Spatial distribution analysis of critical temperature in epitaxial Y-Ba-Cu-O film using variable temperature scanning laser microscopy

Abstract

We have investigated the spatial distribution of superconducting transition in an epitaxial YBa 2 Cu 3 O 7 film using variable temperature scanning laser microscope (VTSLM). VTSLM creates an image of the ac voltage response, ( ), due to an ac modulated laser beam, which is proportional to d d (). In the resistive transition region, there is a strong correlation between the VTSLM images and the resistance of the sample. When the sample is making a poor thermal contact to the heat bath, the large ( ) region shifts toward the ends of the bridge while the sample resistance decreases. This result is due to the variation of surface temperature along the sample created by the heating at the contact resistance and/or the poor thermal contact between the sample and the heat bath. However, even after improving thermal contact, we still observe the distribution of superconducting transition. Since the local superconducting transition occurs within 1 K, we conclude that any samples with superconducting transition width larger than 1 K have local nonuniformity.Index Terms-Critical temperature, films, high temperature superconductor, nonuniformity, scanning laser microscope.

The Distribution of Transport Current in YBCO Coated Conductor With Zipper Striations

“…The bias current was applied along the direction of the striations. Detailed information about VTSLM can be found in our earlier publications [7], [8]. Fig.…”

Mapping the current distribution in YBa2Cu3O7−x thin films with striations

“…When measuring current flow in the direction of the striations, extra care is devoted to ensure good gold coverage over each stripe of the sample providing uniform contact resistance for all stripes. Detailed information about VTSLM can be found in our earlier publications [16,17].…”

“…In addition, the possible existence of higher grain boundary angles in CC processes may create non-uniform current percolation [12]. Direct and indirect mapping of the current distribution in the HTS layer has been accomplished by a variety of methods including magneto-optical imaging [12], scanning Hall probe [13], and hot spot scanning techniques such as low temperature scanning electron microscopy (LTSEM) [14], low temperature scanning laser microscopy (LTSLM) [15], and variable temperature scanning laser microscopy (VTSLM) [16,17]. In this letter, we use VTSLM to map the transport current distributions in striated YBCO films and coated conductors.…”

Observation of nonuniform current transport in epitaxial YBa2Cu3O7−x film near the superconducting transition temperature

“…The temperature of the film was controlled by a cryogenic system of cryostat and a temperature controller. The detailed experimental setup can be found in previous reports [11][12][13]17]. where dV is ac voltage signal, j b ðx; yÞ local current density, oqðx;yÞ oT the derivative of resistivity with respect to temperature, K the disturbed area due to the laser beam, dT the increase in temperature due to heating caused by the laser beam, respectively [18].…”

“…Earlier our group reported the observation of the spatial distribution of the superconducting transition temperature T c using variable temperature scanning laser microscopy, which measures the response due to the laser hot-spot near the superconducting transition [11][12][13].…”