This week's seminars

[Cond.Matt. & Stat.Mech.Section]

  CONDENSED MATTER AND
STATISTICAL PHYSICS SECTION

INFORMAL SEMINAR


Wednesday, 26 May   -    4:15 p.m.

  Luigi Stasi Seminar Room -  Leonardo Bldg. - first floor

D.N. ARISTOV      ( Petersburg Nuclear Physics Institute )

  "Y-junction connecting Luttinger liquids:    Fixed point structure  
and conductances"

Abstract


We study the transport properties of three quantum wires (with  
possibly different interaction strength), connected through a Y- 
junction, within the scattering state formalism.  We first formulate  
the problem in current algebra language and focus on the case of a  
symmetric setup, for which the scattering matrix and the matrix of  
conductances is parametrized by two variables.  For these we derive  
coupled RG equations, performing a ladder summation up to infinite  
order in the interaction.  The fixed point structure and the implicit  
solution of these equations is presented.  We show that higher order  
terms beyond the ladder approximation do not change the scaling  
behavior near the fixed points.  For sufficiently strong attractive  
interaction a new fixed point with unusual properties is found.

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CONDENSED MATTER AND STATISTICAL PHYSICS SECTION




SEMINAR on   Disorder and strong electron correlations





Thursday, 27 May   -  11:30 a.m.



Luigi Stasi Seminar Room,  Leonardo Building - first floor





C. SALOMON     ( Ecole Normale Superieure, Paris )





"The equation of state of strongly interacting Fermi gases"



Abstract



In this talk, we will present recent experimental work performed at  
ENS on the thermodynamics of strongly interacting 6Li Fermi gases.  We  
have developed a general method to probe with high precision the  
thermodynamics of locally homogeneous ultracold gases [1].  This  
allows stringent tests of recent many-body theories.  First, we focus  
on the finite-temperature Equation of State (EoS) of the unpolarized  
unitary gas.

Precise thermometry is provided by adding to the trapped 6Li unitary  
gas a small amount of bosonic 7Li that is weakly perturbing the  
system.  We show that the low-temperature properties of the strongly  
interacting normal phase are well described by Fermi liquid theory and  
we localize the superfluid phase transition.  Second, we address the  
zero-temperature EoS of the spin-polarized system.  Surprisingly,  
despite strong interactions, the normal polarized phase behaves as a  
mixture of two ideal gases: a Fermi gas of bare majority atoms and a  
non-interacting gas of dressed quasi-particles, the Fermi polarons.  
Finally, we will report on the extension of our study to the BEC-BCS  
crossover in the low temperature limit [2].  A detailed comparison  
with theories including Monte-Carlo calculations and the Lee-Huang- 
Yang corrections for low-density bosonic and fermionic superfluids is  
presented.  Our equation of state can be directly used to describe low  
density neutron matter such as the outer shell of neutron stars.



[1] S. Nascimbène, N. Navon, K. Jiang, F. Chevy, and C. Salomon,  
Nature 463, 1057 (2010)

[2] N. Navon, S. Nascimbène, F. Chevy, and C. Salomon,  Science  
Express, published on line April 15, 2010