Rigorous evidence of metallicity of a molecular crystal consisting of single-component neutral molecules is disclosed by observing the Fermi surface through magnetic quantum oscillations. Torque magnetometry measurements of de Haas-van Alphen oscillatory signals in a single crystal of [Ni(tmdt)2] molecules (tmdt = trimethylenetetrathiafulvalenedithiolate) were performed by using a sensitive microcantilever at low temperatures in high magnetic fields to 45 T. The observed signals for all directions of magnetic field revealed unambiguously the presence of three-dimensional Fermi surfaces for both holes and electrons. The results are consistent with electronic band structure calculations for [Ni(tmdt)2].

No abstract

To understand the role of intramolecular degrees of freedom in forming mesophases, thermodynamic analysis was performed for 4-n-alkyl-4′-isothiocyanatobiphenyl (nTCB, n is the number of carbon atoms in the alkyl group), which exhibits the crystal E (CrE) phase as a mesophase. The heat capacities of 2TCB and 5TCB were measured by adiabatic calorimetry. Their entropies of transition (Δtrs S) were compared with those of other nTCBs (n ≤ 10). Δtrs S of the phase transition from the ordered crystal to CrE phase increased with their alkyl chain length, whereas that of fusion of the CrE phase remained essentially constant. These behaviors clearly show that the alkyl chain of nTCB is fully disordered even in the CrE phase. Through the comparison of Δtrs S among 5TCB, 4-pentyl-4′-cyanobiphenyl (5CB), and pentylbiphenyl, the role of the alkyl chain for the formation of mesophases is discussed.

Structure of a complex superstructure self-organized by thermotropic mesogen, 1,2-bis(4'- n-alkoxybenzoyl)hydrazine [BABH(n), where n is the number of carbon atoms in an alkoxy chain] was studied while paying special attention to the structure at the molecular level. Maximum entropy (MEM) analysis revealed that the molecular cores form two kinds of aggregates: Jungle gym with 3-fold junctions roughly on P minimal surface and spherical shells.

Quasi-binary (QB) picture of thermotropics, which regards a neat thermotropic liquid crystal as a binary system consisting of (semi)rigid core and molten alkyl chain, was assessed experimentally for the most famous (and representative) thermotropic mesogenic series nCB. By adding n-heptane as solvent, the smectic A phase was induced in 7CB-n-heptane system. Small angle x-ray diffraction showed that the QB picture holds not only in the phase behavior but also in the structure. It is suggested that the melting of 8CB and 9CB to isotropic liquid via smectic and nematic liquid crystals can be understood as a thermotropic-lyotropic crossover.

No abstract

Resistance and magnetic torque measurements are reported in a layered organic superconductor, β"-(BEDT-TTF)4[(H3O)Ga(C2O4)3]C6H5NO2 with Tc=4.8 K, where BEDT-TTF stands for bis(ethylenedithio)tetrathiafulvalene. Because of the large anion between the BEDT-TTF conducting layers, the superconductivity of this salt is highly anisotropic. In magnetic fields parallel to the conducting layers for T = 0.4 K, the magnetic torque shows a large diamagnetic signal associated with hysteresis up to ∼21 T, suggesting the upper critical field Hc2 > ∼ 21 T at 0.4 K. The large reduction of the diamagnetic signal is observed above 16 T, which shows a Fulde and Ferrell, and Larkin and Ovchinnikov (FFLO) phase transition. For T = 0.5 K, the interlayer resistance has non-zero value in a wide field region up to Hc2, arising from the Josephson vortex dynamics. Successive dips in the second derivative curves of the resistance are observed between 16 T and Hc2, which are ascribed to the commensurability effect between the Josephson vortex lattice and the order parameter oscillation of the FFLO phase. The commensurability effect is observed only in nearly parallel fields, showing that the FFLO phase is stable in a very limited field angle region. The temperature-field phase diagram is determined.

We have measured the resistivity of the organic conductor TTF-TCNQ under high pressure up to 8.0 GPa using a cubic anvil apparatus. Below 3 GPa, the pressure dependence of the charge-density-wave (CDW) transition temperature, T CDW , is consistent with previous results, except for the observation of the ''49 K-transition'' at around 1 GPa. Above 3 GPa, T CDW decreases with increasing pressure but the CDW state survives even at 8.0 GPa. At 8.0 GPa, however, the resistivity shows metallic behavior below 25 K after the CDW transition with T CDW ¼ 31 K. The origin of suppression is discussed in terms of the imperfect nesting originating from the increase in the interchain transfer integral, the significant deviation from the third-order commensurability, as well as the bandwidth broadening for both TTF and TCNQ stacks. The complete suppression of the CDW phase is expected near 9 GPa.