Are critical resistance and exponents at the 2D superconductor-insulator transition universal? · revision history

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Title

Are critical resistance and exponents at the 2D superconductor-insulator transition universal?

Plain

Theory predicted that at the switch between superconductor and insulator the film resistance takes a universal value set by Planck constant and the electron charge, with simple scaling laws. Experiments find different values and exponents in different films.

Precise

The dirty-boson theory (Fisher 1990) predicts a universal critical sheet resistance $R_{c} = h/(4e^{2})$ and universal $z\nu$ at the B- or disorder-tuned transition. Measured $R_{c}$ varies by a factor of several and $z\nu$ ranges from $\sim 0.6$ to above 2; Ga films show a divergent effective $z\nu$ characteristic of a quantum Griffiths singularity (Xing et al. 2015). Classify the universality classes of the 2D transition with $1/r$ Coulomb interaction and quenched disorder, and determine whether $R_{c}$ and $z\nu$ are universal within each class.

Settled by

Scaling analyses at $T$ far below the crossover scale in several material classes, with sample-to-sample comparison of $R_{c}$ and $z\nu$, matched to a theory assigning each to a class.

Kind

well-posed

Answer type

classification

References

(empty)

Literature status

contested

Status note

A discontinuous (first-order) disorder-driven transition was reported in amorphous InOx films (Charpentier et al., Nature Physics 21, 104, 2025), which would place at least some films outside any continuous universality class.

Posed since

1990