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Motivated by recent work on strain-induced pseudomagnetic fields in Dirac and Weyl semimetals, we analyze the possibility of analogous fields in two-dimensional nodal superconductors. We consider the prototypical case of a d -wave superconductor, a representative of the cuprate family, and find that the presence of weak, spatially varying strain leads to pseudomagnetic fields and Landau quantization of Bogoliubov quasiparticles in the low-energy sector. A similar effect is induced by the presence of generic, weak doping gradients. In contrast to genuine magnetic fields in superconductors, the strain- and doping-gradient-induced pseudomagnetic fields couple in a way that preserves time-reversal symmetry and is not subject to the screening associated with the Meissner effect. These effects can be probed by tuning weak applied supercurrents which lead to shifts in the energies of the Landau levels and hence to quantum oscillations in thermodynamic and transport quantities. [ABSTRACT FROM AUTHOR]

Recently developed parity ( P ) and time-reversal ( T ) symmetric non-Hermitian systems govern a rich variety of new and characteristically distinct physical properties, which may or may not have a direct analog in their Hermitian counterparts. We study here a non-Hermitian, PT-symmetric superconducting Hamiltonian that possesses a real quasiparticle spectrum in the PT-unbroken region of the Brillouin zone. Within a single-band mean-field theory, we find that real quasiparticle energies are possible when the superconducting order parameter itself is either Hermitian or anti-Hermitian. Within the corresponding Bardeen-Cooper-Schrieffer (BCS) theory, we find that several properties are characteristically distinct and novel in the non-Hermitian pairing case than its Hermitian counterpart. One of our significant findings is that while a Hermitian superconductor gives a second-order phase transition, the non-Hermitian one produces a robust first-order phase transition. The corresponding thermodynamic properties and the Meissner effect are also modified accordingly. Finally, we discuss how such a PT-symmetric pairing can emerge from an antisymmetric potential, such as the Dzyloshinskii-Moriya interaction, but with an external bath, or complex potential, among others. [ABSTRACT FROM AUTHOR]

We have studied the evolution of magnetic flux pinning behavior in the Meissner phase and the mixed state for the high-Tc single-crystal La2-xSrxCuO4 (x=0.09) superconductor using the polarized neutron imaging method with varying magnetic field and temperature. In the Meissner state expulsion of magnetic field (switched on during the measurements) is visualized, and the signatures of a mixed state with increasing temperature are observed. However, for flux pinning behavior in the range 5K≤T≤15K and Hext=63.5mT (switched off during the measurements), the evolution of the fringe pattern indicates magnetic flux pinning inside the bulk of the sample. At 25K≤T≤32K, a continuous decrease in inhomogeneously distributed pinned magnetic flux is observed, with the sample reaching a normal conducting state at Tc (≈32 K). The flux pinning behavior is also explored as a function of Hext at T=5K. As expected, with increasing Hext an increase in fringe density is observed, indicating an increase in magnetic flux pinning in the bulk of the sample. A comparison between calculated and experimentally visualized pinned magnetic fluxes shows good agreement. This implies quantification of pinned magnetic flux inside the sample, which is not possible with any other technique for bulk samples. [ABSTRACT FROM AUTHOR]

We consider a two-leg boson ladder in an artificial U(1) gauge field and show that, in the presence of interleg attractive interaction, the flux induced vortex state can be melted by dislocations. For increasing flux, instead of the Meissner to vortex transition in the commensurate-incommensurate universality class, first, an Ising transition from the Meissner state to a charge density wave takes place, then, at higher flux, the melted vortex phase is established via a disorder point where incommensuration develops in the rung current correlation function and in momentum distribution. Finally, the quasi-long-range ordered vortex phase is recovered for sufficiently small interaction. Our predictions for the observables, such as the spin current and the static structure factor, could be tested in current experiments with cold atoms in bosonic ladders. [ABSTRACT FROM AUTHOR]

In this paper we demonstrate the necessity of including the generally omitted collective-mode contributions in calculations of the Meissner effect for nonuniform superconductors. We consider superconducting pairing with nonzero center-of-mass momentum, as is possibly relevant to high transition temperature cuprates, cold atoms, and color superconductors in quantum chromodynamics. For the concrete example of the Fulde-Ferrell phase we present a quantitative calculation of the superfluid density, showing not only that the collective-mode contributions are appreciable but also that they derive from the amplitude mode of the order parameter. This latter mode is generally viewed as being invisible in conventional superconductors. However, our analysis shows that it is extremely important in pair-density-wave-type superconductors, where it destroys stable superfluidity well before the mean-field order parameter vanishes. [ABSTRACT FROM AUTHOR]

