Vibronic interaction in crystals with the Jahn-Teller centers in the elementary energy bands concept
| Autor: | S. A. Bercha, D. M. Bercha, M. Sznajder, K. E. Glukhov |
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| Jazyk: | angličtina |
| Rok vydání: | 2015 |
| Předmět: |
Physics
Phase transition Condensed Matter - Mesoscale and Nanoscale Physics Physics and Astronomy (miscellaneous) Jahn-Teller effect Band gap Jahn–Teller effect group theory Ab initio Wyckoff positions FOS: Physical sciences Condensed Matter Physics Potential energy adiabatic potentials lcsh:QC1-999 Crystal Vibronic coupling Mesoscale and Nanoscale Physics (cond-mat.mes-hall) Atomic physics lcsh:Physics Monoclinic crystal system |
| Zdroj: | Condensed Matter Physics, Vol 18, Iss 3, p 33705 (2015) |
| Popis: | The order-disorder type phase transition caused by the vibronic interaction (collective Jahn-Teller effect) in a monoclinic CuInP$_2$S$_6$ crystal is analyzed. For this purpose, a trigonal protostructure model of CuInP$_2$S$_6$ is created, through a slight change in the crystal lattice parameters of the CuInP$_2$S$_6$ paraelectric phase. In parallel to the group-theoretical analysis, the DFT-based {\it ab initio} band structure calculations of the CuInP$_2$S$_6$ protostructure, para-, and ferriphases are performed. Using the elementary energy bands concept, a part of the band structure from the vicinity of the forbidden energy gap, which is created by the $d$-electron states of copper, has been related with a certain Wyckoff position where the Jahn-Teller's centers are localized. A construction procedure of the vibronic potential energy matrix is generalized for the case of crystal using the elementary energy bands concept and the group theoretical method of invariants. The procedure is illustrated by the creation of the adiabatic potentials of the $\Gamma_5$-$\Gamma_5$ vibronic coupling for the protostructure and paraphase of the CuInP$_2$S$_6$ crystal. A structure of the obtained adiabatic potentials is analyzed, followed by conclusions on their transformation under a phase transition and the discussion on the possibility for the spontaneous polarization to arise in this crystal. Comment: 17 pages, 7 figures |
| Databáze: | OpenAIRE |
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