for broader application of single-photon technologies, relaxing the cryogenic constraints for single-photon detection at telecom wavelength. Superconducting nanowire single-photon detectors for new material platforms [9–11]. In particular, van (SNSPD’s) constitute an established technology for der Waals (vdW) heterostructures of 2D materials broadband, sensitive and fast detection of faint optical [12–15] and high-T c superconductors [9, 16–24] signals [1–3]. These detectors, based on low T c have received interest as candidates for the devel- superconducting thin films such as NbN or WSi, opment of next-generation SNSPD’s with increased provide high efficiency [4], fast response (∼ ns) capabilities. [2, 3] and excellent timing resolution (∼ ps) [5]. Cuprate superconductors are natural candidates SNSPD’s can be integrated in free-space and fiber- to push SNSPD technology to higher temperatures coupled architectures [1, 2], as well as planar photonic [9]. A cuprate-based SNSPD could operate above circuits [6, 7]. However, their operating temper- liquid nitrogen temperatures (77 K) offering a ature is usually limited to T ≤ 4 K by the T c critical technological advantage. Fabrication of of the thin films. To date, the highest operating cuprate detectors has proven to be very challen- temperature for an SNSPD is 11 K, demonstrated ging, as cuprates degrade rapidly under ambient in a MgB2 nanostrip [8]. Expanding single-photon conditions. Despite extensive research efforts, most detection to higher operating temperatures, longer cuprate nanostructures exhibit flux-flow behaviour wavelengths and faster response motivates the search characterized by smooth current–voltage (I–V) © 2023 The Author(s). Published by IOP Publishing Ltd 2D Mater. 10 (2023) 021001 characteristics that preclude SNSPD operation [16, temperature dependent measurements of the two- 22, 23]. Sharp and hysteretic transport character- terminal resistance R, normalized to its value at 120 K istics, as those of conventional SNSPD thin films, (R120K ) for three BSCCO/hBN nanopatterned detect- were reported for high-quality YBa2 Cu3 O7- δ (YBCO) ors and an exfoliated, unpatterned BSCCO flake (ref- nanowires along with the observation of dark counts erence sample). All the curves show clear supercon- [18, 19, 21]. To date, conventional fabrication ducting transitions, where R/R120K drops to close to approaches based on lift-off methods or heavy ion 0 resistance, with a residual resistance value stem- milling have not realized the prospect of a cuprate ming from the contact resistance in this two-terminal SNSPD. device. The critical temperature of the BSCCO nano- We explore an alternative approach based on exfo- structures T c , defined from the mid-point of the liated, 2D cuprate Bi2 Sr2 CaCu2 O8-δ (BSCCO). Novel superconducting transition, ranges between 60 and fabrication methods allow us to harness the pristine 80 K. The lowered T c and broadened SC transition superconducting properties of few-layer BSCCO of the patterned flakes likely derive from microscopic [24–26]. We report multiple nanostructures with disorder and/or He-ion implantation [30, 31]. Still, sharp, hysteretic I–V characteristics combined with the critical temperatures remain close to their nom- high T c (70–80 K). Optoelectronic measurements inal value and near liquid nitrogen temperatures. of the BSCCO nanostructures reveal single-photon The upturn of the resistance below T c stems from sensitivity up to a record temperature of T = 20 K. contact resistance at the BSCCO/Au interface form- The detection speed and efficiency remain low for ing a Schottky barrier. For two-terminal measure- these proof-of-concept cuprate nanodetectors. ments with low excitation current (10–100 nA in this measurement) the contact resistance contribu- 1. Results and discussion tion becomes sizable. When applying a DC offset cur- rent, as done below, this Schottky barrier is greatly 1.1. Device fabrication and transport lowered. characterization Figure 1(c) shows the I–V characteristics of the Figure 1(a) summarizes the detector concept and fab- BSCCO nanostructures for different temperatures, rication. We fabricate vdW heterostructures of few- and the inset shows the corresponding colour plot for layer BSCCO encapsulated with a top hBN inside the full temperature range. The I–V curve at T = 10 K an Ar-filled glovebox [27]. We use a bottom con- features an abrupt transition to the resistive state at tact approach with thin metallic electrodes to bypass a critical current. The combination of high T c and lift-off methods, which lead to oxidation of few-layer low critical current Ic proves that the nano-patterning BSCCO. In order to preserve superconductivity in confines the supercurrent into a