Exchange Constants and Neutron Spectra of Iron Pnictide Materials (2009)
We show that the neutron scattering spectra observed in CaFe$_2$As$_2$ by Zhao et al (arXiv:0903.2686v1) and the highly unusual spatially anisotropic exchange constants in the iron pnictides derived...
Pnictides as frustrated quantum antiferromagnet close to a quantum phase transition (2008)
Uhrig, Goetz S., Holt, Michael, Oitmaa, Jaan, Sushkov, Oleg P., Singh, Rajiv R. P.
We present a detailed description of the dynamics of the magnetic modes in the recently discovered superconducting pnictides using reliable self-consistent spin-wave theory and series expansion....
Thermodynamic Properties of Kagome Antiferromagnets with different Perturbations (2008)
Singh, Rajiv R. P., Rigol, Marcos
We discuss the results of several small perturbations to the thermodynamic properties of Kagome Lattice Heisenberg Model (KLHM) at high and intermediate temperatures, including Curie impurities,...
Singh, Rajiv R. P., Huse, David A.
A proposed ground state for the Kagome Lattice Heisenberg Model (KLHM) consists of a Valence Bond Crystal (VBC) with a 36-site unit cell. We calculate the low-lying triplet and singlet excitations in...
Ground State of the Kagome Lattice Heisenberg Antiferromagnet (2007)
Singh, Rajiv R. P., Huse, David A.
Using series expansions around the dimer limit, we show that the ground state of the Heisenberg Antiferromagnet on the Kagome Lattice appears to be a Valence Bond Crystal (VBC) with a 36-site unit...
Rigol, Marcos, Bryant, Tyler, Singh, Rajiv R. P.
We discuss recently introduced numerical linked-cluster (NLC) algorithms that allow one to obtain temperature-dependent properties of quantum lattice models, in the thermodynamic limit, from exact...
Numerical Linked-Cluster Algorithms. II. t-J models on the square lattice (2007)
Rigol, Marcos, Bryant, Tyler, Singh, Rajiv R. P.
We discuss the application of a recently introduced numerical linked-cluster (NLC) algorithm to strongly correlated itinerant models. In particular, we present a study of thermodynamic observables:...
Kagome lattice antiferromagnets and Dzyaloshinsky-Moriya interactions (2007)
Rigol, Marcos, Singh, Rajiv R. P.
We study the consequences of in-plane (D_p) and out-of-plane (D_z) Dzyaloshinsky-Moriya (DM) interactions on the thermodynamic properties of spin-1/2} Heisenberg model on the kagome lattice using...
Bryant, Tyler, Singh, Rajiv R. P.
We study ground state properties and excitation spectra for hard-core Bosons on square and triangular lattices, at half filling, using series expansion methods. Nearest-neighbor repulsion between the...
Magnetic Susceptibility of the Kagome Antiferromagnet ZnCu3(OH)6Cl2 (2007)
Rigol, Marcos, Singh, Rajiv R. P.
We analyze the experimental data for the magnetic susceptibility of the material ZnCu3(OH)6Cl2 in terms of the Kagome Lattice Heisenberg model (KLHM), discussing possible role of impurity spins,...
Fjaerestad, John O., Zheng, Weihong, Singh, Rajiv R. P., McKenzie, Ross H., Coldea, Radu
We use series expansion methods to study ground- and excited-state properties in the helically ordered phase of spin-1/2 frustrated antiferromagnets on an anisotropic triangular lattice. We calculate...
Numerical Linked-Cluster Approach to Quantum Lattice Models (2006)
Rigol, Marcos, Bryant, Tyler, Singh, Rajiv R. P.
We present a novel algorithm that allows one to obtain temperature dependent properties of quantum lattice models in the thermodynamic limit from exact diagonalization of small clusters. Our...
Excitation spectra of the spin-1/2 triangular-lattice Heisenberg antiferromagnet (2006)
Zheng, Weihong, Fjaerestad, John O., Singh, Rajiv R. P., McKenzie, Ross H., Coldea, Radu
We use series expansion methods to calculate the dispersion relation of the one-magnon excitations for the spin-1/2 triangular-lattice nearest-neighbor Heisenberg antiferromagnet above a...
Anomalous Excitation Spectra of Frustrated Quantum Antiferromagnets (2005)
Zheng, Weihong, Fjaerestad, John O., Singh, Rajiv R. P., McKenzie, Ross H., Coldea, Radu
We use series expansions to study the excitation spectra of spin-1/2 antiferromagnets on anisotropic triangular lattices. For the isotropic triangular lattice model (TLM) the high-energy spectra show...
