arXiv subjects

Steven A. Kivelson

Publications and source records attributed to Steven A. Kivelson.

At least 163 records · Page 9Linked to original sources

arXiv2005

Disorder induced non-Fermi liquid near a metal-superconductor quantum phase transition

We study the flux-driven superconductor-metal transition in ultrasmall cylinders observed experimentally by Liu {\em et.al.}(Science 294, 2332 (2001)). Where $T_c\to 0$, there is a quantum critical point, and a large fluctuation conductivity is observed in the proximate metallic phase over a wide range of $T$ and flux . However, we find that the predicted (Gaussian) fluctuation conductivity in the neighborhood of the quantum critical point is 4 orders of magnitude smaller than observed experimentally. We argue that the breakdown of Anderson's theorem at any non-integer flux leads to a broad fluctuation region reflecting the existence of ``rare regions'' with local superconducting order. We calculate the leading order correction to the conductivity within a simple model of statistically induced Josephson coupled local ordered regions that rationalizes the existing data.

cond-mat.supr-con↗

arXiv2005

Surface pinning of fluctuating charge order: an "extraordinary" surface phase transition

We study the mean-field theory of charge-density wave (CDW) order in a layered system, including the effect of the long-range Coulomb interaction and of screening by uncondensed electrons. We particularly focus on the conditions necessary for an ``extraordinary'' transition, in which the surface orders at a higher temperature, and is more likely to be commensurate, than the bulk. We interpret recent experiments on NaCCOC as indicating the presence of commensurate CDW at the surface that is not present in the bulk. More generally, we show that poor screening of the Coulomb interaction tends to stabilize incommensurate order, possibly explaining why the CDW order in LSCO and NbSe2 remains incommensurate to T -> 0, despite the small magnitude of the incommensurability.

cond-mat.supr-con↗

arXiv2005

Enhancement of superconductivity by local inhomogeneity

We study the effect of inhomogeneity of the paring interaction or the background potential on the superconducting transition temperature, T_c. In the weak coupling BCS regime, we find that inhomogeneity which is incommensurate with the Fermi surface nesting vectors enhances T_c relative to its value for the uniform system. For a fixed modulation strength we find that the highest T_c is reached when the characteristic modulation length scale is of the order of the superconducting coherence length.

cond-mat.supr-con↗

arXiv2005

Spectral function of a Luttinger liquid coupled to phonons and angle-resolved photoemission measurements in the cuprate superconductors

We compute the finite-temperature single-particle spectral function of a one-dimensional Luttinger liquid coupled to an optical phonon band. The calculation is performed exactly for the case in which electron-phonon coupling is purely forward scattering. We extend the results to include backward scattering with a renormalization group treatment. The dispersion contains a change in velocity at the phonon energy, qualitatively similar to the case of electron-phonon coupling in a Fermi liquid. If the backward scattering part of the the electron-phonon interaction is not too strong compared to the forward scattering part, coupling to phonons also produces a pronounced peak in the spectral function at low energies. The calculated spectral function is remarkably similar to the angle-resolved photoemission spectra of the high-temperature superconductors, including the apparent presence of "nodal quasiparticles," the presence of a "kink" in the dispersion, and the non-Fermi-liquid frequency and temperature dependencies. Although a microscopic justification has not been established for treating the electronic dynamics of the cuprates as quasi-one-dimensional, at the very least we take the quality of the comparison as evidence of the non-Fermi-liquid character of the measured spectra.

cond-mat.str-el↗

arXiv2004

Quasiparticle scattering and local density of states in graphite

We determine the effect of quasiparticle interference on the spatial variations of the local density of states (LDOS) in graphite in the neighborhood of an isolated impurity. A number of characteristic behaviors of interference are identified in the Fourier transformed spectrum. A comparison between our results and scanning tunneling microscopy (STM) experiments could provide a critical test of the range (of energy) of applicability of the Fermi liquid description of graphite, where some evidence of the breakdown of Fermi liquid theory has recently been discussed. Moreover, given the similarity between the band structures of graphite and that of nodal quasiparticles in a d-wave superconductor, a comparison between results in the two materials is useful for understanding the physics of the cuprates.

