arXiv subjects

T. Senthil

Publications and source records attributed to T. Senthil.

At least 163 records · Page 9Linked to original sources

arXiv2007

Quantum spin nematics, dimerization, and deconfined criticality in quasi-one dimensional spin-1 magnets

We study theoretically the destruction of spin nematic order due to quantum fluctuations in quasi-one dimensional spin-1 magnets. If the nematic ordering is disordered by condensing disclinations then quantum Berry phase effects induce dimerization in the resulting paramagnet. We develop a theory for a Landau-forbidden second order transition between the spin nematic and dimerized states found in recent numerical calculations. Numerical tests of the theory are suggested.

cond-mat.str-el↗

arXiv2007

Emergence of Artificial Photons in an Optical Lattice

We establish the theoretical feasibility of direct analog simulation of the compact U(1) lattice gauge theories in optical lattices with dipolar bosons. We discuss the realizability of the topological Coulomb phase in extended Bose-Hubbard models in several optical lattice geometries. We predict the testable signatures of this emergent phase in noise correlation measurements, thus suggesting the possible emergence of artificial light in optical lattices.

cond-mat.str-el↗

arXiv2006

Higher angular momentum Kondo liquids

Conventional heavy Fermi liquid phases of Kondo lattices involve the formation of a "Kondo singlet" between the local moments and the conduction electrons. This Kondo singlet is usually taken to be in an internal s-wave angular momentum state. Here we explore the possibility of phases where the Kondo singlet has internal angular momentum that is d-wave. Such states are readily accessed in a slave boson mean field formulation, and are energetically favorable when the Kondo interaction is between a local moment and an electron at a nearest neighbor site. The properties of the d-wave Kondo liquid are studied. Effective mass and quasiparticle residue show large angle dependence on the Fermi surface. Remarkably in certain cases, the quasiparticle residue goes to zero at isolated points (in two dimensions) on the Fermi surface. The excitations at these points then include a free fractionalized spinon. We also point out the possibility of quantum Hall phenomena in two dimensional Kondo {\em insulators}, if the Kondo singlet has complex internal angular momentum. We suggest that such d-wave Kondo pairing may provide a useful route to thinking about correlated Fermi liquids with strong anisotropy along the Fermi surface.

cond-mat.str-el↗

arXiv2006

Amperean Pairing Instability in the U(1) Spin Liquid State with Fermi Surface and Application to $κ-(BEDT-TTF)_2 Cu_2 (CN)_3$

Recent experiments on the organic compound $κ-(BEDT-TTF)_2 Cu_2 (CN)_3$ 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 on a Fermi surface mediated by the U(1) gauge field. We show that this state can explain many of the observed low temperature phenomena and discuss testable consequences.

cond-mat.str-el↗

arXiv2006

Possible ferro-spin nematic order in NiGa2S4

We explore the possibility that the spin-1 triangular lattice magnet NiGa2 S4 may have a ferro-nematic ground state with no frozen magnetic moment but a uniform quadrupole moment. Such a state may be stabilized by biquadratic spin interactions. We describe the physical properties of this state and suggest experiments to help verify this proposal. We also contrast this state with a `non-collinear' nematic state proposed earlier by Tsunetsugu and Arikawa for NiGa2S4 .

cond-mat.str-el↗

arXiv2006

On non-Fermi liquid quantum critical points in heavy fermion metals

Heavy electron metals on the verge of a quantum phase transition to magnetism show a number of unusual non-fermi liquid properties which are poorly understood. This article discusses in a general way various theoretical aspects of this phase transition with an eye toward understanding the non-fermi liquid phenomena. We suggest that the non-Fermi liquid quantum critical state may have a sharp Fermi surface with power law quasiparticles but with a volume not set by the usual Luttinger rule. We also discuss the possibility that the electronic structure change associated with the possible Fermi surface reconstruction may diverge at a different time/length scale from that associated with magnetic phenomena.

cond-mat.str-el↗

arXiv2006

Vortex description of the fractionalized phase in exciton bose condensate

As 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 picture. A bundle of vortex/anti-vortex pairs of all flavors of excitons corresponds to the magnetic flux line and a point at which the vortices and anti-vortices recombine is identified as magnetic monopole. This completes the magnetic sector of the low energy excitation in the fractionalized phase.

