Field-induced thermal metal-to-insulator transition in underdoped LSCO

The transport of heat and charge in cuprates was measured in undoped and heavily-underdoped single crystal La 2− x Sr x CuO 4+ δ (LSCO). In underdoped LSCO, the thermal conductivity is found to decrease with increasing magnetic field in the T→0 limit, in striking contrast to the increase observed in all superconductors, including cuprates at higher doping. The suppression of superconductivity with magnetic field shows that a novel thermal metal-to-insulator transition occurs upon going from the superconducting state to the field-induced normal state.