1,214 research outputs found

    Coupling of phonons and spin waves in triangular antiferromagnet

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    We investigate the influence of the spin-phonon coupling in the triangular antiferromagnet where the coupling is of the exchange-striction type. The magnon dispersion is shown to be modified significantly at wave vector (2pi,0) and its symmetry-related points, exhibiting a roton-like minimum and an eventual instability in the dispersion. Various correlation functions such as equal-time phonon correlation, spin-spin correlation, and local magnetization are calculated in the presence of the coupling.Comment: 6 pages, 5 figures; references added, minor text revisions, submitted to PR

    General Relationship Between the Entanglement Spectrum and the Edge State Spectrum of Topological Quantum States

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    We consider (2+1)-dimensional topological quantum states which possess edge states described by a chiral (1+1)-dimensional Conformal Field Theory (CFT), such as e.g. a general quantum Hall state. We demonstrate that for such states the reduced density matrix of a finite spatial region of the gapped topological state is a thermal density matrix of the chiral edge state CFT which would appear at the spatial boundary of that region. We obtain this result by applying a physical instantaneous cut to the gapped system, and by viewing the cutting process as a sudden "quantum quench" into a CFT, using the tools of boundary conformal field theory. We thus provide a demonstration of the observation made by Li and Haldane about the relationship between the entanglement spectrum and the spectrum of a physical edge state.Comment: 7 pages, 2 figures. A presentation of this work can be found in the following talk at KITP: http://online.itp.ucsb.edu/online/compqcm10/qi

    ZQZ_Q Topological Invariants for Polyacetylene, Kagome and Pyrochlore lattices

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    Adiabatic ZQZ_Q invariants by quantized Berry phases are defined for gapped electronic systems in dd-dimensions (Q=d+1Q=d+1). This series includes Polyacetylene, Kagome and Pyrochlore lattice respectively for d=1,2d=1,2 and 3. The invariants are quantum QQ-multimer order parameters to characterize the topological phase transitions by the multimerization. This fractional quantization is protected by the global ZQZ_Q equivalence. As for the chiral symmetric case, a topological form of the Z2Z_2-invariant is explicitly given as well.Comment: 4 pgages, 4 figure

    Exact supersymmetry in the relativistic hydrogen atom in general dimensions -- supercharge and the generalized Johnson-Lippmann operator

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    A Dirac particle in general dimensions moving in a 1/r potential is shown to have an exact N = 2 supersymmetry, for which the two supercharge operators are obtained in terms of (a D-dimensional generalization of) the Johnson-Lippmann operator, an extension of the Runge-Lenz-Pauli vector that relativistically incorporates spin degrees of freedom. So the extra symmetry (S(2))in the quantum Kepler problem, which determines the degeneracy of the levels, is so robust as to accommodate the relativistic case in arbitrary dimensions.Comment: 4 pages, 1 figur

    Theory of magnetoelectric resonance in two-dimensional S=3/2S=3/2 antiferromagnet Ba2CoGe2O7{\rm Ba_2CoGe_2O_7} via spin-dependent metal-ligand hybridization mechanism

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    We investigate magnetic excitations in an S=3/2S=3/2 Heisenberg model representing two-dimensional antiferromagnet Ba2CoGe2O7{\rm Ba_2CoGe_2O_7}. In terahertz absorption experiment of the compound, Goldstone mode as well as novel magnetic excitations, conventional magnetic resonance at 2 meV and both electric- and magnetic-active excitation at 4 meV, have been observed. By introducing a hard uniaxial anisotropy term Λ(Sz)2\Lambda (S^z)^2, three modes can be explained naturally. We also indicate that, via the spin-dependent metal-ligand hybridization mechanism, the 4 meV excitation is an electric-active mode through the coupling between spin and electric-dipole. Moreover, at 4 meV excitation, an interference between magnetic and electric responses emerges as a cross correlated effect. Such cross correlation effects explain the non-reciprocal linear directional dichroism observed in Ba2CoGe2O7{\rm Ba_2CoGe_2O_7}.Comment: 5 pages, 3 figure

