The fermionic limit of the delta-function Bose gas: a pseudopotential approach

We use first-order perturbation theory near the fermionic limit of the delta-function Bose gas in one dimension (i.e., a system of weakly interacting fermions) to study three situations of physical interest. The calculation is done using a pseudopotential which takes the form of a two-body delta''-function interaction. The three cases considered are the behavior of the system with a hard wall, with a point where the strength of the pseudopotential changes discontinuously, and with a region of finite length where the pseudopotential strength is non-zero (this is sometimes used as a model for a quantum wire). In all cases, we obtain exact expressions for the density to first order in the pseudopotential strength. The asymptotic behaviors of the densities are in agreement with the results obtained from bosonization for a Tomonaga-Luttinger liquid, namely, an interaction dependent power-law decay of the density far from the hard wall, a reflection from the point of discontinuity, and transmission resonances for the interacting region of finite length. Our results provide a non-trivial verification of the Tomonaga-Luttinger liquid description of the delta-function Bose gas near the fermionic limit.Comment: LaTeX, 17 pages, no figure

A multispecies Calogero-Sutherland model

Motivated by the concept of ideal mutual statistics, we study a multispecies Calogero-Sutherland model in which the interaction parameters and masses satisfy some specific relations. The ground state is exactly solvable if those relations hold, both on a circle and on a line with a simple harmonic potential. In the latter case, the one-particle densities can be obtained using a generalization of the Thomas-Fermi method. We calculate the second virial coefficients in the high temperature expansion for the pressure. We show that the low-energy excitations are the same as those of a Gaussian conformal field theory. Finally, we discuss similar relations between the statistics parameters and charges for a multispecies anyon model in a magnetic field.Comment: 27 pages, LaTeX, no figures; all sections have been significantly expanded from the previous version of 13 pages; a new section on low-energy excitations; to appear in Nucl. Phys.

Semiclassical analysis of two- and three-spin antiferromagnets and anyons on a sphere

We do a semiclassical analysis for two or three spins which are coupled antiferromagnetically to each other. The semiclassical wave functions transform correctly under permutations of the spins if one takes into account the Wess-Zumino term present in the path integral for spins. The Wess-Zumino term here is a total derivative which has no effect on the energy spectrum. The semiclassical problem is related to that of anyons moving on a sphere with the statistics parameter $\theta$ being $2 \pi S$ for two spins and $3 \pi S$ for three spins. Finally, we present a novel way of deriving the semiclassical wave functions from the spin wave functions.Comment: 16 pages, plain tex, 1 figure available on request, IISc-CTS-93-

Integers and Fractions

This article briefly reviews the quantum Hall effect and the contributions of the winners of the 1998 Nobel Prize in Physics.Comment: LaTeX, 6 pages, no figures. On the 1998 Nobel Prize in Physics. To appear in Current Scienc

Non-equilibrium Green's function formalism and the problem of bound states

The non-equilibrium Green's function formalism for infinitely extended reservoirs coupled to a finite system can be derived by solving the equations of motion for a tight-binding Hamiltonian. While this approach gives the correct density for the continuum states, we find that it does not lead, in the absence of any additional mechanisms for equilibration, to a unique expression for the density matrix of any bound states which may be present. Introducing some auxiliary reservoirs which are very weakly coupled to the system leads to a density matrix which is unique in the equilibrium situation, but which depends on the details of the auxiliary reservoirs in the non-equilibrium case.Comment: Revtex4, 32 pages including 5 figures; some corrections made, this is the version published in Phys Rev

One-dimensional fermions with incommensurate hopping close to dimerization

We study the spectrum of fermions hopping on a chain with a weak incommensuration close to dimerization; both q, the deviation of the wave number from pi, and delta, the strength of the incommensuration, are small. For free fermions, we use a continuum Dirac theory to show that there are an infinite number of bands which meet at zero energy as q approaches zero. In the limit that the ratio q/delta ---> 0, the number of states lying inside the q = 0 gap is nonzero and equal to 2 delta / pi^2. Thus the limit q ---> 0 differs from q = 0; this can be seen clearly in the behavior of the specific heat at low temperature. For interacting fermions or the XXZ spin-1/2 chain, we use bosonization to argue that similar results hold.Comment: Revtex, 9 pages including 2 epsf figure