1,214 research outputs found

### Coupling of phonons and spin waves in triangular antiferromagnet

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

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

### $Z_Q$ Topological Invariants for Polyacetylene, Kagome and Pyrochlore lattices

Adiabatic $Z_Q$ invariants by quantized Berry phases are defined for gapped
electronic systems in $d$-dimensions ($Q=d+1$). This series includes
Polyacetylene, Kagome and Pyrochlore lattice respectively for $d=1,2$ and 3.
The invariants are quantum $Q$-multimer order parameters to characterize the
topological phase transitions by the multimerization. This fractional
quantization is protected by the global $Z_Q$ equivalence. As for the chiral
symmetric case, a topological form of the $Z_2$-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

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 $S=3/2$ antiferromagnet ${\rm Ba_2CoGe_2O_7}$ via spin-dependent metal-ligand hybridization mechanism

We investigate magnetic excitations in an $S=3/2$ Heisenberg model
representing two-dimensional antiferromagnet ${\rm Ba_2CoGe_2O_7}$. 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 $\Lambda (S^z)^2$, 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 ${\rm
Ba_2CoGe_2O_7}$.Comment: 5 pages, 3 figure

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

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 â€˜Measurementâ€™ was smaller than the value of â€˜Calculationâ€™ 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 yearâ€™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 $RMnO_3$ crystals

We have investigated the role of the 4$f$ moment on the magnetoelectric (ME)
effect of orthorhombic $R$MnO$_{3}$ ($R$=rare earth ions). In order to clarify
the role of the 4$f$ moment, we prepared three samples: (Eu,Y)MnO$_{3}$ without
the 4$f$ moment, TbMnO$_{3}$ with the anisotropic 4$f$ moment, and
(Gd,Y)MnO$_{3}$ with the isotropic 4$f$ moment. The ferroelectric behaviors of
these samples are different from each other in a zero magnetic field.
(Eu,Y)MnO$_{3}$ and (Gd,Y)MnO$_{3}$ show the ferroelectric polarization along
the a axis in the ground state, while TbMnO$_{3}$ shows it along the c axis.
Such difference may arise from the influence of the anisotropic Tb$^{3+}$ 4$f$
moment. The direction of the ferroelectric polarization of $R$MnO$_{3}$ is
determined by the internal magnetic field arising from the 4$f$ 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

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 $S=1,2$ 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 Gd$_{\textbf{0.7}}$Tb$_{\textbf{0.3}}$MnO$_{\textbf 3}$

A broad continuum-like spin excitation (1--10 meV) with a peak structure
around 2.4 meV has been observed in the ferroelectric $ab$ spiral spin phase of
Gd$_{0.7}$Tb$_{0.3}$MnO$_3$ 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 $E$ 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 $A$-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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