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Orbital Currents in Underdoped CupratesJan 04 2002Orbital currents, either fluctuating or static, have emerged as promising candidates for a description of the pseudogap state in underdoped cuprates. I shall review the evolution of these ideas and describe some experiments which have been proposed to ... More

Strong rules for nonconvex penalties and their implications for efficient algorithms in high-dimensional regressionMar 12 2014We consider approaches for improving the efficiency of algorithms for fitting nonconvex penalized regression models such as SCAD and MCP in high dimensions. In particular, we develop rules for discarding variables during cyclic coordinate descent. This ... More

From high temperature supercondutivity to quantum spin liquid: progress in strong correlation physicsAug 15 2007Sep 13 2007This review gives a rather general discussion of high temperature superconductors as an example of a strongly correlated material. The argument is made that in view of the many examples of unconventional superconductors discovered in the past twenty years, ... More

Orbital currents and cheap vortices in underdoped cupratesOct 04 2002Dec 02 2002In the past several years, we have developed a theory for the underdoped cuprates in collaboration with X.-G. Wen, based on an SU(2) formulation of the t-J model. In this formulation, the staggered flux state plays a central role as the progenitor of ... More

Proposal for Creating a Spin-polarized p_x+ip_y State and Majorana FermionsJul 15 2009Jul 23 2009The spin polarized p_x + ip_y superconductor is known to support Majorana states but so far there has been no example. We propose a simple setup to create such a state by depositing a ferromagnetic metal on a non-centrosymmetric superconductor with strong ... More

Decoupled Spin Chains in Ba$_3$CuSb$_2$O$_9$Feb 25 2012Inspired by recent measurements on Ba$_3$CuSb$_2$O$_9$, we explore the interplay of spin and orbital degrees of freedom in a triangular lattice for possible spin liquid-like behaviour. Our effective Hamiltonian describes the magnetic Cu layer by considering ... More

Amperean pairing and the pseudogap phase of cuprate superconductorsJan 02 2014Apr 18 2014The enigmatic pseudogap phase in underdoped cuprate high T_c superconductors has long been recognized as a central puzzle of the T_c problem. Recent data show that the pseudogap is likely a distinct phase, characterized by a medium range and quasi-static ... More

Pseudogap and Competing States in Underdoped CupratesJul 21 2003I shall argue that the high Tc problem is the problem of doping into a Mott insulator. Furthermore, the well documented pseudo-gap phenomenon in underdoped cuprates holds the key to understanding this physics. Phase fluctuation alone cannot explain this ... More

Pseudogaps in Underdoped CupratesDec 14 1998It has become clear in the past several years that the cuprates show many unusual properties, both in the normal and superconducting states, especially in the underdoped region. In particular, gap-like behavior is observed in magnetic properties, c-axis ... More

Emergent U(1) gauge theory with fractionalized boson/fermion from the bose condensation of exciton in multi-band insulatorJul 07 2005Aug 08 2005Fractionalized phases are studied in a low energy theory of exciton bose condensate in a multi-band insulator. It is shown that U(1) gauge theory with either fractionalized boson or fermion can emerge out of a single model depending on the coupling constants. ... More

U(1) Gauge Theory of the Hubbard Model : Spin Liquid States and Possible Application to k-(BEDT-TTF)_2 Cu_2 (CN)_3Feb 04 2005Feb 10 2005We formulate a U(1) gauge theory of the Hubbard model in the slave-rotor representation. From this formalism it is argued that spin liquid phases may exist near the Mott transition in the Hubbard model on triangular and honeycomb lattices at half filling. ... More

Non Magnetic Impurities in the Spin-Gap Phase of the CuprateNov 23 1998It is now well established that Zn doping of high-$T_C$ cuprates reduces their $T_C$ and triggers the appearence of a spin glass phase. In this context, we have solved exactly the problem of N non magnetic impurities in the staggered flux phase of the ... More

Spin susceptibility and the pi-excitation in underdoped cupratesOct 08 1997The dynamical spin susceptibility chi'' at wave vector (pi, pi) and the spectrum pi'' of the spin-triplet particle--particle excitation with center of mass momentum (pi, pi) (pi-excitation) are considered in the slave-boson formulation of the t--J-model. ... More

