317 research outputs found
Spin textures and spin-wave excitations in doped Dirac-Weyl semimetals
We study correlations and magnetic textures of localized spins, doped in
three-dimensional Dirac semimetals. An effective field theory for magnetic
moments is constructed by integrating out the fermionic degrees of freedom. The
spin correlation shows a strong anisotropy, originating from spin-momentum
locking of Dirac electrons, in addition to the conventional Heisenberg-like
ferromagnetic correlation. The anisotropic spin correlation allows
topologically nontrivial magnetic excitation textures such as a transient
hedgehog state, as well as the ferromagnetic ground state. The spin-wave
dispersion in ferromagnetic Weyl semimetal also becomes anisotropic, being less
dispersed perpendicular to the magnetization.Comment: 5 pages, 3 figures + 9 pages of Supplemental Materia
Pairing symmetry transitions in the even-denominator FQHE system
Transitions from a paired quantum Hall state to another quantum Hall state in
bilayer systems are discussed in the framework of the edge theory. Starting
from the edge theory for the Haldane-Rezayi state, it is shown that the
charging effect of a bilayer system which breaks the SU(2) symmetry of the
pseudo-spin shifts the central charge and the conformal dimensions of the
fermionic fields which describe the pseudo-spin sector in the edge theory. This
corresponds to the transition from Haldane-Rezayi state to Halperin's 331
state, or singlet d-wave to triplet p-wave ABM type paired state in the
composite fermion picture.
Considering interlayer tunneling, the tunneling rate-capacitance phase
diagram for the paired bilayer system is discussed
Electron Correlation Induced Spontaneous Symmetry Breaking and Weyl Semimetal Phase in a Strongly Spin-Orbit Coupled System
We study theoretically the electron correlation effect in a three-dimensional
Dirac fermion system which describes a topologically nontrivial state. It is
shown within the mean-field approximation that time-reversal and inversion
symmetries of the system are spontaneously broken in the region where both
spin-orbit coupling and electron correlation are strong. This phase is
considered as an analog of that in the lattice quantum chromodynamics. It is
also shown that in the presence of magnetic impurities, electron correlation
enhances the appearance of the Weyl semimetal phase between the topological
insulator phase and the normal insulator phase.Comment: 4 pages, 3 figure
Gap evolution in nu=1/2 bilayer quantum Hall systems
Fractional quantum Hall states in bilayer system at total filling fraction
are examined numerically under some ranges of the layer separation
and interlayer tunneling. It is shown that the ground state changes
continuously from two-component state to one-component state as the interlayer
tunneling rate is increased, while the lowest excited state changes
discontinuously. This fact explains observed unusual behavior of the activation
energy which reveals upward cusp as a function of interlayer tunneling. Some
trial wave functions for the ground state and quasihole states are inspected.Comment: 4 pages, 6 figure
Weyl semimetal phase in solid-solution narrow-gap semiconductors
We theoretically investigate ferromagnetic ordering in magnetically doped
solid-solution narrow-gap semiconductors with the strong spin-orbit interaction
such as Cr-doped Bi(SeTe). We compute the spontaneous
magnetization of impurities and itinerant electrons, and estimate the critical
temperature as a function of the concentration of magnetic dopants and the
strength of the spin-orbit interaction. It is found that the critical
temperature is proportional to the concentration of dopants and enhanced with
the strong spin-orbit interaction. It is also found that the ferromagnetic
transition could make the system turn to the Weyl semimetal which possesses a
pair of Weyl points separating in the momentum space.Comment: 5 pages, 5 figure
Skyrmion-induced anomalous Hall conductivity on topological insulator surfaces
Electron spin-momentum locking together with background magnetic textures can
significantly alter the electron transport properties. We theoretically
investigate the electron transport at the interface between a topological
insulator and a magnetic insulator with magnetic skyrmions on the top. In
contrast to the conventional topological Hall effect in normal metals, the
skyrmions yield an additional contribution to the anomalous Hall conductivity
even in the absence of in-plane magnetic texture, arising from the phase factor
characteristic to Dirac electrons acquired at skyrmion boundary.Comment: 10 pages, 4 figures; published versio
