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Electron Dynamics of Crystalline 4-He at High Pressures



Eric L. Shirley, H. K. Mao, Yang Ding, Peter Eng, Yong Q. Cai, Paul Chow, Yuming Xiao, Jinfu Shu, Russell J. Hemley, Chichang Kao, Wendy L. Mao


At high pressures, helium crystallizes as a unique insulator with the widest known electronic band gap. However, in the vicinity of the band gap and above, electronic excitations have been previously inaccessible to direct measurements. Using an optimized inelastic X-ray scattering spectroscopy technique, we have succeeded in probing the electronic structure of single-crystal 4He in a high-pressure diamond-anvil cell. At 13.4 GPa, we observed the full electron excitation spectrum, including a cut-off edge near 23.3 eV, a sharp exciton peak, and a series of excitation peaks at 26 eV to 45 eV. We determined the excitonic dispersion in the Gamma-M direction over two Brillouin zones. Measurements at 11.9 GPa to 17 GPa show a strong linear dependence of the Gamma-point exciton energy and the 4He molar volume under compression. The agreement between our experimental results and ab initio calculations supports use of the theoretical approach for studying system under extreme environments beyond current experimental limits.
Nature Physics


crystalline, diamond anvil cell, exciton, helium, x-ray


Shirley, E. , Mao, H. , Ding, Y. , Eng, P. , Q., Y. , Chow, P. , Xiao, Y. , Shu, J. , Hemley, R. , Kao, C. and Mao, W. (2010), Electron Dynamics of Crystalline 4-He at High Pressures, Nature Physics (Accessed May 20, 2024)


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Created October 29, 2010, Updated May 7, 2018