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Nature. 2015 Oct 8;526(7572):237-40. doi: 10.1038/nature15261.

Universal Fermi liquid crossover and quantum criticality in a mesoscopic system.

Author information

1
Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA.
2
BME-MTA Exotic Quantum Phases "Lendület" Group, Institute of Physics, Budapest University of Technology and Economics, H-1521 Budapest, Hungary.
3
Department of Physics, University of Oradea, Oradea 410087, Romania.
4
Faculty of Physics, Adam Mickiewicz University, Poznań 61-614, Poland.
5
Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 96100, Israel.

Abstract

Quantum critical systems derive their finite-temperature properties from the influence of a zero-temperature quantum phase transition. The paradigm is essential 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 renormalization group calculations, a universal crossover from quantum critical non-Fermi liquid behaviour 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 independent electronic reservoirs. On detuning the exchange couplings we observe the Fermi liquid scale T*, at energies below which the spin is screened conventionally by the more strongly coupled channel. We extract a quadratic dependence of T* on gate voltage close to criticality, and validate an asymptotically exact description of the universal crossover between strongly correlated non-Fermi liquid and Fermi liquid states.

PMID:
26450057
DOI:
10.1038/nature15261

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