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

Spontaneous Currents in Spinless Fermion Lattice Models at the Strong-Coupling Limit

What kind of lattice Hamiltonian manifestly has an ordered state with spontaneous orbital currents? We consider interacting spinless fermions on an array of square plaquettes, connected by weak hopping; the array geometry may be a 2 x 2L ladder, a 2 x 2 x 2L "tube", or a 2L x 2L square grid. At half filling, we derive an effective Hamiltonian in terms of pseudospins, of which one component represents orbital currents, and find the conditions sufficient for orbital current long-range order. We consider spinfull variants of the aforesaid spinless models and make contact with other spinfull models in the literature purported to possess spontaneous currents.Comment: added two new references following recent communicatio

Anomalous Attenuation of Transverse Sound in 3He

We present the first measurements of the attenuation of transverse sound in superfluid 3He-B. We use fixed path length interferometry combined with the magneto-acoustic Faraday effect to vary the effective path length by a factor of two, resulting in absolute values of the attenuation. We find that attenuation is significantly larger than expected from the theoretical dispersion relation, in contrast to the phase velocity of transverse sound. We suggest that the anomalous attenuation can be explained by surface Andreev bound states.Comment: 4 pages, 5 figures, accepted to Phys. Rev. Let

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

Nonlinear field-dependence and f-wave interactions in superfluid 3He

We present results of transverse acoustics studies in superfluid ^{3}He-B at fields up to 0.11 T. Using acoustic cavity interferometry, we observe the Acoustic Faraday Effect for a transverse sound wave propagating along the magnetic field, and we measure Faraday rotations of the polarization as large as 1710^{\circ}. We use these results to determine the Zeeman splitting of the Imaginary Squashing mode, an order parameter collective mode with total angular momentum J=2. We show that the pairing interaction in the f-wave channel is attractive at a pressure of P=6 bar. We also report nonlinear field dependence of the Faraday rotation at frequencies substantially above the mode frequency not accounted for in the theory of the transverse acoustic dispersion relation formulated for frequencies near the mode. Consequently, we have identified the region of validity of the theory allowing us to make corrections to the analysis of Faraday rotation experiments performed in earlier work.Comment: 7 pages, 5 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 $(0,0)$ and two electron bands centered at $(0,\pi)$ and $(\pi,0)$ in the unfolded BZ. A SDW order in such a model is generally a combination of two components with momenta $(0,\pi)$ and $(\pi,0)$, both yield $(\pi,\pi)$ order in the folded zone. Neutron experiments, however, indicate that only one component is present. We show that $(0,\pi)$ or $(\pi,0)$ 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 $(0,\pi)$ or $(\pi,0)$ 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 $J_1-J_2$ model of localized spins.Comment: reference list updated, typos are correcte