arXiv subjects

K. S. Bedell

Publications and source records attributed to K. S. Bedell.

8 recordsLinked to original sources

arXiv2008

Spin Collective Modes of Two-Species Fermi Liquids: Helium-3 and Atomic Gases near the Feshbach Resonance

We present theoretical findings on the spin collective modes of a two-species Fermi liquid, prepared alternatively in a polarized equilibrium or a polarized non-equilibrium state. We explore the effects on these modes of a diverging s-wave scattering length, as occurs near a Feshbach resonance in a Fermionic atomic gas. We compare these atomic gas modes with those of the conventional Helium-3 system, and we find that they differ from the conventional systems, and that the gap and spin stiffness are tunable via the Feshbach resonance.

cond-mat.other↗

arXiv2007

Acoustic attenuation probe for fermion superfluidity in ultracold atom gases

Dilute gas Bose-Einstein condensates (BEC's), currently used to cool fermionic atoms in atom traps, can also probe the superfluidity of these fermions. The damping rate of BEC-acoustic excitations (phonon modes), measured in the middle of the trap as a function of the phonon momentum, yields an unambiguous signature of BCS-like superfluidity, provides a measurement of the superfluid gap parameter and gives an estimate of the size of the Cooper-pairs in the BEC-BCS crossover regime. We also predict kinks in the momentum dependence of the damping rate which can reveal detailed information about the fermion quasi-particle dispersion relation.

cond-mat.other↗

arXiv1999

Coexistence of superconductivity and ferromagnetism in ferromagnetic metals

In this paper we address the question of coexistence of superconductivity and ferromagnetism in the high temperature superconductor RuSr$_2$GdCu$_2$O$_{8-δ}$. 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. We discuss the physical features which are different in this model and the standard BCS model and consider their experimental consequences.

cond-mat.supr-con↗

arXiv1998

Effect of Ferromagnetic Spin Correlations on Superconductivity in Ferromagnetic Metals

We study the renormalization of the quasiparticle properties in weak ferromagnetic metals, due to spin fluctuations, away from the quantum critical point for small magnetic moment. We explain the origin of the s-wave superconducting instability in the ferromagnetic phase and find that the vertex corrections are small and Migdal's theorem is satisfied away from the quantum critical point.

cond-mat.str-el↗

arXiv1998

Robustness of a Local Fermi Liquid against Ferromagnetism and Phase Separation II

This is a response to a recent paper by van Dongen, Uhrig, and E. Müller-Hartmann. We clarify the issues, which the above authors apparently did not fully appreciate, by referring to the microscopic foundations of Landau's Fermi Liquid Theory, its general application to the theory of metals and the theory of local Fermi Liquids.

cond-mat.str-el↗

arXiv1997

S-wave Superconductivity in Weak Ferromagnetic Metals

We investigate the behavior of weak ferromagnetic metals close to the ferromagnetic critical point. We show that in the limit of small magnetic moment the low temperature metallic phase is rigorously described by a local ferromagnetic Fermi liquid that has a momentum-independent self-energy. Whereas, non-Fermi liquid features develop at higher temperatures. Furthermore, we find that an instability towards s-wave superconductivity is possible when the exchange splitting is comparable to the superconducting gap.

cond-mat.str-el↗

arXiv1994

Direct Calculation of Spin-Stiffness for Spin-1/2 Heisenberg Models

The spin-stiffness of frustrated spin-1/2 Heisenberg models in one and two dimensions is computed for the first time by exact diagonalizations on small clusters that implement spin-dependent twisted boundary conditions. Finite-size extrapolation to the thermodynamic limit yields a value of $0.14\pm 0.01$ for the spin-stiffness of the unfrustrated planar antiferromagnet. We also present a general discussion of the linear-response theory for spin-twists, which ultimately leads to the moment sum-rule.

cond-mat↗

arXiv1993

Non-Analytic Contributions to the Self-Energy and the Thermodynamics of Two-Dimensional Fermi Liquids

We calculate the entropy of a two-dimensional Fermi Liquid(FL) using a model with a contact interaction between fermions. We find that there are $T^2$ contributions to the entropy from interactions separate from those due to the collective modes. These $T^2$ contributions arise from non-analytic corrections to the real part of the self-energy which may be calculated from the leading log dependence of the imaginary part of the self-energy through the Kramers-Kronig relation. We find no evidence of a breakdown in Fermi Liquid theory in 2D and conclude that FL in 2D are similar to 3D FL's.

cond-mat↗