Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Y61: Superconductivity: Other SC Materials and Disorder -VRecordings Available
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Sponsoring Units: DCMP Chair: Sanu Mishra, Los Alamos National Laboratory Room: Hyatt Regency Hotel -Field |
Friday, March 18, 2022 8:00AM - 8:12AM |
Y61.00001: Modeling Inhomogeneous Superconductors in a Finite Element Formulation of Time-Dependent Ginzburg-Landau Theory Aiden V Harbick, Reese Clawson, Benjamin L Francis, Mark K Transtrum Modern superconducting radio frequency (SRF) applications require precise control of a wide range of material properties, from microscopic material parameters to mesoscopic/macroscopic surface structures. Mesoscopic simulation of superconductors has proven itself to be a powerful tool in SRF development, connecting microscopic properties to the mesoscopic structures of the material. We outline a finite element formulation of the Time-Dependent Ginzburg-Landau equations which allows for inhomogeneous material parameters, and discuss how these parameters connect to microscopic properties. We demonstrate a few applications of this formulation. First, we model vortex nucleation in Nb3Sn grain boundaries using microscopic parameters from DFT and inhomogeneities similar to real world cavities. We also study dissipation due to nano-hydrides in bulk Nb. |
Friday, March 18, 2022 8:12AM - 8:24AM |
Y61.00002: Modeling Polar Order in Compressively Strained Strontium Titanate Lily Hallett, John W Harter The perovskite oxide SrTiO3 (STO) is both a dilute superconductor and an incipient ferroelectric whereby polar order can be induced through strain, chemical substitution, or isotope exchange. Recently, it has been shown that superconductivity is substantially enhanced in films that are deep within the polar phase, suggesting that inversion symmetry breaking may play an important role in the superconducting pairing mechanism. Carefully characterizing the nature of the polar order in STO is crucial for understanding how it may facilitate electron pairing in this material. In this work, we use density functional theory to compute the ground state structure and phonon spectrum of compressively strained STO thin films and develop a statistical model to simulate the structural phase transitions and polar order. By using computational methods that explicitly incorporate the effects of temperature and disorder on large supercells, we find that, contrary to common belief, the polar phase transition has significant order-disorder character. We place our results in the greater context of proposed superconducting pairing mechanisms in STO. |
Friday, March 18, 2022 8:24AM - 8:36AM |
Y61.00003: The effect of epitaxial strain and doping on electron-phonon coupling and superconducting properties of nitride superconductors from first principles Betul Pamuk, Guru S Khalsa Superconducting transition metal nitrides have been identified as an important materials class for low temperature superconducting electronics. The recent epitaxial integration of nitride superconductors with nitride semiconductors, opens new avenues for integrated semiconductor/superconductor devices [Nature 555, 183–189 (2018)], but due to a lattice mismatch, the superconducting material may be strained by several percent. In this work, using first-principles techniques, we explore the effect of strain and doping on the electron-phonon coupling and superconducting transition temperature of superconducting transition metal nitrides. |
Friday, March 18, 2022 8:36AM - 8:48AM |
Y61.00004: Supercurrents and spontaneous time-reversal symmetry breaking by nonmagnetic disorder in unconventional superconductors Clara N Breiø, Peter J Hirschfeld, Brian M Andersen We explore the emergence of orbital currents and associated time-reversal symmetry breaking (TRSB) arising solely from nonmagnetic disorder in unconventional superconductors. This study is relevant to unconventional superconductors reporting signs of TRSB below Tc. Specifically, we solve a model of a disordered d-wave superconductor and trace the origin of current loops for sufficiently high disorder levels. Since the pure d-wave superconducting state does not exhibit TRSB by itself, it is surprising that such persistent currents arise purely from nonmagnetic disorder. In this talk, a detailed theoretical investigation of this effect will be presented. We show that time-reversal symmetry breaking occurs in a broad range of disorder levels in a d-wave superconductor and that the generation of the currents can be traced to local extended s-wave pairing. The locally induced s-wave pairing leads to energetically favored regions of s+id order which is known to support spontaneous currents in the presence of inhomogeneous density modulations. |
Friday, March 18, 2022 8:48AM - 9:00AM |
Y61.00005: Anisotropic superconductivity and unusually robust electronic critical field in single crystal La7Ir3 Daniel A Mayoh, Sam Holt, Toshiro Takabatake, Geetha Balakrishnan, Martin R Lees Unconventional superconductivity remains one of the most interesting problems in condensed matter physics. For all superconductors, the topology of the electronic band structure, along with the underlying crystal structure, play vital roles in determining the superconducting properties of the material. Systems lacking a centre of inversion exhibit a nonuniform lattice potential, giving rise to a Rashba-type antisymmetric spin-orbit coupling which allows for an admixture of singlet and triplet pairs. This may give rise to exotic superconducting band structures, time-reversal symmetry breaking and magnetoelectric effects such as upper critical fields that exceed the Pauli limit. The discovery of time-reversal symmetry breaking in the hexagonal noncentrosymmetric superconductor La7Ir3 [1] provided a large family of materials that may host exotic superconducting behaviours. Here we present our recent success in synthesising high-quality single crystals of La7Ir3 [2]. We also present experimental data on the unusually robust upper critical field as determined from electrical resistivity measurements in single crystals of La7Ir3. |
