Download Spécialité de M2 : Concepts Fondamentaux de la Physique

PROPOSITION DE SUJET DE THESE
ANNEE 2014
Nom du laboratoire : Laboratoire de Physique des Solides
Adresse : Bâtiment 510 Université Paris XI ORSAY
Nom du ou des responsables de la thèse : Hélène Bouchiat et Sophie Guéron
E-mail :[email protected], [email protected] Téléphone : 01 69 15 53 14
Page web : http://chercheurs.lps.u-psud.fr/Spm/spip.php?rubrique1
Financement envisagé : Ministere, ANR
Ecole doctorale : ED107
Experimental detection of orbital magnetism of Dirac Fermions
Résumé (en anglais) : Graphene’s honeycomb atomic arrangement leads to the now famous
linear dispersion relation of its Dirac spectrum, with a perfect electron/hole symmetry
around half filling. This leads to original properties that have by now been thoroughly
explored in conduction experiments. In contrast, graphene’s orbital magnetism has mainly
remained unexplored up to now, despite intriguing theoretical predictions that show that
this thermodynamic quantity contains information not revealed in conduction experiments.
A first computation from 1956 finds that graphene’s orbital moment is singular and
diamagnetic at half filling: F). This diamagnetism explains graphite’s well known
strong diamagnetism. Orbital magnetism is also a subject pursued theoretically in our
laboratory,’s theory group, in particular in the context of the Berry phase of Dirac Fermions.
Our goal is to detect this diamagnetism in graphene and determine its dependence with
doping. The experiment is challenging, since the amplitude of the orbital magnetism is small,
and paramagnetic impurities can dominate the signal in samples of insufficient quality.
The measurement will use Hall bars, that are compatible with an electrostatic control of
graphene’s doping level. Monolayer graphene as well as bilayers will be measured. We will
also investigate MoS2, a layered semiconductor whose orbital magnetism is predicted to be
maximal in the middle of the gap!
In addition to the orbital magnetism due to the band structure of these materials, we will
pursue the detection of quantum orbital magnetism, at low temperature. Such quantum effects
are related to persistent mesoscopic currents predicted for infinite two dimensional layers, but
never yet observed.
Mots clés 4 ou 5 (en anglais) : 2D quantum transport, Orbital magnetism,
Profil, compétences souhaitées (en anglais) : Quantum mechanics, statistical physics,
electronic properties of solids, experiments at low temperature .