Field-induced length changes in the spin-liquid candidate κ\kappa-(BEDT-TTF)2_2Cu2_2(CN)3_3

Measurements of the coefficient of thermal expansion on the spin-liquid candidate $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ 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} $\leq$ 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}$_c$ $\leq$ 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 κ\kappa-(BEDT-TTF)2_2Cu2_2(CN)3_3

The quasi-two-dimensional organic charge-transfer salt $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ 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 $T <$ 9 K. We tentatively assign the latter effects to $B$-induced magnetic clusters suspected to nucleate around crystal imperfections. These $B$-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

Influence of the substrate temperature on the layer properties made by an atmospheric plasma jet using different precursors

In this work the surface temperature of porous polymer scaffolds treated with an atmospheric plasma jet was determined by theoretical estimations and infrared was measurements. Based on these results the scaffolds were coated with functional plasma polymer layers using this plasma jet and different precursors. The influence of the substrate temperature on the plasma polymer layer properties like thickness and chemical reactivity was investigated

Evidence for electronically-driven ferroelectricity in the family of strongly correlated dimerized BEDT-TTF molecular conductors

By applying measurements of the dielectric constants and relative length changes to the dimerized molecular conductor $\kappa$-(BEDT-TTF)$_2$Hg(SCN)$_2$Cl, we provide evidence for order-disorder type electronic ferroelectricity which is driven by charge order within the (BEDT-TTF)$_2$ dimers and stabilized by a coupling to the anions. According to our density functional theory calculations, this material is characterized by a moderate strength of dimerization. This system thus bridges the gap between strongly dimerized materials, often approximated as dimer-Mott systems at 1/2 filling, and non- or weakly dimerized systems at 1/4 filling exhibiting charge order. Our results indicate that intra-dimer charge degrees of freedom are of particular importance in correlated $\kappa$-(BEDT-TTF)$_2$X salts and can create novel states, such as electronically-driven multiferroicity or charge-order-induced quasi-1D spin liquids.Comment: 6 pages, 4 figures + Supplementary Information (8 pages, 8 figures

Temperature dependence of structural and electronic properties of the spin-liquid candidate kappa-(BEDT-TTF)2Cu2(CN)3

We investigate the effect that the temperature dependence of the crystal structure of a two dimensional organic charge-transfer salt has on the low-energy Hamiltonian representation of the electronic structure. For that, we determine the crystal structure of kappa-(BEDT-TTF)2Cu2(CN)3 for a series of temperatures between T=5 K and 300 K by single crystal X-ray diffraction and analyze the evolution of the electronic structure with temperature by using density functional theory and tight binding methods. We find a considerable temperature dependence of the corresponding triangular lattice Hubbard Hamiltonian parameters. We conclude that even in the absence of change of symmetry, the temperature dependence of quantities like frustration and interaction strength can be significant and should be taken into account.Comment: 8 pages, 9 figure

The MAT-253 Ultra — a novel high-resolution, multi-collector gas source mass spectrometer

We present the design, performance and representative applications of the MAT 253 Ultra – the first prototype of a new class of high-resolution gas source isotope ratio mass spectrometers