Neadijabatska renormalizacija optičkih fonona u visoko dopiranom grafenu

master's thesis

• Title (english): Non-adiabatic phonons in highly-doped graphene
• Author: Nina Girotto
• Mentor: Dino Novko (mentor)
• Mentor: Hrvoje Buljan (komentor)
• Committee member: Hrvoje Buljan (predsjednik povjerenstva)
• Committee member: Dino Novko (član povjerenstva)
• Committee member: Mario Novak (član povjerenstva)
• Committee member: Ivan Kupčić (član povjerenstva)
• Committee member: Željko Skoko (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2020-07-09, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

U ovom radu, ispituje se valjanost upotrebe adijabatske Born-Oppenheimer aproksimacije kod opisa interakcije elektrona i jezgara u visoko dopiranom grafenu. Usporedbom rezultata modela čvrste veze i teorije funkcionala gustoće (DFT) za disperziju fonona dopiranog grafena, pokazuje se da adijabatski tretman fonona dovodi do velike renormalizacije E_2g fononskog moda u Γ točki, što nije ispravan rezultat. Kako bi se dobio ispravan vibracijski spektar, potrebno je uključiti dinamičke (neadijabatske) efekte elektron-fonon interakcije. Oni izazivaju velike promjene u dugovalnom dijelu vibracijskog spektra. Neadijabatska korekcija dobivena je kroz vlastitu energiju fonona, a efekt je dokazan i u DFT-u izračunom elektron-fonon interakcije. Metoda je zatim primijenjena na dopirani grafan. Dinamički efekti u dopiranom grafanu izraženiji su nego u dopiranom grafenu.

Abstract (english)

In this seminar the validity of an adiabatic Born-Oppenheimer approximation in the description of electron-phonon interactions in highly doped graphene is examined. Comparing the tight - binding approximation model results and the ones obtained within density functional theory (DFT), it is shown that an adiabatic treatment of phonons leads to a huge renormalization of the E_2g phonon mode in the Brillouin zone center, which is an incorrect result. In order to obtain a correct vibration spectrum, dynamical (nonadiabatic) effects of an electron-phonon interaction should be taken into account. They produce non-negligible changes in the long-wave part of the spectrum. Nonadiabatic correction is obtained through phonon self-energy calculation, while its effect is proved also within a DFT calculation of electron-phonon interaction parameters. This method is then applied to doped graphane. Dynamical effects in doped graphane are more pronounced than in doped graphene.

• Keywords: grafen; fononi; Born-Oppenheimer aproksimacija; DFT; Wannierove funkcije; elektron-fonon interakcija; grafan
• Keywords (english): graphene; phonons; Born-Oppenheimer approximation; DFT; Wannier functions; electron-phonon interaction; graphane
• Language: croatian
• URN:NBN: urn:nbn:hr:217:806183
• Study programme: Title: Physics; specializations in: Research; Course: Research; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: magistar/magistra fizike (magistar/magistra fizike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2020-08-21 12:05:16