4,608 research outputs found
Theoretical study of even denominator fractions in graphene: Fermi sea versus paired states of composite fermions
The physics of the state at even denominator fractional fillings of Landau
levels depends on the Coulomb pseudopotentials, and produces, in different GaAs
Landau levels, a composite fermion Fermi sea, a stripe phase, or, possibly, a
paired composite fermion state. We consider here even denominator fractions in
graphene, which has different pseudopotentials as well as a possible four fold
degeneracy of each Landau level. We test various composite fermion Fermi sea
wave functions (fully polarized, SU(2) singlet, SU(4) singlet) as well as the
paired composite fermion states in the n=0 and Landau levels and predict
that (i) the paired states are not favorable, (ii) CF Fermi seas occur in both
Landau levels, and (iii) an SU(4) singlet composite fermion Fermi sea is
stabilized in the appropriate limit. The results from detailed microscopic
calculations are generally consistent with the predictions of the mean field
model of composite fermions
Radion Phenomenology in Realistic Warped Space Models
We investigate the phenomenology of the Randall-Sundrum radion in realistic
models of electroweak symmetry breaking with bulk gauge and fermion fields,
since the radion may turn out to be the lightest particle in such models. We
calculate the coupling of the radion in such scenarios to bulk fermion and
gauge modes. Special attention needs to be devoted to the coupling to massless
gauge fields (photon, gluon), since it is well known that loop effects may be
important for these fields. We also present a detailed explanation of these
couplings from the CFT interpretation. We then use these couplings to determine
the radion branching fractions and discuss some of the discovery potential of
the LHC for the radion. We find that the gamma-gamma signal is enhanced over
most of the range of the radion mass over the gamma-gamma signal of a SM Higgs,
as long as the RS scale is sufficiently low. However, the signal significance
depends strongly on free parameters that characterize the magnitude of bare
brane-localized kinetic terms for the massless gauge fields. In the absence of
such terms, the signal can be be enhanced over the traditional RS1 models
(where all standard model fields are localized on the IR brane), but the signal
can also be reduced compared to RS1 if the brane localized terms are sizeable.
We also show that for larger radion masses, where the gamma-gamma signal is no
longer significant, one can use the usual 4 lepton signal to discover the
radion.Comment: 28 pages, 7 figure
Luttinger theorem for the strongly correlated Fermi liquid of composite fermions
While an ordinary Fermi sea is perturbatively robust to interactions, the
paradigmatic composite-fermion (CF) Fermi sea arises as a non-perturbative
consequence of emergent gauge fields in a system where there was no Fermi sea
to begin with. A mean-field picture suggests two Fermi seas, of composite
fermions made from electrons or holes in the lowest Landau level, which occupy
different areas away from half filling and thus appear to represent distinct
states. We show that in the microscopic theory of composite fermions, which
satisfies particle-hole symmetry in the lowest Landau level to an excellent
degree, the Fermi wave vectors at filling factors and are the
same, and are generally consistent with the experimental findings of Kamburov
{\em et al.} [Phys. Rev. Lett. {\bf 113}, 196801 (2014)]. Our calculations
suggest that the area of the CF Fermi sea may slightly violate the Luttinger
area rule.Comment: 21 pages, 17 figures including supplemental material, published
versio
European studies: Taking stock and looking ahead
This essay is an attempt to generalize experiences of Central and Eastern European universities in the field of European Studies over the past 20 years. The paper follows the logic of business analysis in order to come up with proposals for future action
And the first shall be the last
This study analyzes the puzzle of Hungarian economic drifting in a long run perspective. The underlying puzzle for the investigation is why bad policies are invariably popular and good policies unpopular, thus why political and economic rationality never overlap. The first part of the article summarizes in eight points the basic features of the postwar period. Then six lessons are offered, which might be useful for other countries in transition or for students of comparative economics and politics, lessons that can be generalized on the basis of the individual country experience
Regulation of fast-spiking basket cell synapses by the chloride channel ClC-2.
Parvalbumin-expressing, fast-spiking basket cells are important for the generation of synchronous, rhythmic population activities in the hippocampus. We found that GABAA receptor-mediated synaptic inputs from murine parvalbumin-expressing basket cells were selectively modulated by the membrane voltage- and intracellular chloride-dependent chloride channel ClC-2. Our data reveal a previously unknown cell type-specific regulation of intracellular chloride homeostasis in the perisomatic region of hippocampal pyramidal neurons
Phase Diagram of Fractional Quantum Hall Effect of Composite Fermions in Multi-Component Systems
While the integer quantum Hall effect of composite fermions manifests as the
prominent fractional quantum Hall effect (FQHE) of electrons, the FQHE of
composite fermions produces further, more delicate states, arising from a weak
residual interaction between composite fermions. We study the spin phase
diagram of these states, motivated by the recent experimental observation by
Liu {\em et al.} \cite{Liu14a,Liu14b} of several spin-polarization transitions
at 4/5, 5/7, 6/5, 9/7, 7/9, 8/11 and 10/13 in GaAs systems. We show that the
FQHE of composite fermions is much more prevalent in multicomponent systems,
and consider the feasibility of such states for systems with
components for an SU() symmetric interaction. Our results apply to
GaAs quantum wells, wherein electrons have two components, to AlAs quantum
wells and graphene, wherein electrons have four components (two spins and two
valleys), and to an H-terminated Si(111) surface, which can have six
components. The aim of this article is to provide a fairly comprehensive list
of possible incompressible fractional quantum Hall states of composite
fermions, their SU() spin content, their energies, and their phase
diagram as a function of the generalized "Zeeman" energy. We obtain results at
three levels of approximation: from ground state wave functions of the
composite fermion theory, from composite fermion diagonalization, and, whenever
possible, from exact diagonalization. Effects of finite quantum well thickness
and Landau level mixing are neglected in this study. We compare our theoretical
results with the experiments of Liu {\em et al.} \cite{Liu14a,Liu14b} as well
as of Yeh {\em et al.} \cite{Yeh99} for a two component system.Comment: 29 pages, 6 figure
High Resolution Valley Spectroscopy of Si Quantum Dots
We study an accumulation mode Si/SiGe double quantum dot (DQD) containing a
single electron that is dipole coupled to microwave photons in a
superconducting cavity. Measurements of the cavity transmission reveal
dispersive features due to the DQD valley states in Si. The occupation of the
valley states can be increased by raising temperature or applying a finite
source-drain bias across the DQD, resulting in an increased signal. Using
cavity input-output theory and a four-level model of the DQD, it is possible to
efficiently extract valley splittings and the inter- and intra-valley tunnel
couplings
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