Zheng, Weihong, Singh, Rajiv R. P., McKenzie, Ross H., Coldea, Radu
We present the temperature dependence of the uniform susceptibility of spin-half quantum antiferromagnets on spatially anisotropic triangular lattices, using high-temperature series expansions. We...
Magnon and Hole Excitations in the Two-Dimensional Half-filled Hubbard Model (2005)
Zheng, Weihong, Singh, Rajiv R. P., Oitmaa, J., Sushkov, O. P., Hamer, C. J.
Spin and hole excitation spectra and spectral weights are calculated for the half-filled Hubbard model, as a function of $t/U$. We find that the high energy spin spectra are sensitive to charge...
Zheng, Weihong, Singh, Rajiv R. P., McKenzie, Ross H., Coldea, Radu
We present the temperature dependence of the uniform susceptibility of spin-half quantum antiferromagnets on spatially anisotropic triangular lattices, using high-temperature series expansions. We...
Zheng, Weihong, Singh, Rajiv R. P., McKenzie, Ross H., Coldea, Radu
We present the temperature dependence of the uniform susceptibility of spin-half quantum antiferromagnets on spatially anisotropic triangular lattices, using high-temperature series expansions. We...
Zheng, Weihong, Singh, Rajiv R. P., McKenzie, Ross H., Coldea, Radu
We present the temperature dependence of the uniform susceptibility of spin-half quantum antiferromagnets on spatially anisotropic triangular-lattices, using high temperature series expansions. We...
Sengupta, Pinaki, Zheng, Weihong, Singh, Rajiv R. P.
Motivated by the geometry of spins in the material CaCu$_2$O$_3$, we study a two-layer, spin-half Heisenberg model, with nearest-neighbor exchange couplings J and \alpha*J along the two axes in the...
Modeling Amyloid Beta Peptide Insertion into Lipid Bilayers (2003)
Mobley, David L., Cox, Daniel L., Singh, Rajiv R. P., Maddox, Michael W., Longo, Marjorie L.
Inspired by recent suggestions that the Alzheimer's amyloid beta peptide (A beta) can insert into cell membranes and form harmful ion channels, we model insertion of the 40 and 42 residue forms of...
Dynamical Structure Factor for the Alternating Heisenberg Chain: A Linked Cluster Calculation (2003)
Hamer, Chris J., Zheng, Weihong, Singh, Rajiv R. P.
We develop a linked cluster method to calculate the spectral weights of many-particle excitations at zero temperature. The dynamical structure factor is expressed as a sum of exclusive structure...
Hysteresis loops of Co-Pt perpendicular magnetic multilayers (2003)
Mobley, David L., Pike, Christopher R., Davies, Joseph E., Cox, Daniel L., Singh, Rajiv R. P.
We develop a phenomenological model to study magnetic hysteresis in two samples designed as possible perpendicular recording media. A stochastic cellular automata model captures cooperative behavior...
Simulations of Oligomeric Intermediates in Prion Diseases (2003)
Mobley, David L., Cox, Daniel L., Singh, Rajiv R. P., Kulkarni, Rahul V., Slepoy, Alexander
We extend our previous stochastic cellular automata based model for areal aggregation of prion proteins on neuronal surfaces. The new anisotropic model allow us to simulate both strong beta-sheet and...
Sengupta, Pinaki, Sandvik, Anders W., Singh, Rajiv R. P.
We have used the stochastic series expansion (SSE) quantum Monte Carlo (QMC) method to study the three-dimensional (3D) antiferromagnetic Heisenberg model on cubic lattices with in-plane coupling J...
Sengupta, Pinaki, Scalettar, Richard T., Singh, Rajiv R. P.
We use quantum Monte Carlo methods and single-mode approximation to study the magnon dispersion in the 2D half-filled Hubbard and phonon-coupled Heisenberg models. We find that in the Hubbard model...
Spinons in a Crossed-Chains Model of a 2D Spin Liquid (2001)
Starykh, Oleg A., Singh, Rajiv R. P., Levine, Gregory C.
Using Random Phase Approximation, we show that a crossed-chains model of a spin-1/2 Heisenberg spins, with frustrated interchain couplings, has a non-dimerized spin-liquid ground state in 2D, with...
Sandvik, Anders W., Singh, Rajiv R. P.
We use quantum Monte Carlo simulations and numerical analytic continuation to study high-energy spin excitations in the two-dimensional S=1/2 Heisenberg antiferromagnet at low temperature. We present...
Comment on "Kagome Lattice Antiferromagnet Stripped to Its Basics" (2000)
White, Steven R., Singh, Rajiv R. P.
Density matrix renormalization group (DMRG) calculations on large systems (up to 3096 spins) indicate that the ground state of the Heisenberg model on a 3-chain Kagome strip is spontaneously...
