92 research outputs found
Lattice effects in the quasi-two-dimensional valence-bond-solid Mott insulator EtMeP[Pd(dmit)]
The organic charge-transfer salt EtMeP[Pd(dmit)] is a
quasi-two-dimensional Mott insulator with localized spins = 1/2 residing on
a distorted triangular lattice. Here we report measurements of the uniaxial
thermal expansion coefficients along the in-plane = - and
-axis as well as along the out-of-plane -axis for temperatures 1.4\,K
T 200\,K. Particular attention is paid to the lattice effects
around the phase transition at = 25\,K into a low-temperature
valence-bond-solid phase and the paramagnetic regime above where effects of
short-range antiferromagnetic correlations can be expected. The salient results
of our study include (i) the observation of strongly anisotropic lattice
distortions accompanying the formation of the valence-bond-solid, and (ii) a
distinct maximum in the thermal expansion coefficients in the paramagnetic
regime around 40\,K. Our results demonstrate that upon cooling through
the in-plane -axis, along which the valence bonds form, contracts
while the second in-plane -axis elongates by the same relative amount.
Surprisingly, the dominant effect is observed for the out-of-plane -axis
which shrinks significantly upon cooling through . The pronounced
anomaly in around 40\,K is attributed to short-range magnetic
correlations. It is argued that the position of this maximum, relative to that
in the magnetic susceptibility around 70\,K, speaks in favor of a more
anisotropic triangular-lattice scenario for this compound than previously
thought.Comment: 6 pages, 4 figures, submitted to Phys. Rev.
Critical Behavior in Doping-Driven MetalInsulator Transition on Single-Crystalline Organic Mott-FET
We present the carrier transport properties in the vicinity of a
doping-driven Mott transition observed at a field-effect transistor (FET)
channel using a single crystal of the typical two-dimensional organic Mott
insulator -(BEDT-TTF)CuN(CN)Cl (-Cl).The FET shows a
continuous metalinsulator transition (MIT) as electrostatic doping proceeds.
The phase transition appears to involve two-step crossovers, one in Hall
measurement and the other in conductivity measurement. The crossover in
conductivity occurs around the conductance quantum , and hence is not
associated with "bad metal" behavior, which is in stark contrast to the MIT in
half-filled organic Mott insulators or that in doped inorganic Mott insulators.
Through in-depth scaling analysis of the conductivity, it is found that the
above carrier transport properties in the vicinity of the MIT can be described
by a high-temperature Mott quantum critical crossover, which is theoretically
argued to be a ubiquitous feature of various types of Mott transitions. [This
document is the unedited Authors' version of a Submitted Work that was
subsequently accepted for publication in Nano Letters, copyright \copyright
American Chemical Society after peer review. To access the final edited and
published work see http://dx.doi.org/10.1021/acs.nanolett.6b03817]Comment: 40 pages, 16 figures in Nano Letters, ASAP (2017
Effects of the Zero-Mode Landau Level on Inter-Layer Magnetoresistance in Multilayer Massless Dirac Fermion Systems
We report on the experimental results of interlayer magnetoresistance in
multilayer massless Dirac fermion system -(BEDT-TTF)I under
hydrostatic pressure and its interpretation. We succeeded in detecting the
zero-mode Landau level (n=0 Landau level) that is epected to appear at the
contact points of Dirac cones in the magnetic field normal to the
two-dimensional plane. The characteristic feature of zero-mode Landau carriers
including the Zeeman effect is clearly seen in the interlayer
magnetoresistance.Comment: 2 pages, 2 figure
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