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Optical and Hall-effect measurements have been performed on single crystals of Pb0.77Sn0.23Se, a IV-VI mixed chalcogenide. The temperature dependent (10-300 K) reflectance was measured over 40-7000 cm −1 (5-870 meV) with an extension to 15,500 cm −1 (1.92 eV) at room temperature. The reflectance was fit to the Drude-Lorentz model using a single Drude component and several Lorentz oscillators. The optical properties at the measured temperatures were estimated via KramersKronig analysis as well as by a Drude-Lorentz fit. The carriers were p-type with the carrier density determined by Hall measurements. A signature of valence intraband transition is found in the lowenergy optical spectra. It is found that the valence-conduction band transition energy as well as the free-carrier effective mass reach minimum values at 100 K, suggesting temperature-driven band inversion in the material. Density functional theory calculation for the electronic band structure are also presented.

We study Poisson-noise induced switching between coexisting vibrational states in driven nonlinear micromechanical resonators. In contrast to Gaussian noise induced switching, the measured logarithm of the switching rate is proportional not to the reciprocal noise intensity, but to its logarithm, for fixed pulse area. We also find that the switching rate logarithm varies as a square root of the distance to the bifurcation point, instead of the conventional scaling with exponent 3/2.

We report measurements of Shubnikov-de Haas (SdH) oscillations in single crystals of BiTeCl at magnetic fields up to 31 T and at temperatures as low as 0.4 K. Two oscillation frequencies were resolved at the lowest temperatures, F 1 = 65 ± 4 Tesla and F 2 = 156 ± 5 Tesla. We also measured the infrared optical reflectance (R(ω)) and Hall effect; we propose that the two frequencies correspond respectively to the inner and outer Fermi sheets of the Rashba spin-split bulk conduction band. The bulk carrier concentration was ne ≈ 1 × 10 19 cm −3 and the effective masses m * 1 = 0.20m 0 for the inner and m * 2 = 0.27m 0 for the outer sheet. Surprisingly, despite its low effective mass, we found that the amplitude of F 2 is very rapidly suppressed with increasing temperature, being almost undetectable above T ≈ 4 K.

PACS 78.30.-j-Infrared and Raman spectra PACS 78.20.-e-Optical properties of bulk materials and thin films Abstract-Shubnikov-de Haas (SdH) oscillations, Hall effect, and optical reflectance (R(ω)) measurements have been performed on single crystals of BiTeBr. Under magnetic fields up to 32 tesla and at temperatures as low as 0.4 K, the SdH data shows a single oscillation frequency F = 102 ± 5 tesla. The combined transport and optical studies establish that the SdH effect originates from the Rashba spin-split bulk conduction band, with the chemical potential situated about 13 meV below the crossing (Dirac) point. The bulk carrier concentration was ne ≈ 5 × 10 18 cm −3 and the effective mass m * 1 = 0.16m0. Combining SdH and optical data, we reliably determine the Rashba parameters for the bulk conduction band of BiTeBr: the Rashba energy ER = 28 meV and the momentum spin-split kR = 0.033Å −1. Hence, the bulk Rashba coupling strength αR = 2ER/kR is found to be 1.7 eVÅ.