Kinetic Energy, Condensation Energy, Optical Sum Rule and Pairing Mechanism in High-Tc Cuprates

TL;DR

This paper investigates the microscopic mechanisms of high-Tc superconductivity in cuprates, highlighting the role of kinetic energy and spin fluctuations, and explains the doping-dependent behaviors and optical sum rule violations.

Contribution

It demonstrates that kinetic energy cooperatively induces superconductivity in underdoped cuprates via a feedback effect, contrasting with the conventional view of correlation energy dominance.

Findings

Kinetic energy decreases below T_c in underdoped cuprates due to feedback effects.

The crossover from BCS to unconventional behavior occurs with hole doping.

The decrease of kinetic energy is absent in electron-doped cuprates.

Abstract

The mechanism of high-Tc superconductivity is investigated with interests on the microscopic aspects of the condensation energy. The theoretical analysis is performed on the basis of the FLEX approximation which is a microscopic description of the spin-fluctuation-induced-superconductivity. Most of phase transitions in strongly correlated electron system arise from the correlation energy which is copmetitive to the kinetic energy. However, we show that the kinetic energy cooperatively induces the superconductivity in the underdoped region. This unusual decrease of kinetic energy below T_c is induced by the feedback effect. The feedback effect induces the magnetic resonance mode as well as the kink in the electronic dispersion, and alters the properties of quasi-particles, such as mass renormalization and lifetime. The crossover from BCS behavior to this unusual behavior occurs for hole dopings. On the other hand, the decrease of kinetic energy below T_c does not occur in the electron-doped region. We discuss the relation to the recent obserbation of the violation of optical sum rule.