21,849 research outputs found
Improved Composite-Boson Theory of Monolayer and Bilayer Quantum Hall Ferromagnets
An improved composite-boson theory of quantum Hall ferromagnets is formulated
both for the monolayer and bilayer systems. In this scheme the field operator
describes solely the physical degrees of freedom representing the deviation
from the ground state. Skyrmions are charged excitations confined to the lowest
Landau level. By evaluating the excitation energy of one skyrmion in the
interlayer-coherent phase it is shown that the bilayer QH state becomes stabler
as the interlayer density difference becomes larger.Comment: 14 pages including 1 figure; Physics Letters A (to be published
Tauberian theorem for value functions
For two-person dynamic zero-sum games (both discrete and continuous
settings), we investigate the limit of value functions of finite horizon games
with long run average cost as the time horizon tends to infinity and the limit
of value functions of -discounted games as the discount tends to zero.
We prove that the Dynamic Programming Principle for value functions directly
leads to the Tauberian Theorem---that the existence of a uniform limit of the
value functions for one of the families implies that the other one also
uniformly converges to the same limit. No assumptions on strategies are
necessary.
To this end, we consider a mapping that takes each payoff to the
corresponding value function and preserves the sub- and super- optimality
principles (the Dynamic Programming Principle). With their aid, we obtain
certain inequalities on asymptotics of sub- and super- solutions, which lead to
the Tauberian Theorem. In particular, we consider the case of differential
games without relying on the existence of the saddle point; a very simple
stochastic game model is also considered
Metastable phase in the quantum Hall ferromagnet
Time-dependent capacitance measurements reveal an unstable phase of electrons
in gallium arsenide quantum well that occurs when two Landau levels with
opposite spin are brought close to degeneracy by applying a gate voltage. This
phase emerges below a critical temperature and displays a peculiar
non-equilibrium dynamical evolution. The relaxation dynamics is found to follow
a stretched exponential behavior and correlates with hysteresis loops observed
by sweeping the magnetic field. These experiments indicate that metastable
randomly-distributed magnetic domains are involved in the relaxation process in
a way that is equivalently tunable by a change in gate voltage or temperature.Comment: 7 pages, including 4 figures Changes made to introduction Added
figure Submitted to SS
Mutual Composite Fermion and composite Boson approaches to balanced and imbalanced bilayer quantum Hall system: an electronic analogy of the Helium 4 system
We use both Mutual Composite Fermion (MCF) and Composite Boson (CB) approach
to study balanced and im-balanced Bi-Layer Quantum Hall systems (BLQH) and make
critical comparisons between the two approaches. We find the CB approach is
superior to the MCF approach in studying ground states with different kinds of
broken symmetries. In the phase representation of the CB theory, we first study
the Excitonic superfluid state (ESF). The theory puts spin and charge degree
freedoms in the same footing, explicitly bring out the spin-charge connection
and classify all the possible excitations in a systematic way. Then in the dual
density representation of the CB theory, we study possible intermediate phases
as the distance increases. We propose there are two critical distances and three phases as the distance increases. When ,
the system is in the ESF state which breaks the internal symmetry,
when , the system is in an Pseudo-spin density wave
(PSDW) state which breaks the translational symmetry, there is a first order
transition at driven by the collapsing of magneto-roton minimum at a
finite wavevector in the pseudo-spin channel. When , the
system becomes two weakly coupled Composite Fermion Fermi Liquid
(FL) state. There is also a first order transition at . We
construct a quantum Ginzburg Landau action to describe the transition from ESF
to PSDW which break the two completely different symmetries. By using the QGL
action, we explicitly show that the PSDW takes a square lattice and analyze in
detail the properties of the PSDW at zero and finite temperature.Comment: 29 PRB pages, 18 figures, 2 tables, REVTEX
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