narrow, pristine BSCCO nanostructures, we use a helium focused BSCCO channel, as the intrinsic Ic for an unpatterned ion beam (He-FIB) to pattern our BSCCO/hBN BSCCO flake is several orders of magnitude larger. heterostructures [28]. The doping level (and elec- The critical current density of the nano-constriction tronic properties) of few-layer BSCCO can be locally is JC ∼ 7x106 A cm−1 , comparable to previous reports modified by light He-ion irradiation [29–31]. Dir- on high-quality nanowires based on YBCO thin films ect patterning of insulating BSCCO areas can restrict [18, 19]. The appearance of a single, well-defined the supercurrent to flow exclusively along channels of voltage jump at Ic reflects a robust superconduct- crystalline, non-irradiated BSCCO that preserve high ing state of the undamaged channel in the BSCCO T c . Importantly, for low ion doses the He-FIB irradi- nanoconstriction. As T increases, the I–V character- ation does not etch through the encapsulating hBN istics become flux-flow like. However remarkably, the layer (see figure S4). This non-invasive patterning sharply transition at Ic persists up to T = 30 K. technique allows us to produce high-quality nano- Strikingly we observe a strong hysteresis in the I– structures based on 2D BSCCO flakes that remain V curves with respect to the sweeping direction of the protected by the encapsulating hBN. This method bias current I b , as shown in figure 1(d) at T = 20 K. also provides very high lateral resolution, allowing the As I is decreased below I c , the superconducting state writing of complex patterns with ∼ nm resolution. in the nanostructure is not recovered. Instead, the The left inset in figure 1(a) shows an scanning elec- nanowire switches back into its superconducting state tron microscopy (SEM) image of a He-FIB defined at a lower retrapping current I r . The occurrence of the nanostructure in our BSCCO/hBN stacks. This device hysteresis is a linked to the sharp I–V characteristics at is 250 nm wide and 2.7 µm long. See Methods and I c and the high normal state resistance in the BSCCO sections S1 and S2 of the SI for further details on the nanostructure [18–21]. It also intricately depends on device fabrication. the thermal properties of the superconducting devices We study the transport properties of the fab- [20]. In our nano-structured BSCCO constrictions, ricated BSCCO nanostructures and compare them the thermal conductance is reduced both in-plane, to pristine BSCCO flakes. In figure 1(b) we present across the disordered irradiated BSCCO regions [30], 2 2D Mater. 10 (2023) 021001 Figure 1. Two-dimensional superconducting cuprate nanowires for photodetection. (a) Illustration of the detector concept. A high-T c superconducting BSCCO flake is encapsulated with hBN and then nanopatterned using a focused He-ion beam. The resulting nanostructure is current-biased (I b ) in a two-terminal configuration. Left inset shows an SEM image of the nanowire in Device A, scale bar has 1 µm length. Right inset depicts a schematic cross-section of the vdW heterostructure. (b) Two-terminal resistance vs. temperature of the BSCCO nanostructures. All curves have been normalized to the resistance value at 120 K, before the superconducting transition. Black curve shows the four-terminal resistance for a reference, unpatterned BSCCO flake. For all nanostructures, T c ranges between 60–80 K. (c) I–V characteristics of device A for increasing temperature. The abrupt voltage jump 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 I c (T) dependence. Beyond 50 K, the smooth I–V characteristics preclude a reliable extraction of I c . (d) I–V characteristic for device A at T = 20 K, exhibiting a sharp voltage jump along with a well-defined hysteresis loop. Vertical offset between red and blue traces is due to Joule heating effects in the DC measurement. Inset shows I c (T) and I r (T). Hysteresis loop remains finite up to T = 30 K. and out-of-plane, as the 2D flake lies on the substrate figure 1(d)) highlighting their potential as supercon- without any lattice matching [32]. Figure S5 in the SI ducting nanodetectors with single photon sensitivity demonstrates the ubiquity of hysteretic behaviour in and high operating temperature. these nanostructures. Such hysteretic behaviour is a key requirement 1.2. Photo-induced switching events in the BSCCO for SNSPD. The nucleation of a self-sustaining resist- nanostructure ive region after photo-absorption induces Joule heat- We now characterize the optoelectronic response of ing, precluding the recovery of the superconduct- the BSCCO nano-constriction at a temperature of ing state when approaching Ic from above. Super- T = 20 K, where figure 2(c) shows a sketch of the conducting nanowire detectors are kept well