Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session A48: Superconductivity:Josephson JunctionsLive
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Sponsoring Units: DCMP Chair: Bing Lv, University of Texas at Dallas Patrick Cheung, University of Texas at Dallas |
Monday, March 15, 2021 8:00AM - 8:12AM Live |
A48.00001: Circuit-QED-based investigations of two-dimensional Josephson junction arrays in the quantum regime Hiroki Ikegami, Cosmic Raj, Yasunobu Nakamura Josephson junction arrays (JJAs) offer model systems for studying various quantum many-body phenomena. One of the remarkable phenomena in JJAs is the quantum phase transition between superconducting and insulating phases, which occurs due to the competition between the Josephson energy EJ and the charging energy EC. Here we study dynamics of two-dimensional JJAs in the quantum critical regime (EJ ~ EC) using a circuit-QED approach. We find that the internal loss of the cavity at the zero-temperature limit increases steeply as approaching the quantum critical point. Furthermore, unlike in the classical superconducting regime (EJ >> EC) where the cavity loss exhibits a peak at transition temperature Tc due to dissipative motion of free vortices generated by the Berezinskii-Kosterlitz-Thouless mechanism [1], we do not observe a peak in the cavity loss at Tc in the quantum critical regime. These observations suggest that the loss mechanism is different from that in the classical superconducting regime. In the talk, we will discuss the results in connection with the quantum phase transition. |
Monday, March 15, 2021 8:12AM - 8:24AM Live |
A48.00002: Wide Josephson Junction on InAs quantum well: missing Shapiro steps in non-topological regime Matthieu Dartiailh, Joseph Cuozzo, Bassel Heiba Elfeky, William a Mayer, Joseph Yuan, Kaushini S Wickramasinghe, Enrico Rossi, Javad Shabani Josephson junctions hosting Majorana fermions have been predicted to exhibit a 4π periodic current phase relation. One experimental consequence of this periodicity is the disappearance of odd steps in Shapiro steps experiments. Experimentally, missing odd Shapiro steps have been observed in a number of materials systems with strong spin-orbit coupling and have been interpreted in the context of topological super-conductivity. Here we report on missing odd steps in topologically trivial Josephson junctions fabricated on InAs quantum wells. We ascribe our observations to the high transparency of our junctions allowing Landau-Zener transitions and the existence of long junctions modes well isolated from the continuum. We analyze our results using a bi-modal transparency distribution which demonstrates that only few modes carrying 4π periodic current are sufficient to describe the disappearance of odd steps. Furthermore we show that the probability of Landau-Zener is shown is independent of the drive frequency. Our findings highlight the elaborate circumstances that have to be considered in the investigation of the 4π Josephson junctions in relationship to topological superconductivity. |
Monday, March 15, 2021 8:24AM - 8:36AM Live |
A48.00003: Spatial control of supercurrent distribution in Josephson junctions William Schiela, Matthieu Dartiailh, Kasra Sardashti, Fatemeh Barati, Neda Lotfizadeh, Joseph Yuan, Mehdi Hatefipour, William Strickland, Bassel Heiba Elfeky, Javad Shabani Spatially separated Majorana zero modes (MZM) have generated interest as a promising basis for encoding topologically protected quantum information, but their hallmark non-Abelian exchange statistics have yet to be observed. One way to probe the non-Abelian phase is to perform a braiding sequence in real space, in which localized MZMs from different fermionic modes are moved around one another prior to fusion, and to sense the resulting charge excitation (or lack thereof). A prerequisite for such an experiment is the stable transport of MZMs on a timescale that is adiabatic compared to the inverse energy gap yet limited by the quasiparticle poisoning time. This may be achieved by controlling the charge distribution in a planar Josephson junction using an array of discrete electrostatic gates. We report preliminary device design and characterization of the junction critical current as a function of magnetic field applied perpendicular to the plane. We study this Fraunhofer pattern in the topologically trivial regime to reconstruct the supercurrent distribution in the channel and determine its spatial dependence on the applied gate voltages. |
Monday, March 15, 2021 8:36AM - 8:48AM Live |
