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D. V. Khveshchenko

Publications and source records attributed to D. V. Khveshchenko.

At least 55 records · Page 3Linked to original sources
arXiv2003

Entanglement and decoherence in near-critical qubit chains

We study the problem of environmentally-induced decoherence in a near-critical one-dimensional system of N>>1 coupled qubits. Using the Jordan-Wigner fermion representation of the qubit operators we identify the decoherence rates relevant for the two-qubit reduced density matrix. We find that a desirable onset of massive shared entanglement in the near-critical regime comes at the expense of decoherence which also tends to increase as the system is tuned towards criticality. Our results reveal rather contradictory general requirements that future designs of a qubit chain-based quantum information processor will need to satisfy.

cond-mat↗
arXiv2003

Decoherence of one-dimensional flying qubits due to their cross-talk and imperfections

We study decoherence of propagating spin-1/2 excitations in generic (non-integrable and/or disordered) spin chains. We find the relevant decoherence times to be shorter in both the near-critical and diffusive regimes (if any), which fact might have important implications for the recently proposed spin chain-based implementations of quantum information processing.

cond-mat.str-el↗
arXiv2003

Anomalous dimensions of gauge-invariant amplitudes in massless effective gauge theories of strongly correlated systems

We use the radial gauge to calculate the recently proposed ansatz for the physical electron propagator in such effective models of strongly correlated electron systems as the $QED_3$ theory of the pseudogap phase of the cuprates. The results of our analysis help to settle the recent dispute about the sign and the magnitude of the anomalous dimension which characterizes the gauge invariant amplitude in question and set the stage for computing other, more physically relevant, ones.

cond-mat↗
arXiv2003

Elusive physical electron propagator in QED-like effective theories

We study the previously conjectured form of the physical electron propagator and its allegedly Luttinger type of behavior in the theory of the pseudogap phase of high-temperature copper-oxide superconductors and other effective QED-like models. We demonstrate that, among a whole family of seemingly gauge-invariant functions, the conjectured "stringy ansatz" for the electron propagator is the only one that is truly invariant. However, contrary to the results of the earlier works, it appears to have a negative anomalous dimension, which makes it a rather poor candidate to the role of the physical electron propagator. Instead, we argue that the latter may, in fact, feature a "super-Luttinger" behavior characterized by a faster than any power-law decay: G(x) ~ exp(-const ln^2|x|).

cond-mat↗
arXiv2003

Planar Dirac fermions in long-range-correlated random vector potential

We study the behavior of two-dimensional Dirac fermions in the presence of a static long-range-correlated random vector potential. By applying an exact path integral representation for the propagator of a spinor particle we obtain asymptotics of the gauge invariant spectral function and the correlation function of the local density of states, both in the ballistic regime of sufficiently high energies. We also discuss localization properties of the random Dirac wave functions in the complementary zero energy limit and the putative localization scenario.

cond-mat↗
arXiv2003

Two different quasiparticle scattering rates in vortex line liquid phase of layered d-wave superconductors

We carry out a quantum mechanical analysis of the behavior of nodal quasiparticles in the vortex line liquid phase of planar d-wave superconductors. Applying a novel path integral technique we calculate a number of experimentally relevant observables and demonstrate that in the low-field regime the quasiparticle scattering rates deduced from photoemission and thermal transport data can be markedly different from that extracted from tunneling, specific heat, superfluid stiffness or spin-lattice relaxation time.

cond-mat↗
arXiv2003

Excitonic instability in two-dimensional degenerate semimetals

We study the possibility of excitonic pairing in layered degenerate semimetals such as graphite, where the electron density of states almost vanishes at the Fermi level and, therefore, the Coulomb interactions remain essentially unscreened. By focusing on the Dirac-like low-energy electron excitations and numerically solving a non-linear gap equation for the order parameter, we obtain a critical value of the Coulomb coupling and establish the Kosterlitz-Thouless-like nature of a putative semimetal-to-excitonic insulator transition.

cond-mat↗
arXiv2002

Gauge (non-)invariant Green functions of Dirac fermions coupled to gauge fields

We develop a unified approach to both infrared and ultraviolet asymptotics of the fermion Green functions in the condensed matter systems that allow for an effective description in the framework of the Quantum Electrodynamics. By applying a path integral representation to the previously suggested form of the physical electron propagator we demonstrate that in the massless case this gauge invariant function features a "stronger-than-a-pole" branch-cut singularity instead of the conjectured Luttinger-like behavior. The obtained results alert one to the possibility that construction of physically relevant amplitudes in the effective gauge theories might prove more complex than previously thought.

cond-mat↗
arXiv2002

Elusive gauge-invariant fermion propagator in QED-like effective theories: round II

