Finite-temperature formalism and applications

Jaime Merino, A. Levy Yeyati

Monique Combescot, Shiue-Yuan Shiau, Yia‐Chung Chang

This Letter provides the missing part of the newly constructed many-body formalism for composite quantum particles: the introduction of a finite temperature. The finite T formalism we propose deeply relies on the existence of a compact closure relation for the (overcomplete) set of N-composite-particle states. As a first application, we here calculate the energy mean value of the exciton gas outside the condensation regime. We show that carrier exchanges increase its temperature dependence compared to elementary bosons, a signature of the degree-of-freedom increase resulting from the particle composite nature.

Vitor Rocha Vieira

The finite-temperature real-time field theories for spin (1/2 are derived with use of a functional-integral approach, and their application to problems of equilibrium and nonequilibrium statistical mechanics discussed. These formalisms have a standard Wick's theorem and linked-graph theorem, leading to the use of Feynman diagrams. Similar to the problems with bosons or fermions, the calculation of equilibrium quantities requires the consideration of the imaginary-time branch, leading to a three-component formalism, instead of the usual two-component formalism, typical of real-time field theories.