Search for anomalous internal magnetic fields in high-Tcsuperconductors as evidence for broken time-reversal symmetry

Abstract

Several recent models of high-${\mathit{T}}_{\mathit{c}}$ superconductivity predict static internal magnetic fields along the c axis due to spontaneously broken parity and time-reversal symmetries. Muon spin relaxation has been used to study the internal fields in c-axis-oriented samples of sintered ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ and of thick-film ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$. The magnitude, anisotropy, and temperature dependence of the observed fields favor a nuclear dipolar origin. Any anomalous fields at ${\mathrm{\mu }}^{+}$ sites in bulk ${\mathrm{CuO}}_2$ superconductors must be ≲0.08 mT.