The ultra-strong light-matter coupling regime is achieved when the normalized Rabi frequency of the coupled system becomes comparable to the resonant frequency of the system itself.[1] This has already been achieved in several systems, particularly in the MIR and THz spectral range (e.g. [2,3]). The starting point of our investigation is the system where the cyclotron transition of a GaAs/AlGaAs 2DEG is in ultra-strong coupling with a THz metasurface formed by an array of split-ring resonators (SRRs), that constitute our cavities.[4,5,6] In the first part of the seminar, I will present our efforts in moving to a hybrid system where the coupled system is etched into Hall-bars and measured in transport under illumination, taking advantage of the phenomenon of microwave-induced resistance oscillations (MIROs)[7,8]. In the second part, graphene is used as 2DEG in view of the predicted Dicke phase transition[9]: the interaction was first investigated without magnetic field[10], revealing graphene’s mobility to be the main limitation for achieving strong coupling in the first place. This was instead reached by reducing the dimensionality of the graphene layer etching nanoribbons.[11]
[1]Ciuti, Bastard, Carusotto, PRB 72, 115303 (2005)
[2]Todorov, Andrews, Colombelli, De Liberato, Ciuti, Klang, Strasser, Sirtori, PRL 105, 196402 (2010)
[3]Günter, Anappara, Hees, Sell, Biasol, Sorba, De Liberato, Ciuti, Tredicucci, Leitenstorfer, Huber Nature 458, 178 (2009)
[4]Scalari, Maissen, Turcinkova, Hagenmüller, De Liberato, Ciuti, Reichl, Schuh, Wegscheider, Beck, Faist, Science 335, 1323 (2012)
[5]Hagenmüller, De Liberato, Ciuti, PRB 81, 235303 (2010)
[6]Maissen, Scalari, Valmorra, Beck, Faist, Cibella, Leoni, Reichl, Charpentier, Wegscheider, PRB 90, 205309 (2014)
[7]Mani, Smet, von Klitzing, Narayanamurti, Johnson, Umansky, Nature 420, 646 (2002)
[8]Zudov, Du, Simmons, Reno, PRB 64, 201311 (2001)
[9] Hagenmüller and Ciuti, PRL 109, 267403 (2012)
[10]Valmorra, Scalari, Maissen, Fu, Schönenberger, Choi, Park, Beck, Faist, Nano Letters 13, 3193 (2013)
[11]Liu, Luxmoore, Mikhailov, Savostianova, Valmorra, Faist, Nash, Nature Communications 6, 8969 (2015)
Quantum Optoelectronics Group, Institute for Quantum Electronics, ETH Zurich