Friday, March 18, 2022 9:00AM - 9:12AM |
Y61.00006: Electronic Structure and doping dependence of the electron nematic series SrxBa(1-x)Ni2As2 Dushyant Narayan, PEIPEI HAO, Kyle Gordon, A. Garrison G Linn, Haoxiang Li, Bryan Berggren, Hope Whitelock, Christopher Eckberg, Prathum Saraf, John C Collini, Johnpierre Paglione, Daniel S Dessau The interplay between competing ordered states and superconductivity has long been identified as key to understanding high-temperature superconductivity. In the case of the iron pnictide superconductors, superconductivity coexists with SDW order and electronic nematicity. BaNi2As2, a structural analogue of the high temperature pnictide superconductor BaFe2As2 has recently been reported to host CDW order and electronic nematicity in conjunction with superconductivity. Interestingly, as a function of Sr doping, CDW and nematicity in the system is suppressed. Upon suppression of this order to absolute zero, a dramatic, six-fold enhancement of the superconducting transition temperature is observed. This system could thus serve as a model system to study the enhancement of superconductivity in the vicinity of quantum critical fluctuations. Here we present detailed high-resolution ARPES measurements of the SrxBa1-xNi2As2 series, comparing the measured band dispersion and Fermi surfaces to advanced electronic structure calculations beyond density functional theory. Utilizing both the experimental and theoretical data, in addition to showing CDW replication, we show large correlation effects not captured in conventional density functional theory. |
Friday, March 18, 2022 9:12AM - 9:24AM |
Y61.00007: Martensitic transformation in V3Si single crystal: 51V NMR evidence for coexistence of cubic and tetragonal phases Albert A Gapud, Arneil P Reyes The Martensitic transformation (MT) in A15 binary-alloy superconductor V3Si is a second-order, displacive structural transition from cubic to tetragonal symmetry, at temperature Tm a few K above the superconducting transition temperature Tc = 17 K. Though studied extensively, the MT has not yet been conclusively linked with a transition to superconductivity, and remains relevant due to renewed interest in soft phonon modes, whileV3Si continues to be of interest, e.g. due to similarities with Fe-As superconductors. Previous NMR studies on the MT in V3Si have been on powder samples, and with little emphasis on temperature dependence during the transformation. Here we study a high-quality single crystal, where quadrupolar splitting and Knight shift of NMR spectra for 51V allowed us to distinguish between spectra from transverse chains of V as a function of temperature. This revealed evidence of the coexistence of untransformed cubic phase and transformed tetragonal phase over a few K below and above Tm, and that the Martensitic lengthening of one axis occurs in a plane perpendicular to the crystal growth axis, as twinned domains. The data below Tm suggest that superconductivity may only be fully realized upon complete transformation to the tetragonal phase. More details on the effects on relaxation time T1, the electric field gradient, and the hyperfine field due to spin/orbital susceptibility of electrons are also discussed. |
Friday, March 18, 2022 9:24AM - 9:36AM |
Y61.00008: Anomalous high-temperature THz non-linearity in superconductors near the metal-insulator transition Dipanjan Chaudhuri, David Barbalas, Ralph Romero, Fahad Mahmood, John Jesudasan, Pratap Raychaudhuri, Peter N Armitage The interplay of strong disorder and superconductivity is a topic of long-term interest in condensed matter physics. Here we explore the non-linear THz response of superconducting NbN films both in the clean limit and close to the 3D metal-insulator transition. For the cleanest samples, the magnitude of the non-linear χ(3) response follows the expectation for the superconducting order parameter. In contrast, for high disorder samples near the metal-insulator transition the χ(3) nonlinearity persists to temperatures as high as even 4 times the Tc of the cleanest sample. We discuss the possible origins of this remarkably large nonlinearity, including the possibility that it arises in an enhancement of the temperature scales of superconductivity close to localization. Our work highlights the importance of finite frequency nonlinear THz experiments in detecting superconducting correlations even into regions where long-range ordered superconductivity does not persist. |
Friday, March 18, 2022 9:36AM - 9:48AM |
