arXiv subjects

A. M. Tsvelik

Publications and source records attributed to A. M. Tsvelik.

At least 91 records · Page 5Linked to original sources

arXiv2010

Analysis of the Quasiparticle Spectral Function in the Underdoped Cuprates

We applied the approach of K.-Y. Yang, T. M. Rice and F.-Ch. Zhang (YRZ) to analyze the high resolution angular resolved photo-emission spectroscopy (ARPES) data in BiSCO obtained recently at Brookhaven. In the YRZ ansatz a constant RVB gap is assumed which leads to Luttinger zeros along the antiferromagnetic Brillouin zone (AFBZ) and four Fermi pockets centered on the nodal directions. We relax the assumption of a constant RVB gap function, treating it as a Ising order parameter accompanied by thermal fluctuations. If these thermal fluctuations are very strong leading to strictly short range correlations in the spatial dependence of the RVB gap, then the reconstruction of the Fermi surface into pockets will not survive. We examined the intermediate case of critical fluctuations leading to a power law falloff of the RVB gap correlations. To this end we followed the analysis recently developed by two of us to treat the effect of the power law correlations in the antiferromagnetic 2-dimensional xy model on the single electron Green's function. The partial truncation of the Fermi surface to form pockets survives in the presence of power law correlations. The linewidth of the quasiparticle peaks increases with the exponent of the power law correlations. If this exponent is set at the value of critical fluctuations in the 2-dimensional Ising model a relatively small linewidth is obtained. If this exponent is doubled, a linewidth comparable to the values found in recent ARPES experiments on underdoped BiSCO (Tc = 65 K) at T = 140K was obtained. The anisotropic suppression of the quasiparticle peak around the Fermi pockets hides the back side of the pockets closest to the AFBZ to give essentially Fermi arcs seen experimentally.

cond-mat.str-el↗

arXiv2010

Covering the Fermi Surface with Patches of Quarkyonic Chiral Spirals

We argue that in cold, dense quark matter, in the limit of a large number of colors the ground state is unstable with respect to creation of a complicated Quarkyonic Chiral Spiral (QCS) state, in which both chiral and translational symmetries are spontaneously broken. The entire Fermi surface is covered with patches of QCSs, whose number increases as the quark density does. The low energy excitations are gapless, given by Wess-Zumino-Novikov-Witten model plus transverse kinetic terms localized about different patches.

hep-ph↗

arXiv2010

Effects of thermal phase fluctuations in a 2D superconductor: an exact result for the spectral function

We consider the single particle spectral function for a two-dimensional clean superconductor in a regime of strong critical thermal phase fluctuations. In the limit where the maximum of the superconducting gap is much smaller than the Fermi energy we obtain an exact expression for the spectral function integrated over the momentum component perpendicular to the Fermi surface.

cond-mat.supr-con↗

arXiv2010

Influence of thermal phase fluctuations on the single particle Green function in a 2D d-wave superconductor

We study the single-particle Green function for a two-dimensional superconductor in a regime of strong classical phase fluctuations. Although the developed approach is valid for any symmetry, we concentrate on d-wave superconductors. We obtain analytical expressions for the Green function below the transition temperature and have worked out a way to extrapolate it for a finite temperatures above $T_c$. Along with analytical expressions for a certain limits of parameters we outline the qualitative features of the spectral function.

cond-mat.supr-con↗

arXiv2010

Superconductivity generated by coupling to a Cooperon in a 2-dimensional array of 4-leg Hubbard ladders

Starting from an array of four-leg Hubbard ladders weakly doped away from half-filling and weakly coupled by inter-ladder tunneling, we derive an effective low energy model which contains a partially truncated Fermi surface and a well defined Cooperon excitation formed by a bound pair of holes. An attractive interaction in the Cooper channel is generated on the Fermi surface through virtual scattering into the Cooperon state. Although the model is derived in the weak coupling limit of a four-leg ladder array, an examination of exact results on finite clusters for the strong coupling t-J model suggests the essential features are also present for a strong coupling Hubbard model on a square lattice near half-filling.

cond-mat.supr-con↗

arXiv2010

Striped pnictides as new strongly correlated systems

The recent experimental evidence in favor of stripe ordering in ferropnictides [Chuang {\it et. al.}, Science {\bf 327},181 (2010)] points to the new field of study for strongly correlated systems. Here we argue that due to the smallness of the chemical potential in ferropnictides the effects of stripe modulation are likely to be much more pronounced than in the cuprates leading to stronger degree of one-dimensionality. This may allow to treat the striped pnictides as an array of coupled one-dimensional spin liquids making them a good testing ground for various ideas concerning strongly correlated states originally proposed for the cuprates.

