991 research outputs found
When chiral photons meet chiral fermions - Photoinduced anomalous Hall effects in Weyl semimetals
The Weyl semimetal is characterized by three-dimensional linear band touching
points called Weyl nodes. These nodes come in pairs with opposite chiralities.
We show that the coupling of circularly polarized photons with these chiral
electrons generates a Hall conductivity without any applied magnetic field in
the plane orthogonal to the light propagation. This phenomenon comes about
because with all three Pauli matrices exhausted to form the three-dimensional
linear dispersion, the Weyl nodes cannot be gapped. Rather, the net influence
of chiral photons is to shift the positions of the Weyl nodes. Interestingly,
the momentum shift is tightly correlated with the chirality of the node to
produce a net anomalous Hall signal. Application of our proposal to the
recently discovered TaAs family of Weyl semimetals leads to an
order-of-magnitude estimate of the photoinduced Hall conductivity which is
within the experimentally accessible range.Comment: 9 pages, 4 figure
Staggered Currents in the Vortex Core
We study the electronic structure of the vortex core in the cuprates using
the U(1) slave-boson mean-field wavefunctions and their Gutzwiller projection.
We conclude that there exists local orbital antiferromagnetic order in the core
near optimal doping. We compare the results with that of BCS theory and analyze
the spatial dependence of the local tunneling density of states.Comment: 4 pages, 3 figure
Experimental observation of hidden Berry curvature in inversion-symmetric bulk 2H-WSe2
We investigate the hidden Berry curvature in bulk 2H-WSe2 by utilizing the
surface sensitivity of angle resolved photoemission (ARPES). The symmetry in
the electronic structure of transition metal dichalcogenides is used to
uniquely determine the local orbital angular momentum (OAM) contribution to the
circular dichroism (CD) in ARPES. The extracted CD signals for the K and K'
valleys are almost identical but their signs, which should be determined by the
valley index, are opposite. In addition, the sign is found to be the same for
the two spin-split bands, indicating that it is independent of spin state.
These observed CD behaviors are what are expected from Berry curvature of a
monolayer of WSe2. In order to see if CD-ARPES is indeed representative of
hidden Berry curvature within a layer, we use tight binding analysis as well as
density functional calculation to calculate the Berry curvature and local OAM
of a monolayer WSe2. We find that measured CD-ARPES is approximately
proportional to the calculated Berry curvature as well as local OAM, further
supporting our interpretation.Comment: 6 pages, 3 figure
Low-Frequency Optical Conductivity in Inhomogeneous d-wave Superconductors
Motivated by the recent optical conductivity experiments on
Bi_2Sr_2CaCu_2O_{8+delta} films, we examine the possible origin of
low-frequency dissipation in the superconducting state. In the presence of
spatial inhomogeneity of the local phase stiffness rho_s, it is shown that some
spectral weight is removed from omega=0 to finite frequencies and contribute to
dissipation. A case where both rho_s and the local normal fluid density are
inhomogeneous is also considered. We find an enhanced dissipation at low
frequency if the two variations are anti-correlated.Comment: To appear in Phys. Rev.
Observation of a multiferroic critical end point
The study of abrupt increases in magnetization with magnetic field known as
metamagnetic transitions has opened a rich vein of new physics in itinerant
electron systems, including the discovery of quantum critical end points with a
marked propensity to develop new kinds of order. However, the electric analogue
of the metamagnetic critical end point, a "metaelectric" critical end point has
not yet been realized. Multiferroic materials wherein magnetism and
ferroelectricity are cross-coupled are ideal candidates for the exploration of
this novel possibility using magnetic-field (\emph{H}) as a tuning parameter.
Herein, we report the discovery of a magnetic-field-induced metaelectric
transition in multiferroic BiMnO in which the electric polarization
(\emph{P}) switches polarity along with a concomitant Mn spin-flop transition
at a critical magnetic field \emph{H}. The simultaneous metaelectric
and spin-flop transitions become sharper upon cooling, but remain a continuous
crossover even down to 0.5 K. Near the \emph{P}=0 line realized at
\emph{H}18 T below 20 K, the dielectric constant
() increases significantly over wide field- and temperature
(\emph{T})-ranges. Furthermore, a characteristic power-law behavior is found in
the \emph{P}(\emph{H}) and (\emph{H}) curves at \emph{T}=0.66 K.
These findings indicate that a magnetic-field-induced metaelectric critical end
point is realized in BiMnO near zero temperature.Comment: 6 pages, 3 figure
Numerical Test of Disk Trial Wave function for Half-Filled Landau Level
The analyticity of the lowest Landau level wave functions and the relation
between filling factor and the total angular momentum severely limits the
possible forms of trial wave functions of a disk of electrons subject to a
strong perpendicular magnetic field. For N, the number of electrons, up to 12
we have tested these disk trial wave functions for the half filled Landau level
using Monte Carlo and exact diagonalization methods. The agreement between the
results for the occupation numbers and ground state energies obtained from
these two methods is excellent. We have also compared the profile of the
occupation number near the edge with that obtained from a field-theoretical
method. The results give qualitatively identical edge profiles. Experimental
consequences are briefly discussed.Comment: To be published in Phys. Rev. B. 9 pages, 6 figure
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