Intra-unit-cell magnetic order in stoichiometric La 2 CuO 4

Muon spin rotation measurements, supported by magnetization experiments, have been carried out in a stoichiometric high-${T}_{c}$ parent compound ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$ in a temperature range from 2 to 340 K and in transverse magnetic fields up to 5 T. Along with the antiferromagnetic local field, muon spin rotation spectra indicate the presence of an additional source of magnetic field on the muon. The characteristic splitting of about 45 G, which comes from this additional magnetic field, is consistent with spontaneous circulating currents.