Dirac Fermion and Plasmon Dynamics in Graphene and 3D Topological Insulators

Abstract

Light–matter interactions illuminate the nature of solids and provide a second look on associated carrier dynamics. In particular, graphene and 3D topological insulators (3D TI) with broadband electromagnetic excitation have revealed to host exotic dynamic interactions. Much of Dirac‐point physics arises from discrete lattice symmetries and nontrivial Z2 classification of Bloch states. In this review, ongoing spectroscopic works on graphene and 3D TI are presented, where special attention is on the far‐infrared terahertz (THz) spectroscopy that characterizes the intraband dynamics. The constant absorbance of graphene upon interband particle–hole generation exhibits nonclassical results of gapless dispersion, which can be elucidated by the relativistic Dirac equations with zero rest mass. The massless Dirac fermions on graphene and 3D TI surface exhibit distinct phenomena compared to the conventional systems. First, the transient responses after pulse excitation reveal the semimetallic states of the gapless electronic dispersion, where the Fermi energy in equilibrium determines the crossover from metallic to semiconducting states. Second, the 2D Dirac plasmon dispersion of graphene and 3D TI surface exhibits unconventional density dependence in comparison to the massive electronic systems. The novel optical phenomena in graphene and 3D TI surface can serve for advanced optoelectronic and optospintronic applications.

Emerging Dirac materials for THz plasmonics

“…( 6) in terms of the n 1/4 electron density dependence instead of the conventional n 1/2 one in a 2DEG system. This scenario depicts Dirac and topological materials as a viable alternative to design metamaterials for THz plasmonic devices with electrical detectability and tunable characteristics [42,43]. Both latter aspects come from the large plasmon lifetime and the possibility to select specific spectral region by the combined use of ad hoc plasmonic gratings and electrical gate bias.…”

Topological quantum devices: a review

“…[26][27][28][29] It has been shown that topological phenomena can also emerge in collective excitations, such as phonons, 30,31 magnons, 32 and plasmons. 33 On the other hand, topological flat band (FB) presents another topological manifestation, in analogy to Landau level which is topological without band inversion; while a singular band touching point between a FB and a dispersion band can be viewed as a Berry flux center, in analogy to a Dirac point. 11,[34][35][36][37] Remarkably, the FB is dispersionless whose single-particle energy E(k) is independent of momentum k, so that the kinetic energy is completely quenched in the FB.…”

Electronic correlation determining correlated plasmons in Sb-doped Bi2Se3

“…In recent years, the field of plasmonics has attracted considerable attention because of its novel technological applications including confining light into sub-wavelength dimensions [13][14][15][16]. As such, efforts have been made to study the Dirac [17][18][19][20][21] and surface plasmons [20,[22][23][24][25] at low energies that have been shown to occur in TIs with the aim of producing highly efficient, highspeed plasmonic devices [26][27][28]. In fact, Bi2Se3 has already been demonstrated as teraheartz photodetector [29][30][31] exploiting the plasmonic modes arising from its topological surface states and thermoplasmonic devices [32].…”