Magnetic melting of the 2D vortex lattice in thin <i>a</i>-MoGe films: Electrical transport perspective

With increasing magnetic field, the vortex lattice in a 2D type II superconductor is expected to melt via an intermediate liquid phase ("hexatic fluid"). This orientational order-preserving hexatic fluid state has been observed in recent STM studies in relatively clean thin films of a-MoGe [1]. The Monte Carlo simulations on a classical 2D XY model support the STM studies and, furthermore, they predict that the persistence of orientational correlations in the hexatic phase leads to the slowing down of the vortex dynamics as described by a Vogel-Fulcher-Tammann (VFT) law. We report the results of the resistivity measurements on weakly disordered, 22 nm-thick a-MoGe films over a wide range of temperatures and fields up to 18 T to characterize the 2D vortex melting from a transport perspective. We find that the temperature dependence of the resistivity indeed follows a VFT law over a wide range of fields, consistent with numerical simulations. Our results thus unambiguously show that electrical transport measurements may be used to detect signatures of the hexatic phase.
[1] I. Roy et al., Phys. Rev. Lett. 122, 047001 (2019).