below readout circuit and section 5 of the SI illustrates the T c and biased close to their critical current I b ∼ I c . complete optoelectronic setup. The BSCCO nano- Photo-induced hotspots are nucleated and grow due constriction is current-biased close to its switching to Joule heating leading to a thermal runaway of current I b ∼ 0.97 I c and connected in parallel to a load the detector, which latches into the resistive state resistor RLoad . The load resistor shunts the current until the bias current is shunted [33]. Thus, a voltage once the nanostructure turns resistive, and enables drop takes place in the shunting circuit due to the free-running detection as the device self-resets after resistive switching of the nanodetector. Remarkably, a time τ . We illuminate the biased BSCCO nanode- the observed hysteretic behaviour of the BSCCO tector using a CW laser at a telecom wavelength of nano-constrictions persists up to T = 30 K (see λ = 1550 nm, and monitor the voltage drop across 3 2D Mater. 10 (2023) 021001 Figure 2. Photo-induced voltage signal in Bi2212 nanowires. (a) Photo-induced voltage drop at the load resistor over time for 50 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 time is τ = 712 µs. Switching rate of the detector along the red dashed line in (a). Optoelectronic measurement schematic and spatial photovoltage 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-induced which does not include a Bias Tee to isolate the bias clicks that appear only at elevated photon fluxes (DC) and readout (AC) paths. It is worth noting that are absent in dark conditions. Figure 2(a) illustrates the contact resistance in these devices also sets some the appearance of these switching events under laser limitations on the choice for parallel load resistors, as illumination. well as energy dissipation and capacitance in the con- Using an oscilloscope we measure the time- tact interfaces that may affect the shunting dynamics. domain traces of the photo-induced clicks. We find We identify the photo-active area by scanning the that each click (figure 2(b)) features a fast rise time laser beam across the device and measuring with the (few µs) and a slow decay time τ = 712 µs, obtained AC Lock-in technique. As expected, peaks at the nar- fitting the falling edge of the pulse. The full recov- rowest area of the device where the superconduct- ery time of the device lasts about 2 milliseconds. ing state is closest to its transition. In figure 2(c), we The observed τ is much slower than the reset overlay the photo-voltage mapping V ph with a SEM time of conventional SNSPD’s(∼ ns) [2, 3] and image of the device. Having located the detector’s act- the reported intrinsic photoresponse time of cuprate ive area, we now measure its switching rate using a superconductors [26, 34]. This slow relaxation time is Zurich UHLFI as a fast voltmeter. Figure 2(d) shows consistent across all devices (figure S7). the measured switching rate of the detector in a scan We believe the observed timescale to be an across the nano-constriction (indicated by the red extrinsic effect, as the hotspot dynamics in a BSCCO dashed line in figure 2(c)). As the laser spot illu- nanostructure are expected to be orders of mag- minates the ‘wings’ of the nanostructure, the switch- nitude faster. In previous work, we found the intrinsic ing rate is constant and increases five-fold at the thermal relaxation time of BSCCO bolometers to be nanostructure’s narrowest, most sensitive area. The in the order of nanoseconds [24]. These limitations high spatial sensitivity of the switching rate indicates likely stem from a non-optimized electrical circuit, that the clicks do not originate from a heating, 4 2D Mater. 10 (2023) 021001 Figure 3. Single photon sensitivity at T = 20 K. (a) Switching rate and dark count rate of device A at 20 K for increasing bias current. Vertical segments indicate the bias points examined in (c). (b) Distribution of the photo-induced switching events in device A for increasing optical power at 20 K,Ib = 0.97Ic . The switching event distribution is consistent with Poissonian statistics of 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 to its maximum value. The switching statistics for Ib = 0.97Ic follow a linear dependence, indicating single-photon sensitivity of the nanodetector. For Ib = 0.85Ic , the switching rate follows a power law of exponent m ≈ 3, indicating multi-photon sensitivity of device A at lower bias currents. Switching events recorded at 20 K. The maximum switching rate for Ib = 0.97Ic and Ib = 0.85Ic are 450 Hz and 38 Hz, respectively. Maximum optical power is 100 pW. bolometric effect. Instead, this observation points nanodetector changes and the switching rate does not towards Cooper pair breaking and a subsequent ava- fully saturate [35, 36]. lanche effect leading to nanowire switching. 