Spin-charge coupling in quantum wires at zero magnetic field

We discuss an approximation for the dynamic charge response of nonlinear spin-1/2 Luttinger liquids in the limit of small momentum. Besides accounting for the broadening of the charge peak due to two-holon excitations, the nonlinearity of the dispersion gives rise to a two-spinon peak, which at zero temperature has an asymmetric line shape. At finite temperature the spin peak is broadened by diffusion. As an application, we discuss the density and temperature dependence of the Coulomb drag resistivity due to long-wavelength scattering between quantum wires.Comment: 16 pages, 5 figures. This is an extended version of "Coulomb drag from spin-charge coupling at zero magnetic field

Disentangling Scaling Properties in Anisotropic Fracture

Structure functions of rough fracture surfaces in isotropic materials exhibit complicated scaling properties due to the broken isotropy in the fracture plane generated by a preferred propagation direction. Decomposing the structure functions into the even order irreducible representations of the SO(2) symmetry group (indexed by $m=0,2,4...$) results in a lucid and quickly convergent description. The scaling exponent of the isotropic sector ($m=0$) dominates at small length scales. One can reconstruct the anisotropic structure functions using only the isotropic and the first non vanishing anisotropic sector ($m=2$) (or at most the next one ($m=4$)). The scaling exponent of the isotropic sector should be observed in a proposed, yet unperformed, experiment.Comment: 5 pages, 8 figure

Adiabatic Pumping in Interacting Systems

A dc current can be pumped through an interacting system by periodically varying two independent parameters such as magnetic field and a gate potential. We present a formula for the adiabatic pumping current in general interacting systems, in terms of instantaneous properties of the system, and find the limits for its applicability. This formula generalizes the scattering approach for noninteracting pumps. We study the pumped spin in a system that exhibits the two-channel Kondo effect as an application of the adiabatic pumping formula. We find that a quantized spin of $\hbar$ is transferred between the two channels as the temperature approaches zero, and discuss the non-Fermi liquid features of this system at finite temperatures.Comment: 4 pages and 1 figur

Condensation of Photons coupled to a Dicke Field in an Optical Microcavity

Motivated by recent experiments reporting Bose-Einstein condensation (BEC) of light coupled to incoherent dye molecules in a microcavity, we show that due to a dimensionality mismatch between the 2D cavity-photons and the 3D arrangement of molecules, the relevant molecular degrees of freedom are collective Dicke states rather than individual excitations. For sufficiently high dye concentration the coupling of the Dicke states with light will dominate over local decoherence. This system also shows Mott criticality despite the absence of an underlying lattice in the limit when all dye molecules become excited.Comment: 4 pages + supplementary materia

Two-dimensional Valence Bond Solid (AKLT) states from t2gt_{2g} electrons

Two-dimensional AKLT model on a honeycomb lattice has been shown to be a universal resource for quantum computation. In this valence bond solid, however, the spin interactions involve higher powers of the Heisenberg coupling $(\vec{S}_i \cdot \vec{S}_j)^n$, making these states seemingly unrealistic on bipartite lattices, where one expects a simple antiferromagnetic order. We show that those interactions can be generated by orbital physics in multiorbital Mott insulators. We focus on $t_{2g}$ electrons on the honeycomb lattice and propose a physical realization of the spin-$3/2$ AKLT state. We find a phase transition from the AKLT to the Neel state on increasing Hund's rule coupling, which is confirmed by density matrix renormalization group (DMRG) simulations. An experimental signature of the AKLT state consists of protected, free spins-1/2 on lattice vacancies, which may be detected in the spin susceptibility