Tunneling effect on composite fermion pairing state in bilayer quantum Hall system

We discuss the composite fermion pairing state in bilayer quantum Hall systems. After the evaluation of the range of the inter-layer separation in which the quantum Hall state is stabilized, we discuss the effect of inter-layer tunneling on the composite fermion pairing state at \nu=1/2. We show that there is a cusp at the transition point between the Halperin (3,3,1) state and the Pfaffian state.Comment: 6 pages, 4 figures, accepted for publication in Phys. Rev.

Theory of Incompressible States in a Narrow Channel

We report on the properties of a system of interacting electrons in a narrow channel in the quantum Hall effect regime. It is shown that an increase in the strength of the Coulomb interaction causes abrupt changes in the width of the charge-density profile of translationally invariant states. We derive a phase diagram which includes many of the stable odd-denominator states as well as a novel fractional quantum Hall state at lowest half-filled Landau level. The collective mode evaluated at the half-filled case is strikingly similar to that for an odd-denominator fractional quantum Hall state.Comment: 4 pages, REVTEX, and 4 .ps file

Parity Effect in a Small Superconducting Particle

Matveev and Larkin calculated the parity effect on the ground state energy of a small superconducting particle in the regimes where the mean level spacing is either large or small compared to the bulk gap. We perform a numerical calculation which extends their results into the intermediate regime, where the level spacing is of the same order as the bulk gap.Comment: 6 LaTeX pages, including 2 EPS figures; corrected reference and spellin

Spin phase diagram of the nu_e=4/11 composite fermion liquid

Spin polarization of the "second generation" nu_e=4/11 fractional quantum Hall state (corresponding to an incompressible liquid in a one-third-filled composite fermion Landau level) is studied by exact diagonalization. Spin phase diagram is determined for GaAs structures of different width and electron concentration. Transition between the polarized and partially unpolarized states with distinct composite fermion correlations is predicted for realistic parameters.Comment: 5 pages, 3 figure

Tuning of the Gap in a Laughlin-Bychkov-Rashba Incompressible Liquid

We report on our investigation of the influence of Bychkov-Rashba spin-orbit interaction (SOI) on the incompressible Laughlin state. We find that experimentally obtainable values of the spin-orbit coupling strength can induce as much as a 25% increase in the quasiparticle-quasihole gap Eg at low magnetic fields in InAs, thereby increasing the stability of the liquid state. The SOI-modulated enhancement of Eg is also significant for filling factors 1/5 and 1/7, where the FQH state is usually weak. This raises the intriguing possibility of tuning, via the SO coupling strength, the liquid to solid transition to much lower densities.Comment: 4 pages, 3 figure

Can Induced Theta Vacua be Created in Heavy Ion Collisions?

The development of the early Universe is a remarkable laboratory for the study of most nontrivial properties of particle physics. What is more remarkable is the fact that these phenomena at the QCD scale can be, in principle, experimentally tested in heavy ion collisions. We expect that, in general, an arbitrary theta-state would be created in the heavy ion collisions, similar to the creation of the disoriented chiral condensate with an arbitrary isospin direction. It should be a large domain with a wrong $\theta\neq 0$ orientation. We test this idea numerically in a simple model where we study the evolution of the phases of the chiral condensates in QCD with two quark flavors with non-zero theta-parameter. We see the formation of a non-zero theta-vacuum with the formation time of the order of $10^{-23}$ seconds. This result will have important implications for a possible axion search experiment at RHIC.Comment: 4 pages, 3 figures, Latex, Discussion of experimental signatures adde

Optical-conductivity sum rule in cuprates and unconventional charge density waves: a short review

We begin with an overview of the experimental results for the temperature and doping dependences of the optical-conductivity spectral weight in cuprate superconductors across the whole phase diagram. Then we discuss recent attempts to explain the observed behavior of the spectral weight using reduced and full models with unconventional $d_{x^2-y^2}$ charge-density waves.Comment: 17 pages, RevTeX4, 4 EPS figures; Invited paper for a special issue of Low Temperature Physics dedicated to the 20th anniversary of HTS

Spin textures, screening and excitations in dirty quantum Hall ferromagnets

We study quantum Hall ferromagnets in the presence of a random electrostatic impurity potential. Describing these systems with a classical non-linear sigma model and using analytical estimates supported by results from numerical simulations, we examine the nature of the ground state as a function of disorder strength, $\Delta$, and deviation, $\delta \nu$, of the average Landau level filling factor from unity. Screening of an impurity potential requires distortions of the spin configuration, and in the absence of Zeeman coupling there is a disorder-driven, zero-temperature phase transition from a ferromagnet at small $\Delta$ and $|\delta \nu|$ to a spin glass at larger $\Delta$ or $|\delta \nu|$. We examine ground-state response functions and excitations.Comment: 4 pages, 3 figure

Response Function of the Fractional Quantized Hall State on a Sphere II: Exact Diagonalization

We study the excitation spectra and the dynamical structure factor of quantum Hall states in a finite size system through exact diagonalization. Comparison is made between the numerical results so obtained and the analytic results obtained from a modified RPA in the preceding companion paper. We find good agreement between the results at low energies.Comment: 22 pages (REVTeX 3.0). 10 figures available on request. Complete postscript file (including figures) for this paper are available on the World Wide Web at http://cmtw.harvard.edu/~simon/ ; Preprint number HU-CMT-94S0

Fluctuation-Driven Quantum Phase Transitions in Clean Itinerant Ferromagnets

The quantum phase transition in clean itinerant ferromagnets is analyzed. It is shown that soft particle-hole modes invalidate Hertz's mean-field theory for $d \leq 3$. A renormalized mean-field theory predicts a fluctuation-induced first order transition for $1 < d \leq 3$, whose stability is analyzed by renormalization group techniques. Depending on microscopic parameter values, the first order transition can be stable, or be pre-empted by a fluctuation-induced second order transition. The critical behavior at the latter is determined. The results are in agreement with recent experiments.Comment: 4 pp., REVTeX, no figs; final version as publishe