Master and PhD project topics
Master level research projects
Cavity Higgs polaritons
Thanks to strong light-matter interactions in cavity-coupled systems, new important vacuum phenomena are emerging in condensed matter physics. In analogy with exciton- and phonon-polaritons that are now routinely observed in semiconductors an exciting perspective is to tune or even enhance the properties of a superconductor (SC) at equilibrium by dressing it with vacuum photons. Strong light-matter interactions offer unprecedented control opportunities of SC states since they can be shaped by modifying the spatial geometry and spectrum of the cavity electromagnetic modes. Beyond static properties such as enhancing the SC transition temperature, of particular interest is the possibility to directly couple the SC Higgs mode, a superconducting analogue of the Higgs boson well-known from high-energy physics, to a THz cavity mode. In this setting a new hybrid light-matter excitation coined the Higgs polariton is formed. To date none of the effects described above has been observed.
2D SC transition metal dichalcogenides (TMDs) like NbSe2, and NbS2 are extremely attractive platforms to demonstrate these effects. Their 2D nature make them particularly suitable for integrating into deep sub-wavelength THz cavities based on split-ring resonators which have been used successfully to produce strong light-matter polariton state in semiconductor heterostructures. During this internship, the fabrication of TMD-based van der Waals heterostructure will be carried out and integrated into THz split resonant cavities. An originality of the project will be to go beyond static properties like Tc and explore the effect of strong light matter coupling on the SC excitation spectrum and search for spectroscopic fingerprints of the Higgs polariton via Raman and THz spectroscopic techniques. The work will be performed in close collaboration with THz cavity experts at the LSI lab of Ecole Polytechnique.
- Alloca et al. Phys. Rev. B 99, 020504 (2021)
- Garcia Vidal et al. Science 373, eabd0336 (2021)
- Grasset et al. npj Quantum Materials 7, 4 (2022)
- K. Katsumi et al. Phys. Rev. Lett. 120, 117001 (2018)
Optical probe of Moiré engineered 2D superconducting materials
During the internship, the student will initiate the fabrication of TMD-based VdW heterostructures displaying SC properties using exfoliation techniques. Samples of NbSe2 will be fabricated and characterized as a function of thickness and twist angle. The obtained samples will be first measured by transport measurements to assess their presence of SC and its critical temperature. Going beyond traditional transport measurements, an originality of the project will be the use of low temperature spectroscopic techniques with micron-size spatial resolution like Raman scattering to probe the SC state.
- M. Kennes et al. Nature Physics, 17, 155 (2021)
- Grasset et al. Physical Review Letters 122, 127001 (2019)
- Yoshikawa et al. Nature Physics (2021)
Contact: Yann Gallais
Strain tuned quantum phase transitions
In this internship we propose to implement a novel uni-axial strain optical set-up recently developed in the SQUAP team of MPQ to tune charge density-wave and nematic orders across QCP. The resulting strain tuned electronic orders will be monitored by Raman spectroscopy and transport measurements. Candidate materials of interests are transition metal dichalcogenides (TMDs) displaying both charge density wave and superconductivity, and also chalcogenides like FeSe with both nematic and superconducting orders.
- J.C. Philippe et al. Phys. Rev. Lett. 129, 187002 (2022)
- Straquadine et al. Phys. Rev. X 12, 021046 (2022)
Contact: Yann Gallais