New experimental signatures of the pseudogap phase in
cuprates
Louis Taillefer
Département de physique Université de Sherbrooke
Phase diagram of cuprates. In zero field, superconductivity exists in a dome
below Tc (dashed line). When it is removed by a magnetic field,
various underlying ground states are revealed: doped Mott insulator with
antiferromagnetic order (AF, brown); pseudogap phase below a temperature
T* (PG, yellow), ending at a T = 0 critical point p*
(red dot); charge-density wave phase (CDW, blue), contained inside the PG
phase; a strange metal region just above p*, which gives way to
a Fermi liquid state (FL, gray region) at highest doping.
The pseudogap phase of cuprate superconductors is arguably the most enigmatic
phase of quantum matter. We aim to shed new light on this phase by investigating
the non-superconducting ground state of several cuprate materials at low
temperature, by suppressing superconductivity with a magnetic field [1].
Hall effect and thermal conductivity measurements across the pseudogap critical
doping p* reveal a sharp drop in carrier density n from
n = 1 + p above p* to n = p below
p* [2], signaling a major transformation
of the Fermi surface. From specific heat measurements, we observe the classic
thermodynamic signatures of quantum criticality: the electronic specific heat
shows a sharp peak at p*, where it varies in temperature as
T logT [3]. At p* and just above, the
electrical resistivity is linear in T at low T, with an inelastic scattering
rate that obeys the Planckian limit [4]. Finally, the pseudogap
phase is found to have a large negative thermal Hall conductivity, as a result
of phonons acquiring chirality in a magnetic field [5].
Understanding the mechanisms responsible for these various new signatures
will help elucidate the nature of the pseudogap phase.
References:
[1] Proust & Taillefer, Annu. Rev. Condens. Matter Phys. 10, 409 (2019).
[2] Badoux et al., Nature 531, 210 (2016); Collignon et al., Phys. Rev. B 95, 224517 (2017).
[3] Michon et al., Nature 567, 218 (2019).
[4] Legros et al., Nat. Phys. 15, 142 (2019); Grissonnanche et al., Nature 595, 667 (2021).
[5] Grissonnanche et al., Nature 571, 376 (2019); Nat. Phys. 16, 1108 (2020).
