Evidence of zero-point fluctuation of vortices in a very weakly pinned a -MoGe thin film

Abstract

In a Type II superconductor, the vortex core behaves like a normal metal. Consequently, the single-particle density of states in the vortex core of a conventional Type II superconductor remains either flat or (for very clean single crystals) exhibits a peak at zero bias due to the formation of Caroli-de Gennes-Matricon bound state inside the core. Here we report an unusual observation from scanning tunneling spectroscopy measurements in a weakly pinned thin film of the conventional s-wave superconductor a-MoGe, namely, that a soft gap in the local density of states continues to exist even at the center of the vortex core. We ascribe this observation to rapid fluctuation of vortices about their mean position that blurs the boundary between the gapless normal core and the gapped superconducting region outside. Analyzing the data as a function of magnetic field we show that the variation of fluctuation amplitude as a function of magnetic field is consistent with quantum zero-point motion of vortices.

High-frequency crossover from vortex-mass enhancement to pinning

“…Recent experimental results [1] for the vortex mass of superconducting YBa 2 Cu 3 O 7−δ using terahertz spectroscopy are in good agreement with the theory of Kopnin and Vinokur [2] which describes the dynamics of quasiparticles in the vortex core; results of zero-point fluctuation of vortices in a-MoGe thin film [3] agree with Suhl's estimate of the vortex mass [4]. While there is good agreement in these cases, other measurements [5,6] of vortex mass are not in agreement with this theory.…”

“…The order parameter ψ varies on the scale of ξ which is much larger than the atomic distance 3 √ Ω 0 ; the sum over n x and n y can be replaced by integrals, writing For a large sample we can neglect edge corrections and approximate integrals by infinite integrals of Gaussian stripes with the center in the sample and zero elsewhere. That is, in the subsequent step, the infinite sum over m, after being shifted by q x ρa/(4π), is then replaced by the sum over interval −q x ρa/(4π) < m < aL y /(2πρ) − q x ρa/(4π).…”

Low-frequency electrodynamics in the mixed state of superconducting NbN and a-MoGe films using two-coil mutual inductance technique

“…Compared to bulk superconductors, the 2D vortex lattice in thin films is much more fragile and susceptible to perturbations [8][9][10][11]. Consequently, thermal [12,13] and quantum [14,15] fluctuations can play a much more dominant role in these systems. Recently, a variety of vortex liquid states, where true dissipationless transport is not seen even at vanishingly low currents, have indeed been reported [16][17][18] in weakly pinned superconducting films made of conventional superconductors.…”

Transient vortex dynamics and evolution of Bose metal from a 2D superconductor on MoS2

“…In the substrate-free regime, vortex motion is predominantly subsided by intervortex interaction [8] and the subsequent formation of the vortex lattice once a sufficient number of vortices are injected into the system by an external field [20,21]. The dissipative core makes the vortex motion overdamped [8,22], and there should be a timescale associated with the formation of the vortex lattice and the subsequent reaching of the low-resistance equilibrium state. This time-scale need to depend on the superfluid viscosity, vortex mobility, intervortex interaction, vortex lattice elasticity, and pinning strength.…”