Research

The terahertz (THz) domain lies at the intersection of photonics and electronics. THz waves are characterized by a frequency between 100 GHz and 10 THz, corresponding to the natural vibration frequency of many molecules, a wavelength between 30µm and 3mm, which gives them high penetrating power, and low energy (0.4 to 4 meV), making them completely harmless, particularly to living organisms. In addition, many materials are transparent to THz radiation, also known as T-rays. However, these rays are reflected by metals and absorbed by polar liquids, including water. These specific properties give rise to a large number of applications for THz spectroscopy and THz imaging in fields as varied as cosmology, non-destructive testing, security, heritage studies, and more.

But THz spectroscopy also makes it possible to probe a large number of fundamental physical phenomena in condensed matter and living matter. Indeed, the energy of THz waves corresponds to that of many elementary excitations, such as plasmons, magnons, phonons, Landau inter-level transitions, and electron spin resonances.

The TOP platform's activities include fundamental research based on THz spectroscopy techniques, research focused on developing new sensors and emitters, and more applied research combining THz imaging and spectroscopy with agronomy, for example.

THz research at the Montpellier site began in 1983 with the publication of a theoretical article by M. Dyakonov [1], a professor at the University. In 2002, W. Knap reported the first detection of THz radiation by a nanotransistor [2]. The team, composed of F. Teppe, N. Dyakonova, D. Coquillat, and W. Knap, developed this activity at the site from 2003 to 2013. Following the filing of several patents related to the development and integration of THz sources and detectors, the start-up T-Waves Technologies, now Terakalis, was created in 2013. Terakalis develops non-destructive testing systems for industrial materials based on THz imagers derived from the team's patents.

At the same time, in 2001 [3] the Institute of Electronics and Systems (IES UMR 5214) launched a project to simulate physical phenomena in electronic components in the THz frequency range. The development of an experimental activity at the IES, initially led by L. Chusseau and J. Torres, brought the two laboratories closer together, notably through the creation of a Scientific Interest Group called "TeraLab" in 2010. With the support of the CNRS, the University of Montpellier, and the Occitanie region, and in a spirit of unity and structuring of the regional cluster, the Terahertz Occitanie Platform (TOP), at the interface between the L2C and the IES, was created in 2017.

Since 2012, new research activities have been developed within the TOP platform. In solid-state physics, a magneto-spectroscopy system for probing the band structure of topological and Dirac materials has been developed by S. Ruffenach and F. Teppe [5]. More recently, a Landau spectroscopy system unique in Europe, developed in 1993 by W. Knap, was restarted by C. Consejo and F. Teppe to study the cyclotron emission of Dirac materials [6, 7]. And most recently, a THz magneto-photoconductivity spectroscopy system was developed by C. Bray, C. Consejo, K. Maussang, and F. Teppe [8] to study electron spin resonances in two-dimensional materials such as graphene. In biophysics, S. Ruffenach, L. Varani, and J. Torres are developing near-field THz spectroscopy systems to study quantum electrodynamic interactions between proteins [9]. Finally, C. Bray, N. Diakonova, and D. Coquillat have developed an imaging system to study plants [10].

All these tools, emitters, detectors, and spectrometers were pooled together when the Terahertz Occitanie Platform (TOP) was created.

[1] M. Dyakonov and M. Shur, Phys. Rev. Lett. 71, 2465 (1993).
[2] W. Knap et al., Appl. Phys. Lett. 81, 4637 (2002).
[3] E. Starikov et al. J. Appl. Phys. 89, 1161 (2001).
[4] V. Gruzinskis et al., Phys. Stat. Sol. (b) 204, 77 (1997).
[5] F. Teppe et al. Nature Communications 7, 12576 (2016).
[6] D. But et al., Nature Photonics 13, 783–787 (2019).
[7] S. Gebert, C. Consejo et al., Nature Photonics 17, 244–249 (2023).
[8] C. Bray, K. Maussang et al., Phys. Rev. B 106, 245141 (2022).
[9] M. Lechelon, et al., Science Adv. 8(7): eabl5855 (2022)
[10] Y. Abautret, et al., OPTICS EXPRESS 28, 35018-35037 (2020).