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Unified understanding of superconductivity and Mott transition in alkali-doped fullerides from first principles.

Nomura Y, Sakai S, Capone M, Arita R - Sci Adv (2015)

Bottom Line: More remarkably, the critical temperatures T c's calculated from first principles quantitatively reproduce the experimental values.The driving force behind the surprising phase diagram of A 3C60 is a subtle competition between Hund's coupling and Jahn-Teller phonons, which leads to an effectively inverted Hund's coupling.Our results establish that the fullerides are the first members of a novel class of molecular superconductors in which the multiorbital electronic correlations and phonons cooperate to reach high T c s-wave superconductivity.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Physics, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.

ABSTRACT
Alkali-doped fullerides A 3C60 (A = K, Rb, Cs) are surprising materials where conventional phonon-mediated superconductivity and unconventional Mott physics meet, leading to a remarkable phase diagram as a function of volume per C60 molecule. We address these materials with a state-of-the-art calculation, where we construct a realistic low-energy model from first principles without using a priori information other than the crystal structure and solve it with an accurate many-body theory. Remarkably, our scheme comprehensively reproduces the experimental phase diagram including the low-spin Mott-insulating phase next to the superconducting phase. More remarkably, the critical temperatures T c's calculated from first principles quantitatively reproduce the experimental values. The driving force behind the surprising phase diagram of A 3C60 is a subtle competition between Hund's coupling and Jahn-Teller phonons, which leads to an effectively inverted Hund's coupling. Our results establish that the fullerides are the first members of a novel class of molecular superconductors in which the multiorbital electronic correlations and phonons cooperate to reach high T c s-wave superconductivity.

No MeSH data available.


Related in: MedlinePlus

Frequency dependence of effective onsite interactions.The effective intra- and interorbital interactions (Ueff = U + UV + Uph and U′eff = U′ + U′V + U′ph, respectively) consist of the constrained random-phase approximation (cRPA) onsite Coulomb repulsion (U, U′), the dynamical screening from the off-site interactions (UV = U′V), and the phonon-mediated interactions (Uph, U′ph). The data are calculated for Cs3C60 with  at 40 K. We assume the cRPA Coulomb interactions to be static, whose validity is substantiated in Section B in the Supplementary Materials. Inset: Frequency dependence of Ueff and U′eff along the Matsubara frequency axis.
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Figure 3: Frequency dependence of effective onsite interactions.The effective intra- and interorbital interactions (Ueff = U + UV + Uph and U′eff = U′ + U′V + U′ph, respectively) consist of the constrained random-phase approximation (cRPA) onsite Coulomb repulsion (U, U′), the dynamical screening from the off-site interactions (UV = U′V), and the phonon-mediated interactions (Uph, U′ph). The data are calculated for Cs3C60 with at 40 K. We assume the cRPA Coulomb interactions to be static, whose validity is substantiated in Section B in the Supplementary Materials. Inset: Frequency dependence of Ueff and U′eff along the Matsubara frequency axis.

Mentions: The solid curves in Fig. 3 show Ueff(ω) and U′eff(ω), where we find U′eff(ω) > Ueff(ω) up to ω ~0.2 eV except a narrow region around ω = 0.1 eV. This remarkable inversion of the low-energy interactions is associated with the negative value of Jeff(0) discussed below because the relation U′eff(ω) ~ Ueff(ω) − 2Jeff(ω) holds. As is apparent from U > U′ and U + UV > U′ + U′V (plotted by dotted and dashed curves in Fig. 3), it is the phonon contribution (Uph, U′ph, and Jph) that causes the inversion. In fact, Uph(ω) and U′ph(ω) have strongly ω-dependent structures for ω ≲ 0.2 eV because of the intramolecular Jahn-Teller phonons with the frequencies up to ~0.2 eV (2), which are comparable to the t1u bandwidth ~0.5 eV.


Unified understanding of superconductivity and Mott transition in alkali-doped fullerides from first principles.

Nomura Y, Sakai S, Capone M, Arita R - Sci Adv (2015)

Frequency dependence of effective onsite interactions.The effective intra- and interorbital interactions (Ueff = U + UV + Uph and U′eff = U′ + U′V + U′ph, respectively) consist of the constrained random-phase approximation (cRPA) onsite Coulomb repulsion (U, U′), the dynamical screening from the off-site interactions (UV = U′V), and the phonon-mediated interactions (Uph, U′ph). The data are calculated for Cs3C60 with  at 40 K. We assume the cRPA Coulomb interactions to be static, whose validity is substantiated in Section B in the Supplementary Materials. Inset: Frequency dependence of Ueff and U′eff along the Matsubara frequency axis.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4643794&req=5

Figure 3: Frequency dependence of effective onsite interactions.The effective intra- and interorbital interactions (Ueff = U + UV + Uph and U′eff = U′ + U′V + U′ph, respectively) consist of the constrained random-phase approximation (cRPA) onsite Coulomb repulsion (U, U′), the dynamical screening from the off-site interactions (UV = U′V), and the phonon-mediated interactions (Uph, U′ph). The data are calculated for Cs3C60 with at 40 K. We assume the cRPA Coulomb interactions to be static, whose validity is substantiated in Section B in the Supplementary Materials. Inset: Frequency dependence of Ueff and U′eff along the Matsubara frequency axis.
Mentions: The solid curves in Fig. 3 show Ueff(ω) and U′eff(ω), where we find U′eff(ω) > Ueff(ω) up to ω ~0.2 eV except a narrow region around ω = 0.1 eV. This remarkable inversion of the low-energy interactions is associated with the negative value of Jeff(0) discussed below because the relation U′eff(ω) ~ Ueff(ω) − 2Jeff(ω) holds. As is apparent from U > U′ and U + UV > U′ + U′V (plotted by dotted and dashed curves in Fig. 3), it is the phonon contribution (Uph, U′ph, and Jph) that causes the inversion. In fact, Uph(ω) and U′ph(ω) have strongly ω-dependent structures for ω ≲ 0.2 eV because of the intramolecular Jahn-Teller phonons with the frequencies up to ~0.2 eV (2), which are comparable to the t1u bandwidth ~0.5 eV.

Bottom Line: More remarkably, the critical temperatures T c's calculated from first principles quantitatively reproduce the experimental values.The driving force behind the surprising phase diagram of A 3C60 is a subtle competition between Hund's coupling and Jahn-Teller phonons, which leads to an effectively inverted Hund's coupling.Our results establish that the fullerides are the first members of a novel class of molecular superconductors in which the multiorbital electronic correlations and phonons cooperate to reach high T c s-wave superconductivity.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Physics, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.

ABSTRACT
Alkali-doped fullerides A 3C60 (A = K, Rb, Cs) are surprising materials where conventional phonon-mediated superconductivity and unconventional Mott physics meet, leading to a remarkable phase diagram as a function of volume per C60 molecule. We address these materials with a state-of-the-art calculation, where we construct a realistic low-energy model from first principles without using a priori information other than the crystal structure and solve it with an accurate many-body theory. Remarkably, our scheme comprehensively reproduces the experimental phase diagram including the low-spin Mott-insulating phase next to the superconducting phase. More remarkably, the critical temperatures T c's calculated from first principles quantitatively reproduce the experimental values. The driving force behind the surprising phase diagram of A 3C60 is a subtle competition between Hund's coupling and Jahn-Teller phonons, which leads to an effectively inverted Hund's coupling. Our results establish that the fullerides are the first members of a novel class of molecular superconductors in which the multiorbital electronic correlations and phonons cooperate to reach high T c s-wave superconductivity.

No MeSH data available.


Related in: MedlinePlus