[Paper Review] Current-Induced Superconductor-Insulator Transition in Granular High-T_c Superconductors

Y. Kopelevich, C. A. M. dos Santos+2 more|arXiv (Cornell University)|Aug 20, 2001

Physics of Superconductivity and Magnetism3 citations

TL;DR

This study demonstrates a current-induced superconductor-insulator quantum phase transition in granular high-Tc superconductors, driven by the dynamics of Josephson intergranular vortices. Using resistivity and I-V measurements under varying current and magnetic fields, the authors identify a threshold current I_c(H) that triggers a transition from a superconducting to an insulating state, with scaling collapse of resistance data confirming a zero-temperature quantum transition analogous to the field-tuned transition.

ABSTRACT

In this work we report a systematic study of electrical current effects on superconducting properties of granular Y$_{1-x}$Pr$_{x}$Ba$_{2}$Cu$_{3}$O$_{7-δ}$ samples with x close to the critical Pr concentration above which the superconductivity vanishes. The results indicate the occurrence of superconductor-insulator quantum phase transition (SIT) driven by the applied electrical current, and suggest that the current-induced SIT can be considered as the dynamical counterpart of the magnetic-field- tuned SIT.

Motivation & Objective

• To investigate the role of electrical current in driving a quantum phase transition from superconducting to insulating state in granular high-Tc superconductors.
• To determine whether the dynamics of Josephson intergranular vortices governs the transition under applied current.
• To test the hypothesis that a current-induced transition is the dynamical counterpart of the well-known field-tuned superconductor-insulator transition.
• To analyze the critical behavior near the transition point using finite-temperature scaling of resistance data.
• To compare the critical exponents of the current-driven transition with those of the field-tuned transition for consistency.

Proposed method

• Resistivity and four-probe dc transport measurements were performed on Y1-xPrxBa2Cu3O7-δ (x=0.45) thin films with applied currents up to 100 mA and magnetic fields up to 100 Oe.
• Low-current I-V characteristics were analyzed using the power-law equation V = c(T,H)(I - I_th(T,H))^n(T,H), where I_th is the threshold current for vortex motion.
• Scaling analysis was applied to resistance R = V/I as a function of the scaling variable |δ|/T^{1/α}, with δ = I - I_c(H), to test for universal critical behavior.
• The critical exponent α was extracted from log-log plots of dR/dI at I_c vs. T^{-1}, and data collapse was used to validate the scaling hypothesis.
• The analysis assumed the hard-core boson model, with the superconducting order parameter magnitude Ψ₀ remaining constant at T_c0, indicating phase fluctuations dominate.
• Measurements were repeated at different magnetic fields to map I_c(H) and compare with field-tuned transition behavior.

Experimental results

Research questions

• RQ1 Does an applied electrical current induce a superconductor-insulator quantum phase transition in granular high-Tc superconductors?
• RQ2 What is the role of Josephson intergranular vortex dynamics in mediating the current-induced transition?
• RQ3 Can the current-driven transition be described by the same finite-temperature scaling laws as the field-tuned transition?
• RQ4 Are the critical exponents of the current-induced transition consistent with those of the field-tuned transition?
• RQ5 Is the threshold current I_c(H) determined by vortex depinning or by intrinsic Josephson coupling?

Key findings

• The superconducting transition temperature T_c0 = 33 K remains unchanged under applied current or magnetic field, indicating that the transition is not driven by changes in the order parameter magnitude.
• A threshold current I_th ≈ 5 mA at 4.6 K was observed, with I-V characteristics well described by a power law with exponent n ≈ 3, indicating vortex flow dynamics.
• The critical current I_c(H) decreases with increasing magnetic field, with I_c = 16.2 mA at H = 2.85 Oe and I_c = 7 mA at H = 9.5 Oe, consistent with vortex delocalization.
• Scaling collapse of resistance data onto two branches (I < I_c and I > I_c) using the scaling variable |δ|/T^{1/α} confirms a universal quantum phase transition at zero temperature.
• The extracted critical exponent α ≈ 1.84, 1.72, and 1.3 for H = 2.85, 5.7, and 9.5 Oe, respectively, are in good agreement with values from field-tuned transitions in similar systems.
• The results support the existence of a zero-temperature current-driven depinning transition of Josephson vortices, analogous to the field-tuned transition, with the current acting as a control parameter.