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Jun 28, 2018
06/18

by
S. A. Owerre

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Motivated by recent quantum Monte Carlo (QMC) simulations of the quantum Kagome ice model by Juan Carrasquilla, et al., [Nature Communications 6, 7421 (2015)], we study the ground state properties of this model on the triangular lattice. In the presence of a magnetic field $h$, the Hamiltonian possesses competing interactions between a $Z_2$-invariant easy-axis ferromagnetic interaction $J_{\pm\pm}$ and a frustrated Ising term $J_z$. As in the U(1)-invariant model, we obtain four classical...

Topics: Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1511.01843

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Jun 29, 2018
06/18

by
S. A. Owerre

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We study the quantum Kagom\'e ice hardcore bosons, which corresponds to the XY limit of quantum spin ice Hamiltonian. We estimate the values of the zero-temperature thermodynamic quantities using the large-$S$ expansion. We show that our semi-classical analysis is consistent with finite temperature quantum Monte Carlo estimates.

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1604.02633

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Jun 29, 2018
06/18

by
S. A. Owerre

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Motivated by the fact that many bilayer quantum magnets occur in nature, we generalize the study of thermal Hall transports of spin excitations to bilayer magnetic systems. It is shown that bilayer magnetic systems can be coupled either ferromagnetically or antiferromagnetically. We study both scenarios on the honeycomb lattice and show that the system realizes topologically nontrivial magnon bands induced by alternating next-nearest-neighbour Dzyaloshinsky-Moriya interaction (DMI). As a...

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1604.05292

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Jun 29, 2018
06/18

by
S. A. Owerre

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Topological magnon insulators in insulating Kagom\'e ferromagnets have been extensively studied in a series of papers. It has been established that Dzyaloshinskii-Moriya interaction (DMI) is the key ingredient to observe a nontrivial topological magnon with edge modes. However, insulating antiferromagnets on the Kagom\'e lattice are frustrated systems considered as a playground for studying quantum spin liquid physics. In these systems the DMI can induce a coplanar but noncollinear magnetic...

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1609.03563

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Jun 30, 2018
06/18

by
S. A. Owerre

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In this Letter, we identify a noncoplanar chiral spin texture on the distorted kagom\'e-lattice antiferromagnets induced by the presence of a magnetic field applied perpendicular to the distorted kagom\'e plane. The noncoplanar chiral spin texture has a nonzero scalar spin chirality similar to a chiral quantum spin liquid with broken time-reversal symmetry. In the noncoplanar regime we observe nontrivial topological magnetic excitations and thermal Hall response through the emergent...

Topics: Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1701.05199

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Jun 29, 2018
06/18

by
S. A. Owerre

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This paper presents a connection between the topological properties of hardcore bosons and that of magnons in quantum spin magnets. We utilize the Haldane-like hardcore bosons on the honeycomb lattice as an example. We show that this system maps to a spin-$1/2$ quantum XY model with a next-nearest-neighbour Dzyaloshinsky-Moriya interaction. We obtain the magnon excitations of the quantum spin model and compute the edge states, Berry curvature, thermal and spin Nernst conductivities. Due to the...

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1603.06495

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Jun 29, 2018
06/18

by
S. A. Owerre

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Quite recently, magnon Hall effect of spin excitations has been observed experimentally on the kagome and pyrochlore lattices. Thermal Hall conductivity $\kappa^{xy}$, changes sign as a function of magnetic field or temperature on the kagome lattice, and $\kappa^{xy}$ changes sign upon reversing the sign of the magnetic field on the pyrochlore lattice. Motivated by these recent exciting experimental observations, we theoretically propose a simple realization of magnon Hall effect in a two-band...

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1603.04331

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Jun 29, 2018
06/18

by
S. A. Owerre

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We investigate the nature of a $Z_2$-invariant XY ring-exchange interaction with a frustrated Ising coupling on the triangular lattice. In the limit of pure XY ring-exchange interaction, we show that the classical ground state is degenerate resulting from the $Z_2$-invariance of the Hamiltonian. Quantum fluctuations lift these classical degenerate ground states and produce an unusual state whose excitation spectrum exhibits a gapped maximum quadratic dispersion near ${\bf k}=0$ and vanishes at...

