The quest for electron-hole superfluidity

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• Prof David Nielson, University of Camerino, Italy
• Wednesday 22 April 2015, 14:00-15:00
• Mott Seminar Room (Mott Building Room 531), Cavendish Laboratory.

If you have a question about this talk, please contact Teri Bartlett.

Interacting electrons and holes in solids are predicted to form a superfluid at high temperatures thanks to the Coulomb pairing which is very strong compared with the pairing interaction in conventional superconductors. [1] The electrons and holes must kept apart in two adjacent thin conducting layers separated by a thin insulating barrier, so they strongly attract but cannot recombine.[2,3,4]

There have been major experimental projects to realise this phenomenon in double quantum wells in semiconductor heterostructures of GaAs.[5,6] However, these have led to rather inconclusive results. In this talk the issue of the optimal ranges for the experimental parameters, temperature, well width, well separation, will be discussed.

Also discussed will be the theoretical issue of the self-consistent treatment of the screening of the electron-hole pair Coulomb interaction in the presence of a superfluid quantum condensate,[7] and the relative importance of screening in the weak-coupled BCS regime, the cross-over regime and the Bose-Einstein condensation regime. Finally, the dependence of the phenomenon on dimensionality will be discussed, contrasting the superfluid properties for two coupled two-dimensional quantum well sheets with the superfluid properties for two coupled quasi-one dimensional wires.[8]

[1] Room-temperature superfluidity in graphene bilayers, Hongki Min, Rafi Bistritzer, Jung-Jung Su, and A. H. MacDonald, , Physical Review B 78 , 121401® (2008). [2] Feasibility of superfluidity of paired spatially separated electrons and holes; a new superconductivity mechanism, Yu. E. Lozovik and V.I. Yudson, JETP Letters 22, 274 (1975). [3] Effects of density imbalance on the BCS -BEC crossover in semiconductor electron-hole bilayers, P. Pieri, D. Neilson, and G.C. Strinati, Physical Review B 75 , 113301 (2007). [4] High-Temperature Superfluidity in Double-Bilayer Graphene, A. Perali, D. Neilson, and A. R. Hamilton, Physical Review Letters 110, 146803 (2013). [5] Anomalous Coulomb Drag in Electron-Hole Bilayers, A. F. Croxall, K. Das Gupta, C. A. Nicoll, M. Thangaraj, H. E. Beere, I. Farrer, D. A. Ritchie, and M. Pepper, Physical Review Letters 101, 246801 (2008). [6] Coulomb Drag in the Exciton Regime in Electron-Hole Bilayers, J. A. Seamons, C. P. Morath, J. L. Reno, and M. P. Lilly, Physical Review Letters 102, 026804 (2009). [7] Excitonic superfluidity and screening in electron-hole bilayer systems, D. Neilson, A. Perali, and A. R. Hamilton, Physical Review B 89 , 060502® (2014). gap amplification at a shape resonance in superlattice of quantum stripes: mechanism for high-Tc, A. Perali, A. Bianconi, A. Lanzara, and N.L. Saini, Solid State Communications 100, 186 (1996).

This talk is part of the Semiconductor Physics Group Seminars series.

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