MAGNETOPHONON OSCILLATIONS IN THE TRANSVERSE AND LONGITUDINAL MAGNETORESISTANCE OF HG1-XCDXTE

The transverse and longitudinal magnetoresistance (MR) as well as the longitudinal magneto-thermoelectric coefficient of n-type Hg1-xCdxTe ( MCT) (0.20 < x < 0.33) have been measured at various temperatures (40 less than or equal to T less than or equal to 140K) as a function of m agnetic field (0 less than or equal to B less than or equal to 18 kG). Both the transverse and the longitudinal MR clearly exhibit oscillati ons which are described in terms of magnetophonon (MP) transitions inv olving the HgTe-like and the CdTe-like longitudinal optical (LO) phono ns of MCT. The field positions of the transverse MR maxima agree with the calculated MP resonances taking into account nonparabolic bands (k . p model for narrow-gap zinc-blende-type semiconductors) and the pol aron effect. Those of the longitudinal MR minima are found to coincide with the oscillation minima in the longitudinal magneto-thermoelectri c coefficient. However, these minima are shifted by pi/2 to lower fiel ds with respect to the positions of the MP resonances. This phase shif t was predicted by Barker(13,14) for the case of strong Landau level d amping but has not been previously observed. In contrast, the MP oscil lation minima of the longitudinal MR and the oscillation maxima of the transverse MR of n-type InSb (investigated here for comparison) occur exactly at the fields of the MP resonances. Only the oscillation mini ma of the longitudinal magneto-thermoelectric coefficient are slightly shifted to the side below the MP resonance fields. With regard to the band parameters and the dominant polar optical mode scattering of cha rge carriers InSb very much resembles MCT. InSb, however; is a binary compound whereas MCT is a solid solution. Thus, the phase shift by pi/ 2 to lower fields observed for the oscillation minima in the longitudi nal MR and magneto-thermoelectric coefficient of MCT may be due to all oy scattering. The temperature coefficients of the MP resonance fields of MCT are found to be substantially smaller than those reported by T akita et al.(11) and McClure et al.(10) The larger temperature coeffic ients are presumably due to unresolved two-phonon structures of the MP oscillations.