Emergent honeycomb lattice in LiZn2Mo3O8Aug 12 2013We introduce the idea of emergent lattices, where a simple lattice decouples into two weakly-coupled lattices as a way to stabilize spin liquids. In LiZn2Mo3O8, the disappearance of 2/3rds of the spins at low temperatures suggests that its triangular ... More

Confinement and Bose Condensation in Gauge Theory of High-Tc SuperconductorsJul 01 1999The issue of confinement and bose condensation is studied for gauge models of high-Tc superconductors. First the Abelian-Higgs model in (2+1)D, i.e., XY-model coupled to lattice gauge field $a_{\mu}$ with coupling $g$, is studied taking into account both ... More

Exact Density of States in a System of Disordered Two Dimensional Dirac Fermions in the Unitarity Limit: The d-wave SuperconductorNov 23 1998Feb 16 1999In this paper we present a method to compute the exact density of states induced by $N$ non magnetic impurities in a system of two dimensional Dirac fermions in the unitarity limit. We review the case of the $\pi$-flux phase of the Heisenberg model and ... More

Cuprates as doped U(1) spin liquidsJun 02 2004We explore theoretically the notion that the underdoped cuprates may be viewed as doped U(1) spin liquid Mott insulators. We pursue a conceptually clear version of this idea that naturally incorporates several aspects of the phenomenology of the cuprates. ... More

Lightly doped dimerized spin chain in the one-dimensional t-J-J' modelSep 11 2003Apr 09 2004We study the one-dimensional t-J-J'-model in the limit of small hole doping $x$ and small $J/t$, $J'/t$. Special emphasis is put on the regime $J'/J \approx .5$ where a spin gap is present at small doping and the undoped spin chain is strongly dimerized. ... More

Renormalized mean-field theory of the neutron scattering in cuprate superconductorsJul 06 2001The magnetic excitation spectrum of the t-t'-J-model is studied in mean-field theory and compared to inelastic neutron-scattering (INS) experiments on YBCO and BSCCO superconductors. Within the slave-particle formulation the dynamical spin response is ... More

Order from Disorder: Non Magnetic Impurities in the Spin-gap Phase of the CupratesFeb 25 1998Jul 06 1998We solve the problem of $N$ non magnetic impurities in the staggered flux phase of the Heisenberg model which we assume to be a good mean-field approximation for the spin-gap phase of the cuprates. The density of states is evaluated exactly in the unitary ... More

Staggered flux vortices and the superconducting transition in the layered cupratesSep 19 2003We propose an effective model for the superconducting transition in the high-T_c cuprates motivated by the SU(2) gauge theory approach. In addition to variations of the superconducting phase we allow for local admixture of staggered flux order. This leads ... More

Slave Boson Approach to The Neutron Scattering in YBCO SuperconductorsNov 03 1998Apr 06 1999The evolution of the so-called `41meV resonance' in the magnetic response of YBCO cuprates is studied with slave-boson theory for the t-t'-J-model. The resonance appears as a collective spin fluctuation in the d-wave superconducting (SC) state. It is ... More

Kondo Effect in High-T_c CupratesFeb 12 1997Feb 25 1997We study the Kondo effect due to the nonmagnetic impurity, e.g., Zn, in high-T_c cuprates based on the spin-change separated state. In the optimal or overdoped case with the Kondo screening, the residual resistivity is dominated by the spinons while the ... More

New Collective Modes in the Superconducting Ground States in the Gauge Theory Description of the CupratesNov 29 2002May 27 2003In the slave boson mean field treatment of the t-J model, the ground state for small doping is a d-wave superconductor. A conventional superconductor has collective modes associated with the amplitude and phase of the pairing order parameter. Here, the ... More

Energy Scales in the Local Magnetic Excitation Spectrum of YBCOOct 16 2001The wave-vector integrated dynamical spin susceptibility chi_{2D}(omega) of YBCO cuprates is considered. chi_{2D} is calculated in the superconducting state from a renormalized mean-field theory of the t-t'-J-model, based on the slave-boson formulation. ... More

