108 research outputs found
RKKY signals characterizing the topological phase transitions in Floquet Dirac semimetals
Recently, the Floquet -type material has been proposed as an
ideal platform for realizing various phases, i.e., the spin-degenerate Dirac
semimetal (DSM) can be turned into the Weyl semimetal (WSM), and even to the
Weyl half-metal (WHM). Instead of the conventional electrical methods, we use
the RKKY interaction to characterize the topological phase transitions in this
paper. It is found that detecting the Ising term is feasible for
distinguishing the phase transition of DSM/WSM, since the emergence of is
induced by the broken spin degeneracy. For the case with impurities deposited
on axis (the line connecting the Weyl points), the Heisenberg term
coexists with in the WSM, while is filtered out and only
survives in the WHM. This magnetic filtering effect is a reflection of the
fully spin-polarized property (one spin band is in the WSM phase while the
other is gapped) of the WHM, and it can act a signal to capture the phase
transition of WSM/WHM. This signal can not be disturbed unless the direction of
the impurities greatly deviates from axis. Interestingly, as the impurities
are moved into the - plane, there arises another signal (a dip structure
for at the phase boundary), which can also identify the phase transition
of WSM/WHM. Furthermore, we have verified that all magnetic signals are robust
to the term that breaks the electron-hole symmetry. Besides characterizing the
phase transitions, our results also suggest that the Floquet DSMs are power
platforms for controlling the magnetic interaction.Comment: 15 pages, 10 figure
Modulation of chiral anomaly and bilinear magnetoconductivity in Weyl semimetals by impurity-resonance states
The phenomenon of nonlinear transport has attracted tremendous interest
within the condensed matter community. We present a theoretical framework for
nonlinear transport based on the nonequilibrium retarded Green's function, and
examine the impact of disorder on nonlinear magnetotransport in Weyl semimetals
(WSMs). It is demonstrated that bilinear magnetoconductivity can be induced in
disordered WSMs by several mechanisms, including impurity-induced tilting of
the Weyl cones, Lorentz-force-induced normal orbital magnetic moment, and
chiral anomaly arising from the Berry-curvature-induced anomalous orbital
magnetic moment. Additionally, we observe that the localization of Weyl
fermions by impurity scattering will lead to resonant dips in both the chiral
chemical potential and magnetoconductivity when the Fermi energy approaches the
impurity resonance states. Our findings offer a theoretical proposition for
modulating nonreciprocal transport in topological semimetals.Comment: 5 figure
Anisotropic RKKY interaction in semi-Dirac semimetals
In -dimensional systems with purely linear dispersion, the
Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction typically follows an isotropic
decaying law ()
in doped (undoped) case, where denotes the density of states
(DOS). However, this law is not valid in semi-Dirac semimetal (S-DSM), which is
noted for its anisotropic dispersion, i.e., linear in certain axes but
parabolic in the orthogonal axes. By exploring the magnetic interaction in
-dimensional (2D) S-DSM and two types of 3D S-DSMs, new laws are derived for
the direction-dependent RKKY interaction. Compared to , the
interaction here decays much more slowly with the impurity distance as
impurities are deposited on the relativistic axis, while a faster decaying law
is exhibited with impurities deposited on the non-relativistic axis. The former
is induced by the prolonged decaying rate of the carrier propagator and the
modified DOS with smaller power , while the latter is caused by the
modification to the energy of the carrier propagator. The both are attributed
to the anisotropy of the semi-Dirac dispersion. We have further discussed the
case with spin-momentum locking. Some phenomena (not exist in DSMs) are
highlighted, including the strong magnetic anisotropy with spin model,
and the creation (annihilation) of Dzyaloshinskii-Moriya (DM) terms with
impurities deposited on the relativistic (non-relativistic) axis. Our work
provides an alternative option to identify the anisotropic nature of semi-Dirac
dispersion by measuring the RKKY interaction
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