2,664 research outputs found
Transference of Transport Anisotropy to Composite Fermions
When interacting two-dimensional electrons are placed in a large
perpendicular magnetic field, to minimize their energy, they capture an even
number of flux quanta and create new particles called composite fermions (CFs).
These complex electron-flux-bound states offer an elegant explanation for the
fractional quantum Hall effect. Furthermore, thanks to the flux attachment, the
effective field vanishes at a half-filled Landau level and CFs exhibit
Fermi-liquid-like properties, similar to their zero-field electron
counterparts. However, being solely influenced by interactions, CFs should
possess no memory whatever of the electron parameters. Here we address a
fundamental question: Does an anisotropy of the electron effective mass and
Fermi surface (FS) survive composite fermionization? We measure the resistance
of CFs in AlAs quantum wells where electrons occupy an elliptical FS with large
eccentricity and anisotropic effective mass. Similar to their electron
counterparts, CFs also exhibit anisotropic transport, suggesting an anisotropy
of CF effective mass and FS.Comment: 5 pages, 5 figure
Coherent oscillations and giant edge magnetoresistance in singly connected topological insulators
A topological insulator has a pair of extended states at the edge in the bulk insulating regime. We study a geometry in which such edge states will manifest themselves in a qualitative manner through periodic oscillations in the magnetoconductance of a singly connected sample coupled to leads through narrow point contacts. Detailed calculations identify the parameters for which these oscillations are expected to be the strongest, and also show their robustness to disorder. Such oscillations can be used as a spectroscopic tool of the edge states. A large change in the device resistance at small B, termed giant edge magnetoresistance, can have potential for application. © 2009 The American Physical Society.published_or_final_versio
Anaesthetic management of a parturient with severe pulmonary stenosis undergoing Caesarean section
We report the successful management of a parturient with severe pulmonary stenosis undergoing Caesarean section. Anaesthesia was managed with combined spinal and epidural anaesthetic technique. During the intraoperative period, haemodynamic parameters were well maintained. There were no episodes of haemodynamic fluctuations or oxygen desaturation. The patient delivered a full-term, normal foetus.Keywords: anaesthesia: obstetric; anaesthetic technique: spinal, epidural; complications, pulmonary stenosis, pregnanc
Composite Fermion Metals from Dyon Black Holes and S-Duality
We propose that string theory in the background of dyon black holes in
four-dimensional anti-de Sitter spacetime is holographic dual to conformally
invariant composite Dirac fermion metal. By utilizing S-duality map, we show
that thermodynamic and transport properties of the black hole match with those
of composite fermion metal, exhibiting Fermi liquid-like. Built upon
Dirac-Schwinger-Zwanziger quantization condition, we argue that turning on
magnetic charges to electric black hole along the orbit of Gamma(2) subgroup of
SL(2,Z) is equivalent to attaching even unit of statistical flux quanta to
constituent fermions. Being at metallic point, the statistical magnetic flux is
interlocked to the background magnetic field. We find supporting evidences for
proposed holographic duality from study of internal energy of black hole and
probe bulk fermion motion in black hole background. They show good agreement
with ground-state energy of composite fermion metal in Thomas-Fermi
approximation and cyclotron motion of a constituent or composite fermion
excitation near Fermi-point.Comment: 30 pages, v2. 1 figure added, minor typos corrected; v3. revised
version to be published in JHE
Anomalous structure in the single particle spectrum of the fractional quantum Hall effect
The two-dimensional electron system (2DES) is a unique laboratory for the
physics of interacting particles. Application of a large magnetic field
produces massively degenerate quantum levels known as Landau levels. Within a
Landau level the kinetic energy of the electrons is suppressed, and
electron-electron interactions set the only energy scale. Coulomb interactions
break the degeneracy of the Landau levels and can cause the electrons to order
into complex ground states. In the high energy single particle spectrum of this
system, we observe salient and unexpected structure that extends across a wide
range of Landau level filling fractions. The structure appears only when the
2DES is cooled to very low temperature, indicating that it arises from delicate
ground state correlations. We characterize this structure by its evolution with
changing electron density and applied magnetic field. We present two possible
models for understanding these observations. Some of the energies of the
features agree qualitatively with what might be expected for composite
