Vortex-like excitations in a non-superconducting single-layer compound Bi$_{2+x}$Sr$_{2-x}$CuO$_{6+δ}$ single crystal in high magnetic fields

Abstract

The in-plane $ρ_{ab}(H,T)$ and the out-of-plane $ρ_c(H,T)$ magneto-transport in magnetic fields up to 28 T has been investigated in high quality non-superconducting (down to 20 mK) La-free Bi$_{2+x}$Sr$_{2-x}$CuO$_{6+δ}$ single crystal. By measuring the angular dependence of the in-plane and out-of-plane magnetoresistivities at temperatures from 1 K down to 30 mK, we present evidence for the presence of vortex-like excitations in a non-superconducting cuprate in the insulating state. Such excitations have previously been observed by the detection of a Nernst signal in superconducting cuprates at $T>T_c$ in magnetic fields.