Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session B22: Superconductivity: Theory-I |
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Sponsoring Units: DCMP Chair: Andrey Chubukov, University of Minnesota Room: Room 214 |
Monday, March 6, 2023 11:30AM - 11:42AM |
B22.00001: Andreev reflection spectroscopy in strongly paired superconductors Cyprian K Lewandowski, Etienne Lantagne-Hurtubise, Alex R Thomson, Stevan Nadj-Perge, Jason F Alicea Motivated by recent experiments on low-carrier-density superconductors, including twisted multilayer graphene, we study signatures of the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) evolution in Andreev reflection spectroscopy. We establish that in a standard quantum point contact geometry, Andreev reflection in a BEC superconductor is unable to mediate a zero-bias conductance beyond e^2/h per lead channel. This bound is shown to result from a duality that links the sub-gap conductance of BCS and BEC superconductors. We then demonstrate that sharp signatures of BEC superconductivity, including perfect Andreev reflection, can be recovered by tunneling through a suitably designed potential well. We propose various tunneling spectroscopy setups to experimentally probe this recovery. |
Monday, March 6, 2023 11:42AM - 11:54AM |
B22.00002: Pair density waves revealed by Andreev reflection spectra Wan-Ju Li, Yi-Hsuan Liu, Ting-Kuo Lee The pair density wave (PDW) state is recently proposed to be present in high temperature superconductors. |
Monday, March 6, 2023 11:54AM - 12:06PM |
B22.00003: Superconductivity in quantum Hall edge states Julien Barrier, Na Xin, Andre K Geim One can induce a supercurrent in a normal metal N by placing it between two superconducting electrodes S. It consists in transferring Cooper pairs through simultaneous conversion of electrons and holes at the NS interface. In a magnetic field, the electrons' and holes' trajectories bend and can no longer merge at the NS interface, rapidly destroying the proximity supercurrent. In ballistic systems however, electrons' and holes' trajectories can occasionally return to the same position after multiple bounces on mesoscopic edges [1]. In the QH regime, electrons and holes propagate in the same direction on the same edge, which does not support a supercurrent unless one manages to couple oppositely propagating edges. This can be achieved via chiral Andreev edge states in the superconducting sheath, resulting in critical current of ~1nA at 1.5T [2]. Narrow devices would show better coupling but increased backscattering. |
Monday, March 6, 2023 12:06PM - 12:18PM |
B22.00004: Criticality in the crossed Andreev reflection of a quantum Hall edge Vladislav Kurilovich, Leonid Glazman We develop a theory of the non-local transport of two counter-propagating ν = 1 quantum Hall edges coupled via a narrow disordered superconductor. The system is self-tuned to the critical point between trivial and topological phases by the competition between tunneling processes with or without particle-hole conversion. The critical conductance is a random, sample-specific quantity with a zero average and unusual bias dependence. The negative values of conductance are relatively stable against variations of the carrier density, which may make the critical state to appear as a topological one. Our theory provides an interpretation of recent experiments [Nature Physics 13, 693 (2017), Phys. Rev. X 12, 021057] and has important ramifications for an ongoing search for Majorana zero modes. |
Monday, March 6, 2023 12:18PM - 12:30PM |
B22.00005: Manipulating Andreev bound states in bilayer graphene Josephson junction Geon-Hyoung Park, Sein Park, Kenji Watanabe, Takashi Taniguchi, Gil-Ho Lee Andreev bound states (ABS) are supercurrent-carrying modes which are bounded in a normal conductor in proximity Josephson junction. ABSs manifest unique phase-dependent energy spectrums according to the interrelation of channel length (L) and superconducting coherence length (ξs) of the junction. Depending on the ratio of L to ξs, one can varies the number of ABS modes from one pair (L/ξs <!--[if gte msEquation 12]> lang=EN-US style='font-size:11.0pt;mso-bidi-font-size:10.0pt;font-family:"Cambria Math",serif; |
Monday, March 6, 2023 12:30PM - 12:42PM Author not Attending |
