Abstract
Electrons with a linear energy/momentum dispersion are called massless Dirac electrons and represent the low-energy excitations in exotic materials such as graphene and topological insulators. Dirac electrons are characterized by notable properties such as a high mobility, a tunable density and, in topological insulators, a protection against backscattering through the spin–momentum locking mechanism. All those properties make graphene and topological insulators appealing for plasmonics applications. However, Dirac electrons are expected to present also a strong nonlinear optical behaviour. This should mirror in phenomena such as electromagnetic-induced transparency and harmonic generation. Here we demonstrate that in Bi2Se3 topological insulator, an electromagnetic-induced transparency is achieved under the application of a strong terahertz electric field. This effect, concomitantly determined by harmonic generation and charge-mobility reduction, is exclusively related to the presence of Dirac electron at the surface of Bi2Se3, and opens the road towards tunable terahertz nonlinear optical devices based on topological insulator materials.
Highlights
Electrons with a linear energy/momentum dispersion are called massless Dirac electrons and represent the low-energy excitations in exotic materials such as graphene and topological insulators
THz research has been oriented either on investigating novel radiation sources based on frequency conversion, optical rectification[7,8,9] and relativistic electrons[10,11,12,13,14,15], and in studying the properties of plasmon-based systems whose optical properties such as absorption, dispersion and scattering can be engineered at THz frequencies[16,17,18]
THz response of two-dimensional (2D) metallic systems characterized by massless Dirac electrons
Summary
Electrons with a linear energy/momentum dispersion are called massless Dirac electrons and represent the low-energy excitations in exotic materials such as graphene and topological insulators. We demonstrate that in Bi2Se3 topological insulator, an electromagnetic-induced transparency is achieved under the application of a strong terahertz electric field This effect, concomitantly determined by harmonic generation and charge-mobility reduction, is exclusively related to the presence of Dirac electron at the surface of Bi2Se3, and opens the road towards tunable terahertz nonlinear optical devices based on topological insulator materials. Nonlinear optical phenomena have a crucial importance in modern physics giving rise to fundamental applications such as coherent control of excitations in condensed matter, and harmonic generation and frequency conversion in optically active materials[1,2,3] In this case, the use of materials whose electromagnetic response can be fully controlled by an applied radiation field plays a fundamental role in ultrafast electromagnetic pulse generation and shaping[4]. Under an oscillating THz electric field E(t) 1⁄4 E0 cosnt, electrons gain (for zero scattering) a momentum pðtÞ1⁄4 À eE0 n sinnt
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