Field-induced microwave absorption in high-T c superconducting powders: Evidence for a superconducting glass phase at low T

Measurements of the magnetic-field-induced microwave absorption, P(H), in micron-sized powders of the high-temperature superconductor Y1Ba2Cu3O7 at several microwave frequencies for 1.3 K≤T≤Tc are reported. The hysteresis loops [P(H) vs H] observed at low temperatures (T≤16 K) indicate the presence of spontaneous circulating currents within the sample. These hysteresis loops and dc magnetization data (taken for both field-cooled and zero-field-cooled states) combine to suggest that the magnetic moments of these loops are in a ‘‘spin-glass-like’’ state.