Energy Gap Structure in Bilayer Oxide SuperconductorsJan 09 1995Mar 15 1995We consider a model for bilayer superconductors where an interlayer pairing amplitude $\Delta_\perp$ co-exists with intralayer pairing $\Delta_\|$ of $d_{x^2 - y^2}$ symmetry. This model is motivated by a recent photoemission experiment reporting the ... More

A Proposal to Use Neutron Scattering to Measure Scalar Spin Chirality Fluctuations in Kagome LatticesOct 10 2012In the theory of quantum spin liquids, gauge fluctuations are emergent excitations at low energy. The gauge magnetic field is proportional to the scalar spin chirality, S1.(S2xS3). It is therefore highly desirable to measure the fluctuation spectrum of ... More

Formation of proto-cluster: a virialized structure from gravo-turbulent collapse II. A two-dimensional analytical model for rotating and accreting systemMar 25 2016Most stars are born in the gaseous proto-cluster environment. The knowledge of this intermediate stage gives more accurate constraints on star formation characteristics. We demonstrate that a virialized globally supported structure, in which star formation ... More

Observation of emergent photon in Monte Carlo simulation of exciton condensateMar 23 2006Jun 07 2006Using Monte Carlo simulation, we studied fractionalized phases in a model of exciton bose condensate and found evidence for an emergent photon in a finite size system. The fractionalized phase is a meta-stable Coulomb phase where an emergent photon arises ... More

Transport phenomenology for a holon-spinon fluidOct 08 1996We propose that the normal-state transport in the cuprate superconductors can be understood in terms of a two-fluid model of spinons and holons. In our scenario, the resistivity is determined by the properties of the holons while magnetotransport involves ... More

Spinon Phonon Interaction and Ultrasonic Attenuation in Quantum Spin LiquidsNov 24 2010Several experimental candidates for quantum spin liquids have been discovered in the past few years which appear to support gapless fermionic $S = {1\over 2}$ excitations called spinons. The spinons may form a Fermi sea coupled to a $U(1)$ gauge field, ... More

Optical Conductivity From Pair Density WavesAug 03 2016We present a theory of optical conductivity in systems with finite-momentum Cooper pairs. In contrast to the BCS pairing where AC conductivity is purely imaginary in the clean limit, there is nonzero AC absorption across the superconducting gap for finite-momentum ... More

Superconductivity at very low density: the case of strontium titanateMay 05 2016Jun 07 2016Doped strontium titanate becomes superconducting at a density as low as n = 5 x 10^17 cm^-3, where the Fermi energy is orders of magnitude smaller than the longitudinal-optical-phonon frequencies. In this limit the only optical mode with a frequency which ... More

Why are Orbital Currents Central to High Tc Theory?Sep 25 2002Oct 07 2002We explain qualitatively why the staggered flux state plays a central role in the SU(2) formulation of the t-J model, which we use to model the pseudogap state in underdoped cuprates. This point of view is supported by studies of projected wavefunctions. ... More

Density of States of a d-wave Superconductor in the Presence of Strong Impurity Scatterers: a Non Perturbative ResultFeb 15 2000Jun 08 2000We present a method to compute the density of states induced by N non magnetic impurities in a d-wave superconductor, in the unitary limit of very strong scatering centers. For frequencies very small as compared to the superconducting gap ($\omega \ll ... More

Formation of proto-cluster: a virialized structure from gravo-turbulent collapse I. Simulation of cluster formation in collapsing molecular cloudMar 25 2016Stars are often observed to form in clusters. It is therefore important to understand how such a region of concentrated mass is assembled out of the diffuse medium and its properties eventually prescribe the important physical mechanisms and determine ... More

Observation of two distinct pairs fluctuation lifetimes and supercurrents in the pseudogap regime of cuprate junctionsSep 06 2016Pairs fluctuation supercurrents and inverse lifetimes were measured on epitaxial c-axis junctions of the cuprates in the pseudogap regime, with a $PrBa_2Cu_3O_{7-\delta}$ barrier sandwiched in between two $YBa_2Cu_3O_{7-\delta}$ or doped $YBa_2Cu_3O_y$ ... More

Quantum critical point in the Kondo-Heisenberg model on the honeycomb latticeOct 10 2006May 01 2007We study the Kondo--Heisenberg model on the honeycomb lattice at half-filling. Due to the vanishing of the density of states at the fermi level, the Kondo insulator disappears at a finite Kondo coupling even in the absence of the Heisenberg exchange. ... More

