Quantum Griffiths singularity of superconductor-metal transition in Ga thin films

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Science  15 Oct 2015:
DOI: 10.1126/science.aaa7154

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The Griffiths singularity in a phase transition, caused by disorder effects, was predicted more than 40 years ago. Its signature, the divergence of dynamical critical exponent, is challenging to observe experimentally. Here we report the experimental observation of the quantum Griffiths singularity in a 2D superconducting system. We measure transport properties of atomic thin Ga films and find the films undergo superconductor-metal transitions with increasing magnetic field. Approaching the zero temperature quantum critical point, we observe divergence of the dynamical critical exponent, which is consistent with the Griffiths singularity behavior. We interpret the observed superconductor-metal quantum phase transition as the infinite-randomness critical point, where the properties of the system are controlled by rare large superconducting regions.

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