cond-mat.str-el↗

arXiv2006

Spin nematics and magnetization plateau transition in anisotropic Kagome magnets

We study S=1 kagome antiferromagnets with isotropic Heisenberg exchange $J$ and strong easy axis single-ion anisotropy $D$. For $D \gg J$, the low-energy physics can be described by an effective $S=1/2$ $XXZ$ model with antiferromagnetic $J_z \sim J$ and ferromagnetic $J_\perp \sim J^2/D$. Exploiting this connection, we argue that non-trivial ordering into a "spin-nematic" occurs whenever $D$ dominates over $J$, and discuss its experimental signatures. We also study a magnetic field induced transition to a magnetization plateau state at magnetization 1/3 which breaks lattice translation symmetry due to ordering of the $S^z$ and occupies a lobe in the $B/J_z$-$J_z/J_\perp$ phase diagram.

cond-mat.str-el↗

arXiv2005

Fractionalization, topological order, and quasiparticle statistics

We argue, based on general principles, that topological order is essential to realize fractionalization in gapped insulating phases in dimensions $d \geq 2$. In $d=2$ with genus $g$, we derive the existence of the minimum topological degeneracy $q^g$ if the charge is fractionalized in unit of $1/q$, irrespective of microscopic model or of effective theory. Furthermore, if the quasiparticle is either boson or fermion, it must be at least $q^{2g}$.

cond-mat.str-el↗

arXiv2005

Competing orders, non-linear sigma models, and topological terms in quantum magnets

A number of examples have demonstrated the failure of the Landau-Ginzburg-Wilson(LGW) paradigm in describing the competing phases and phase transitions of two dimensional quantum magnets. In this paper we argue that such magnets possess field theoretic descriptions in terms of their slow fluctuating orders provided certain topological terms are included in the action. These topological terms may thus be viewed as what goes wrong within the conventional LGW thinking. The field theoretic descriptions we develop are possible alternates to the popular gauge theories of such non-LGW behavior. Examples that are studied include weakly coupled quasi-one dimensional spin chains, deconfined critical points in fully two dimensional magnets, and two component massless $QED_3$. A prominent role is played by an anisotropic O(4) non-linear sigma model in three space-time dimensions with a topological theta term. Some properties of this model are discussed. We suggest that similar sigma model descriptions might exist for fermionic algebraic spin liquid phases.

cond-mat.str-el↗

arXiv2005

Neel order, quantum spin liquids and quantum criticality in two dimensions

This paper is concerned with the possibility of a direct second order transition out of a collinear Neel phase to a paramagnetic spin liquid in two dimensional quantum antiferromagnets. Contrary to conventional wisdom, we show that such second order quantum transitions can potentially occur to certain spin liquid states popular in theories of the cuprates. We provide a theory of this transition and study its universal properties in an $ε$ expansion. The existence of such a transition has a number of interesting implications for spin liquid based approaches to the underdoped cuprates. In particular it considerably clarifies existing ideas for incorporating antiferromagnetic long range order into such a spin liquid based approach.

cond-mat.str-el↗

arXiv2005

Algebraic spin liquid as the mother of many competing orders

We study the properties of a class of two-dimensional interacting critical states -- dubbed algebraic spin liquids -- that can arise in two-dimensional quantum magnets. A particular example that we focus on is the staggered flux spin liquid, which plays a key role in some theories of underdoped cuprate superconductors. We show that the low-energy theory of such states has much higher symmetry than the underlying microscopic spin system. This symmetry has remarkable consequences, leading in particular to the unification of a number of seemingly unrelated competing orders. The correlations of these orders -- including, in the staggered flux state, the Neel vector and the order parameter for the columnar and box valence-bond solid states -- all exhibit the SAME slow power-law decay. Implications for experiments in the pseudogap regime of the cuprates and for numerical calculations on model systems are discussed.

cond-mat.str-el↗

arXiv2005

Ordering near the percolation threshold in models of 2D interacting bosons with quenched dilution

Randomly diluted quantum boson and spin models in two dimensions combine the physics of classical percolation with the well-known dimensionality dependence of ordering in quantum lattice models. This combination is rather subtle for models that order in two dimensions but have no true order in one dimension, as the percolation cluster near threshold is a fractal of dimension between 1 and 2: two experimentally relevant examples are the O(2) quantum rotor and the Heisenberg antiferromagnet. We study two analytic descriptions of the O(2) quantum rotor near the percolation threshold. First a spin-wave expansion is shown to predict long-ranged order, but there are statistically rare points on the cluster that violate the standard assumptions of spin-wave theory. A real-space renormalization group (RSRG) approach is then used to understand how these rare points modify ordering of the O(2) rotor. A new class of fixed points of the RSRG equations for disordered 1D bosons is identified and shown to support the existence of long-range order on the percolation backbone in two dimensions. These results are relevant to experiments on bosons in optical lattices and superconducting arrays, and also (qualitatively) for the diluted Heisenberg antiferromagnet.