Fermions, which have proven effective for interpreting other experiments in
this regime. At the same time, a simple model with electrons localized on
ordered lattice sites also generates structure similar to those observed in the
experiment. Neither of these models alone is sufficient to explain the
observations across the entire range of densities measured. The discovery of
this unexpected prominent structure in the single particle spectrum of an
otherwise thoroughly studied system suggests that there exist core features of
the 2DES that have yet to be understood.Comment: 15 pages, 10 figure
Spectral weight transfer in a disorder-broadened Landau level
In the absence of disorder, the degeneracy of a Landau level (LL) is
, where is the magnetic field, is the area of the sample
and is the magnetic flux quantum. With disorder, localized states
appear at the top and bottom of the broadened LL, while states in the center of
the LL (the critical region) remain delocalized. This well-known phenomenology
is sufficient to explain most aspects of the Integer Quantum Hall Effect (IQHE)
[1]. One unnoticed issue is where the new states appear as the magnetic field
is increased. Here we demonstrate that they appear predominantly inside the
critical region. This leads to a certain ``spectral ordering'' of the localized
states that explains the stripes observed in measurements of the local inverse
compressibility [2-3], of two-terminal conductance [4], and of Hall and
longitudinal resistances [5] without invoking interactions as done in previous
work [6-8].Comment: 5 pages 3 figure
Fermentation process for alcoholic beverage production from mahua (Madhuca indica J. F. Mel.) flowers
Mahua flowers are rich in sugar (68-72%), in addition to a number of minerals and one of the most important raw materials for alcohol fermentation. The present investigation was for the development of a non-distilled alcoholic beverage from Mahua flowers. Eighteen (18) treatment combinations consisting of two temperatures (25 and 30°C), three pH (4.0, 4.5 and 5.0) and three period of fermentation (7, 14 and 21 days) were used in the fermentation conditions. The maximum yield of ethanol (9.51 %) occurred at 25°C with pH 4.5 after 14 days of fermentation of Mahua flower juice. The fermented non-distilled alcoholic beverage contained total sugar (8.83 mg/ml), reducing sugar (0.82 mg/ml), total soluble solids (6.37°Brix) titrable acidity (0.65 %), and volatile acidity (0.086%). Methanol was not detected at any stage of fermentation. The developed fermented alcoholic beverage had characteristic flavor and aroma of Mahua flowers with about 7 to 9% alcohol.Keywords: Madhuca indica, ethanol, reducing sugar, fermentation.African Journal of Biotechnology Vol. 12(39), pp. 5771-577
Fractional quantum Hall effect in the absence of Landau levels
It has been well-known that topological phenomena with fractional
excitations, i.e., the fractional quantum Hall effect (FQHE) \cite{Tsui1982}
will emerge when electrons move in Landau levels. In this letter, we report the
discovery of the FQHE in the absence of Landau levels in an interacting fermion
model. The non-interacting part of our Hamiltonian is the recently proposed
topologically nontrivial flat band model on the checkerboard lattice
\cite{sun}. In the presence of nearest-neighboring repulsion (), we find
that at 1/3 filling, the Fermi-liquid state is unstable towards FQHE. At 1/5
filling, however, a next-nearest-neighboring repulsion is needed for the
occurrence of the 1/5 FQHE when is not too strong. We demonstrate the
characteristic features of these novel states and determine the phase diagram
correspondingly.Comment: 6 pages and 4 figure
Higher-Energy Composite Fermion Levels in the Fractional Quantum Hall Effect
Even though composite fermions in the fractional quantum Hall liquid are well established, it is not yet known up to what energies they remain intact. We probe the high-energy spectrum of the 1/3 liquid directly by resonant inelastic light scattering, and report the observation of a large number of new collective modes. Supported by our theoretical calculations, we associate these with transitions across two or more composite fermions levels. The formation of quasiparticle levels up to high energies is direct evidence for the robustness of topological order in the fractional quantum Hall effect
A Realistic Radiative Fermion Mass Hierarchy in Non-supersymmetric SO(10)
A non-supersymmetric grand unified theory can exhibit a "radiative fermion
mass hierarchy", in which the heavier quarks and leptons get mass at tree level
and the lighter ones get mass from loop diagrams. Recently the first predictive
model of this type was proposed. Here it is analyzed numerically and it is
shown to give an excellent fit to the quark and lepton masses and mixings,
including the CP phase violating phase . A relation between the
neutrino angle and the atmospheric neutrino angle is obtainedComment: 13 pages, 4 figures, RevTeX
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