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 the 1.3. Statistics of the switching events and absorption of stray photons, likely coming from the single-photon sensitivity thermal emission from the room-temperature object- We characterize the sensitivity of our BSCCO nan- ive. As the bias current is increased, the switching rate odetectors by studying the switching rate as a func- grows surpasses the dark switching rate as the detector tion of applied bias current I b and incident optical becomes more sensitive to the high flux of 1550 nm power P. All following measurements are performed photons. at T = 20 K. In order to reliably discern switch- We analyze the statistics of the observed switch- ing events from the noise floor, we define a voltage ing events fixed temperature of T = 20 K and for threshold based on the detector’s switching statist- varying optical powers and bias current configura- ics under no illumination at each I b . The following tions. We record switching events in 5 min windows. discussion is consistent for different choices of this The distribution of few-photon detection events in threshold. The protocol to define the threshold is fur- SNSPD’s can be described through Poissonian stat- ther detailed in section S7 of the SI. istics, as the switching events are rare and uncorrel- First, we fix the optical power on the detector ated. In figure 3(b), we illustrate the distribution of and vary the applied bias current I b . For SNSPD- switching events at I b = 0.97 I c for increasing optical type detectors, the sensitivity and detection efficiency power. At low optical power (1 pW), very few clicks strongly depend on I b , increasing as I b approaches I c . are observed and the switching events exhibit a highly These detectors reach single-photon sensitivity for I b skewed Poissonian-like distribution. As the optical I c , at the cost of increased false counts due to thermal power is increased, the switching rate of the detector fluctuations and/or stray photons. Figure 3(a) shows increases and the distribution evolves towards higher the switching rate of the detector for increasing I b mean values µ and variances σ 2 . The distribution of under P = 60 pW illumination and in dark condi- the observed clicks is compatible with Poissonian stat- tions. We find that the switching rate of our BSCCO istics arising from few-photon absorption events in nanowire rapidly grows for I b ⩾ 0.9 I c . A full sat- the BSCCO nanodetector. The bins in figure 3(b) cor- uration of the detector’s switching rate, indicative of respond to 60 millisecond time windows. full internal quantum efficiency, was not observed. Lastly, we present the power dependence of the The growth of the switching rate slows down signi- switching rate of our BSCCO superconducting nan- ficantly for I b ⩾ 0.97 I c , suggesting that a full satura- odetectors. As the sensitivity of SNSPD-type detect- tion could be achieved. The non-saturating switching ors depends strongly on the applied bias current rate is common in nanoconstriction detectors where [36, 37], we study the sensitivity of our devices at the device geometry leads to a position-dependent I c . two different bias conditions, highlighted by the ver- Thus, as Ib is increased the effective active area of the tical colored segments in figure 3(a). The low-bias 5 2D Mater. 10 (2023) 021001 condition (orange) corresponds to Ib = 0.85 Ic and estimated, as the microscopic details of the irradi- the high-bias condition (blue) is Ib = 0.97 Ic . ation are unknown. (c) Another plausible scenario is Figure 3(c) shows the power dependence of the existence of a highly efficient, nanometric region the switching rate in the high and low-bias condi- inside the detector where photodetection takes place. tions. The few-photon sensitivity of an SNSPD-type Assuming an absorption coefficient of 17% [39] and detector can be inferred from the power depend- full quantum efficiency, we can estimate the area of ence of its switching rate. The probability to detect such a region to be ∼ 80 nm2 . This scenario is remin- k photons (switching event caused by simultan- iscent of switching events around local microscopic eous absorption of k photons) is given by P [k] ∝ defects and cannot be ruled out. e−λ λk /k!, where λ is the mean (absorbed) photon The microscopic details of the physical processes number in the detector per unit time. For a single- occurring after photo-absorption in the BSCCO photon detector the switching rate should increase nanostructures remain an open question. Even linearly with incident power P [k = 1] ∝ λ. We though our experiment does not probe the detection observe a linear (m = 0.95 ≈ 1) power dependence mechanism of this system, our results are consist- of the switching rate in the high-bias condition ent with an agnostic hotspot model. In this scenario (I b ∼ 0.97 I c ). When the bias current is lowered, the photon energy is absorbed by the superconduct- the switching rate of the BSCCO detector is strongly ing condensate, locally breaking Cooper pairs. The reduced and exhibits a markedly different depend- Cooper pair density is suppressed in the hotspot, ence. For low bias (I b ∼ 0.85 I c ), the dependence precluding the supercurrent from flowing across the falls closer to a power law of exponent m = 2.93 ≈ 3, full width of the nanostructure. The hotspot grows indicative of multi-photon (two and three-photon) through avalanche effect due to Joule heating, even- events dominating the detector’s response. Exten- tually causing the entire nanowire width to become ded data supporting this observation is presented in resistive. This avalanche effect can give rise to macro- section 8 of the SI. scopic voltage signals from a microscopic perturba- This behaviour is consistent with a single-photon tion (single-photon absorption). sensitivity of the BSCCO nano-constrictions at T = The observation of strong hysteresis in the I–V 20 K for telecom photons, where the observation of characteristics of our nanodetectors supports the multi-photon sensitivity at lower bias current fur- nucleation of a self-sustaining hotspot. We observe ther supports the SNSPD-like characteristics of the complete latching of the nanodetector after photo- BSCCO nanodetectors [36, 37]. As discussed before, absorption in the absence of a shunting circuit, prov- far from the superconducting transition, the energy ing that the avalanche effect can be triggered optically. deposited by a single absorbed photon is not enough In literature, hotspots in cuprate thin films have been to trigger a switching event and multiple simultan- observed directly through thermal imaging [40] and eous photons need to be absorbed. Multi-photon indirectly through transport measurements [41, 42]. sensitivity is rarely observed in commercial SNSPD’s, The large thermal conductivity κ of cuprates has lim- as large fill factor designs make simultaneous absorp- ited cuprate nanostructures to the flux-flow regime, tion of multiple photons in the same area extremely where an avalanche effect does not take place and ulti- unlikely. Instead, for detectors featuring constric- mate sensitivity cannot be achieved. Suppression of tions, these events are more prominent and their the thermal conductance in these 2D vdW nanostruc- photon sensitivity is strongly bias-dependent [36]. In tures could explain the existence of a self-sustaining our case, the CW nature of the illumination also pro- hotspot. This behaviour is not expected for Au- motes multi-photon contributions to the switching capped thin films studied in other reports [16, 18]. rate. We believe that tailoring of thermal and electronic The detection efficiency can be roughly estimated properties will be key for developing next-generation using the incident power, number of switching events quantum sensors based on cuprate nanostructures. and the optical cross-section of the detector. Fur- Achieving this while preserving the superconduct- ther details on the efficiency estimation are provided ing properties of the material may prove challen- in section S11 of the SI. In the high-bias condi- ging. Possible advances of the device fabrication are tion where single-photon sensitivity is observed, we discussed in section 4 of the SI. Other avenues to estimate a lower bound for the detector efficiency enhance detector performance include the design of η ≈ 3.3 × 10−4 . Several factors may contribute to of optical gratings and nanoantennas to boost the this low figure-of-merit: (a) due to the large super- absorption in the material. The integration in planar conducting gap of BSCCO, the energy of a single photonic architectures, highly compatible with 2D telecom photon would only break around a dozen materials, could also boost the device’s efficiency Cooper pairs. The resulting quasiparticle generation [6, 7, 24]. Lastly, the material properties of BSCCO process that leads to a resistive switching may there- also show promise for detection of single-photons fore not be efficient [38]. (b) the effective (elec- at shorter wavelengths, as well as its application for tronic) width of the active region may be smaller than photodetectors resilient to high magnetic fields [43]. 6 2D Mater. 