330 research outputs found
Hybridization and Decay of Magnetic Excitations in two-dimensional Triangular Lattice Antiferromagnets
Elementary quasiparticles in solids such as phonons and magnons occasionally
have nontrivial interactions between them, as well as among themselves. As a
result, their energy eigenvalues are renormalized, the quasiparticles
spontaneously decay into a multi-particle continuum state, or they are
hybridized with each other when their energies are close. As discussed in this
review, such anomalous features can appear dominantly in quantum magnets but
are not, a priori, negligible for magnetic systems with larger spin values and
noncollinear magnetic structures. We review the unconventional magnetic
excitations in two-dimensional triangular lattice antiferromagnets and discuss
their implications on related issues.Comment: 18 pages, 9 figure
Magnon topology and thermal Hall effect in trimerized triangular lattice antiferromagnet
The non-trivial magnon band topology and its consequent responses have been
extensively studied in two-dimensional magnetisms. However, the triangular
lattice antiferromagnet (TLAF), the best-known frustrated two-dimensional
magnet, has received less attention than the closely related Kagome system,
because of the spin-chirality cancellation in the umbrella ground state of the
undistorted TLAF. In this work, we study the band topology and the thermal Hall
effect (THE) of the TLAF with (anti-)trimerization distortion under the
external perpendicular magnetic field using the linearized spin wave theory. We
show that the spin-chirality cancellation is removed in such case, giving rise
to the non-trivial magnon band topology and the finite THE. Moreover, the
magnon bands exhibit band topology transitions tuned by the magnetic field. We
demonstrate that such transitions are accompanied by the logarithmic divergence
of the first derivative of the thermal Hall conductivity. Finally, we examine
the above consequences by calculating the THE in the hexagonal manganite
YMnO, well known to have anti-trimerization.Comment: 6 + 7 pages, 3 + 5 figures, 0 + 1 table; Journal reference adde
Sizable suppression of magnon Hall effect by magnon damping in CrGeTe
Two-dimensional (2D) Heisenberg honeycomb ferromagnets are expected to have
interesting topological magnon effects as their magnon dispersion can have
Dirac points. The Dirac points are gapped with finite second nearest neighbor
Dzyaloshinskii-Moriya interaction, providing nontrivial Berry curvature with
finite magnon Hall effect. Yet, it is unknown how the topological properties
are affected by magnon damping. We report the thermal Hall effect in
CrGeTe, an insulating 2D honeycomb ferromagnet with a large Dirac
magnon gap and significant magnon damping. Interestingly, the thermal Hall
conductivity in CrGeTe shows the coexisting phonon and magnon
contributions. Using an empirical two-component model, we successfully estimate
the magnon contribution separate from the phonon part, revealing that the
magnon Hall conductivity was 20 times smaller than the theoretical calculation.
Finally, we suggest that such considerable suppression in the magnon Hall
conductivity is due to the magnon damping effect in CrGeTe.Comment: 15 pages, 3 figures. Accepted for publication in Phys. Rev.
Symmetry breaking and unconventional charge ordering in single crystal NaRuO
The interplay of charge, spin, and lattice degrees of freedom in matter leads
to various forms of ordered states through phase transitions. An important
subclass of these phenomena of complex materials is charge ordering (CO),
mainly driven by mixed-valence states. We discovered by combining the results
of electrical resistivity (), specific heat, susceptibility
(\textit{T}), and single crystal x-ray diffraction (SC-XRD) that
NaRuO with the monoclinic tunnel type lattice (space group
2/) exhibits an unconventional CO at room temperature while retaining
metallicity. The temperature-dependent SC-XRD results show successive phase
transitions with super-lattice reflections at \textbf{q}=(0, ,
0) and \textbf{q}=(0, , ) below
(365 K) and only at \textbf{q}=(0, , 0) between
and (630 K). We interpreted these as an
evidence for the formation of an unconventional CO. It reveals a strong
first-order phase transition in the electrical resistivity at
(cooling) = 345 K and (heating) = 365 K. We argue that the
origin of the phase transition is due to the localized 4 Ru-electrons. The
results of our finding reveal an unique example of Ru/Ru mixed
valance heavy \textit{d} ions.Comment: 10 pages, 9 figure
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