B22.00006: Andreev Interferometers based on Quantum Point Contacts José Chávez-Garcia, Smitha Nair, Asbjørn Drachmann, Sangeeth Kallatt, Rasmus Christensen, Sergei Gronin, Geoff C Gardner, Michael J Manfra, Constantin Schrade, Charles Marcus, Morten Kjaergaard Two dimensional systems proximitized with superconductors have been demonstrated to serve as versatile platform for studying Andreev physics. Here, we create several superconducting interferometers involving two planar Josephson junctions. We probe the limits of balancing such a circuit – that is minimizing the difference of their respective Andreev energies – in addition to demonstrating a dynamic and reversible superconducting diode effect. We compare these results to a simple model that highlights the contribution from high channel transparencies as well as its impact on the higher Josephson harmonics. |
Monday, March 6, 2023 12:42PM - 12:54PM |
B22.00007: Conductance matrix symmetries of multiterminal semiconductor-superconductor devices Andrea Maiani, Max Geier, Karsten Flensberg Nonlocal tunneling spectroscopy of multiterminal semiconductor-superconductor hybrid devices is a powerful tool to investigate the Andreev bound states below the parent superconducting gap. We examine how to exploit both microscopic and geometrical symmetries of the system to extract information on the normal and Andreev transmission probabilities from the multiterminal electric or thermoelectric differential conductance matrix under the assumption of an electrostatic potential landscape independent of the bias voltages, as well as the absence of leakage currents. These assumptions lead to several symmetry relations on the conductance matrix. Next, by considering a numerical model of a proximitized semiconductor wire with spin-orbit coupling and two normal contacts at its ends, we show how such symmetries can be used to identify the direction and relative strength of Rashba versus Dresselhaus spin-orbit coupling. Finally, we study how a voltage-bias-dependent electrostatic potential as well as quasiparticle leakage breaks the derived symmetry relations and investigate characteristic signatures of these two effects. |
Monday, March 6, 2023 12:54PM - 1:06PM |
B22.00008: Inhomogeneous Superconductivity due to Surfaces Pramodh V Senarath Yapa Arachchige, Sean Chen, Joseph Maciejko, Frank Marsiglio Depending on competing on-site and nearest-neighbour interactions, the extended Hubbard model can host a variety of mixed s-, p- and d-wave superconducting phases. Phase transitions between these phases occur as a function of the interaction strengths, temperature and electron density, leading to a rich phase diagram. In a system with periodic boundary conditions, the order parameters are uniform in space and can be characterized by the dominant/sub-dominant components. In this work, we investigate the effect of surfaces on the mixed-symmetry phases using a real-space Bogoliubov-de Gennes method. We present the inhomogeneous order parameter profiles and show how the dominant superconducting phase can be different near the surface versus the bulk. |
Monday, March 6, 2023 1:06PM - 1:18PM |
B22.00009: Chiral surface superconductivity in half-Heusler semimetals Ronny Thomale, Domenico Di Sante, Joerg Schmalian, Tilman Schwemmer We propose the metallic and weakly dispersive surface states of half Heusler semimetals as a possible domain for unconventional superconductivity. Using density functional theory (DFT) calculations and the random phase approximation (RPA), we analyse the surface band structure of LuPtBi and its propensity towards Cooper pair formation induced by screened electron-electron interactions. Pair wave functions transforming under the two-fold degenerate E irreducible representation of the surface's $C_{3v}$ point group are found to be favoured by unconventional mechanisms over a wide range of parameters. We show that this naturally results in a chiral superconducting condensate that spontaneously breaks time-reversal symmetry and features pairs of dispersing Majorana edge modes. |
Monday, March 6, 2023 1:18PM - 1:30PM |
B22.00010: Spin-charge separation and unconventional superconductivity in t-J model on honeycomb lattice Zhengyuan Yue The physical nature of doped Mott-insulator has been intensively studied for more than three decades. It is well known that the single band Hubbard model or t-J model on bipartite lattice is the simplest model to describe a Mott-insulator. Unfortunately, the key mechanism of superconductivity in these toy models is still under controversial so far. Here we propose a new mechanism for the d+id-wave superconductivity (SC) that occurs in the low-doping region of the honeycomb lattice t-J model based on Grassmann tensor product state simulation and spin-charge separation formulation. Moreover, in the presence of anti-ferromagnetic order, a continuum effective field theory for the holons near half-filling is developed, and it reveals the compitition between attractive and repulsive holon interactions induced by the exchange of spinons and gauge fluctuations, respectively. At a large value of t/J, the repulsive interaction dominates, leading to the non-Fermi liquid behavior; while in a moderate range of t/J, the attraction dominates and leads to the superconducting order. Possible experimental detection of spin-charge separation phenomena are also discussed. |
