Electron-phonon interactions in local degenerate electronic states in solids
Failid
Kuupäev
2024-06-06
Autorid
Ajakirja pealkiri
Ajakirja ISSN
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Kirjastaja
Abstrakt
Elektronide interaktsioon kristallvõre võnkumistega ehk elektron-foononinteraktsioon määrab tahke keha paljud füüsikalised omadused. Doktoritöö keskendub kristallide lisanditsentritele, kus kaks ergastatud ja sama energiaga elektronolekut (nn kõdunud olekut) on interaktsioonis kahekordselt kõdunud (võrdse energiaga) lokaalse võnkemoodiga (Jahn-Telleri efekt) ja lisaks ka kõigi kahekordselt kõdunud kristallvõre võnkumistega, mille arvuline suurusjärk on ~10²³. Loodud on puhtalt kvantmehhaaniline meetod, mis võimaldab arvutada lisanditsentri interaktsiooni kristallvõre võnkumistega ja kirjeldada olulisi kvantmehhaanilisi efekte. Varasemad arvutusmeetodid suudavad arvesse võtta kuni paarkümmend võnkemoodi, mistõttu pole võimalik kvantmehhaaniliselt kirjeldada näiteks ajaliselt pöördumatuid protsesse. Väljatöötatud meetodit rakendades on arvutatud kristalli lisanditsentri optiline neeldumisspekter ja esimest ja teist järku Ramanhajumise spektrid erinevate interaktsioonitugevuste puhul.
Kõdunud elektron- ja võnkeolekute interaktsioonil tekib süsteemis spontaanne sümmeetria rikkumine ning elektron- ja võnkeolekute segunemine. Spontaanne sümmeetria rikkumine, mis on seotud kõdunud ehk samaväärsete energiaolekutega, on füüsikalise maailma universaalne nähtus, mis peitub paljude aine ja universumi omadusi suunavate protsesside taga. Suure paugu järgse universumi arengut juhtisid erinevat tüüpi spontaansed sümmeetria rikkumised. Selliste süsteemide potentsiaalset energiat saab kirjeldada koonilise lõikumisega potentsiaalipinnaga, mis oluliselt määrab süsteemi evolutsiooni. Täiendav interaktsioon aine oma moodidega suunab relaksatsiooni teatavate konfiguratsioonide suunas ja võimaldab ainetes ergastatud olekute relaksatsiooni põhiolekusse.
Biomolekulides on kõdunud elektron- ja võnkeolekute interaktsioon seotud mitmete oluliste efektidega, näiteks fotosünteesiga. DNA-s põhjustab elektronide ja võnkumiste interaktsioon tümiin aluste omavahelist reageerimist, mis takistab DNA transkriptsiooni ja võib põhjustada vähki. Kuna koonilised potentsiaalipindade lõikumised määravad suuresti molekulaarsüsteemide ja tahkiste fotofüüsikalised ja -keemilised omadused, on nende süsteemide uurimine viimastel aastakümnetel tublisti hoogu juurde saanud.
Kasutades loodud arvutusmeetodit on uuritud ergastatud seisundis Jahn-Telleri efektiga kristalli lisanditsentri kiirgusvaba relaksatsiooni tänu tsentri interaktsioonile kristallvõre võnkumistega. Esmakordselt on visualiseeritud lainefunkstiooni evolutsioon läbi koonilise potentsiaalilõike. Seni on arvatud, et antud protsess toimub femtosekund skaalal, doktoritöö arvutused näitavad aga, et üleminek ergastatud Jahn-Telleri olekust põhiolekusse toimub pikosekund skaalas ja on suunatud teatavate koordinaatide suunas. Lisaks laine funktsiooni evolutsioonile ja energia relaksatsioonile on esmakordselt uuritud ka pöörlemisrelaksatsiooni, mis on seotud pöörlemismomenti omavate võnkekvantide emiteerimisega. Pöörlemise kvanthõõrdumine Jahn-Telleri süsteemis erineb klassikalisest – arvustuste kohaselt võib pöörlemismoment pöörlemise vahefaasides kasvada ja ületada isegi esialgset väärtust. Tegu on ootamatu nähtusega, mis on võimalik kvantsüsteemides.
Lahendatud on ka pikki aastaid vaidluse all olnud Jahn-Telleri E ⊗ e ja Renner-Telleri süsteemi põhioleku sümmeetria ja näidatud selle sõltuvust lineaarse ja ruutvibrooninteraktsiooni tugevustest.
