arXiv subjects

A. A. Nersesyan

Publications and source records attributed to A. A. Nersesyan.

22 records · Page 2Linked to original sources

arXiv1994

Influence of Long-Range Coulomb Interactions on the Metal-Insulator Transition in One-Dimensional Strongly Correlated Electron Systems

The influence of long-range Coulomb interactions on the properties of one-dimensional (1D) strongly correlated electron systems in vicinity of the metal-insulator phase transition is considered. It is shown that unscreened repulsive Coulomb forces lead to the formation of a 1D Wigner crystal in the metallic phase and to the transformation of the square-root singularity of the compressibility (characterizing the commensurate-incommensurate transition) to a logarithmic singularity. The properties of the insulating (Mott) phase depend on the character of the short-wavelength screening of the Coulomb forces. For a sufficiently short screening length the characteristics of the charge excitations in the insulating phase are totally determined by the Coulomb interaction and these quasipartic les can be described as quasiclassical Coulomb solitons.

cond-mat↗

arXiv1994

Gapless Phases in an s=1/2 Quantum Spin Chain with Bond Alternation

The $S=1/2$ XXZ spin chain with the staggered XY anisotropy $$ H = J \sum_{n}^{N} (S^{x}_{n} S^{x}_{n+1} + S^{y}_{n} S^{y}_{n+1} + ΔS^{z}_{n} S^{z}_{n+1}) - δ\sum_{n}^{N} (-1)^{n} (S^{x}_{n} S^{x}_{n+1} - S^{y}_{n} S^{y}_{n+1}) $$ is shown to possess gapless, Luttinger-liquid-like phases in a wide range of its parameters: the XY-like phase and spin nematic phases, the latter characterized by a two-spin order parameter breaking translational and spin rotation symmetries. In the simplest, exactly solvable case $Δ= 0$, the spectrum remains gapless at arbitrary $J$ and $δ$ and is described by two massless Majorana (real) fermions with different velocities $v_{\pm} = |J \pm δ|$. At $|δ| < J$ the staggered XY anisotropy does not influence the ground state of the system (XY phase). At $|δ| > J$, due to level crossing, a spin nematic state is realized, with $\uparrow \uparrow \downarrow \downarrow$ and $\uparrow \downarrow \downarrow \uparrow$ local symmetry of the $xx$ and $yy$ spin correlations. The spin correlation functions are calculated and the effect of thermally induced spin nematic ordering in the XY phase ("order from disorder") is discussed. The role of a finite $Δ$ is studied in the limiting cases $|δ| \ll J$

cond-mat↗

arXiv1994

Disorder Effects in Two-Dimensional d-wave Superconductors

Influence of weak nonmagnetic impurities on the single-particle density of states $ρ(ω)$ of two-dimensional electron systems with a conical spectrum is studied. We use a nonperturbative approach, based on replica trick with subsequent mapping of the effective action onto a one-dimensional model of interacting fermions, the latter being treated by Abelian and non-Abelian bosonization methods. It is shown that, in a d-wave superconductor, the density of states, averaged over randomness, follows a nontrivial power-law behavior near the Fermi energy: $ρ(ω) \sim |ω|^α$. The exponent $α>0$ is calculated for several types of disorder. We demonstrate that the property $ρ(0) = 0$ is a direct consequence of a {\it continuous} symmetry of the effective fermionic model, whose breakdown is forbidden in two dimensions. As a counter example, we consider another model with a conical spectrum - a two-dimensional orbital antiferromagnet, where static disorder leads to a finite $ρ(0)$ due to breakdown of a {\it discrete} (particle-hole) symmetry.

cond-mat↗

arXiv1993

Scaling Properties of the Two-Chain Model

Scaling properties of a self-dual field-theoretical model, describing two weakl$spinless Luttinger chains, are studied. A crossover to a sine-Gordon massive phase, with strongly developed two-particleinterchain correlations, is described. It is argued that, in a wide range of the in-chain interaction, renormalization of the interchain hopping amplitude is determined by the Luttinger liquid effects.

cond-mat↗