Sommaire:

In Ikushima group, we are working on the ultimate control of electrons and light using advanced semiconductor technology. One of our targets is terahertz (THz) light, which lies in the band between radio waves and optical waves. We conduct research on fundamental physics utilizing semiconductor quantum structures, including single THz photon detection, THz amplification, and electron-phonon strong coupling (resonant polaron). Furthermore, we are exploring novel mechanisms that could bring transformative advancements not only in electronics and photonics but also in the field of information science, such as terahertz photonic circuits and optically programmable CMOS. In this seminar, I would like to focus on my work “detection of Landau emission in graphene” [1]. We provide experimental evidence for the occurrence of inter-LL radiative transitions in an electrically biased graphene Hall bar, where the wavelength of emission can be tuned by varying the applied magnetic field. A quantum-well based charge sensitive infrared phototransistor (CSIP) is used for detecting weak THz emission from graphene (Fig. 1(a)). THz emission is observed at around 5 T when the Hall voltage exceeds the corresponding LL energy spacing ΔELL01/e between the zero-energy (N = 0) and first excited (N = +1 or N = −1) LLs. We also investigated the emission spectra through measurements of the QW spectrum of the CSIP (Fig. 1(b)). The emission spectra are well explained by the N = +1 → 0 (or N = −1 → 0) inter-LL radiative transition in monolayer graphene. The linewidth of the emission spectra is estimated to be on the order of LF meV, even though no explicit LL splitting is observed in the magnetotransport at 5 T. I would like to discuss the possibilities and challenges of amplifying THz waves also. [1] F. Inamura et al., APL Photonics 9, 116LF1 (2024)

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