4,021 research outputs found
Entanglement Spectrum and Entanglement Thermodynamics of Quantum Hall Bilayers at nu=1
We study the entanglement spectra of bilayer quantum Hall systems at total
filling factor nu=1. In the interlayer-coherent phase at layer separations
smaller than a critical value, the entanglement spectra show a striking
similarity to the energy spectra of the corresponding monolayer systems around
half filling. The transition to the incoherent phase can be followed in terms
of low-lying entanglement levels. Finally, we describe the connection between
those two types of spectra in terms of an effective temperature leading to
relations for the entanglement entropy which are in full analogy to canonical
thermodynamics.Comment: New findings in Eqs.(5)-(8) and pertaining discussion, and addendum
to the title, version as publishe
Composite Fermions in Modulated Structures: Transport and Surface Acoustic Waves
Motivated by a recent experiment of Willett et al. [Phys. Rev. Lett. 78, 4478
(1997)], we employ semiclassical composite-fermion theory to study the effect
of a periodic density modulation on a quantum Hall system near Landau level
filling factor nu=1/2. We show that even a weak density modulation leads to
dramatic changes in surface-acoustic-wave (SAW) propagation, and propose an
explanation for several key features of the experimental observations. We
predict that properly arranged dc transport measurements would show a structure
similar to that seen in SAW measurements.Comment: Version published in Phys. Rev. Lett. Figures changed to show SAW
velocity shift. LaTeX, 5 pages, two included postscript figure
Assessing the renal response in patients with potassium disorders: a shift in emphasis from the TTKG to the urine K+/creatinine ratio
This article briefly reviews the reasons for replacing the transtubular K+ gradient (TTKG) with the urine K+/creatinine ratio, as a tool for evaluating the response of the kidney in patients with potassium disorders. An appreciation of the magnitude and importance of the intrarenal recycling of urea led to the realization that a large amount of urea is reabsorbed daily in the terminal collecting duct and that this renders invalid the assumption, used by the TTKG, that there is minimal solute reabsorption downstream of the cortical collecting duct (CCD). The urine-to-plasma osmolality ratio can therefore not be used to calculate the volume of fluid exiting the CCD nor the concentration of K+ in the luminal fluid in this nephron segment. We now recommend the use of the K+/creatinine ratio in random urine samples to estimate the rate of K+ excretion. A ratio of less than 1.5 mmol K+/mmol creatinine would be expected if the kidney is responding appropriately to hypokalaemia from a non-renal cause, and a ratio greater than 20 mmol K+/mmol creatinine would be appropriate as the renal response to hyperkalaemia
Nonlocal Charge Transport Mediated by Spin Diffusion in the Spin-Hall Effect Regime
A nonlocal electric response in the spin-Hall regime, resulting from spin
diffusion mediating charge conduction, is predicted. The spin-mediated
transport stands out due to its long-range character, and can give dominant
contribution to nonlocal resistance. The characteristic range of nonlocality,
set by the spin diffusion length, can be large enough to allow detection of
this effect in materials such as GaAs despite its small magnitude. The
detection is facilitated by a characteristic nonmonotonic dependence of
transresistance on the external magnetic field, exhibiting sign changes and
decay.Comment: 4 pages, 2 figure
Magnetic degeneracy and hidden metallicity of the spin density wave state in ferropnictides
We analyze spin density wave (SDW) order in iron-based superconductors and
electronic structure in the SDW phase. We consider an itinerant model for
Fe-pnictides with two hole bands centered at and two electron bands
centered at and in the unfolded BZ. A SDW order in such a
model is generally a combination of two components with momenta and
, both yield order in the folded zone. Neutron
experiments, however, indicate that only one component is present. We show that
or order is selected if we assume that only one hole band
is involved in the SDW mixing with electron bands. A SDW order in such 3-band
model is highly degenerate for a perfect nesting and hole-electron interaction
only, but we show that ellipticity of electron pockets and interactions between
electron bands break the degeneracy and favor the desired or
order. We further show that stripe-ordered system remains a metal for
arbitrary coupling. We analyze electronic structure for parameters relevant to
the pnictides and argue that the resulting electronic structure is in good
agreement with ARPES experiments. We discuss the differences between our model
and model of localized spins.Comment: reference list updated, typos are correcte
- …