1,415 research outputs found

### Time-Reversal Symmetry Breaking and Spontaneous Anomalous Hall Effect in Fermi Fluids

We study the spontaneous non-magnetic time-reversal symmetry breaking in a
two-dimensional Fermi liquid without breaking either the translation symmetry
or the U(1) charge symmetry. Assuming that the low-energy physics is described
by fermionic quasiparticle excitations, we identified an "emergent" local
$U(1)^N$ symmetry in momentum space for an $N$-band model. For a large class of
models, including all one-band and two-band models, we found that the
time-reversal and chiral symmetry breaking can be described by the $U(1)^N$
gauge theory associated with this emergent local $U(1)^N$ symmetry. This
conclusion enables the classification of the time-reversal symmetry-breaking
states as types I and II, depending on the type of accompanying spatial
symmetry breaking. The properties of each class are studied. In particular, we
show that the states breaking both time-reversal and chiral symmetries are
described by spontaneously generated Berry phases. We also show examples of the
time-reversal symmetry-breaking phases in several different microscopically
motivated models and calculate their associated Hall conductance within a
mean-field approximation. The fermionic nematic phase with time-reversal
symmetry breaking is also presented and the possible realizations in strongly
correlated models such as the Emery model are discussed.Comment: 18 pages, 8 figure

### First-Principles Wannier Functions of Silicon and Gallium Arsenide

We present a self-consistent, real-space calculation of the Wannier functions
of Si and GaAs within density functional theory. We minimize the total energy
functional with respect to orbitals which behave as Wannier functions under
crystal translations and, at the minimum, are orthogonal. The Wannier functions
are used to calculate the total energy, lattice constant, bulk modulus, and the
frequency of the zone-center TO phonon of the two semiconductors with the
accuracy required nowadays in ab-initio calculations. Furthermore, the centers
of the Wannier functions are used to compute the macroscopic polarization of Si
and GaAs in zero electric field. The effective charges of GaAs, obtained by
finite differentiation of the polarization, agree with the results of linear
response theory.Comment: 12 pages, 2 PostScript figures, RevTeX, to appear in Physical Review

### Electron energy spectrum and the Berry phase in graphite bilayer

We emphasize that there exist four Dirac-type points in the electron-energy
spectrum of a graphite bilayer near the point K of its Brillouin zone. One of
the Dirac points is at the point K, and three Dirac points lie nearby. Each of
these three points generates the Berry phase $\pi$, while the Dirac point at K
gives the phase $-\pi$. It is these four points that determine the Berry phase
in the bilayer. If an electron orbit surrounds all these points, the Berry
phase is equal to $2\pi$.Comment: 4 pages, 2 figures, submitted to Phys. Rev. B ; expande

### Mott scattering at the interface between a metal and a topological insulator

We compute the spin-active scattering matrix and the local spectrum at the
interface between a metal and a three-dimensional topological band insulator.
We show that there exists a critical incident angle at which complete (100%)
spin flip reflection occurs and the spin rotation angle jumps by $\pi$. We
discuss the origin of this phenomena, and systematically study the dependence
of spin-flip and spin-conserving scattering amplitudes on the interface
transparency and metal Fermi surface parameters. The interface spectrum
contains a well-defined Dirac cone in the tunneling limit, and smoothly evolves
into a continuum of metal induced gap states for good contacts. We also
investigate the complex band structure of Bi$_2$Se$_3$.Comment: published versio

### Coordinate shift in the semiclassical Boltzmann equation and the anomalous Hall effect

We propose a gauge invariant expression for the side jump associated with
scattering between particular Bloch states. Our expression for the side jump
follows from the Born series expansion for the scattering T-matrix in powers of
the strength of the scattering potential. Given our gauge invariant side jump
expression, it is possible to construct a semiclassical Boltzmann theory of the
anomalous Hall effect which expresses all previously identified contributions
in terms of gauge invariant quantities and does not refer explicitly to
off-diagonal terms in the density-matrix response.Comment: 6 pages, 1 fugure. submitted to PR

### Optical injection and terahertz detection of the macroscopic Berry curvature

We propose an experimental scheme to probe the Berry curvature of solids. Our
method is sensitive to arbitrary regions of the Brillouin zone, and employs
only basic optical and terahertz techniques to yield a background free signal.
Using semiconductor quantum wells as a prototypical system, we discuss how to
inject Berry curvature macroscopically, and probe it in a way that provides
information about the underlying microscopic Berry curvature.Comment: 4 pages, accepted in Physical Review Letter

### Response of a particle in a one-dimensional lattice to an applied force: Dynamics of the effective mass

We study the behaviour of the expectation value of the acceleration of a
particle in a one-dimensional periodic potential when an external homogeneous
force is suddenly applied. The theory is formulated in terms of modified Bloch
states that include the interband mixing induced by the force. This approach
allows us to understand the behaviour of the wavepacket, which responds with a
mass that is initially the bare mass, and subsequently oscillates around the
value predicted by the effective mass. If Zener tunneling can be neglected, the
expression obtained for the acceleration of the particle is valid over
timescales of the order of a Bloch oscillation, which are of interest for
experiments with cold atoms in optical lattices. We discuss how these
oscillations can be tuned in an optical lattice for experimental detection.Comment: 15 pages, 12 figure

### Anatomy of the quantum melting of the two dimensional Wigner crystal

The Fermi liquid-Wigner crystal transition in a two dimensional electronic
system is revisited with a focus on the nature of the fixed node approximation
done in quantum Monte Carlo calculations. Recently, we proposed (Phys. Rev.
Lett. 94, 046801 (2005)) that for intermediate densities, a hybrid phase (with
the symmetry of the crystal but otherwise liquid like properties) is more
stable than both the liquid and the crystal phase. Here we confirm this result
both in the thermodynamic and continuum limit. The liquid-hybrid transition
takes place at rs=31.5 +/- 0.5. We find that the stability of the hybrid phase
with respect to the crystal one is tightly linked to its delocalized nature. We
discuss the implications of our results for various transition scenarii
(quantum hexatic phase, supersolid, multiple exchange, microemulsions) proposed
in the literature.Comment: 14 pages, 16 figure

### Maximally localized Wannier function within linear combination of pseudo-atomic orbital method: Implementation and applications to transition-metal-benzene complex

Construction of maximally localized Wannier functions (MLWFs) has been
implemented within the linear combination of pseudo-atomic orbital (LCPAO)
method. Detailed analysis using MLWFs is applied to three closely related
materials, single benzene (Bz) molecule, organometallic Vanadium-Bz infinite
chain, and V$_2$Bz$_{3}$ sandwich cluster. Two important results come out from
the present analysis: 1) for the infinite chain, the validity of the basic
assumption in the mechanism of Kanamori and Terakura for the ferromagnetic (FM)
state stability is confirmed; 2) for V$_2$Bz$_3$, an important role played by
the difference in the orbital energy between the edge Bzs and the middle Bz is
newly revealed: the on-site energy of p$\delta$ states of edge Bzs is higher
than that of middle Bz, which further reduces the FM stability of V$_2$Bz$_3$.Comment: 19 pages and 5 figure

### Existence of the Stark-Wannier quantum resonances

In this paper we prove the existence of the Stark-Wannier quantum resonances
for one-dimensional Schrodinger operators with smooth periodic potential and
small external homogeneous electric field. Such a result extends the existence
result previously obtained in the case of periodic potentials with a finite
number of open gaps.Comment: 30 pages, 1 figur

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