Yasuhiro Nakazawa

Thermodynamics of BEDT-TTF based dimeric salts

Abstract The low-temperature electronic properties of (BEDT-TTF) 2 X are studied by specific heat measurements, especially focusing on the dimeric systems. The β′-(BEDT-TTF) 2 ICl 2 salt shows a similar behavior to the Mott insulating phase in κ-(BEDT-TTF) 2 X system. The cooling rate dependence of low-temperature specific heat of κ-(d 8 ;BEDT-TTF) 2 Cu[N(CN) 2 ]Br salt is also studied and appreciable variation in both electronic and lattice specific heat are not observed within the present experiments.

Low-temperature heat capacity measurements of κ-(BEDT-TTF)4Hg2.89Br8

Abstract Low-temperature heat capacity measurements of single crystals of κ -(BEDT-TTF) 4 Hg 2.89 Br 8 , which is known as a strongly correlated organic system were performed. We observe an interesting behavior in lattice heat capacity associated with the chain structure of mercury atoms in the anion layers. The electronic heat capacity coefficient, γ was found to be about 2–3 times larger than those of well known 10 K class superconductors.

Novel superconductivity coexisting with incipient electric-multipolar order in CePt3Si

We measured the specific heat Cp of an annealed sample of CePt3Si in magnetic fields B up to 10 T and confirmed two conspicuous anomalies in the temperature range where no apparent magnetic anomalies were found in the susceptibility. The lower-temperature anomaly at 2.2 K was depressed with increasing B and seemed to get absorbed around 4 T into the other one around 2.8 K. The latter anomaly continues to grow into a solid peak with increasing B. These features imply that neither of these transitions is due to long-range antiferromagnetism (AF) as originally proposed, but they are reminiscent of quadrupolar transitions found in certain Ce-based Kondo compounds, in which two distinct anomalies were also observed in Cp and identified as a quadrupolar transition followed by an AF transition at a slightly lower T. In the case of CePt3Si, the lower-T anomaly is not due to AF but to a new phase transition of yet-unknown nature, and in this new phase the superconductivity emerges at 0.8 K. We thereby hypothesize that the superconductivity could be mediated by magnetic or other electronic excitations under the influence of the quadrupolar-like order induced around 2.8 K and that CePt3Si would be the first example of an unconventional superconductor coexisting with electric-multipolar order.

Melting and interlayer coherence of vortices in the quasi-two-dimensional organic superconductor, α-(BEDT-TTF)2NH4Hg(SCN)4

Abstract In the vortex state of the quasi-two-dimensional superconductor, α-(BEDT-TTF) 2 NH 4 Hg(SCN) 4 , it was found that the onset of the out-of-plane ac susceptibility forms a characteristic line well below the H c 2 line. The observation of absence of frequency dependence suggests that this is a melting line of vortices, rather than a crossover line of vortex dynamics. The out-of-plane resistivity measurements show that the interlayer coherence between pancake vortices is established well above this melting line.

Intercalation of High-Tc Oxides with Organic Molecules

Exposure of Bi- and Tl- high-Tc oxides to vapor of benzene or phthalocyanines results in formation of intercalation compounds where c-axis is expanded with respect to that of the host oxide due to insertion of the organic molecules between the double Bi-O (or Tl-O) layers. Electronic and vibrational modes of both the guest organic and the host inorganic constituents are significantly modified as compared to the starting materials. The intercalated samples exhibit strongly enhanced non-linear magnetism with a complex field dependence, which is tentatively ascribed to the orbital magnetism of pi-electrons of organic molecules.