Relativistic electronic structure of the Pb (001) surface

The surface electronic band structure of the Pb (001) was calculated using the self-consistent, first-principles linear-augmented-plane-wave method and the norm-conserving pseudopotentiai method. In the nonrelativistic case, forbidden gaps appear above and below the Fermi levelin the bulk projected band structure of lead. An occupied surface state at the point and two surface states in a wide forbidden gap above E_F are found. A characteristic feature of the electronic structure of the Pb (001) surface is the absence of a surface state within the forbidden S-P gap in the vicinity of the point. The inclusion of scalar-relativistic effects leads to the merger of several S-P gaps into one wide gap extending throughout the entire Brillouin zone. At the same time, the occupied state at point extends to point and its energy decreases by 2 eV. New, relatively weak surface states in the direction and unoccupied states in the vicinity of the point appear. An unoccupied surface state is found at the bottom of the forbidden gap at point . Including the contribution of the spinorbit pseudopotentiai leads to the appearance of two-spin orbit gas; however, the surface level structure is practically unchanged (except for the disappearance of the unoccupied surface state of P_z-symmetry at point ).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 47–53, October, 1991.     

Giant Rashba-type spin splitting at polar surfaces of BiTeI

On the basis of relativistic ab initio calculations, we show that both Te- and I-terminated surfaces of the polar layered semiconductor BiTeI hold surface states with a giant Rashba-type spin splitting. The Te-terminated surface state has nearly isotropic free-electron-like dispersion with a positive effective mass, which along with the giant spin splitting makes BiTeI fulfilling the requirements demanded by many semiconductor-spintronics applications. The I-terminated surface state with its negative effective-mass dispersion reproduces nicely the situation with the Rashba-split surface state on surfaces of noble-metal based surface alloys. The crucial advantage of BiTeI as compared with the surface alloys is the location of the I-terminated surface state in a quite wide band gap.     

Thermal aberrations and high power frequency conversion in a barium nitrate Raman laser

Raman frequency conversion of high average power pulsed Nd:YAG laser radiation into the near IR spectral region in a barium nitrate Raman laser was studied with the emphasis on thermal effects inside the Raman-active medium. The probe-beam technique together with numerical reconstruction, done by integrating the transient heat conduction and paraxial wave equations, revealed dynamics of the induced distortions featuring high-order optical aberrations. By utilizing the Zernike expansion of the reconstructed phase profile and implementing a special focusing geometry of the pump beam, partial compensation of the distortions was realized in a stable configuration of the Raman cavity. Generation of the first-, second-, and third-order Stokes radiation with output power of 17, 9.5, and 5.5 W corresponding to a quantum conversion efficiency of 32, 21, and 13% is reported.     

Dynamics of the BiTeI lattice at high pressures

Raman measurements of the phonon spectrum of BiTeI at pressures of up to 20 GPa have been performed. A decrease in the linewidth of E² vibration by almost a factor of 2 with an increase in the pressure to 3 GPa has been detected. The frequencies of all four Raman active modes increase monotonically with the pressure. These lines are observed in spectra up to ～8 GPa. Sharp change in the spectrum occurs at pressures of 8–9 GPa, indicating a transition to the high-pressure phase, which holds up to 20 GPa. This transition is reversible and hardly has any hysteresis. A sample in the high-pressure phase is single crystal.     

Structure and composition analysis of multilayer nanocoating deposited onto inner surfaces of tubes by pulsed laser deposition

The features of multilayer nanocoating deposition onto inner surfaces of tubes with a small diameter by pulsed laser deposition are discussed. The coating composition and structure have been studied, and it has been shown that atoms belonging to different layers are significantly mixed.     

Vibrational modes on the Al\,(111) - (\sqrt 3 \times \sqrt 3 )R30^\circ - Na surface

The vibrational spectra on the $Al\,(111) - (\sqrt 3 \times \sqrt 3 )R30^\circ - Na$ surface are calculated by the embedded atom method. Surface relaxation, dispersion of surface phonons, local density of surface states, and polarization of vibrational modes of adatoms and substrate atoms are discussed in the present paper. The theoretical results obtained agree well with the available experimental data and can be used for their interpretation.     

Observation of Raman conversion for 70-fs pulses in KGd(WO4)2 crystal in the regime of impulsive stimulated Raman scattering

Raman conversion of femtosecond pulses in a solid-state medium is reported. Stimulated Raman scattering (SRS) was observed in an impulsive SRS regime when the pump pulse's duration was comparable with the period of Raman-active vibration. The generation of super broadband radiation, which is a distinguishing feature of impulsive SRS, is shown.