Condensed Matter Seminar: Dr. Florian Le Mardelé, Laboratoire National des Champs Magnétiques Intenses Grenoble


Location: 184 Nieuwland Science Hall (View on map )

Evidence of 3D Dirac conical bands in TlBiSeS by infrared and magneto-optical spectroscopy

Dr. Florian Le Mardelé
Laboratoire National des Champs Magnétiques Intenses

The elegant Dirac equation proposed by Paul Dirac in 1928 to describe relativistic particles in particles physics has, in the last decades, reborn in condensed matter physics, more precisely in the field of topological semimetal (TSM). In the latter, the electronic band structure shows linear dispersion. Those linear bands dispersion generate relativistic quasi- particles of spin 1/2, name Dirac fermions. The most eponym member of those system must be graphene. Besides, the richness of the Bloch band structure allows the realization of quasi-particle that was not experimentally observe in particle physic such as the massless Weyls fermions. It also induces some new physical phenomena with no counterpart in particle
physic such as Nodal line semimetal, Fermi arc states or even Berry magnetic monopole.

Questioning the electronic properties of the TSM, to access their band structure, is a challenging part of condensed matter physics. The energy dispersion of these relativistic particles does not usually disperse in a broad range of energy but is rather constrained in a low energy range around the Dirac (Weyl) node. So, in order to experimentally interact detected Dirac and Weyl fermions, the Fermi energy must be in the vicinity of the crossing points.

In this talk, I will present the compound TlBiSeS which is a rare realization of a 3D semimetal with a conically dispersing band that is isolated from other contributions in a broad energy range. The system will be characterized optically via infrared and magneto-optical spectroscopy. The compound shows different optical respond with respect the doping concentration, but when it is chemically tuned to reduce anti-site defect, we find a linear frequency dependence of the optical conductivity below 0.5 eV. Landau level spectroscopy allows us to describe the system with a massive Dirac model.

Hosted by Prof. Assaf