Transverse, effective charge

Like other zinc-blende type compounds GeSi is an infrared active material. The optical phonon at the F-point is associated with an electric dipole moment which is related to the transverse effective charge e. In terms of ap and its volume derivative (see eq. (49) of Ref. [8]), is given by... 

Ves S, Strossner K, Cardona M (1986) Pressure dependence ofthe optical phonon frequencies and the transverse effective charge in AlSb. Solid State Common 57 483 86 Katayama Y, Tsuji K, Oyanagi H, Shimomura O (1998) Extended X-ray absorption fine structure study on hquid selenium under pressure. J Non-Cryst Solids 232-234 93-98 Gauthier M, Polian A, Besson J, Chevy A (1989) Optical properties of gallium selenide under high pressure. Phys Rev B 40 3837-3854... 

Goi AR, Siegle H, Syassen K et al (2001) Effect of pressure on optical phonon modes and transverse effective charges in GaN and AIN. Phys Rev B 64 035205... 

Reparaz JS, Muniz LR, Wagner MR et al (2010) Reduction of the transverse effective charge of optical phonons in ZnO under pressure. Appl Phys Lett 96 231906... 

Structure, then for every tetrahedron there is another tetrahedron which has the exact opposite orientation the electric fields of the dipoles compensate each other. If, however, all tetrahedra have the same orientation or some other mutual orientation that does not allow for a compensation, then the action of all dipoles adds up and the whole crystal becomes a dipole. Two opposite faces of the crystal develop opposite electric charges. Depending on the direction of the acting force, the faces being charged are either the two faces experiencing the pressure (longitudinal effect) or two other faces in a perpendicular or an inclined direction (transversal effect). 

In metals, where there is only one type of charge carrier, the Hall coefficient, Rb = (Ey / jxB), is very useful for measuring both the carrier density and the magnetic field B. Since the secondary field Ey and B are orthogonal, the Hall effect is a transverse effect and the Hall tensor is of rank three. It relates the axial vector Bj. to the antisymme-trical second-rank tensor Ey, which is equivalent to p yjx, where p y = PxyzBz-... 

In Section 19-E we found contributions to the effective charge 7 of the oxygen due to the matrix clement between an sp hybrid and a d slate and due to the matrix element For an oxygen displacement perpendicular to the Ti—O axis, the predicted transverse charge is simply this Z. However, for displacements along the Ti—O axis there are contributions from the transfer of charge between ions just as there were in the alkali halides, for which we obtained the transverse charge in Section 14-C. 

A) Simplified microscopic model of a quartz crystal lattice B) Longitudinal effect C) Transverse effect Si " and 2 O refer to centers of gravity (circles) for charges associated with the two types of atoms, where the tetrahedral "Si04 structure has been projected onto a plane (as a hexagon)... 

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