Staggered flux fluctuations and the quasiparticle scattering rate in the SU(2) gauge theory of the t-J modelDec 04 2002Dec 05 2002We study staggered flux fluctuations around the superconducting state of the SU(2) meanfield theory for the two-dimensional t-J-model and their effect on the electron spectral function. The quasiparticle peaks near the saddlepoints get strongly broadened ... More

Spinon-Phonon Interaction in Algebraic Spin LiquidsMar 04 2013Motivated by a search for experimental probes to access the physics of fractionalized excitations called spinons in a spin liquids, we study the interaction of spinons with lattice vibrations. We consider the case of algebraic spin liquid, when spinons ... More

Isotope effect on the superfluid density in conventional and high-temperature superconductorsSep 13 2010We investigate the isotope effect on the London penetration depth of a superconductor which measures $n_S/m^*$, the ratio of superfluid density to effective mass. We use a simplified model of electrons weakly coupled to a single phonon frequency $\omega_E$, ... More

Doped dimerized spin chains: Another path to superconductivityDec 09 2002Jun 11 2003This paper has been withdrawn by the authors, since we have come to believe that the present approach is not convergent at small doping. We will shortly submit an improved theory of the tJJ' model at small J/t in the dilute hole limit. This will be a ... More

Local Moment Formation in the Superconducting State of a Doped Mott InsulatorMay 15 2002Sep 20 2002A microscopic theory is presented for the local moment formation near a non-magnetic impurity or a copper defect in high-T_c superconductors. We use a renormalized meanfield theory of the t-J model for a doped Mott insulator and study the fully self-consistent, ... More

Study of the triangular lattice tV model near x=1/3Jan 11 2004We study extended Hubbard model on a triangular lattice near doping $x=1/3$, which may be relevant for the recently discovered superconductor Na$_x$CoO$_2 \cdot y$H$_2$O. By generalizing this model to $N$ fermionic species, we formulate a meanfield description ... More

Reply to Comment on ``Scaling of the quasiparticle spectrum for d-wave superconductors''May 06 1997Volovik and Kopnin make two seperate points regarding our recent paper (S. H. Simon and P. A. Lee, PRL 78, 1548 (1997); cond-mat/9611133). First they note that the scaling regime we address in our paper is limited by the curvature of the Fermi surface, ... More

Theory of Underdoped CupratesJun 15 1995Jun 15 1995We develop a slave-boson theory for the t-J model at finite doping which respects an SU(2) symmetry -- a symmetry previously known to be important at half filling. The mean field phase diagram is found to be consistent with the phases observed in the ... More

Erratum: Engineering a p+ip Superconductor: Comparison of Topological Insulator and Rashba Spin-Orbit Coupled Materials [Phys. Rev. B 83, 184520 (2011)]Aug 10 2011In this erratum, we revisit the issue of bulk-disorder on proposals to realize an effective p+ip superconductor from spin-orbit coupled materials. Contrary to the claim in [Phys. Rev. B 83, 184520 (2011)], we show that the pair breaking effects of bulk-disorder ... More

Robustness of Majorana Fermion induced Fractional Josephson EffectMar 25 2011It is shown in previous works that the coupling between two Majorana end states in superconducting quantum wires leads to fractional Josephson effect. However, in realistic experimental conditions, multiple bands of the wires are occupied and the Majorana ... More

Majorana End-States in Multi-band Microstructures with Rashba Spin-Orbit CouplingNov 29 2010A recent work [1] demonstrated, for an ideal spinless p+ip superconductor, that Majorana end-states can be realized outside the strict one-dimensional limit, so long as: 1) the sample width does not greatly exceed the superconducting coherence length ... More

Edge-currents in superconductors with a broken time-reversal symmetryJan 07 2005Jul 05 2005We analyze edge currents and edge bands at the surface of a time-reversal symmetry breaking d_{x^2-y^2}+id_{xy} superconductor. We show that the currents have large Friedel oscillations with two interfering frequencies: \sqrt{2}k_F from sub-gap states, ... More