Müller-Hartmann, Erwin, Singh, Rajiv R. P., Knetter, Christian, Uhrig, Götz S.
We study a generalized Shastry-Sutherland model for the material SrCu$_2$(BO$_3$)$_2$. Along a line in the parameter space, we can show rigorously that the model has a first order phase transition...
Dimer Order with Striped Correlations in the J_1-J_2 Heisenberg Model (1999)
Singh, Rajiv R. P., Weihong, Zheng, Hamer, C. J., Oitmaa, J.
Ground state energies for plaquette and dimer order in the $J_1-J_2$ square-lattice spin-half Heisenberg model are compared using series expansion methods. We find that these energies are remarkably...
Gapless Singlet modes in the Kagome strips: A study through DMRG and strong coupling analysis (1999)
Pati, Swapan K., Singh, Rajiv R. P.
Recently Azaria et al have studied strips of the Kagome-lattice in the weak-coupling limit, where they consist of two spin-half chains on the outside weakly coupled to an array of half-integer spins...
Weihong, Zheng, McKenzie, Ross H., Singh, Rajiv R. P
We study the spin-half Heisenberg models on an anisotropic two-dimensional lattice which interpolates between the square-lattice at one end, a set of decoupled spin-chains on the other end, and the...
Singh, Rajiv R. P, Weihong, Zheng
We study the spin-half Heisenberg chain with alternating nearest neighbor interactions $J_1(1+\delta)$ and $J_1(1-\delta)$ and a uniform second neighbor interaction $J_2=y (1-\delta)$ by series...
Alternating Spin and Orbital Dimerization in Strong-coupling Two-band Models (1998)
Pati, Swapan K., Singh, Rajiv R. P., Khomskii, Daniel I.
We study a one-dimensional Hamiltonian consisting of coupled SU(2) spin and orbital degrees of freedom. Using the density matrix renormalization group, we calculate the phase-diagram and the ground...
Quantum phase transitions in the Triangular-lattice Bilayer Heisenberg Model (1998)
Singh, Rajiv R. P., Elstner, Norbert
We study the triangular lattice bilayer Heisenberg model with antiferromagnetic interplane coupling $J_\perp$ and nearest neighbour intraplane coupling $J= \lambda J_\perp$, which can be ferro- or...
Elstner, Norbert, Singh, Rajiv R. P.
Experimental data for the uniform susceptibility, magnetization and specific heat for the material Cu2(C5H12N2)2Cl4 (abbreviated CuHpCl) as a function of temperature and external field are compared...
Elstner, Norbert, Singh, Rajiv. R. P.
By combining conventional finite-temperature many-body perturbation theory with cluster expansions, we develop a systematic method to carry out high order arbitrary temperature perturbative...
Tests of magnetic Hamiltonians for CaV_4O_9 (1997)
Gelfand, Martin P., Singh, Rajiv R. P.
We study the uniform magnetic susceptibility and spin-gap for recently proposed Heisenberg model Hamiltonians for CaV_4O_9 based on the orbital ordering scenario of Marini and Khomskii and the LDA...
Field Dependence of the Magnetization for the spin-ladder material Cu_2(C_5H_{12}N_2)_2Cl_4 (1996)
Weihong, Zheng, Singh, Rajiv R. P., Oitmaa, J.
We have developed a series expansion method for calculating the uniform magnetization, M, as a function of the applied field h for Heisenberg systems at T=0. The method involves introducing Ising...
Singh, Rajiv R. P., Adler, Joan
We study the two and four dimensional Nishimori multicritical point via high temperature expansions for the $\pm J$ distribution, random-bond, Ising model. In $2d$ we estimate the the critical...
Studies of Quantum Spin Ladders at T=0 and at High Temperatures by Series Expansions (1996)
Oitmaa, J., Singh, Rajiv R. P, Weihong, Zheng
We have carried out extensive series studies, at T=0 and at high temperatures, of 2-chain and 3-chain spin-half ladder systems with antiferromagnetic intrachain and both antiferromagnetic and...
Isotropic Spin Wave Theory of Short-Range Magnetic Order (1996)
Sokol, Alexander, Singh, Rajiv R. P., Elstner, Norbert
We present an isotropic spin wave (ISW) theory of short-range order in Heisenberg magnets, and apply it to square lattice S=1/2 and S=1 antiferromagnets. Our theory has three identical (isotropic)...
Spinons, Solitons and Magnons in One-dimensional Heisenberg-Ising Antiferromagnets (1995)
We calculate the excitation spectra for the one-$d$ Heisenberg-Ising antiferromagnets by expansions around the Ising limit. For $S=1/2$, the calculated expansion coefficients for the spinon-spectra...
