Properties of the vortex liquid in the classical and quantum regime

The properties of vortex matter in thin films of amorphous NbGe is investigated in regimes that have not been studied before. By designing a device of alternating strong and weak pinning stripes we were able to measure the shear viscosity of the 2D flux line liquid above the 2D melting line. Good agreement is observed with the predictions of the theory of Nelson and Halperin. By studying the properties of an 18 nm thick film down to very low temperatures we entered the regime where quantum fluctuations influence the spectrum of vortex vibrations. It is seen that melting at T = 0 takes place well below the transition to the normal state at B-c2(0). From resistivity measurements it follows that thermally activated creep in the liquid regime at relatively high temperatures crosses over to quantum creep at low temperatures. The crossover temperature as well as typical results for the energy barriers and Euclidean action are presented.