cond-mat.mes-hall↗

arXiv2004

Drag resistance of 2D electronic microemulsions

Motivated by recent experiments of Pillarisetty {\it et al}, \prl {\bf 90}, 226801 (2003), we present a theory of drag in electronic double layers at low electron concentration. We show that the drag effect in such systems is anomolously large, it has unusual temperature and magnetic field dependences accociated with the Pomeranchuk effect, and does not vanish at zero temperature.

cond-mat.str-el↗

arXiv2004

Order by disorder, without order, in a two-dimensional spin system with O(2) symmetry

We present a rigorous proof of an ordering transition for a two-component two-dimensional antiferromagnet with nearest and next-nearest neighbor interactions. The low-temperature phase contains two states distinguished by local order among columns or, respectively, rows. Overall, there is no magnetic order in accord with the classic Mermin-Wagner theorem. The method of proof employs a rigorous version of "order by disorder," whereby a high degeneracy among the ground states is lifted according to the differences in their associated spin-wave spectra.

math-ph↗

arXiv2004

Quasi-1D dynamics and nematic phases in the 2D Emery model

We consider the Emery model of a Cu-O plane of the high temperature superconductors. We show that in a strong-coupling limit, with strong Coulomb repulsions between electrons on nearest-neighbor O sites, the electron-dynamics is strictly one dimensional, and consequently a number of asymptotically exact results can be obtained concerning the electronic structure. In particular, we show that a nematic phase, which spontaneously breaks the point- group symmetry of the square lattice, is stable at low enough temperatures and strong enough coupling.

cond-mat.str-el↗

arXiv2002

The types of Mott insulator

There are two classes of Mott insulators in nature, distinguished by their responses to weak doping. With increasing chemical potential, Type I Mott insulators undergo a first order phase transition from the undoped to the doped phase. In the presence of long-range Coulomb interactions, this leads to an inhomogeneous state exhibiting ``micro-phase separation.'' In contrast, in Type II Mott insulators charges go in continuously above a critical chemical potential. We show that if the insulating state has a broken symmetry, this increases the likelihood that it will be Type I. There exists a close analogy between these two types of Mott insulators and the familiar Type I and Type II superconductors.

cond-mat.str-el↗

arXiv2002

Theory of the Quantum Hall Smectic Phase, I: Low Energy Properties of the Quantum Hall Smectic Fixed Point

We develop an effective low energy theory of the Quantum Hall (QH) Smectic or stripe phase of a two-dimensional electron gas in a large magnetic field in terms of its Goldstone modes and of the charge fluctuations on each stripe. This liquid crystal phase corresponds to a fixed point which is explicitly demonstrated to be stable against quantum fluctuations at long wavelengths. This fixed point theory also allows an unambiguous reconstruction of the electron operator. We find that quantum fluctuations are so severe that the electron Green function decays faster than any power-law, although slower than exponentially, and that consequently there is a deep pseudo-gap in the quasiparticle spectrum. We discuss, but do not resolve the stability of the quantum Hall smectic to crystallization. Finally, the role of Coulomb interactions and the low temperature thermodynamics of the QH smectic state are analyzed.

cond-mat.mes-hall↗

arXiv2002

Competing Order in the Mixed State of High Temperature Superconductors

We examine the low temperature behavior of the mixed state of a layered superconductor in the vicinity of a quantum critical point separating a pure superconducting phase from a phase in which a competing order coexists with superconductivity. At zero temperature, we find that there is an avoided critical point in the sense that the phase boundary in the limit $B\to 0$ does not connect to the B=0 critical point. Consequently, there exists a quasi-1D regime of the phase diagram, in which the competing order is largely confined to 1D ``halos'' about each vortex core, and in which interactions between neighboring vortices, although relevant at low temperature, are relatively weak.

cond-mat.supr-con↗

arXiv2001

What the resonance peak cannot do

In certain cuprates, a spin 1 resonance mode is prominent in the magnetic structure measured by neutron scattering. It has been proposed that this mode is responsible for significant features seen in other spectroscopies, such as photoemission and optical absorption, which are sensitive to the charge dynamics, and even that this mode is the boson responsibile for ``mediating'' the superconducting pairing. We show that its small (measured) intensity and weak coupling to electron-hole pairs (as deduced from the measured lifetime) disqualifies the resonant mode from either proposed role.

