Single-component molecular material hosting antiferromagnetic and spin-gapped Mott subsystems

Takagi, Ryuzo; Hamai, Takamasa; Gangi, Hiro; Miyagawa, Kazuya; Zhou, Biao; Kobayashi, Akiko; Kanoda, K.

doi:10.1103/physrevb.95.094420

Cited by 8 publications

(11 citation statements)

References 47 publications

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“…2(b). We note that the dpσ anisotropic hyperfine coupling constant, B d = 0.02 − 0.03 kOe/(μ B dpσ ) [23], is negligibly small; therefore, K aniso selectively probes the pπ spins. K aniso coincides with B π χ/2 at high temperatures; however, it rapidly deviates downward from B π χ/2 upon cooling, clearly indicating an accelerated increase in the dpσ spin contribution to χ .…”

Section: Experimental Methodsmentioning

confidence: 89%

“…5(a)] and, at the lowest temperature, spread symmetrically with clear edges at ±2.1 MHz, superposed by a sharp central peak. As mentioned above, the hyperfine coupling constant of the 13 C nucleus with the pπ spin is 100-fold larger than that with the dpσ spin [20,23]; thus the spectral broadening is attributed to the pπ spins. To evaluate the size of the ordered moment, we simulated 13 C NMR powder spectra, assuming that the AF moments are flopped to arbitrary directions in the plane normal to the applied field (see Appendix A).…”

Section: Af Order Spectramentioning

confidence: 85%

“…Considering the quantum effect beyond mean-field approximation, which is indispensable for the understanding of strongly correlated systems [6,7,42], the Coulomb interaction should enhance the Mottness of the dpσ -hybridized pπ band and lead to a band splitting. This is supported by the fact that all bands made of two pπ orbitals and a dpσ orbital are Mott insulating in Cu(tmdt) 2 [23]. Two cases are conceivable; the bands have a gap at F [ Fig.…”

Section: Discussionmentioning

confidence: 97%

“…On the other hand, in Cu(tmdt) 2 , the dpσ orbital level comes down close to the two pπ orbitals and all three orbitals accommodate three electrons [19]. There, a peculiar type of multiorbital Mott insulator is realized, with dpσ antiferromagnetic (AF) and pπ spin-gapped Mott subsystems [21][22][23]. This indicates that the pπ orbital also bears strong electron-electron correlations.…”

Section: Introductionmentioning

confidence: 99%

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Multiorbital antiferromagnetic metal induced by intramolecular self-doping

Takagi

Gangi

Miyagawa

et al. 2020

Phys. Rev. Research

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The orbital of electrons in a solid affects their mutual interaction, which is a key to emergent phenomena. Therefore, control of the interplay between distinct orbitals makes the behavior of solids fertile. Such a case is substantiated by the aggregation of the molecule, M(tmdt) 2 , which contains π orbitals extended over the organic ligand, tmdt, and a level-tunable d orbital centered at the metal ion M. Among them, Au(tmdt) 2 exemplifies the critical π-d mixing, which arguably causes an over-100 K antiferromagnetic metal whose nature remains elusive. Here, we track the π-d interplay in Au(tmdt) 2 with dual orbital-resolved probes, 13 C NMR and synchrotron x-ray diffraction. We find substantial intramolecular (interorbital) redistribution of electrons on cooling, triggering a commensurate π-d antiferromagnetic metal to emerge, which invokes an orbital-selective doped Mott insulator caused by intramolecular self-doping. This demonstrates that vital traffic of electrons between distinct orbitals brings about an unique correlated phase.

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Section: Experimental Methodsmentioning

confidence: 89%

Section: Af Order Spectramentioning

confidence: 85%

Section: Discussionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Multiorbital antiferromagnetic metal induced by intramolecular self-doping

Takagi

Gangi

Miyagawa

et al. 2020

Phys. Rev. Research

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“…indeed, NMR studies of Cu(tmdt) 2 found that the dpσ and pπ orbitals host antiferromagnetic and spin-gapped Mott subsystems, respectively 8,9 . For M = Ni, Pt and Zn, the dpσ orbitals lie away (upward in the former two and downward in the latter) from the two pπ orbitals located near the Fermi level 4, 10 .…”

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confidence: 99%

Spin-gapped Mott insulator with the dimeric arrangement of twisted molecules Zn(tmdt) 2

