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11:00» Séminaire du LPTMS : Fabian HeidrichMeinsner 
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11:00» Séminaire du LPTMS : Olga Goulko 
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11:00» Séminaire du LPTMS : Todor Mishonov 
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Outofequilibrium dynamics of interacting fermions in one dimension
Fabian HeidrichMeisner LMU Munich
In this talk, I will discuss the application of the timedependent density matrix renormalization group (TDDMRG) technique to the problem of
calculating steadystate currents in interacting nanostructures and more generally, the nonequilibrium dynamics of interacting fermions in one dimension.
A paradigmatic model that captures essential features of quantum dots with spin and charge fluctuations is the singleimpurity
Anderson model. Although experiments on semiconductor structures that are believed to be well described by the SIAM have been available
for a long time, no full solution for the currentvoltage characteristics is available yet. Here, I present TDDMRG results for this problem,
providing accurate data in the zerotemperature limit [1]. Besides steadystate currents, we are further interested in properties of the steady state such as spin and charge fluctuations. Moreover, particles flowing through a nanostructure give rise to a rapid increase of entanglement between the leads, which I shall also discuss. Similar results will be presented for the case of nonequilibrium transport through an extended interaction region, namely a Mott insulator [2]. Here, I will use TDDMRG to study the dielectric breakdown of
this state.
Finally, I shall discuss a simple, yet still experimentally example, namely the expansion of interacting fermions, released from a confining potential, into a onedimensional lattice [35]. This setup is currently being used in experiments with cold atoms to study ballistic and diffusive dynamics far from equilibrium. Here,
I will illustrate several intriguing and at times counterintuitive phenomena that one can encounter, such as metastable states [4].
[1] HeidrichMeisner, Feiguin, Dagotto, Phys. Rev B 79, 235336 (2009)
[2] HeidrichMeisner, Gonzalez, AlHassanieh, Feiguin, Rozenberg, Dagotto, in preparation.
[3] HeidrichMeisner, Rigol, Muramatsu, Feiguin, Dagotto: Phys. Rev. A 78, 013620 (2008)
[4] HeidrichMeisner, Manmana, Rigol, Muramatsu, Feiguin, Dagotto, Phys. Rev. A 80, 041603(R) (2009)
[5] Langer, HeidrichMeisner, Gemmer, McCulloch, Schollwöck, Phys. Rev. B 79, 214409 (2009)6 juillet, 11h
LPTMSbatiment 100, salle 201, Orsay
The imbalanced Fermi gas at Unitarity
Olga Goulko (DAMTP, Cambridge University, UK)
Lattice field theory is a useful tool for studying strongly interacting theories in condensed matter physics. A prominent example
is the unitary Fermi gas: a twocomponent system of fermions interacting with divergent scattering length. With Monte Carlo methods this system can be studied from first principles. In presence of an imbalance (unequal number of particles in the two components) a sign problem arises, which makes conventional algorithms inapplicable. We
will show how to apply reweighting techniques to generalise the recently developed worm algorithm to the imbalance case, and present results for thermodynamic observables, in particular the critical temperature, for equal, as well as unequal number of fermions in the
two spin components.Jeudi 8 juillet à 11h
LPTMSbatiment 100, salle 201, Orsay
Superconductivity of overdoped cuprates: the modern face of the ancestral twoelectron exchange
Todor Mishonov, Sofia
The singlesite twoelectron exchange amplitude J_sd between the Cu 4s
and Cu 3d_{x^2y^2} states is found to be the pairing mechanism of
highT_c overdoped cuprates. The noninteracting part of the Hamiltonian
spans the copper Cu 4s, Cu 3d_{x^2y^2} and oxygen O 2p_x and O 2p_y
states. Within the standard BCS treatment an explicit expression for the
momentum dependence of the gap Delta_p is derived and shown to fit the
angleresolved photoemission spectroscopy (ARPES) data. The basic
thermodynamic and electrodynamic properties of the model (specific heat
C(T), London penetration depth lambda(T)) are analytically derived. These
are directly applicable to cuprates without complicating structural
accessories (chains, double CuO_2 planes, etc.). We advocate that the
pairing mechanism of overdoped and underdoped cuprates is the same, as T_c
displays smooth doping dependence. Thus, a longstanding puzzle in physics
is possibly solved.Mardi 13 juillet à 11h
LPTMSbatiment 100, salle 201, Orsay