Abstract
Alkali-doped fullerides show a wide range of electronic phases in function of alkali atoms and the degree of doping. Although the presence of strong electron correlations is well established, recent investigations also give evidence for dynamical Jahn–Teller instability in the insulating and the metallic trivalent fullerides. In this work, to reveal the interplay of these interactions in fullerides with even electrons, we address the electronic phase of tetravalent fulleride with accurate many-body calculations within a realistic electronic model including all basic interactions extracted from first principles. We find that the Jahn–Teller instability is always realized in these materials too. In sharp contrast to the correlated metals, tetravalent system displays uncorrelated band-insulating state despite similar interactions present in both fullerides. Our results show that the Jahn–Teller instability and the accompanying orbital disproportionation of electronic density in the degenerate lowest unoccupied molecular orbital band is a universal feature of fullerides.
Highlights
Alkali-doped fullerides show a wide range of electronic phases in function of alkali atoms and the degree of doping
The same para dynamical JT effect was found in the metallic phase of A3C60 close to MH transition, whereas the pseudorotation of JT deformation at different sites are expected to be correlated with further departure from the MH transition due to the increase of the band energy[30]
It is well established that the t1u lowest unoccupied molecular orbital (LUMO) band mainly defines the electronic properties of fullerides[1]
Summary
Alkali-doped fullerides show a wide range of electronic phases in function of alkali atoms and the degree of doping. The same para dynamical JT effect was found in the metallic phase of A3C60 close to MH transition, whereas the pseudorotation of JT deformation at different sites are expected to be correlated with further departure from the MH transition due to the increase of the band energy[30] These findings have found confirmation in a very recent investigation of Cs3C60 fulleride, showing an almost unchanged infrared spectrum on both sides in the vicinity of MH metal– insulator transition, whereas displaying its significant variation when the material was brought deeper into the metallic phase[31]. Our calculations have shown that the metallic phase in these systems exhibits an orbital disproportionation of electronic density as a result of the dynamical JT instability[30] This successful theoretical approach is applied here for the investigation of the electronic phase in the A4C60 fullerides, containing an even number of doped electrons per site. As in A3C60, the ground state of A4C60 displays again the orbital disproportionation of electronic density, identifying it as a universal key feature of the electronic phases of alkali-doped fullerides
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