Nematic fluctuations in the cuprate superconductor $\mathrm{Bi} _2\mathrm{Sr} _2\mathrm{CaCu} _2\mathrm{O} _{8+\delta }$

Résumé

Establishing the presence and the nature of a quantum critical point in their phase diagram is a central enigma of the high-temperature superconducting cuprates. It could explain their pseudogap and strange metal phases, and ultimately their high superconducting temperatures. Yet, while solid evidences exist in several unconventional superconductors of ubiquitous critical fluctuations associated to a quantum critical point, in the cuprates they remain undetected until now. Here using symmetry-resolved electronic Raman scattering in the cuprate $\mathrm{Bi} _2\mathrm{Sr} _2\mathrm{CaCu} _2\mathrm{O} _{8+\delta }$, we report the observation of enhanced electronic nematic fluctuations near the endpoint of the pseudogap phase. While our data hint at the possible presence of an incipient nematic quantum critical point, the doping dependence of the nematic fluctuations deviates significantly from a canonical quantum critical scenario. The observed nematic instability rather appears to be tied to the presence of a van Hove singularity in the band structure.