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

作者：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^*

来源：Nature Communications, 2015, 6(1): 9814.

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 Bi2Se3, we report an unprecedentedly large modulation depth of 2,400% at 1.5 THz with very low optical fluence of 45 mu J 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.

• 出版日期2015-10