Anomalous Spin Excitation Spectrum of the Heisenberg Model in a Magnetic FieldOct 07 2001Mar 04 2002Making the assumption that high energy fermions exist in the two dimensional spin-1/2 Heisenberg antiferromagnet we present predictions based on the pi-flux ansatz for the dynamic structure factor when the antiferromagnet is subject to a uniform magnetic ... More

Vortex Structure in Underdoped CupratesAug 29 2000In underdoped cuprates the normal state is highly anomalous and is characterized as a pseudogap phase. The question of how to describe the ``normal'' core of a superconducting vortex is an outstanding open problem. We show that the SU(2) formulation of ... More

Exotic S=1 spin liquid state with fermionic excitations on triangular latticeAug 15 2011Aug 22 2011Motivated by recent experiments on the material Ba_3NiSb_2O_9 we consider a spin-one quantum antiferromagnet on a triangular lattice with the Heisenberg bilinear and biquadratic exchange interactions and a single-ion anisotropy. Using a fermionic "triplon" ... More

STAIR Codes: A General Family of Erasure Codes for Tolerating Device and Sector FailuresJun 20 2014Jun 23 2014Practical storage systems often adopt erasure codes to tolerate device failures and sector failures, both of which are prevalent in the field. However, traditional erasure codes employ device-level redundancy to protect against sector failures, and hence ... More

Multichannel Generalization of Kitaev's Majorana End States and a Practical Route to Realize Them in Thin FilmsJul 26 2010Nov 29 2010The ends of one-dimensional p+ip superconductors have long been predicted to possess localized Majorana fermion modes. We show that Majorana end states survive beyond the strict 1D single-channel limit so long as the sample width does not exceed the superconducting ... More

Theory of Thermal Hall Effect in Quantum MagnetsApr 22 2009Jul 28 2010We present a theory of the thermal Hall effect in insulating quantum magnets, where the heat current is totally carried by charge-neutral objects such as magnons and spinons. Two distinct types of thermal Hall responses are identified. For ordered magnets, ... More

Spin-triplet p-wave pairing in a 3-orbital model for iron pnictide superconductorsApr 10 2008Sep 26 2008We examine the possibility that the superconductivity in the newly discovered FeAs materials may be caused by the Coulomb interaction between d-electrons of the iron atoms. We find that when the Hund's rule ferromagnetic interaction is strong enough, ... More

Power-law Conductivity inside the Mott gap: application to $κ-(BEDT-TTF)_2Cu_2(CN)_3$Jun 01 2007The charge dynamics of spin-liquid states described by U(1) gauge theory coupling to fermionic spinons is discussed in this paper. We find that the gapless spinons give rise to a power law optical conductivity inside the charge gap. The theory is applied ... More

Theory of spin excitations in undoped and underdoped cupratesOct 12 1998Mar 24 1999We consider the magnetic properties of high Tc cuprates from a gauge theory point of view, with emphasis on the underdoped regime. Underdoped cuprates possess certain antiferromagnetic correlations, as evidenced, for example, by different temperature ... More

Theory of Quasi-Particles in the Underdoped High Tc Superconducting StateSep 09 1997Dec 13 1997The microscopic theory of superconducting (SC) state in the SU(2) slave-boson model is developed. We show how the pseudogap and Fermi surface (FS) segments in the normal state develop into a d-wave gap in the superconducting state. Even though the superfluid ... More

Bipolaronic charge excitations in t-J two-leg laddersAug 20 1997We present a low-energy effective model for the charge degrees of freedom in two-leg t-J ladders. Starting from SU(2) mean-field theory, we exclude the spin degrees of freedom which have an energy gap. At low temperatures, the mean-field solution is the ... More

Specific heat and validity of quasiparticle approximation in the half-filled Landau levelFeb 27 1996We calculate the specific heat of composite fermion system in the half-filled Landau level. Two different methods are used to examine validity of the quasiparticle approximation when the two-body interaction is given by $V(q) = V_0 / q^{2-\eta}$ ($1 \le ... More

A Proposal to Measure the Quasiparticle Poisoning Time of Majorana Bound StatesDec 31 2013We propose a method of measuring the fermion parity lifetime of Majorana fermion modes due to quasiparticle poisoning. We model quasiparticle poisoning by coupling the Majorana modes to electron reservoirs, explicitly breaking parity conservation in the ... More

