Quantum Qhase Transition And Quantum Griffiths Singularity In Niobium-Based Nanopattened Films

Ginzburg-Landau theory,as a core description,has phenomenological summarized a series of classical thermodynamic(ferromagnetic and superconducting)phase transition,except two types: topological and quantum phase transition.Hence,relevant researches are expected to establish a novel basis in material science and physics,thus accumulating the progress in non-dissipative electronic devices design and topological quantum computing.Quantum phase transition,such as phase transition about superconductinginsulation and superconducting-weakly localized metal,focuses on the evolution of condensed matter among ground states.In the latter,a strange phenomenon named Griffiths singularity exists with critical exponent diverged.In this thesis,we focus on characteristics of quantum phase transition and quantum Griffiths singularity in superconducting niobium-based porous films,and details are as follows.We deposite superconducting Nb films with uniformly distributed nano pores.Results suggest that the prepared Nb films exhibit continuously superconducting transition temperature until applied vertical magnetic field reaches to critical value,superconducting-weakly localized metal phase transition thus successfully occurring in Nb films.Furthermore,relevant isothermal magnetoresistance curves near the critical area of phase transition are confirmed intersecting a series of points rather than a typical single one,which corresponds to different characteristics of dynamic index zv simulated by finite scale analysis rather than a typical fixed one typical under different temperatures.Note that the index changes continuously on the critical line,increases rapidly at low temperature,and diverges near 0K.The phenomenon is consistent with quantum Griffiths singularity.Also,we deposite superconducting Nb N films with pores regulated.Weak-linked superconducting islands in films have been established by the hexagonal closs packing structure among pores.For the duration of reaction ion etching(RIE)on Nb N films can regulate the pore size,the adjustment of weak link(phase coherence)degree is realistic.Depended on this,two superconducting quantum phase transitions are observed in porous Nb N films: superconducting-quantum metal-insulation phase transition regulated by pore size and quantum metal-weakly localized metal phase transition induced by magnetic field,which are extensions of superconducting-insulation phase transition and superconducting-weakly localized metal phase transition,respectively.And quantum Griffiths singularity also occurs near the critical area of superconducting-weakly localized metal phase transition.h/2e superconducting quantum magnetoresistance oscillation occurs in both superconducting and quantum metal state in nano porous Nb N films,indicating that cooper pair dominates transport process,that is,the quantum metal state in Nb N film is Bose metal state.And corresponding dynamic process of boson in superconductingquantum metal phase transition can be clarified by combination of simulation through Landau mean field theory and variation of amplitudes versus temperature in different quantum state samples.Results suggest a two-process transition with the increase of disorder: the motion of magnetic flux thermal excitation,the physical image described by Landau mean field theory,and the quantum metal state with large quantum fluctuations.