56,368 research outputs found
NMR Probing Spin Excitations in the Ring-Like Structure of a Two-Subband System
Resistively detected nuclear magnetic resonance (NMR) is observed inside the
ring-like structure, with a quantized Hall conductance of 6e^2/h, in the phase
diagram of a two subband electron system. The NMR signal persists up to 400 mK
and is absent in other states with the same quantized Hall conductance. The
nuclear spin-lattice relaxation time, T1, is found to decrease rapidly towards
the ring center. These observations are consistent with the assertion of the
ring-like region being a ferromagnetic state that is accompanied by collective
spin excitations.Comment: 4 pages, 4 figure
Topological Imbert-Fedorov shift in Weyl semimetals
The Goos-H\"anchen (GH) shift and the Imbert-Fedorov (IF) shift are optical
phenomena which describe the longitudinal and transverse lateral shifts at the
reflection interface, respectively. Here, we report the GH and IF shifts in
Weyl semimetals (WSMs) - a promising material harboring low energy Weyl
fermions, a massless fermionic cousin of photons. Our results show that GH
shift in WSMs is valley-independent which is analogous to that discovered in a
2D relativistic material - graphene. However, the IF shift has never been
explored in non-optical systems, and here we show that it is valley-dependent.
Furthermore, we find that the IF shift actually originates from the topological
effect of the system. Experimentally, the topological IF shift can be utilized
to characterize the Weyl semimetals, design valleytronic devices of high
efficiency, and measure the Berry curvature
Pole expansion of self-energy and interaction effect on topological insulators
We study effect of interactions on time-reversal-invariant topological
insulators. Their topological indices are expressed by interacting Green's
functions. Under the local self-energy approximation, we connect topological
index and surface states of an interacting system to an auxiliary
noninteracting system, whose Hamiltonian is related to the pole-expansions of
the local self-energy. This finding greatly simplifies the calculation of
interacting topological indices and gives an noninteracting pictorial
description of interaction driven topological phase transitions. Our results
also bridge studies of the correlated topological insulating materials with the
practical dynamical-mean-field-theory calculations.Comment: 4.2 pages, 3 figures, reference added, typos correcte
Global Phase Diagram of Disordered Type-II Weyl Semimetals
With electron and hole pockets touching at the Weyl node, type-II Weyl
semimetal is a newly proposed topological state distinct from its type-I
cousin. We numerically study the localization effect for tilted type-I as well
as type-II Weyl semimetals and give the global phase diagram. For dis- ordered
type-I Weyl semimetal, an intermediate three-dimensional quantum anomalous Hall
phase is confirmed between Weyl semimetal phase and diffusive metal phase.
However, this intermediate phase is absent for disordered type-II Weyl
semimetal. Besides, near the Weyl nodes, comparing to its type-I cousin,
type-II Weyl semimetal possesses even larger ratio between the transport
lifetime along the direction of tilt and the quantum lifetime. Near the phase
boundary between the type-I and the type-II Weyl semimetals, infinitesimal
disorder will induce an insulating phase so that in this region, the concept of
Weyl semimetal is meaningless for real materials.Comment: 7 pages, 5 figure
Numerical Study of Universal Conductance Fluctuation in Three-dimensional Topological Semimetals
We study the conductance fluctuation in topological semimetals. Through
statistic distribution of energy levels of topological semimetals, we determine
the dominant parameters of universal conductance fluctuation (UCF), i.e., the
number of uncorrelated bands , the level degeneracy , and the symmetry
parameter . These parameters allow us to predict the zero-temperature
intrinsic UCF of topological semimetals by the Altshuler-Lee-Stone theory.
Then, we obtain numerically the conductance fluctuations for topological
semimetals of quasi-1D geometry. We find that for Dirac/Weyl semimetals, the
theoretical prediction coincides with the numerical results. However, a
non-universal conductance fluctuation behavior is found for topological nodal
line semimetals, i.e., the conductance fluctuation amplitude increases with the
enlargement of SOC strength. We find that such unexpected parameter-dependent
phenomena of conductance fluctuation are related to Fermi surface shape of 3D
topological semimetals. These results will help us to understand the existing
and future experimental results of UCF in 3D topological semimetals.Comment: 9 pages, 8 figure
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