Ultra-high modulation depth exceeding 2,400% in optically controlled topological surface plasmons

• Published in: Nature communications Vol. 6; no. 1; p. 8814
• Main Authors: Sim, Sangwan, Jang, Houk, Koirala, Nikesh, Brahlek, Matthew, Moon, Jisoo, Sung, Ji Ho, Park, Jun, Cha, Soonyoung, Oh, Seongshik, Jo, Moon-Ho, Ahn, Jong-Hyun, Choi, Hyunyong
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 30.10.2015; Nature Publishing Group; Nature Pub. Group
• Subjects: 140/125; 639/301/119/2792; 639/624/400/1021; 639/925; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms9814

Modulating light via coherent charge oscillations in solids is the subject of intense research topics in opto-plasmonics. Although a variety of methods are proposed to increase such modulation efficiency, one central challenge is to achieve a high modulation depth (defined by a ratio of extinction with/without light) under small photon-flux injection, which becomes a fundamental trade-off issue both in metals and semiconductors. Here, by fabricating simple micro-ribbon arrays of topological insulator Bi 2 Se 3 , we report an unprecedentedly large modulation depth of 2,400% at 1.5 THz with very low optical fluence of 45 μJ cm −2 . This was possible, first because the extinction spectrum is nearly zero due to the Fano-like plasmon–phonon-destructive interference, thereby contributing an extremely small denominator to the extinction ratio. Second, the numerator of the extinction ratio is markedly increased due to the photoinduced formation of massive two-dimensional electron gas below the topological surface states, which is another contributor to the ultra-high modulation depth. For optical control of plasmons metals require a large amount of power in the control pulse, yielding a small modulation depth. Here, Sim et al. fabricate arrays of Bi 2 Se 3 and report a modulation depth of 2,400% at 1.5 THz with an optical fluence of 45 μJ/cm 2 , demonstrating a novel route for controlling plasmons.