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DTSTART;TZID=Europe/Paris:20240312T140000
DTEND;TZID=Europe/Paris:20240312T160000
DTSTAMP:20260419T095114
CREATED:20240311T113441Z
LAST-MODIFIED:20240311T115801Z
UID:10118-1710252000-1710259200@fermi.univ-tlse3.fr
SUMMARY:Ground-state phases of the one-dimensional SU(N)-symmetric Kondo lattice model. - (Keisuke Totsuka / LPT / Seminar). - 12/03/2024\, 11 H.
DESCRIPTION:Keisuke Totsuka  (YITP\, Kyoto) \nSeminar LPT\, 12/03/2024\, 11H\, 3R4\, Conference hall \nSummary\nThe Kondo-lattice model and its variants (e.g.\, the Kondo-Heisenberg model)\, in which itinerant fermions interact with immobile magnetic moments via spin-exchange coupling (Kondo coupling)\, have been playing an important role in understanding the physics of heavy-fermion systems. In this talk\, I begin by quickly explaining how the SU(N) Kondo-lattice model\, in which the spin SU(2) symmetry is generalized to SU(N)\, is realized in actual physical systems (e.g.\, cold fermions and twisted bilayer graphene)\, and then I focus on the ground-state properties of its one-dimensional version. Specifically\, when the Kondo coupling is sufficiently large\, we find ferromagnetic metallic phases that can be established rigorously as well as several insulating ones. I also show that the SU(N) Kondo-lattice model provides a natural condensed-matter realization of supersymmetric [i.e.\, SU(N|1)] models. Various (insulating) phases at small Kondo coupling are then explored using the machinery of bosonization and various conformal field theory (CFT) techniques\, and the results are compared with the predictions of the Lieb-Schultz-Mattis-type (or anomaly-matching) argument. \n\n \n 
URL:https://fermi.univ-tlse3.fr/event/tba-keisuke-totsuka-lpt-seminar-12-03-2024-11-h/
LOCATION:salle de séminaire 3ème étage\, Bâtiment 3r1 Université Toulouse III\, Toulouse\, 31400\, France
CATEGORIES:Events,LPT,Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20240326T140000
DTEND;TZID=Europe/Paris:20240326T153000
DTSTAMP:20260419T095114
CREATED:20240325T073856Z
LAST-MODIFIED:20240325T084658Z
UID:10120-1711461600-1711467000@fermi.univ-tlse3.fr
SUMMARY:Large-deviation analysis of rare resonances for the Many-Body localization transition. - (Marco Tarzia / LPT / Seminar). - 26/03/2024\, 14 H.
DESCRIPTION:Marco Tarzia (LPTMC) \nSeminar LPT\, 26/03/2024\, 14H\, 3R1\, seminar room\, 3rd floor \nAbstract :\nA central theoretical issue at the core of the current research on many-body localization (MBL) consists in characterizing the statistics of rare long-range resonances in many-body eigenstates. This is of paramount importance to understand : (i) the critical properties of the MBL transition and the mechanism for its destabilization through quantum avalanches ; (ii) the unusual transport and anomalously slow out-of-equilibrium relaxation when the transition is approached from the metallic side. In order to study and characterize such long-range rare resonances\, we develop a large-deviations approach based on an analogy with the physics of directed polymers in random media\, and in particular with their freezing glass transition on infinite-dimensional graphs. The basic idea is to enlarge the parameter space by adding an auxiliary parameter (which plays the role of the inverse temperature in the directed polymer formulation) which allows us to fine-tune the effect of anomalously large outliers in the far-tails of the probability distributions of the transmission amplitudes between far-away many-body configurations in the Hilbert space. We apply this approach to the study of a class of disordered quantum spin chains in a transverse field. This analysis shows the existence of a broad disorder range in which rare\, long-distance resonances\, that in finite-size systems may only form for a few specific realizations of the disorder and a few specific choice of the random initial state\, are expected to destabilize the MBL phase in the thermodynamic limit\, while the genuine MBL transition is shifted to much larger values of the disorder than originally thought.
URL:https://fermi.univ-tlse3.fr/event/large-deviation-analysis-of-rare-resonances-for-the-many-body-localization-transition-marco-tarzia-lpt-seminar-2-03-2024-14-h/
LOCATION:salle de séminaire 3ème étage\, Bâtiment 3r1 Université Toulouse III\, Toulouse\, 31400\, France
CATEGORIES:Events,LPT,Seminars
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20240329T110000
DTEND;TZID=Europe/Paris:20240329T123000
DTSTAMP:20260419T095114
CREATED:20240323T084353Z
LAST-MODIFIED:20240325T084606Z
UID:10177-1711710000-1711715400@fermi.univ-tlse3.fr
SUMMARY:Propriétés thermiques des aimants quantiques frustrés. - (Frédéric Mila / LPT / Seminar). - 29/03/2024\, 11 H.
DESCRIPTION:Frédéric Mila (EPFL) \nSeminar LPT\, 29/03/2024\, 11H\, 3R1\, seminar room\, 3rd floor \nAbstract :\nThe thermal properties of frustrated quantum magnets are a real challenge because\, when formulated in the natural configuration basis\, Quantum Monte Carlo simulations suffer from a very serious minus sign problem that excludes simulations below temperatures of the order of the coupling constants. In this talk\, I will review recent numerical progress made on two fronts : (i) Quantum Monte Carlo simulations in the dimer basis [1]. In this basis\, there is no minus sign problem for fully frustrated models\, and simulations can be performed down to arbitrarily low temperature. With these simulations\, we have identified the presence of a thermal critical point terminating a line of first-order transitions in the fully frustrated bilayer model [1]. (ii) Tensor network simulations [2\,3]. Using ancilla spins and a partial trace\, the thermal ensemble can be accurately obtained by imaginary time evolution of a purified state\, leading to reliable results down to temperatures only a few percents of the coupling constants regardless of the level of frustration. Using this approach\, we have been able to show that the peak of the specific heat around 2 GPa and 4 K in SrCu2(BO3)2 is a thermal critical point akin to that of the fully frustrated bilayer [2]\, and to numerically verify the long-standing prediction that the spin-1/2 J1-J2 model on the square lattice has a thermal Ising transition for large enough J2/J1 [3]. \n[1] J. Stapmanns\, P. Corboz\, F. Mila\, A. Honecker\, B. Normand\, and S. Wessel\, Phys. Rev. Lett. 121\, 127201 (2018). \n[2] J. Larrea Jimenez\, S. P. G. Crone\, E. Fogh\, M. E. Zayed\, R. Lortz\, E. Pomjakushina\, K. Conder\, A. M. Läuchli\, L. Weber\, S. Wessel\, A. Honecker\, B. Normand\, Ch. Rüegg\, P. Corboz\, H. M. Ronnow and F. Mila\, Nature 592\, 370 (2021). \n[3] O. Gauthé and F. Mila\, Phys. Rev. Lett. 128\, 227202 (2022).
URL:https://fermi.univ-tlse3.fr/event/proprietes-thermiques-des-aimants-quantiques-frustres-frederic-mila-lpt-seminar-29-03-2024-11-h/
LOCATION:salle de séminaire 3ème étage\, Bâtiment 3r1 Université Toulouse III\, Toulouse\, 31400\, France
CATEGORIES:Events,LPT,Seminars
END:VEVENT
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