Magnetic low-temperature specific heat of YBa2Cu3O7−δ due to localized charge carriers

Abstract The specific heat of an YBa 2 Cu 3 O 7−δ single crystal has been measured in the temperature range from 38 mK to 40 K in different magnetic fields. A significant specific heat contribution remains after subtracting lattice and nuclear terms. This additional contribution could be observed between 38 mK and 15 K and has been investigated in detail. Similarities to other substances, especially Si:P, are pointed out. Charge carriers localized by disorder and correlation effects are suggested as a possible cause of this contribution.