Y61.00009: Learning from disorder in superconductors with scanning probe microscopy and data analytics Petro Maksymovych, Jun Wang, Brian Lerner, Jiaqiang Yang, Brian C Sales, Eugene F Dumitrescu, Benjamin J Lawrie Disorder is a powerful approach to elicit and control superconducting properties, as evidenced from record Tc's, quantum phase transitions and exotic quasiparticles, predicted or evidenced in the presence of disorder. Systematic characterization of disorder fields in superconductors requires generally capturing orders of magnitude in length and temperature scales, posing a potent problem for both data acquistion and analysis. Here we will demonstrate emerging approaches to categorize disorder in notoriously heterogeneous scanning tunneling microscopy (STM) images of unconventional superconductors. From the information centric point of view, understanding the structure of these datasets amounts to effective and physically meaningful data compression. We will discuss compressibility of various kinds of STM data, and demonstrate the follow-on applications of compressive sensing, machine learning and information theory as a way to understand the results of the experiments and improve data acquisition. In particular, similarity learning emerges as a consistent strategy to categorize disorder with minimum prior knowledge. Finally, we apply disorder analysis to differentiate between Josephson and Andreev currents on the atomic scale. |
Friday, March 18, 2022 9:48AM - 10:00AM |
Y61.00010: Topological defects in superconducting open nanotubes under gradual and abrupt switch-on of the transport current and magnetic field Vladimir M Fomin, Igor Bogush Dynamics of the order parameter in superconducting membranes of a complex geometry under a strong transport current in an external homogeneous magnetic field becomes intricate. The normal component of the external magnetic field becomes inhomogeneous. This can be used to control the superconducting behavior. We analyze a thin superconducting Nb open nanotube using the time-dependent Ginzburg-Landau equation coupled with the electric scalar potential. Near the critical transport current, the dissipation processes are driven by the vortex and phase-slip dynamics. The transition between the vortex and phase-slip regimes is found to depend on the external magnetic field only weakly if the magnetic field and/or the transport current are switched on gradually. In the case of an abrupt switch-on of the magnetic field or transport current, the system can be triggered to the stable phase-slip regime, within a certain window of parameters. As a result, a hysteresis effect in the current-voltage characteristics is predicted in the superconducting open nanotubes. Generally, the system state in open nanotubes near the critical transport current depends on the way, in which the final external parameters (transport current and magnetic field) are achieved, constituting the memory effect. |
Friday, March 18, 2022 10:00AM - 10:12AM |
Y61.00011: Diffuse x-ray scattering study of the oxide superconductor Ba1-xKxBiO3 Sylvia L Griffitt, Marin Spaić, Dayu Zhai, Damjan Pelc, Zachary W Anderson, Matthew J Krogstad, Raymond Osborn, Martin Greven Despite much effort, the local structure of the high-Tc superconductor Ba1-xKxBiO3 remains poorly understood. Here we present extensive diffuse x-ray scattering measurements on single crystal of Ba1-xKxBiO3, with data on either side of the semiconductor-metal transition at x ~ 0.35. Bismuth valence disproportionation that leads to a breathing distortion of the oxygen octahedra and causes a charge-density wave provides a good explanation for the structure of the undoped material. However, the 3D-pair distribution function (3D-ΔPDF) obtained from our diffuse x-ray scattering data indicates that this picture may not be appropriate for the doped system. The oxygen octahedra in ABiO3 perovskites are known to tilt in order to accommodate atoms on the A site. Our 3D-ΔPDF and accompanying Monte Carlo modeling work indicates that various tilt modes are prominent in the metallic regime, along with substantial size-effect distortions caused by potassium doping. These lattice deformations lead to a lowered local symmetry, with profound implications for both the normal and superconducting states. |
Friday, March 18, 2022 10:12AM - 10:24AM |
Y61.00012: Monte Carlo modeling of local structure in Ba1-xKxBiO3 Marin Spaić, Sylvia L Griffitt, Dayu Zhai, Zachary W Anderson, Damjan Pelc, Matthew J Krogstad, Raymond Osborn, Martin Greven Ba1-xKxBiO3 exhibits a plethora of remarkable phenomena, such as charge-density wave (CDW) order, a metal-insulator transition, and high-temperature superconductivity. While the average structural symmetry of this perovskite has been documented in detail, crucial questions pertaining to local structural symmetry and short-range order remain unanswered. Here we present a semi-phenomenological Monte Carlo study of several models of the local structure of Ba1-xKxBiO3 near the metal-insulator transition. The models are based on various hypotheses about the underlying physics and chemistry and informed by diffuse x-ray scattering data. In this way, we provide a framework to qualitatively test various hypotheses and for interpretation of these data. This allows us to answer some of the long-standing questions regarding remnant short-range CDW order, the interplay of frustrated tilts and polar distortions, and the possibility of local symmetry breaking in Ba1-xKxBiO3 . |
Friday, March 18, 2022 10:24AM - 10:36AM Withdrawn |
Y61.00013: Machine Learning and Electronic Structure Methods in the Prediction of the Superconducting Critical Temperature of Metals Omololu Akin-Ojo, Firas Shuaib We apply the techniques of Machine Learning (ML) to build ML models that can predict the superconducting critical temperatures $T_c$ of metals. The models |
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