A48.00004: Current-Phase Relationship of Josephson Junctions with NbxSi1-x Barriers Miranda Thompson, Manuel A Castellanos-Beltran, Anna Fox, Peter Hopkins, Paul David Dresselhaus, Samuel P Benz We characterized the current-phase relationship (CΦR) of Josephson junctions with niobium doped amorphous silicon barriers. We performed an indirect measurement of the CΦR by incorporating the test junction into an RF-SQUID inductively coupled to a DC-SQUID magnetometer. We observed deviations from the typical sinusoidal relationship. This non-sinusoidal CΦR also causes non-integer Shapiro steps. We measured both SIS and SNS junctions and observed the CΦR changing with barrier composition. Additionally, non-sinusoidal CΦR can be observed in high-current-density junctions used for mixed-signal and microwave circuits. Understanding the CΦR and its effects on junction behavior is necessary for accurate modeling, such as that required by the IARPA-SuperTools program. These intrinsically shunted Josephson junctions are particularly useful for applications requiring high junction density, such as superconducting computing and waveform synthesis. More accurate junction models will enable higher performance of large-scale superconductive circuits. |
Monday, March 15, 2021 8:48AM - 9:00AM Live |
A48.00005: Conductance spectroscopy of Andreev bound states in multi-terminal Josephson junctions Hanho Lee, Natalia Pankratova, Roman Kuzmin, Kaushini S Wickramasinghe, Maxim G Vavilov, Javad Shabani, Vladimir Manucharyan Multi-terminal Josephson junctions (JJs) can host unconventional Andreev bound states (ABSs) of which the energy levels depend on multiple superconducting phases. It is interesting that zero-energy ABSs may exist in multi-terminal JJs [1]. A recent report of critical current measurements on multi-terminal JJs implies the existence of multi-terminal ABSs [2]. In addition, we study conductance spectroscopy through quantum point contacts between multi-terminal JJs and normal leads. Device fabrications and phase-dependent conductance on multi-terminal JJs will be discussed. |
Monday, March 15, 2021 9:00AM - 9:12AM Live |
A48.00006: Impact of junction length on the supercurrent resilience against magnetic field in hybrid nanowire Josephson junctions Vukan Levajac, Chun-Xiao Liu, Grzegorz Mazur, Nick van Loo, Elvedin Memisevic, Daan Waardenburg, Ghada Badawy, Sasa Gazibegovic, Erik P. A. M. Bakkers, Sebastian Heedt, Marina Quintero-Peréz, Michael Wimmer, Leo Kouwenhoven, Jiyin Wang We study InSb/Al nanowire Josephson junctions of various lengths patterned by lithographically defined shadow-walls. All devices show comparable induced superconductivity and global back gate tunability at zero magnetic field. While the supercurrent in longer junctions (100nm-160nm) is suppressed above parallel fields of 0.6T-0.8T in the entire back gate range, in shorter junctions (30nm-40nm) we are able to detect switching current up to 1.2T parallel field with a supercurrent revival in some devices.. We also compare the switching current and the induced superconductivity in perpendicular magnetic fields (in-plane/out-of-plane) and find that in 30nm-40nm junctions these evolutions are qualitatively similar – both induced gap and switching current have higher out-of-plane than in-plane critical field - while in the junctions of 160nm switching current has opposite behaviour with in-plane critical field being higher. Our results confirm the importance of junction length in the supercurrent response to magnetic field and show that hybrid nanowire Josephson junctions can be engineered to reproducibly support supercurrent at parallel fields above 1T - allowing for observations of the supercurrent effects relevant for topological superconductivity in InSb/Al hybrid devices. |
Monday, March 15, 2021 9:12AM - 9:24AM Live |
A48.00007: Gate-Dependent Transport in Multi-Terminal Josephson Junctions Gino Graziano, Joon Sue Lee, Sean Harrington, Mihir Pendharkar, Chris J Palmstrom, Vlad Pribiag Josephson coupling of three or more superconducting leads through a material with few conducting modes has been predicted to give rise to topological effects. Such behavior, of relevance for topologically-protected quantum bits, would lead to specific transport features measured between terminals, with topological phase transitions occurring as a function of relative phase and voltage biases. Here we study the effects on transport of several top-gating arrangements on multi-terminal Josephson junctions with many conducting modes based on an InAs 2DEG proximitized with an epitaxial aluminum layer and many conducting modes. The superconducting features can be accurately simulated by a network of RCSJ junctions. [1] |
Monday, March 15, 2021 9:24AM - 9:36AM Live |
