1,128 research outputs found
Jordan-Wigner Approach to Dynamic Correlations in 2D Spin-1/2 Models
We discuss the dynamic properties of the square-lattice spin-1/2 XY model
obtained using the two-dimensional Jordan-Wigner fermionization approach. We
argue the relevancy of the fermionic picture for interpreting the neutron
scattering measurements in the two-dimensional frustrated quantum magnet
Cs_2CuCl_4.Comment: Presented at 12-th Czech and Slovak Conference on Magnetism,
Ko\v{s}ice, 12-15 July 200
Spin dynamics of counterrotating Kitaev spirals via duality
Incommensurate spiral order is a common occurrence in frustrated magnetic
insulators. Typically, all magnetic moments rotate uniformly, through the same
wavevector. However the honeycomb iridates family Li2IrO3 shows an
incommensurate order where spirals on neighboring sublattices are
counter-rotating, giving each moment a different local environment.
Theoretically describing its spin dynamics has remained a challenge: the Kitaev
interactions proposed to stabilize this state, which arise from strong
spin-orbit effects, induce magnon umklapp scattering processes in spin-wave
theory. Here we propose an approach via a (Klein) duality transformation into a
conventional spiral of a frustrated Heisenberg model, allowing a direct
derivation of the dynamical structure factor. We analyze both Kitaev and
Dzyaloshinskii-Moriya based models, both of which can stabilize counterrotating
spirals, but with different spin dynamics, and we propose experimental tests to
identify the origin of counterrotation.Comment: 4 pages, 3 figures; appendix 5 pages, 2 figure
The key ingredients of the electronic structure of FeSe
FeSe is a fascinating superconducting material at the frontier of research in
condensed matter physics. Here we provide an overview on the current
understanding of the electronic structure of FeSe, focusing in particular on
its low energy electronic structure as determined from angular resolved
photoemission spectroscopy, quantum oscillations and magnetotransport
measurements of single crystal samples. We discuss the unique place of FeSe
amongst iron-based superconductors, being a multi-band system exhibiting strong
orbitally-dependent electronic correlations and unusually small Fermi surfaces,
prone to different electronic instabilities. We pay particular attention to the
evolution of the electronic structure which accompanies the
tetragonal-orthorhombic structural distortion of the lattice around 90 K, which
stabilizes a unique nematic electronic state. Finally, we discuss how the
multi-band multi-orbital nematic electronic structure has an impact on the
understanding of the superconductivity, and show that the tunability of the
nematic state with chemical and physical pressure will help to disentangle the
role of different competing interactions relevant for enhancing
superconductivity.Comment: 21 pages, 11 figures, to appear in Annual Review of Condensed Matter
Physic
Intelligence challenges in countering hybrid threats
The subject of hybrid threats has been in focus for some time now, for both academia and practitioners in various security and defense-related fields, but research is still unfocused enough and opinions yet too divergent to allow for a joint understanding of the term, as is the case with other terms in the sphere of security, too (the easiest to mention being ”terrorism”). Our lack of a common understanding of the phenomenon with our closest allies is inevitably a weakness, in a world where many categories of threats are closely interconnected and tend to transgress
physical and virtual borders alike. Therefore, the need for a closer look at the concept is bound to lead us to more effective approaches in handling the consequences of hybrid threats
Quantum phase transition in the Plaquette lattice with anisotropic spin exchange
I study the influence of anisotropic spin exchange on a quantum phase
transition in the Plaquette lattice driven by the purely quantum effect of
singlet formation. I study the influence of i) a Dzyaloshinskii-Moriya exchange
and ii) four spin exchange on the transition point by evaluating spin--spin
correlations and the spin gap with exact diagonalization. The results point to
a stabilization of the Neel-like long range order when the
Dzyaloshinskii-Moriya exchange is added, whereas the four-spin exchange might
stabilize the singlet order as well as the Neel-like order depending on its
strength.Comment: LaTeX article with 4 pages and 3 figures, prepared with material for
the ICM 200
Spin waves in La_2CuO_4: band structure and correlation effects
We calculate the antiferromagnetic spin wave dispersion in the half-filled
(electronic density n=1) Hubbard model for a two-dimensional square lattice,
using the random phase approximation (RPA) in a broken symmetry (spin density
wave) ground state. Our results for the spin wave dispersion, \omega(\vec q),
are compared with high-resolution inelastic neutron scattering performed on
La_2CuO$_4. The effects of different band structures and different values of
the on-site Coulomb interaction on the spin wave spectrum is studied.
Particular attention is put on the high energy dispersion values
\omega(\pi/2,\pi/2) and \omega(0,\pi).Comment: 4 pages, 2 figure
Spin wave theory for antiferromagnetic XXZ spin model on a triangle lattice in the presence of an external magnetic field
Spin wave theory is applied to a quantum antiferromagnetic XXZ model on a
triangle lattice in the presence of an in-plane magnetic field. The effect of
the field is found to enhance the quantum fluctuation and to reduce the
sublattice magnetization at the intermediate field strength in the anisotropic
case. The possible implication to the field driven quantum phase transition
from a spin solid to a spin liquid is discussed.Comment: 5 pages,4 figure
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