Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session M61: Superconductivity: Magnetic Field and VortexRecordings Available
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Sponsoring Units: DCMP Chair: Morten Eskildsen, University of Notre Dame Room: Hyatt Regency Hotel -Field |
Wednesday, March 16, 2022 8:00AM - 8:12AM |
M61.00001: Field-angle dependent vortex lattice phase diagrams in MgB2 Grace M Longbons, Allan Leishman, Nathan S Chalus, Nikolai Zhigadlo, Robert Cubitt, Morten R Eskildsen The vortex lattice (VL) phase diagram in the superconductor MgB2 for H || c consists of three phases labeled F, L and I. All three phases have a triangular symmetry and differ only in their orientation relative to the MgB2 crystalline axes. Here, the F phase is oriented along the crystalline a-axis and the I phase is characterized by the VL oriented along the a*-axis within the hexagonal basal plane. In the intermediate L phase, the VL undergoes a continuous rotation between these two high symmetry orientations. Previously, a rotation of the magnetic field about the crystalline a-axis was shown to suppress the L phase at a tricritical point at an angle of 83° [A. Leishman et al., Phys. Rev. B 103, 094516 (2021).]. Here we are reporting on similar measurements, but rotating the field about the a*-axis. This shifts the tricritical point both to a lower critical angle and a lower magnetic field. I will discuss how this can be understood based on the anisotropic vortex-vortex interaction in MgB2. |
Wednesday, March 16, 2022 8:12AM - 8:24AM |
M61.00002: Magnetic circuit for Abrikosov vortices: Vortex motion in a periodic labyrinth of magnetic T and I-shaped elements under and above a superconducting film Vitalii K Vlasko-Vlasov, Andreas Rydh, Ralu Divan, Daniel Rosenmann, Andreas Glatz, Allan Leishmann, Ulrich Welp, Wai K Kwok We report on the comprehensive study of the arrays of magnetic T and I-letter-shaped thin permalloy elements on the Abrikosov vortex dynamics in superconducting niobium films deposited under or above the magnetic pattern. Direct observations of the vortex motion using magneto-optical imaging technique, supported by transport measurements at temperatures close to Tc, show that the TI-elements create a robust magnetic potential for vortices, which can be easily reconfigured with rotating a moderate in-plane field. Such a tunable magnetic potential allowing control of the vortex trajectories can be a useful tool for manipulating vortices in fluxonic devices, and have a potential for implementing vortex braiding in quantum Majorana operations. |
Wednesday, March 16, 2022 8:24AM - 8:36AM |
M61.00003: Optical vortex manipulation for topological quantum computation Chengyun Hua, Matthew Brahlek, Eugene F Dumitrescu, Gábor Halász, Benjamin J Lawrie Topological quantum computation based on Majorana bound states may enable new paths to fault-tolerant quantum computing. Several recent experiments have suggested that the vortex cores of topological superconductors, such as iron-based superconductors, may host Majorana bound states at zero energy. However, quantum computation with these zero-energy vortex bound states requires precise and fast manipulation of individual vortices, which is difficult to do in a scalable manner. To address this issue, we propose a control scheme based on local heating via, for example, scanning optical microscopy to braid vortex-bound Majorana zero modes in a two-dimensional topological superconductor. First, we derive the conditions required for transporting a single vortex between two defects in the superconducting material by trapping it with a hot spot generated by local optical heating. Equipped with critical conditions for the vortex motion, we then establish the ideal material properties for vortex braiding and describe how transition errors resulting from finite speed and/or temperature can be minimized. Our work paves the way toward optical or microscopic control of zero-energy vortex bound states in two-dimensional topological superconductors. |
Wednesday, March 16, 2022 8:36AM - 8:48AM |
M61.00004: London and Campbell penetration depths in single crystals of Mo8Ga41 superconductor Sunil Ghimire, Kamal R Joshi, Kyuil Cho, Makariy A Tanatar, Cedomir Petrovic, Ruslan Prozorov Zero-field London penetration depth, λL(T), and Campbell penetration depth, λC(T), in DC magnetic fields up to 8 T, was measured in single crystals of Mo8Ga41 superconductor using tunnel diode resonator (TDR). In addition, the absolute value, λL(0) = 260 ± 10 nm, was extracted from the lower critical field, Hc1 , measurements using NV-centers in diamond optical magnetometry. The obtained superfluid density, ρs , follows very well clean isotropic single-gap weak-coupling BCS s−wave curve in the whole temperature range. The Campbell penetration depth was used to extract magnetic relaxation-free critical current density as a function of temperature and magnetic field. The results and the constructed vortex phase diagram are compared to other magnetic measurements of this and comparable superconductors. |
