Thermodynamic signatures of quantum criticality in cuprate superconductors.
basic_science · Level V
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- Record sourced from PubMed, PMID 30760922.
- Also identified by DOI 10.1038/s41586-019-0932-x.
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Abstract
The three central phenomena of cuprate (copper oxide) superconductors are linked by a common doping level p*-at which the enigmatic pseudogap phase ends and the resistivity exhibits an anomalous linear dependence on temperature, and around which the superconducting phase forms a dome-shaped area in the phase diagram<sup>1</sup>. However, the fundamental nature of p* remains unclear, in particular regarding whether it marks a true quantum phase transition. Here we measure the specific heat C of the cuprates Eu-LSCO and Nd-LSCO at low temperature in magnetic fields large enough to suppress superconductivity, over a wide doping range<sup>2</sup> that includes p*. As a function of doping, we find that C<sub>el</sub>/T is strongly peaked at p* (where C<sub>el</sub> is the electronic contribution to C) and exhibits a log(1/T) dependence as temperature T tends to zero. These are the classic thermodynamic signatures of a quantum critical point<sup>3-5</sup>, as observed in heavy-fermion<sup>6</sup> and iron-based<sup>7</sup> superconductors at the point where their antiferromagnetic phase comes to an end. We conclude that the pseudogap phase of cuprates ends at a quantum critical point, the associated fluctuations of which are probably involved in d-wave pairing and the anomalous scattering of charge carriers.