cond-mat.str-el↗

arXiv2010

Influence of Thermal Fluctuations of Spin Density Wave Order Parameter on the Quasiparticle Spectral Function

The two-dimensional model of itinerant electrons coupled to an anti-ferromagnetic order parameter is considered. In the mean field solution the Fermi surface undergoes reconstruction, and breaks into disconnected ``pockets''. We have studied the effect of the thermal fluctuations of the order parameter on the spectral density in such system. These fluctuations lead to a finite width of the spectral line scaling linearly with temperature. Due to the thermal fluctuations the quasi-particle spectral weight is transfered into a magnetic Brillouin zone. This can be interpreted as restoration of ``arcs'' of the non-interacting Fermi surface.

cond-mat.str-el↗

arXiv2009

Confinement of fractional quantum number particles in a condensed matter system

The idea of confinement states that in certain systems constituent particles can be discerned only indirectly being bound by an interaction whose strength increases with increasing particle separation. Though the most famous example is the confinement of quarks to form baryons and mesons in (3+1)-dimensional Quantum Chromodynamics, confinement can also be realized in the systems of condensed matter physics such as spin-ladders which consist of two spin-1/2 antiferromagnetic chains coupled together by spin exchange interactions. Excitations of individual chains (spinons) carrying spin S=1/2, are confined even by an infinitesimal interchain coupling. The realizations studied so far cannot illustrate this process due to the large strength of their interchain coupling which leaves no energy window for the spinon excitations of individual chains. Here we present neutron scattering experiments for a weakly-coupled ladder material. At high energies the spectral function approaches that of individual chains; at low energies it is dominated by spin 0,1 excitations of strongly-coupled chains.

cond-mat.str-el↗

arXiv2008

On the spin-liquid phase of one dimensional spin-1 bosons

We consider a model of one dimensional spin-1 bosons with repulsive density-density interactions and antiferromagnetic exchange. We show that the low energy effective field theory is given by a spin-charge separated theory of a Tomonaga-Luttinger Hamiltonian and the O(3) nonlinear sigma model describing collective charge and spin excitations respectively. At a particular ratio of the density-density to spin-spin interaction the model is integrable, and we use the exact solutions to provide an independent derivation of the low energy effective theory. The system is in a superfluid phase made of singlet pairs of bosons, and we calculate the long-distance asymptotics of certain correlation functions.

cond-mat.other↗

arXiv2008

Midgap states in corrugated graphene: Ab-initio calculations and effective field theory

We investigate the electronic properties of corrugated graphene and show how rippling-induced pseudomagnetic fields alter graphene's low-energy electronic properties by combining first principles calculations with an effective field theory. The formation of flat bands near the Fermi level corresponding to pseudo-Landau levels is studied as a function of the rippling parameters. Quenched and relaxed ripples turn out to be fundamentally different is this respect: It is demonstrated, both numerically and analytically, that annealing of quenched ripples can destroy the flat bands.

cond-mat.mes-hall↗

arXiv2008

Twist instability in strongly correlated carbon nanotubes

We show that strong Luttinger correlations of the electron liquid in armchair carbon nanotubes lead to a significant enhancement of the onset temperature of the putative twist Peierls instability. The instability results in a spontaneous uniform twist deformation of the lattice at low temperatures, and a gapped ground state. Depending on values of the coupling constants the umklapp electron scattering processes can assist or compete with the twist instability. In case of the competition the umklapp processes win in wide tubes. In narrow tubes the outcome of the competition depends on the relative strength of the e-e and e-ph backscattering. Our estimates show that the twist instability may be realized in free standing (5,5) tubes.

cond-mat.str-el↗

arXiv2008

Modelling Magnetic Fluctuations in the Stripe Ordered State

The nature of the interplay between superconductivity and magnetism in the cuprates remains one of the fundamental unsolved problems in high temperature superconductivity. Whether and how these two phenomena are interdependent is perhaps most sharply seen in the stripe phases of various copper-oxide materials. These phases, involving a mixture of spin and charge density waves, do not yet admit a complete, overarching theoretical treatment. However aspects of this problem can be analyzed. In this work, we focus on the magnetic side of stripe physics. To this end, we study a simple model of a stripe-ordered phase consisting of an array of alternating coupled doped and undoped two-leg Hubbard-like ladders. To obtain the magnetic response, we employ already available dynamical susceptibilities of the individual two-leg ladders and treat the interladder coupling in a random phase approximation. Strikingly, we find two possible scenarios for the ordered state induced by the coupling between ladders: the spin modulation can occur either along or perpendicular to the direction of the stripes. These two scenarios are differentiated according to different microscopic realizations of the component doped ladders. However inelastic neutron scattering experiments on the two stripe ordered cuprates, La_{1.875}Ba_{0.125}CuO_4 and La_{2-x}Sr_xCuO_4, do not readily distinguish between these two scenarios due to manner in which stripes form in these materials.

