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Coherent tunneling of lithium defect pairs in KCl crystals
Author(s) -
Weis R.,
Enss C.,
Würger A.,
Luty F.
Publication year - 1997
Publication title -
annalen der physik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.009
H-Index - 68
eISSN - 1521-3889
pISSN - 0003-3804
DOI - 10.1002/andp.19975090402
Subject(s) - quantum tunnelling , degenerate energy levels , impurity , ion , physics , lithium atom , condensed matter physics , lithium (medication) , dipole , atomic physics , molecular physics , quantum mechanics , ionization , medicine , endocrinology
The tunneling of two lithium ion impurities on next‐nearest neighbor sites in potassium chloride are investigated both experimentally and theoretically. The strong dipolar interaction leads to coherent tunneling motion of the two defect ions between degenerate off‐center positions. Comparing data of rotary echo experiments for impurity pairs 7 Li— 7 Li, 6 Li— 6 Li, and 7 Li— 6 Li with theory permits a thorough investigation of the isotope effect and of the effect of the interaction on the tunnel states. Our findings confirm the tunneling model with <111> off‐center states to be valid even for strongly interacting impurities. Using degenerate perturbation theory in terms of two‐particle states, we obtain essentially exact expressions for the tunneling spectrum and the dynamical susceptibility which agree well with the measured data.