The pseudogap critical point of cuprate superconductors: an overview by different techniques

Recent high field transport measurements on cuprate superconductors [1][2] highlighted an intriguing region in the phase diagram of hole doped cuprates: the pseudogap critical point called p*. Indeed, at p* the pseudogap vanishes with a clear signature: a drop in the carrier density from 1+p to p carriers when we enter the pseudogap phase at p*. Thereafter, this signature raised a lot of questions about the origin of the pseudogap phase and the nature of this transition. In the light of my previous PhD works, we will see how we can give some answers about this topic. During my PhD, thermal transport [3] and high field specific heat [4] were developed and measured on Eu-LSCO and Nd-LSCO cuprates. Thermal transport puts in evidence two main findings: A) the pseudogap is a metal in satisfying the Wiedemann-Franz law B) the drop in carrier density at p* is present even inside the superconducting state. The main finding of specific heat is to exhibit a log(T) divergence at p*: archetype of quantum fluctuations located at p* and associated to a quantum phase transition.

Motivated by these findings, we will see the interests for measuring optics in the same compounds.

The on going Post-doc project in optics will be presented with some preliminary results.

[1] Badoux et al, Nature 531, 7593 (2016)

[2] Collignon et al, PRB 95, 224517 (2017)

[3] Michon et al., PRX 8, 041010 (2018)

[4] Michon et al., Nature 567, 218–222 (2019)