cond-mat.supr-con↗

arXiv2008

Isospin excitations of a trapped 1D gas of attractively interacting fermions

We consider a gas of fermions with a short-range attractive intercomponent interaction in a parabolic external potential and derive the conditions of the local density approximation. The obtained spectrum of quasiparticle (isospin) excitations shows equidistant low-energy levels, which is equivalent to a linear momentum dependence and is fundamentally different from the ordinary Dirac spectrum in the spatially uniform case.

cond-mat.str-el↗

arXiv2007

Friedel oscillations of Density of States in a one-dimensional Mott insulator and Incommensurate Charge Density Wave/Superconductor

Oscillations of local density of states generated by a single scalar impurity potential are calculated for one-dimensional systems with dynamically generated charge or spin gap. At zero temperature the oscillations develop at finite wave vector ($π$ for the Mott insulator and $2k_F$ for ICDW/SC) and at frequencies larger than the soliton spectral gap $m$. Their amplitude has a broad maximum at $ω\approx 3m$, where $m$ is the gap magnitude.

cond-mat.supr-con↗

arXiv2007

Spontaneous symmetry breakings in graphene subjected to in-plane magnetic field

Application of the magnetic field parallel to the plane of the graphene sheet leads to the formation of electron- and hole-like Fermi surfaces. Such situation is shown to be unstable with respect to the formation of an excitonic condensate even for an arbitrary weak magnetic field and interaction strength. At temperatures lower than the mean-field temperature the order parameter amplitude is formed. The order parameter itself is a U(2) matrix allowing for the combined rotations in the spin and valley spaces. These rotations smoothly interpolate between site and bond centered spin density waves and spin flux states. The trigonal warping, short range interactions, and the three particle Umklapp processes freeze some degrees of freedom at temperatures much smaller than the mean-field transition temperature and make either Berezinskii-Kosterlitz-Thouless (driven either by vortices or half-vortices) or Ising type transitions possible. Strong logarithmic renormalization for the coupling constants of these terms by the Coulomb interaction are calculated within one-loop renormalization group. It is found that in the presence of the Coulomb interaction some short range interaction terms become much greater than one might expect from the naive dimensionality counting.

cond-mat.mes-hall↗

arXiv2007

Spin-liquid model of the sharp resistivity drop in $La_{1.85}Ba_{0.125}CuO_4$

We use the phenomenological model proposed in our previous paper [Phys. Rev. Lett. {\bf 98}, 237001 (2007)] to analyse the magnetic field dependence of the onset temperature for two-dimensional fluctuating superconductivity $T^{**} (H)$. We demonstrate that the slope of $T^{**} (H)$ progressively goes down as $H$ increases, such that the upper critical field progressively increases as $T$ decreases. The quantitative agreement with the recent measurements of $T^{**} (H)$ in $La_{1.85}Ba_{0.125}CuO_4$ is achieved for the same parameter value as was derived in our previous publication from the analysis of the electron self energy.

cond-mat.supr-con↗

arXiv2007

Two-Dimensional Superconducting Fluctuations in Stripe-Ordered La(1.875)Ba(0.125)CuO(4)

Recent spectroscopic observations of a d-wave-like gap in stripe-ordered La(2-x)Ba(x)CuO(4) with x=1/8 have led us to critically analyze the anisotropic transport and magnetization properties of this material. The data suggest that concomitant with the spin ordering is an electronic decoupling of the CuO(2) planes. We observe a transition (or crossover) to a state of two-dimensional (2D) fluctuating superconductivity, which eventually reaches a 2D superconducting state below a Berezinskii-Kosterlitz-Thouless transition. Thus, it appears that the stripe order in La(2-x)Ba(x)CuO(4) frustrates three-dimensional superconducting phase order, but is fully compatible with 2D superconductivity and an enhanced T_c.

cond-mat.supr-con↗

arXiv2007

Evidence for the PSL(2$|$2) Wess-Zumino-Novikov-Witten model as a model for the plateau transition in Quantum Hall effect: Evaluation of numerical simulations

In this paper I revise arguments in favour of the PSL(2$|$2) Wess-Zumino-Novikov-Witten (WZNW) model as a theory of the plateau transition in Integer Quantum Hall effect. I show that all available numerical data (including the correlation length exponent $ν$) are consistent with the predictions of such WZNW model with the level $k=8$.

cond-mat.mes-hall↗