Optical Flux Lattices for Ultracold Atomic Gases

We show that simple laser configurations can give rise to "optical flux lattices", in which optically dressed atoms experience a periodic effective magnetic flux with high mean density. These potentials lead to narrow energy bands with non-zero Chern number. Optical flux lattices will greatly facilitate the achievement of the quantum Hall regime for ultracold atomic gases

Skyrmions in Quantum Hall Systems with Realistic Force-Laws

We study the charged excitations of quantum Hall systems at integer filling fractions $\nu=2n+1$, for a force-law that takes account of the finite width of the electron gas. For typical values of this width, in the limit of vanishing Zeeman energy we find that the low-energy excitations are ``skyrmions'' not only at $\nu=1$ but also at higher filling fractions. Our results lead to the prediction that, in typical samples, abrupt transitions to charged excitations with very large spins should be observable at filling fractions higher than $\nu=1$ if the Zeeman energy is reduced sufficiently.Comment: 5 pages, 3 ps-figures, revtex with epsf.tex and multicol.sty. To appear in Physical Review

Designing Topological Bands in Reciprocal Space

Motivated by new capabilities to realise artificial gauge fields in ultracold atomic systems, and by their potential to access correlated topological phases in lattice systems, we present a new strategy for designing topologically non-trivial band structures. Our approach is simple and direct: it amounts to considering tight-binding models directly in reciprocal space. These models naturally cause atoms to experience highly uniform magnetic flux density and lead to topological bands with very narrow dispersion, without fine-tuning of parameters. Further, our construction immediately yields instances of optical Chern lattices, as well as band structures of higher Chern number, |C|>1

The longitudinal resistance of a quantum Hall system with a density gradient

Following recent experiments, we consider current flow in two dimensional electronic systems in the quantum Hall regime where a gradient in the electron density induces a spatial variation in the Hall resistivity. Describing the system in terms of a spatially varying local resistivity tensor, we show that in such a system the current density is generically non-uniform, with the current being pushed towards one side of the sample. We show that, for sufficiently large density gradient, the voltage along that side is determined by the change of the Hall resistivity, and is independent of the microscopic longitudinal resistivity, while the voltage on the opposite side is small and determined by both longitudinal and Hall resistivities. We solve some particular models in detail, and propose ways by which the microscopic longitudinal resistivity may be extracted from measurements of the longitudinal voltage on both sides of the sample.Comment: 9 pages, 3 figure

Exact Groundstates of Rotating Bose Gases close to a Feshbach Resonance

We study the groundstates of rotating Bose gases when interactions are affected by a nearby Feshbach resonance. We show that exact groundstates at high angular momentum can be found analytically for a general and realistic model for the resonant interactions. We identify parameter regimes where the exact groundstates are exotic fractional quantum Hall states, the excitations of which obey non-abelian exchange statistics.Comment: 4 page

Edge excitations and Topological orders in rotating Bose gases

The edge excitations and related topological orders of correlated states of a fast rotating Bose gas are studied. Using exact diagonalization of small systems, we compute the energies and number of edge excitations, as well as the boson occupancy near the edge for various states. The chiral Luttinger-liquid theory of Wen is found to be a good description of the edges of the bosonic Laughlin and other states identified as members of the principal Jain sequence for bosons. However, we find that in a harmonic trap the edge of the state identified as the Moore-Read (Pfaffian) state shows a number of anomalies. An experimental way of detecting these correlated states is also discussed.Comment: Results extended to larger systems. Improved presentatio

Optical response of high-TcT_c cuprates: possible role of scattering rate saturation and in-plane anisotropy

We present a generalized Drude analysis of the in-plane optical conductivity $\sigma_{ab}$($T$,$\omega$) in cuprates taking into account the effects of in-plane anisotropy. A simple ansatz for the scattering rate $\Gamma$($T$,$\omega$), that includes anisotropy, a quadratic frequency dependence and saturation at the Mott-Ioffe-Regel limit, is able to reproduce recent normal state data on an optimally doped cuprate over a wide frequency range. We highlight the potential importance of including anisotropy in the full expression for $\sigma_{ab}$($T$,$\omega$) and challenge previous determinations of $\Gamma$($\omega$) in which anisotropy was neglected and $\Gamma$($\omega$) was indicated to be strictly linear in frequency over a wide frequency range. Possible implications of our findings for understanding thermodynamic properties and self-energy effects in high-$T_c$ cuprates will also be discussed.Comment: 8 pages, 7 figures. To be published in Physical Review