Thesis focus on the problem of “Excitonic condensation in semimetal – semiconductor transition systems” to investigate the nature of the excitonic condensation state in these models by using MF theory. Electronic correlation in the systems is described by the two-band model including electron – phonon interaction and the extended Falicov-Kimball model involving electron – phonon interaction. | MINISTRY OF EDUCATION VIETNAM ACADEMY OF SCIENCE AND TRAINING AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY - DO THI HONG HAI EXCITONIC CONDENSATION IN SEMIMETAL SEMICONDUCTOR TRANSITION SYSTEMS Major Theoretical Physics and Maths Physics Code SUMMARY OF PHYCICS DOCTORAL THESIS Hanoi 2020 The thesis has been completed at Graduate University of Science and Technology Vietnam Academy of Science and Technology. Supervisor 1 . Phan Van Nham Supervisor 2 . Tran Minh Tien Reviewer 1 Reviewer 2 Reviewer 3 The thesis will be defended to the thesis committee for the Doctoral Degree at Graduate University of Science and Technology Vietnam Academy of Science and Technology on 2020. Hardcopy of the thesis can be found at - Library of Graduate University of Science and Technology - National Library of Vietnam. INTRODUCTION 1. Motivation The condensate state of the electron-hole pairs or excitons has recently become one of the attractive research objects. Electrons and holes have semi-integer spin so the excitons act as bosons and if the temperature is sufficiently low these excitons can condense in a new macroscopic phase-coherent quantum state called an excitonic insulator EI. Although first theoretical of the excitonic condensation state in the semimetal SM and semiconductor SC systems was proposed over a half of century ago but the experimental realization has proven to be quite challenging. In recent years materials promising to observe EI state have been investigated such as mixed-valent rare-earth chalcogenide transition-metal dichalcogenide 1T -TiSe2 semiconductor Ta2 NiSe5 layer double graphene . which have increased the studies of the excitonic condensation state both the theoretical side and the experimental side. On the theoretical side the excitonic condensation state is often studied through investi- gating the extended Falicov-Kimball model by many different methods such as the .
