Oleg A. Starykh
University of Utah
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Featured researches published by Oleg A. Starykh.
Physical Review B | 2011
E. M. Stoudenmire; Jason Alicea; Oleg A. Starykh; Matthew P. A. Fisher
Among the broad spectrum of systems predicted to exhibit topological superconductivity and Majorana fermions, one-dimensional wires with strong spin-orbit coupling provide one of the most promising experimental candidates. Here we investigate the fate of the topological superconducting phase in such wires when repulsive interactions are present. Using a combination of density matrix renormalization group, bosonization, and Hartree\char21{}Fock techniques, we demonstrate that while interactions degrade the bulk gap\char22{}consistent with recent results of Gangadharaiah et al.\char22{}they also greatly expand the parameter range over which the topological phase arises. In particular, we show that with interactions this phase can be accessed over a broader chemical potential window, thereby leading to greater immunity against disorder-induced chemical potential fluctuations in the wire. We also suggest that in certain wires strong interactions may allow Majorana fermions to be generated without requiring a magnetic field.
Nature Physics | 2007
Masanori Kohno; Oleg A. Starykh; Leon Balents
The search for elementary excitations with fractional quantum numbers is a central challenge in modern condensed-matter physics. It has long been speculated that two-dimensional frustrated magnets might support quantum disordered states with neutral spin-1/2 excitations known as spinons. Despite decades of search, however, no clear experimental examples have been found. We explore the possibility for several materials using a realistic model, the spin-1/2 spatially anisotropic frustrated Heisenberg antiferromagnet in two dimensions. Here, we derive an effective Schrodinger equation valid in the weak interchain coupling regime. The dynamical spin correlations from this approach agree quantitatively without fitting parameters with inelastic neutron measurements of the triangular antiferromagnet Cs2CuCl4. In such antiferromagnets, the spectrum is composed of an incoherent continuum arising from the effects of one-dimensional spinons of individual chains, and a sharp dispersing peak, due to coherently propagating ‘triplon’ bound states of two spinons. We argue that triplons are generic features of spatially anisotropic frustrated antiferromagnets, which arise because the bound spinon pair lowers its kinetic energy by propagating between chains.
Physical Review Letters | 2004
Oleg A. Starykh; Leon Balents
We investigate the spatially anisotropic square lattice quantum antiferromagnet. The model describes isotropic spin-1/2 Heisenberg chains (exchange constant J) coupled antiferromagnetically in the transverse (J( perpendicular )) and diagonal (J(x)), with respect to the chain, directions. Classically, the model admits two ordered ground states-with antiferromagnetic and ferromagnetic interchain spin correlations-separated by a first-order phase transition at J( perpendicular )=2J(x). We show that in the quantum model this transition splits into two, revealing an intermediate quantum-disordered columnar dimer phase, both in two dimensions and in a simpler two-leg ladder version. We describe quantum-critical points separating this spontaneously dimerized phase from classical ones.
Physical Review B | 2010
Oleg A. Starykh; Hosho Katsura; Leon Balents
We report a thorough theoretical study of the low temperature phase diagram of Cs_2CuCl_4, a spatially anisotropic spin S=1/2 triangular lattice antiferromagnet, in a magnetic field. Our results, obtained in a quasi-one-dimensional limit in which the system is regarded as a set of weakly coupled Heisenberg chains, are in excellent agreement with experiment. The analysis reveals some surprising physics. First, we find that, when the magnetic field is oriented within the triangular layer, spins are actually most strongly correlated within planes perpendicular to the triangular layers. This is despite the fact that the inter-layer exchange coupling in Cs_2CuCl_4 is about an order of magnitude smaller than the weakest (diagonal) exchange in the triangular planes themselves. Second, the phase diagram in such orientations is exquisitely sensitive to tiny interactions, heretofore neglected, of order a few percent or less of the largest exchange couplings. These interactions, which we describe in detail, induce entirely new phases, and a novel commensurate-incommensurate transition, the signatures of which are identified in NMR experiments. We discuss the differences between the behavior of Cs_2CuCl_4 and an ideal two-dimensional triangular model, and in particular the occurrence of magnetization plateaux in the latter. These and other related results are presented here along with a thorough exposition of the theoretical methods, and a discussion of broader experimental consequences to Cs_2CuCl_4 and other materials.
