Muon-Spin Rotation Measurements of the Magnetic Field Dependence of the Vortex-Core Radius and Magnetic Penetration Depth inNbSe2

Abstract

Muon-spin rotation spectroscopy (µSR) has been used to measure the internal magnetic field distribution in NbSe2 for Hc1 ≪ H < 0.25 Hc2. The deduced profiles of the supercurrent density Js indicate that the vortex-core radius ρ0 in the bulk decreases sharply with increasing magnetic field. This effect, which is attributed to increased vortex-vortex interactions, does not agree with the dirty-limit microscopic theory. A simple phenomenological equation in which ρ0 depends on the intervortex spacing is used to model this behaviour. In addition, we find for the first time that the in-plane magnetic penetration depth λ ab increases linearly with H in the vortex state of a conventional superconductor.

Field dependence of the vortex structure ind-wave ands-wave superconductors

“…From both definitions of ξ 1 and ξ 2 (i.e., the initial slope of |∆(r)| and the maximum current), we obtain a similar dependence on H. The shrinkage of the core radius was also reported in STM and µSR experiments. 10,7 There, the results of the field dependence were analyzed in the dirty limit theory by the Wigner-Seitz method (i.e., a circular unit cell is used instead of the periodic boundary condition of the vortex lattice). In our study, we obtain the field dependence in the clean limit, where we treat the periodic boundary condition exactly.…”

“…Specific heat experiments [3][4][5][6] inform us of low energy excitations. Muon spin resonance (µSR) 7,8 and small angle neutron scattering (SANS) investigate the internal field distribution of the vortex structure. Scanning tunneling microscopy (STM) [9][10][11][12] directly observes the LDOS.…”

Low Energy Quasiparticle Excitation in the Vortex State of Borocarbide SuperconductorYNi2B2C

“…Figure 3 shows that the linear Hdependent Bardeen-Stephen relation yields a more consistent fit to the data than another model does. Since the QPs localized in the core mainly contribute to the flux flow dissipation, this fact shows that the number of the QPs trapped within each core is independent of H. Therefore, the scenario of the core shrinking with H as an origin of nonlinear H-dependent C p proposed by several groups [4,[9][10][11] is completely excluded. In addition and more importantly, the fact that the existence of the CD with a comparable radius with ξ little affects the ∆C p implies that the QPs within the core radius ξ are not important for the total heat capacity in the pristine YNi 2 B 2 C. On the basis of these results, we are led to conclude that in YNi 2 B 2 C the extended QP states around the vortex core play an important role in determining the superconducting properties, similar to d-wave superconductors.…”

“…For instance, several authors proposed the shrinking of the vortex core with H [4, [9][10][11], but the physical origin behind this phenomenon is unclear. Another group ascribed it to the field-induced gap nodes [8], but this scenario is beyond the applicability of the original argument [12].…”

Muon spin rotation studies of electronic excitations and magnetism in the vortex cores of superconductors

“…In contrast, the experiments of Refs. [2,3] used energetic (∼ 4 MeV) µ + that stop at interstitial or bond sites in the bulk of the sample where they directly probe the local magnetic fields. The term "bulk" means that the stopping range of these faster muons is approximately 150 mg/cm 2 , which requires samples ∼ 1 mm thick.…”