RevDedup: A Reverse Deduplication Storage System Optimized for Reads to Latest BackupsFeb 04 2013Jun 27 2013Scaling up the backup storage for an ever-increasing volume of virtual machine (VM) images is a critical issue in virtualization environments. While deduplication is known to effectively eliminate duplicates for VM image storage, it also introduces fragmentation ... More

When does Magnetization Depend on the Boundary?Jun 27 2012In this paper, we investigate in general how thermodynamic quantities such as the polarization, magnetization and the magneto-electric tensor are affected by the boundaries. We show that when the calculation with periodic boundary conditions does not ... More

Bounding the graviton mass with binary pulsar observationsDec 10 2001By comparing the observed orbital decay of the binary pulsars PSRB1913+16 and PSRB1534+12 to that predicted by general relativity due to gravitational-wave emission, we are able to bound the mass of the graviton to be less than $7.6\times10^{-20} \text{eV}/c^2$ ... More

Scaling of the quasiparticle spectrum for d-wave superconductorsNov 19 1996In finite magnetic field H, the excitation spectrum of the low energy quasiparticles in a 2 dimensional d-wave superconductor exhibits a scaling with respect to $H^{1/2}$. This property can be used to calculate scaling relations for various physical quantities ... More

Spin-gap formation in cuprates: gauge theoryDec 22 1993We analyze the phase diagram of single and bi-layer cuprates using the gauge-field description of the t-J model. For $T>T_{\text{BE}}$ the in-plane fermion-pairing order parameter $\Delta_{\scriptscriptstyle\parallel}$ is eliminated by gauge field fluctuations, ... More

Edge-Ferromagnetism from Majorana Flat-Bands: Application to Split Tunneling-Conductance Peaks in the High-Tc CupratesMar 27 2013In mean-field descriptions of nodal d-wave superconductors, generic edges exhibit dispersionless Majorana fermion bands at zero-energy. These states give rise to an extensive ground-state degeneracy, and are protected by time-reversal (TR) symmetry. We ... More

Magnetism and Mott Transition: A Slave-rotor StudyJan 27 2011Apr 05 2011Motivated by the debate of spin-density-wave (SDW) versus local-moment (LM) picture in the iron-based superconducting (FeSC) materials, we consider a two-band orbital-symmetric Hubbard model in which there is robust Fermi surface nesting at $(\pi,0)$. ... More

Static Electric Field in a 1D Systems without BoundariesMay 25 2011In this brief report, we show that in a 1D system with unit-cell doubling, the coefficient of the $\theta$-term is not only determined the topological index, $\int i\bra{u_k}\frac{\d}{\d k}\ket{u_k}{\rm d}k$. Specifically, the relative position between ... More

Numerical Studies of Quantum Oscillations in the Superconducting vortex mixed stateDec 17 2008We studied the quantum oscillations in superconducting vortex mixed states with d-wave pairing. We showed that the Onsager relation does not always apply. Furthermore, at mean field level the quantum oscillations from electron pockets are suppressed by ... More

Bounding the mass of the graviton using binary pulsar observationsSep 13 2001May 14 2002The close agreement between the predictions of dynamical general relativity for the radiated power of a compact binary system and the observed orbital decay of the binary pulsars PSR B1913+16 and PSR B1534+12 allows us to bound the graviton mass to be ... More

Topological Superconductivity and Majorana Fermions in Metallic Surface-StatesJan 10 2012Heavy metals, such as Au, Ag, and Pb, often have sharp surface states that are split by strong Rashba spin-orbit coupling. The strong spin-orbit coupling and two-dimensional nature of these surface states make them ideal platforms for realizing topological ... More

The Unusual Superconducting State of Underdoped CupratesFeb 12 1997There is increasing experimental evidence that the superconducting energy gap $\Delta_0$ in the underdoped cuprates is independent of doping concentration $x$ while the superfluid density is linear in $x$. We show that under these conditions, thermal ... More

Staggered-flux normal state in the weakly doped t-J modelMay 07 2003A normal (non-superconducting) ground state of the t-J model may be variationally approximated by a Gutzwiller-projected wave function. Within this approximation, at small hole doping near half-filling, the normal state favors staggered-flux ordering. ... More