Physical Review E | 2000
Oleg A. Starykh; Philippe R. J. Jacquod; Evgenii E. Narimanov; A. Douglas Stone
We consider the effect of dynamical localization on the widths of the resonances in open wave-chaotic dielectric cavities. We show that dynamical localization leads to a log-normal distribution of the resonance widths which scales with the localization length in excellent agreement with the results of numerical calculations for open rough microcavities.
Physical Review B | 2005
Oleg A. Starykh; Akira Furusaki; Leon Balents
We study the phase diagram of two models of spin-1/2 antiferromagnets composed of corner-sharing tetrahedra, the basis of the pyrochlore structure. Primarily, we focus on the Heisenberg antiferromaget on the checkerboard lattice (also called the planar pyrochlore and crossed-chains model). This model has an anisotropic limit, when the dimensionless ratio of two exchange constants, J_\times/J > 1, we construct a few candidate global phase diagrams for the model, and discuss the nature of the quantum phase transitions contained therein. Finally, we apply our quasi-one-dimensional techniques to an anisotropic limit of the three-dimensional pyrochlore antiferromagnet, an approximate model for magnetism in GeCu2O4. A crossed dimer state is predicted here as well.
Physical Review Letters | 2009
Jason Alicea; Andrey V. Chubukov; Oleg A. Starykh
We consider the phase diagram of a spatially anisotropic 2D triangular antiferromagnet in a magnetic field. Classically, the ground state is umbrellalike for all fields, but we show that the quantum phase diagram is much richer and contains a 1/3-magnetization plateau, two commensurate planar states, two incommensurate chiral umbrella phases, and, possibly, a spin density wave state separating the two chiral phases. Our analysis sheds light on several recent experimental findings for Cs2CuBr4.
Physical Review Letters | 2013
Andrey V. Chubukov; Oleg A. Starykh
We analyze instabilities of the collinear up-up-down state of a two-dimensional quantum spin-S spatially anisotropic triangular lattice antiferromagnet in a magnetic field. We find, within the large-S approximation, that near the end point of the plateau, the collinear state becomes unstable due to the condensation of two-magnon bound pairs rather than single magnons. The two-magnon instability leads to a novel two-dimensional vector chiral phase with alternating spin currents but no magnetic order in the direction transverse to the field. This phase breaks a discrete Z(2) symmetry but preserves a continuous U(1) one of rotations about the field axis. It possesses orbital antiferromagnetism and displays a magnetoelectric effect.
Journal of Applied Physics | 1998
Rajiv R. P. Singh; Oleg A. Starykh; P. J. Freitas
Motivated by the geometry of the materials Na2Ti2As2O and Na2Ti2Sb2O, we study a square-lattice Heisenberg antiferromagnet, with spins located at the bond centers. The largest exchange constant J couples neighboring spins in a given row or column. This leads to a mesh of isolated spin chains running along the X and Y axes. A weaker exchange constant J′ couples the nearest-neighbor spins on the lattice. Classically, J′ fails to fix the relative spin orientation for different chains and hence the ground state is highly degenerate. Quantum order by disorder effect is studied by spin-wave theory and numerical methods. It is shown that a four-sublattice order is favored by quantum fluctuations. However, several arguments are presented that suggest that the ground state of the system remains disordered, thus providing us with a paradigm for a two-dimensional spin liquid.
Physical Review B | 2006
Oleg A. Starykh; Andrey V. Chubukov; Alexander G. Abanov
The excitation spectrum of an