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Results for “superfluid vortices”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Reversible ordering and disordering of the vortex lattice in UPt 3

When studied by small-angle neutron scattering the vortex lattice (VL) in UPt 3 undergoes a gradual disordering as a function of time due to 235 U fission. This temporarily heats regions of the sample above the critical temperature, where, upon re-cooling, the vortices remain in a quenched disordered state. Furthermore, the disordering rate is proportional to the magnetic field, suggesting that it is governed by collective VL properties such as the elastic moduli. An ordered VL can be re-formed by applying a small field oscillation, showing that the fission does not cause detectable radiation damage to the UPt 3 crystals, even after long exposure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Time-reversal symmetry breaking in two-dimensional nonequilibrium viscous fluids

In this work, we study the rheological signatures of departure from equilibrium in two-dimensional viscous fluids with and without internal spin. Under the assumption of isotropy, we provide the most general linear constitutive relations for stress and couple stress in terms of the velocity and spin fields. Invoking Onsager's regression hypothesis for fluctuations about steady states, we derive the Green-Kubo formulas relating the transport coefficients to time-correlation functions of the fluctuating stress. In doing so, we show that one of the nonequilibrium transport coefficients, the odd viscosity, requires time-reversal symmetry breaking in the case of systems without internal spin. However, the Green-Kubo relations for systems with internal spin also show that there is a possibility for nonvanishing odd viscosity even when time-reversal symmetry is preserved. Furthermore, we find that breakdown of equipartition in nonequilibrium steady states results in the decoupling of the two rotational viscosities relating the vorticity and the internal spin.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Non-Equilibrium relaxation, aging scaling, and critical depinning dynamics of skyrmions in disordered magnetic films. Final Report

Technical applications of type-II superconductors, especially high-Tc compounds, in external magnetic fields require an effective flux pinning mechanism to reduce Ohmic losses due to flux creep and flow. Naturally abundant point defects, dislocations, and twin boundaries as well as artificially introduced disorder may serve as effective pinning centers for magnetic vortices. The properties of interacting flux lines subject to strong thermal fluctuations and point-like or extended pinning centers have therefore been a major research focus in condensed matter physics, and considerable progress has been achieved in the characterization and mathematical description of the equilibrium phases and non-equilibrium steady states of vortex matter. Detailed studies of the rich phase diagrams that reveal novel glassy states as well as the associated complex dynamical phenomena have in turn enriched the theoretical understanding of condensed matter systems, elucidating specifically the kinetics of elastic objects driven through disordered media and the important role of topological defects such as vortices and dislocations in various materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Transient heat transfer of superfluid He 4 in nonhomogeneous geometries: Second sound, rarefaction, and thermal layer

Transient heat transfer in superfluid 4 He (He II) is a complex process that involves the interplay of the unique counterflow heat-transfer mode, the emission of second-sound waves, and the creation of quantized vortices. Many past researches focused on homogeneous heat transfer of He II in a uniform channel driven by a planar heater. Here, we report our systematic study of He II transient heat transfer in nonhomogeneous geometries that are pertinent to emergent applications. By solving the He II two-fluid equations of motion coupled with Vinen's equation for vortex-line density, we examine and compare the characteristics of transient heat transfer from planar, cylindrical, and spherical heaters in He II. Our results show that as the heater turns on, an outgoing second-sound pulse emerges, within which the vortex-line density grows rapidly. These vortices attenuate the second sound and result in a heated He II layer in front of the heater, i.e., the thermal layer. In the planar case where the vortices are created throughout the space, the second-sound pulse is continuously attenuated, leading to a thick thermal layer that diffusely spreads following the heat pulse. On the contrary, in the cylindrical and the spherical heater cases, vortices are created mainly in a thin thermal layer near the heater surface. As the heat pulse ends, a rarefaction tail develops following the second-sound pulse, in which the temperature drops. This rarefaction tail can promptly suppress the thermal layer and take away the deposited thermal energy. The effects of the heater size, heat flux, pulse duration, and temperature on the thermal-layer dynamics are discussed. We also show how the peak heat flux for the onset of boiling in He II can be studied in our model.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Vortex phase diagram of the kagome superconductor CsV 3 ⁢Sb 5

