Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Y57: Superconductivity: Josephson & Tunneling-IIRecordings Available
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Sponsoring Units: DCMP Chair: Richard Klemm, University of Central Florida Room: Hyatt Regency Hotel -Clark |
Friday, March 18, 2022 8:00AM - 8:12AM |
Y57.00001: Parametric exploration of zero-energy modes in three-terminal InSb-Al nanowire devices Jiyin Wang, Nick van Loo, Grzegorz P Mazur, Vukan Levajac, Filip K Malinowski, Mathilde Lemang, Francesco Borsoi, Ghada Badawy, Sasa Gazibegovic, John M Hornibrook, David Reilly, Erik P. A. M. Bakkers, Marina Quintero-Perez, Sebastian Heedt We systematically study three-terminal InSb-Al nanowire devices by using radio-frequency reflectometry. Tunneling spectroscopy measurements on both ends of the hybrid nanowires are performed while systematically varying the chemical potential, magnetic field and junction transparencies. Identifying the lowest-energy state allows for the construction of lowest- and zero-energy state diagrams, which show how the states evolve as a function of the aforementioned parameters. Importantly, comparing the diagrams taken for each end of the hybrids enables the identification of energy states which do not coexist simultaneously, ruling out significant amount of the parameter space as candidates for a topological phase. Furthermore, altering junction transparencies filters out zero-energy states sensitive to the local gate potential. Such a measurement strategy significantly reduces the time necessary to identify a potential topological phase and unambiguously reveals the trivial origin of the observed zero-bias peaks. |
Friday, March 18, 2022 8:12AM - 8:24AM Withdrawn |
Y57.00002: Tunneling Response of Graphite-hBN-NbSe2 Planar Junctions Adam K Williams, Evan J Telford, Cory R Dean Tunneling current from an electrode to sample is directly proportional to the density of states of the sample at the energy which is biased. This is most clearly determined via scanning tunneling spectroscopy, however this method is not suitable for a growing number of materials that are unstable without encapsulation. By using a 2-dimensional electrode and dielectric, a tunneling spectrum can be measured on an encapsulated sample. A tunneling spectrum from a planar junction can however be smeared by spatial inhomogeneity of the electrode, which can be ameliorated by increasing physical thickness of dielectric. This work examines the tunneling spectrum of mechanically exfoliated graphite to encapsulated NbSe2 with various thicknesses of hBN dielectrics. |
Friday, March 18, 2022 8:24AM - 8:36AM |
Y57.00003: A shot noise probe to detect pairing in quantum materials Jiasen Niu, John Jesudasan, Ruchi Tomar, Pratap Raychaudhuri, Milan P Allan Shot noise is a powerful tool for determining the effective charge in mesoscopic systems, including superconductors and fractional quantum Hall systems. In a superconductor-insulator-superconductor tunnel junction, Andreev reflection leads to an effective charge of multiple electron charges. I will present a newly developed, low temperature (1.5 K), wide bandwidth (100 kHz-5 MHz) noise-measurement amplifier with a resolution down to 0.002 nV2/Hz. I will show measured shot noise in Nb/Al-AlOx/Nb and NbN/oxide/Ag tunnel junctions, and describe possibilities to measure shot noise in conventional and unconventional superconductors. |
Friday, March 18, 2022 8:36AM - 8:48AM |
Y57.00004: Reduced Critical Currents and Anomalous Zero-Bias Finite Resistance in SIS Junctions Maxwell Wisne, Venkat Chandrasekhar, Cameron J Kopas, Mark Field, Jayss Marshall, Hilal Cansizoglu, Kameshwar Yadavalli, Matthew J Reagor Al/AlOx/Al tunnel junctions play a critical role in superconducting qubit devices. The inherent nonlinear inductance and tunability of the Josephson energy allows for control over qubit transition states. Consequently, it is important to characterize the properties of the junction as they impact the coherence time of the qubit. Here we report on the results of dc transport measurements on Al/AlOx/Al junctions, both in stand-alone structures and transmon configurations. The critical currents of these junctions are almost an order of magnitude smaller than estimates based on measurements of the superconducting gap and normal state resistance. These devices also show a finite differential resistance at zero current bias even at temperatures as low as 25 mK, similar to what has been observed earlier by Iansiti et al. [1] and Kautz and Martinis [2]. We will discuss possible explanations for the reduced critical currents and the finite zero-bias differential resistance. |
Friday, March 18, 2022 8:48AM - 9:00AM |