The interaction of electrons with crystal lattice vibrations, or electron-phonon interaction, determines many physical properties of a solid body. The doctoral thesis focuses on the impurity centres of crystals, where the doubly degenerated excited electronic state interacts with the doubly degenerated local vibrational mode (Jahn-Teller system) and in turn with all crystal lattice vibrations, the numerical magnitude of which is ~10²³. For the first time, a purely quantum mechanical theory and corresponding calculations are presented to describe the interaction between the crystal impurity centre and the crystal lattice vibrations and to describe important quantum mechanical effects. Previous computational methods have been able to account for up to a few dozen vibrational modes, making it impossible to describe irreversible processes quantum mechanically. The developed method was used to calculate the absorption spectra of the crystal impurity centre and the first and second-order Raman scattering spectra for various strengths of vibronic interaction. The interaction of degenerate electronic and vibrational states causes spontaneous symmetry breaking and mixing of electronic and vibrational states in the system, including the phonons of the bulk. Spontaneous symmetry breaking associated with degenerate or equivalent energy states is a universal phenomenon in the physical world, underlying many processes that guide the properties of matter and the universe. The development of the post-Big Bang universe was driven by different types of spontaneous symmetry breaking. The potential energy of such systems can be described by the conical intersection of the potential surface. At the same time, the additional interaction of the system with bulk modes directs relaxation towards certain configurations and allows relaxation towards the ground state in excited states of condensed matter. In biomolecules, the interaction of degenerate electronic and vibrational states is associated with several important effects, such as photosynthesis. In DNA, the interaction of electrons and vibrations causes thymine bases to react with each other, preventing DNA transcription and potentially causing cancer. Since conical intersections of potential surfaces largely determine the photophysical and photochemical properties of molecular systems and solids, the study of these systems has gained momentum in recent decades, especially after the development of experimental methods with femtosecond resolution. Using the created calculation method, the radiation-free relaxation of the impurity centre of a crystal with the Jahn-Teller effect in the excited state has been investigated due to the interaction of the centre with vibrations of the crystal lattice. The doctoral dissertation describes the relaxation of quasi-monochromatic and non-selective excitation, and the evolution of the wave function through a conic potential cross-section is visualized for the first time. Until now, it has been assumed that this process occurs on a femtosecond scale; however, the doctoral thesis calculations show that the transition from the excited Jahn-Teller state to the ground state occurs on a picosecond scale. In addition to energy relaxation, rotational relaxation, which is related to the emission of phonons with rotational momentum, has also been studied for the first time. The quantum friction of rotation in the Jahn-Teller system is different from the classical one – according to calculations, the rotational moment can grow in the intermediate stages of the rotation and even exceed the initial value. This is an unexpected phenomenon that is possible in quantum systems. The ground state symmetry of the Jahn-Teller E ⊗ e and Renner-Teller system, which has been in dispute for many years, has also been solved and its dependence on the strengths of the linear and quadratic vibronic interactions has been shown.
The interaction of electrons with crystal lattice vibrations, or electron-phonon interaction, determines many physical properties of a solid body. The doctoral thesis focuses on the impurity centres of crystals, where the doubly degenerated excited electronic state interacts with the doubly degenerated local vibrational mode (Jahn-Teller system) and in turn with all crystal lattice vibrations, the numerical magnitude of which is ~10²³. For the first time, a purely quantum mechanical theory and corresponding calculations are presented to describe the interaction between the crystal impurity centre and the crystal lattice vibrations and to describe important quantum mechanical effects. Previous computational methods have been able to account for up to a few dozen vibrational modes, making it impossible to describe irreversible processes quantum mechanically. The developed method was used to calculate the absorption spectra of the crystal impurity centre and the first and second-order Raman scattering spectra for various strengths of vibronic interaction. The interaction of degenerate electronic and vibrational states causes spontaneous symmetry breaking and mixing of electronic and vibrational states in the system, including the phonons of the bulk. Spontaneous symmetry breaking associated with degenerate or equivalent energy states is a universal phenomenon in the physical world, underlying many processes that guide the properties of matter and the universe. The development of the post-Big Bang universe was driven by different types of spontaneous symmetry breaking. The potential energy of such systems can be described by the conical intersection of the potential surface. At the same time, the additional interaction of the system with bulk modes directs relaxation towards certain configurations and allows relaxation towards the ground state in excited states of condensed matter. In biomolecules, the interaction of degenerate electronic and vibrational states is associated with several important effects, such as photosynthesis. In DNA, the interaction of electrons and vibrations causes thymine bases to react with each other, preventing DNA transcription and potentially causing cancer. Since conical intersections of potential surfaces largely determine the photophysical and photochemical properties of molecular systems and solids, the study of these systems has gained momentum in recent decades, especially after the development of experimental methods with femtosecond resolution. Using the created calculation method, the radiation-free relaxation of the impurity centre of a crystal with the Jahn-Teller effect in the excited state has been investigated due to the interaction of the centre with vibrations of the crystal lattice. The doctoral dissertation describes the relaxation of quasi-monochromatic and non-selective excitation, and the evolution of the wave function through a conic potential cross-section is visualized for the first time. Until now, it has been assumed that this process occurs on a femtosecond scale; however, the doctoral thesis calculations show that the transition from the excited Jahn-Teller state to the ground state occurs on a picosecond scale. In addition to energy relaxation, rotational relaxation, which is related to the emission of phonons with rotational momentum, has also been studied for the first time. The quantum friction of rotation in the Jahn-Teller system is different from the classical one – according to calculations, the rotational moment can grow in the intermediate stages of the rotation and even exceed the initial value. This is an unexpected phenomenon that is possible in quantum systems. The ground state symmetry of the Jahn-Teller E ⊗ e and Renner-Teller system, which has been in dispute for many years, has also been solved and its dependence on the strengths of the linear and quadratic vibronic interactions has been shown.
Kirjeldus
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