Volume 119, Number 4, August 2017
|Number of page(s)||7|
|Section||Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties|
|Published online||03 November 2017|
Phonon effects in the excitonic condensation induced in the extended Falicov-Kimball model
1 Graduate University of Science and Technology, Vietnam Academy of Science and Technology 18 Hoang Quoc Viet, Cau Giay, Hanoi, Vietnam
2 Institute of Physics, Vietnam Academy of Science and Technology - 10 Dao Tan, Cau Giay, Hanoi, Vietnam
3 Department of Physics, Hanoi University of Mining and Geology - Duc Thang, Bac Tu Liem, Hanoi, Vietnam
4 Physics Department, Hue University's college of Education - 34 Le Loi, Hue, Vietnam
5 Institute of Research and Development, Duy Tan University - 3 Quang Trung, Danang, Vietnam
Received: 26 May 2017
Accepted: 13 September 2017
A ground state of the excitonic condensate in the 2D extended Falicov-Kimball model involving the coupling of electrons and vibrational degrees of freedom has been investigated. Adapting the unrestricted Hartree-Fock approximation, we have derived a set of explicitly self-consistent equations determining both an excitonic order parameter and a lattice distortion when both the electron-phonon coupling and the electron-electron interaction are treated on an equal footing. A ground-state phase diagram of the excitonic condensate depending on the model parameters is constructed. The phase diagram shows us that a window of the excitonic condensate with lattice distortion increases when increasing the electron-phonon coupling or moving up the f-electron level, whereas, it is confined in between two critical values of the Coulomb interaction. The Coulomb interaction and the electron-phonon coupling have been affirmed to act together in establishing the excitonic condensate phase with lattice distortion in dichalcogenide systems. The BCS-BEC crossover of the excitonic condensation in the systems is also addressed.
PACS: 71.35.Lk – Collective effects (Bose effects, phase space filling, and excitonic phase transitions) / 71.10.Li – Excited states and pairing interactions in model systems / 67.85.Hj – Bose-Einstein condensates in optical potentials
© EPLA, 2017
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