10 (2023) 021001 In summary, we report single-photon sensitivity Our devices are typically kept in the cryostat for at T = 20 K for telecom photons in nanostruc- 2–4 week measurement runs. Careful thermal cyc- tures based on exfoliated 2D cuprate superconductor ling can preserve the detector’s SC properties. Pro- BSCCO. This proof-of-concept nanodetector sets the longed exposure to air leads to oxidation due to oxy- highest operation temperature reported to date for gen out-diffusion and water creep through the SiO2 an SNSPD-type detector, establishing BSCCO-based roughness. vdW nanostructures as a promising platform for next-generation quantum sensors. 3.2. Transport and optoelectronic setup We characterize the optoelectronic properties of the vdW BSCCO nanowires using an Attodry800 optical 2. Note cryostat with a base temperature of 8 K. We maintain a temperature of 20 K on the sample using a stand- During the elaboration of this text, we became ard calibrated microheater + Cernox thermometer aware of a similar work published in arXiv after combination. We ensure proper thermalization of the ours. This complementary work by Charaev et al sample with the cryostat’s cold finger. employs similar fabrication methods, highlighting For transport characterization, we perform both the potential for next-generation SNSPD’s based on AC Lock-in measurements and DC measurements. high-temperature superconductors. The reference is For the AC Lock-In measurements, we use a 10 nA Charaev et al arXiv:2208.05674 (2022). AC excitation current at a reference frequency of 126 Hz. An SRS860x Lock-In amplifier is used 3. Methods both for sourcing and sensing. DC measurements are performed using a combination of DC sources 3.1. Device fabrication (Yokogawa GS200, Keithley 2450) and a multimeter We fabricate our samples through the dry-transfer (Keithley 2700). It is worth noting that for Device C, technique inside an Ar-filled glovebox (H2 O, the normal state resistance is very large (∼100 KΩ), O2 < 0.8 ppm). Few-layer flakes of optimally making a voltage bias circuit favourable over a cur- doped BSCCO (10–20 nm) are exfoliated using rent bias circuit. polydimethylsiloxane (PDMS) stamps, then trans- Laser excitation is provided by a telecom CW ferred onto pre-patterned metallic electrodes (Ti/Au, diode laser (Thorlabs SFL1550P), driven by a DC cur- 2/20 nm). BSCCO flakes are then encapsulated using rent source (Keithley 2400). The laser beam is first pre-selected thin hBN flakes (∼ 20 nm). We probe attenuated using neutral density filters. Then, it is the two-terminal resistance of our devices using a aligned and focused onto the sample using a com- probe-station inside the glovebox. The entire process bination of room-temperature galvanic mirrors and is performed in less than 20 min to avoid degradation a cryogenic three-axis piezo stage for the sample. of few-layer BSCCO flakes. The entire vdW assembly At optimal focus, the laser has a beam width of process is done at room temperature. w0 ∼ 2 µm. The optical power is measured using a The chip is then pasted onto a stub for He-FIB power meter. We calibrate the laser excitation power using silver paste and the contacts of the device are in the range between 10 nW and 1 µW. Then we intro- bonded onto the metallic stub, so the entire device duce a neutral density filter of density D = 4 in the remains grounded during patterning. Outside the optical path, which attenuates the optical power by glovebox, the devices are always in vacuum using a four orders of magnitude. commercial vacuum container. Therefore, the device The detector is current-biased, connected in par- is only exposed momentarily, for example during allel to a load resistor. The voltage drop at the load res- bonding. istor generated by the detector’s resistive switching is In the He-FIB we work with 30 KeV acceleration recorded using a Zurich UHFLI (10 MΩ input imped- voltage for the Helium beam, and typical emission ance, 600 MHz bandwidth, 1.8 GSa s−1 sampling currents between 2–5 pA. For each sample, we cal- rate). A low-noise amplifier with 45 dB gain and ibrate the optimal He ion dose in order to locally bandwidth between 100 Hz and 100 KHz is used to turn BSCCO insulating. This process is discussed in pre-amplify the voltage spikes. The Zurich UHLFI section 2 of the SI, as well as in [22]. Typical ion doses records switching events for 5 min at each optical range between 20–90 pC µm−2 . Crucially, for low ion power and bias current setting. Time—domain traces doses, the Helium ion beam does not etch through the of the switching events are recorded using the oscillo- encapsulating hBN layer so the BSCCO flakes remain scope function of the Zurich UHFLI with a sampling protected. We fabricate simple nanowires as well as rate of 175 MHz. Alternatively, we study the photo- complex structures (see section 1 of the SI). Lastly, we voltage signal of the device using an optical chop- remove the sample from the metallic stub and bond per and a Lock-In amplifier (SRS860x) referenced at the chip to a pre-grounded PCB. The PCB is then the chopper frequency. Optimizing the optical coup- loaded into our optical cryostat. ling to the detector becomes easier in this ‘slower’ 7 2D Mater. 