Superconducting La3-xS4compounds

Abstract
Superconducting La3S4 single crystals containing a definite number of cation vacancies are analysed by magnetic susceptibility, specific heat, upper critical magnetic field and low temperature X-ray diffraction measurements. The authors find experimental proof that the cubic to tetragonal distortion of the unit cell found in crystals close to stoichiometric La3S4 is of Jahn-Teller band type. The strongest electron-phonon coupling and the maximum superconducting transition temperature is found when the cubic to tetragonal phase transformation is just suppressed by doping with vacancies.