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Resonance Superfluidity in a Quantum Degenerate Fermi Gas

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Kokkelmans S., Holland M., Walser R., Chiofalo M.

Acta Physica Polonica A

2002

vol. 101

issue 3

387-397

We consider the superfluid phase transition that arises when a Feshbach resonance pairing occurs in a dilute Fermi gas. This is related to the phenomenon of superconductivity described by the seminal Bardeen-Cooper-Schrieffer theory. In superconductivity, the phase transition is caused by a coupling between pairs of electrons within the medium. This coupling is perturbative and leads to a critical temperature T_c which is small compared to the Fermi temperature T_F. Even high-T_c superconductors typically have a critical temperature which is two orders of magnitude below T_F. Here we describe a resonance pairing mechanism in a quantum degenerate gas of potassium (^{40} K) atoms which leads to superfluidity in a novel regime - a regime that promises the unique opportunity to experimentally study the cross-over from the Bardeen-Cooper-Schrieffer phase of weakly-coupled fermions to the Bose-Einstein condensate of strongly-bound composite bosons. We find that the transition to a superfluid phase is possible at the high critical temperature of about 0.5 T_F. It should be straightforward to verify this prediction, since these temperatures can already be achieved experimentally.

Experimental Control of the Number of Ionized Donors in an AlGaAs/GaAs Heterostructure

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Denk P., Schlösser T., Ensslin K., Holland M.

Acta Physica Polonica A

1995

vol. 88

issue 5

977-981

The high mobility of electrons in AlGaAs-GaAs heterostructures relies on the concept of modulation doping. As a sample is cooled down to T = 4.2 K under a fixed gate bias the number of ionized donors can be frozen and is then independent on the gate potential. We discuss the consequences of this procedure on the electron density and mobility in a two-dimensional electron gas. For a laterally patterned sample we find that the amplitude of the potential modulation can be maximized for a given carrier density by a suitably chosen cool-down voltage.

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2 Acta Physica Polonica A

1 2002

1 1995

2 Holland M.

1 Chiofalo M.

1 Denk P.

1 Ensslin K.

1 Kokkelmans S.

1 Schlösser T.

1 Walser R.

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Resonance Superfluidity in a Quantum Degenerate Fermi Gas

Experimental Control of the Number of Ionized Donors in an AlGaAs/GaAs Heterostructure