Atypical behavior of collective modes in two-dimensional Fermi liquids.

Using the Landau kinetic equation to study the non-equilibrium behavior of interacting Fermi systems is one of the crowning achievements of Landau's Fermi liquid theory. While thorough study of transport modes has been done for standard three-dimensional Fermi liquids, an equally in-depth analysis for two dimensional Fermi liquids is lacking. In applying the Landau kinetic equation (LKE) to a two-dimensional Fermi liquid, we obtain unconventional behavior of the zero sound mode c 0. As a function of the usual dimensionless parameter s = ω/q v F, we find two peculiar results: first, for |s| > 1 we see the propagation of an undamped mode for weakly interacting systems. This differs from the three dimensional case where an undamped mode only propagates for repulsive interactions and the mode experiences Landau damping for any arbitrary attractive interaction. Second, we find that regardless of interaction strength, a propagating mode is forbidden for |s| < 1. This is profoundly different from the three-dimensional case where a mode can propagate, albeit damped. In addition, we present a revised Pomeranchuk instability condition for a two-dimensional Fermi liquid as well as equations of motion for the fluid that follow directly from the LKE. In two dimensions, we find a constant minimum for all Landau parameters for ℓ ⩾ 1 which differs from the three dimensional case. Finally we discuss the effect of a Coulomb interaction on the system resulting in the plasmon frequency ω p exhibiting a crossover to the zero sound mode.

Consequences of the inherent density dependence in one dimensional Dirac materials.

Dirac materials are systems in which the dispersion is linear in the vicinity of the Dirac points. As a consequence of this linear dispersion, the Fermi velocity is independent of density and these systems exhibit unusual behavior and possess unique physical properties that are of considerable interest. In this work we study the ground state behavior of 1D Dirac materials in two ways. First, using the Virial theorem, we find agreement with a previous result in regards to the total average ground state energy. Namely, that the total average ground state energy, regardless of dimensionality, is found to be [Formula: see text] where r s is a dimensionless constant that's a measure of density and [Formula: see text] is a constant independent of r s . As a consequence, thermodynamic results as well as the characteristic exponents of 1D Fermi systems are density independent. Second, using conventional techniques, i.e. Tomanaga-Luttinger theory, we find several unique properties that are a direct consequence of the dispersion. Specifically, the collective modes of the system exhibit electron density independence predicted from the Virial theorem. Finally, possible experimental realization of our predictions of density independent exponents are briefly discussed.

Coexistence of superconductivity and ferromagnetism in ferromagnetic metals.

We address the question of coexistence of superconductivity and ferromagnetism. Using a field theoretical approach we study a one-fermion effective model of a ferromagnetic superconductor in which the quasiparticles responsible for the ferromagnetism form the Cooper pairs as well. For the first time we solve self-consistently the mean-field equations for the superconducting gap and the spontaneous magnetization. We discuss the physical features which are different in this model and the standard BCS model and consider their experimental consequences.

Atrial natriuretic peptide blocks the renal vasoconstrictor response to hypertonic saline in the dog.

The role of atrial natriuretic peptide to modulate the renal tubuloglomerular feedback response was examined in the dehydrated anesthetized dog using an infusion of hypertonic sodium chloride to increase renal plasma sodium concentration by 30 mEq/l as the stimulus to activate the tubuloglomerular feedback. Two sequential infusions of hypertonic sodium chloride into the renal artery for 10 min were separated by 90 min, and various interventions were introduced before the second hypertonic saline infusion. In the first group of dogs, the first infusion of hypertonic saline resulted in a significant decrease in renal blood flow from 234 +/- 36 to 199 +/- 31 ml/min, but when atriopeptin III (APIII) was infused into the renal artery at 3 x 10(-10) mol/min, the repeat infusion of hypertonic saline resulted in a significant increase in blood flow from 221 +/- 28 to 269 +/- 35 ml/min that was maintained throughout the 10 min of hypertonic saline. In the second group of dogs only the vehicle for APIII was infused during the second hypertonic saline infusion. In these dogs, renal blood flow decreased significantly the first time from 201 +/- 17 to 170 +/- 16 ml/min, and the second time from 232 +/- 22 to 177 +/- 20 ml/min. In a third group of dogs, the vasodilator sodium nitroprusside, a stimulator of smooth muscle soluble guanylate cyclase, was infused into the renal artery during the second hypertonic saline infusion.(ABSTRACT TRUNCATED AT 250 WORDS)