We performed temperature- and doping-dependent high-resolution Raman spectroscopy experiments on YBa₂Cu₃O_7-δ to study B_1g phonons. The temperature dependence of the real part of the phonon self-energy shows a distinct kink at T = T_B1g above T_c due to softening, in addition to the one due to the onset of the superconductivity. T_B1g is clearly different from the pseudogap temperature with a maximum in the underdoped region and resembles charge density wave onset temperature, T_CDW. We attribute the B_1g-phonon softening to an energy gap on the Fermi surface induced by a charge density wave order, which is consistent with the results of a recent electronic Raman scattering study. Our work demonstrates a way to investigate Fermi surface instabilities above T_c via phonon Raman studies.

Authors: Dongjin Oh, Dongjoon Song, Younsik Kim, Shigeki Miyasaka, Setsuko Tajima, Jin Mo Bok, Yunkyu Bang, Seung Ryong Park, and Changyoung Kim

Publication date: 29 December 2021

Link: https://doi.org/10.1103/PhysRevLett.127.277001