20.500.12556/RUL-154235 Študija kovinskega stanja Yb$_2$AC$_{60}$ (A=K, Rb, Cs) z metodo jedrske magnetne resonance Study of metallic state Yb$_2$AC$_{60}$ (A=K, Rb, Cs) with a nuclear magnetic resonance method Superprevodnost, Jahn-Tellerjev pojav in Mottovo izolatorsko stanje so le tri izmed širšega nabora faz, ki so prisotne v faznem diagramu alkalijskih fuleridov A$_3$C$_{60}$ (A=Na, K, Rb, Cs). Osnovni cilj te magistrske naloge pa je raziskati dopirane fulerene, pri katerih se odmaknemo od polovične zasedenosti prevodnega pasu. V tem magistrskem delu smo proučevali spojine Yb$_2$AC$_{60}$ (A= K, Rb, Cs) z metodo jedrske magnetne resonance (NMR). Poznavanje strukture molekulskih orbtal $t_{1u}$, ki tvorijo elektronski pas, nam da namig, da so spojine kovinske. Z jedrsko magnetno resonanco smo pri temperaturnem razponu od 20 K do 340 K izmerili $^{13}$C NMR spektre in tako dobili vpogled v širino na polovični širini in relativni premik $^{13}$C NMR frekvence. Prav tako smo določili spinsko mrežne relaksacijske čase $T_1$ za vse tri spojine pri različnih temperaturah. Temperaturno neodvisni premik $^{13}$C NMR spektrov ter $\frac{1}{T_1T}$ parametra kažeta na kovinsko stanje z majhno gostoto stanj na Fermijevi energiji raziskovanih spojin. Poleg tega smo opazili večanje vrednosti $\frac{1}{T_1T}$ nad približno 200 K. To namiguje na dodaten mehanizem, ki prispeva k spinsko-mrežni relaksaciji in predlagan razlog je intrinzična C$_{60}^{5-}$ dinamika. Okrepitev spinsko-mrežne relaksacije je možno opisati znotraj Bloembergen-Purcell-Pound (BPP) modela, iz katerega smo izluščili frekvence $\tau_0$ in aktivacijske energije $E_a$ za opis intrinzične dinamike. Vrednosti $E_a$ se gibljejo v razponu med 62 meV do 106 meV in so primerljive vrednostim za Jahn-Teller dinamiko nekaterih drugih alkalijskih fuleridov. Superconductivity, the Jahn-Teller phenomenon, and Mott’s insulating state are just three of the broader range of phases present in the phase diagram of alkali metal fullerides A$_3$C$_{60}$ (A=Na, K, Rb, Cs). The primary goal of this master’s thesis is to investigate doped fullerenes where we deviate from half-occupancy of the conduction band. In this master’s work, we examined compounds Yb$_2$AC$_{60}$ (A=K, Rb, Cs) using nuclear magnetic resonance (NMR) as the method. Understanding the structure of molecular orbitals $t_{1u}$, forming the electronic band, suggests metallic properties of the compounds. With nuclear magnetic resonance, we measured $^{13}$C NMR spectra in the temperature range from 20 K to 340 K, providing insights into the half-width and relative shift of $^{13}$C NMR frequency. Additionally, we determined spin lattice relaxation times $T_1$ for all three compounds at various temperatures. Temperature-independent shifts of $^{13}$C NMR spectra and the $\frac{1}{T_1T}$ parameter indicate a metallic state with a low density of states at the Fermi energy for the studied compounds. Moreover, an increase in $\frac{1}{T_1T}$ values above approximately 200 K suggests an additional mechanism contributing to spin-lattice relaxation, attributed to intrinsic C$_{60}^{5-}$ dynamics. The reinforcement of spin-lattice relaxation is describable within the Bloembergen-Purcell-Pound (BPP) model, from which we extracted frequencies $\tau_0$ and activation energies $E_a$ to describe intrinsic dynamics. The values of $E_a$ range from 62 meV to 106 meV and are comparable to the values for Jahn-Teller dynamics in some other alkali metal fullerides. Jedrska magnetna resonanca alkalijski fuleridi spinskomrežni relaksacijski čas Korringa relacija molekularna dinamika Bloembergen-Purcell-Pound model Nuclear magnetic resonance alkali fullerides spin-lattice relaxation time Korringa relation molecular dynamics BPP model true false false Slovenski jezik Angleški jezik Magistrsko delo/naloga 2024-02-03 08:15:04 2024-02-03 08:15:14 2024-03-05 10:38:09 0000-00-00 00:00:00 2024 0 0 0000-00-00 NiDoloceno NiDoloceno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 139708 187705091 12013.pdf 12013.pdf 1 34FD62EB9382FC4D8DBDDE1BA8E211B6 dc06ceeb7c33f2153dd0f02e9d58273094b8c021252f84a5009daf384bbb32a2 fa7de93d-c263-11ee-a87c-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=180517 Fakulteta za matematiko in fiziko 0 0 0