149 research outputs found
Field-induced length changes in the spin-liquid candidate -(BEDT-TTF)Cu(CN)
Measurements of the coefficient of thermal expansion on the spin-liquid
candidate -(BEDT-TTF)Cu(CN) have revealed distinct and
strongly anisotropic lattice effects around 6 K - a possible spin-liquid
instability. In order to study the effects of a magnetic field on the
low-temperature spin-liquid state, dilatometric measurements have been
conducted both as a function of temperature at \emph{B} = const. and as a
function of field at \emph{T} = const. While the 6 K anomaly is found to be
insensitive to magnetic fields \emph{B} 10 T, the maximum field applied,
surprisingly strong \emph{B}-induced effects are observed for magnetic fields
applied along the in-plane \emph{b}-axis. Above a threshold field of 0.5 T <
\emph{B} 1 T, a jump-like anomaly is observed in the \emph{b}-axis
lattice parameter. This anomaly, which is located at 8.7 K at \emph{B} = 1 T,
grows in size and shifts to lower temperatures with increasing the magnetic
field. Although the anomaly bears resemblance to a first-order phase
transition, the lack of hysteresis suggests otherwise.Comment: 3 pages, 3 figures, proceedings of ISCOM 2011, physica status solidi
(c)(in press
Low-temperature lattice effects in the spin-liquid candidate -(BEDT-TTF)Cu(CN)
The quasi-two-dimensional organic charge-transfer salt
-(BEDT-TTF)Cu(CN) is one of the prime candidates for a
quantum spin-liquid due the strong spin frustration of its anisotropic
triangular lattice in combination with its proximity to the Mott transition.
Despite intensive investigations of the material's low-temperature properties,
several important questions remain to be answered. Particularly puzzling are
the 6\,K anomaly and the enigmatic effects observed in magnetic fields. Here we
report on low-temperature measurements of lattice effects which were shown to
be particularly strongly pronounced in this material (R. S. Manna \emph{et
al.}, Phys. Rev. Lett. \textbf{104}, 016403 (2010)). A special focus of our
study lies on sample-to-sample variations of these effects and their
implications on the interpretation of experimental data. By investigating
overall nine single crystals from two different batches, we can state that
there are considerable differences in the size of the second-order phase
transition anomaly around 6\,K, varying within a factor of 3. In addition, we
find field-induced anomalies giving rise to pronounced features in the sample
length for two out of these nine crystals for temperatures 9 K. We
tentatively assign the latter effects to -induced magnetic clusters
suspected to nucleate around crystal imperfections. These -induced effects
are absent for the crystals where the 6\,K anomaly is most strongly pronounced.
The large lattice effects observed at 6\,K are consistent with proposed pairing
instabilities of fermionic excitations breaking the lattice symmetry. The
strong sample-to-sample variation in the size of the phase transition anomaly
suggests that the conversion of the fermions to bosons at the instability is
only partial and to some extent influenced by not yet identified
sample-specific parameters
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