共查询到20条相似文献,搜索用时 31 毫秒
1.
Bergkvist S Rosengren A Saers R Lundh E Rehn M Kastberg A 《Physical review letters》2007,99(11):110401
A two-dimensional system of atoms in an anisotropic optical lattice is studied theoretically. If the system is finite in one direction, it is shown to exhibit a transition between a two-dimensional superfluid and a one-dimensional Mott insulating chain of superfluid tubes. Monte Carlo simulations are consistent with the expectation that the phase transition is of Kosterlitz-Thouless type. The effect of the transition on experimental time-of-flight images is discussed. 相似文献
2.
《Superlattices and Microstructures》1998,23(1):103-106
A dipole-oriented two-dimensional exciton system in electrically biased GaAs/AlGaAs coupled quantum wells has been studied through photoluminescence. The system has a sample-dependent built-in random potential which traps excitons at low temperature. The average photoluminescence photon energy shows a sudden reduction when the excitation intensity exceeds a critical value at low temperatures. This suggests a phase transition from a Bose glass to superfluid phase. 相似文献
3.
We propose the Bose-Einstein condensation and superfluidity of quasi-two-dimensional spatially indirect magnetobiexcitons in a slab of superlattice with alternating electron and hole layers consisting from the semiconducting quantum wells (QWs) and graphene superlattice in high magnetic field. For this system the instability of the ground state of interacting two-dimensional indirect magnetoexcitons in a slab of superlattice with alternating electron and hole layers in high magnetic field is found. The density of superfluid component ns(T) and the temperature of the Kosterlitz-Thouless phase transition to the superfluid state in the system of two-dimensional indirect magnetobiexcitons, interacting as electrical quadrupoles, are obtained for both QW and graphene realizations. 相似文献
4.
We have studied the collective properties of two-dimensional (2D) excitons immersed within a quantum well which contains 2D excitons and a two-dimensional electron gas (2DEG). We have also analyzed the excitations for a system of 2D dipole excitons with spatially separated electrons and holes in a pair of quantum wells (CQWs) when one of the wells contains a 2DEG. Calculations of the superfluid density and the Kosterlitz–Thouless (K–T) phase transition temperature for the 2DEG-exciton system in a quantum well have shown that the K–T transition temperature increase with increasing exciton density and that it might be possible to have fast long-range transport of excitons. The superfluid density and the K–T transition temperature for dipole excitons in CQWs in the presence of a 2DEG in one of the wells increases with increasing inter-well separation. 相似文献
5.
We study finite-temperature phase transitions in a two-dimensional boson Hubbard model with zero-point quantum fluctuations via Monte Carlo simulations of a quantum rotor model and construct the corresponding phase diagram. Compressibility shows a thermally activated gapped behavior in the insulating regime. Finite-size scaling of the superfluid stiffness clearly shows the nature of the Kosterlitz-Thouless transition. The transition temperature T(c) confirms a scaling relation T(c) proportional, rho(0)(x), with x=1.0. Some evidence of anomalous quantum behavior at low temperatures is presented. 相似文献
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7.
The Kosterlitz-Thouless phase transition in a system of exciton-polaritons in a microcavity is studied. The transition temperature
to superfluid state was found as a function of exciton-photon detuning. A nonquadratic dispersion law was taken into account
in the framework of the self-consistent harmonic approximation (SCHA).
The text was submitted by the authors in English. 相似文献
8.
The s=1 spinor Bose condensate at zero temperature supports ferromagnetic and polar phases that combine magnetic and superfluid ordering. We analyze the topological defects of the polar condensate, correcting previous studies, and show that the polar condensate in two dimensions is unstable at any finite temperature; instead, there is a nematic or paired superfluid phase with algebraic order in exp(2itheta), where theta is the superfluid phase, and no magnetic order. The Kosterlitz-Thouless transition out of this phase is driven by unbinding of half-vortices (the spin-disordered version of the combined spin and phase defects found by Zhou), and the anomalous universal 8T(c)/pi stiffness jump at the transition is confirmed in numerical simulations. The anomalous stiffness jump is a clear experimental signature of this phase and the corresponding phase transition. 相似文献
9.
We consider excitons in a two-dimensional periodic potential and study the linear response of the excitonic superfluid to an electromagnetic wave at low and high densities. It turns out that the static structure factor for small wavevectors is very sensitive to a change of density and temperature. It is a consequence of the fact that thermal fluctuations play a crucial role at small wavevectors, since exchanging the order of the two limits, zero temperature and vanishing wavevector, leads to different results for the structure factor. This effect could be used for high accuracy measurements in the superfluid exciton phase, which might be realized by a gated electron-hole gas, for instance, in coupled quantum wells or double layer materials. The transition of the exciton system from the superfluid state to a non-superfluid state and its manifestation by light scattering are discussed. 相似文献
10.
