FisMat2017 - Submission - View

Abstract's title: Excitonic condensation and quadriexcitons in a symmetric electron-hole bilayer with valley degeneracy: QMC simulations
Submitting author: Stefania De Palo
Affiliation: CNR-IOM Democritos, Istituto Officina dei Materiali
Affiliation Address: Via Bonomea 265, I-34136 Trieste, Italy
Country: Italy
Oral presentation/Poster (Author's request): Oral presentation
Other authors and affiliations: F. Tramonto (Dipartimento di Fisica, Universita` di Trieste, strada Costiera 11, 34151 Trieste, Italy) S. Moroni (CNR-IOM DEMOCRITOS, Istituto Officina dei Materiali, and 3SISSA Scuola Internazionale Superiore di Studi Avanzati, Via Bonomea 265, I-34136 Trieste, Italy) Gaetano Senatore (Dipartimento di Fisica, Universita` di Trieste, strada Costiera 11, 34151 Trieste, Italy)

The realization of systems of spatially separated electrons and holes, in the search of the equilibrium excitonic condensate foreseen by [1], has gone on for more than two decades, but so far the condensate has eluded experimental detection [2]. It has been recently suggested that a substantial enhancement of the electron-hole attraction, to favour the condensate, could be obtained in coupled graphene bilayers [3]; a couple of experimental realizations has promptly followed [4]. Such systems have a quadratic energy dispersion on a wide density range and a twofold valley degeneracy in each bilayer.

We have embarked in extensive QMC simulations of an electron-hole bilayer with mass symmetry and twofold valley degeneracy (in each layer), to partially mimic the situation encountered in the coupled graphene bilayers proposed in [2]. Our goal is to provide benchmark results for the electron-hole bilayer investigating the qualitative and quantitative effects of the valley degeneracy, inferred by comparison with the conventional electron-hole bilayer possessing only spin degeneracy [5].

We have studied systems of 168 particles, for in-layer densities corresponding to 1≤rs ≤8 and inter-layer distances 1≤d/aB ≤4. We find an excitonic condensate for rs≳1 at intermediate distances, whereas a quadriexciton fluid [6] and a plasma fluid are stable respectively at smaller and larger distances. The region of stability of the excitonic condensate is significantly shrunk with respect to the system without valley degeneracy [5]. Moreover we observe for the first time the formation of quadriexcitons, first predicted by Wang and  Kittel [6] 45 years ago. 


[1] Yu. E. Lozovik and V. I. Yudson, JETP Lett. 22, 274 (1975).

[2] See, e.g., J. A. Seamons et al.,  Phys. Rev. Lett. 102, 026804 (2009) and references therein.

[3] A. Perali, D. Neilson, and A. R. Hamilton, Phys. Rev. Lett. 110, 146803 (2013).

[4] J. I. A. Li, T. Taniguchiet al.,Phys. Rev. Lett. 117, 046802 (2016);  K. Lee et al.,Phys. Rev. Lett. 117, 046803 (2016).

[5] S. De Palo, F. Rapisarda, and G. Senatore, Phys. Rev. Lett. 88, 206401 (2002); R. Maezono 
et al., Phys. Rev. Lett. 110, 216407 (2013).

[6] J.S. Wang and C. Kittel, Phys. Lett. 42A, 189 (1972).