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1603.04208

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Jun 29, 2018
06/18

by
S. A. Owerre

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Quantum Monte Carlo (QMC) simulation has uncovered nonzero Berry curvature and bosonic edge states in hardcore-Bose-Hubbard model on the gapped honeycomb lattice. The competition between the chemical potential and staggered onsite potential leads to an interesting quantum phase diagram comprising superfluid phase, Mott insulator, and charge density wave insulator. In this paper, we present a semiclassical perspective of this system by mapping to a spin-$1/2$ quantum XY model. We give an...

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1603.07989

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Jun 28, 2018
06/18

by
S. A. Owerre

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We use spin wave theory to investigate the ground state properties of the $Z_2$-invariant quantum XXZ model on the triangular lattice in the ferromagnetic phase. The Hamiltonian comprises nearest and next-nearest-neighbour Ising couplings, external magnetic fields, and a $Z_2$-invariant ferromagnetic coupling. We show that quantum fluctuations are suppressed in this system, hence linear spin wave theory gives reasonable estimates of the ground state thermodynamic properties. Our results show...

Topics: Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1511.02311

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Jun 29, 2018
06/18

by
S. A. Owerre

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In frustrated magnets the Dzyaloshinsky-Moriya interaction arising from spin-orbit coupling can induce a magnetic long-range order. Here, we report a theoretical prediction of thermal Hall effect in frustrated kagom\'e magnets such as KCr$_3$(OH)$_6$(SO4)$_2$ and KFe$_3$(OH)$_{6}$(SO$_{4}$)$_2$. The thermal Hall effects in these materials are induced by scalar spin chirality as opposed to DMI in previous studies. The scalar spin chirality originates from magnetic-field-induced chiral spin...

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1608.04561

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Jun 29, 2018
06/18

by
S. A. Owerre

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Topological magnon bands and magnon Hall effect in insulating collinear ferromagnets are induced by the Dzyaloshinskii-Moriya interaction (DMI) even at zero magnetic field. In the geometrically frustrated star lattice, a coplanar/noncollinear $\mathbf q=0$ magnetic ordering may be present due to spin frustration. This magnetic structure, however, does not exhibit topological magnon effects even with DMI in contrast to collinear ferromagnets. We show that a magnetic field applied perpendicular...

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1608.08605

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Jun 29, 2018
06/18

by
S. A. Owerre

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It has been recently shown that in the Heisenberg (anti)ferromagnet on the honeycomb lattice, the magnons (spin wave quasipacticles) realize a massless two-dimensional (2D) Dirac-like Hamiltonian. It was shown that the Dirac magnon Hamiltonian preserves time-reversal symmetry defined with the sublattice pseudo spins and the Dirac points are robust against magnon-magnon interactions. The Dirac points also occur at nonzero energy. In this paper, we propose a simple realization of nontrivial...

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1602.06772

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Jun 30, 2018
06/18

by
S. A. Owerre; M. B. Paranjape

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We consider the one dimensional, periodic spin chain with $N$ sites, similar to the one studied by Haldane \cite{hal}, however in the opposite limit of very large anisotropy and small nearest neighbour, anti-ferromagnetic exchange coupling between the spins, which are of large magnitude $s$. For a chain with an even number of sites we show that actually the ground state is non degenerate and given by a superposition of the two N\'eel states, due to quantum spin tunnelling. With an odd number of...

Topics: Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1404.6706

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Jun 29, 2018
06/18

by
S. A. Owerre

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We investigate an ultra-thin film of topological insulator (TI) multilayer as a model for a three-dimensional (3D) Weyl semimetal. We introduce tunneling parameters $t_S$, $t_\perp$, and $t_D$, where the former two parameters couple layers of the same thin film at small and large momenta, and the latter parameter couples neighbouring thin film layers along the $z$-direction. The Chern number is computed in each topological phase of the system and we find that for $t_S,t_D>0$, the tunneling...

Topics: Mesoscale and Nanoscale Physics, Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1602.00618

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Jun 28, 2018
06/18

by
S. A. Owerre; A. A. Burkov; Roger G. Melko

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We present a large-$S$ study of a quantum spin ice Hamiltonian, introduced by Huang, et al., [PRL 112, 167203 (2014)], on the kagome lattice. This model involves a competition between the frustrating Ising term of classical kagome ice, a Zeeman magnetic field $h$,and a nearest-neighbor transverse spin-flip term $S^x_iS^x_j - S^y_iS^y_j$. Recent Quantum Monte Carlo (QMC) simulations by Carrasquilla, et al., [Nature Communications, 6, 7421, (2015)], uncovered lobes of a disordered phase for large...

