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Title: Finite range and upper branch effects on itinerant ferromagnetism in repulsive Fermi gases: Bethe–Goldstone ladder resummation approach

We investigate the ferromagnetic transition in repulsive Fermi gases at zero temperature with upper branch and effective range effects. Based on a general effective Lagrangian that reproduces precisely the two-body s-wave scattering phase shift, we obtain a nonperturbative expression of the energy density as a function of the polarization by using the Bethe–Goldstone ladder resummation. For hard sphere potential, the predicted critical gas parameter k{sub F}a=0.816 and the spin susceptibility agree well with the results from fixed-node diffusion Monte Carlo calculations. In general, positive and negative effective ranges have opposite effects on the critical gas parameter k{sub F}a: While a positive effective range reduces the critical gas parameter, a negative effective range increases it. For attractive potential or Feshbach resonance model, the many-body upper branch exhibits an energy maximum at k{sub F}a=α with α=1.34 from the Bethe–Goldstone ladder resummation, which is qualitatively consistent with experimental results. The many-body T-matrix has a positive-energy pole for k{sub F}a>α and it becomes impossible to distinguish the bound state and the scattering state. These positive-energy bound states become occupied and therefore the upper branch reaches an energy maximum at k{sub F}a=α. In the zero range limit, there exists a narrow window (0.86
Authors:
Publication Date:
OSTI Identifier:
22403480
Resource Type:
Journal Article
Resource Relation:
Journal Name: Annals of Physics (New York); Journal Volume: 351; Other Information: Copyright (c) 2014 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; BETHE-GOLDSTONE EQUATION; BOUND STATE; DIFFUSION; ENERGY DENSITY; FERMI GAS; FERROMAGNETISM; LAGRANGIAN FUNCTION; MONTE CARLO METHOD; PHASE SHIFT; POLARIZATION; RESONANCE; S MATRIX; S WAVES; SCATTERING; SPHERES; SPIN; TWO-BODY PROBLEM