Effects of density imbalance on the BCS-BEC crossover in semiconductor electron-hole bilayers

Pieri, P.; Neilson, David; Strinati, G. C.

doi:10.1103/physrevb.75.113301

Cited by 72 publications

(109 citation statements)

References 51 publications

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“…(Here k ðeÞ F and k ðhÞ F are the Fermi wave numbers in the layers with n-and p-doping, respectively.) Indeed, such a mismatch is expected 61 to weaken the robustness of the exciton-condensate phase in which the condensed e-h pairs have zero total momentum ' K. However, preliminary calculations including screening in the condensed phase [62][63][64] ARTICLE persists even in the presence of these values of Dk F , with T c scales comparable to those reported here. On the other hand, a mismatch in the Fermi wave numbers of the two fluids may favour Fulde-Ferrell-Larkin-Ovchinnikov 65 or Sarma 66 phases.…”

Section: Discussionsupporting

confidence: 57%

“…However, it was shown theoretically that e-h superfluidity can only appear at experimentally reachable temperatures when the system is already in the so-called BCS-BEC crossover 64 . In this regime, superfluidity is robust against density imbalance, and there is strong evidence from both theory and experiment 61,68,69 that it is not killed by the Fermi surface mismatches up to 50%.…”

Section: Discussionmentioning

confidence: 95%

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Anomalous low-temperature Coulomb drag in graphene-GaAs heterostructures

et al. 2014

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Vertical heterostructures combining different layered materials offer novel opportunities for applications and fundamental studies. Here we report a new class of heterostructures comprising a single-layer (or bilayer) graphene in close proximity to a quantum well created in GaAs and supporting a high-mobility two-dimensional electron gas. In our devices, graphene is naturally hole-doped, thereby allowing for the investigation of electron-hole interactions. We focus on the Coulomb drag transport measurements, which are sensitive to many-body effects, and find that the Coulomb drag resistivity significantly increases for temperatures o5-10 K. The low-temperature data follow a logarithmic law, therefore displaying a notable departure from the ordinary quadratic temperature dependence expected in a weakly correlated Fermi-liquid. This anomalous behaviour is consistent with the onset of strong interlayer correlations. Our heterostructures represent a new platform for the creation of coherent circuits and topologically protected quantum bits.

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Section: Discussionsupporting

confidence: 57%

Section: Discussionmentioning

confidence: 95%

Anomalous low-temperature Coulomb drag in graphene-GaAs heterostructures

et al. 2014

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“…Fermionic (electron/hole) exchange effects in exciton-exciton interactions 21 which destroy "boseness" of excitons 22 and are disastrous [23][24][25] for the BEC are suppressed at low densities if the dipole-dipole interaction of excitons is sufficiently strong 26,27 . Excessive carriers 28 also suppressing BEC 29,30 can be compensated by injection of carriers with an opposite charge 10 . Finally, in the spatially separated 31,32 continuous wave pumping regime cooled (charge compensated 33 ) excitons flow to the studied area of the QW.…”

Section: Introductionmentioning

confidence: 99%

Anisotropic superfluidity of two-dimensional excitons in a periodic potential

2017

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We study anisotropies of helicity modulus, excitation spectrum, sound velocity and angle-resolved luminescence spectrum in a two-dimensional system of interacting excitons in a periodic potential. Analytical expressions for anisotropic corrections to the quantities characterizing superfluidity are obtained. We consider particularly the case of dipolar excitons in quantum wells. For GaAs/AlGaAs heterostructures as well as MoS2/hBN/MoS2 and MoSe2/hBN/WSe2 transition metal dichalcogenide bilayers estimates of the magnitude of the predicted effects are given. We also present a method to control superfluid motion and to determine the helicity modulus in generic dipolar systems.

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“…However, the independent tunability of the hopping integral t 1,2 (or the effective bandwidth) within each layer has no counterpart in the case of superconductors. We note that the parameters t 1,2 are related to the effective mass m 1,2 appearing in the continuum limit [18,19]. When ξ k,1 = −ξ k,2 , the first term on the RHS disappears, while the first term in the square is maximized.…”

mentioning

confidence: 99%

Exciton condensate modulation in electron-hole bilayers: A real-space visualization

Zhu

Bishop

2010

Phys. Rev. B

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We study the texture of the exciton condensate at low temperatures in an independently gated electron-hole bilayer system. A model Hamiltonian is solved in real space within a mean-field approximation. It is found that, with increased electron-hole density polarization, the system experiences phase transformations from the zero center-of-mass momentum superfluid state, through one-and two-dimensional exciton pair modulated states, into the normal state. At weak density polarization, the modulating state resembles the Larkin-Ovchinikov state in superconductors in the presence of an exchange field in the weak-coupling BCS limit, and becomes stripe-like in the strong coupling BEC limit. In the one-dimensional modulated phase, the density of states exhibits low-energy intra-gap resonance quasiparticle states, which are localized in the nodal region. The Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state [1,2] represents a class of unconventional superconducting states, where the superconducting order parameter modulates in real space. It is dual to the other more familiar class of unconventional superconducting states, in which the superconducting order parameter modulates (or even changes sign) in momentum space. In the FFLO state, the Cooper pairs form between two electrons with (k + q/2, ↑) and (−k + q/2, ↓) of momentum and spin configuration. The center-of-mass momentum q is dependent on the extent to which the Fermi surface is Zeeman split by an exchange field. Although the FFLO state was predicted more than four decades ago, an undisputed verification of this state in superconductors remains a great experimental challenge. A major reason lies in the fact that, in most superconductors, the Pauli paramagnetic effect of the applied magnetic field is negligibly small compared with the orbital breaking effect. Owing to recent advances in the discovery of new materials and new technology, there is a revival of interest in the FFLO-type modulated states in a wide range of systems. Among them, newly discovered heavy fermion superconductors [3,4,5], low-dimensional organic superconductors [6,7,8,9,10], and trapped cold Fermion atoms [11,12,13,14,15,16] are good candidates for the emergence of a superconducting FFLO state. In parallel, semiconductor bilayer systems [17] represent another promising context for the concept of FFLO-like states and the fundamental physics of the BCS-BEC crossover, in which there is condensation of electron and hole pairs.In electron-hole bilayers, the density of the electrons and holes can be varied independently of each other. The effect of electron-hole density imbalance here resembles the exchange effect of an applied magnetic field in a superconductor. Such an effect on the BCS-BEC crossover in semiconductor electron-hole bilayers has recently been investigated at zero temperature by Pieri and co-workers [18], where an instability toward to the FFLO phase was identified. A more recent study [19], by treating the FFLO phase and the Sarma phase [20] on an equal footing, indicated that the FFLO ...

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Effects of density imbalance on the BCS-BEC crossover in semiconductor electron-hole bilayers

Cited by 72 publications

References 51 publications

Anomalous low-temperature Coulomb drag in graphene-GaAs heterostructures

Anomalous low-temperature Coulomb drag in graphene-GaAs heterostructures

Anisotropic superfluidity of two-dimensional excitons in a periodic potential

Exciton condensate modulation in electron-hole bilayers: A real-space visualization

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