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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.


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Double occupancy, size of spin, weights of intramolecular configurations, spectral functions at 40 K, and schematic pictures of representative intramolecular configurations.(A) Volume dependence of the double-occupancy D = 〈ni↑ni↓〉 (red), the interorbital interspin correlation 〈ni↑nj↓〉 (green), and the size S of the spin per molecule (blue). (B) Spectral functions of several fcc A3C60 systems at 40 K. For comparison, we show the DFT density of states for fcc K3C60 ( = 722 Å3) as the shaded area. (C) Weights of several onsite configurations appearing in the quantum Monte Carlo simulations. (210) [(111)] generically denotes the configurations of {n1,n2,n3} = {2,1,0}, {0,2,1}, {1,0,2}, {2,0,1}, {1,2,0}, {0,1,2} [{n1,n2,n3} = {1,1,1}], with ni being the occupation of orbital i. N ≠ 3 with N = n1 + n2 + n3 denotes the configurations away from half filling. (D) Illustrative pictures for the (111) and (210) configurations. The up and down arrows indicate the up- and down-spin electrons, respectively.
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Figure 4: Double occupancy, size of spin, weights of intramolecular configurations, spectral functions at 40 K, and schematic pictures of representative intramolecular configurations.(A) Volume dependence of the double-occupancy D = 〈ni↑ni↓〉 (red), the interorbital interspin correlation 〈ni↑nj↓〉 (green), and the size S of the spin per molecule (blue). (B) Spectral functions of several fcc A3C60 systems at 40 K. For comparison, we show the DFT density of states for fcc K3C60 ( = 722 Å3) as the shaded area. (C) Weights of several onsite configurations appearing in the quantum Monte Carlo simulations. (210) [(111)] generically denotes the configurations of {n1,n2,n3} = {2,1,0}, {0,2,1}, {1,0,2}, {2,0,1}, {1,2,0}, {0,1,2} [{n1,n2,n3} = {1,1,1}], with ni being the occupation of orbital i. N ≠ 3 with N = n1 + n2 + n3 denotes the configurations away from half filling. (D) Illustrative pictures for the (111) and (210) configurations. The up and down arrows indicate the up- and down-spin electrons, respectively.

Mentions: We find, through a detailed analysis (Section F in the Supplementary Materials), that the unusual multiorbital interactions indeed drives the exotic s-wave superconductivity: (i) U′eff > Ueff and Jeff < 0 around ω = 0 generate a singlet pair of electrons (leading to a Cooper pair) (19), which sit on the same orbital rather than on different orbitals as shown by 〈ni↑ni↓〉 > 〈ni↑nj↓〉 in Fig. 4A. (ii) Jeff further enhances the pairing through a coherent tunneling of pairs between orbitals [the Suhl-Kondo mechanism (29, 30)].


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)

Double occupancy, size of spin, weights of intramolecular configurations, spectral functions at 40 K, and schematic pictures of representative intramolecular configurations.(A) Volume dependence of the double-occupancy D = 〈ni↑ni↓〉 (red), the interorbital interspin correlation 〈ni↑nj↓〉 (green), and the size S of the spin per molecule (blue). (B) Spectral functions of several fcc A3C60 systems at 40 K. For comparison, we show the DFT density of states for fcc K3C60 ( = 722 Å3) as the shaded area. (C) Weights of several onsite configurations appearing in the quantum Monte Carlo simulations. (210) [(111)] generically denotes the configurations of {n1,n2,n3} = {2,1,0}, {0,2,1}, {1,0,2}, {2,0,1}, {1,2,0}, {0,1,2} [{n1,n2,n3} = {1,1,1}], with ni being the occupation of orbital i. N ≠ 3 with N = n1 + n2 + n3 denotes the configurations away from half filling. (D) Illustrative pictures for the (111) and (210) configurations. The up and down arrows indicate the up- and down-spin electrons, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Double occupancy, size of spin, weights of intramolecular configurations, spectral functions at 40 K, and schematic pictures of representative intramolecular configurations.(A) Volume dependence of the double-occupancy D = 〈ni↑ni↓〉 (red), the interorbital interspin correlation 〈ni↑nj↓〉 (green), and the size S of the spin per molecule (blue). (B) Spectral functions of several fcc A3C60 systems at 40 K. For comparison, we show the DFT density of states for fcc K3C60 ( = 722 Å3) as the shaded area. (C) Weights of several onsite configurations appearing in the quantum Monte Carlo simulations. (210) [(111)] generically denotes the configurations of {n1,n2,n3} = {2,1,0}, {0,2,1}, {1,0,2}, {2,0,1}, {1,2,0}, {0,1,2} [{n1,n2,n3} = {1,1,1}], with ni being the occupation of orbital i. N ≠ 3 with N = n1 + n2 + n3 denotes the configurations away from half filling. (D) Illustrative pictures for the (111) and (210) configurations. The up and down arrows indicate the up- and down-spin electrons, respectively.
Mentions: We find, through a detailed analysis (Section F in the Supplementary Materials), that the unusual multiorbital interactions indeed drives the exotic s-wave superconductivity: (i) U′eff > Ueff and Jeff < 0 around ω = 0 generate a singlet pair of electrons (leading to a Cooper pair) (19), which sit on the same orbital rather than on different orbitals as shown by 〈ni↑ni↓〉 > 〈ni↑nj↓〉 in Fig. 4A. (ii) Jeff further enhances the pairing through a coherent tunneling of pairs between orbitals [the Suhl-Kondo mechanism (29, 30)].

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