Measurements of the IV characteristics of site-diluted Josephson-junction arrays have revealed intriguing effects of percolative disorder on the phase transition and the vortex dynamics in a two-dimensional XY system. Different from other types of phase transitions, the Kosterlitz-Thouless transition was eliminated with the introduction of percolative disorder far below the percolation threshold. Even after the Kosterlitz-Thouless order had been removed, the system remained superconducting at low temperatures by establishing a different type of order. Near the percolation threshold, evidence was found that, as a consequence of the underlying fractal structure, the critical dynamics of the phase degrees of freedom persisted down to zero temperature. 相似文献
11.
We study one-dimensional disordered bosons at large commensurate filling. Using a real space renormalization group approach, we find a new random fixed point which controls a phase transition from a superfluid to an incompressible Mott glass. The transition can be tuned by changing the disorder distribution even with vanishing interactions. We derive the properties of the transition, which suggest that it is in the Kosterlitz-Thouless universality class. 相似文献
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13.
We theoretically investigate a phase transition of Frenkel exciton polaritons in an organic nanofiber. Assuming a phenomenological Hamiltonian, we derive a mean field equation for the condensation after finding an effective action for the phenomenon using the functional integral method and stationary phase analysis. From a solution of the mean field equation, we construct a phase diagram for the condensation and highlight features that distinguish J- and H-aggregates. We also detail a connection with the superradiant phase transition, which has been studied using the Dicke model. 相似文献
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15.
The formation of a superfluid exciton liquid in a system of spatially separated electrons and holes in a system of two coupled
quantum wells is predicted and its properties are investigated. The ground-state energy and the equilibrium density of the
exciton liquid are calculated as functions of distance D between the quantum wells. The properties of a rarefied exciton gas with dipole-dipole repulsions are considered, where this
gas is the metastable phase for D<1.9a* and the stable phase for D<1.9a* (a* is the radius of the two-dimensional exciton). The gas-liquid quantum transition is examined for increasing D. The Berezinskii-Kosterlitz-Thouless transition temperatures, at which superfluidity arises in the system, are found for
different values of D. Possible experimental manifestations of the predicted effects are discussed.
Zh. éksp. Teor. Fiz. 111, 1879–1895 (May 1997) 相似文献
16.
A. É. Filippov 《Physics of the Solid State》1998,40(9):1546-1549
The molecular dynamics method is used to examine the ordering of interacting subsystems in a two-component, two-dimensional
Coulomb gas, consisting of equal amounts of positively and negatively charged particles, which simulates the behavior of a
system of interacting vortices. In particular, it is found that when the system temperature is lowered from the Kosterlitz-Thouless
transition point, additional ordering of the vortex chains may take place. It is noted that this process may stimulate the
development of vortex chains observed in real superfluid, magnetic, and superconducting systems. Possible applications of
the molecular dynamics method to phase separation and the ordering of adiabatically slowly moving subsystems in the collective
field of a fast subsystem are considered.
Fiz. Tverd. Tela (St. Petersburg) 40, 1701–1704 (September 1998) 相似文献
17.
We report the calculation of cavity exciton-polariton phase diagram including realistic structural disorder. With increasing density polaritons first undergo a quasiphase transition toward a Bose glass: the condensate is localized in at least one minimum of the disorder potential. A further increase of the density leads to a percolation process of the polariton fluid giving rise to a Kosterlitz-Thouless phase transition toward superfluidity. The spatial representation of the condensate wave function as well as the spectrum of elementary excitations are obtained from the Gross-Pitaevskii equation for all the phases. 相似文献
18.
A generalized XY model with interaction V(θ) = 2 J{1 - [cos2 (θ/2)]p2} is studied by Monte Carlo renormalization group method on two-dimensional random triangle lattice. For p = √2, a line of fixed points has been found. It characterizes that there is a Kosterlitz-Thouless phase transition. For p = 2, a first order phase transition has been found. Both of them show the relationship between the nature of phase transition and the class of interactions. 相似文献
19.
The transformation of the electronic excitation energy in a plane-layered nanostructure with two-dimensional J-aggregates of a cyanine dye has been studied theoretically. The dependences of the plasmon–exciton interaction energy on the system parameters have been determined. In the case of small values of the Rabi frequency, the rates of nonradiative energy transfer from surface plasmon–polaritons of the metal substrate to molecular excitons of J-aggregates have been calculated in terms of the perturbation theory. The dispersion laws for hybrid plasmon–exciton states have been determined, and it has been shown that the Rabi splitting can range up to 100 meV. 相似文献
20.
In layered superconductors (SC) with small interlayer Josephson coupling vortex-antivortex phase fluctuations characteristic of quasi two-dimensional (2D) Kosterlitz-Thouless behavior are expected to be observable at some energy scale T(d). While in the 2D case T(d) is uniquely identified by the KT temperature T(KT) where the universal value of the superfluid density is reached, we show that in a generic anisotropic 3D system T(d) is controlled by the vortex-core energy, and can be significantly larger than the 2D scale T(KT). These results are discussed in relation to recent experiments in cuprates, which represent a typical experimental realization of layered anisotropic SC. 相似文献