Emergence of quantum Griffiths singularity in disordered TiN thin films

TL;DR

This study demonstrates the emergence of quantum Griffiths singularity in disordered TiN thin films, showing diverging critical exponents near quantum phase transitions across various disorder levels.

Contribution

It provides experimental evidence of quantum Griffiths singularity in both superconductor-metal and superconductor-insulator transitions in disordered TiN films, extending understanding of quantum critical phenomena.

Findings

Diverging critical exponent observed near quantum phase transitions.

Quantum Griffiths singularity robust across disorder levels.

Magnetoresistance obeys activated scaling at criticality.

Abstract

The association of quantum Griffiths singularity (QGS) to the magnetic-field-induced superconductor-metal transition predicts the unconventional diverging behaviour of dynamical critical exponent in low disorder crystalline two-dimensional superconductors. But whether this state exists in the superconducting systems exhibiting superconductor-insulator transition remains elusive. Here, we report the emergence of quantum Griffiths singularity in ultrathin disordered TiN thin films with more than two orders of magnitude variation in their normal state resistance. For both superconductor-metal transition and superconductor-insulator transition types, a diverging critical exponent is observed while approaching the quantum phase transition. Further, the magnetoresistance isotherms obey a direct activated scaling governed by an infinite-randomness fixed critical point. Finally, this work establishes the robustness of the QGS phenomenon towards a wide range of temperature and also towards a wide range of disorder strength as correlated with the normal state resistance.