Equilibrium and Dynamic Vortex States near Absolute Zero in a Weak Pinning Amorphous Film

By developing and employing a mode-locking measurement with pulsed currents, we successfully determine the dynamic melting field B...(T) for a driven vortex lattice of an amorphous Mo^sub x^Ge^sub 1...x^ film in the limit of zero temperature (T ... 0) and complete a dynamic as well as a static vortex phase diagram. At T = 0, the mixed state in the absence of pinning comprises vortex-lattice and quantum-vortex-liquid (QVL) phases, and the melting field separating the two phases is identified as B...(0). Comparison of the dynamic and static phase diagrams reveals that, when the weak pinning is introduced into the pin-free system, a disordered phase emerges just above the vortex-lattice phase and a threshold field separating the two phases is slightly suppressed from B...(0), indicative of defect-induced disordering of the lattice. By contrast, a melting field into QVL is much enhanced from B...(0) up to a point near the upper critical field, resulting in a significant suppression of the QVL phase. This is attributed to the stronger effective pinning at lower T, which survives quantum fluctuations. (ProQuest: ... denotes formulae/symbols omitted.)