53 research outputs found
NMR Evidence for Antiferromagnetic Transition in the Single-Component Molecular System, [Cu(tmdt)]
The magnetic state of the single-component molecular compound,
[Cu(tmdt)], is investigated by means of H-NMR. An abrupt spectral
broadening below 13 K and a sharp peak in nuclear spin-lattice relaxation rate,
, at 13 K are observed as clear manifestations of a second-order
antiferromagnetic transition, which is consistent with the previously reported
magnetic susceptibility and EPR measurement. The ordered moment is estimated at
/molecule. The temperature-dependence of
above the transition temperature indicates one-dimensional spin
dynamics and supports that the spins are on the central part of the molecule
differently from other isostructural compounds.Comment: 13pages, 5 figure
Excitonic instability of two-dimensional tilted Dirac cones
The electron-electron Coulomb interaction in Dirac-Weyl semimetals harbours a
novel paradigm of correlation effects that hybridizes diverse realms of
solid-state physics with their relativistic counterpart. Driving spontaneous
mass acquisition, the excitonic condensate of strongly-interacting massless
Dirac fermions is one such example whose exact nature remains debated. Here, by
focussing on the two-dimensional tilted Dirac cones in the organic salt
-(BEDT-TTF)I, we show that the excitonic instability is
controlled by a small chemicalpotential shift and an in-plane magnetic field.
In combined analyses based on renormalization-group approaches and ladder
approximation, we demonstrate that the nuclear relaxation rate is an excellent
probe of excitonic-spin fluctuations in an extended parameter region.
Comparative nuclear magnetic resonance (NMR) experiments show good agreements
with this result, jointly revealing the importance of intervalley nesting
between field-induced, spin-split Fermi pockets of opposite charge polarities.
Our work provides an accurate framework to search for excitonic instability of
strongly-interacting massless fermions.Comment: 26 pages, 5 figures, 1 supplementary file (9 pages, 3 figures
Electron Correlations in the Quasi-Two-Dimensional Organic Conductor -(BEDT-TTF)I investigated by C NMR
We report a C-NMR study on the ambient-pressure metallic phase of the
layered organic conductor -(BEDT-TTF)I [BEDT-TTF:
bisethylenedithio-tetrathiafulvalene], which is expected to connect the physics
of correlated electrons and Dirac electrons under pressure. The orientation
dependence of the NMR spectra shows that all BEDT-TTF molecules in the unit
cell are to be seen equivalent from a microscopic point of view. This feature
is consistent with the orthorhombic symmetry of the BEDT-TTF sublattice and
also indicates that the monoclinic sublattice, which should make three
molecules in the unit cell nonequivalent, is not practically influential on the
electronic state in the conducting BEDT-TTF layers at ambient pressure. There
is no signature of charge disproportionation in opposition to most of the
-type BEDT-TTF salts.
The analyses of NMR Knight shift, , and the nuclear spin-lattice
relaxation rate, , revealed that the degree of electron correlation,
evaluated by the Korringa ratio [)], is in an
intermediate regime. However, NMR relaxation rate is enhanced above
200K, which possibly indicates that the system enters into a quantum
critical regime of charge-order fluctuations as suggested theoretically.Comment: 19pages, 6figure
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