Voltage-driven magnetization switching and spin pumping in Weyl semimetals
We demonstrate electrical magnetization switching and spin pumping in
magnetically doped Weyl semimetals. The Weyl semimetal is a new class of
topological semimetals, known to have nontrivial coupling between the charge
and the magnetization due to the chiral anomaly. By solving the
Landau-Lifshitz-Gilbert equation for a multilayer structure of a Weyl
semimetal, an insulator and a metal whilst taking the charge-magnetization
coupling into account, magnetization dynamics is analyzed. It is shown that the
magnetization dynamics can be driven by the electric voltage. Consequently,
switching of the magnetization with a pulsed electric voltage can be achieved,
as well as precession motion with an applied oscillating electric voltage. The
effect requires only a short voltage pulse and may therefore be more
energetically efficient for us in spintronics devices compared to conventional
spin transfer torque switching.Comment: 5 pages, 4 figure
Crossed responses of spin and orbital magnetism in topological insulators
Crossed magnetic responses between spin and orbital angular momentum are
studied in time-reversal symmetric topological insulators. Due to spin-orbit
coupling in the quantum spin Hall systems and three-dimensional topological
insulators, the magnetic susceptibility has crossed (intersectional) components
between spin and orbital part of magnetism. In this study, the crossed
susceptibility for the orbital magnetization is studied in two- and
three-dimensional topological insulator models, in which an external magnetic
field interacts with the electron spin by Zeeman coupling via distinct
g-factors for conduction and valence energy bands. The crossed susceptibility
in two-dimensional quantum spin Hall insulators shows a quantized signature of
the topological phase in response to Zeeman coupling via an
averaged g-factor, and the quantization persists even when
-conservation of electrons is broken by a tilted magnetic field. The
bulk orbital magnetization is interpreted by the persistent edge current
attributed to the chiral anomaly at the (1+1)-dimensional boundary. In
three-dimensional topological insulators, we found that the crossed
susceptibility is proportional to the difference of g-factors of conduction and
valence electrons, which is qualitatively different from the two-dimensional
case. Steep changes of the crossed susceptibility in three dimensions at the
phase transition points are explained by the surface Dirac fermion theory.
Finally, dependence of the crossed susceptibility on g-factors in two- and
three-dimensional cases is discussed from the viewpoint of time-reversal and
particle-hole symmetries.Comment: 8 pages, 4 figure
Two-orbital effective model for magnetic Weyl semimetal in Kagome-lattice shandite
We construct a two-orbital effective model for a ferromagnetic Kagome-lattice
shandite, , a candidate material of magnetic Weyl
semimetals, by considering one orbital from Co, and one orbital from
interlayer Sn. The energy spectrum near the Fermi level, and the configurations
of the Weyl points, computed by using our model, are similar to those obtained
by first principle calculations. We show also that nodal rings appear even with
spin-orbit coupling when the magnetization points in-plane direction.
Additionally, magnetic properties of and other
shandite materials are discussed.Comment: 5 pages, 6 figure
Theory for spin torque in Weyl semimetal with magnetic texture
The spin-transfer torque is a fundamental physical quantity to operate the
spintronics devices such as racetrack memory. We theoretically study the
spin-transfer torque and analyze the dynamics of the magnetic domain walls in
magnetic Weyl semimetals. Owing to the strong spin-orbit coupling in Weyl
semimetals, the spin-transfer torque can be significantly enhanced, because of
which they can provide a more efficient means of controlling magnetic textures.
We derive the analytical expression of the spin-transfer torque and find that
the velocity of the domain wall is one order of magnitude greater than that of
conventional ferromagnetic metals. Furthermore, due to the suppression of
longitudinal conductivity in the thin domain-wall configuration, the
dissipation due to Joule heating for the spin-transfer torque becomes much
smaller than that in bulk metallic ferromagnets. Consequently, the fast-control
of the domain wall can be achieved with smaller dissipation from Joule heating
in the Weyl semimetals as required for application to low-energy-consumption
spintronics devices.Comment: 11 pages, 1 figur
- β¦