Bulk silicon has a six-fold orbital degneracy that can be lifted by both strain and quantum confinement. Under strain, the six-fold valley degeneracy in the silicon conduction band is reduced to two-fold. Quantum confinement further reduces this degeneracy, resulting in a non-degneratre conduction band minimum.
Selected publications on this topic:
“The critical role of substrate disorder in valley splitting in Si quantum wells.” S. F. Neyens, R. H. Foote, B. Thorgrimsson, T. J. Knapp, T. McJunkin, L. M. K. Vandersypen, P. Amin, N. K. Thomas, J. S. Clarke, D. E. Savage, M. G. Lagally, Mark Friesen, S. N. Coppersmith, and M. A. Eriksson, Appl. Phys. Lett. 112, 243107 (2018). [Journal Article | arXiv]
“Fast coherent manipulation of three-electron states in a double quantum dot.” Zhan Shi, C. B. Simmons, D. R. Ward, J. R. Prance, X. Wu, Teck Seng Koh, John King Gamble, D. E. Savage, M. G. Lagally, Mark Friesen, S. N. Coppersmith, and M. A. Eriksson, Nature Comm. 5, 3020 (2014). [Journal Article | arXiv]
“Semiconductor Quantum Dot Qubits.” M. A. Eriksson, S. N. Coppersmith, and M. G. Lagally, MRS Bulletin 38, 794 (2013). [Journal Article]
“Disorder-induced valley-orbit hybrid states in Si quantum dots.” John King Gamble, M. A. Eriksson, S. N. Coppersmith, and Mark Friesen, Phys. Rev. B 88, 035310 (2013). [Journal Article | arXiv]
“Silicon Quantum Electronics.” F. A. Zwanenburg, Andrew S. Dzurak, Andrea Morello, Michelle Y. Simmons, L. C. L. Hollenberg, Gerhard Klimeck, S. Rogge, S. N. Coppersmith, and M. A. Eriksson, Rev. Mod. Phys. 85, 961 (2013). [Journal Article | arXiv]