Universal Fermi liquid crossover and quantum criticality in a mesoscopic system

Keller, A. J. and Peeters, L. and Moca, Pascu Catalin and Weymann, I. and Mahalu, D. and Zaránd, Gergely Attila (2015) Universal Fermi liquid crossover and quantum criticality in a mesoscopic system. NATURE, 526 (7572). pp. 237-240. ISSN 0028-0836

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Abstract

Quantum critical systems derive their finite temperature properties from the influence of a zero temperature quantum phase transition.1 The paradigm is es- sential for understanding unconventional high-Tc superconductors and the non- Fermi liquid properties of heavy fermion compounds. However, the microscopic origins of quantum phase transitions in complex materials are often debated. Here we demonstrate experimentally, with support from numerical renormaliza- tion group calculations, a universal crossover from quantum critical non-Fermi liquid behavior to distinct Fermi liquid ground states in a highly controllable quantum dot device. Our device realizes the non-Fermi liquid two-channel Kondo state, based on a spin-1/2 impurity exchange-coupled equally to two indepen- dent electronic reservoirs. Arbitrarily small detuning of the exchange couplings results in conventional screening of the spin by the more strongly coupled chan- nel for energies below a Fermi liquid scale T∗. We extract a quadratic dependence of T∗ on gate voltage close to criticality and validate an asymptotically exact de- scription of the universal crossover between strongly correlated non-Fermi liquid and Fermi liquid states.

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