Wednesday, March 16, 2022 8:48AM - 9:00AM |
M61.00005: Current induced vortex nucleation in periodic 2-D superconducting hole arrays Abdulwahab Al Luhaibi, Andreas Glatz, John B Ketterson In the presence of a periodic lattice of patterned pinning sites in a superconducting film, together with a proper choice of an external magnetic field, a commensurate vortex array can be prepared. Above some critical applied d.c. current the lattice breaks loose from these pins and drifts between them, momentarily repinning at each site. This generates an a.c. current in the film, the fundamental frequency of which increases with the applied d.c. current. We have simulated this behavior using the time Dependent Ginzburg-Landau formalism (TDGL)† for arrays of circular pinning sites having differing diameters, pinning strengths and spacings. Depending on conditions, the harmonic content of the resulting signal can be high. If, in addition, an external a.c. current is superimposed on the d.c. current, the vortex site-hopping frequency can be pulled and locked to the applied frequency over some range of applied frequencies that depends on the strength of the a.c. current. |
Wednesday, March 16, 2022 9:00AM - 9:12AM Withdrawn |
M61.00006: Vortex bound states and Majorana zero mode from superconducting proximity effect Margarita Davydova, Liang Fu We study a thin metal film in proximity with an s-wave superconductor under a perpendicular magnetic field leading to Abrikosov vortices, when the coherence length in the proximitized layer is much larger than the one of the parent superconductor ξN >> ξS. The induced pair potential restores to its value at infinity over the distance ξS from the vortex center, rather than the induced coherence length ξN. Using quasiclassical approximation, we show that the presence of multiple lengthscales leads to qualitative changes in the properties of the vortex bound states in comparison to conventional ones. |
Wednesday, March 16, 2022 9:12AM - 9:24AM |
M61.00007: Domain Boundary Dissolution of Six and Twelve-fold Anisotropic Vortex Lattices Daniel M Minogue, Morten R Eskildsen, Charles M Reichhardt, Cynthia Reichhardt When superconductors are exposed to a magnetic field, it penetrates the material in the form of quantized vortices. These vortices are repulsive and, will organize themselves into an ordered lattice with a symmetry and orientation that depend on the form of their interaction potential. One such potential, manifested in the two-band superconductor MgB2, is a combined 6 and 12 fold anisotropy which produces a triangular lattice with various orientations based on the ratio of the two anisotropic terms. Here, a large ratio resulting in two distinct domains of vortices and a low ratio forming a single domain. We have investigated the phase transition between the two domain ordering to the single domain using a molecular dynamics simulation. It was found that the system does not evolve completely by only changing the aforementioned ratio, but requires the application of additional perturbation through oscillating the effective density of the vortices which facilitates the phase transition and reduces the difference in the relative angle of the two domains logarithmically with respect to time. This is in agreement with small-angle neutron scattering studies carried out by our group [Louden et al., Phys. Rev. B 99,144515 (2019)]. |
Wednesday, March 16, 2022 9:24AM - 9:36AM |
M61.00008: Dynamics of Magnetic Vortices with Twofold Anisotropic Interaction Potential Edward J Roe, Morten R Eskildsen, Cynthia Reichhardt, Charles M Reichhardt The dynamics of vortices in type-II superconductors has been studied extensively in systems with an isotropic vortex-vortex interaction potential; however, much less is known about systems in which the potential is anisotropic. We use molecular dynamics simulations to study the dynamics of vortices with twofold anisotropic interactions, for driving forces applied along the two principal symmetry directions of the interaction potential. The simulations are performed with varying numbers of randomly placed pinning sites to represent the defects which are always present in real materials. We find that as the anisotropy of the potential is increased, the vortex lattice defect density becomes less sensitive to the magnitude of the applied drive. Furthermore, the system exhibits a hysteresis effect in which, for a decreasing drive, an ordered state persists down to currents below the threshold current at which the ordered state first forms for an increasing drive. We discuss these results and their possible underlying mechanisms. |
Wednesday, March 16, 2022 9:36AM - 9:48AM Withdrawn |