A48.00008: Long range Josephson coupling across a half metallic ferromagnet at high temperatures David Sanchez-Manzano, Salvatore Mesoraca, Fabian Cuellar, Mariona Cabero, Victor Rouco, Gloria Orfila, Xavier Palermo, Adrian Balan, Lourdes Marcano, Anke Sander, Mirko Rocci, Javier Garcia Barriocanal, Fernando Gallego, Alberto Rivera, Federico Mompean, Mar Garcia Hernandez, Jose Maria Gonzalez-Calbet, Carlos Leon, Sergio Valencia, Cheryl Feuillet-Palma, Nicolas Bergeal, Alexandre Buzdin, Jerome Lesueur, Javier E Villegas, Jacobo Santamaria Ferromagnetism and singlet superconductivity are antagonistic phenomena. At interfaces with a ferromagnet, the singlet pairing amplitude decays over nanometric distances. In presence of magnetization inhomogeneities, however, equal spin triplet Cooper pairs can be generated, allowing the coupling of superconductors in Josephson junctions across magnetic barriers over much longer distances. We demonstrate extremely long range high-temperature Josephson coupling across the half-metallic manganite La0.7Sr0.3MnO3 combined with the superconducting cuprate YBa2Cu3O7. This is shown in planar junctions which display the hallmarks of Josephson physics: critical current oscillations (Fraunhofer pattern) and quantum phase locking under microwave excitation (Shapiro steps). The conjunction of quantum coherent transport and full spin polarization can bring unique opportunities for the practical realization of superconducting spintronics, and novel strategies in quantum computing. |
Monday, March 15, 2021 9:36AM - 9:48AM Live |
A48.00009: In-situ growth and fabrication of planar ferromagnetic semiconductor-based Josephson junctions Keita Ishihara, Le Duc Anh, Masaaki Tanaka The superconductor(S)/ferromagnet(F)/superconductor(S) structures attract attention as a platform of unconventional superconductivity. For the realization of practical SFS devices and novel emergent states such as Majorana fermions, improvement of the S/F interface quality is required. We report an in-situ epitaxial growth using molecular beam epitaxy (MBE) and fabrication of nano-size Josephson junctions (JJs) with s-wave superconductor Al electrodes grown on (In,Fe)As or InAs/(Ga,Fe)Sb heterostructures, where (In,Fe)As and (Ga,Fe)Sb are Fe-doped FMSs. The InAs junctions are made ferromagnetic either by doping Fe [(In,Fe)As] or by the magnetic proximity effect from an Fe-doped FMS [(Ga,Fe)Sb] [1]. We fabricate planar Al/FMS/Al JJ structures with a nano-size trench (< 100 nm) by electron beam lithography. Electrical transport measurements confirmed that the Al layers are superconducting with critical temperature TC of 1 – 1.2 K. In the presentation, we will further discuss many aspects of epitaxial growth and electrical transport measurements in these ferromagnetic JJs. |
Monday, March 15, 2021 9:48AM - 10:00AM Live |
A48.00010: Experimental probes and modeling of Majorana bound states parity transitions in S-TI-S lateral Josephson junctions Guang Yue, Xiong Yao, Deepti Jain, Jisoo Moon, Seongshik Oh, Alexey Bezryadin, Dale J Van Harlingen It is predicted that S-TI-S lateral Josephson junctions, fabricated by depositing electrodes of a conventional superconductor (S) on the surface of a topological insulator (TI), exhibit Majorana bound states (MBS) at locations in the junction where the phase difference is an odd-multiple of π, i.e. at the cores of the Josephson vortices. There is evidence for this from the lifting of odd nodes in the critical current diffraction patterns and the observation of supercurrent features at magnetic fields where the MBS enter the junction. In this talk, we report progress on experiments on Nb-Bi2Se3-Nb junctions designed to probe the parity states of MBS pairs and the transitions between them via measurements of the critical current distribution and supercurrent fluctuations. These experiments, in conjunction with modeling of the critical current transitions, give information about parity lifetimes and open the door to understand the factors such as quasiparticle poisoning that limit them. |
Monday, March 15, 2021 10:00AM - 10:12AM Live |
A48.00011: Tracking the location of Majorana states bound to Josephson vortices in S/TI/S junctions by Scanning SQUID Microscopy Gilbert Arias, Guang Yue, Jessica Montone, Dale J Van Harlingen It is predicted that Majorana bound states (MBS) emerge on the surface of a topological insulator proximitized by a conventional s-wave superconductor. In a Superconductor-Topological Insulator-Superconductor (S-TI-S) Josephson junction, the MBS are localized at the cores of Josephson vortices where the phase difference across the junction is an odd-multiple of π. They can be manipulated by applying fields and currents to carry out braiding operations for quantum information processing. The position and motion of these vortices may be tracked with local magnetic imaging. We are developing a Scanning SQUID Microscope (SSM) in which the probe is a submicron superconducting pickup loop inductively-coupled to a commercial dc SQUID, providing the required field sensitivity and spatial resolution. In this talk, we report our progress towards cooling down our SSM in a dry dilution refrigerator and imaging the Josephson vortices and the currents carried by the Majorana states in S-TI-S devices. |
