FisMat2017 - Submission - View

Abstract's title: ultra-fast time resolved spectroscopy in superconductors
Submitting author: Tommaso Cea
Affiliation: IMDEA
Affiliation Address: IMDEA Nanoscience Institute, Calle Faraday 9, Madrid
Country: Spain
Oral presentation/Poster (Author's request): Oral presentation
Other authors and affiliations: Lara Benfatto ISC, Flavio Giorgianni PSI

The enormous technological advances made in the last decades in non-linear THz spectroscopy1,2 allowed the di- rect observation of ultra-fast (ps) time-resolved oscilla- tions of the transmitted electric fields3–5. This technique reveals to be a very powerful method to study the spec- tral features of several superconducting (SC) compounds (as e.g. NbN and MgB2), that exhibit a spectral gap in the THz region3–6, thus opening new perspectives to- ward the understanding of the interaction of light with matter in the field of superconductivity.

In the following we focus on the case of the non-linear THz-pump-THz-probe spectroscopy on single-band s- wave superconductors, aiming to provide a theoretical explanation of the observed oscillations of the electric field transmitted by NbN samples5. By using the for- malism developed in our recent work6 we compute the non-linear time-dependent transmitted field, reproducing the experimental results of the Ref.5 with great precision and showing that the oscillations can be interpreted as well as originating from the quasi-particle (Cooper pairs) excitation processes in the equilibrium regime. Further- more, we also shed light on how the spectral features of the incoming pump field can determine the main fre- quency of the transmitted oscillations, explaining why for a narrow pump field centered at a frequency Ω the transmitted signal oscillates at , while in the case of a broad incoming pump field it oscillates at 2∆.

A final discussion is devoted to the behavior of the long-time decay of the transmitted probe.


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3  R. Matsunaga and R. Shimano, Phys. Rev. Lett. 109187002 (2012).

4  R. Matsunaga, Y. I. Hamada, K. Makise, Y. Uzawa, H. Terai, Z. Wang, and R. Shimano, Phys. Rev. Lett. 111, 057002 (2013). 

5  R. Matsunaga, N. Tsuji, H. Fujita, A. Sugioka, K. Makise, Y. Uzawa, H. Terai, Z. Wang, H. Aoki, and R. Shimano, Science 345, 1145 (2014),

6  T. Cea, C. Castellani, and L. Benfatto, Phys. Rev. B 93, 180507 (2016).