The physical states of Fermi systems

Philippe Nozières

Bruno Juliá Díaz, Arnau Rios Huguet, Héctor Briongos Merino +2 more

At finite temperatures, the sharp distinction between occupied and unoccupied states near the Fermi surface becomes blurred, as the filling of the states is ruled by the Fermi distribution. This leads to significant changes in the physical properties of the system. Analyzing these effects is crucial for understanding phenomena like electrical and thermal conductivity, as well as the response of materials to external perturbations. Moreover, working at nonzero temperatures allows us to study transitions between quantum and classical regimes, shedding light on the statistical mechanics that govern systems from condensed matter to nuclear physics and astrophysics.

Lihong Zhou, Xiaoling Cui, Wei Yi

We investigate the pairing physics in a three-component Fermi-Fermi mixture, where a few fermionic impurities are immersed in a noninteracting two-component Fermi gas with synthetic spin-orbit coupling (SOC), and interact attractively with one spin species in the Fermi gas. Because of the interplay of SOC and the spin-selective interaction, the molecular state intrinsically acquires a nonzero center-of-mass momentum, which results in a new type of Fulde-Ferrell (FF) pairing in spin-orbit coupled Fermi systems. The existence of the Fermi sea can also lead to the competition between FF-like molecular states with different center-of-mass momenta, which corresponds to a first-order transition between FF phases in the thermodynamic limit. As the interaction strength is tuned, a polaron-molecule transition occurs in the highly imbalanced system, where the boundary varies nonmonotonically with SOC parameters and gives rise to the reentrance of polaron states. The rich physics in this system can be probed using existing experimental techniques.

Ph. Nozières, Daniel W. Hone, M. E. Rose

Nicolas Sator, Nicolas Pavloff, Lénaïc Couëdel

The concepts of statistical physics have been used to study fermionic systems rapidly after the birth of the “new" quamtum mechanics in 1925. This proved to be extremely fruitful and led to major advances in atomic and solid state physics. Fermi-Dirac statistics was introduced in 1926 by Enrico Fermi and Paul Dirac. It was used by Ralph Fowler in 1926 to describe the collapsed state of a star (a so-called white dwarf ) and by Arnold Sommerfeld in 1928 to describe conduction electrons in solids. This chapter first presents some general results and then discusses a choice of specific systems.

R. F. Bishop