Raman spectrum in the pseudogap phase of the underdoped cuprates: effect of phasecoherence and the signature of the KT-type superconducting transition

Abstract

The temperature evolution of the Raman spectrum of the underdoped cuprates is studied inthe thermal phase fluctuation scenario with an XY-type lattice model for the phase degreeof freedom. It is found that the pair breaking Raman peak depends sensitively on the phasecoherence of the pairing order parameter. As a result, the integrated Raman intensity in both theB1g andthe B2g channels exhibits a dramatic drop across the Kosterlitz–Thouless (KT) transition temperature (TKT), when vortex-like phase fluctuation is proliferated. This result, which is consistent withexperimental observations, provides further support for the thermal phase fluctuationscenario of the pseudogap phase and the KT-type nature of the superconducting transitionin underdoped cuprates.