Strong Electron-Phonon Coupling and its Influence on the Transport and Optical Properties of Hole-Doped Single-Layer InSe

Abstract

We show that hole states in recently discovered single-layer InSe are strongly renormalized by the coupling with acoustic phonons. The coupling is enhanced significantly at moderate hole doping (∼10 13 cm −2 ) due to hexagonal warping of the Fermi surface. While the system remains dynamically stable, its electron-phonon spectral function exhibits sharp low-energy resonances, leading to the formation of satellite quasiparticle states near the Fermi energy. Such many-body renormalization is predicted to have two important consequences. First, it suppresses significantly charge carrier mobility reaching ∼1 cm 2 V −1 s −1 at 100 K in free-standing sample. Second, it gives rise to unusual temperature-dependent optical excitations in the mid-infrared region. Relatively small charge carrier concentrations and realistic temperatures suggest that these excitations may be observed experimentally.Two-dimensional (2D) indium selenide (InSe) is a recently discovered semiconductor receiving considerable attention because of its attractive electronic properties. Thin films InSe have been proposed to be suitable for field-effect transistor applications due to their high carrier mobilities, reported to exceed 10 3 cm 2 V −1 s −1 at room temperature [1][2][3][4]. Other interesting properties of this material include tunable band gap [5-8], fullydeveloped quantum Hall effect [2], anomalous optical response [2,5,9,10], superior flexibility [11], as well as excellent thermal [12,13] and thermoelectric [14] characteristics. These observations, along with its ambient stability [15], make low-dimensional InSe an appealing candidate for numerous practical applications [16].Single-layer (SL) InSe is a layered semiconductor with an indirect energy gap in the visible range. Its electronic structure is characterized by peculiar flat regions in the valence band [17], giving rise to a giant van Hove singularity in the hole density of states [18,19]. This feature is known as a "Mexican-hat"-like band, and has been predicted for the whole family of In 2 X 2 and Ga 2 X 2 (X=S,Se,Te) compounds [17,20]. Interestingly, this peculiar shape evolves into the conventional parabolic band with increasing material's thickness, as has been theoretically predicted for InSe [18,21] and recently confirmed by angular resolved photoemission spectroscopy [22]. This observation makes ultrathin InSe films especially attractive for further studies. The interest to flat-band materials is motivated by exotic physical properties of such systems, closely related to various many-body instabilities and strong correlation effects [23][24][25][26][27]. Recent experimental discovery of flat bands and associated many-body phenomena including superconductivity in magic-angle twisted bilayer graphene [28,29] enhances enormously the interest to the problem.Electron-phonon interaction in the case of narrow bands can be dramatically different from the conven-tional case and can play a more important role. In particular, a strong electron-phonon coupling in the magicangle twisted b...

Tunable spin-orbit coupling in two-dimensional InSe

“…The zero of energy is set to the monolayer conduction band edge, so that E v ≈ −2.8 eV is the energy of the monolayer's topmost valence band at the Γ-point. We neglect the valence band dispersion in InSe monolayers, as earlier studies 1,[51][52][53] have shown that it is approximately flat over a large central part of the Brillouin zone. We also neglect any k-dependence in t vv for the same reason.…”

Structure-driven intercalated architecture of septuple-atomic-layer $MA_2Z_4$ family with diverse properties from semiconductor to topological insulator to Ising superconductor

“…Monolayer InSe (Fig. 1(a)) of group-III monochalcogenides 33 consisting of quadruple-atomic-layer n = 4 monolayer can be used in photocatalyst 34 and the hole-doped monolayer InSe even has a strong electron-phonon coupling, which affects its transport and optical properties 35,36 . As to the quintupleatomic-layer n = 5 monolayer structure (Fig.…”

Plasmonic Hot Electron Induced Layer Dependent Anomalous Fröhlich Interaction in InSe

“…In polar materials, optical phonons couple strongly with elementary charges due to long range Coulomb interactions induced by the macroscopic polarization field resulting from the atomic displacement, known as Fröhlich interaction 6 . Therefore, scattering with optical phonons limits the mobility in 2D semiconductors at RT significantly 7,8 . Intriguingly, 2D Fröhlich interaction is markedly different from its bulk analogue as reported in a recent theoretical work 9 .…”