Within FLEET, Chris Vale studies topological phenomena in 2-D gases of ultracold fermionic atoms, investigating cold atom implementations of Floquet topological superfluidity, nonequilibrium enhancements to the superconducting critical temperature and new forms of topological matter based on optically induced spin-orbit coupling in 2-D atomic gases, in Research Theme 3.įLEET's research theme 3 studies systems that are temporarily driven out of thermal equilibrium to investigate the qualitatively different physics displayed and new capabilities for dynamically controlling their behaviour.Ĭhris leads the study of quantum gases at Swinburne University of Technology. The study of many-body quantum systems with strong inter-particle interactions is of great interest for the understanding of novel materials. Ultracold atomic lab at Swinburne University of Technology. The team then studied excitations in the gas above and below the superfluid phase transition T c using two-photon Bragg spectroscopy. Unitary Fermi gases allow precise testing of theories of interacting fermions. In a unitary gas, elastic collisions become resonant and the thermodynamic properties of the gas become universal functions of the temperature and density. "We cooled and confined a highly dilute gas of Li 6 atoms, realising a unitary Fermi gas, which exhibits the strongest interactions allowed by quantum mechanics with a contact potential," explains Prof Vale. The ultracold atomic gases formed and studied in Prof Chris Vale's lab at Swinburne allow very precise tuning of interactions between atoms. This study provides quantitative benchmarks for dynamical theories of strongly-correlated fermions. Strong similarities were identified in the temperature dependence of sound in the unitary Fermi gas and the behaviour of phonons in liquid helium, which was one of the first superfluids identified historically. >T c At even higher temperatures, collective propagation of sound-wave vanishes, and excitation is dominated by the energy of individual particles.>T c Above the transition temperature, the strongly-damped mode occurs at the crossover between collisionless hydrodynamic regimes.lower than T c In the colder, superfluid mode, damping is dominated by collisions with thermally excited quasiparticles and is well described by (QRPA) theory.At low energies, this energy travels via the collective movement of many particles moving in sync-essentially, as sound waves-quantified using quasiparticles known as phonons.īelow the superfluid transition temperature T c these sound waves in a unitary Fermi gas can propagate without collisions and are driven by ripples in the phase of the superfluid order parameter (wave-function)-this mode is known as the Bogoliubov-Anderson (BA) phonon.Ībove T c, the sound waves become more strongly-damped, and collisions play a dominant role.
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