1. G. D. Mahan, Solid State Phys. 51, 81 (1998); F. Giazotto et al., Rev. Mod. Phys. 78, 217 (2006).
2. A value of ZT = 2.4 at room temperature was reported for p-type Bi2Te 3/Sb2Te 3 superlattice devices, see R. Venkatasubramanian et al., Nature 413, 597 (2001).
3. For a preliminary report of this work see M. Rontani and L. J. Sham, Appl. Phys. Lett. 77, 3033 (2000).
4. See B. C. Sales, D. Mandrus, and R. K. Williams, Science 272, 1325 (1996), and references therein.
5. G. D. Mahan and J. O. Sofo, Proc. Natl. Acad. Sci. USA, 93, 7436 (1996).