Y57.00005: Superconducting diode effect in InSb nanowires with Tin shell Bomin Zhang, Victor Aguilar, Po Zhang, Mihir Pendharkar, Connor Dempsey, Joon Sue Lee, Sean Harrington, Ghada Badawy, Sasa Gazibegovic, Jason Jung, An-His Chen, Susheng Tan, Marcel Verheijen, Moira Hocevar, Erik P. A. M. Bakkers, Chris J Palmstrom, Sergey M Frolov We study Josephson Junction in InSb nanowires with 15nm Tin shells. We observe critical current diffraction patterns skewed and inversion-symmetric in magnetic field and bias direction. The effect is stronger when the external magnetic field is aligned perpendicular to the nanowire, in the substrate plane. i.e. in the most likely direction of the effective spin-orbit field in the junction. The effect is also tunable by gate voltage. We discuss this effect in the context of phi0-Josephson junction physics, one consequence of which is known in recent literature as superconducting diode effect. We consider alternative explanations such as the effective magnetic field and perform numerical simulations to understand our findings. |
Friday, March 18, 2022 9:00AM - 9:12AM |
Y57.00006: Phase tunning of Al-MoTe2-Al Josephson junction with asymmetric SQUID Zheyi Zhu, Stephan Kim, Shiming Lei, Leslie M Schoop, Robert J Cava, N. Phuan Ong Proximity-induced superconducting pairing in topological material is an attractive topic because of its potential realization of topological superconductivity, and Josephson effect is one of the powerful tools to study. However, the phase freedom of the Josephson effect has not been fully explored yet. With the help of asymmetric SQUID, we are able to tune the phase across the planer SNS junction made from type-II Weyl semimetal MoTe2 and Al contact. The current phase relation of SNS junction is measured, and subharmonic structure appears at finite voltage regime, which is explained by multiple Andreev reflection scheme. |
Friday, March 18, 2022 9:12AM - 9:24AM |
Y57.00007: Magnetic field- and electro-chemical potential- driven 0-pi transitions in an InSb-Al nanowire Josephson junction Vukan Levajac, Hristo Barakov, Nick van Loo, Grzegorz P Mazur, Francesco Borsoi, Ghada Badawy, Sasa Gazibegovic, Erik P. A. M. Bakkers, Sebastian Heedt, Yuli Nazarov, Jiyin Wang Recent developments in shadow-wall lithography techniques yield hybrid nanowire Josephson junctions with magnetic field-resilient supercurrent that can be embedded in more complex hybrid devices to study supercurrent phenomena in high magnetic fields. We fabricate a superconducting quantum interference device (SQUID) with two InSb-Al nanowire Josephson junctions as two arms in the dc-SQUID architecture. Local bottom gates are used to fix and sweep the electro-chemical potential of the junctions used as the reference and investigated arm, respectively. We perform switching current measurements and detect SQUID oscillations at parallel magnetic fields up to ~0.75T. The oscillation patterns measured while sweeping the gate of the investigated arm reveal multiple pi-shifted segments at high field which gate range gradually extends as the field increases. Some of these pi-segments are present at zero field as well and can be attributed to presence of an accidental quantum dot – as confirmed by tunnel spectroscopy. Other pi-segments can be tracked to oscillation patterns of various shapes at zero field. In order to understand these various evolutions, we develop a model for transport through a quantum dot coupled to a transmission channel in a hybrid Josephson junction. |
Friday, March 18, 2022 9:24AM - 9:36AM |
Y57.00008: Unconventional supercurrent phase in Ising superconductor Josephson junction with atomically thin magnetic insulator Hiroshi Idzuchi, Falko Pientka, Katie F Huang, Ken Harada, Onder Gul, Young Jae Shin, Loi T Nguyen, Na H Jo, Daisuke Shindo, Robert J Cava, Paul C Canfield, Philip Kim In two-dimensional (2D) NbSe2 crystal, which lacks inversion symmetry, strong spin-orbit coupling aligns the spins of Cooper pairs to the orbital valleys, forming Ising Cooper pairs (ICPs). The unusual spin texture of ICPs can be further modulated by introducing magnetic exchange. Here, we report unconventional supercurrent phase in van der Waals heterostructure Josephson junctions (JJs) that couples NbSe2 ICPs across an atomically thin magnetic insulator (MI) Cr2Ge2Te6. By constructing a superconducting quantum interference device (SQUID), we measure the phase of the transferred Cooper pairs in the MI JJ. We demonstrate a doubly degenerate nontrivial JJ phase (ϕ), formed by momentum-conserving tunneling of ICPs across magnetic domains in the barrier. The doubly degenerate ground states in MI JJs provide a two-level quantum system that can be utilized as a new dissipationless component for superconducting quantum devices. Our work boosts the study of various superconducting states with spin-orbit coupling, opening up an avenue to designing new superconducting phase-controlled quantum electronic devices. |
Friday, March 18, 2022 9:36AM - 9:48AM |
Y57.00009: 0-π transition and 0-π Josephson junctions in van der Waals superconductor-ferromagnet heterostructures Kaifei Kang, Helmuth Berger, Kenji Watanabe, Takashi Taniguchi, László Forró, Jie Shan, Kin Fai Mak |
