Bose glass and Fermi glass

Area of Science:

• Condensed Matter Physics
• Quantum Materials
• Superconductivity

Background:

• Two-dimensional (2D) superconducting materials exhibit a quantum phase transition from a localized state to superconductivity.
• This transition involves bosons (Cooper pairs) forming from a Fermi glass and progressing through a Bose glass phase.
• A universal description for the Fermi glass to Bose glass transition has been lacking.

Purpose of the Study:

• To establish a universal expression for the quantum phase transition from Fermi glass to Bose glass in 2D superconductors.
• To investigate the universality of this transition by analyzing distinct material systems.
• To propose a new model for the transition dynamics.

Main Methods:

• Experimental renormalization group flow analysis using a simple $\beta$-function.
• Analysis of two distinct 2D superconducting systems: a Nd-based layered perovskite and an ultrathin Pb film.
• Comparison of experimental data with conventional self-consistent $\beta$-function models.

Main Results:

• Experimental data for Fermi glass aligned with the conventional self-consistent $\beta$-function.
• Observed unexpected flows perpendicular to the conventional $\beta$-function in the weakly localized regime of both systems.
• Identified a new two-dimensional critical sheet resistance near $\hbar^2/e^2$ for the transition.

Conclusions:

• A universal experimental renormalization group flow from Fermi glass to Bose glass has been discovered.
• The findings reveal novel transition dynamics in the weakly localized regime, deviating from conventional models.
• A new universal transition from Bose glass to Fermi glass is proposed, characterized by a specific critical sheet resistance.