Is the pseudogap endpoint p* a quantum critical point
In plain words
Near 19 percent hole doping the pseudogap vanishes, and there the electronic heat capacity peaks and resistance becomes linear in temperature, signs of a phase transition at zero temperature.
Precise statement
With superconductivity suppressed by fields of several hundred kG, determine whether the endpoint $p*$ (0.19 to 0.23 depending on family) is a quantum critical point with an order parameter ($C/T \sim \operatorname{log}(1/T)$, Hall number change from $p\ \text{to}\ 1+p$) or a change of Fermi-surface topology without broken symmetry. An answer identifies the transition type and, if one exists, the order parameter whose fluctuations give the log divergence.
What would settle it
Detection of the order parameter (or proof of its absence) by a symmetry-sensitive probe in the same high-field regime where C/T diverges.
Status in the literature
High-field specific heat (2019) found $C/T \sim \log(1/T)$ at $p*$ in Nd- and Eu-substituted La2-xSrxCuO4, but the associated order parameter is unidentified.
Related problems
- Special case of What is the pseudogap state of underdoped cuprates
See also
- Related Is the pseudogap temperature T* a thermodynamic phase transition
- Related Microscopic origin of T-linear resistivity in strange metals
- Related Why T-linear resistivity persists across the overdoped cuprate range
- Related What reconstructs the underdoped cuprate Fermi surface into small pockets