The thermodynamics of normal Fermi-systems

Kristian Fenech

This thesis presents two measurements of the properties of a two-dimensional Fermi gas. The first series of measurements examine the role of interactions in defining the dimensionality of the system. From this, the parameter space where two-dimensional kinematics can be observed is established. Using this result, the thermodynamic properties and equations of state of an attractive Fermi gas in the normal phase are determined through the measurement of the density distribution of the trapped gas.

Frédéric Chevy, Ch Salomon

Joseph M. Kinast

Partha Goswami

A relation between the thermodynamic potential and certain spectral-weight functions in mixed singlet-triplet states of a Fermi fluid with weakly attractive interaction is established. The entire thermodynamics of the system can be derived using this relation. A similar relation is also established for an assembly of spinless, interacting bosons in the ordered phase. The latter corresponds to the Kadanoff-Baym relation for the normal phase when the necessary conditions are fulfilled. Crossover scaling forms for the susceptibility and the deviation of pressure from its critical value for the Bose system are calculated using the established relation. These forms are in general agreement with those obtained earlier by renormalization-group approaches to the problem.

Salvador Miracle-Solé, Derek W. Robinson

Digvijay Kharga, Hiroyuki Tajima, Pieter van Wyk +2 more

We theoretically investigate normal-state properties of a unitary Bose-Fermi mixture. Including strong hetero-pairing fluctuations, we evaluate the Bose and Fermi chemical potential, internal energy, pressure, entropy, as well as specific heat at constant volume $C_V$, within the framework of a combined strong-coupling theory with exact thermodynamic identities. We show that hetero-pairing fluctuations at the unitarity cause non-monotonic temperature dependence of $C_V$, being qualitatively different from the monotonic behavior of this quantity in the weak- and strong-coupling limit. On the other hand, such an anomalous behavior is not seen in the other quantities. Our results indicate that the specific heat $C_V$, which has recently become observable in cold atom physics, is a useful quantity for understanding strong-coupling aspects of this quantum system.