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Register a new userLow-loss two-dimensional plasmon modes in antimonene
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The effects of spin-orbit (SOC) and electron-phonon coupling on the collective excitation of doped monolayer Sb$_2$ are investigated using density functional and many-body perturbation theories. The spin-orbit coupling is exclusively important for the monolayer Sb$_2$ and it leads to the reconstruction of the electronic band structure. In particular, plasmon modes of monolayer Sb$_2$ are quite sensitive to the SOC and are characterized by very low damping rates owing to small electron-phonon scatterings. Our results show plasmons in antimonene are significantly less damped compared to monolayer graphene when plasmon energies are $hbar omega> 0.2$ eV due to smaller plasmon-phonon coupling in the former material.
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We report on strong coupling of the charge carrier plasmon $omega_{PL}$ in graphene with the surface optical phonon $omega_{SO}$ of the underlying SiC(0001) substrate with low electron concentration ($n=1.2times 10^{15}$ $cm^{-3}$) in the long wavelength limit ($q_parallel rightarrow 0$). Energy dependent energy-loss spectra give for the first time clear evidence of two coupled phonon-plasmon modes $omega_pm$ separated by a gap between $omega_{SO}$ ($q_parallel rightarrow 0$) and $omega_{TO}$ ($q_parallel >> 0$), the transverse optical phonon mode, with a Fano-type shape, in particular for higher primary electron energies ($E_0 ge 20eV$). A simplified model based on dielectric theory is able to simulate our energy - loss spectra as well as the dispersion of the two coupled phonon-plasmon modes $omega_pm$. In contrast, Liu and Willis [1] postulate in their recent publication no gap and a discontinuous dispersion curve with a one-peak structure from their energy-loss data.
Antimonene -- a single layer of antimony atoms -- and its few layer forms are among the latest additions to the 2D mono-elemental materials family. Numerous predictions and experimental evidence of its remarkable properties including (opto)electronic, energetic or biomedical, among others, together with its robustness under ambient conditions, have attracted the attention of the scientific community. However, experimental evidence of its electrical properties is still lacking. Here, we characterized the electronic properties of mechanically exfoliated flakes of few-layer (FL) antimonene of different thicknesses (~ 2-40 nm) through photoemission electron microscopy, kelvin probe force microscopy and transport measurements, which allows us to estimate a sheet resistance of ~ 1200 $Omega$sq$^{-1}$ and a mobility of ~ 150 cm$^2$V$^{-1}$s$^{-1}$ in ambient conditions, independent of the flake thickness. Alternatively, our theoretical calculations indicate that topologically protected surface states (TPSS) should play a key role in the electronic properties of FL antimonene, which supports our experimental findings. We anticipate our work will trigger further experimental studies on TPSS in FL antimonene thanks to its simple structure and significant stability in ambient environments.
Two-dimensional (2D) antimony (Sb, antimonene) recently attracted interest due to its peculiar electronic properties and its suitability as anode material in next generation batteries. Sb however exhibits a large polymorphic/allotropic structural diversity, which is also influenced by the Sbs support. Thus understanding Sb heterostructure formation is key in 2D Sb integration. Particularly 2D Sb/graphene interfaces are of prime importance as contacts in electronics and electrodes in batteries. We thus study here few-layered 2D Sb/graphene heterostructures by atomic-resolution (scanning) transmission electron microscopy. We find the co-existence of two Sb morphologies: First is a 2D growth morphology of layered beta-Sb with beta-Sb(001)||graphene(001) texture. Second are one-dimensional (1D) Sb nanowires which can be matched to beta-Sb with beta-Sb[2-21] perpendicular to graphene(001) texture and are structurally also closely related to thermodynamically non-preferred cubic Sb(001)||graphene(001). Importantly, both Sb morphologies show rotational van-der-Waals epitaxy with the graphene support. Both Sb morphologies are well resilient against environmental bulk oxidation, although superficial Sb-oxide layer formation merits consideration, including formation of novel epitaxial Sb2O3(111)/beta-Sb(001) heterostructures. Exact Sb growth behavior is sensitive on employed processing and substrate properties including, notably, the nature of the support underneath the direct graphene support. This introduces the substrate underneath a direct 2D support as a key parameter in 2D Sb heterostructure formation. Our work provides insights into the rich phase and epitaxy landscape in 2D Sb and 2D Sb/graphene heterostructures.
Collective modes in two dimensional topological superconductors are studied by an extended random phase approximation theory while considering the influence of vector field of light. In two situations, the s-wave superconductors without spin-orbit-coupling (SOC), and the hybrid semiconductor and s-wave superconductor layers with strong SOC, we get the analytical results for longitudinal modes which are found to be indeed gapless. Further more, the effective modes volumes can be calculated, the electric and magnetic fields can be expressed as the creation and annihilation operators of such modes. So, one can study the interaction of them with other quasi-particles through fields.
The collective excitation spectrum of two-dimensional (2D) antimonene is calculated beyond the low energy continuum approximation. The dynamical polarizability is computed using a 6-orbitals tight-binding model that properly accounts for the band structure of antimonene in a broad energy range. Electron-electron interaction is considered within the random phase approximation. The obtained spectrum is rich, containing the standard intra-band 2D plasmon and a set of single inter-band modes. We find that spin-orbit interaction plays a fundamental role in the reconstruction of the excitation spectrum, with the emergence of novel inter-band branches in the continuum that interact with the plasmon.
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