The screening response of the kagome superconductor CsV 3 ⁢Sb 5 was obtained from high-resolution ac mutual inductance measurements. At zero applied magnetic field and low temperatures, we observe no evidence for gapless quasiparticles, while near T c we find evidence for enhanced fluctuations. A rich vortex state appears above H c⁢1 ≈30 Oe, exhibiting successive emergence of vortex phases. For a fixed magnetic field, lowering the temperature below T c⁡ (H) leads to a wide range of vortex liquid state in a landscape of weak pinning potential, which gives rise to an irreversibility line. Further lowering the temperature, we identify the vortex melting line followed by the peak effect manifested in enhanced vortex pinning strength and critical current. Finally, we suggest that such an unusual behavior, where the peak effect region is fully contained within the vortex lattice state below the irreversibility line, is a consequence of the strong anisotropy and weak bulk pinning in CsV 3 ⁢Sb 5 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Driven responses of periodically patterned superconducting films

Here, we simulate the motion of a commensurate vortex lattice in a periodic lattice of artificial circular pinning sites having different diameters, pinning strengths, and spacings using the time-dependent Ginzburg-Landau formalism. Above some critical DC current density J c , the vortices depin, and the resulting steady-state motion then induces an oscillatory electric field E (t) with a defect "hopping" frequency f 0 , which depends on the applied current density and the pinning landscape characteristics. The frequency generated can be locked to an applied AC current density over some range of frequencies, which depends on the amplitude of the DC as well as the AC current densities. Both synchronous and asynchronous collective hopping behaviors are studied as a function of the supercell size of the simulated system and the (asymptotic) synchronization threshold current densities determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Observing the Suppression of Superconductivity in RbEuFe 4 As 4 by Correlated Magnetic Fluctuations

In this Letter, we describe quantitative magnetic imaging of superconducting vortices in RbEuFe 4 As 4 in order to investigate the unique interplay between the magnetic and superconducting sublattices. Our scanning Hall microscopy data reveal a pronounced suppression of the superfluid density near the magnetic ordering temperature in good qualitative agreement with a recently developed model describing the suppression of superconductivity by correlated magnetic fluctuations. Furthermore, these results indicate a pronounced exchange interaction between the superconducting and magnetic subsystems in RbEuFe 4 As 4 , with important implications for future investigations of physical phenomena arising from the interplay between them.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Nonlinear inductive response of pinned superconducting vortices in artificial pinning sites

Using the time dependent Ginzburg-Landau equations, we simulate the inductive responses of a variety of thin-film systems containing patterned antidots with different sizes and shapes. The results for all shapes show that the kinetic inductance diverges as the applied current approaches a critical current that is below the BCS depairing current. In conclusion, exploiting the similarity of the observed current-voltage behavior to that of Josephson junctions, we obtain an empirical equation that well fits the inductivity curve as a function of the applied current.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Reversible ratchet effects in a narrow superconducting ring

We study the ratchet effect in a narrow pinning-free superconductive ring based on time-dependent GinzburgLandau (TDGL) equations. Voltage responses to external dc and ac currents at various magnetic fields are studied. Due to asymmetric barriers for flux penetration and flux exit in the ring-shaped superconductor, the critical current above which the flux-flow state is reached, as well as the critical current for the transition to the normal state, are different for the two directions of applied current. Furthermore, these effects cooperatively cause ratchet signal reversal at high magnetic fields, which has not been reported to date in a pinning-free system. The ratchet signal found here is larger than those induced by asymmetric pinning potentials. Our results also demonstrate the feasibility of using mesoscopic superconductors to employ a superconducting diode effect in versatile superconducting devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Magnetic circuit for Abrikosov vortices: Vortex motion in a periodic labyrinth of magnetic T and I-shaped elements under a superconducting film

Here we explore tailored labyrinth-like vortex motion in a niobium film placed on top of periodic arrays of T and I -shaped permalloy elements by imaging the vortex distribution in magnetic fields applied perpendicular to the superconducting layer under different in-plane polarizations of the TI structure. At low temperatures, we observe pronounced meandering of vortex motion around the TI elements. Remarkably, vortices can easily penetrate the sample along the TI columns even though the average vortex pinning in the patterned area is larger than in a bare niobium film. Accordingly, at temperatures close to the superconducting transition temperature, T c , the voltagecurrent curves in the patterned area show an earlier departure from the zero-resistivity state at small currents, followed by slower growth with increasing current as compared to the un-patterned film. We present a model based on magnetostatic interactions between magnetic charges at the edges of the polarized TI-elements and single magnetic charges of induced vortices to account for this behavior. We expect that similar magnetic structures imposing labyrinth-like vortex motion could be used for collective entanglement of vortices envisioned in quantum circuit operations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Dissipation of moving vortices in thin films

