Electron spin dynamics of the superconductorCaC6probed by ESR

Abstract

Conduction Electron Spin Resonance (CESR) was measured on a thick slab of CaC6 in the normal and superconducting state. Non-linear microwave absorption measurements in the superconducting state describe CaC6 as an anisotropic BCS superconductor. CESR data in the normal state characterize CaC6 as a three-dimensional (3D) metal. The analysis suggests that the scattering of conduction electrons is dominated by impurities and supports the description of superconductivity in the dirty limit. A surprising increase of the CESR intensity below Tc can not be explained by the theoretically predicted change in spin susceptibility. It is interpreted as a vortex enhanced increase of the effective skin depth. The study of the spin dynamics in the superconducting state and the discovery of the vortex enhanced increase of the skin depth poses a challenge to theory to provide a comprehensive description of the observed phenomena.

Far-infrared signature of the superconducting gap in intercalated graphiteCaC6

“…The dirty limit behavior is in accordance with magnetic penetration depth 3 and conduction-electron-spin-resonance measurements. 18 Assuming a Fermi velocity v F = 5.3ϫ 10 7 cm s −1 ͑Ref. 6͒ the calculated mean free path amounts to l mfp = v F / ␥ = 450 nm.…”

Giant microwave absorption in fine powders of superconductors

“…A quantitative analysis for K 3 C 60 yields the vortex pinning force constant that can be hardly determined by other means. Our observation allowed us to explain long-standing microwave anomalies in superconductors 29,30 and it may lead to pertinent applications in microwave communication techniques. prepared and characterized the single crystal K 3 C 60 .…”

“…The enigmatic and yet unexplained increase of the electron spin resonance signal in superconductors right below T c (Refs. 29,30) also highlights the need to study further the electromagnetic absorption in superconductors.…”

Muon spin rotation study of the magnetic penetration depth in the intercalated graphite superconductorCaC6

“…9 For the extremely air sensitive superconductor CaC 6 , bulk measurement of the superconducting properties would be thus very important. We also notice that a new unambiguous bulk determination of ρ(T ) could also help in clarifying the nature of the CaC 6 conduction regime, since both dirty limit 9,16,17 and clean limit 15,18 regime have been reported so far. This system is also interesting from the point of view of µSR data analysis, since it is a low κ = λ/ξ superconductor with reduced, in field, vortex phase.…”