Friday, March 18, 2022 9:48AM - 10:00AM |
Y57.00010: AC Josephson effect in higher-order topological insulator WTe2 Artem Kononov, Martin Endres, Roy Haller, Fabian Oppliger, Hasitha Suriya Arachchige, Jiaqiang Yan, David G Mandrus, Christian Schonenberger WTe2 is a layered transitional metal dichalcogenide, known for its topological properties. In the form of a monolayer it is a 2D topological insulator and as a bulk material it is a type-II Weyl semimetal. Recently, another topological phase in WTe2 has been predicted. The new phase is a higher-order topological insulator with helical hinge states. The evidence of such 1D states along certain crystallographic directions in thin WTe2 has been obtained in a number of experiments employing Josephson junctions. |
Friday, March 18, 2022 10:00AM - 10:12AM |
Y57.00011: Higher Harmonic Supercurrents in Multi-Terminal Josephson Junctions Ethan G Arnault, Francois Amet, Sara Idris, Aeron C McConnell, Lingfei Zhao, Trevyn Larson, Kenji Watanabe, Takashi Taniguchi, Gleb Finkelstein The dynamical properties of multi-terminal Josephson junctions have attracted interest, driven by the promise of new insights into synthetic topological phases of matter and Floquet states. This study has recently culminated in the discovery of Cooper multiplets, where the splitting of Cooper pairs allows a series of Andreev reflections which entangles four (or more) electrons. In this talk, we show that multiplet resonances can also emerge as a simple consequence of the three terminal RCSJ model. The supercurrent appears due to the absence of average phase dynamics at values that correspond to the multiplet condition nV1 = -mV2. Along these lines, the supercurrent carries large harmonic contributions in its current phase relation. Remarkably, these lines emerge in a nanofabricated three-terminal graphene Josephson junction, in an analog three terminal Josephson junction circuit, and in a simulated RCSJ model. We describe parameter considerations that best optimize the detection of these multiplet lines for future engineering of higher harmonic supercurrent flows. |
Friday, March 18, 2022 10:12AM - 10:24AM |
Y57.00012: Direct growth of Josephson junctions and nanoSQUIDs using focused ion beam induced deposition JOSE MARIA DE TERESA, Fabian Sigloch, PABLO ORÚS, SORAYA SANGIAO Focused ion beam induced deposition (FIBID) using the W(CO)6 precursor allows the direct growth of superconducting nanostructures with very high lateral resolution and without the need of any resists. In the past, we have successfully grown superconducting W-C nanowires with 50 nm width using a Ga+-FIB and with 20 nm width using a He+-FIB. In the present contribution, we will show our current efforts to directly grow Josephson junctions and nanoSQUIDs by Ga+-FIBID using the W(CO)6 precursor. By combining two large rectangular patterns with two narrow nanowires, we successfully create Dayem-bridge-based nanoSQUIDs on flat SiO2//Si substrates with dimensions 300 nm x 700 nm. From current-versus-voltage measurements under various applied magnetic fields, the expected periodic voltage response as a function of the penetrating magnetic flux is obtained, confirming that well-behaved Josephson junctions form at the nanowires and a SQUID response is achieved. Given the high resistance of W-C at the normal state, the SQUID transfer coefficient obtained is large, in the range of 1 mV/Φ0 for a driving current around 8 μA. Interestingly, the same growth strategy of these nanoSQUIDs has been successfully implemented on cantilevers for future applications in advanced scanning probe microscopy. |
Friday, March 18, 2022 10:24AM - 10:36AM |
Y57.00013: Effects of Current-Phase Relationship on SFQ Pulses Miranda Thompson, Manuel A Castellanos-Beltran, Peter Hopkins, Paul D Dresselhaus, Samuel P Benz The Current-Phase Relation (CΦR) of Josephson junctions (JJs) is typically assumed to be sinusoidal, but this is not always the case. For any type of JJ, the CΦR is only required to be 2π periodic and an odd function of phase. Therefore, physics allows many possible non-sinusoidal CΦRs. We will show that incorporating JJs with non-sinusoidal CΦRs into an SFQ circuit changes the shape and timing of the pulses. Therefore, understanding the CΦR and its effects on junction behavior is necessary for accurate modeling of SFQ circuits. For JJs with tunable barrier parameters, such as the NbxSi1-x barriers used at NIST, this could eventually lead to the optimization of the CΦR to improve circuit performance. We are performing indirect measurements of the CΦR of JJs with insulating and normal-metal barriers by incorporating the test junction into an RF-SQUID coupled via mutual inductance to a DC-SQUID magnetometer. By measuring the CΦR, it is possible to use this information to optimize the bias current and circuit parameters of single flux quantum (SFQ) circuits. |
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