We comment on the recent attempt by M. Franz et al [1] to further justify their earlier calculation of the gauge-invariant electron propagator in the context of the QED_3 theory of the pseudogap phase in cuprates [2]. First, we use the method of "reductio ad absurdum" to demonstrate the inconsistency of the argument offered in [2] and then present a direct calculation of the disputed fermion amplitudes, thus unequivocally proving that the previously proposed form of the electron propagator: 1) does exhibit a negative anomalous dimension, as pointed out in [3]; 2) is different from the so-called Brown's function whose anomalous dimension turns out to be positive when computed in a covariant gauge. Lastly, we conjecture that the true physical electron propagator (whose exact form still remains to be found) may feature a "super-Luttinger" behavior characterized by a faster than a power-law decay G(x)~exp(-const\ln^2|x|).

cond-mat.str-el↗
arXiv2002

Interacting random Dirac fermions in superconducting cuprates

We study the effects of quasiparticle interactions on disorder-induced localization of Dirac-like nodal excitations in superconducting high-$T_c$ cuprates. As suggested by the experimental ARPES and terahertz conductivity data in $Bi_2Sr_2CaCu_2O_{8+δ}$, we focus on the interactions mediated by the order parameter fluctuations near an incipient second pairing transition $d\to d+is$. We find interaction corrections to the density of states, specific heat, and conductivity as well as phase and energy relaxation rates and assess the applicability of the recent localization scenarios for non-interacting random Dirac fermions to the cuprates.

cond-mat↗
arXiv2001

Magnetic field-induced insulating behavior in highly oriented pyrolitic graphite

We propose an explanation for the apparent semimetal-insulator transition observed in highly oriented pyrolitic graphite in the presence of magnetic field perpendicular to the layers. We show that the magnetic field opens an excitonic gap in the linear spectrum of the Coulomb interacting quasiparticles, in a close analogy with the phenomenon of dynamical chiral symmetry breaking in the relativistic theories of the 2+1-dimensional Dirac fermions. Our strong-coupling appoach allows for a non-perturbative description of the corresponding critical behavior.

cond-mat↗
arXiv2001

Ghost excitonic insulator transition in layered graphite

Some unusual properties of layered graphite, including a linear energy dependence of the quasiparticle damping and weak ferromagnetism at low doping, are explained as a result of the proximity of a single graphene sheet to the excitonic insulator phase which can be further stabilized in a doped system of many layers stacked in the staggered ($ABAB...$) configuration.

cond-mat↗
arXiv2001

Incipient nodal pairing in planar d-wave superconductors

The possibility of a second pairing transition $d\to d+is$ ($d+id^\prime$) in planar $d$-wave superconductors which occurs in the absence of external magnetic field, magnetic impurities or boundaries is established in the framework of the non-perturbative phenomenon of dynamical chiral symmetry breaking in the system of $2+1$-dimensional Dirac-like nodal quasiparticles. We determine the critical exponents and quasiparticle spectral functions that characterize the corresponding quantum critical behavior and discuss some of its potentially observable spectral and transport features.

cond-mat↗
arXiv2001

Nesting symmetries and diffusion in disordered d-wave superconductors

The low-energy density of states (DOS) of disordered 2D d-wave superconductors is extremely sensitive to details of both the disorder model and the electronic band structure. Using diagrammatic methods and numerical solutions of the Bogoliubov-de Gennes equations, we show that the physical origin of this sensitivity is the existence of a novel diffusive mode with momentum close to $(π,π)$ which is gapless only in systems with a global nesting symmetry. We find that in generic situations, the DOS vanishes at the Fermi level. However, proximity to the highly symmetric case may nevertheless lead to observable non-monotonic behavior of the DOS in the cuprates.

cond-mat↗
arXiv1999

Fermi edge singularities in X-ray spectra of strongly correlated fermions

We discuss the problem of the X-ray absorption in a system of interacting fermions and, in particular, those features in the X-ray spectra that can be used to discriminate between conventional Fermi-liquids and novel "strange metals". Focusing on the case of purely forward scattering off the core-hole potential, we account for the relevant interactions in the conduction band by means of the bosonization technique. We find that the X-ray Fermi edge singularities can still be present, although modified, even if the density of states vanishes at the Fermi energy, and that, in general, the relationship between the two appears to be quite subtle.

cond-mat↗
arXiv1999

Coulomb Drag in Double Layers with Correlated Disorder

We study the effect of correlations between impurity potentials in different layers on the Coulomb drag in a double-layer electron system. It is found that for strongly correlated potentials the drag in the diffusive regime is considerably enhanced as compared to conventional predictions. The appropriate experimental conditions are discussed, and the new experiments are suggested.

cond-mat.mes-hall↗
arXiv1998

Phonon Mediated Transresistivity in a Double Layer Composite Fermion System

We consider the fractional drag in a double layer system of two-dimensional electrons in the half-filled lowest Landau level. At sufficiently large inter-layer separations the drag is dominated by exchange of acoustic phonons and exhibits novel temperature and inter-layer distance dependences. At low temperatures the phonon mediated drag is strongly enhanced with respect to the case of zero magnetic field.

cond-mat↗