Strongly Correlated Superconductivity

Capone, Massimo; Fabrizio, Michele; Castellani, C.; Tosatti, Erio

doi:10.1126/science.1071122

Cited by 260 publications

(304 citation statements)

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“…Analysis of a simple model (1) revealed a stunning variety of phases in the immediate neighborhood of the Mott metal-insulator transition near half filling. The variety is greater than either that predicted for the three band case fullerides [14], or that experimentally known in fullerides [2] as well as in doped organics (with lower symmetry than MPcs) near half filling [1]. Many of the phases described above will individually merit an in-depth study.…”

Section: Pacs Numbersmentioning

confidence: 85%

“…[7,8]. It was also suggested [7,14] -although without a calculation of T c -that SCS is a "high temperature superconductor" in the sense that the SCS superconducting gap may reach values several orders of magnitudes greater than the corresponding BCS value (that would be attained for U = 0), ∆ BCS ∼hω 0 e −1/λ , where λ = 2ρ 0 |J ef f |, ρ 0 is the density of states at the Fermi level per spin and band.…”

Section: Pacs Numbersmentioning

confidence: 99%

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Strong Correlations in Electron Doped Phthalocyanine Conductors Near Half Filling

et al. 2004

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We propose that electron doped nontransition metal-phthalocyanines (MPc) like ZnPc and MgPc, similar to those very recently reported, should constitute novel strongly correlated metals. Due to orbital degeneracy, Jahn-Teller coupling and Hund's rule exchange, and with a large on-site Coulomb repulsion, these molecular conductors should display, particularly near half filling at two electrons/molecule, very unconventional properties, including Mott insulators, strongly correlated superconductivity, and other intriguing phases. PACS numbers:Building novel metals by doping molecular crystals such as polyacetylene, fullerenes, TTF-TCNQ, (TMTSF) 2 X, (TMTTF) 2 X and (BEDT-TTF) 2 X salts, etc., is a well trodden route [1,2], but remains an exciting and ever moving front. Very recently the Delft group showed that thin films of transition metal phthalocyanines (MPcs) FePc, CoPc, NiPc, CuPc, initially insulating, can be turned genuinely metallic through potassium doping [3]. Electron doping appears to take place largely in the twofold degenerate lowest unoccupied e g molecular orbital (LUMO) [4,5] of the molecules. The simplest rigid band model naturally explains, according to [3], why the MPcs, initially insulating when pristine (n = 0) [6], become metallic upon increasing doping (0 < n < 4), ending up again as insulators at full doping (n = 4). It is not yet clear whether stoichiometric compound phases may exist here as they do in alkali doped fullerides, but there is an otherwise striking overall analogy, to the point that even the conductance values reported at optimal metallic doping are close in magnitude and temperature (in)dependence to those of K x C 60 films.While the pursuit of metallicity-cum-magnetism in the transition metal doped MPcs [5] will in the future constitute an interesting goal in itself, the scope of this note is to point out newer directions and possibilities that can make slightly different metallic doped MPcs, yet to be realized, potentially even more exciting. Doped MPcs are not, we claim, regular metals, but constitute strongly correlated electron systems, akin to doped two-band Mott insulators. Characterized by a strong on-site electron repulsion, by the e g orbital degeneracy, and by intra-site Jahn-Teller and electron-electron multiplet couplings, the doped MPc molecular system should approach near n = 2, as foreshadowed by recent studies [7,8,9] a novel unstable fixed point heralding a wealth of possible low-temperature phenomena and phases. We conduct in this letter a preliminary exploration of this scenario by addressing theoretically -and thus proposing the experimental realization of -new metals obtained through electron doping of ZnPc, MgPc and other such non-transition metal MPcs. The extra electrons should flow into the MPc 2e g lowest unoccupied molecular orbital (LUMO) [4], to form a two band metal. The LUMO states are ligand shell orbitals loosely surrounding the central metal ion, with a large intramolecular Coulomb repulsion U in comparison with the narrow electron bandwidth...

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Section: Pacs Numbersmentioning

confidence: 85%

Section: Pacs Numbersmentioning

confidence: 99%

Strong Correlations in Electron Doped Phthalocyanine Conductors Near Half Filling

et al. 2004

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“…Theoretical calculations to explain the insulating and superconducting properties of bulk fullerene materials fall into two major categories: molecular level calculations which determine the effective interactions of intramolecular electrons, 4,5,6,7,8,9,10,11 and lattice level calculations based on an effective Hamiltonian in which the intramolecular degrees of freedom have been integrated out. 12,13,14 Although much of the work has focused on the phonon mechanism for superconductivity in the alkali-C 60 's, some authors have proposed a purely electronic mechanism. In particular, it was argued by Chakravarty, Kivelson and co-workers (CK) that electronic interactions within a single C 60 molecule can lead to an effective attraction between charge carriers.…”

Section: Introductionmentioning

confidence: 99%

Quantum Monte Carlo calculation of the electronic binding energy in aC60molecule

et al. 2005

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Electronic energies are calculated for a Hubbard model on the C60 molecule using projector quantum Monte Carlo (QMC). Calculations are performed to accuracy high enough to determine the pair binding energy for two electrons added to neutral C60. The method itself is checked against a variety of other quantum Monte Carlo methods as well as exact diagonalization for smaller molecules. The conclusion is that the ground state with two extra electrons on one C60 molecule is a triplet and, over the range of parameters where QMC is reliable, has a slightly higher energy than the state with electrons on two separate molecules, so that the pair is unbound.

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“…In such a state, the coupling between localized fermions and bosonic excitations, which is mediated by charge dynamics, is naively expected to be strongly suppressed 16,17 .…”

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confidence: 99%

Witnessing the formation and relaxation of dressed quasi-particles in a strongly correlated electron system

et al. 2014

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The non-equilibrium approach to correlated electron systems is often based on the paradigm that different degrees of freedom interact on different timescales. In this context, photo-excitation is treated as an impulsive injection of electronic energy that is transferred to other degrees of freedom only at later times. Here, by studying the ultrafast dynamics of quasi-particles in an archetypal strongly correlated charge-transfer insulator (La 2 CuO 4 þ d ), we show that the interaction between electrons and bosons manifests itself directly in the photo-excitation processes of a correlated material. With the aid of a general theoretical framework (Hubbard-Holstein Hamiltonian), we reveal that sub-gap excitation pilots the formation of itinerant quasi-particles, which are suddenly dressed by an ultrafast reaction of the bosonic field.

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Strongly Correlated Superconductivity

Cited by 260 publications

References 20 publications

Strong Correlations in Electron Doped Phthalocyanine Conductors Near Half Filling

Strong Correlations in Electron Doped Phthalocyanine Conductors Near Half Filling

Quantum Monte Carlo calculation of the electronic binding energy in aC60molecule

Witnessing the formation and relaxation of dressed quasi-particles in a strongly correlated electron system

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