arXiv subjects

Yingzi Zhang

Publications and source records attributed to Yingzi Zhang.

2 recordsLinked to original sources

arXiv2007

I-V characteristics of the vortex state in MgB2 thin films

The current-voltage (I-V) characteristics of various MgB2 films have been studied at different magnetic fields parallel to c-axis. At fields \mu0H between 0 and 5T, vortex liquid-glass transitions were found in the I-V isotherms. Consistently, the I-V curves measured at different temperatures show a scaling behavior in the framework of quasi-two-dimension (quasi-2D) vortex glass theory. However, at \mu0 H >= 5T, a finite dissipation was observed down to the lowest temperature here, T=1.7K, and the I-V isotherms did not scale in terms of any known scaling law, of any dimensionality. We suggest that this may be caused by a mixture of σband vortices and πband quasiparticles. Interestingly, the I-V curves at zero magnetic field can still be scaled according to the quasi-2D vortex glass formalism, indicating an equivalent effect of self-field due to persistent current and applied magnetic field.

cond-mat.supr-con↗

arXiv2006

Reversible magnetization and critical fluctuations in systematically doped YBa$_2$Cu$_3$O$_{7-δ}$ single crystals

The temperature and field dependence of reversible magnetization have been measured on a YBa$_2$Cu$_3$O$_{7-δ}$ single crystal at six different doping concentrations. It is found that the data above 2 T can be described by the scaling law based on the GL-LLL (lowest Landau level approach based on Ginzburg-Landau theory) critical fluctuation theory yielding the values of the slope of upper critical field $-\mathrm{d}H_{\mathrm{c2}}(T)/\mathrm{d}T$ near $T_\mathrm{c}$. This set of values is self-consistent with that obtained in doing the universal scaling for the six samples. Based on a simple Ginzburg-Landau approach, we determined the doping dependence of the coherence length $ξ$ which behaves in a similar way as that determined from $ξ= \hbar v_\mathrm{F}/E_\mathrm{sc}$ with $E_\mathrm{sc}$ the superconducting energy scale. Our results may suggest a growing coherence length towards more underdoping.

cond-mat.supr-con↗