Maître de conférences à Sorbonne Université
Tour 12/13 - 5ème étage, bureau 516 (campus Jussieu)
Tél: 01 44 27 84 26
With Bernard Bernu, we propose a Ph. D. on series expansions in spin models.
The abstract and PDF are available on the EDPIF website : here.
Mots clés : systèmes magnétiques frustrés 2D, liquides de spins, solides de liens de valence,
ordre de Néel, vortex, chiralité, algorithme Wang-Landau, systèmes fortement corrélés hors équilibre...
Key words : frustrated 2D spin systems, spin liquids, valence bond solids,
Néel order, vortices, chirality, Wang-Landau algorithm, out of equilibrium strongly correlated systems...
- Depuis 2013 : Maître de Conférence au LPTMC
- 2012-2013 : Post-doctorat dans le groupe d'Olivier Parcollet, à l'IPhT, CEA, Saclay
- 2010-2012 : Post-doctorat dans le groupe de Frédéric Mila, à l'ITP, EPFL, Lausanne, avec enseignement.
- 2007-2010 : Thèse dirigée par Claire Lhuillier et Grégoire Misguish, au LPTMC, avec monitorat.
- 2006-2007 : Master 2 Systèmes Complexes, UPMC
- 2004-2008 : ENS Cachan
Link to arXiv with almost all my publications: link arXiv Messio, except these two:
The influence of surface tension gradients on drop coalescence
F. Blanchette, L. Messio and J. W. M. Bush,
Physics of Fluids, 21, 072107 (2009).
Experimental observation using particle image velocimetry of inertial waves in a rotating fluid [Site du FAST]
L. Messio, C. Morize, M. Rabaud and F. Moisy,
Exp. Fluids 2007, 44, 519-528 (2008).
Mon manuscrit de thèse, ainsi que la présentation se trouvent sur le site des [Thèses en ligne]
(Titre : Etats fondamentaux et excitations de systèmes magnétiques frustrés, du classique au quantique)
RECHERCHEI work on spin models encountered in a large number of experimental compounds like Herbertsmithite, Kapellasite... These two cited materials are well described by interacting spins S=1/2 on the nodes of a kagome lattice (they are Mott insulators).Herbertsmithite KapellasiteDepending on the interactions (first neighbors, second neigbours, ferro/antiferromagnetic, multi-spin exchange, Dzyaloshinskii-Moriya interactions,... ), the phase of the ground state can have very unexpected properties (spin liquids, Néél orders with large unit cells, valence bond solids...).
I am interested in the description and characterization of all these phases and in the different methods used to track them. Among them are Schwinger boson mean-field theory, exact diagonalization, quantum Monte Carlo simulations, high temperature series expansions...
Spin liquids are exotic phases quite difficult to apprehend as few simple and eloquent examples exist. They are unordered... but not disordered phases with topological properties, fractional excitations. Phase transitions between different spin liquids can occur.
Two mean-field theories on discrete lattices easily lead to the obtention of spin liquids: the fermionic and bosonic mean-field theories.
Both of them are derived to approximate unsolvable spin model (here, an example of first, second and third neighbor interactions on the kagome lattice):
The projective symmetry group classification distinguish the different spin liquids through quantum symmetry numbers. We have adapted this theory to include time-reversal symmetry breaking phases (Phys. Rev. B, 87, 125127 (2013), Phys. Rev. B 93, 094437 (2016))
We have applied these theories to the kagome lattice with first neighbor interactions ( Phys. Rev. B 92, 060407 (2015)) and with Dzyaloshinskii-Moriya interaction (Phys. Rev. Lett., 108, 207204 (2012), Phys. Rev. L 118, 267201 (2017) to describe Herbertsmithite. In the case of Kapellasite, further neighbor interactions are needed (Phys. Rev. Lett., 109, 037208 (2012)).
Néel ordered phases
Frustration (as encountered on the antiferromagnetic triangle), induces unusual Néel orders. From symmetry considerations, a list of 'symmetric' Néel orders can be established, leading to new proposals for the ground states of kagome compounds. For example, the cuboc2 order is supposed to have similarities with the spin liquid encountered in Kapellasite, whereas the cuboc1 order is one of the many degenerate ground state of the kagome antiferromagnet.
The classical limit of these frustrated spin models, although their apparent simplicity, is already a very rich problem. The possibility to obtain chiral orders and vortices in long range ordered classical phases has been studied in Phys. Rev. B, 83, 184401 (2011).
Electronic out of equilibrium systems
I am also interested in out of equilibrium strongly correlated systems and participate to the [TRIQS] project.
A new algorithm describing the real time evolution of interacting quantum dots, using the Keldysh technic, has been elaborated in Computer Physics Communications 196, 398 (2015)
High temperature series expansions
The partition function Z of a spin system can be expanded in powers of beta, the inverse temperature (high temperature series expansions). ln(Z)/N is well defined in the thermodynamic limit (N is the number of sites), and can directly be expanded in this limit.
In Phys. Rev. B 101, 140403, a method previously defined as the entropy method is generalized and applied to the antiferromagnetic kagome lattice, with several perturbations (impurities, Ising anisotropy, DM interactions, further neighbor interactions...).
Phase transitions induced by the order by disorder mechanism
In some situations, the ground state is degenerate, but entropic effects lift this degeneracy. Thus, a symmetry can be broken at finite temperature, even if the ground state does not break it. It was studied in the case of the classical and quantum kagome lattice with first and third neighbor interactions (arXiv 2007.15985), using spin waves, Monte Carlo simulations and high temperature series expansions.