    Analysis of indoor environment and performance of net-zero energy building with vacuum glazed windows

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    The total energy and indoor thermal environment of an office building, which aims at the net-zero energy building, were measured and analysed. The annual total primary energy consumption of ‘Measurement’ was smaller than the value of ‘Calculation’ at design phase and achieved net-zero. The result of analysis of the thermal environment shows that the comfortable thermal environment was maintained. Also, the insulation performance and heat balance of the vacuum glazed windows in winter was evaluated. The overall heat transfer coefficients calculated by using the monitoring data were almost equal to the rated overall heat transfer coefficient and the high insulation performance of vacuum glazed windows was maintained even in the second year’s operation. In addition, the amount of heat gain due to solar radiation on the window surface was much larger than the amount of heat loss due to transmission. The vacuum glazed windows with high thermal insulation performance on the south side can reduce the heating load and contribute to the achievement of net-zero in the buildings

    Internal magnetic field effect on magnetoelectricity in orthorhombic RMnO3RMnO_3 crystals

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    We have investigated the role of the 4ff moment on the magnetoelectric (ME) effect of orthorhombic RRMnO3_{3} (RR=rare earth ions). In order to clarify the role of the 4ff moment, we prepared three samples: (Eu,Y)MnO3_{3} without the 4ff moment, TbMnO3_{3} with the anisotropic 4ff moment, and (Gd,Y)MnO3_{3} with the isotropic 4ff moment. The ferroelectric behaviors of these samples are different from each other in a zero magnetic field. (Eu,Y)MnO3_{3} and (Gd,Y)MnO3_{3} show the ferroelectric polarization along the a axis in the ground state, while TbMnO3_{3} shows it along the c axis. Such difference may arise from the influence of the anisotropic Tb3+^{3+} 4ff moment. The direction of the ferroelectric polarization of RRMnO3_{3} is determined by the internal magnetic field arising from the 4ff moment.Comment: 2 pages, 1 figure, the proceeding of International Conference of Magnetism, to be published in the Journal of Magnetism and Magnetic Material

    Topological Classification of Gapped Spin Chains :Quantized Berry Phase as a Local Order Parameter

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    We characterize several phases of gapped spin systems by local order parameters defined by quantized Berry phases. This characterization is topologically stable against any small perturbation as long as the energy gap remains finite. The models we pick up are S=1,2S=1,2 dimerized Heisenberg chains and S=2 Heisenberg chains with uniaxial single-ion-type anisotropy. Analytically we also evaluate the topological local order parameters for the generalized Affleck-Kennedy-Lieb-Tasaki (AKLT) model. The relation between the present Berry phases and the fractionalization in the integer spin chains are discussed as well.Comment: 6 pages, 4 figures, accepted for publication in Phys. Rev.

    Electric-dipole active two-magnon excitation in {\textit{ab}} spiral spin phase of a ferroelectric magnet Gd0.7_{\textbf{0.7}}Tb0.3_{\textbf{0.3}}MnO3_{\textbf 3}

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    A broad continuum-like spin excitation (1--10 meV) with a peak structure around 2.4 meV has been observed in the ferroelectric abab spiral spin phase of Gd0.7_{0.7}Tb0.3_{0.3}MnO3_3 by using terahertz (THz) time-domain spectroscopy. Based on a complete set of light-polarization measurements, we identify the spin excitation active for the light EE vector only along the a-axis, which grows in intensity with lowering temperature even from above the magnetic ordering temperature but disappears upon the transition to the AA-type antiferromagnetic phase. Such an electric-dipole active spin excitation as observed at THz frequencies can be ascribed to the two-magnon excitation in terms of the unique polarization selection rule in a variety of the magnetically ordered phases.Comment: 11 pages including 3 figure
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