arXiv subjects

M. M. Parish

Publications and source records attributed to M. M. Parish.

22 records · Page 2Linked to original sources

arXiv2007

Finite temperature phase diagram of a polarised Fermi condensate

The two-component Fermi gas is the simplest fermion system displaying superfluidity, and as such finds applications ranging from the theory of superconductivity to QCD. Ultracold atomic gases provide an exceptionally clean realization of this system, where the interatomic interaction and the atom species population are both independent, tuneable parameters. This allows one to investigate the Fermi gas with imbalanced spin populations, which had previously been experimentally elusive, and this prospect has stimulated much theoretical activity. Here we show that the finite temperature phase diagram contains a region of phase separation between the superfluid and normal states that touches the boundary of second-order superfluid transitions at a tricritical point, reminiscent of the phase diagram of $^3$He-$^4$He mixtures. A variation of interaction strength then results in a line of tricritical points that terminates at zero temperature on the molecular Bose-Einstein condensate (BEC) side. On this basis, we argue that tricritical points will play an important role in the recent experiments on polarised atomic Fermi gases.

cond-mat.other↗

arXiv2007

Polarized Fermi condensates with unequal masses: Tuning the tricritical point

We consider a two-component atomic Fermi gas within a mean-field, single-channel model, where both the mass and population of each component are unequal. We show that the tricritical point at zero temperature evolves smoothly from the BEC- to BCS-side of the resonance as a function of mass ratio r. We find that the interior gap state proposed by Liu and Wilczek is always unstable to phase separation, while the breached pair state with one Fermi surface for the excess fermions exhibits differences in its DoSs and pair correlation functions depending on which side of the resonance it lies. Finally, we show that, when r > 3.95, the finite temperature phase diagram of trapped gases at unitarity becomes topologically distinct from the equal mass system.

cond-mat.other↗

arXiv2005

Fermion-mediated BCS-BEC Crossover in Ultracold Potassium-40 Gases

Studies of Feshbach resonance phenomena in fermionic alkali gases have drawn heavily on the intuition afforded by a Fermi-Bose theory which presents the Feshbach molecule as a featureless Bose particle. While this model may provide a suitable platform to explore the lithium-6 system, we argue that its application to potassium-40, where the hyperfine structure is inverted, is inappropriate. Introducing a three-state Fermi model, where a spin state is shared by the open and closed channel states, we show that effects of ``Pauli blocking'' are recorded in the internal structure of the condensate wave function.

cond-mat.other↗

arXiv2003

Non-saturating magnetoresistance in heavily disordered semiconductors

The resistance of a homogeneous semiconductor increases quadratically with magnetic field at low fields and, except in very special cases, saturates at fields much larger than the inverse of the carrier mobility, a number typically of order 1 Tesla. Here, we argue that a macroscopically disordered and strongly inhomogeneous semiconductor will instead show a non-saturating magnetoresistance, with typically a quasi-linear behaviour up to very large fields, and possibly also extending down to very low fields, depending on the degree of inhomogeneity. We offer this as a possible explanation of the observed anomalously large magnetoresistance in doped silver chalcogenides. Furthermore, our model of an inhomogeneous semiconductor can be developed into magnetoresistive devices that possess a large, controllable, linear response.

cond-mat↗