139La NMR and NQR investigations of the superconductor LaBa2Cu3O7−δ

Topologically stable gapped state in a layered superconductor

“…Proposals have been made to explain it, such as by Varma [8], based on microscopic orbital currents. Indeed polarized neutron diffraction experiments [9,10] indicate a magnetic order below the pseudogap, but NMR/NQR [11,12] and μSR [13,14] experiments set a very restrictive limit to the maximum magnetic field inside the superconductor, hereafter called h max , which cannot be larger than h max ∼ 0.1 to 0.01 G. We show here that the skyrmion state breaks the time reversal symmetry and links the pseudogap to the weak internal magnetic field h max .…”