Helical instability of charged vortices in layered superconductors

Abstract

It is shown that the electric charge of vortices can result in a helical instability of straight vortex lines in layered superconductors, particularly Bi-based cuprates or organic superconductors. This instability may result in a phase transition to a uniformly twisted vortex state, which could be detected by torque magnetometry, neutron diffraction, electromagnetic or calorimetric measurements.PACS numbers: PACS numbers: 74.25. Bt, 74.25.Ha, 74.25.Qt Vortices in superconductors carry the quantized magnetic flux φ 0 = 2×10 −7 Oe·cm 2 resulting from the macroscopic phase coherence of superconducting state. Vortices also carry a non-quantized electric charge q caused by the suppression of superconductivity in the vortex core [1][2][3][4][5][6]. In low-T c s-wave superconductors this charge is usually negligible and does not manifest itself in the electromagnetic response of vortices driven by the Lorentz force of superconducting currents. However, the situation changes in superconductors with short coherence length ξ, low superfluid density and unconventional pairing symmetry combined with the competition of superconductivity with non-superconducting spin or charged ordered states, as characteristic of high-T c cuprates, recently discovered oxypnictides or organic superconductors [7]. For cuprates, theoretical estimates [1-4] predict a relatively large fraction ∼ 10 −3 of the electron charge e per each pancake vortex residing on the ab planes, yet even larger charge of different sign was observed by nuclear quadrupole resonance [8]. It has been suggested [1] that the vortex charge could change the sign of the Hall coefficient observed in cuprates [9] or result in structural transformations of the vortex lattice [10].In this paper we show that vortex charge can cause an intrinsic helical instability of a rectilinear vortex and a phase transition to a twisted vortex state. This instability is different from the helical instability of vortices driven by either currents flowing along the vortex line [12] or by screw dislocations [13] or twisted vortex states in rotating liquid He [14]. The buckling instability of vortices results from the Coulomb repulsion of charged pancake vortices which tend to shift away from the straight line along the c-axis as illustrated by Fig. 1. Such charge fragmentation is inhibited by the vortex line tension caused by weak magnetic and Josephson coupling of vortex pancakes [17,18], and also by charge screening, which confines the relative displacements of pancakes on neighboring ab planes within the Thomas-Fermi screening length λ T F . Thus, the helical instability would be most pronounced in layered materials with low vortex line tension and λ T F ∼ ξ, as characteristic of high-T c cuprates, ferropnictides or organic superconductors.To calculate properties of spiral vortices we write the excess linear charge ρ(r) in a vortex as followsHere the first term is the BCS contribution resulting from the change in the chemical potential µ around the core,1/2 is the modulus of the order param...

General strategies to improve thermoelectric performance with an emphasis on tin and germanium chalcogenides as thermoelectric materials

“…They assumed the presence of quasi-one-dimensional states as the cause of the unique nature of DOS. Electron-phonon interactions can also induce distortions of the DOS; some of these phenomena are "phonondrag", [55][56][57][58][59][60][61][62] "Nielsen-Taylor pseudo-phonon-drag effect", 63 "polaron mass enhancements", 64 etc.…”

“…Still, phonons with a shorter mean free path and higher frequency contribute more to thermal conductivity than phonon-drag. 7,33,[56][57][58][59][60][61] The 'Phonondrag' effect is signicant only in materials where phonons are not strongly scattered and have long mean free paths and the strong electron-phonon interaction. 99 Phonon-drag has a more signicant contribution from the longitudinal phonon modes than the transverse modes due to the greater group velocities in the former mode.…”

Charge-induced vortex lattice instability

“…6 In related work, Gurevich found that if a single vortex line is charged, it becomes unstable to chiral distortion. 24 In our model the Abrikosov configuration is transformed to an A-B-C-type of tripling of the vortex unit cell along the c-axis as sketched in Fig. 4.…”

Force-free state in a superconducting single crystal and angle-dependent vortex helical instability

“…He pointed out that, if the sample is carrying a current in a longitudinal magnetic field (force-free configuration), the vortices can develop a helical geometry and cutting of the flux lines can occur [30]. We have to note that recently, in layered superconductors, helical instability has been proposed [31], but the origin and the magnetic field and electrical current configurations of this helical instability are fully different from force-free configuration.The main source of dissipation of a superconductor in the force-free configuration is the helical instability studied by Clem for a single vortex [32] and for a vortex lattice by Brandt [33]. The origin of this instability is in the transport current generating self-magnetic fields.…”

“…He pointed out that, if the sample is carrying a current in a longitudinal magnetic field (force-free configuration), the vortices can develop a helical geometry and cutting of the flux lines can occur [30]. We have to note that recently, in layered superconductors, helical instability has been proposed [31], but the origin and the magnetic field and electrical current configurations of this helical instability are fully different from force-free configuration.…”