In this letter, moving vortices in thin superconducting films are considered within the time-dependent London description. The dissipation due to out-of-core normal excitations for two vortices moving together turns out to have a minimum for the separation vector $\textit{a}$ parallel to the velocity and equal to $a_m$ ≈ 2.2 Λ , where Λ is the Pearl length. The minimum entropy production suggests that moving vortices should have a tendency to form chains along the velocity with a period of the order $a_m$.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Interaction between moving Abrikosov vortices in type-II superconductors

Herein the self-energy of a moving vortex is shown to decrease with increasing velocity. The interaction energy of two parallel slowly moving vortices differs from the static case by a small term ∝ v 2 ; the “slow” motion is defined as having the velocity v < v c = c 2 / 4 π σ λ , where σ ( T ) is the conductivity of normal excitations and λ ( T ) is London penetration depth. For higher velocities, v > v c ( T ) , the interaction energy of two vortices situated along the velocity direction is enhanced and in the perpendicular direction is suppressed compared to the static case.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Diamagnetic mechanism of critical current non-reciprocity in multilayered superconductors

The suggestion that non-reciprocal critical current (NRC) may be an intrinsic property of non-centrosymmetric superconductors has generated renewed theoretical and experimental interest motivated by an analogy with the non-reciprocal resistivity due to the magnetochiral effect in uniform materials with broken spatial and time-reversal symmetry. Theoretically it has been understood that terms linear in the Cooper pair momentum do not contribute to NRC, although the role of higher-order terms remains unclear. In this work we show that critical current non-reciprocity is a generic property of multilayered superconductor structures in the presence of magnetic field-generated diamagnetic currents. In the regime of an intermediate coupling between the layers, the Josephson vortices are predicted to form at high fields and currents. Experimentally, we report the observation of NRC in nanowires fabricated from InAs/Al heterostructures. The effect is independent of the crystallographic orientation of the wire, ruling out an intrinsic origin of NRC. Non-monotonic NRC evolution with magnetic field is consistent with the generation of diamagnetic currents and formation of the Josephson vortices. This extrinsic NRC mechanism can be used to design novel devices for superconducting circuits.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Magnetic droplet solitons

Magnetic droplet solitons are dynamical magnetic textures that form due to an attractive interaction between spin waves in thin films with perpendicular magnetic anisotropy. Spin currents and the spin torques associated with these currents enable their formation as they provide a means to excite non-equilibrium spin-wave populations and compensate their decay. Recent years have seen rapid advances in experiments that realize and study magnetic droplets. Important advances include the first direct x-ray images of droplets, determination of their threshold and sustaining currents, measurement of their generation and annihilation time, and evidence for drift instabilities, which can limit their lifetime. This perspective discusses these studies and contrasts these solitons to other types of spin-current excitations, such as spin-wave bullets, and static magnetic textures, including magnetic vortices and skyrmions. Magnetic droplet solitons can also serve as current controlled microwave frequency oscillators with potential applications in neuromorphic chips as nonlinear oscillators with memory.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Tunable Magnetic Labyrinth for Abrikosov Vortices

We study Abrikosov vortex dynamics in a superconducting layer covered with an array of T- and I-shaped magnetically soft permalloy elements. Application of the in-plane field H // polarizes thin permalloy bars forming the array and creates a periodic network of mutually perpendicular lines of the attractive or repulsive magnetic potential for vortices along the bar edges, which can be easily tuned by the rotation of H // . Magneto-optical imaging of the vortex trajectories confirms that such a reconfigurable magnetic potential dominates the vortex motion in a wide temperature range and can be a useful tool for manipulating vortices in fluxonic devices for low-loss microelectronics.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Vortex-induced anomalies in the superconducting quantum interference patterns of topological insulator Josephson junctions

The superconducting quantum interference (SQI) patterns of Josephson junctions fabricated from hybrid structures that interface an s-wave superconductor with a topological insulator can be used to detect signatures of novel quasiparticle states. Here, we compare calculated and experimental SQI patterns obtained from hybrid junctions fabricated on cadmium arsenide, a two-dimensional topological insulator. The calculations account for the effects of Abrikosov (anti-) vortices in the superconducting contacts. They describe the experimentally observed deviations of the SQI from an ideal Fraunhofer pattern, including anomalous phase shifts, node lifting, even/odd modulations of the lobes, irregular lobe spacing, and an asymmetry in the positive/negative magnetic field. We also show that under a current bias, these vortices enter the electrodes even if there is no intentionally applied external magnetic field. The results show that Abrikosov vortices in the electrodes of the junctions can explain many of the observed anomalies in the SQI patterns of topological insulator Josephson junctions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