Superconducting magnet cryostat system for terahertz spectroscopy

• Subject Area: Condensed Matter Physics
• Term: Funded in 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 495542626

The superconducting magnet cryostat system requested by the group of Prof. Lange allows for the investigation of ultrastrongly and deep-strongly light-matter coupled cavity quantum electrodynamical (c-QED) structures in the terahertz (THz) spectral range. Tailoring near fields of THz modes by quantitative, parameter-free numerical simulations, our group designs and fabricates light-matter coupled structures for c-QED experiments, as well as near-field enhancing resonators enabling THz experiments with atomically strong fields. This subwavelength control of electromagnetic fields plays a central role for our group’s aim to investigate extreme limits of light-matter interaction in which optical nonlinearities occur on time scales significantly shorter than a single cycle of light. Recent research highlights include nonlinearities of Landau electrons beyond Kohn’s theorem, the observation of dynamical Bloch oscillations and high-harmonics generation, lightwave acceleration of Dirac electrons in topological insulators, minimally dissipative spin switching in antenna-enhanced THz near fields, non-adiabatic control of deep-strongly light-matter coupled electrons in switchable THz resonators, and the observation of carrier-wave Rabi flopping of ultrastrongly coupled resonances.The requested magnet cryostat will allow us to continue this research and explore novel directions of THz subcycle physics in condensed-matter systems. The system’s key features include magnetic fields of up to 6 T while providing an exceptionally large and symmetric optical aperture corresponding to an opening angle of 45°, permitting tight focusing and thus strong THz field amplitudes, in the focal plane. These properties will enable the investigation of strong-field THz dynamics in magnetic fields, which in particular concerns our Landau polariton c-QED systems. Here, we aim for previously inaccessible light-matter coupling strengths, where the vacuum Rabi frequency significantly exceeds the carrier frequency of light. Furthermore, we will explore novel c-QED concepts including superconducting resonators or atomically thin materials such as transition metal dichalcogenides, in magnetic fields. Transitioning from linear to non-perturbatively nonlinear dynamics, we expect to unveil novel phenomena including high-order nonlinearities, generation of non-classical light, resonances generated by nonlinear interactions of cavity polaritons, or phase transitions.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Supraleitendes Magnetkryostatsystem für Terahertz-Spektroskopie
• Instrumentation Group: 0120 Supraleitende Labormagnete
• Applicant Institution: Technische Universität Dortmund
• Leader: Professor Dr. Christoph Lange