交大學刊;;Science Bulletin National Chiao-Tung University

Permanent URI for this collectionhdl:11536/137391

Browse

Now showing 1 - 2 of 2

Effect of Band Structure on Longitudinal Magnetoresistance in Semimetals and Semiconductors
(交大學刊編輯委員會, 1974-03)
吳啟宗
;
蔡健三
;
Chhi-Chong Wu
;
Jensan Tsai
The effect of the Cohen nonellipsoidal nonparabolic (NENP) band structure on the propagation of ultrasound in a semimetal such as bismuth in the presence of a dc magnetic field is investigated by using a quantum-mechanical treatment which is valid at high frequencies and in strong magnetic fields. It is found that the longitudinal magnetoresistance oscillates with the dc magnetic field. This dependence on the dc magnetic field arises from the nonlinear effect of the energy bands owing to the NENP model for the energy band structure of bismuth. We compare these results with those of the ellipsoidal parabolic (EP) band structure of bismuth. We also present numerical results for the nondegenerate and degenerate semiconductors like n-type InSb. It is found that the longitudinal magnetoresistance in the nondehenerate case changes with the dc magnetic field only for the nonparabolic band structure. In the degenerate case, however, the longitudinal magnetoresistance for the parabolic and nonparabolic band structures will oscillate with the dc magnetic field. These oscillations are interpreted as the so-called "giant quantum oscillations " which occur in a degenerate electron gas.
Magnetoacoustic Phenomena in SrTiO3
(交大學刊編輯委員會, 1973-02)
蔡建三
;
吳啟宗
;
Jensan Tsai
;
Chhi-Chong Wu
The effects of parabolic and nonparabolic band structures on the propagation of ultrasound in SrTiO3 in the presence of a dc magnetic field have been studied by using a quanium treatment which is valid at high frequencies and in strong magnetic fields. The major interaction between the ultrasound and conduction electrons is via deformation coupling. Results are shown that the absorption coefficient and sound velocity depend strongly on the sound frequency and longitudinal dc magnetic field. At the high field region, some oscillations in the absorption coefficient and sound velocity with the dc magnetic field occur at the high ultrasonic frequencies. These oscillations are interpreted as the so-called "giant quantum oscillations" which can be observed when the seperation between Landau levels is greater than their thermal broadenings in the region of high frequencies. It is also shown that some discontinuities in the absorption coefficient and change in sound velocity occur in the region of strong magnetic fields.