Possible Origin of Anisotropic Resistive Hysteresis in the Vortex State of Untwinned YBa₂Cu₃O₇ Single Crystals

The origin of resistive hysteresis in untwinned YBa₂Cu₃O₇ single crystals is investigated for time scales from 1 to 10³ sec and for frequencies from 10¹ to 10⁶ Hz. The absence of resistive “subloops” upon partial heating and cooling, the lack of time dependence, and the decreasing hysteresis with the increasing angle between the applied magnetic field and crystalline c axis suggest that the hysteresis is not a direct evidence of a first-order vortex-solid melting transition. A current-induced nonequilibrium effect is proposed as the possible origin for the hysteresis.