Mechanism of superconductivity in K3C60.

Abstract

Using electronic states and phonon states from the first-principles calculations and including both conventional electron-phonon charge coupling and Jahn-Teller coupling, we predict Tc and other superconducting properties.The only adjustable parameter in the theory is the screening length, R. Using Rsc = 0.8-1.0 A, we rind excellent agreement with experiment for Tc (16-18 K)

Doped Semimetal Clusters: Ternary, Intermetalloid Anions [Ln@Sn7Bi7]4– and [Ln@Sn4Bi9]4– (Ln = La, Ce) with Adjustable Magnetic Properties

“…In the recent past, the concept of metal doping has also been discussed for molecular compounds, in so-called endohedral clusters, such as metallofullerenes . Alkali metals as well as lanthanide ions inserted into the crystal structure or encapsulated inside carbon cages, respectively, caused significant changes in chemical and physical properties, such as metallic or superconducting characteristics for solid state M x C 60 (M = K, x = 3) and different magnetic properties for Ln@C 82 (Ln = La, Eu, Gd), upon variation of the interstitial lanthanide ion …”

The role of electron–vibron interaction and local pairing in conductivity and superconductivity of alkali-doped fullerides

“…exp(− H/T ) denotes averaging procedure where Ξ is a partition function. The effective Hamiltonian (12) does not account Coulomb correlations between electrons on neighboring sites, therefore to study conduction or insulation of the material we should proceed from the full Hamiltonian (1). The on-site Coulomb repulsions U, U , the on-site exchange interaction energy J and the Coulomb repulsion between neighboring sites V determine the change of energy at transfer of an electron from a site to a nearby site.…”

“…The positive correlation between T c and the lattice constant found in K-and Rb-doped fullerides has been understood in terms of the standard BCS theory: the density of states of conduction electrons is ν ∝ 1/W , and T c = 1.14 ω exp(−1/λν), thus the smaller W the large T c . Therefore superconductivity of A 3 C 60 is often described with Eliashberg theory in terms of electron-phonon coupling and Tolmachev's pseudopotential µ * [11][12][13]. In the same time there is another approach to describe phases of alkali-doped fulleride -the model of local pairing [14][15][16][17][18].…”

“…The positive correlation between T c and the lattice constant found in K-and Rb-doped fullerides has been understood in terms of the standard BCS theory. Therefore superconductivity of A 3 C 60 is often described with Eliashberg theory in terms of electron-phonon coupling and Tolmachev's pseudopotential µ * [1][2][3]. However this material shows a surprising phase diagram [4], in which a high transition temperature of s-wave superconducting state emerges next to a Mott insulating phase as a function of the lattice spacing.…”

Renormalization-group approach to the Coulomb pseudopotential forC60

“…Experimental evidence [5][6][7][8][9][10], supported by numerous phonon calculations [11][12][13][14][15][16][17][18], indicates that some of the intraball phonon modes are very high in energy and sufficiently strongly coupled to the electrons to account for these high T c s. Most of the phonon calculations assume that the Coulomb repulsion between the electrons comprising a pair are small, as they are in a usual metallic superconductor. (Effective Coulomb interactions are typically parameterized by a dimensionless number µ * = N(E F )U * [19], where N(E F ) is the density of states at the Fermi Surface (FS) and U * is an effective interaction matrix element between electrons at the FS.…”