1,341 research outputs found
From tunneling to photoemission: correlating two spaces
Correlating the data measured by tunneling and photoemission spectroscopies
is a long-standing problem in condensed matter physics. The quasiparticle
interference, recently discovered in high-Tc cuprates, reveals a possibility to
solve this problem. Application of modern phase retrieval algorithms to Fourier
transformed tunneling data allows to recover the distribution of the
quasiparticle spectral weight in the reciprocal space of solids measured
directly by photoemission. This opens a direct way to unify these two powerful
techniques and may help to solve a number of problems related with space/time
inhomogeneities predicted in strongly correlated electron systems.Comment: more info at http://www.imp.kiev.ua/~kord/AC-ARPES/index.htm
A MEMS Coriolis-Based Mass-Flow-to-Digital Converter for Low Flow Rate Sensing
This article presents a microelectromechanical system (MEMS) Coriolis-based mass-flow-to-digital converter (Φ DC) that can be used with both liquids and gases. It consists of a micromachined Coriolis mass flow sensor and a CMOS interface circuit that drives it into oscillation and digitizes the resulting mass flow information. A phase-locked loop (PLL) drives the sensor at its resonance frequency (fD), while a low 1/f noise switched-capacitor (SC) proportional-integral (PI) controller maintains a constant drive amplitude. Mass flow through the sensor causes Coriolis-force-induced displacements, which are detected by co-integrated sense capacitors. In-phase (I) and quadrature (Q) components of these displacements are then digitized by two continuous-time delta-sigma modulators (CT- ΔΣ Ms) with finite impulse response (FIR)-DACs and passive mixers. Their outputs are used to accurately estimate and cancel sense path delay, thus improving sensor stability. To ensure constant sensitivity over a wide range of fluid densities, a background sensitivity tuning (BST) scheme adjusts the sense capacitors' bias voltage as a function of fD, which is a good proxy for fluid density. Implemented in a standard 0.18- μm CMOS technology, the interface circuit consumes 13 mW from a 1.8-V supply. The proposed MEMS Coriolis Φ DC achieves a state-of-the-art noise floor of 80 μg/h/√ Hz and a zero stability (ZS) of ±0.31 mg/h, which is at par with MEMS thermal flow sensors.</p
Hartree-Fock Theory of Hole Stripe States
We report on Hartree-Fock theory results for stripe states of two-dimensional
hole systems in quantum wells grown on GaAs (311)A substrates. We find that the
stripe orientation energy has a rich dependence on hole density, and on
in-plane field magnitude and orientation. Unlike the electron case, the
orientation energy is non-zero for zero in-plane field, and the ground state
orientation can be either parallel or perpendicular to a finite in-plane field.
We predict an orientation reversal transition in in-plane fields applied along
the direction.Comment: 5 pages including 4 figure
Effect of Sugarcane Pressmud Biocompost on Dry Matter Yield and Nutrient Uptake in Maize
An experiment was conducted to determine the nutrient contents and manurial value of biocompost, collected from Matiari Sugar Mill, Matiari and analyzed for macro nutrients N, P and K. The biocompost was evaluated in a pot experiment on maize crop with eight treatments in factorial combinations of two rates of biocompost (0 and 10 tons ha-1) and four fertilizer treatments (0-0-0, 150-0-0, 150-75-0 and 150-75-60 kg ha-1 N, P and K) . The treatments were replicated three times in a randomized complete block design and maize was grown for 7 weeks. The soil was a clay loam (31% clay) with EC 0.35 dSm-1, pH 7.87, low in organic matter (0.80%) and Olsen P (7.0 mg kg-1) and high in NH4OAC-K (320 mg kg-1). The nutrient contents of biocompost were 1.8% N, 1.83% P and 0.9% K. Results revealed that there were pronounced positive effects of addition of biocompost, as well as N on plant height and dry weights of maize. Plant analysis data showed that the effect biocompost and mineral fertilizers was non-significant with respect to N, P and K contents. Soil analytical data showed that the EC values of post harvest samples increased with the application of biocompost while pH was not affected. Soil organic matter, Olsen P and NH4OAC-K increased significantly with the application of biocompost. Fertilizer application also increased Olsen P and NH4OAC-K contents in soil. The results of this study showed that biocompost can be used along with mineral fertilizers to increase maize growth and dry matter yield. Keywords: Maize, Dry matter yield, Pressmud Biocompost
Anisotropic transport in unidirectional lateral superlattice around half-filling of the second Landau level
We have observed marked transport anisotropy in short period (a=92 nm)
unidirectional lateral superlattices around filling factors nu=5/2 and 7/2:
magnetoresistance shows a sharp peak for current along the modulation grating
