2D Boson Research Articles

A giant shot of radiation intensity as eventualevidence of Bose-Einstein condensation of excitons in doublequantum wells in GaAs/AlGaAs

In this paper we present a low-temperature (T<30 K)photoluminescence (PL) study of space-indirect excitons inGaAs/AlGaAs double quantum wells at pumping density P andexternal electric field Vdc. At certainexternal parameter values (P, T and Vdc) part of thespectral profile of the indirect exciton (IX) line reveals anenormous increase (shot) of PL intensity (threefold), whichfluctuates in time on the characteristic scale of tens ofseconds. To explain this anomalous behaviour we use thetheoretical model of the Bose-Einstein condensation effect whichtakes place in a system of 2D bosons which, in addition toextended states, have a discrete energy spectrum below thebottom of the free zone.

Excited State Effects in the Dielectric Function of a 2D Boson System

We present calculations for the dielectric function and collective modes of a two-dimensional interacting gas of bosons (excitons) in the xy plane which can be polarized by the application of an electric field in the z direction. Previous work has explored the response of the density fluctuations while excitons lie in their intrinsic ground state. We extend the formalism here by taking into account the internal degrees of freedom of the excitons, and their possible interplay with the density-fluctuation modes of the system. In the limit of low temperature, we find collective normal modes related to the various degrees of freedom. Our calculations of the corresponding intrinsic oscillator strength show that optical-like modes associated to the excited states become increasingly damped when temperature is raised, as the occupation factors change the overall response.

Bose-Einstein condensation in a two-dimensional, trapped, interacting gas

We study the Bose-Einstein condensation phenomenon in a two-dimensional (2D) system of bosons subjected to a harmonic-oscillator-type confining potential. The interaction among the 2D bosons is described by a \ensuremath{\delta} function in configuration space. Solving the Gross-Pitaevskii equation within the two-fluid model we calculate the condensate fraction, ground-state energy, and specific heat of the system. Our results indicate that interacting bosons have similar behavior to those of an ideal system for weak interactions.

Vortices and 2D Bosons: A Path-Integral Monte Carlo Study

The vortex system in a high-T_c superconductor has been studied numerically using the mapping to 2D bosons and the path-integral Monte Carlo method. We find a single first-order transition from an Abrikosov lattice to an entangled vortex liquid. The transition is characterized by an entropy jump dS = 0.4 k_B per vortex and layer (parameters for YBCO) and a Lindemann number c_L = 0.25. The increase in density at melting is given by d\rho = 6.0*10^{-4} / \lambda(T)^2. The vortex liquid corresponds to a bosonic superfluid, with \rho_s = \rho even in the limit \lambda -> \infty.

Helicity modulus and fluctuating type-II superconductors: Elastic approximation and numerical simulations

We develop the helicity modulus as a criterion for superconducting order in the mixed phase of a fluctuating type II superconductor. We show that there is a duality relation between this helicity modulus and the superfluid density of a system of analog 2D bosons. We show that the vortex line lattice exhibits a perfect Meissner effect with respect to a shearing perturbation of the applied magnetic field, and this becomes our creterion for "longitudinal superconductivity" parallel to the applied field. We present arguments based on the 2D boson analogy, as well as the results of numerical simulations, that suggest that longitudinal superconductivity can persist into the vortex line liquid state for systems of finite thickness, comparable to those commonly found in experiments.

Canonical Bose-Einstein condensation of interacting bosons in two dimensions

The onset of Bose-Einstein condensation in a 2D gas of bosons in a parabolic confinement potential is investigated. For such a system of non-interacting bosons, both the grand-canonical and the canonical partition function are calculated. The canonical partition function of a system of harmonically interacting bosons in 2D is obtained analytically. Both in the case of interacting and of non-interacting bosons, a distinct peak in the specific heat is found at a critical temperature and the dependence of this critical temperature on the number of particles and on the interparticle interaction strength is investigated.

Bose and vortex glasses in high temperature superconductors.

A theory of the Bose glass transition is developed. Mapping vortex trajectories onto world lines of 2D bosons gives a glass transition line as the locus where bosons become localized in the random potential. We describe the glass-to-liquid transition induced by columnar disorder in both dilute and dense vortex systems. A vortex glass transition in the light of the developed description is discussed.

Eikonal approximation in the theory of two-dimensional fermions with long-range current-current interactions.

We study the behavior of response functions of two-dimensional (2D) fermions interacting via a long-range transverse gauge field in the eikonal approximation. We observe that an exponentially vanishing wave-function renormalization prevents divergences in the density-density correlation function and the pairing susceptibility. The wave-function renormalization also shows up in a suppression of the dHvA effect. Elaborating on an observation recently made by Ioffe, Lidsky, and Altschuler, we also infer an effective bosonic description which makes it possible to reproduce our eikonal results in terms of free 2D bosons.

ANYON SUPERCONDUCTIVITY AND CHARGE-VORTEX DUALITY

We review recent work on a bosonic formulation of both anyon superconductivity and the fractional quantum Hall effect (FQHE). Central to this approach is the concept of charge-vortex duality in two-dimensional (2d) boson systems. A formal duality transformation which takes one from a particle to a vortex representation of a 2d boson model is described in detail. The duality transformation is employed to obtain detailed properties of both the FQHE hierarchy and a hierarchy of anyon superconducting phases.

Fermionizing the Z 2-orbifold

We demonstrate the equivalence of free 2D bosons, taking values on a symmetric Z 2-orbifold, to various fermionic theories. The fermions satisfy boundary conditions like ω(−π, t)=ω ∗(π, t) and can be free or interact through Thirring couplings.