Quantum Phase Transition in HTSC Thick Films: YBa2Cu3O x , YBa2Cu3O x (5 % Ag-Doped) in a Strong Pulsed Magnetic Field up to 32 T at Low Temperatures (58–100 K), Current Densities and Stress-Effect

Abstract

We have researched the influence of pulsed magnetic fields up to 32 T on the magneto-resistance of thick films (50 Mk) of YBa 2 Cu 3 O x and YBa 2 Cu 3 O x (5 % Ag-doped) that were produced from synthesized powders. (Figs. 1-9): concentrate with 6.85-6.9 % O 2 and a tail fraction 6.5-6.6 % O 2 .We observed a linear plot at currents of more than 1 mA at 77 K in YBa 2 Cu 3 O x (5 % Ag-doped) at B > 5 T and in the concentrate YBa 2 Cu 3 O x samples with I = 1 mA, T = 68.2 K. Pulsed magnetic fields up to 32 T, at I = 1 mA had practically no influence on the value of the magnetoresistance in the concentrate YBa 2 Cu 3 O x specimens at T = 57.9 K and up to 17 T for YBa 2 Cu 3 O x (5 % Ag) at 77 K (Meissner effect). However, for B > 17 T, YBa 2 Cu 3 O x (5 % Ag) at 77 K demonstrates a tendency toward lower resistance.In the presence to 10 pulses in a cyclic pulsed magnetic field of 32 T, there is a sharp change of magnetic properties of an HTSC that can lead to nontrivial changes in the transition temperature, due to the strong mechanic stresses, sharp change value structure, and because one of the phases becomes superconducting (Figs. 3A, 3B). The behavior of the magnetoresistance of S-N-S contacts in pulsed magnetic Analysis of microscopic models of quantum phase transitions was made in a granular superconductor in an attempt to explain the results on the studied HTSC-films and to give a physical interpretation to the deduced parameters of some experiments on the basis of "spin (vortex) glass" (vortex ice).