Thermomagnetic vortex transport: Transport entropy revisited

Abstract

Traditionally the Nernst and Ettingshausen effects in the vortex liquid are described in terms of the "transport entropy" of vortices, S d . According to current theories, the main contribution to S d is originated from the electromagnetic free energy, F em , which includes kinetic and magnetic energy of superconducting currents circulating around vortex cores. However, this concept contradicts the London postulate, according to which a supercurrent consists of macroscopic number of particles in a single quantum state and does not transfer any entropy. Here we resolve this contradiction and show that the transport entropy is just ordinary thermodynamic entropy transferred by cores. Only in this form the theory becomes simultaneously consistent with the London postulate and the Onsager principle. The revised theory explains measured temperature dependence S d . The linear increase of S d at low temperatures is determined by the entropy of electrons in the core, then S d reaches a maximum at roughly Tc/2 and then vanishes due to increase of the background entropy.

Optical manipulation of single flux quanta

“…The early observations of vortex flows in weak thermal gradients were interpreted on the basis that vortices behave as entropy-carrying particles, which obey general thermal diffusion laws and therefore are in search of colder places in the superconductor. However, theoretical investigations revisiting the problem of entropy transport in superconductors show that the vortex superconducting current does not carry entropy 14 . In the limit of a London magnetic penetration depth λ much larger than the coherence length ξ , the vortex core is very small and its contribution to the energy can be neglected 15 .…”

Universal bound to the amplitude of the vortex Nernst signal in superconductors

“…With φ 0 = h/2e = 2.07 × 10 −15 Tm 2 [1], one finds S d = 3 ×10 −14 J/K. m. As discussed in the supplement [18], this falls well below the theoretically expected S d [12]. Fig.…”

“…The vortex origin of the peak signal below T c remains undisputed and its quantitative amplitude unexplained. Theoretical tradition has linked the magnitude of the finite Nernst signal to the motion of vortices under the influence of a thermal gradient due to the excess entropy of the normal core [4,[10][11][12]. As a consequence, the magnitude of the Nernst response is Here we present a study of the Nernst effect in two superconductors, namely two-dimensional Nb-doped SrTiO 3 and α-MoGe.…”

A quantitative vortex-fluid description of Nernst effect in Bi-based cuprate high-temperature superconductors

“…The origin of S f is still under debate in the literature [39]. Nevertheless, inspired by Andersonʼs simple idea based on BKT scenario near T c , it is possible to develop an order-disorder balance argument to obtain an expression for S f in a dense vortex fluid, as we do now.…”

“…As vortex contains higher entropy (and heat) than surrounding fluid, thus a vortex flow is driven by -T . This results in a heat transport with an energy = f f U TS , where S f is the transport entropy per unit length of a vortex [38,39]. In the steady state, thermal force should be balanced by damping force, Thermal diffusion and the transport velocity is the same for vortices and anti-vortices as they have the same thermodynamic properties, as illustrated in figure 2.…”