Missions

The objective of this research is to examine how the reduced dimensionality of transition metal dichalcogenides (TMDs) such as NbSe₂ and NbS₂, along with the absence of inversion symmetry, influences the Higgs and Bardasis-Schrieffer collective modes and their interaction with collective modes associated with charge density wave order, as observed in static Raman measurements.

This theoretical work will combine analytical and numerical approaches. We will employ multi-band tight-binding models incorporating the Rashba term, which is intrinsic to TMDs. Interband pairing interactions will be introduced in various allowed channels, and their impact on the properties of collective modes will be analyzed. Finally, we will compute the corresponding Raman response functions and optical conductivity in the presence of a superconducting current, following a standard field-theoretical treatment.

Activities

- Study of quasi-2D superconductivity in TMDs and the effects of spin-orbit coupling and singlet-triplet spin mixing observed in thin layers of NbSe2 and NbS2 on the collective modes of the superconductor.
- Calculation of Raman response functions and THz optical conductivity of thin layers of TMDs in the presence of a current flow
- Investigation of strong and ultra-strong coupling of collective modes of a quasi-2D superconductor to THz metamaterials, assessing the possibility of a "Higgs polariton" condensate and other exotic phases.

Skills

Qualification: PhD in theoretical physics
Knowledge: Solid background in condensed-matter physics
Operational skills/expertise: Analytical calculations and numerical methods

Work Context

The recruited postdoc will join the Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), a joint research unit of CNRS and the University of Strasbourg, specifically within the Magnetism of Nanostructured Objects department.

The control of a material's properties using light is an emerging field with potentially vast applications. Within this domain, enhancing or modifying superconductivity holds a particular interest, especially since the discovery of superconducting states in several materials at temperatures significantly higher than their equilibrium critical temperature. Superconductivity control via light can be achieved through two distinct approaches. The first involves exciting relevant collective modes using light pulses tuned to their energy. A second promising approach consists of directly coupling the collective modes of the superconductor with quantum vacuum fluctuations by leveraging strong light-matter coupling in cavities. The objective here is to exploit these hybrid light-matter states to design new equilibrium phases of matter, i.e., without external excitation.

The position is located in a sector under the protection of scientific and technical potential (PPST), and therefore requires, in accordance with the regulations, that your arrival is authorized by the competent authority of the MESR.