8,943 research outputs found
Competing Nematic, Anti-ferromagnetic and Spin-flux orders in the Ground State of Bilayer Graphene
We analyze the phase diagram of the Bilayer graphene (BLG) at zero
temperature and doping. Assuming that at the high energies the electronic
system of BLG can be described within a weak coupling theory (consistent with
the experimental evidence), we systematically study the evolution of the
couplings with going from high to low energies. The divergences of the
couplings at some energies indicates the tendency towards certain symmetry
breakings. Carrying out this program, we found that the phase diagram is
determined by microscopic couplings defined on the short distances (initial
conditions). We explored all plausible space of these initial conditions and
found that the three states have the largest phase volume of the initial
couplings: nematic, antiferromagnetic and spin flux (a.k.a quantum spin Hall).
In addition, ferroelectric and two superconducting phases and appear only near
the very limits of the applicability of the weak coupling approach.
The paper also contains the derivation and analysis of the renormalization
group equations and the group theory classification of all the possible phases
which might arise from the symmetry breakings of the lattice, spin rotation,
and gauge symmetries of graphene.Comment: 19 pages, 16 figure
Entanglement Measure for Composite Systems
A general description of entanglement is suggested as an action realized by
an arbitrary operator over given disentangled states. The related entanglement
measure is defined. Because of its generality, this definition can be employed
for any physical systems, pure or mixed, equilibrium or nonequilibrium, and
characterized by any type of operators, whether these are statistical
operators, field operators, spin operators, or anything else. Entanglement of
any number of parts from their total ensemble forming a multiparticle composite
system can be determined. Interplay between entanglement and ordering,
occurring under phase transitions, is analysed by invoking the concept of
operator order indices.Comment: 6 pages, Revte
Kinetics of the Phase Separation Transition in Cold-Atom Boson-Fermion Mixtures
We study the kinetics of the first order phase separation transition in
boson-fermion cold-atom mixtures. At sufficiently low temperatures such a
transition is driven by quantum fluctuations responsible for the formation of
critical nuclei of a stable phase. Based on a microscopic description of
interacting boson-fermion mixtures we derive an effective action for the
critical droplet and obtain an asymptotic expression for the nucleation rate in
the vicinity of the phase transition and near the spinodal instability of the
mixed phase. We also discuss effects of dissipation which play a dominant role
close to the transition point, and identify the regimes where quantum
nucleation can be experimentally observed in cold-atom systems.Comment: 4 pages 1 figure, typos correcte
Possible types of the evolution of vacuum shells around the de Sitter space
All possible evolution scenarios of a thin vacuum shell surrounding the
spherically symmetric de Sitter space have been determined and the
corresponding global geometries have been constructed. Such configurations can
appear at the final stage of the cosmological phase transition, when isolated
regions (islands) of the old vacuum remain. The islands of the old vacuum are
absorbed by the new vacuum, expand unlimitedly, or form black holes and
wormholes depending on the sizes of the islands as well as on the density and
velocity of the shells surrounding the islands.Comment: 3 pages, 1 figur
Making an analogy between a multi chain interaction in charge density wave transport and the use of wavefunctionals to form soliton- anti soliton pairs
A numerical simulation shows that a massive Schwinger model used to formulate
solutions to charge density wave (CDW) transport is insufficient for transport
of soliton- anti soliton pairs through a pinning gap model of CDW transport.
However, a model Hamiltonian with Peierls condensation energy used to couple
adjacent chains (or transverse wave vectors) permits formation of soliton -
anti soliton pairs that could be used to transport CDW through a potential
barrier. There are analogies between this construction and the false vacuum
hypothesis used for showing a necessary and sufficient condition for wave
functionals for formation of soliton - anti soliton pairs. This can be
established by either use of the Bogomol'nyi inequality or through an
experimental artifact resulting through use of the false vacuum hypothesis to
obtain a proportional distance between the soliton - anti soliton pair charge
centersComment: 17 pages, 3 figure
Spontaneously Broken Spacetime Symmetries and Goldstone's Theorem
Goldstone's theorem states that there is a massless mode for each broken
symmetry generator. It has been known for a long time that the naive
generalization of this counting fails to give the correct number of massless
modes for spontaneously broken spacetime symmetries. We explain how to get the
right count of massless modes in the general case, and discuss examples
involving spontaneously broken Poincare and conformal invariance.Comment: 4 pages; 1 figure; v2: minor corrections. version to appear on PR
Gravitation Interaction and Electromagnetic Interaction in the Relativistic Universe with Total Zero and Local Non-Zero Energy
In the model of flat expansive homogeneous and isotropic relativistic
universe with total zero and local non-zero energy the gravitation energy of
bodies and the elecromagnetic energy of charged bodies can be localised.Comment: LaTeX, 10 pages, 1 figur
Cyclotron enhancement of tunneling
A state of an electron in a quantum wire or a thin film becomes metastable,
when a static electric field is applied perpendicular to the wire direction or
the film surface. The state decays via tunneling through the created potential
barrier. An additionally applied magnetic field, perpendicular to the electric
field, can increase the tunneling decay rate for many orders of magnitude. This
happens, when the state in the wire or the film has a velocity perpendicular to
the magnetic field. According to the cyclotron effect, the velocity rotates
under the barrier and becomes more aligned with the direction of tunneling.
This mechanism can be called cyclotron enhancement of tunneling
U_A(1) Anomaly at high temperature: the scalar-pseudoscalar splitting in QCD
We estimate the splitting between the spatial correlation lengths in the
scalar and pseudoscalar channels in QCD at high temperature. The splitting is
due to the contribution of the instanton/anti-instanton chains in the thermal
ensemble, even though instanton contributions to thermodynamic quantities are
suppressed. The splitting vanishes at asymptotically high temperatures as
, where is the beta function
coefficient.Comment: 5 p
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