Topics: Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1512.03930

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Jun 30, 2018
06/18

by
S. A. Owerre

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We study a molecular dimer model that takes higher order interaction term as well as antisymmetric term into account. We mainly focus on the theoretical quantum properties that are of interest. We numerically diagonalize the system and investigate different phenomena which include oscillations of ground state energy splitting, magnetization steps, Schottky anomaly, torque oscillations, and magnetocaloric effects. Indeed, we show that these interactions can exotically influence these phenomena,...

Topics: Mesoscale and Nanoscale Physics, Strongly Correlated Electrons, Condensed Matter

Source: http://arxiv.org/abs/1411.6555

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Jun 29, 2018
06/18

by
S. A. Owerre

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In ultra-thin film of topological insulator, the hybridization between the top and bottom surfaces opens an energy gap and forms two degenerate quantum anomalous Hall states, which give rise to a quantum spin Hall state. In this paper, we demonstrate that a Weyl semimetal can be realized in an ultra-thin film of topological insulator heterostructure in a similar way to that of the surface state of a strong three-dimensional (3D) topological insulator studied by Burkov and Balents . We find that...

Topics: Mesoscale and Nanoscale Physics, Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1601.03707

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Jun 29, 2018
06/18

by
S. A. Owerre

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In this Letter, we study the magnetic transport in AA-stacked bilayer honeycomb chiral magnets coupled either ferromagnetically or antiferromagnetically. For both couplings, we observe chirality-induced gaps, chiral protected edge states, magnon Hall and magnon spin Nernst effects of magnetic spin excitations. For ferromagnetically coupled layers, thermal Hall and spin Nernst conductivities do not change sign as function of magnetic field or temperature similar to single-layer honeycomb...

Topics: Mesoscale and Nanoscale Physics, Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1605.07971

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Jun 26, 2018
06/18

by
S. A. Owerre; J. Nsofini

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In recent years, studies on cyclic molecular nanomagnets have captivated the attention of researchers. These magnets are finite in size and contain very large spins. They are interesting because they possess macroscopic quantum tunneling of N\'eel vectors. For antiferromagnetic molecular nanomagnets with finite number of even-numbered coupled spins, tunneling involves two classical localized N\'eel ground states separated by a magnetic energy barrier. The question is: can such phenomena be...

Topics: Strongly Correlated Electrons, Mesoscale and Nanoscale Physics, Condensed Matter

Source: http://arxiv.org/abs/1502.05684

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Jun 28, 2018
06/18

by
S. A. Owerre

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We study the physics of quantum spin Hall (QSH) effect and topological quantum phase transition on the porphyrin lattice. We show that in a special limit the pristine model on this lattice reduces to the usual topological insulator (TI) thin film model. By incorporating explicit time reversal symmetry (TRS) breaking interactions, we explore the topological properties of this model and show that it exhibits an ordinary insulator phase, a quantum anomalous Hall (QAH) phase, and a quantum spin...

Topics: Quantum Physics, Mathematical Physics, Condensed Matter, High Energy Physics - Lattice,...

Source: http://arxiv.org/abs/1506.09204

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Jun 29, 2018
06/18

by
Christian Boudreault; S. A. Owerre; M. B. Paranjape

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We consider the one-dimensional spin chain for arbitrary spin $s$ on a periodic chain with $N$ sites, the generalization of the chain that was studied by Blume and Capel \cite{bc}: $$H=\sum_{i=1}^N \left(a (S^z_i)^2+ b S^z_iS^z_{i+1}\right).$$ The Hamiltonian only involves the $z$ component of the spin thus it is essentially an Ising \cite{Ising} model. The Hamiltonian also figures exactly as the anisotropic term in the famous model studied by Haldane \cite{haldane} of the large spin Heisenberg...

Topics: Mathematics, High Energy Physics - Theory, Mathematical Physics, Condensed Matter, Strongly...

Source: http://arxiv.org/abs/1601.06195