Tigran Sedrakyan

Vortices in spin-orbit-coupled Bose-Einstein condensates

Realistic methods to create vortices in spin-orbit-coupled Bose-Einstein condensates are discussed. It is shown that, contrary to common intuition, rotation of the trap containing a spin-orbit condensate does not lead to an equilibrium state with static vortex structures but gives rise instead to nonequilibrium behavior described by an intrinsically time-dependent Hamiltonian. We propose here the following alternative methods to induce thermodynamically stable static vortex configurations: (i) to rotate both the lasers and the anisotropic trap and (ii) to impose a synthetic Abelian field on top of synthetic spin-orbit interactions. Effective Hamiltonians for spin-orbit condensates under such perturbations are derived for most currently known realistic laser schemes that induce synthetic spin-orbit couplings. The Gross-Pitaevskii equation is solved for several experimentally relevant regimes. The new interesting effects include spatial separation of left- and right-moving spin-orbit condensates, the appearance of unusual vortex arrangements, and parity effects in vortex nucleation where the topological excitations are predicted to appear in pairs. All these phenomena are shown to be highly nonuniversal and depend strongly on a specific laser scheme and system parameters.

Penetration of external field into regular and random arrays of nanotubes: Implications for field emission

We develop an analytical theory of polarization of a vertically aligned array of carbon nanotubes (NTs) in external electric field. Such arrays are commonly utilized in field-emission devices, due to the known electrostatic effect of strong field enhancement near the tip of an individual NT. A small ratio of the NT radius to the separation between neighboring NTs allows us to obtain asymptotically exact solution for the distribution of induced charge density along the NT axes. For a regular array, this solution allows us to trace the suppression of the field penetration with increasing the density of NTs in the array. We demonstrate that for a random array, fluctuations in the NT density terminate the applicability of our result at distances from the NT tips much larger than the field penetration depth, where the induced charge density is already exponentially small. Our prime conclusion is that, due to collective screening of the external field by the array, the field-emission current decreases drastically for dense arrays compared to an individual NT. We argue that the reason why the strong field emission, described by the Fowler-Nordheim law and observed in realistic arrays, is the strong dispersion in heights of the constituting NTs.

Composite fermion state of spin-orbit coupled bosons

Department of Physics, Yale University, New Haven, Connecticut 06520, USA(Dated: August 31, 2012)We consider spinor Bose gas with the isotropic Rashba spin-orbit coupling in 2D. We argue that atlow density its groundstate is a composite fermion state with a Chern-Simons gauge field and fillingfactor one. The chemical potential of such a state scales with the density as µ ∝ n

Crossover from Weak Localization to Shubnikov-de Haas Oscillations in a High-Mobility 2D Electron Gas

We study the magnetoresistance deltarho(xx)(B)/rho(0) of a high-mobility 2D electron gas in the domain of magnetic fields B, intermediate between the weak localization and the Shubnikov-de Haas oscillations, where deltarho(xx)(B)/rho(0) is governed by the interaction effects. Assuming short-range impurity scattering, we demonstrate that in the second order in the interaction parameter lambda a linear B dependence, deltarho(xx)(B)/rho(0) approximately lambda(2)omega(c)/E(F) with a temperature-independent slope, emerges in this domain of B (here omega(c) and E(F) are the cyclotron frequency and the Fermi energy, respectively). Unlike previous mechanisms, the linear magnetoresistance is unrelated to the electron executing the full Larmour circle, but rather originates from the impurity scattering via the B dependence of the phase of the impurity-induced Friedel oscillations.

Absence of Bose condensation on lattices with moat bands

We study hard-core bosons on a class of frustrated lattices with the lowest Bloch band having a degenerate minimum along a closed contour, the moat, in the reciprocal space. We show that at small density the ground state of the system is given by a noncondensed state, which may be viewed as a state of fermions subject to Chern-Simons gauge field. At fixed density of bosons, such a state exhibits domains of incompressible liquids. Their fixed densities are given by fractions of the reciprocal-space area enclosed by the moat.

Pseudogap in underdoped cuprates and spin-density-wave fluctuations

We analyze fermionic spectral function in the spin-density-wave (SDW) phase of quasi-two-dimensional (quasi-2D) cuprates at small but finite

Smearing of the two-dimensional kohn anomaly in a nonquantizing magnetic field: Implications for interaction effects

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Statistical transmutation in Floquet driven optical lattices

. We use a nonperturbative approach and sum up infinite series of thermal self-energy terms, keeping at each order nearly divergent

Spontaneous Formation of a Nonuniform Chiral Spin Liquid in a Moat-Band Lattice

(T/J)|\text{log}\text{ }ϵ|

Boundary Wess-Zumino-Novikov-Witten model from the pairing Hamiltonian

terms, where