Unified Formalism for calculating Polarization, Magnetization, and more in a Periodic InsulatorAug 31 2011Nov 15 2011In this paper, we propose a unified formalism, using Green's functions, to integrate out the electrons in an insulator under uniform electromagnetic fields. We derive a perturbative formula for the Green's function in the presence of uniform magnetic ... More

Topological Insulator and the $θ$-vacuum in a system without boundariesDec 09 2010Dec 10 2010In this paper we address two questions concerning the effective action of a topological insulator in one and three dimensional space without boundaries, such as a torus. The first is whether a uniform $\theta$-term with $\theta=\pi$ is generated for a ... More

Transport Properties of a spinon Fermi surface coupled to a U(1) gauge fieldAug 14 2007With the organic compound $\kappa$-(BEDT-TTF)$_2$-Cu$_2$(CN)$_3$ in mind, we consider a spin liquid system where a spinon Fermi surface is coupled to a U(1) gauge field. Using the non-equilibrium Green's function formalism, we derive the Quantum Boltzmann ... More

Effect of Hund coupling in the one-dimensional SU(4) Hubbard modelSep 30 2003The one-dimensional SU(4) Hubbard model perturbed by Hund coupling is studied, away from half-filling, by means of renormalization group and bosonization methods. A spectral gap is always present in the spin-orbital sector irrespective of the magnitude ... More

Proposal for detecting spin-chirality terms in Mott insulators via resonant inelastic x-ray scatteringJun 15 2011Sep 12 2011We consider the question of whether resonant inelastic x-ray scattering (RIXS) can be used to detect many-body excitations that are coupled to the spin-chirality terms S_i . (S_j x S_k) in a Mott insulator. We find that while the spin-chirality terms ... More

Microwave Conductivity due to Scattering from Extended Linear Defects in d-Wave SuperconductorsSep 05 2001Recent microwave conductivity measurements of detwinned, high-purity, slightly overdoped YBa$_{2}$Cu$_{3}$O$_{6.993}$ crystals reveal a linear temperature dependence and a near-Drude lineshape for temperatures between 1 and 20 K and frequencies ranging ... More

Overscreened Kondo fixed point in S=1 spin liquidDec 20 2012We propose a possible realization of the overscreened Kondo impurity problem by a magnetic s=1/2 impurity embedded in a two-dimensional S=1 U(1) spin liquid with a Fermi surface. This problem contains an interesting interplay between non-Fermi-liquid ... More

Engineering a p+ip Superconductor: Comparison of Topological Insulator and Rashba Spin-Orbit Coupled MaterialsMar 10 2011Apr 17 2011We compare topological insulator materials and Rashba coupled surfaces as candidates for engineering p+ip superconductivity. Specifically, in each type of material we examine 1) the limitations to inducing superconductivity by proximity to an ordinary ... More

Kondo Vortices, Zero Modes, and Magnetic Ordering in a Kondo Lattice ModelMar 25 2009Motivated by the mysteries of the heavy fermion quantum critical point, we investigate the competition between Kondo screening and magnetic ordering in the honeycomb Kondo lattice at half filling. We examine the destruction of the Kondo phase by proliferating ... More

Possible effects of charge frustration in Na$_x$CoO$_2$: bandwidth suppression, charge orders and resurrected RVB superconductivityOct 16 2003Charge frustration due to further neighbor Coulomb repulsion can have dramatic effects on the electronic properties of Na$_x$CoO$_2$ in the full doping range. It can significantly reduce the effective mobility of the charge carriers, leading to a low ... More

Staggered-spin contribution to nuclear spin-lattice relaxation in two-leg antiferromagnetic spin-1/2 laddersJul 13 1998We study the nuclear spin-lattice relaxation rate $1/T_1$ in the two-leg antiferromagnetic spin-1/2 Heisenberg ladder. More specifically, we consider the contribution to $1/T_1$ from the processes with momentum transfer $(\pi,\pi)$. In the limit of weak ... More

Bosons, gauge fields, and high-Tc cupratesJul 21 1996A simple model of a degenerate two-dimensional Bose liquid interacting with a fluctuating gauge field is investigated as a possible candidate to describe the charge degree of freedom in the normal state of the cuprate superconductors. We show that the ... More

