Occupation of a resonant level coupled to a chiral Luttinger liquid

We consider a resonant level coupled to a chiral Luttinger liquid which can be realized, e.g., at a fractional quantum Hall edge. We study the dependence of the occupation probability n of the level on its energy \epsilon for various values of the Luttinger-liquid parameter g. At g<1/2 a weakly coupled level shows a sharp jump in n(\epsilon) at the Fermi level. As the coupling is increased, the magnitude of the jump decreases until \sqrt{2g}, and then the discontinuity in n(\epsilon) disappears. We show that n(\epsilon) can be expressed in terms of the magnetization of a Kondo impurity as a function of magnetic field.Comment: 5 pages including 1 figur

Generalized two-leg Hubbard ladder at half-filling: Phase diagram and quantum criticalities

The ground-state phase diagram of the half-filled two-leg Hubbard ladder with inter-site Coulomb repulsions and exchange coupling is studied by using the strong-coupling perturbation theory and the weak-coupling bosonization method. Considered here as possible ground states of the ladder model are four types of density-wave states with different angular momentum (s-density-wave state, p-density-wave state, d-density-wave state, and f-density-wave state) and four types of quantum disordered states, i.e., Mott insulating states (S-Mott, D-Mott, S'-Mott, and D'-Mott states, where S and D stand for s- and d-wave symmetry). The s-density-wave state, the d-density-wave state, and the D-Mott state are also known as the charge-density-wave (CDW) state, the staggered-flux (SF) state, and the rung-singlet state, respectively. Strong-coupling approach naturally leads to the Ising model in a transverse field as an effective theory for the quantum phase transitions between the SF state and the D-Mott state and between the CDW state and the S-Mott state, where the Ising ordered states correspond to doubly degenerate ground states in the staggered-flux or the charge-density-wave state. From the weak-coupling bosonization approach it is shown that there are three cases in the quantum phase transitions between a density-wave state and a Mott state: the Ising (Z_2) criticality, the SU(2)_2 criticality, and a first-order transition. The quantum phase transitions between Mott states and between density-wave states are found to be the U(1) Gaussian criticality. The ground-state phase diagram is determined by integrating perturbative renormalization-group equations. It is shown that the S-Mott state and the SF state exist in the region sandwiched by the CDW phase and the D-Mott phase.Comment: 21 pages, 10 figure

Resonant tunnelling in interacting 1D systems with an AC modulated gate

We present an analysis of transport properties of a system consisting of two half-infinite interacting one-dimensional wires connected to a single fermionic site, the energy of which is subject to a periodic time modulation. Using the properties of the exactly solvable Toulouse point we derive an integral equation for the localised level Keldysh Green's function which governs the behaviour of the linear conductance. We investigate this equation numerically and analytically in various limits. The period-averaged conductance G displays a surprisingly rich behaviour depending on the parameters of the system. The most prominent feature is the emergence of an intermediate temperature regime at low frequencies, where G is proportional to the line width of the respective static conductance saturating at a non-universal frequency dependent value at lower temperatures.Comment: 12 pages, 3 figures (eps files

Conductance of a helical edge liquid coupled to a magnetic impurity

Transport in an ideal two-dimensional quantum spin Hall device is dominated by the counterpropagating edge states of electrons with opposite spins, giving the universal value of the conductance, $2e^2/h$. We study the effect on the conductance of a magnetic impurity, which can backscatter an electron from one edge state to the other. In the case of isotropic Kondo exchange we find that the correction to the electrical conductance caused by such an impurity vanishes in the dc limit, while the thermal conductance does acquire a finite correction due to the spin-flip backscattering.Comment: 5 pages, 2 figure