10 (2023) 021001 configuration (see figure 2(c)). A schematic of the [3] Gol’tsmann G N, Okunev O, Chulkova G, Lipatov A, optoelectronic setup for single-photon detection is Semenov A, Smirnov K, Voronov B, Dzardanov A, Williams C and Sobolewski R 2001 Picosecond shown in figure S6. superconducting single-photon optical detector Appl. Phys. Lett. 79 705–7 Data availability statement [4] Marsili F et al 2013 Detecting single infrared photons with 93% system efficiency Nat. Photon. 7 210–4 The data that support the findings of this study are [5] Korzh B et al 2020 Demonstration of sub-3 ps temporal resolution with a superconducting nanowire single-photon available upon reasonable request from the authors. detector Nat. Photon. 14 250–5 [6] Pernice W H P, Schuck C, Minaeva O, Li M, Goltsmann G N, Acknowledgments Sergienko A V and Tang H X 2012 High-speed and high-efficiency travelling wave single-photon detectors R L M acknowledges fruitful discussions with Gior- embedded in nanophotonic circuits Nat. Commun. 3 1325 [7] Münzberg J, Vetter A, Beutel F, Hartmann W, Ferrari S, gio di Battista and support with the He-FIB by Hanan Pernice W H P and Rockstuhl C 2018 Superconducting Herzig Sheinfux, Johann Osmond and Helena Loz- nanowire single-photon detector implemented in a 2D ano. D K E acknowledges support from the Min- photonic crystal cavity Optica 5 658 istry of Economy and Competitiveness of Spain [8] Shibata H, Takesue H, Honjo T, Akazaki T and Tokura Y 2010 Single-photon detection using magnesium diboride through the ‘Severo Ochoa’ program for Centres of superconducting nanowires Appl. Phys. Lett. 97 212504 Excellence in R&D (SE5-0522), Fundació Privada [9] Santavicca D F 2018 Prospects for faster, higher-temperature Cellex, Fundació Privada Mir-Puig, the Generalitat de superconducting nanowire single-photon detectors Catalunya through the CERCA program, the H2020 Supercond. Sci. Technol. 31 040502 [10] Parlato L et al 2017 Investigation of dark counts in innovative Programme under Grant Agreement No. 820378, materials for superconducting nanostripe single-photon Project: 2D × SIPC and the La Caixa Foundation. K detector applications Photon Count. Appl. 10229 1022901 W and T T acknowledge support from the Elemental [11] Lian S J, Cheng B, Cui X and Miao F 2019 Van der Waals Strategy Initiative conducted by the MEXT, Japan, heterostructures for high-performance device applications: challenges and opportunities Adv. Mater. 32 1903800 Grant No. JPMXP0112101001, JSPS KAKENHIGrant [12] Lee G-H et al 2019 Graphene-based Josephson junction No. JP20H00354 and the CREST (JPMJCR15F3), microwave bolometer Nature 586 42–46 JST P S acknowledges support from the Alexander- [13] Walsh E D et al 2021 Josephson junction infrared von-Humboldt Foundation and the German Fed- single-photon detector Science 372 409–12 eral Ministry for Education and Research through [14] Di Battista G, Seifert P, Watanabe K, Taniguchi T, Fong K C, Principi A and Efetov D K 2022 Revealing the thermal the Feodor-Lynen program. R L M acknowledges properties of superconducting magic-angle twisted bilayer that this Project has received funding from the “Sec- graphene Nano Lett. 22 6465–70 retaria d’Universitats I Recerca de la Generalitat de [15] Orchin G J et al 2019 Niobium diselenide superconducting Catalunya, as well as the European Social Fund (L’FSE photodetectors Appl. Phys. Lett. 114 251103 [16] Arpaia R, Ejrnaes M, Parlato L, Tafuri F, Cristiano R, inverteix en el teu futur)—FEDER. Golubev D, Sobolewski R, Bauch T, Lombardi F and Pepe G P 2015 High-temperature nanowires for photon Author contributions detection Physica C 509 16–21 [17] Xing X, Balasubramanian K, Bouscher S, Zohar O, Nitzav Y, D K E, P S and R L M conceived and designed the Kanigel A and Hayat A 2020 Photoresponse above 85 K of selective epitaxy grown high-Tc superconducting microwires experiments; R L M and P S performed the experi- Appl. Phys. Lett. 117 032602 ments; R L M, J R D and P S fabricated the devices; [18] Arpaia R, Golubev D, Baghdadi R, Ciancio R, Drazic G, R L M and D K E analyzed the data; K K, T T, K W Orgiani P, Montemurro D, Bauch T and Lombardi F 2017 contributed materials; R M and D K E supported the Transport properties of ultrathin YBaCuO nanowires: a route to single-photon detection Phys. Rev. B 96 064525 experiments: R L M and D K E wrote the paper with [19] Andersson E, Arpaia R, Trabaldo E, Bauch T and Lombardi F insight from R H H. 2020 Fabrication and electrical transport characterization of high quality underdoped YBa2 Cu3 O7-δ nanowires ORCID iDs Supercond. Sci. Technol. 