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 X48: Superconductivity: Critical Current, Magnetic Field Effects, and Vortex PhysicsLive
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Sponsoring Units: DCMP Chair: Michael Sentef, Max Planck Inst Structure & Dynamics of Matter |
Friday, March 19, 2021 8:00AM - 8:12AM Live |
X48.00001: Conductivity of superconductors in the flux flow regime Michael Smith, Anton Andreev, Mikhail Feigel'man, Boris Spivak We develop a theory of conductivity of type-II superconductors in the flux flow regime taking into account random spatial fluctuations of the system parameters, such as the gap magnitude Δ(r) and the diffusion coefficient D(r). We find a contribution to the conductivity that is proportional to the inelastic relaxation time τin, which is much longer than the elastic relaxation time. This new contribution is due to Debye-type relaxation, and it can be much larger than the conventional flux flow conductivity due to Bardeen and Stephen. The new contribution is expected to dominate in clean superconductors at low temperatures and in magnetic fields much smaller than Hc2. |
Friday, March 19, 2021 8:12AM - 8:24AM Live |
X48.00002: Fission induced vortex lattice disordering in UPt3 Keenan Avers, Stephen Kuhn, Allan Leishman, William J Gannon, Lisa DeBeer-Schmitt, Charles Dewhurst, Dirk Honecker, Robert Cubitt, William Paul Halperin, Morten Eskildsen The vortex lattice (VL) in UPt3 was studied using small-angle neutron scattering, and found to undergo a gradual disordering due to neutron beam induced fission of 235U. The fission events temporarily heat regions of the sample above the critical temperature, in which the vortices remain in a disordered state (most likely a quenched vortex glass) upon re-cooling. The disordering rate is proportional to the magnetic field, indicating that it is governed by the collective elastic properties of the vortex matter. An ordered VL can be re-formed by applying a small field oscillation, indicating that the fission does not cause significant radiation damage to UPt3 on the time scale of the neutron scattering experiments. The ability to introduce localized quenched disorder, which at the same time is reversible, presents a novel avenue for vortex matter studies. |
Friday, March 19, 2021 8:24AM - 8:36AM Live |
X48.00003: Effect of pinning on nonlinear dynamics and dissipation of a trapped vortex driven by a strong surface current in a superconducting film. Manula Randhika Pathirana Walive Pathiranage, Alexander V Gurevich We report numerical simulations of a trapped elastic vortex driven by a strong ac magnetic field $H(t)=H\sin\omega t$ parallel to the surface of a superconducting film. The power dissipated by the oscillating vortex driven by the ac Meissner current has been calculated by taking into account the vortex line tension, viscous drag and different pinning landscapes, including bulk, surface and cluster pinning. We show that the global surface resistance $\bar{R}_i(H)$ averaged over different statistical realizations of a random pinning potential exhibits a linear increase at small fields and levels off at higher fields. At high field amplitudes $R_i(H)$ was calculated, taking into account a nonlinear Larkin-Ovchinnikov (LO) viscous drag coefficient $\eta(v)$. Our numerical results show that at high fields $R_i(H)$ becomes a nonmonotonic function of $H$ which {\it decreases} with $H$ at higher frequencies. We also observed the jumpwise LO instability of fast perpendicular vortices in a film with weak pinning at small field amplitudes and frequencies. |
Friday, March 19, 2021 8:36AM - 8:48AM Live |
X48.00004: Magnetic melting of the 2D vortex lattice in thin a-MoGe films: Electrical transport perspective Bal Pokharel, Jasminka Terzic, Dragana Popovic, Surajit Dutta, John Jesudasan, Pratap Raychaudhuri, Ilaria Maccari, Lara Benfatto With increasing magnetic field, the vortex lattice in a 2D type II superconductor is expected to melt via an intermediate liquid phase ("hexatic fluid"). This orientational order-preserving hexatic fluid state has been observed in recent STM studies in relatively clean thin films of a-MoGe [1]. The Monte Carlo simulations on a classical 2D XY model support the STM studies and, furthermore, they predict that the persistence of orientational correlations in the hexatic phase leads to the slowing down of the vortex dynamics as described by a Vogel-Fulcher-Tammann (VFT) law. We report the results of the resistivity measurements on weakly disordered, 22 nm-thick a-MoGe films over a wide range of temperatures and fields up to 18 T to characterize the 2D vortex melting from a transport perspective. We find that the temperature dependence of the resistivity indeed follows a VFT law over a wide range of fields, consistent with numerical simulations. Our results thus unambiguously show that electrical transport measurements may be used to detect signatures of the hexatic phase. |
Friday, March 19, 2021 8:48AM - 9:00AM Live |
