Observation of thickness-tuned universality class in superconducting β - W thin films

The interplay between quenched disorder and critical behavior in quantum phase transitions is conceptually fascinating and of fundamental importance for understanding phase transitions. However, it is still unclear whether or not the quenched disorder influences the universality class of quantum phase transitions. More crucially, the absence of superconducting-metal transitions under in-plane magnetic fields in 2D superconductors imposes constraints on the universality of quantum criticality. Here, we observe the thickness-tuned universality class of superconductor-metal transition by changing the disorder strength in b - W films with varying thickness. The finite-size scaling uncovers the switch of universality class: quantum Griffiths singularity to multiple quantum criticality at a critical thickness of tcL1 ti 8 nm and then from multiple quantum criticality to single criticality at tcL2 ti 16 nm. Moreover, the superconducting-metal transition is observed for the first time under in-plane magnetic fields and the universality class is changed at tc1 ti 8 nm. The observation of thickness-tuned universality class under both out-of-plane and in-plane magnetic fields provides broad information for the disorder effect on superconducting-metal transitions and quantum criticality. (c) 2021 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.

Automated summary

The experimental investigation on the influence of quenched disorder on the universality class of quantum phase transitions revealed the thickness-tuned universality class of superconductor-metal transition, showing different quantum criticality behaviors at different thicknesses. The observations of superconducting-metal transitions under in-plane magnetic fields provide valuable information on the disorder effect on quantum criticality.