Akane Akutsu-Sato

Fermi-surface topology and the effects of intrinsic disorder in a class of charge-transfer salts containing magnetic ions, \beta''-(BEDT-TTF)_4[(H_3O)M(C_2O_4)_3]Y

We report high-field magnetotransport measurements on β″ -(BEDT-TTF)[(HO)M(CO) ]Y, where M =Ga, Cr, and Fe and Y=CHN. We observe similar Shubnikov-de Haas oscillations in all compounds, attributable to four quasi-two-dimensional Fermi-surface pockets, the largest of which corresponds to a cross-sectional area ≈8.5% of the Brillouin zone. The cross-sectional areas of the pockets are in agreement with the expectations for a compensated semimetal, and the corresponding effective masses are ∼m , rather small compared to those of other BEDT-TTF salts. Apart from the case of the smallest Fermi-surface pocket, varying the M ion seems to have little effect on the overall Fermi-surface topology or on the effective masses. Despite the fact that all samples show quantum oscillations at low temperatures, indicative of Fermi liquid behavior, the sample and temperature dependence of the interlayer resistivity suggest that these systems are intrinsically inhomogeneous. It is thought that intrinsic tendency to disorder in the anions and/or the ethylene groups of the BEDT-TTF molecules leads to the coexistence of insulating and metallic states at low temperatures. A notional phase diagram is given for the general family of β″-(BEDT-TTF) [(HO)M(CO)]Y salts.

Suppression of superconductivity in a molecular charge transfer salt by changing guest molecule: β″-(BEDT-TTF)4[(H3O)Fe(C2O4)3](C6H5CN)x(C5H5N)1−x

SQUID magnetometry and transport measurements combined with crystal structure refinement have been used to examine the variation in superconducting properties (Tc and Meissner fraction) in the molecular superconductor β″-(BEDT-TTF)4[(H3O)Fe(C2O4)3]·C6H5CN on replacing the C6H5CN guest molecule with pyridine (C5H5N). Up to approximately 65% pyridine substitution there is only a small decrease in Tc and Meissner fraction but above that the superconductivity is suppressed.

Structures and properties of new superconductors, β″-(ET)4[(H3O)Ga(C2O4)3]Sol [Sol = nitrobenzene and pyridine]

The title compounds containing diamagnetic Ga III are superconductors. The nitrobenzene salt shows a broad metal-semiconductor transition at 160 K but becomes superconductor below 7.5 K. The Meissner volume of a powder sample at 1.8 K is estimated at 31 %. The pyridine salt also has a broad upturn in resistance at 130 K, a re-entrant metallic phase below 60 K, and a resistance loss below 1.5 K. The loss vanishes with applying magnetic field, suggesting that it is also superconductor.

Superstructures of donor packing arrangements in a series of molecular charge transfer salts

Three conducting BEDT-TTF charge-transfer salts with tris(oxalato)metallate anions have unit cells containing both[small alpha] and [small beta][double prime] donor packing motifs.

Magnetotransport measurements on β″-(BEDT-TTF)4[H3O) Ga3+ (C2O4)3]. C6H5NO2

Transport measurements have been carried out on single crystals of the charge transfer salt β-(BEDT-TTF) 4 [(H 3 O)Ga 3+ (C 2 O 4 ) 3 ]. C 6 H 5 NO 2 , using magnetic fields of up to 33 T and temperatures down to 0.55 K. The material is found to be superconducting with T c 7.5 K and an in-plane critical field B c2 ≥ 33 T, and to exhibit Shubnikov-de Haas (SdH) oscillations. The temperature and angle dependence of the Shubnikov-de Haas oscillations and the upper critical field are reported, allowing information about the anisotropy of the upper critical field, effective mass m*, and the Fermi-surface (FS) of the material to be deduced.

Structures and physical properties of BEDT-TTF salts containing channels of protons

Charge transfer salts with stoichiometry β″-(BEDT-TTF) [M(CO),](18-crown-6 ether)(9HO), where M= Cr, Ga or Fe and x= 2 or 3 are reported. Their structures suggest that proton migration is possible. Variable temperature resistivity measurements on the Cr salt show metallic behaviour down to 180K. Magnetic susceptibility of the Cr salt is paramagnetic down to 1.8 K. Preliminary impedance measurements suggest that the proton conductivities of the Cr and Ga salts are the order of 10 S cm at 300 K.

Millimetre-wave response of the novel organic superconductors β-ET4[(H3O)M(C2O4)3].S (M=Fe3+, S= C6H5CN and C6H5NO2)

The high frequency (f=70 GHz) magneto-optical response of β-ET 4 [(H 3 O)M(C 2 O 4 ) 3 ].S, where M=Fe 3+ , S=C 6 H 5 CN and C 6 H 5 NO 2 , has been investigated in the temperature range 1.4 K < T < 120 K. The angle dependence of the EPR spectra and the anisotropy of the g-factors for the two materials are presented.