Monday, March 15, 2021 10:12AM - 10:24AM Live |
A48.00012: Robust supercurrent in graphene Josephson junctions assisted by strong spin-orbit interaction Taro Wakamura, NianJheng WU A magnetic field is known to destroy the spin-singlet Cooper pair via the Zeeman effect. But the orbital effect of a magnetic flux also destroys proximity-induced superconductivity. Since spin-orbit interactions (SOI) can moderate these effects thanks to the spin-momentum locking it provides, one can wonder if supercurrent can be made more robust to an orbital magnetic field in materials with enhanced spin-orbit interaction. To investigate this question, we compare Josephson junctions built with two different graphene-based systems, a hBN/G/hBN stack, or a hBN/WS2/G stack, in which strong SOI have been induced in graphene via the van der Waals-coupled WS2. We measure the supercurrent induced through these systems in varying perpendicular magnetic fields and for different junction lengths. |
Monday, March 15, 2021 10:24AM - 10:36AM Live |
A48.00013: Reopening of the superconducting gap in a planar Josephson junction Abhishek Banerjee, Md. Ahnaf Rahman, He-Ran Wang, Mingrui Li, Anders Kringhøj, Asbjørn C C Drachmann, Alexander Whiticar, Omri Lesser, Tyler Lindemann, Sergei Gronin, Geoffrey C. Gardner, Yuval Oreg, Ady Stern, Michael Manfra, Charles M Marcus The reopening of the superconducting gap is a long-sought after hallmark of topological superconductivity. Here we study a one-dimensional superconductor formed in a planar Josephson junction that can undergo a topological phase transition in the presence of an in-plane magnetic field. As the external magnetic field is increased, we observe the closing and reopening of the superconducting gap, followed immediately by the appearance of a zero-bias mode, suggesting the formation of a topological state. We test the topological origin of the gap reopening by studying its dependence on superconducting phase difference, chemical potential and magnetic field direction. |
Monday, March 15, 2021 10:36AM - 10:48AM Live |
A48.00014: Superconductivity in Planar Germanium Quantum Wells Kushagra Aggarwal, Andrea Hofmann, Daniel Jirovec, Ivan Prieto, Amir Sammak, Marc Botifoll, Sara Martí-Sánchez, Menno Veldhorst, Jordi Arbiol, Giordano Scappucci, Jeroen Danon, Georgios Katsaros The coupling of the superconducting macroscopic wave functions across a weak link has provided rich avenues for fundamental physics and technological advancements. Such weak links made from semiconductors provide further knobs such as spin-orbit coupling and Zeeman splitting to explore non-trivial spin textures and exotic states. Planar Ge confining hole states, compatible with Si foundry, has emerged as a technologically mature semiconducting platform [1]. Here, we demonstrate transparent coupling between superconductors and a Ge quantum well, with high magnetic field resilience. Investigating current distributions in the fabricated Josephson Junctions via the modulation of the superconducting phase difference provides insight into the underlying Andreev transport occurring through the semiconducting weak link. Our results pave the way towards the integration of already demonstrated spin qubits in planar germanium with induced superconductivity on the same platform. [1] Scappucci, G., et al. (2020). The germanium quantum information route. arXiv:2004.08133v1 |
Monday, March 15, 2021 10:48AM - 11:00AM Live |
A48.00015: High Resolution Measurements of the Superconducting Energy Gaps of Assymetrical all-MgB2 Thin Film Josephson Junctions Roberto Ramos, Joseph Lambert, Masahito Nakoda, Michio Naito We have previously analyzed substructure within the two superconducting energy gaps of Magnesium diboride (MgB ) using tunneling spectroscopy [1,2]. The samples consisted of 1-gap(Pb/Sn)/2-gap(MgB2) heterojunctions. Here, we report similar measurements of all-MgB2 Josephson junctions consisting of two c-axis MgB films with very small contribution from the larger σ gap. Due to differences in growth conditions, the two MgB electrodes have different T's and gap values. We analyze data using a modified tunneling model where each electrode is represented as a weighted sum of two BCS densities of states. Our results show (1) a transition from SIS to NIS behavior with temperature and (2) the presence of multiple quasiparticle peaks due to the sums and differences in pairwise combinations of π and σ gap values within each electrode. |
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