cond-mat.str-el↗

arXiv2001

Thermodynamics of the interplay between magnetism and high-temperature superconductivity

The copper-oxide based high temperature superconductors have complex phase diagrams with multiple ordered phases. It even appears that the highest superconducting transition temperatures for certain cuprates are found in samples which display simultaneous onset of magnetism and superconductivity. We show here how the thermodynamics of fluid mixtures - a touchstone for chemists as well as hard and soft condensed matter physics - accounts for this startling observation, as well as many other properties of the cuprates in the vicinity of the instability towards ``striped'' magnetism.

cond-mat.str-el↗

arXiv2000

Electronic Mechanism of Superconductivity in the Cuprates, C$_{60}$, and Polyacenes

On the basis of an analysis of theoretical and numerical studies of model systems, and of experiments on superconductivity in doped C$_{60}$, polyacenes, and the cuprate high temperature superconductors, we propose that a purely electronic mechanism of superconductivity requires structures at an intermediate or mesoscale. Specifically, we address the crucial question of how high temperature superconducting pairing on the mesoscale can arise from purely repulsive electronic interactions.

cond-mat.supr-con↗

arXiv2000

Effects of dissipation on quantum phase transitions

We discuss the effect of dissipation on quantum phase transitions. In particular we concentrate on the Superconductor to Insulator and Quantum-Hall to Insulator transitions. By invoking a phenomenological parameter $α$ to describe the coupling of the system to a continuum of degrees of freedom representing the dissipative bath, we obtain new phase diagrams for the quantum Hall and superconductor-insulator problems. Our main result is that, in two-dimensions, the metallic phases observed in finite magnetic fields (possibly also strictly zero field) are adiabatically deformable from one to the other. This is plausible, as there is no broken symmetry which differentiates them.

cond-mat.mes-hall↗

arXiv2000

Quantum Theory of the Smectic Metal State in Stripe Phases

We present a theory of the electron smectic fixed point of the stripe phases of doped layered Mott insulators. We show that in the presence of a spin gap three phases generally arise: (a) a smectic superconductor, (b) an insulating stripe crystal and (c) a smectic metal. The latter phase is a stable two-dimensional anisotropic non-Fermi liquid. In the abscence of a spin gap there is also a more conventional Fermi-liquid-like phase. The smectic superconductor and smectic metal phases may have already been seen in Nd-doped LSCO.

cond-mat.str-el↗

arXiv1999

Nematic phase of the two-dimensional electron gas in a magnetic field

The two dimensional electron gas (2DEG) in moderate magnetic fields in ultra-clean AlAs-GaAs heterojunctions exhibits transport anomalies suggestive of a compressible, anisotropic metallic state. Using scaling arguments and Monte Carlo simulations, we develop an order parameter theory of an electron nematic phase. The observed temperature dependence of the resistivity anisotropy behaves like the orientational order parameter if the transition to the nematic state occurs at a finite temperature, $T_c \sim 65 mK$, and is slightly rounded by a small background microscopic anisotropy. We propose a light scattering experiment to measure the critical susceptibility.

cond-mat.mes-hall↗

arXiv1999

Topological doping and the stability of stripe phases

We analyze the properties of a general Ginzburg-Landau free energy with competing order parameters, long-range interactions, and global constraints (e.g., a fixed value of a total ``charge'') to address the physics of stripe phases in underdoped high-Tc and related materials. For a local free energy limited to quadratic terms of the gradient expansion, only uniform or phase-separated configurations are thermodynamically stable. ``Stripe'' or other non-uniform phases can be stabilized by long-range forces, but can only have non-topological (in-phase) domain walls where the components of the antiferromagnetic order parameter never change sign, and the periods of charge and spin density waves coincide. The antiphase domain walls observed experimentally require physics on an intermediate lengthscale, and they are absent from a model that involves only long-distance physics. Dense stripe phases can be stable even in the absence of long-range forces, but domain walls always attract at large distances, i.e., there is a ubiquitous tendency to phase separation at small doping. The implications for the phase diagram of underdoped cuprates are discussed.

cond-mat.supr-con↗