Absence of spontaneous magnetism associated with a possible time-reversal symmetry breaking state beneath the surface of (110)-oriented YBa_2Cu_3O_(7-δ) superconducting films

摘要

We report the results of a search for spontaneous magnetism due to a time-reversal symmetry breaking phase in the superconducting state of (110)-oriented YBa_2Cu_3O_(7-δ) films, expected near the surface in this geometry. Zero field and weak transverse field measurements performed using the low-energy muon spin rotation technique with muons implanted a few nm inside optimally doped YBa_2Cu_3O_(7-δ)-(110) films show no appearance of spontaneous magnetic fields below the superconducting temperature down to 2.9 K. Our results give an upper limit of ～0.02 mT for putative spontaneous internal fields.