Momentum and energy conservation are fundamental tenets of physics, which valid physical theories have to satisfy. In the reversible transformation between superconducting and normal phases in the presence of a magnetic field, the mechanical momentum of the supercurrent has to be transferred to the body as a whole and vice versa, the kinetic energy of the supercurrent stays in the electronic degrees of freedom, and no energy is dissipated nor entropy is generated in the process. We argue on general grounds that to explain these processes it is necessary that the electromagnetic field mediates the transfer of momentum between electrons and the body as a whole, and this requires that when the phase boundary between normal and superconducting phases is displaced, a flow and counterflow of charge occurs in a direction perpendicular to the phase boundary. This flow and counterflow does not occur according to the conventional BCS-London theory of superconductivity, therefore we argue that within BCS-London theory the Meissner transition is a "forbidden transition." Furthermore, to explain the phase transformation in a way that is consistent with the experimental observations, requires that (i) the wave function and charge distribution of superconducting electrons near the phase boundary extend into the normal phase, and (ii) that the charge carriers in the normal state have holelike character. The conventional theory of superconductivity does not have these physical elements, the theory of hole superconductivity does. [ABSTRACT FROM AUTHOR]

We present a type of transmon split-junction qubit which can be tuned by Meissner screening currents flowing in the adjacent superconducting film electrodes. The best detected relaxation time (T1) was of the order of 50μs and the dephasing time (T2) about 40μs. The achieved period of oscillation with magnetic field was much smaller than in the usual SQUID-based transmon qubits; thus a strong effective field amplification has been realized. This Meissner qubit allows a strong mixing of the current flowing in the qubit junctions and the currents generated by the Abrikosov vortices. We present a quantitative analysis of the radiation-free relaxation in qubits coupled to the Abrikosov vortices. The observation of coherent quantum oscillations provides strong evidence that the position of the vortex as well as its velocity do not have to accept exact values but can be smeared in the quantum mechanical sense. The eventual relaxation of such states contributes to an increased relaxation rate of the qubit coupled to vortices. Such relaxation is described using basic notions of the Caldeira-Leggett quantum dissipation theory. [ABSTRACT FROM AUTHOR]

We generalize the spin Meissner effect for an exciton-polariton condensate confined in annular geometries to the case of nontrivial topology of the condensate wave function. In contrast to the conventional spin Meissner state, topological spin Meissner states can in principle be observed at arbitrary high magnetic fields not limited by the critical magnetic field value for the condensate in a simply connected geometry. One special example of the topological Meissner states are half-vortices. We show that in the absence of magnetic field, half-vortices in a ring exist in a form of a superposition of elementary half-vortex states, which resolves recent experimental results where such puzzling superposition was observed. Furthermore, we show that if a pure half-vortex state is to be observed, a nonzero magnetic field of a specific magnitude needs to be applied. Studying exciton polaritons in a ring in the presence of TE-TM splitting, we observe spin Meissner states that break the rotational symmetry of the system by developing inhomogeneous density distributions. We classify various states arising in the presence of nonzero TE-TM splitting based on what states they can be continued from by increasing the TE-TM splitting parameter from zero. With further increasing TE-TM splitting, states with broken symmetry may transform into stable half-dark solitons and therefore may serve as a useful tool to generate various nontrivial states of a spinor condensate. [ABSTRACT FROM AUTHOR]

In a magnetic field, superconductivity is manifested by total magnetic field expulsion (Meissner effect) or by the penetration of integer multiples of the flux quantum ɸ0. Here we present experimental results revealing magnetic dipoles formed by Meissner current flowing around artificially introduced topological defects (lattice of antidots). By using scanning Hall probe microscopy, we have detected ordered magnetic dipole lattice generated at spatially periodic antidots in a Pb superconducting film. While the conventional homogeneous Meissner state breaks down, the total magnetic flux of the magnetic dipoles remains quantized and is equal to zero. The observed magnetic dipoles strongly depend on the intensity and direction of the locally flowing Meissner current, making the magnetic dipoles an effective way to monitor the local supercurrent. We have also investigated the first step of the vortex depinning process, where, due to the generation of magnetic dipoles, the pinned Abrikosov vortices are deformed and shifted from their original pinning sites. [ABSTRACT FROM AUTHOR]

We report on local magnetization measurements showing the presence of an unexpectedly strong transverse Meissner effect in the superconducting CuxTiSe2 single crystals. We show that for tilted magnetic fields (Ha) vortices remain aligned with the ab planes up to field Hk~Hp/sinθH (where θH is the angle between the applied field and the ab plane and Hp the first penetration field) and that for Ha>Hk, the field dependence of the vortex direction θB(Ha) can be well described assuming that vortices remain partially locked in the planes forming a staircase structure of average direction θB≠θH. These results indicate the existence of a strong modulation of the vortex core energy along the c axis but its origin remains unclear. [ABSTRACT FROM AUTHOR]