et al. 2017

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Abstract13 C nuclear magnetic resonance measurements were performed for a single-component molecular material Zn(tmdt) 2 , in which tmdt's form an arrangement similar to the so-called κ-type molecular packing in quasi-two-dimensional Mott insulators and superconductors. Detailed analysis of the powder spectra uncovered local spin susceptibility in the tmdt π orbitals. The obtained shift and relaxation rate revealed the singlet-triplet excitations of the π spins, indicating that Zn(tmdt) 2 is a spin-gapped Mott insulator with exceptionally large electron correlations compared to conventional molecular Mott systems. 1A new type of molecular conductors M(tmdt) 2 (M = Ni, Au, Pt, Cu, and Pd) are of current interest not only because it is the first molecular metal composed of a single molecular species 1 but also affords novel electronic states owing to the multi-orbital nature, which conventional charge-transfer salts do not possess. Furthermore, the systems of M(tmdt) 2 are expected to host highly correlated electrons compared with conventional molecular materials with dimeric molecular structures called 2 : 1 compounds, where a dimer playing as one lattice site accommodates one carrier and thus the on-site Coulomb repulsion U is reduced by the spatial extension of the dimer orbital. In case that one molecule accommodates one carrier as in some of the systems M(tmdt) 2 , the U is not reduced by the dimerization.The M(tmdt) 2 consists of a single molecular species in which a transition-metal ion, M, is coordinated by molecular ligands, tmdt, from both sides 2,3 . The pπ molecular orbitals extended over the tmdt ligand lie near the Fermi level, whereas the energy level of the dpσ molecular orbital located around M strongly depends on M. 4-7 For M = Cu, the dpσ orbital lies close to the pπ orbitals, leading to the formation of a dpσ-pπ multi-orbital system 5,7 ;indeed, NMR studies of Cu(tmdt) 2 found that the dpσ and pπ orbitals host antiferromagnetic and spin-gapped Mott subsystems, respectively 8,9 . For M = Ni, Pt and Zn, the dpσ orbitals lie away (upward in the former two and downward in the latter) from the two pπ orbitals located near the Fermi level 4,10 . In these systems, two pπ orbitals in M(tmdt) 2 accommodate two electrons, likely giving pπ-band semimetals; the ab-initio band structure calculation predicts small Fermi pockets 4,10,11 . As expected, Ni(tmdt) 2 and Pt(tmdt) 2 are metals 1,10,12 and appreciable electron correlation was revealed by 13 C nuclear magnetic resonance (NMR) studies 13 .It is to be noticed, however, that Zn(tmdt) 2 is an insulator 14 ; the typical resistivity data are shown in Fig. 1 Fig. 1(a). In the 2 solid, two tmdt ligands are arranged face-to-face and they form a checker-board pattern in two-dimensional layers (Figs. 1(b) and (c)). This type of molecular arrangement is similar to the "κ-type configuration", which is familiar in the 2 : 1 charge-transfer salts represented by κ-(ET) 2 X, including dimer-Mott insulators and over-10-K superconductors 15 . Most remarkably, Zn(tmdt)...

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Interacting chiral electrons at the 2D Dirac points: a review

Hirata¹,

Kobayashi²,

Berthier³

et al. 2021

Rep. Prog. Phys.

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The pseudo-relativistic chiral electrons in 2D graphene and 3D topological semimetals, known as the massless Dirac or Weyl fermions, constitute various intriguing issues in modern condensed-matter physics. In particular, the issues linked to the Coulomb interaction between the chiral electrons attract great attentions due to their unusual features, namely, the interaction is not screened and has a long-ranged property near the charge-neutrality point, in clear contrast to its screened and short-ranged properties in the conventional correlated materials. In graphene, this long-range interaction induces an anomalous logarithmic renormalization of the Fermi velocity, which causes a nonlinear reshaping of its Dirac cone. In addition, for strong interactions, it even leads to the predictions of an excitonic condensation with a spontaneous mass generation. The interaction, however, would seem to be not that large in graphene, so that the latter phenomenon appears to have not yet been observed. Contrastingly, the interaction is probably large in the pressurized organic material α-(BEDT-TTF)2I3, where a 2D massless-Dirac-fermion phase emerges next to a correlated insulating phase. Therefore, an excellent testing ground would appear in this material for the studies of both the velocity renormalization and the mass generation, as well as for those of the short-range electronic correlations. In this review, we give an overview of the recent progress on the understanding of such interacting chiral electrons in 2D, by placing particular emphasis on the studies in graphene and α-(BEDT-TTF)2I3. In the first half, we briefly summarize our current experimental and theoretical knowledge about the interaction effects in graphene, then turn attentions to the understanding in α-(BEDT-TTF)2I3, and highlight its relevance to and difference from graphene. The second half of this review focusses on the studies linked to the nuclear magnetic resonance experiments and the associated model calculations in α-(BEDT-TTF)2I3. These studies allow us to discuss the anisotropic reshaping of a tilted Dirac cone together with various electronic correlations, and the precursor excitonic dynamics growing prior to a condensation. We see these provide unique opportunities to resolve the momentum dependence of the spin excitations and fluctuations that are strongly influenced by the long-range interaction near the Dirac points.

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Single-component molecular material hosting antiferromagnetic and spin-gapped Mott subsystems

Abstract: We investigated a system based solely on a single molecular species, Cu(tmdt) 2 , accommodating d and π orbitals within the molecule.

Cited by 8 publications

References 47 publications

Multiorbital antiferromagnetic metal induced by intramolecular self-doping

Multiorbital antiferromagnetic metal induced by intramolecular self-doping

Spin-gapped Mott insulator with the dimeric arrangement of twisted molecules Zn(tmdt) 2

Interacting chiral electrons at the 2D Dirac points: a review

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