Fermi surface transformation at the pseudogap critical point of a cuprate superconductor

The pseudogap phase of cuprate superconductors is arguably the most enigmatic phase of quantum matter. In particular, a fundamental question remains open: what is the Fermi surface of the pure pseudogap phase? [1]

 

With our collaborators, we have used two new experimental probes to address this question. First, angle-dependent magneto-resistance (ADMR), measured in a field of 45 T, to reveal the shape of the Fermi surface in the cuprate Nd-LSCO. We observe a dramatic change in the ADMR between a doping just above the pseudogap critical doping p* –  where the Fermi surface is found to be a large cylinder – and a doping just below p*, where the ADMR data are most consistent with small hole pockets [2]. This transformation is consistent with the drop in carrier density deduced from prior Hall measurements [3].

 

The second experimental probe is the thermopower, or Seebeck coefficient. In the T = 0 limit, the in-plane Seebeck coefficient of Nd-LSCO is seen to undergo a large increase when doping is reduced below p* [4], consistent with a drop in carrier density. The out-of-plane Seebeck coefficient suddenly changes sign, from positive above p* to negative below [5] – clear evidence that the Fermi surface undergoes a major transformation upon entering the pseudogap phase.

 

The ADMR work was done in collaboration with Y. Fang, G. Grissonnanche, A. Legros, S. Verret, F. Laliberté, C. Collignon, A. Ataei, M. Dion, J. Zhou, D. Graf, M. J. Lawler, P. Goddard, and B. J. Ramshaw. The Seebeck work was done in collaboration with A. Gourgout, G. Grissonnanche, F. Laliberté, A. Ataei, L. Chen, S. Verret, J.-S. Zhou, J. Mravlje, A. Georges, and N. Doiron-Leyraud.

 

[1] Proust & Taillefer, Annu. Rev. Condens. Matter Phys. 10, 409 (2019).

[2] Fang et al., arXiv:2004.01725 (2020).

[3] Collignon et al., Phys. Rev. B 95, 224517 (2017).

[4] Collignon et al., Phys. Rev. B 103, 155102 (2021).

[5] Gourgout et al., arXiv:2106.05959 (2021).