M61.00009: A Possible Novel Phase Transition in the Vortex Plastic Flow Regime in the Highly Anisotropic High-Tc Superconductor HgBa2CuO4 + δ Roswell DeMott, Mun K Chan, Brian P Gorman, Haley M Cole, Michael B Venuti We describe a previously unobserved phase transition in the plastic flow regime of the highly anisotropic superconductor HgBa2CuO4 + δ. This phase transition is marked by a sudden change in the glassy exponent. It is also marked by a change in the behavior of the plastic flow barrier U* as a function of temperature. Before the phase transition, U* decreases linearly with increasing temperature. After the phase transition, there is no clear relationship between U* and temperature. So far, we have been unable to explain this phase transition in terms of any existing theoretical modelss for the plastic flow barrier. In the future, we intend to look for possible causes of this phase transition in the microscopic forces acting on each vortex, independent of previous results on the plastic flow barrier. |
Wednesday, March 16, 2022 9:48AM - 10:00AM |
M61.00010: Towards an optomechanical torque magnetometry platform for detection of individual superconducting vortices. Matt J Rudd, John P Davis, Paul H Kim Cavity optomechanics presents a powerful toolkit for performing high-resolution measurements, with measurements pushing up against the standard quantum limit and even being used to demonstrate quantum behavior of mechanical resonators. However, despite this sensitivity, there have been relatively few applications of optomechanics techniques to the study of fundamental condensed matter questions. We present an optomechanical platform for the investigation of superconducting thin films. Our sensor is cryogenically compatible and enables direct fiber-coupling inside a dilution fridge, mediated by an on-chip waveguide. It is sample agnostic, allowing the investigation of many superconducting materials. Using a torsional element with mechanical resonance frequency in the MHz regime, we anticipate time-resolved magnetometry and real-time observation of the creation and annihilation of vortices in superconducting films. The geometry of the sensor is optimized for torque-mixing resonance spectroscopy, further allowing us to probe the dynamical behavior of such vortices. |
Wednesday, March 16, 2022 10:00AM - 10:12AM |
M61.00011: Vortex Hall effect in the BCS-BEC crossover: Experiment Max Heyl, Kyosuke Adachi, Yusuke Kato, Emil List-Kratochvil, Yoshihiro Iwasa In some of the recently found low carrier density superconductors, the superconducting temperature Tc is in the order of 10-1 of the Fermi temperature TF, which is much higher than that of the superconductors in the Bardeen-Cooper-Schrieffer (BCS) regime, indicating that these new superconductors are in the crossover regime between the BCS limit and the other opposite limit, the Bose-Einstein condensation (BEC). These new systems are perfect candidates to uncover how the transport properties evolve in the largely unexplored BCS-BEC crossover regime. In this work LixZrNCl served as platform for a low carrier density superconductor where the carrier density is systematically controllable over nearly two-orders of magnitude through the amount of intercalated Li [1]. This enabled to navigate the single-crystal ZrNCl within the BCS-BEC crossover in an intercalation-only device structure as previously reported [2]. Several doping levels, i.e., Lithium contents x, were realized and allowed to study how the transport properties evolve in the BCS-BEC crossover regime [3]. In this light, we report a substantial enhancement of the vortex Hall effect by reducing the carrier density towards the crossover regime in this two-dimensional (2D) superconductor. This anomalous behavior in the Hall effect is attributed to vortices, and the time-dependent Ginzburg-Landau (TDGL) theory proves a qualitative scenario enhancement of the vortex Hall effect is caused by the particle-hole asymmetry characteristics in the BCS-BEC crossover. This presentation should be followed by the theory talk by Dr. Adachi. |
Wednesday, March 16, 2022 10:12AM - 10:24AM |
M61.00012: Vortex Hall effect in the BCS-BEC crossover: Theory Kyosuke Adachi, Yusuke Kato, Max Heyl, Yoshihiro Iwasa Superconductivity due to the Cooper pairs, which is described by the Bardeen-Cooper-Schrieffer (BCS) theory, is connected to the Bose-Einstein condensation (BEC) of tightly bound pairs through the BCS-BEC crossover. Recently, the BCS-BEC crossover has been realized in the layered ionic-gating device by controlling carrier doping [1]. In this study, motivated by the recent experiments, we theoretically considered the vortex Hall effect in the BCS-BEC crossover region. Using the phenomenological time-dependent Ginzburg-Landau model [2,3], we found the enhancement of the typical Hall angle toward the crossover region. Further, calculating the temperature dependence of the longitudinal and transverse conductivities due to the vortex liquid, we obtained a possible sign reversal of the Hall effect. In the presentation, we will also discuss the relation to the experimental data explained in the previous talk. |
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