X48.00005: Anomalous and magnetic Hall effect of the Abrikosov vortex in type-II superconductors Hikaru Ueki, Marie Ohuchi, Ezekiel S. Joshua, Takafumi Kita Vortices in type-II superconductors have not only a flux quantum but also charge. This vortex-core charging has attracted the interest of many researchers and numerous theoretical studies have been performed. However, its origin is not yet fully understood. |
Friday, March 19, 2021 9:00AM - 9:12AM Live |
X48.00006: Vortex Structure in a Superconductor under a Rotating Field: Entanglement and Recombination Masaru Kato, Hayato Yokoji In a type-II superconductor under a uniform magnetic field H(Hc1<H<Hc2), quantized magnetic fluxes or vortices enter the superconductor. They are parallel to the external field. Then, what happens if the magnetic field is slightly rotated? In order to answer this question, we have solved the Ginzburg-Landau equations for cuboids under rotated magnetic fields. We have found that for low field, a vortex appears at the center of the superconductor and it is parallel to the magnetic field at that point. For stronger field, when four vortices enter the superconductor, at both sides, two pairs of vortices interact and recombination occurs. As a result, two center vortices form a braid as if they are entangled. |
Friday, March 19, 2021 9:12AM - 9:24AM Live |
X48.00007: Probing magnetization and vortex dynamics in Bi2Sr2CaCu2O8 micromechanical resonator driven using radiation pressure drive. Sudhir Sahu, Supriya Mandal, Sanat Ghosh, Mandar M Deshmukh, Vibhor Singh Techniques from cavity optomechanics provide exquisite control over the motion of mechanical resonator. Here we realize a cavity-optomechanical system consisting of a microwave cavity and a mechanical oscillator from an exfoliated crystal of Bi2Sr2CaCu2O8. We use the radiation-pressure based mechanical drive (optomechanically induced transparency) to probe the electromechanical properties of the mechanical oscillator. In the presence of a magnetic field, we observe a hysteresis in the oscillator's resonant frequency, which can be understood within the critical state model. While sweeping the magnetic field, we observe abrupt jumps in the mechanical frequency, suggesting the charged nature of the vortex core. |
Friday, March 19, 2021 9:24AM - 9:36AM Live |
X48.00008: Nonreciprocal Switching Currents in Superconductor/Semiconductor Heterostructure Devices Ananthesh Sundaresh, Leonid Rokhinson Superconductor-Semiconductor hybrid structures are one of the leading platforms in the search for topological superconductivity. In these heterostructures, s-wave superconductivity combined with the strong spin-orbit coupling (SO) is expected to facilitate p-wave pairing. Direct probing of the symmetry of the order parameter is a daunting task, but presence of the SO in bulk non-centrosymmetric superconductors is expected to modify transport properties and add a linear in current and field correction to the critical current. In this work we report experimental investigation of critical currents in nanowires fabricated from InAs/Al heterostructures. We observe a highly non-monotonic dependence of the correction to the critical current on magnetic field, which is found to be linear at small fields (B<100mT), decreases to zero and switches sign at 200 mT, and vanishes above 300mT, all within the range of fields when the magnitude of the critical current changes only by a few percent. We also find that this dependence is not affected by a variation in wire length or crystallographic orientation but does depend on the relative orientation of the field and the current. |
Friday, March 19, 2021 9:36AM - 9:48AM Live |
X48.00009: Superconducting Vortex Dynamics in Thin Films Near the Critical Temperature Alexander Sirota, Vladimir Talanov During a field cool, superconducting vortices remain mobile only within a narrow temperature range above the vortex freezing temperature, where the vortex dynamics are mainly defined by the interplay between repulsive vortex-vortex and attractive vortex-defect interactions. Below the vortex freezing temperature, vortex pinning by defects becomes so strong that neither vortex-vortex interaction nor thermal activation are able to move the vortex. We study this process by modeling the pinning landscape as a double well potential arising from two defects and examining the time evolution of the probability density of the vortex position. We consider the Pearl limit where the film thickness is much smaller than the bulk penetration depth, which causes long range vortex-defect interactions. Our results show that even a simple model accounting for a single vortex can shed a light onto vortex distributions among defects in superconductors. |
Friday, March 19, 2021 9:48AM - 10:00AM Live |