33 064002 [20] Skocpol W J, Beasley M R and Tinkham M 1974 Self-heating hotspots in superconducting thin-film microbridges J. Appl. Kenji Watanabe  https://orcid.org/0000-0003- Phys. 45 4054 3701-8119 [21] Ejrnaes M, Parlato L, Arpaia R, Bauch T, Lombardi F, Robert H Hadfield  https://orcid.org/0000-0002- Cristiano R, Tafuri F and Pepe G P 2017 Observation of dark 8084-4187 pulses in 10 nm thick YBCO nanostrips presenting hysteretic current voltage characteristics Supercond. Sci. Technol. Dmitri K Efetov  https://orcid.org/0000-0001- 30 12LT02 5862-0462 [22] Lyatti M, Savenko A and Poppe U 2016 Ultrathin YBa2 Cu3 O7-δ films with high critical current density References Supercond. Sci. Technol. 29 065017 [23] Li M, Winkler D and Yurgens A 2015 Single-crystalline [1] Morozov D V, Casaburi A and Hadfield R H 2021 Bi2 Sr2 CaCu2 O8+x detectors for direct detection of Superconducting photon detectors Contemp. Phys. 62 69–91 microwave radiation Appl. Phys.Lett. 106 152601 [2] Holzman I and Ivry Y 2019 Superconducting nanowires for [24] Ghosh S, Jangade D A and Deshmukh M M 2022 Nanowire single-photon detection: progress, challenges, and bolometer using a 2D high-temperature superconductor opportunities Adv. Quantum Technol. 2 1800058 Nanotechnology 34 015304 8 2D Mater. 10 (2023) 021001 [25] Yu Y, Ma L, Cai P, Zhong R, Ye C, Shen J, Gu G D, Chen X H superconducting microbridges Supercond. Sci. Technol. and Zhang Y 2019 High-temperature superconductivity in 16 911–5 monolayer Bi2 Sr2 CaCu2 O8+δ Nature 575 156–63 [35] Zhang L et al 2014 Characterization of superconducting [26] Seifert P et al 2021 A high-Tc van der Waals superconductor nanowire single-photon detector with artificial constrictions based photodetector with ultra-high responsivity and AIP Adv. 4 067114 nanosecond relaxation time 2D Mater. 8 035053 [36] Bitauld D, Marsili F, Gaggero A, Mattioli F, Leoni R, [27] Cao Y et al 2015 Quality heterostructures from Nejad S J, Lévy F and Fiore A 2010 Nanoscale optical two-dimensional crystals unstable in air by their assembly in detector with single-photon and multiphoton sensitivity inert atmosphere Nano Lett. 15 4914–21 Nano Lett. 10 2977–81 [28] Ward B, Notte J A and Economou N 2006 Helium ion [37] Sobolewski R, Verevkin A, Gol’tsman G N, Lipatov A and microscope: a new tool for nanoscale microscopy and Wilsher K 2003 Ultrafast superconducting single-photon metrology J. Vac. Sci. Technol. B 24 2871–4 optical detectors and their applications IEEE Trans. Appl. [29] Cybart S A, Cho E Y, Wong T J, Wehlin B H, Ma M K, Supercond. 13 1151–7 Huynh C and Dynes R C 2015 Nano Josephson [38] Zhao Y G et al 2001 Optical Cooper pair breaking superconducting tunnel junctions in YBa2 Cu3 O7-δ directly spectroscopy of cuprate superconductors Phys. Rev. B patterned with a focused helium ion beam Nat. Nanotech. 63 132507 10 598–602 [39] Sandilands L J, Reijnders A A, Su A H, Baydina V, Xu Z, [30] Müller B, Karrer M, Limberger F, Becker M, Schröppel B, Yang A, Gu G, Pedersen T, Borondics F and Burch K S 2014 Burkhardt C J, Kleiner R, Goldobin E and Koelle D 2019 Origin of the insulating state in exfoliated high-TC Josephson junctions and SQUIDs created by focused helium two-dimensional atomic crystals Phys. Rev. B 90 081402 ion beam irradiation of YBa2 Cu3 O7 Phys. Rev. Appl. [40] Niratisairak S, Johansen T H, Katouda S and Ishibashi T 11 044082 2011 Evolution of a hotspot in a thin BSCCO structured film [31] Cho E Y, Ma M K, Huynh C, Pratt K, Paulson D N, Physica C 471 222–5 Glyantsev V N, Dynes R C and Cybart S A 2015 [41] Xiao Z L, Andrei E Y and Ziemann P 1998 Coexistence of the YBa2 Cu3 O7-δ superconducting quantum interference hot-spot effect and flux-flow instability in high-TC devices with metallic to insulating barriers written with a superconducting films Phys. Rev. B 58 11185 focused helium ion beam Appl. Phys. Lett. [42] Lyatti M, Wolff M A, Savenko A, Kruth M, Ferrari S, 106 252601 Poppe U, Pernice W, Dunin-Borkowski R E and Schuck C [32] Chen X K, Zeng Y J and Chen K Q 2020 Thermal transport 2018 Experimental evidence for hotspot and phase-slip in two-dimensional heterostructures Front. Mater. 7 578791 mechanisms of voltage switching in ultra-thin YBa2 Cu3 O7-δ [33] Engel A, Renema J J, Il’in K and Semenov A 2015 Detection nanowires Phys. Rev. B 98 054505 mechanism of superconducting nanowire single-photon [43] Polakovic T, Armstrong W, Karapetrov G, Meziani Z E and detectors Supercond. Sci. Technol. 28 114003 Novosad V 2020 Unconventional applications of [34] Jukna A and Sobolewski R 2003 Time-resolved superconducting nanowire single photon detectors photoresponse in the resistive flux-flow state in Y-Ba-Cu-O Nanomaterials 10 1198 9