Domain, Specialties : Condensed matter physics
Keywords:
Spectroscoy, Terahertz, Superconductivity, Cavity
Research Unit : LSI / NEE
Summary
Strong light-matter interactions between quantum materials and the vacuum field of cavities at TeraHertz (THz) frequencies is emerging as a new frontier for the control of material properties. Among quantum materials, superconductors (SC) hold a special place and a timely question has arisen regarding the possibility to tune their spectacular properties by dressing their collective modes with THz cavity photons. In this internship, we propose to study the collective modes of NbSe2, an exotic SC exhibiting simultaneously SC and a charge density-wave (CDW) state. Of particular interest will be to investigate the dynamics of its Higgs-mode, an analogue of the Higgs-boson in SCs, and its interaction with the CDW mode. This will be achieved with a combination of equilibrium THz time-domain spectroscopy and pump-probe THz spectroscopy. The first steps towards integration of this SC inside THz cavities and the dressing of its collective modes will carried out.
Full description
Context: Light control of a material’s properties is an emerging field with potentially far-reaching applications. Within this field enhancing or modifying superconductivity (SC) holds a special place ever since the discovery of a superconducting-like state in several materials well above their equilibrium SC temperature [1]. The dynamics of superconductors driven out-of-equilibrium is governed by their collective mode spectrum, and in particular the SC amplitude mode which is an analog of the Higgs mode in high-energy physics [2]. These SC collective modes not only give fingerprints of the nature of the ground state, but also a path to dynamically drive or even control SC order. Light control of SC may be achieved through two main routes. The first involves driving the collective modes with light pulses tuned to their energy, typically in the THz frequency range, which may dynamically modify SC properties such as the pairing potential and explore new regions of the free energy landscape inaccessible via static means. The second route involves dressing the SC collective modes with vacuum fluctuations through strong light-matter coupling in THz cavities [3,4] aiming to harness hybrid light-matter states to engineer novel equilibrium phases of matter without external driving.
Research program: In this Master project we propose to develop a method to perform spectroscopy on micrometer scale 2D materials beyond the current diffraction limitation of standard THz spectroscopy. This new technique uses “on-chip” generation and detection of THz pulses and will allow the candidate to study NbSe2, an exotic SC hosting simultaneously SC and a charge-density-wave (CDW) state. NbSe2 samples will be progressively exfoliated and measured down to the ultimate monolayer 2D limit. These already unprecedented results will pave the way for a PhD thesis for which the candidate will implement pump-probe “on-chip” THz spectroscopy, investigating the dynamics and interaction of the Higgs and CDW modes when driven far away from equilibrium and the possibility to induce long-lived metastable SC states in this system. The thesis project will further aim at dressing its collective modes via integration of this SC inside THz cavities in order to create hybrid light-SC matter states and to explore their impact on SC properties.
[1] Fausti et al. Science 331, 6014 (2011): 189 91.
[2] Pekker and Varma, Annual Review of Condensed Matter Physics 6, (2015): 269 97.
[3] Garcia-Vidal et al. Science 373, 6551 (2021).
[4] Raines et al. Physical Review Research 2, n(2020): 013143.
Environment :
The hosting group “Nouveaux Etats Electroniques” (NEE) is expert in equilibrium and non-equilibrium dynamics of superconductors. The student will operate a KiloHertz amplified laser system providing femtosecond pulses of 5 mJ. Standard THz spectrometer and optical cryostats are installed and regularly operating. The supervisors Yannis Laplace and Romain Grasset have large experience both on THz cavity design and fabrication and THz spectroscopy of superconductors.
Location
École Polytechnique, Palaiseau, France
Internship conditions
- Internship duration: 5 months
- Level of study: Bac+5
- Training: Master 2
- Continuation in PhD thesis: Yes
- Application deadline: 31 décembre 2024
Experimental skills
Langue : Anglais