cond-mat.dis-nn↗

arXiv2005

Vortices and quasiparticles near the "superconductor-insulator" transition in thin films

We study the low temperature behavior of an amorphous superconducting film driven normal by a perpendicular magnetic field (B). For this purpose we introduce a new two-fluid formulation consisting of fermionized field induced vortices and electrically neutralized Bogoliubov quasiparticles (spinons) interacting via a long-ranged statistical interaction. This approach allows us to access a novel non-Fermi liquid phase which naturally interpolates between the low B superconductor and the high B normal metal. We discuss the transport, thermodynamic, and tunneling properties of the resulting "vortex metal" phase.

cond-mat.supr-con↗

arXiv2005

Spontaneous interlayer coherence in bilayer Kondo systems

Bilayer Kondo systems present interesting models to illustrate the competition between the Kondo effect and intermoment exchange. Such bilayers can exhibit two sharply distinct Fermi liquid phases which are distinguished by whether or not the local moments participate in the Fermi sea. We study these phases and the evolution from one to the other upon changing Kondo coupling. We argue that an ordered state with spontaneous interlayer phase coherence generically intervenes between the two Fermi liquids. Such a condensate phase breaks a U(1) symmetry and is bounded by a finite-temperature Kosterlitz-Thouless transition. Based on general arguments and mean-field calculations we investigate the phase diagram and associated quantum phase transitions.

cond-mat.str-el↗

arXiv2005

Ordering in Cs2CuCl4: Is there a proximate spin liquid?

The layered spiral magnet Cs2CuCl4 displays several interesting properties that have been suggested as evidence of proximity to a two dimensional quantum spin liquid. In this paper we study a concrete version of this proposal and suggest experiments that can potentially confirm it. We study universal critical properties of two-dimensional frustrated quantum magnets near the quantum phase transition between a spiral magnetic state and a spin liquid state with gapped bosonic spinons in the framework of the O(4) invariant critical theory proposed earlier(Chubukov et al, cond-mat/9402006). Direct numerical calculation of the anomalous exponent in spin correlations shows that the critical scattering has broad continua qualitatively similar to experiment. More remarkably we show that the enlarged O(4) symmetry leads to the same slow power law decay for the vector spin chirality and the Neel correlations. We show how this may be observed through polarized neutron scattering experiments. A number of other less dramatic consequences of the critical theory are outlined as well.

cond-mat.str-el↗

arXiv2004

Finite temperature properties of quantum Lifshitz transitions between valence bond solid phases: An example of `local' quantum criticality

We study the finite temperature properties of quantum magnets close to a continuous quantum phase transition between two distinct valence bond solid phases in two spatial dimension. Previous work has shown that such a second order quantum `Lifshitz' transition is described by a free field theory and is hence tractable, but is nevertheless non-trivial. At $T>0$, we show that while correlation functions of certain operators exhibit $ω/T$ scaling, they do not show analogous scaling in space. In particular, in the scaling limit, all such correlators are purely {\em local} in space, although the same correlators at T=0 decay as a power law. This provides a valuable microscopic example of a certain kind of `local' quantum criticality. The local form of the correlations arise from the large density of soft modes present near the transition that are excited by temperature. We calculate exactly the autocorrelation function for such operators in the scaling limit. Going beyond the scaling limit by including irrelevant operators leads to finite spatial correlations which are also obtained.

cond-mat.str-el↗

arXiv2004

Quantum matters: Physics beyond Landau's paradigms

Central to our understanding of quantum many particle physics are two ideas due to Landau. The first is the notion of the electron as a well-defined quasiparticle excitation in the many body state. The second is that of the order parameter to distinguish different states of matter. Experiments in a number of correlated materials raise serious suspicions about the general validity of either notion. A growing body of theoretical work has confirmed these suspicions, and explored physics beyond Landau's paradigms. This article provides an overview of some of these theoretical developments.

cond-mat.str-el↗