B. Salameh

Scaling behavior of the longitudinal and transverse transport in quasi-one-dimensional organic conductors

We report on dc and microwave experiments of the low-dimensional organic conductors (TMTSF)2PF6 and (TMTSF)2ClO4 along the a, b′, and c∗ directions. In the normal state of (TMTSF)2PF6 below T=70K, the dc resistivity follows a power law with ρa and ρb′ proportional to T2 while ρc∗∝T. Above T=100K the exponents extracted from the data for the a and c∗ axes are consistent with what is to be expected for a system of coupled one-dimensional chains (Luttinger liquid) and a dimensional crossover at a temperature of about 100K. The b′ axis shows anomalous exponents that could be attributed to a large crossover between these two regimes. The contactless microwave measurements of single crystals along the b′ axis reveal an anomaly between 25 and 55K which is not understood yet. The organic superconductor (TMTSF)2ClO4 is more a two-dimensional metal with an anisotropy ρa/ρb′ of approximately 2 at all temperatures. Such a low anisotropy is unexpected in view of the transfer integrals. Slight indications to one-dimensionality are found in the temperature dependent transport only above 200K. Even along the least conducting c∗ direction no region with semiconducting behavior is revealed up to room temperature.

Two alternating BEDT-TTF packing motifs in α-κ-(BEDT-TTF)2Hg(SCN)3

The first BEDT-TTF charge transfer salt in which alternating electron-donor layers possess α- and κ-type packing motifs has been synthesized. The crystal structure and physical properties of the organic conductor α-κ-(BEDT-TTF)2Hg(SCN)3 are described, including a detailed description of its optical properties. The electronic behavior is dominated by a sharp metal-to-insulator transition at T = 176 K which is due to a first-order structural phase transition. The optical properties in the metallic regime are a superposition of those of the α- and κ-phases, while in the insulating state the spectra become more anisotropic in the conducting plane, and the features of the two layers cannot be distinguished.

Charge Order Breaks Magnetic Symmetry in Molecular Quantum Spin Chains

Charge order affects most of the electronic properties but is believed not to alter the spin arrangement since the magnetic susceptibility remains unchanged. We present electron-spin-resonance experiments on quasi-one-dimensional salts ( PF6, AsF6, and SbF6), which reveal that the magnetic properties are modified below when electronic ferroelectricity sets in. The coupling of anions and organic molecules rotates the g-tensor out of the molecular plane creating magnetically nonequivalent sites on neighboring chains at domain walls. Due to anisotropic Zeeman interaction a novel magnetic interaction mechanism in the charge-ordered state is observed as a doubling of the rotational periodicity of .