3,225 research outputs found
Strongly Correlated Topological Superconductors and Topological Phase Transitions via Green's Function
We propose several topological order parameters expressed in terms of Green's
function at zero frequency for topological superconductors, which generalizes
the previous work for interacting insulators. The coefficient in topological
field theory is expressed in terms of zero frequency Green's function. We also
study topological phase transition beyond noninteracting limit in this zero
frequency Green's function approach.Comment: 10 pages. Published versio
A General Theorem Relating the Bulk Topological Number to Edge States in Two-dimensional Insulators
We prove a general theorem on the relation between the bulk topological
quantum number and the edge states in two dimensional insulators. It is shown
that whenever there is a topological order in bulk, characterized by a
non-vanishing Chern number, even if it is defined for a non-conserved quantity
such as spin in the case of the spin Hall effect, one can always infer the
existence of gapless edge states under certain twisted boundary conditions that
allow tunneling between edges. This relation is robust against disorder and
interactions, and it provides a unified topological classification of both the
quantum (charge) Hall effect and the quantum spin Hall effect. In addition, it
reconciles the apparent conflict between the stability of bulk topological
order and the instability of gapless edge states in systems with open
boundaries (as known happening in the spin Hall case). The consequences of time
reversal invariance for bulk topological order and edge state dynamics are
further studied in the present framework.Comment: A mistake corrected in reference
Optical transmittance of multilayer graphene
We study the optical transmittance of multilayer graphene films up to 65
layers thick. By combing large-scale tight-binding simulation and optical
measurement on CVD multilayer graphene, the optical transmission through
graphene films in the visible region is found to be solely determined by the
number of graphene layers. We argue that the optical transmittance measurement
is more reliable in the determination of the number of layers than the commonly
used Raman Spectroscopy. Moreover, optical transmittance measurement can be
applied also to other 2D materials with weak van der Waals interlayer
interaction.Comment: Europhysics Letters (2014
Hall Effect in the coma of 67P/Churyumov-Gerasimenko
Magnetohydrodynamics simulations have been carried out in studying the solar
wind and cometary plasma interactions for decades. Various plasma boundaries
have been simulated and compared well with observations for comet 1P/Halley.
The Rosetta mission, which studies comet 67P/Churyumov-Gerasimenko, challenges
our understanding of the solar wind and comet interactions. The Rosetta Plasma
Consortium observed regions of very weak magnetic field outside the predicted
diamagnetic cavity. In this paper, we simulate the inner coma with the Hall
magnetohydrodynamics equations and show that the Hall effect is important in
the inner coma environment. The magnetic field topology becomes complex and
magnetic reconnection occurs on the dayside when the Hall effect is taken into
account. The magnetic reconnection on the dayside can generate weak magnetic
filed regions outside the global diamagnetic cavity, which may explain the
Rosetta Plasma Consortium observations. We conclude that the substantial change
in the inner coma environment is due to the fact that the ion inertial length
(or gyro radius) is not much smaller than the size of the diamagnetic cavity.Comment: 23 pages, 6 figur
Vortex configurations of bosons in an optical lattice
The single vortex problem in a strongly correlated bosonic system is
investigated self-consistently within the mean-field theory of the Bose-Hubbard
model. Near the superfluid-Mott transition, the vortex core has a tendency
toward the Mott-insulating phase, with the core particle density approaching
the nearest commensurate value. If the nearest neighbor repulsion exists, the
charge density wave order may develop locally in the core. The evolution of the
vortex configuration from the strong to weak coupling regions is studied. This
phenomenon can be observed in systems of rotating ultra-cold atoms in optical
lattices and Josephson junction arraysComment: 4 pages, 4 figs, Accepted by Physics Review
Ultra-high fidelity qubits for quantum computing
We analyze a system of fermionic Li atoms in an optical trap, and show
that an atom "on demand" can be prepared with ultra-high fidelity, exceeding
0.99998. This process can be scaled to many sites in parallel, providing a
realistic method to initialize N qubits at ultra-high fidelity for quantum
computing. We also show how efficient quantum gate operation can be implemented
in this system, and how spatially resolved single-atom detection can be
performed
Spin filtering and magnetoresistance in ballistic tunnel junctions
We theoretically investigate magnetoresistance (MR) effects in connection
with spin filtering in quantum-coherent transport through tunnel junctions
based on non-magnetic/semimagnetic heterostructures. We find that spin
filtering in conjunction with the suppression/enhancement of the spin-dependent
Fermi seas in semimagnetic contacts gives rise to (i) spin-split kinks in the
MR of single barriers and (ii) a robust beating pattern in the MR of double
barriers with a semimagnetic well. We believe these are unique signatures for
quantum filtering.Comment: Added references + corrected typo
Calculation of Atomic Number States: a Bethe Ansatz Approach
We analyze the conditions for producing atomic number states in a
one-dimensional optical box using the Bethe ansatz method. This approach
provides a general framework, enabling the study of number state production
over a wide range of realistic experimental parameters
A new approach to bulk viscosity in strange quark matter at high densities
A new method is proposed to compute the bulk viscosity in strange quark
matter at high densities. Using the method it is straightforward to prove that
the bulk viscosity is positive definite, which is not so easy to accomplish in
other approaches especially for multi-component fluids like strange quark
matter with light up and down quarks and massive strange quarks.Comment: 7pages, talk given in SQM2008. Minor revisions, including
clarification and updated reference
Topological insulators and superconductors
Topological insulators are new states of quantum matter which can not be
adiabatically connected to conventional insulators and semiconductors. They are
characterized by a full insulating gap in the bulk and gapless edge or surface
states which are protected by time-reversal symmetry. These topological
materials have been theoretically predicted and experimentally observed in a
variety of systems, including HgTe quantum wells, BiSb alloys, and BiTe
and BiSe crystals. We review theoretical models, materials properties
and experimental results on two-dimensional and three-dimensional topological
insulators, and discuss both the topological band theory and the topological
field theory. Topological superconductors have a full pairing gap in the bulk
and gapless surface states consisting of Majorana fermions. We review the
theory of topological superconductors in close analogy to the theory of
topological insulators.Comment: 55 pages, 44 figures, Review article commissioned by the Review of
Modern Physics. Please help us to improve the article by emailing us your
comments and missing reference
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