A. Kolezhuk

Taras Shevchenko National University of Kyiv, Institute of High Technologies, Faculty Member

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Papers by A. Kolezhuk

Circulating Current States in Bilayer Fermionic and Bosonic Systems

Physical Review Letters, 2007

It is shown that fermionic polar molecules or atoms in a bilayer optical lattice can undergo the ... more It is shown that fermionic polar molecules or atoms in a bilayer optical lattice can undergo the transition to a state with circulating currents, which spontaneously breaks the time reversal symmetry. Estimates of relevant temperature scales are given and experimental signatures of the circulating current phase are identified. Related phenomena in bosonic and spin systems with ring exchange are discussed.

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Variational and density-matrix renormalization-group studies of the frustrated antiferromagnetic Heisenberg S=1 quantum spin chain

Physical Review B, 1997

In this paper we study a frustrated antiferromagnetic isotropic Heisenberg S = 1 quantum spin chain

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Massive triplet excitations in a magnetized anisotropic Haldane spin chain

Physical Review B, 2003

Inelastic neutron scattering experiments on the Haldane-gap quantum antiferromagnet Ni(C5D14N2)2N... more Inelastic neutron scattering experiments on the Haldane-gap quantum antiferromagnet Ni(C5D14N2)2N3(PF6) are performed at mK temperatures in magnetic fields of almost twice the critical field Hc applied perpendicular to the spin cahins. Above Hc a re-opening of the spin gap is clearly observed. In the high-field Néel-ordered state the spectrum is dominated by three distinct long-lived excitation branches. Several field-theoretical models are tested in a quantitative comparison with the experimental data.

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Field-induced chiral phase in isotropic frustrated spin chains

Electron Spin Resonance in Sine-Gordon Spin Chains in the Perturbative Spinon Regime

Physical Review Letters, 2005

We report the low-temperature multi-frequency ESR studies of copper pyrimidine dinitrate, a spin-... more We report the low-temperature multi-frequency ESR studies of copper pyrimidine dinitrate, a spin-1 2 antiferromagnetic chain with alternating g-tensor and the Dzyaloshinskii-Moriya interaction, allowing us to test a new theoretical concept proposed recently by Oshikawa and Affleck [Phys. Rev. Lett. 82, 5136 (1999)]. Their theory, based on bosonization and the self-energy formalism, can be applied for precise calculation of ESR parameters of S = 1 2 antiferromagnetic chains in the perturbative spinon regime. Excellent quantitative agreement between the theoretical predictions and experiment is obtained. PACS numbers: 75.40.Gb, 75.10.Jm Quantum fluctuations in low-dimensional magnets give rise to a variety of exotic strongly correlated states, making those systems an extremely attractive ground for testing various theoretical concepts. Isotropic S = 1 2 Heisenberg antiferromagnetic (AFM) chains with uniform nearest-neighbor exchange interactions have a spin singlet ground state; their spin dynamics is determined by a gapless two-particle continuum of spin-1 2 excitations (spinons), whose parameters can be calculated using Bethe ansatz . In an applied magnetic field H the excitation spectrum acquires incommensurate modes but remains gapless . In contrast, in S = 1 2 AFM chains with an alternating g-tensor and the Dzyaloshinskii-Moriya (DM) interaction, a magnetic field induces an energy gap E g ∼ H 2/3 [4], with the effective transverse staggered field [4, 5] playing a key role in the gap formation. Fairly complete theoretical understanding of this phenomenon has been achieved by Oshikawa and Affleck who showed that the gapped phase could be effectively described using the sine-Gordon quantum field theory. A rich excitation spectrum [7] was predicted to be readily apparent in the response functions . Recently, with the help of inelastic neutron scattering [9] and electron spin resonance (ESR) techniques [10, 11, 12] the existence of soliton and breather states in sine-Gordon spin chains has been confirmed experimentally.

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Exactly solvable model of statistical mechanics with a countable set of phases

Physical Review Letters, 1991

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Hole dynamics in an antiferromagnet across a deconfined quantum critical point

Physical Review B, 2007

We study the effects of a small density of holes, δ, on a square lattice antiferromagnet undergoi... more We study the effects of a small density of holes, δ, on a square lattice antiferromagnet undergoing a continuous transition from a Néel state to a valence bond solid at a deconfined quantum critical point. We argue that at non-zero δ, it is likely that the critical point broadens into a non-Fermi liquid 'holon metal' phase with fractionalized excitations. The holon metal phase is flanked on both sides by Fermi liquid states with Fermi surfaces enclosing the usual Luttinger area. However the electronic quasiparticles carry distinct quantum numbers in the two Fermi liquid phases, and consequently the ratio lim δ→0 A F /δ (where A F is the area of a hole pocket) has a factor of 2 discontinuity across the quantum critical point of the insulator. We demonstrate that the electronic spectrum at this transition is described by the 'boundary' critical theory of an impurity coupled to a 2+1 dimensional conformal field theory. We compute the finite temperature quantum-critical electronic spectra and show that they resemble "Fermi arc" spectra seen in recent photoemission experiments on the pseudogap phase of the cuprates.

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Low-energy dynamics of the spin-gap magnet at the critical field

Journal of Magnetism and Magnetic Materials, 2007

ABSTRACT The low-energy dynamics of the spin-gap magnet TlCuCl3 is studied. Closing of the energy... more ABSTRACT The low-energy dynamics of the spin-gap magnet TlCuCl3 is studied. Closing of the energy gap by a magnetic field at the critical field Hc leads to the formation of the field-induced transverse antiferromagnetic order. The magnetic resonance technique allows to probe an energy range 0.05–0.5meV hardly accessible by other means. The measured spin-excitation spectra are described quantitatively within the framework of the effective field theory under an assumption of a weak anisotropy of the exchange interaction. Model calculations demonstrate that low energy dynamics at the critical field is strongly influenced by the longitudinal oscillations of the order parameter.

Frustrated 1D Spin-S chain Below Saturation Magnetization

ABSTRACT Ground states of frustrated spin-S chains in strong magnetic field in the immediate vici... more ABSTRACT Ground states of frustrated spin-S chains in strong magnetic field in the immediate vicinity of saturation are mapped out. For ferromagnetic nearest-neighbor and frustrating antiferromagnetic next-nearest-neighbor exchange interactions generic feature is metamagnetic behavior under the influence of an external magnetic field for small S, in the form of a first-order transition to the fully polarized state. The magnetization jump increases gradually starting from an S-dependent critical value of exchange couplings and takes a maximum in the vicinity of a ferromagnetic Lifshitz point. The metamagnetism results from resonances in the dilute magnon gas caused by an interplay between quantum fluctuations and frustration. For antiferromagnetic nearest neighbor interactions generic feature is emergence of two-component Luttinger liquid phase and series of phase transitions between that phase and chiral phase.

Kinetic Equations and Soliton Diffusion in Low-Dimensional Magnets

by E. Tartakovskaya and A. Kolezhuk

Research Reports in Physics, 1990

A. Kolezhuk

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