Structural properties of the condensate in two-dimensional mesoscopic systems of strongly correlated excitons

Lozovik, Yu. E.; Volkov, S. Yu.; Willander, Magnus

doi:10.1134/1.1780555

Cited by 25 publications

(22 citation statements)

References 31 publications

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“…One has to use ab initio numerical methods to address this quantum many-body problem. Recently a trapped system of two-dimensional dipoles has been studied by Path Integral Monte Carlo method [8] and mesoscopic analog of crystallization has been found. Trapped dipoles with s-wave scattering were investigated [9].…”

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Quantum Phase Transition in a Two-Dimensional System of Dipoles

et al. 2007

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The ground-state phase diagram of a two-dimensional Bose system with dipole-dipole interactions is studied by means of quantum Monte Carlo technique. Our calculation predicts a quantum phase transition from gas to solid phase when the density increases. In the gas phase the condensate fraction is calculated as a function of the density. Using Feynman approximation, the collective excitation branch is studied and appearance of a roton minimum is observed. Results of the static structure factor at both sides of the gas-solid phase are also presented. The Lindeman ratio at the transition point comes to be γ = 0.230(6). The condensate fraction in the gas phase is estimated as a function of the density.The chromium atom has exceptionally large permanent dipole moment and recent realization of Bose-Einstein condensation of 52 Cr[1] has stimulated great interest in properties of dipolar systems at low temperatures. It was observed[2] that dipolar forces lead to anisotropic deformation during expansion of the condensate. In the experiments [1,2], the dipolar forces were competing with short-range scattering. The latter, in principle, can be removed by tuning the s-wave scattering length to zero by Feshbach resonance [3]. This would lead to an essentially pure system of dipoles. On the other hand, lowdimensional systems can be realized by making the confinement in one (or two) directions so tight, that no excitations of the levels of the tight confinement are possible and the system is dynamically two-(or one-) dimensional.A major development has also been done in the present years towards the realization of excitons at temperatures close to the Bose-Einstein condensation temperature [4]. An exciton is much more stable if the electron is spatially separated from the hole (spatially separated excitons). Such an exciton can be modeled as a dipole. If the excitons are in two coupled quantum wells they can be treated effectively as two-dimensional if the size of an exciton is small compared to the mean distance between excitons.One might expect to find a phase transition from gas phase to a crystal one at large density. As the condensate fraction is small at the transition point, perturbative theories, like Gross-Pitaevskii [5] or Bogoliubov [6,7] approaches, will fail to describe accurately this transition. One has to use ab initio numerical methods to address this quantum many-body problem. Recently a trapped system of two-dimensional dipoles has been studied by Path Integral Monte Carlo method [8] and mesoscopic analog of crystallization has been found. Trapped dipoles with s-wave scattering were investigated [9]. So far, there have been no full quantum microscopic computations of the properties of a homogeneous system of dipoles.The Hamiltonian of a homogeneous system of N bosonic dipoles has the formwhere M is the dipole mass and r i , i = 1, N are the positions of dipoles. The expression for the coupling constant C dd depends on the nature of the dipole-dipole interaction. Two possible physical realizations of a twodim...

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Quantum Phase Transition in a Two-Dimensional System of Dipoles

et al. 2007

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“…The remarkable experiments on exciton BEC have motivated rapid development of theoretical ideas 38 . Many interesting effects have been predicted for exciton BECs: existence of non-dissipative electric currents 39 and internal Josephson effect 40 , roton instability 41 , autolocalization 42 and (mesoscopic 43 ) supersolidity 44,45 , BKT transition 46 (crossover 47 ) and vortex formation 48 , features of angle-resolved photoluminescence 49 and nonlinear optical phenomena 50 , as well as topological excitons 51 , dipole superconductivity 52 , and Casimir effect 53 . Another interesting topic are exciton spin effects that have been predicted to lead to a multicomponent BEC 22 , which has been recently observed experimentally 54 .…”

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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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“…A model Bose-Hubbard Hamiltonian has been used to describe a dipole gas in optical lattices and a rich phase diagram was found [5,12]. So far there have been no full quantum microscopic computations of the properties of a homogeneous system.…”

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“…In this case C dd = e 2 D 2 /ε, where e is an electron's charge, ε is the dielectric constant of the semiconductor, and D is the distance between the centers of the quantum wires. This system is 1D counterpart of 2D indirect exciton system in coupled quantum wells, which was extensively studied both theoretically [14,15,16,17], [5] and experimentally [18]. The properties of 1D and 2D systems differ essentially (see below Tonks-Girardeau regime, etc.…”

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Ground-state properties of a one-dimensional system of dipoles

et al. 2005

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A one-dimensional (1D) Bose system with dipole-dipole repulsion is studied at zero temperature by means of a Quantum Monte Carlo method. It is shown that in the limit of small linear density the bosonic system of dipole moments acquires many properties of a system of non-interacting fermions. At larger linear densities a Variational Monte Carlo calculation suggests a crossover from a liquidlike to a solid-like state. The system is superfluid on the liquid-like side of the crossover and is normal in the deep on the solid-like side. Energy and structural functions are presented for a wide range of densities. Possible realizations of the model are 1D Bose atom systems with permanent dipoles or dipoles induced by static field or resonance radiation, or indirect excitons in coupled quantum wires, etc. We propose parameters of a possible experiment and discuss manifestations of the zero-temperature quantum crossover.Up until now Bose-Einstein condensation has been realized in many different atom and molecule species with short-range interactions. At low temperatures such an interaction can be described by a s-wave scattering length and is commonly approximated by a contact pseudopotential. In contrast, some recent work has focused on the realization of dipole condensates [1,2,3,4,5]. In these systems, the dipole-dipole interaction extends to much larger distances and significant differences in the properties (such as the phase diagram and correlation functions) are expected. Another appealing aspect of a system of dipole moments is the relative ease of tuning the effective strength of interactions [6] which makes the system highly controllable. Dipole particles are also considered to be a promising candidate for the implementation of quantum-computing schemes [7,8,9].On the theoretical side dipole condensates have been mainly studied on a semiclassical (Gross-Pitaevskii) [10] or Bogoliubov [11] level. A model Bose-Hubbard Hamiltonian has been used to describe a dipole gas in optical lattices and a rich phase diagram was found [5,12]. So far there have been no full quantum microscopic computations of the properties of a homogeneous system.Recently the Monte Carlo method was used to study helium and molecular hydrogen in nanotubes [13]. Such a geometry, which is effectively one dimensional, leads to completely different properties compared to a threedimensional sample.We consider N repulsive dipole moments of mass M located on a line. The Hamiltonian of such a system is given bŷWe keep in mind two different possible realizations: 1) Cold bosonic atoms, with induced or static dipole momenta, in a transverse trap so tight that excitations of the levels of the transverse confinement are not possible and the system is dynamically one-dimensional. The dipoles themselves can be either induced or permanent. In the case of dipoles induced by an electric field E the coupling has the form C dd = E 2 α 2 , where α is the static polarizability. For permanent magnetic dipoles aligned by an external magnetic field one has C dd = m 2 ...

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Structural properties of the condensate in two-dimensional mesoscopic systems of strongly correlated excitons

Cited by 25 publications

References 31 publications

Quantum Phase Transition in a Two-Dimensional System of Dipoles

Quantum Phase Transition in a Two-Dimensional System of Dipoles

Anisotropic superfluidity of two-dimensional excitons in a periodic potential

Ground-state properties of a one-dimensional system of dipoles

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