|Budget Amount *help
¥2,500,000 (Direct Cost: ¥2,500,000)
Fiscal Year 2003: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2002: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2001: ¥1,100,000 (Direct Cost: ¥1,100,000)
We theoretically studied phonons propagating through superlattices (SLs). We considered a SL structure which acts as a double barrier for phonons. This structure is realized by a bulk material sandwiched between periodic SLs. For phonons normally propagating through this system, we derived analytical formulas for the resonant frequency and the corresponding decay factor. These formulas are especially useful for the design of phonon tunneling devices to be used for the detection or generation of quasi-monochromatic acoustic phonons.
Next, we studied the resonant transmission of phonons propagating through a SL-detector interface. We calculated the phonon transmittance and examined the peculiar resonance peak due to the vibrational mode localized at SL-detector interface. The peak value depends on the number of periods N of SL, and this resonant feature disappears for large N and also small N. Only for an appropriate range of N, we can see the resonance. We derived the N-depandent resonant formula, i.e., generalized Breit-Wigner formula, and discussed the physical meaning.
Furthermore, we numerically studied phonons obliquely propagating through SLs. The notable features of phonons in periodic SLs are mainly related to the appearance of frequency gaps originating from Bragg reflections of phonons. For phonons obliquely propagating through SLs, "intermode" Bragg reflections due to the coupling of different polarization modes can occur besides ordinary "intramode" Bragg reflections, and corresponding frequency gaps are classified according to types of Bragg reflection. On the other hand, it is well known that an inhomogeneity embedded in a periodic SL causes localized vibrational modes inside the frequency gaps. In the present work, we studied the double barrier system and examined the difference between localized modes generated in different types of frequency gap theoretically.