4,028 research outputs found
Berry phase theory of planar Hall effect in Topological Insulators
Negative longitudinal magnetoresistance, in the presence of an external
magnetic field parallel to the direction of an applied current, has recently
been experimentally verified in Weyl semimetals and topological insulators in
the bulk conduction limit. The appearance of negative longitudinal
magnetoresistance in topological semimetals is understood as an effect of
chiral anomaly, whereas it is not well-defined in topological insulators.
Another intriguing phenomenon, planar Hall effect - appearance of a transverse
voltage in the plane of applied co-planar electric and magnetic fields not
perfectly aligned to each other, a configuration in which the conventional Hall
effect vanishes, has recently been suggested to exist in Weyl semimetals. In
this paper we present a quasi-classical theory of planar Hall effect of a
three-dimensional topological insulator in the bulk conduction limit. Starting
from Boltzmann transport equations we derive the expressions for planar Hall
conductivity and longitudinal magnetoconductivity in topological insulators and
show the important roles played by the orbital magnetic moment for the
appearance of planar Hall effect. Our theoretical results predict specific
experimental signatures for topological insulators that can be directly checked
in experiments.Comment: 18 pages, 3 figure
Chiral anomaly as origin of planar Hall effect in Weyl semimetals
In condensed matter physics, the term "chiral anomaly" implies the violation
of the separate number conservation laws of Weyl fermions of different
chiralities in the presence of parallel electric and magnetic fields. One
effect of chiral anomaly in the recently discovered Dirac and Weyl semimetals
is a positive longitudinal magnetoconductance (LMC). Here we show that chiral
anomaly and non-trivial Berry curvature effects engender another striking
effect in WSMs, the planar Hall effect (PHE). Remarkably, PHE manifests itself
when the applied current, magnetic field, and the induced transverse "Hall"
voltage all lie in the same plane, precisely in a configuration in which the
conventional Hall effect vanishes. In this work we treat PHE quasi-classically,
and predict specific experimental signatures for type-I and type-II Weyl
semimetals that can be directly checked in experiments.Comment: 4+ pages; Version accepted in Phys. Rev. Let
Mirror anomaly and anomalous Hall effect in type-I Dirac semimetals
In addition to the well known chiral anomaly, Dirac semimetals have been
argued to exhibit mirror anomaly, close analogue to the parity anomaly of
()-dimensional massive Dirac fermions. The observable response of such
anomaly is manifested in a singular step-like anomalous Hall response across
the mirror-symmetric plane in the presence of a magnetic field. Although this
result seems to be valid in type-II Dirac semimetals (strictly speaking, in the
linearized theory), we find that type-I Dirac semimetals do not possess such an
anomaly in anomalous Hall response even at the level of the linearized theory.
In particular, we show that the anomalous Hall response continuously approaches
zero as one approaches the mirror symmetric angle in a type-I Dirac semimetal
as opposed to the singular Hall response in a type-II Dirac semimetal.
Moreover, we show that, under certain condition, the anomalous Hall response
may vanish in a linearized type-I Dirac semimetal, even in the presence of time
reversal symmetry breaking.Comment: 6 pages, 5 figure
Bulk band inversion and surface Dirac cones in LaSb and LaBi : Prediction of a new topological heterostructure
We perform \textit{ab initio} investigations of the bulk and surface band
structures of LaSb and LaBi and resolve the existing disagreements about the
topological property of LaSb, considering LaBi as a reference. We examine the
bulk band structure for band inversion, along with the stability of surface
Dirac cones (if any) to time-reversal-preserving perturbations, as a strong
diagnostic test for determining the topological character of LaSb, LaBi and
LaSb-LaBi multilayer. A detailed \textit{ab initio} investigation of a
multilayer consisting of alternating unit cells of LaSb and LaBi shows the
presence of band inversion in the bulk and a massless Dirac cone on the (001)
surface, which remains stable under the influence of time-reversal-preserving
perturbations, thus confirming the topologically non-trivial nature of the
multilayer in which the electronic properties can be tailored as per
requirement. A detailed invariant calculation is performed to
arrive at a holistic conclusion
Experimental and materials considerations for the topological superconducting state in electron and hole doped semiconductors: searching for non-Abelian Majorana modes in 1D nanowires and 2D heterostructures
In proximity to an s-wave superconductor, a one- or two-dimensional,
electron- or hole-doped semiconductor with a sizable spin-orbit coupling and a
Zeeman splitting can support a topological superconducting (TS) state. The
semiconductor TS state has Majorana fermions as localized zero-energy
excitations at order parameter defects such as vortices and sample edges. Here
we examine the effects of quenched disorder from the semiconductor surface on
the stability of the TS state in both electron- and hole-doped semiconductors.
By considering the interplay of broken time reversal symmetry (due to Zeeman
splitting) and disorder we derive an expression for the disorder suppression of
the superconducting quasiparticle gap in the TS state. We conclude that the
effects of disorder can be minimized by increasing the ratio of the spin-orbit
energy with the Zeeman splitting. By giving explicit numbers we show that a
stable TS state is possible in both electron- and hole-doped semiconductors for
experimentally realistic values of parameters. We discuss possible suitable
semiconductor materials which should be the leading candidates for the Majorana
search in solid state systems.Comment: 11 pages, 2 figures: v3 published versio
Floating phase in a dissipative Josephson junction array
We consider dissipative quantum phase transitions in Josephson junction
arrays and show that the disordered phase in this extended system can be viewed
as an unusual floating phase in which the states of local -dimensional
elements (single Josephson junctions) can slide past each other despite
arbitrary range spatial couplings among them. The unusual character of the
metal-superconductor quantum critical point can be tested by measurements of
the current voltage characteristic. This may be the simplest and most natural
example of a floating phase.Comment: 4 pages, RevTex4. The revised version contains higher order
renormalization group equations and the corresponding phase diagra
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