Spin-Polarized Tunneling Measurement of the Antisymmetric Fermi-Liquid ParameterG0and Renormalization of the Pauli Limiting Field in A1

Abstract

Spin-polarized tunneling is used to measure the energy difference $\delta$ between spin-up and spin-down electrons in a magnetic field in thin films of superconducting A1. $\delta$ decreases from $2{\mu }_{\mathrm{B}}H$ at low temperature and field to $0.8\left(2{\mu }_{\mathrm{B}}H\right)$ as the phase boundary $T_c\mathrm{}\left(H\right)\mathrm{}$ is approached. This change in $\delta$ provides the first measurement of the $l=0\mathrm{}$ antisymmetric Fermi-liquid parameter $G^0$ in a real metal and the first direct evidence for the renormalization of the Pauli field in high-field superconductivity.