Charge dynamics in a doped Mott insulator

Zheng-Cheng Gu, Center for Advanced Study, Tsinghua University

Abstract: An understanding of the anomalous charge dynamics in the high-Tc cuprates is obtained based on an unconventional correlation between the charge and spin degrees of freedom in a doped Mott insulator. It is shown that the high-temperature optical conductivity is generally associated with a two-component behavior: a Drude like "coherent" part followed by an "incoherent" mid-infrared part. The low-energy part of the optical conductivity gets progressively suppressed with reducing temperature as the system enters into the pseudogap phase with the opening up of a spin gap. The mid-infrared part exhibits a resonance like feature in an underdoped case and continuously evolves into a 1/ω-decay tail at higher doping, indicating that the mid-infrared resonance and 1/ω behavior observed in the cuprates share the same physical origin. Such a high-energy component is further shown to be closely correlated with the ω-peak structure of the density-density correlation functions at different momenta which is systematically consistent with the exact diagonalization results based on the t - J model. The underlying physics is due to a high-energy spin-charge separation in the model, in which the "mode coupling" responsible for the anomalous charge properties is not between the electron and some collective mode but rather between the spinless charge carriers - holons and a topological gauge field associated with the spin dynamics.