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Register a new userHow magnetic field can transform a superconductor into a Bose metal
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We discuss whether a simple theory of superconducting stripes coupled by Josephson tunneling can describe a metallic transport, once the coherent tunneling of pairs is suppressed by the magnetic field. For a clean system, the conclusion we reached is negative: the excitation spectrum of preformed pairs consists of Landau levels, and once the magnetic field exceeds a critical value, the transport becomes insulating. As a speculation, we suggest that a Bose metal can exist in disordered systems provided that the disorder is strong enough to localize some pairs. Then the coupling between propagating and localized pairs broadens the Landau levels, resulting in a metallic conductivity. Our model respects the particle-hole symmetry, which leads to a zero Hall response. And intriguingly, the resulting anomalous metallic state has no Drude peak and the spectral weight of the cyclotron resonance vanishes at low temperatures.
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Experimentally and mysteriously, the concentration of quasiparticles in a gapped superconductor at low temperatures always by far exceeds its equilibrium value. We study the dynamics of localized quasiparticles in superconductors with a spatially fluctuating gap edge. The competition between phonon-induced quasiparticle recombination and generation by a weak non-equilibrium agent results in an upper bound for the concentration that explains the mystery.
The magnetization of a planar heterostructure of periodically alternating type-II superconductor and soft-magnet strips exposed to a transverse external magnetic field is studied. An integral equation governing the sheet current distribution in the Meissner state of the superconductor constituents is derived. The field of complete penetration of magnetic flux in the critical state of the superconductor constituents is calculated for different widths of the superconductor and the soft-magnet constituents and a range of values of the relative permeability of the soft-magnet constituents.
It is shown that the application of sufficiently strong magnetic field to the odd-frequency paired Pair Density Wave state described in Phys. Rev. B 94, 165114 (2016) leads to formation of a low temperature metallic state with zero Hall response. Applications of these ideas to the recent experiments on stripe-ordered La_{1.875}Ba_{0.125}CuO_4 are discussed.
We show that while orbital magnetic field and disorder, acting individually weaken superconductivity, acting together they produce an intriguing evolution of a two-dimensional type-II s-wave superconductor. For weak disorder, the critical field H_c at which the superfluid density collapses is coincident with the field at which the superconducting energy gap gets suppressed. However, with increasing disorder these two fields diverge from each other creating a pseudogap region. The nature of vortices also transform from Abrikosov vortices with a metallic core for weak disorder to Josephson vortices with gapped and insulating cores for higher disorder. Our results naturally explain two outstanding puzzles: (1) the gigantic magnetoresistance peak observed as a function of magnetic field in thin disordered superconducting films; and (2) the disappearance of the celebrated zero-bias Caroli-de Gennes-Matricon peak in disordered superconductors.
We report magnetotransport measurements of the critical field behavior of thin Al films deposited onto multiply connected substrates. The substrates were fabricated via a standard electrochemical process that produced a triangular array of 66 nm diameter holes having a lattice constant of 100 nm. The critical field transition of the Al films was measured near $T_c$ as a function of field orientation relative to the substrate normal. With the field oriented along the normal ($theta=0$), we observe reentrant superconductivity at a characteristic matching field $H_m=0.22,mathrm{T}$, corresponding to one flux quantum per hole. In tilted fields, the position $H^*$ of the reentrance feature increases as $sec(theta)$, but the resistivity traces are somewhat more complex than those of a continuous superconducting film. We show that when the tilt angle is tuned such that $H^*$ is of the order of the upper critical field $H_c$, the entire critical region is dominated by the enhanced dissipation associated with a sub-matching perpendicular component of the applied field. At higher tilt angles a local maximum in the critical field is observed when the perpendicular component of the field is equal to the matching field.
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