Alkali-Doped Fullerides: Narrow-Band Solids with Unusual by Olle Gunnarsson

By Olle Gunnarsson

Alkali-doped fullerides have attracted powerful curiosity in view that their construction turned attainable approximately fifteen years in the past. This booklet offers fresh paintings which could remedy fascinating difficulties coming up from a number of awesome houses. for instance, those solids are superconductors with excessive transition temperatures, even though the similarity among the digital and phonon strength scales may still suppress superconductivity. additionally, the Ioffe–Regel for electric conductivity is strongly violated. The e-book exhibits why superconductivity is however attainable, due to an area pairing mechanism. The Ioffe–Regel situation is derived quantum-mechanically, and it's defined why the underlying assumptions are violated for fullerides and high-Tc cuprates, for instance. The e-book treats digital and delivery homes, reviewing theoretical and experimental effects. It makes a speciality of superconductivity, electric conductivity and metal–insulator transitions, emphasizing the electron–electron and electron–phonon interactions in addition to the Jahn–Teller influence.

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In addition, multiplet effects will sometimes be considered as discussed below. The Hubbard model in Eq. 20) should be distinguished from a Hubbard model sometimes used to describe a free Ceo molecule. In the latter model, each site is a C atom, while in the Hubbard model above, each site is a Ceo molecule. As discussed at the end of Sec. 20) for an A3C60 solid is reasonable, since the nearest neighbor interaction V, neglected in the model, is substantially smaller than the on-site interaction U, included in the model.

Below, we give some simple estimates of the matrix elements d m m -. To obtain the current operator, we now calculate the commutator in Eq. 59). We first consider P ' 1 ' . This operator commutes with HQ in Eq. 54). We therefore consider the commutator with T. [T,P^] =e X (R-i-Ri)<«mjW^L^,Wa- (2-63) ijmm a This leads to the current operator jU) = J l J2 (i^j)mm (R« - R,-) W ' V L ^ i m V (2-64) a The operator P ^ commutes with Hubbard [Eq. 20)], Coulomb multiplet [Eq. 34)] or electron-phonon interaction [Eq.

30) where R is the nearest neighbor separation and —SV is the lowering of the tiu orbital on molecule 1 due to the polarization of the surrounding molecules when an electron is added to molecule 2. 3 for the polarizability a=90 A 3 . In this case the effects of the finite size of the molecules on the screening is small. 3 eV was also obtained by Pederson and Quong. 33 We can see that U is indeed substantially larger than V, and that it is justified to focus on the effects of U at first. In general, we nevertheless expect that the more long-range Coulomb interaction will also play a role, for instance for plasmons, discussed in Chapter 6.

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