Coexistence of antiferromagnetism and superconductivity in single crystal underdoped [formula omitted

Abstract

Muon spin rotation measurements in ultra-clean single crystals of heavily underdoped superconducting YBa 2 Cu 3 O 6 + x ( x ≈ 0.365 ) are presented. The material shows a sharp superconducting transition below T = 15 K . By field cooling and shifting the applied field, we show that the superconducting state pins magnetic flux and develops a flux lattice below T c , indicating that the superconducting state exists throughout the sample on a microscopic scale. At the same temperature, a disordered magnetic state appears on a nanoscale with at least one well-defined internal field probed by the muon. These two states coexist on a nanometer lengthscale and over a narrow region of oxygen doping.