72nd CEMS Colloquium


Prof. Kazushi Kanoda (The University of Tokyo)


17:30 - 18:30, May 29, 2019 (Wednesday)


Okochi-Hall, RIKEN


Diverse Manifestations of Electron Correlation in Organic Conductors


 Coulomb interactions among electrons have huge impacts on their behavior through competitions of charge localization/delocalization and spin order/disorder. Layered BEDT-TTF compounds host flexible lattice geometries and appreciable Coulomb interactions, both of which are varied by pressure or chemical substitution to display diverse emergent phenomena like a showcase of correlation physics. In case of a half-filled band, the Mott metal-insulator transition shows universal quantum criticality at high temperatures1 but exhibits lattice-specific behaviour at low temperatures2; in particular, a Mott insulator with a triangular lattice carries a spin liquid3, which can be doped4 and superconduct. When a band is quarter-filled, electrons on a triangular lattice, which imposes frustration against Wigner crystallization, exhibit an exotic glass5, which crystalizes in a long time6, or a frustration-induced anomalous metal6. Alternatively, electrons are partially ordered, leading to the emergence of massless Dirac fermions, which show Dirac-cone reshaping, anomalous spin correlation and incipient mass-generation instability due to unscreened long-range Coulomb repulsion7. It seems as if organic materials seek for connection to soft-matter physics or particle physics beyond the conventional discipline of solid state physics. In this colloquium, I present our works on the above subjects and briefly touch our recent results on topological spin and charge excitations in a neutral-ionic transition material8.

  1.  T. Furukawa et al., Nat. Physics 11, 221 (2015); Urai et al., submitted.
  2.  T. Furukawa et al., Nat. Commun. 9 307 (2018).
  3.  Y. Zhou et al., Rev. Mod. Phys .89 025003 (2017).
  4.  H. Oike et al., Nat. Commun. 8, 756 (2017).
  5.   F. Kagawa et al., Nat. Phys. 9, 419 (2013); Miyagawa et al., J. Phys. Soc. Jpn.. 88, 034705 (2019). 
  6.  T. Sato et al., Science 357, 1378 (2017); T. Sato et al., Nat. Mat. 18, 229 (2019). 
  7.  M. Hirata et al., Nat. Commun. 7, 12666 (2016); M. Hirata et al., Scinence 358, 1403-1406 (2017). 
  8.  R. Takehara et al., Phys. Rev. B 98 054103 (2018); K. Sunami et al., Sci. Adv. 4 eaau7725 (2018); R. Takehara et al., submitted.