Spin-wave excitation spectra and spectral weights in square lattice antiferromagnets (1995)
Singh, Rajiv R. P., Gelfand, Martin P.
Using a recently developed method for calculating series expansions of the excitation spectra of quantum lattice models, we obtain the spin-wave spectra for square lattice, $S=1/2$ Heisenberg-Ising...
The Spin Stiffness and the Transverse Susceptibility of the Half-filled Hubbard Model (1995)
Shi, Zhu-Pei, Singh, Rajiv R. P.
The $T=0$ spin stiffness $\rho _{s}$ and the transverse susceptibility $\chi _{\perp }$ of the square lattice half-filled Hubbard model are calculated as a function of the Hubbard parameter ratio...
Ising Expansion for the Hubbard Model (1995)
Shi, Zhu-Pei, Singh, Rajiv R. P.
We develop series expansions for the ground state properties of the Hubbard model, by introducing an Ising anisotropy into the Hamiltonian. For the two-dimensional (2D) square lattice half-filled...
Crossover Phase Diagram of 2D Heisenberg Ferro- and Antiferromagnets (1995)
Sokol, Alexander, Elstner, Norbert, Singh, Rajiv R. P.
We propose a single crossover phase diagram applicable to 2D collinear Heisenberg antiferromagnets (AFMs) and ferromagnets (FMs), and show that the scaling regimes of AFMs and FMs are in one-to-one...
Phase Transitions in the Symmetric Kondo Lattice Model in Two and Three Dimensions (1995)
Shi, Zhu-Pei, Singh, Rajiv R. P., Gelfand, Martin P., Wang, Ziqiang
We present an application of high-order series expansion in the coupling constants for the ground state properties of correlated lattice fermion systems. Expansions have been generated up to order...
A Plane of Weakly Coupled Heisenberg Chains: Theoretical Arguments and Numerical Calculations (1994)
Affleck, Ian, Gelfand, Martin P., Singh, Rajiv R. P.
The $S=1/2$, nearest-neighbor, quantum Heisenberg antiferromagnet on the square lattice with spatially anisotropic couplings is reconsidered, with particular attention to the following question: at...
Quantum Critical Scaling in a Moderately Doped Antiferromagnet (1993)
Sokol, Alexander, Glenister, Rodney L., Singh, Rajiv R. P.
Using high temperature expansions for the equal time correlator $S(q)$ and static susceptibility $\chi(q)$ for the t-J model, we present evidence for quantum critical (QC), $z\!=\!1$, behavior at...
Simulations of Oligomeric Intermediates in Prion Diseases
Mobley, David L., Cox, Daniel L., Singh, Rajiv R. P., Kulkarni, Rahul V., Slepoy, Alexander
We extend our previous stochastic cellular automata-based model for two-dimensional (areal) aggregation of prion proteins on neuronal surfaces. The new anisotropic model allows us to simulate both...
Modeling Amyloid β-Peptide Insertion into Lipid Bilayers
Mobley, David L., Cox, Daniel L., Singh, Rajiv R. P., Maddox, Michael W., Longo, Marjorie L.
Inspired by recent suggestions that the Alzheimer's amyloid β peptide (Aβ) can insert into cell membranes and form harmful ion channels, we model insertion of the 40- and 42-residue forms of the...
Simulations of Oligomeric Intermediates in Prion Diseases
Mobley, David L., Cox, Daniel L., Singh, Rajiv R. P., Kulkarni, Rahul V., Slepoy, Alexander
We extend our previous stochastic cellular automata-based model for two-dimensional (areal) aggregation of prion proteins on neuronal surfaces. The new anisotropic model allows us to simulate both...
Modeling Amyloid β-Peptide Insertion into Lipid Bilayers
Mobley, David L., Cox, Daniel L., Singh, Rajiv R. P., Maddox, Michael W., Longo, Marjorie L.
Inspired by recent suggestions that the Alzheimer's amyloid β peptide (Aβ) can insert into cell membranes and form harmful ion channels, we model insertion of the 40- and 42-residue forms of the...
A Mechanism for Copper Inhibition of Infectious Prion Conversion
Cox, Daniel L., Pan, Jianping, Singh, Rajiv R. P.
We employ ab initio electronic structure calculations to obtain two structural models for copper bound in the strongest binding site of the noninfectious form of the prion protein. The models are...
Theoretical Study of DNA Damage Recognition via Electron Transfer from the [4Fe-4S] Complex of MutY
Lin, Jong-Chin, Singh, Rajiv R. P., Cox, Daniel L.
The mechanism of site-specific recognition of DNA by proteins has been a long-standing issue. The DNA glycosylase MutY, for instance, must find the rare 8-oxoguanine-adenine mismatches among the...