X48.00010: Vortex Dynamics and Dissipation under High-Amplitude Microwave Drive Mattia Checchin, Anna Grassellino In this paper, we describe the vortex dynamics under a high-amplitude microwave drive and its effect on the surface resistance of superconductors. The vortex surface resistance is calculated with a Monte Carlo approach, where the vortex equation of motion is solved for a collection of vortex flux lines, each oscillating within a random pinning landscape. This approach is capable of providing a detailed description of the microscopic vortex dynamics and in turn important insights into the microwave-field-amplitude dependence of the vortex surface resistance. The numerical simulations are compared against experimental data of vortex surface resistance at high microwave amplitude measured by means of bulk niobium superconducting radio-frequency cavities operating at 1.3 GHz. The good qualitative agreement of the simulations and experiments suggests that the nonlinear dependence of the trapped-flux surface resistance with the microwave field amplitude is generated by progressive microwave depinning and vortex jumps. |
Friday, March 19, 2021 10:00AM - 10:12AM Live |
X48.00011: Field-Angle Dependent Vortex Lattice Phase Diagram in MgB2 Allan Leishman, Anna Sokolova, Markus Bleuel, Nikolai Zhigadlo, Morten Eskildsen Vortex lattices (VLs) in type-II superconductors can provide unique insights into the interaction of the superconducting order parameter with the underlying crystal lattice. The structure of the VL can be particularly interesting when the applied field is perpendicular to a hexagonal crystal plane, where the six-fold rotation symmetry leads to a near isotropic energy landscape, allowing higher order terms to couple to the VL. |
Friday, March 19, 2021 10:12AM - 10:24AM Live |
X48.00012: Geometric Meissner Effect in Chiral Superconductors Krishanu Roychowdhury A recently identified phenomenon namely a Meissner effect induced by curvature has been investigated in a microscopic lattice model of a chiral superconductor. Preliminary numerical results support the picture given earlier in Phys. Rev. Lett. 120, 217002, which was based on an effective mean-field theory. The geometric Meissner effect has been proposed as a smoking gun evidence for chiral superconductivity, and the long term goal of this work is to tie this effect more closely to more realistic microscopic models. |
Friday, March 19, 2021 10:24AM - 10:36AM Live |
X48.00013: Vortex phase diagram and high-field normal state of underdoped Bi2Sr2-xLaxCuO6+δ. Jasminka Terzic, Bal Pokharel, Shimpei Ono, Dragana Popovic In underdoped cuprates, the value of the upper critical magnetic field (Hc2) and the role of charge and spin orders have been under debate. However, recent studies on the La-214 family have firmly established vortex phase diagrams that include an intermediate, viscous vortex liquid regime, regardless of the presence of charge order. We perform similar studies in underdoped Bi2Sr2-xLaxCuO6+δ (La-Bi2201), which in contrast to La-214 family exhibits only short-range charge order, and no spin order. Measurements of linear transport, voltage-current characteristics and Hall effect in H up to 45 T and temperatures (T) down to 0.017 K, reveal an insulatinglike high-field normal state and qualitatively the same vortex phase diagram as in underdoped La-214 cuprates. Therefore, our results support the universality of the vortex phase diagram with an intermediate phase, i.e. the importance of quantum phase fluctuations as T→0, in underdoped cuprates regardless of the presence of spin or charge orders. |
Friday, March 19, 2021 10:36AM - 10:48AM Live |
X48.00014: Confluence of complex surface impedance and depinning current studies of model defects in Nb films near critical temperature Cougar Garcia, Vladimir Talanov, Alexander Sirota, Dillon Christopher Merenich, Anna Herr, Nicholas Rizzo, Steven M Anlage Studying and manipulation of vortex matter is key to understanding fundamental physics of superconducting materials, improving the properties of superconducting devices, and developing new concepts for superconductor applications. Two major approaches to experimentally characterize vortex dynamics are to measure (i) the (de)pinning current density and flux flow resistance in transport measurements or (ii) surface impedance in resonator based measurements as a function of applied field. In this work we combine both approaches to characterize thin Nb films used in superconducting electronic circuits. We measured the vortex pinning constant, viscous drag, and (de)pinning frequency near the critical temperature using a parallel plate resonator (PPR) technique. In addition, we performed transport measurements to study (de)pinning critical current and the (de)pinning force density as a function of temperature and external magnetic field. The combination of PPR and transport experiments provide results for wide temperature range, which is unachievable by each technique individually. We also compare our experimental results with numerical simulations based on the Ginzburg-Landau equations. |
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