Thermodynamic evidence of quantum criticality at the pseudogap critical point of cuprate superconductors

The emergence of superconductivity in the vicinity of a magnetic quantum critical point (QCP) in heavy-fermion, iron-based, organic and electron-doped cuprate superconductors showcases the important relation between quantum criticality and pairing. In hole-doped cuprates, long-range antiferromagnetic order vanishes with doping well before superconductivity appears. Instead, it is around the critical doping p* where the enigmatic pseudogap phase ends that superconductivity exists. The fact that the electrical resistivity displays a linear temperature dependence at low temperature in all these systems, including hole-doped cuprates [1], is suggestive. Here we provide thermodynamic evidence of a QCP in hole-doped cuprates from low-temperature measurements of the specific heat in magnetic fields up to 35 T, high enough to suppress superconductivity. In LSCO, Eu-LSCO, Nd-LSCO and Bi2201, we observe an electronic specific heat that grows as C/T ~ log(1/T) at p ~ p* [2], the classic thermodynamic signature of quantum criticality.
[1] Legros et al., Nature Physics 15, 142 (2019).
[2] Michon et al., Nature 567, 218 (2019).