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High-harmonic generation in solids - a probe of topology and collective excitations

By: Bruno Amorim
From: International Iberian Nanotechnology Laboratory, Braga, Portugal
At: Building C1, room 1.4.14
[2024-10-07]

When a system is driven by a weak monochromatic perturbation, in the so-called linear response regime, the induced response oscillates with the same frequency of the drive. As the strength of the drive increases, the induced response shows oscillations at multiples of the drive frequency:  this is the phenomenon of harmonic generation, which for moderate drives is usually restricted to low order harmonic generation. For extremely strong drives, we can have high harmonic generation, a highly non-linear non-perturbative effect. High-harmonic generation has long been studied in atomic systems, being at the heart of attosecond physics.
More recently, high-harmonic generation was also observed in crystalline matter [1]. This enabled the use of high-harmonic spectroscopy as a new tool to probe the physics of solid state systems. In this talk,  I will cover the use of high-harmonic generation to probe two interesting aspects of solids state systems:
(1) topological phase transitions, namelly the use of high harmonic generation to detect transitions from trivial insulators to Chern insulators [2];
(2) collective excitations in solids, namelly the dynamics of excitons in two-dimensional semiconductors [3].

References:
 [1] Shambhu Ghimire and David A. Reis, Nature Physics 15, 10–16 (2019).
[2] R. E. F. Silva, Á. Jiménez-Galán, B. Amorim, O. Smirnova and M. Ivanov, Nature Photonics 13, 849–854 (2019).
[3] Eduardo B. Molinero, Bruno Amorim, Mikhail Malakhov, Giovanni Cistaro, Álvaro Jiménez-Galán, Antonio Picón, Pablo San-José, Misha Ivanov and Rui E. F. Silva, Science Advances 10, 10,eadn6985 (2024).