Monday, March 6, 2023 1:30PM - 1:42PM |
B22.00011: Strongly-correlated superconductivity with spin-orbit coupling Brianna Nally, Philip Brydon Motivated by the recent discovery of a field-mediated parity switch within the superconducting state of CeRh2As2 [Khim et al., Science 373, 1012 (2021)], we investigate the superconducting phase diagram of a strongly-coupled Rashba mono- and bilayer. Our model extends the usual two-dimensional Hubbard model by including Rashba spin-orbit coupling due to broken inversion symmetry, and interlayer hopping in the case of the bilayer. The strong correlations due to the on-site repulsion are accounted for within the auxiliary boson mean-field theory. |
Monday, March 6, 2023 1:42PM - 1:54PM |
B22.00012: Andreev reflection in scanning tunneling spectroscopy of unconventional superconductors Pavlo Sukhachov, Felix von Oppen, Leonid Glazman We evaluate the differential conductance measured in a scanning tunneling microscopy (STM) setting at arbitrary electron transmission between STM tip and a two-dimensional superconductor with arbitrary gap structure. Our analytical scattering theory accounts for Andreev reflections, which become prominent at larger transmissions. We show that this provides complementary information about the superconducting gap structure beyond the tunneling density of states, strongly facilitating the ability to extract the gap symmetry and its relation to the underlying crystalline lattice. We use the developed theory to discuss recent experimental results on superconductivity in twisted bilayer graphene. |
Monday, March 6, 2023 1:54PM - 2:06PM |
B22.00013: Anomalous Coulomb drag between a normal metal and a superconductor Hong-Yi Xie A novel Coulomb drag effect between an active monolayer graphene and a passive superconducting LAO/STO interface has been recently observed in experiment. In the superconducting transition regime of the LAO/STO interface, the passive-to-active ratio can reach ~1 at optimal gate voltage and the sign is independent of the carrier type in the graphene layer. The anomalous drag responses can be successfully described by the model of an normal conductor dragging a Josephson junction array via Coulomb fields, and the so-termed Josephson-Coulomb (JC) drag mechanism originates from the interactions between the substantially enhanced dynamical quantum fluctuations of the superconducting phases in the passive layer and the normal electrons in the active layer. In this talk, we present a detailed theoretical description of the JC drag effects in the nonequilibrium many-body formalism. We will see that the JC drag belongs to the broad spectrum of the energy drag, and, more importantly, it manifests the unique role of quantum fluctuations in dominating the interlayer processes. The JC drag devices may also contribute an important piece to modern SC electronics working as current (voltage) transformers or terahertz radiators. |
Monday, March 6, 2023 2:06PM - 2:18PM |
B22.00014: Anisotropic physical properties in the KTaO3 (110) interface Changjiang Liu, Junyi Yang, Xianjing Zhou, Qianheng Du, Deshun Hong, Brandon Fisher, John Pearson, Jidong S Jiang, Ulrich Welp, Dafei Jin, Michael R Norman, Anand Bhattacharya The two-dimensional superconductivity found at the KTaO3 interfaces offers new opportunities for investigating emergent physical phenomena. Depending on the crystalline orientation of the KTaO3 interface, superconducting properties such as Tc can be distinct. Here we report on anisotropic physical properties observed in the electron gas formed at the KTaO3 (110) interface. We find that the transport properties in the normal state are dependent on the crystal axis. This can be understood from an anisotropic electronic band structure calculated from a tight-binding model. At lower temperatures in the superconducting state, we observe a rotational anisotropy in the magnetotransport measurements for in-plane magnetic fields, after careful control of the direction of the magnetic field due to unavoidable sample misalignment during mounting. This observation suggests an anisotropic spin susceptibility at the KTaO3 (110) interface. |
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