Plasmonic Photocurrents in a Two-Dimensional Electron System

Direct electric current generated in a two-dimensional electron system (2DES) with broken spatial inversion symmetry by incoming terahertz (THz) radiation is commonly referred to as the THz photogalvanic current [1]. Typically, the inversion symmetry is broken due to noncentrosymmetric electronic response while THz near field in 2DES may be centrosymmetric or even homogeneous. This paper discusses the essentially different physical mechanism of THz photocurrent generated in 2DES by noncentrosymmetric plasmon modes while the electronic response remains centrosymmetric or even homogeneous. Noncentrosymmetric plasmon modes in 2DES can be excited by the metal grating coupler with a noncentrosymmetric unit cell (Fig. 1) irradiated by incoming THz wave [2]. It is shown that THz photocurrent in 2DES with a noncentrosymmetric grating gate originates from two different physical mechanisms—plasmonic drag and plasmonic ratchet effects [3]. The intensity and asymmetry of the plasmonic near field and hence THz photocurrent can be drastically enhanced by exciting plasmon resonances in the structure [2]. Giant photogalvanic response in 2DES with a noncentrosymmetric grating gate at THz frequencies was demonstrated experimentally [4].

1. L. Ivchenko and G.E. Pikus, Superlattices and Other Heterostructures. Symmetry and Optical Phenomena (Springer, Berlin, 1997).
2. V. Popov, D.V. Fateev, T. Otsuji, Y.M. Meziani, D. Coquillat, and W. Knap, Appl. Phys. Lett. 99, 243504 (2011).
3. V. Popov, Appl. Phys. Lett. 102, 253504 (2013).
4. Y. Kurita, G. Ducournau, D. Coquillat, A. Satou, K. Kobayashi, S. Boubanga Tombet, Y.M. Meziani, V.V. Popov, W. Knap, T. Suemitsu, and T. Otsuji, Appl. Phys. Lett. 104, 251114 (2014).

Fig. 1: Two-dimensional electron system gated by the periodic metal grating with a noncentrosymmetric unit cell (w₁ ≠ w₂, s₁ ≠ s₂). Terahertz photocurrent generates the photovoltage U_ph between the open side contacts.

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