Photoemission Spectra of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup><mml:mrow><mml:mi>C</mml:mi></mml:mrow><mml:mrow><mml:mn>60</mml:mn></mml:mrow><mml:mrow><mml:mspace /><mml:mo>−</mml:mo></mml:mrow></mml:msubsup></mml:mrow></mml:math>: Electron-Phonon Coupling, Jahn-Teller Effect, and Superconductivity in the Fullerides

Gunnarsson, O.; Handschuh, H.; Bechthold, P. S.; Keßler, Barbara; Ganteför, Gerd; Eberhardt, W.

doi:10.1103/physrevlett.74.1875

Cited by 230 publications

(224 citation statements)

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“…7. Gunnarsson et al, 1995 It is interesting that the component with the largest shift relative to the position in the undoped crystal also has the largest width. This suggests that the different components have different electron-phonon couplings.…”

Section: Raman and Neutron Scatteringmentioning

confidence: 99%

“…Gunnarsson et al, (1995) calculated the gap using the Eliashberg equation in the model discussed above, using the couplings deduced from photoemission. They obtained the values 2∆/T c = 3.59 and 3.66 for K 3 C 60 and Rb 3 C 60 , respectively.…”

Section: Reduced Gapmentioning

confidence: 99%

“…For values of λ in the upper range of the estimates, the rather large values of T c can be understood even if it is assumed that the inefficient renormalization of µ * by retardation effects in the fullerides leads to substantially larger µ * than for conventional superconductors. For instance, Gunnarsson et al (1995) solved the Eliashberg equation, using the coupling constants deduced from photoemission for a free C − 60 molecules (see Sec. III.A.4), a t 1u band with the width 1/2 eV and the density of states at the Fermi energy deduced from NMR (see, Sec.…”

Section: Calculated Properties a Transition Temperaturementioning

confidence: 99%

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Superconductivity in fullerides

1997

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Experimental studies of superconductivity properties of fullerides are briefly reviewed. Theoretical calculations of the electron-phonon coupling, in particular for the intramolecular phonons, are discussed extensively. The calculations are compared with coupling constants deduced from a number of different experimental techniques. It is discussed why the A 3 C 60 are not Mott-Hubbard insulators, in spite of the large Coulomb interaction. Estimates of the Coulomb pseudopotential µ * , describing the effect of the Coulomb repulsion on the superconductivity, as well as possible electronic mechanisms for the superconductivity are reviewed. The calculation of various properties within the Migdal-Eliashberg theory and attempts to go beyond this theory are described.

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Section: Raman and Neutron Scatteringmentioning

confidence: 99%

Section: Reduced Gapmentioning

confidence: 99%

Section: Calculated Properties a Transition Temperaturementioning

confidence: 99%

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Superconductivity in fullerides

1997

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“…On the basis on these numbers, we have computed the ground-state energy gain in the approximation (27), and we report it in Table II, along with the corresponding values in the effective-mode scheme, as presented in Ref. [14], and with the exact result, obtained by Lanczos diagonalization [17,18].…”

Section: Many Modes T ⊗ (N H)mentioning

confidence: 99%

Exact zero-point energy shift in thee⊗(nE),t⊗(nH)many-modes dynamic Jahn-Teller systems at strong coupling

Manini

Tosatti

1998

Phys. Rev. B

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We find the exact semiclassical (strong coupling) zero-point energy shifts applicable to the e ⊗ (n E) and t ⊗ (n H) dynamic Jahn-Teller problems, for an arbitrary number n of discrete vibrational modes simultaneously coupled to one single electronic level. We also obtain an analytical formula for the frequency of the resulting normal modes, which has an attractive and apparently general Slater-Koster form. The limits of validity of this approach are assessed by comparison with O'Brien's previous effective-mode approach, and with accurate numerical diagonalizations. Numerical values obtained for t ⊗ (n H) with n = 8 and coupling constants appropriate to C − 60 are used for this purpose, and are discussed in the context of fullerene.

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“…That's a tall order, because, while the frequencies of the H g modes are known from experiments, and different calculations of JT energy E JT more or less agree, the individual values of the coupling constants with the t 1u electrons are hard to establish [34] without resorting to photoemission experiment [35]. Also questionable is whether the simple linear coupling to vibrations, as usually assumed, is sufficient, as has been pointed out [36, 37].…”

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confidence: 99%

Cooling quasiparticles in A3C60 fullerides by excitonic mid-infrared absorption

et al. 2017

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Long after its discovery superconductivity in alkali fullerides A 3 C 60 still challenges conventional wisdom. The freshest inroad in such ever-surprising physics is the behaviour under intense infrared (IR) excitation. Signatures attributable to a transient superconducting state extending up to temperatures ten times higher than the equilibrium T c ∼ 20 K have been discovered in K 3 C 60 after ultra-short pulsed IR irradiation -an effect which still appears as remarkable as mysterious. Motivated by the observation that the phenomenon is observed in a broad pumping frequency range that coincides with the mid-infrared electronic absorption peak still of unclear origin, rather than to TO phonons as has been proposed, we advance here a radically new mechanism. First, we argue that this broad absorption peak represents a "super-exciton" involving the promotion of one electron from the t 1u half-filled state to a higher-energy empty t 1g state, dramatically lowered in energy by the large dipole-dipole interaction acting in conjunction with Jahn Teller effect within the enormously degenerate manifold of t 1u 2 t 1g 1 states. Both long-lived and entropy-rich because they are triplets, the IR-induced excitons act as a sort of cooling mechanism that permits transient superconductive signals to persist up to much larger temperatures.Superconducting alkali doped fullerenes A 3 C 60 are molecular compounds where several actors play together to determine an intriguing physical behaviour. The high icosahedral symmetry of C 60 arXiv:1704.05613v1 [cond-mat.str-el] 19 Apr 2017 2 implies, prior to intermolecular hybridisation, a large degeneracy of the molecular orbitals, thus a strong electronic response to JT molecular distortions lowering that symmetry. In particular, the t 1u LUMO, which accommodates the three electrons donated by the alkali metals, is threefold degenerate and JT coupled to eight fivefold-degenerate molecular vibrations of H g symmetry, which mediate the pairing [1]. The JT effect, favouring low spin, is partly hindered by (Coulomb) Hund's rule exchange, which favours high spin. Therefore the overall singlet pairing strength g, though still sizeable, is way too small compared to the charging energy of each C 3− 60 to justify by simple arguments why A 3 C 60 are s-wave superconductors. The explanation of this puzzle proposed in [2,3] and vindicated by recent experiments emphasises the crucial role of a parent Mott insulating state where the JT coupling effectively inverts Hund's rules, the molecular ground state therefore turning to spin S = 1/2 rather than S = 3/2 [4]. A S = 1/2 antiferromagnetic insulating phase is indeed the ground state in over-expanded NH 3 K 3 C 60 [5,6] and in Cs 3 C 60 [7] at ambient pressure. In the metallic state, attained under pressure in Cs 3 C 60 and at ambient pressure in K 3 C 60 and Rb 3 C 60 , the incipient Mott localisation slows down the coherent motion of quasiparticles while undressing them from charge correlations. As a result, the singlet pairing strength g eventual...

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Photoemission Spectra ofC60−: Electron-Phonon Coupling, Jahn-Teller Effect, and Superconductivity in the Fullerides

Cited by 230 publications

References 31 publications

Superconductivity in fullerides

Superconductivity in fullerides

Exact zero-point energy shift in thee⊗(nE),t⊗(nH)many-modes dynamic Jahn-Teller systems at strong coupling

Cooling quasiparticles in A3C60 fullerides by excitonic mid-infrared absorption

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