Temperature dependence of the dielectric function and critical points of α-SnS from 27 to 350 K

Abstract

We report the temperature dependence of the dielectric function ε = ε1 + iε2 and critical point (CP) energies of biaxial α-SnS in the spectral energy region from 0.74 to 6.42 eV and temperatures from 27 to 350 K using spectroscopic ellipsometry. Bulk SnS was grown by temperature gradient method. Dielectric response functions were obtained using multilayer calculations to remove artifacts due to surface roughness. We observe sharpening and blue-shifting of CPs with decreasing temperature. A strong exciton effect is detected only in the armchair direction at low temperature. New CPs are observed at low temperature that cannot be detected at room temperature. The temperature dependences of the CP energies were determined by fitting the data to the phenomenological expression that contains the Bose–Einstein statistical factor and the temperature coefficient for describing the electron–phonon interaction.

Polarization-dependent optical responses in natural 2D layered mineral teallite

“…Figure 5 h shows the corresponding plot with the measured data (black squares) and the fitted curve (green curve) for k 3 = 1.42. We assume the refractive index of teallite is similar to that of herzenbergite, where n 3 = 4.39 at 520 nm and n 1 = 3.61 at 1560 nm along the armchair direction 47 . Thus, taking these values along with other experimental parameters into account ( = 1.1 mW, laser pulse width τ = 90 fs, repetition rate = 80 MHz, and spot size W = 1.5 µm at the fundamental wavelength = 1560 nm), the magnitude of can be estimated by the following formula 11 where n 1 and n 3 are the real part of refractive index at pump wavelength ( ) and emission wavelength ( ), is the phase mismatch between the fundamental beam and the forward propagating THG emission beam in the transmission optical setup arrangement.…”

Imaging Anisotropic Waveguide Exciton Polaritons in Tin Sulfide

“…The mode coupling is much weaker along the a axis, likely due to the small exciton binding energy. According to the literature, excitons along the b axis are robust with a binding energy of ∼50 meV. The binding energy of excitons along the a axis, on the other hand, is much smaller and E a is close to the fundamental band gap .…”

“…SnS is a post-transition-metal monochalcogenide and a van der Waals (vdW) layered semiconductor with an orthorhombic structure, analogous to that of black phosphorus. , As sketched in Figure b, the two in-plane axes of SnS, namely the a and b axes, are along the zigzag and armchair directions, respectively. SnS has been widely studied due to its unique anisotropic optoelectronic properties − and potential applications related to photodetection and solar energy harvesting. − In particular, the energies of excitons or optical band gaps along the a and b axes of SnS are about E a ≈ 1.39 eV and E b ≈ 1.63 eV, respectively, , which directly affect the polaritonic responses. Note that EPs have previously been studied in other vdW semiconductors (e.g., WSe 2 , MoSe 2, etc.)…”

“…In the model, we placed a vertically polarized excitation dipole ( p z ) right above the sample surface. The optical constants of SnS and SnS 2 were obtained from the literature. ,,, A detailed description of the Comsol model is given in the Supporting Information. The simulation results are shown in Figure k–o and Figure S5, where we plot the real-space images of polariton field amplitude (| E z |) and polariton field ( E z ) of EPs, respectively.…”

“…along the a and b axes of SnS are about Ea ≈ 1.39 eV and Eb ≈ 1.66 eV respectively, 22,23 which directly impact the polaritonic responses. Note that EPs have previously been studied in other vdW semiconductors (e.g.…”