Abstract
The superconductor–insulator (SI) transition in two-dimensional Ta thin films is investigated by controlling both film thickness and magnetic field. An intriguing metallic phase appears between a superconducting and an insulating phase within a range of film thickness and magnetic field. The temperature and electric field scaling analyses are performed to investigate the nature of the SI transition in the thickness-tuned metallic and superconducting samples. The critical exponents product of νz obtained from the temperature scaling analysis is found to be approximately 0.67 in the entire range of film thickness. On the other hand, an apparent discrepancy is measured in the product of ν(z + 1) by the electric filed analysis. The product values are found to be about 1.37 for the superconducting films and about 1.86 for the metallic films respectively. We find that the discrepancy is the direct consequence of electron heating that introduces additional dissipation channels in the metallic Ta films.
Highlights
The superconductor–insulator (SI) transition in two-dimensional Ta thin films is investigated by controlling both film thickness and magnetic field
A superconducting phase corresponds to a vortex glass state in which the condensate of Cooper pairs appears with localized vortices, while an insulating phase corresponds to a Bose glass state in which Cooper pairs are localized by proliferated vortices
Ta thin films are characterized by X-ray diffraction (XRD) and atomic force microscope (AFM) measurements
Summary
The superconductor–insulator (SI) transition in two-dimensional Ta thin films is investigated by controlling both film thickness and magnetic field. An intriguing metallic phase appears between a superconducting and an insulating phase within a range of film thickness and magnetic field. The temperature and electric field scaling analyses are performed to investigate the nature of the SI transition in the thickness-tuned metallic and superconducting samples. The critical exponents product of νz obtained from the temperature scaling analysis is found to be approximately 0.67 in the entire range of film thickness. In addition to the magnetic-field-induced metallic phase, Ta9 and Bi17 thin films within a certain range of film thickness exhibit a disorder-induced metallic phase even at the zero-field and zero-temperature limit. The magnetic-field-induced SI scaling fails to obtain the universal critical resistance, the critical exponents show good agreement with theoretical predictions. One can find the observed deviation reflects essentially the low temperature saturation of magneto-resistance
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