Speaker: 家永紘一郎 (東工大)

Date: Feb. 13th (Tue.) 16:00- 17:00

Style: zoom

Title:  Kibble-Zurek mechanism for dynamical phase transition in driven superconducting vortices

Abstract:

Superconducting vortices, which are formed in type-II superconductors under a magnetic field, behave as nanoparticles interacting repulsively with each other. The vortex system is an excellent platform to study nonequilibrium phenomena associated with vortex dynamics because vortices are driven by electric current controllably and their average velocity can be detected from the voltage. In this seminar, I will mainly talk about the following two topics from our quite recent results obtained in the vortex system driven by electric current[1-3]. I will also show brief results based on the vortex Nernst effect, in which the vortices are driven by heat current[4].
(1) When a driving force is increased, a many-particle system driven over a random potential shows dynamical ordering from a disordered plastic flow to an anisotropically ordered smectic flow state[1,5]. However, it remains unclear whether the dynamical ordering is a true phase transition because of lack of suitable experimental methods. We study the response of vortex flow to the transverse force using a cross‐shaped sample and find the scaling collapse of the transverse current‐voltage curves, which provides clear evidence that the dynamical ordering transition is of second order[2].
(2) Using the dynamical ordering transition mentioned above, we attempt to verify the Kibble-Zurek mechanism. The Kibble-Zurek mechanism[6] describes the formation of topological defects in systems crossing a continuous symmetry-breaking phase transition at a finite quench rate. While this mechanism has been extensively studied for equilibrium transitions[7], its applicability to nonequilibrium transitions has not yet been fully examined. We experimentally study the configurational order of driven vortices in the course of dynamical ordering with various quench rates. A power-law scaling of the defect density with the quench rate and an impulse-adiabatic crossover on the ordered side of the transition are verified[3], which are key predictions of the Kibble-Zurek mechanism. Our results indicate the applicability of the Kibble- Zurek mechanism to other nonequilibrium phase transitions.

[1] S. Maegochi, K. Ienaga, and S. Okuma, Phys. Rev. Res. 4, 033085 (2022).
[2] S. Maegochi, K. Ienaga, and S. Okuma, Sci. Rep. 14, 1232 (2024).
[3] S. Maegochi, K. Ienaga, and S. Okuma, Phys. Rev. Lett. 129, 227001 (2022) (Editors' Suggestion).
[4] K. Ienaga, S. Okuma, et al., Phys. Rev. Lett. 125, 257001 (2020): Nature Commun. (in press).
[5] C. Reichhardt and C. J. Olson Reichhardt, Rep. Prog. Phys. 80, 026501 (2017)
[6] T. W. B. Kibble, J. Phys. A: Math. Gen. 9, 1387 (1976). W. H. Zurek, Nature 317, 505 (1985).
[7] T. Kibble, Phys. Today 60, 9, 47 (2007), A. del Campo and W. H. Zurek, Int. J. Mod. Phys. A 29, 1430018 (2014).