Degenerate Bose liquid in a fluctuating gauge fieldJan 02 1996We study the effect of a strongly fluctuating gauge field on a degenerate Bose liquid, relevant to the charge degrees of freedom in doped Mott insulators. We find that the superfluidity is destroyed. The resulting metallic phase is studied using quantum ... More

Amperean Pairing Instability in the U(1) Spin Liquid State with Fermi Surface and Application to $κ-(BEDT-TTF)_2 Cu_2 (CN)_3$Jul 01 2006Recent experiments on the organic compound $\kappa-(BEDT-TTF)_2 Cu_2 (CN)_3$ raise the possibility that the system may be described as a quantum spin liquid. Here we propose a pairing state caused by the `Amperean' attractive interaction between spinons ... More

Susceptibility of a spinon Fermi surface coupled to a U(1) gauge fieldNov 08 2006We study the theory of a U(1) gauge field coupled to a spinon Fermi surface. Recently this model has been proposed as a possible description of the organic compound $\kappa-(BEDT-TTF)_2 Cu_2 (CN)_3$. We calculate the susceptibility of this system and ... More

Vortex description of the fractionalized phase in exciton bose condensateSep 14 2005Apr 10 2006As a sequel to the previous work [Phys. Rev. B 72, 235104 (2005)] we present a vortex description of the fractionalized phase in exciton bose condensate. Magnetic flux line and monopole of the 3+1D emergent U(1) gauge theory are identified in the exciton ... More

Thermal Hall Effect of Spins in a ParamagnetOct 14 2014Feb 25 2015Theory of Hall transport of spins in a correlated paramagnetic phase is developed. By identifying the thermal Hall current operator in the spin language, which turns out to equal the spin chirality in the pure Heisenberg model, various response functions ... More

Doped t-J Model on a Triangular Lattice: Possible Application to Na$_x$CoO$_2\cdot y$H$_2$0 and Na$_{1-x}$TiO$_2$Apr 16 2003Dec 23 2003We report the finding of time-reversal-symmetry-breaking $d_{x^2-y^2}+ id_{xy}$ superconducting ground state in the slave-boson mean-field theory for the t-J model on triangular lattice. For $t/J=-5$ ($t/J=-9$) pairing exists for $x < 13%$ ($x<8%$) upon ... More

Atmospheric Retrieval Analysis of the Directly Imaged Exoplanet HR 8799bJul 04 2013Sep 18 2013Directly-imaged exoplanets are unexplored laboratories for the application of the spectral and temperature retrieval method, where the chemistry and composition of their atmospheres are inferred from inverse modeling of the available data. As a pilot ... More

Swift Pointing and the Association Between Gamma-Ray Bursts and Gravitational-Wave BurstsApr 11 2003The currently accepted model for gamma-ray burst phenomena involves the violent formation of a rapidly rotating solar mass black hole. Gravitational waves should be associated with the black-hole formation, and their detection would permit this model ... More

Swift Pointing and Gravitational-Wave Bursts from Gamma-Ray Burst EventsApr 23 2003The currently accepted model for gamma-ray burst phenomena involves the violent formation of a rapidly rotating solar-mass black hole. Gravitational waves should be associated with the black-hole formation, and their detection would permit this model ... More

Low-energy behavior of spin-liquid electron spectral functionsOct 02 2012Dec 22 2012We calculate the electron spectral function for a spin-liquid with a spinon Fermi surface and a Dirac spin-liquid. Calculations are based upon the slave-rotor mean-field theory. We consider the effect of gauge fluctuations using a simple model and find ... More

Paired chiral spin liquid with a Fermi surface in S=1 model on the triangular latticeAug 15 2012Dec 24 2012Motivated by recent experiments on Ba3NiSb2O9, we investigate possible quantum spin liquid ground states for spin S=1 Heisenberg models on the triangular lattice. We use Variational Monte Carlo techniques to calculate the energies of microscopic spin ... More

Weak Mott insulators on the triangular lattice: possibility of a gapless nematic quantum spin liquidJul 10 2009Dec 29 2010We study the energetics of Gutzwiller projected BCS states of various symmetries for the triangular lattice antiferromagnet with a four particle ring exchange using variational Monte Carlo methods. In a range of parameters the energetically favored state ... More