while a dip appears for current across the grating. By altering the ratio a/l
(with l=sqrt{hbar/eB_perp} the magnetic length) via changing the electron
density n_e, it is shown that the nu=5/2 anisotropic features appear in the
range 6.6 alt a/l alt 7.2 varying their intensities, becoming most conspicuous
at a/l simeq 6.7. The peak/dip broadens with temperature roughly preserving its
height/depth up to 250 mK. Tilt experiments reveal that the structures are
slightly enhanced by an in-plane magnetic field B_| perpendicular to the
grating but are almost completely destroyed by B_| parallel to the grating. The
observations suggest the stabilization of a unidirectional charge-density-wave
or stripe phase by weak external periodic modulation at the second Landau
level.Comment: REVTeX, 5 pages, 3 figures, Some minor revisions, Added notes and
reference
Quantum magneto-oscillations in a two-dimensional Fermi liquid
Quantum magneto-oscillations provide a powerfull tool for quantifying
Fermi-liquid parameters of metals. In particular, the quasiparticle effective
mass and spin susceptibility are extracted from the experiment using the
Lifshitz-Kosevich formula, derived under the assumption that the properties of
the system in a non-zero magnetic field are determined uniquely by the
zero-field Fermi-liquid state. This assumption is valid in 3D but, generally
speaking, erroneous in 2D where the Lifshitz-Kosevich formula may be applied
only if the oscillations are strongly damped by thermal smearing and disorder.
In this work, the effects of interactions and disorder on the amplitude of
magneto-oscillations in 2D are studied. It is found that the effective mass
diverges logarithmically with decreasing temperature signaling a deviation from
the Fermi-liquid behavior. It is also shown that the quasiparticle lifetime due
to inelastic interactions does not enter the oscillation amplitude, although
these interactions do renormalize the effective mass. This result provides a
generalization of the Fowler-Prange theorem formulated originally for the
electron-phonon interaction.Comment: 4 pages, 1 figur
Mean-field Phase Diagram of Two-Dimensional Electrons with Disorder in a Weak Magnetic Field
We study two-dimensional interacting electrons in a weak perpendicular
magnetic field with the filling factor and in the presence of a
quenched disorder. In the framework of the Hartree-Fock approximation, we
obtain the mean-field phase diagram for the partially filled highest Landau
level. We find that the CDW state can exist if the Landau level broadening
does not exceed the critical value .
Our analysis of weak crystallization corrections to the mean-field results
shows that these corrections are of the order of and
therefore can be neglected
The Onset of Anisotropic Transport of Two-Dimensional Electrons in High Landau Levels: An Isotropic-to-Nematic Liquid Crystal Phase Transition?
The recently discovered anisotropy of the longitudinal resistance of
two-dimensional electrons near half filling of high Landau levels is found to
persist to much higher temperatures T when a large in-plane magnetic field B||
is applied. Under these conditions we find that the longitudinal resistivity
scales quasi-linearly with B||/T. These observations support the notion that
the onset of anisotropy at B||=0 does not reflect the spontaneous development
of charge density modulations but may instead signal an isotropic-to-nematic
liquid crystal phase transition.Comment: 5 pages, 4 figure
Quantum interference between non-magnetic impurities in d_x2-y2-wave superconductors
We study quantum interference of electronic waves that are scattered by
multiple non-magnetic impurities in a d_x2-y2-wave superconductor. We show that
the number of resonance states in the density-of-states (DOS), as well as their
frequency and spatial dependence change significantly as the distance between
the impurities or their orientation relative to the crystal lattice is varied.
Since the latter effect arises from the momentum dependence of the
superconducting gap, we argue that quantum interference is a novel tool to
identify the symmetry of unconventional superconductors.Comment: 4 pages, 4 figure
Effect of bilayer coupling on tunneling conductance of double-layer high T_c cuprates
Physical effects of bilayer coupling on the tunneling spectroscopy of high
T cuprates are investigated. The bilayer coupling separates the bonding
and antibonding bands and leads to a splitting of the coherence peaks in the
tunneling differential conductance. However, the coherence peak of the bonding
band is strongly suppressed and broadened by the particle-hole asymmetry in the
density of states and finite quasiparticle life-time, and is difficult to
resolve by experiments. This gives a qualitative account why the bilayer
splitting of the coherence peaks was not clearly observed in tunneling
measurements of double-layer high-T oxides.Comment: 4 pages, 3 figures, to be published in PR
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