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Magnetic Field Dependent Effective Mass in the Organic Superconductor κ-(BEDT-TTF)_{2}I_{3}

100%

Balthes E., Schweitzer D., Heinen I., Keller H., Biberacher W., Jansen A., Steep E.

Acta Physica Polonica A

1995

vol. 87

issue 4-5

767-772

κ-(BEDT-TTF)_{2}I_{3} is an electronically extreme two-dimensional organic metal with a superconducting transition at around 4 K. In magnetic fields above 12 T the effective mass, as obtained from the temperature dependence of the amplitudes of Shubnikov-de Haas oscillations, is magnetic field dependent as long as the magnetic field is arranged perpendicular to the conducting planes. In contrast to this, by turning the magnetic field by 27° or even only 9° the observed effective mass (as obtained from Shubnikov-de Haas and de Haas-van Alphen measurements) is field independent. We suppose that the occurrence of anyons at temperatures below 1 K in fields above 12 T is the reason for the observed field dependence of the effective mass.

Peculiarities of the Electronic Properties of the κ-Phase Structures (BEDT-TTF)_{2}Cu(N(CN)_{2})X with X=Cl, Br, I

100%

Andres K., Posselt H., Kushch N. D., Kund M., Biberacher W., Saito G.

Acta Physica Polonica A

1995

vol. 87

issue 4-5

761-766

The structure of the title compounds is similar to other κ-phase structures with respect to the checkerboard-like arrangement of the ET dimers (ET = BEDT-TTF) in the conducting planes, but different by the tilt alternation of these dimers in successive planes. The resulting inequivalence of these planes tends to destabilize the metallic state which becomes extremely sensitive to changes in the S-S overlaps of neighbouring ET molecules. Such changes may result from anion substitution, lattice expansion, or also from ordering effects of the ethylene end groups of the ET molecules. They lead to quite different electronic properties of the three isostructural compounds. We focus especially on the strongly pressure-dependent properties of the Cl-compound, where a coexistence of magnetically ordered and superconducting states with rather spectacular superconducting reentrance effects is observed.

Investigations of Fermi Surfaces and Effective Masses of the Organic Superconductors (BEDO-TTF)_{2}ReO_{4}(H_{2}O) and κ-(BEDT-TTF)_{2}I_{3} by Shubnikov-de Haas and de Haas-van Alphen Measurements

84%

Schweitzer D., Balthes E., Karlich S., Heinen I., Keller H. J., Strunz W., Biberacher W., Jansen A. G. M., Steep E.

Acta Physica Polonica A

1995

vol. 87

issue 4-5

749-759

The Fermi surfaces and effective masses of (BEDO-TTF)_{2}ReO_{4}(H_{2}0) and κ-(BEDT-TTF)_{2}I_{3} were investigated by Shubnikov–de Haas (SdH) and de Haas–van Alphen (dHvA) measurements in magnetic fields up to 27 T in the temperature range from 0.5 K to 4.2 K. Two small closed pockets (0.7% and 1.5% of the first Brillouin zone) are observed in (BEDO-TTF)_{2}ReO_{4}(H_{2}0) corresponding very well with two cross-sectional areas of the Fermi surfaces obtained for a hole and an electron pocket from tight binding calculations. In contrast, in κ-(BEDT-TTF)_{2}I_{3} two relatively large closed sections (13% and 85% of the first Brillouin zone) of the Fermi surfaces are observed, again confirming the tight binding calculations. For κ-(BEDT-TTF)_{2}I_{3} in magnetic fields above 12 T the effective mass for the larger orbit, as obtained from the temperature dependence of the SdH-oscillation amplitudes, is magnetic field dependent as long as the field is arranged perpendicular to the conducting planes (Θ = 0°). In contrast, from dHvA measurements - which were performed by turning the magnetic field by 27° with respect to the SdH experiments - the observed effective mass is field independent. We suppose that the occurrence of anyons at temperatures below 1 K and in fields above 12 T might be the reason for the observed field dependence of the effective mass in the SdH investigations under the special angle 0°.

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3 Acta Physica Polonica A

3 1995

3 Biberacher W.

2 Balthes E.

2 Heinen I.

2 Schweitzer D.

2 Steep E.

1 Andres K.

1 Jansen A.

1 Jansen A. G. M.

1 Karlich S.

1 Keller H.

1 Keller H. J.

1 Kund M.

1 Kushch N. D.

1 Posselt H.

1 Saito G.

1 Strunz W.

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Magnetic Field Dependent Effective Mass in the Organic Superconductor κ-(BEDT-TTF)_{2}I_{3}

Peculiarities of the Electronic Properties of the κ-Phase Structures (BEDT-TTF)_{2}Cu(N(CN)_{2})X with X=Cl, Br, I

Investigations of Fermi Surfaces and Effective Masses of the Organic Superconductors (BEDO-TTF)_{2}ReO_{4}(H_{2}O) and κ-(BEDT-TTF)_{2}I_{3} by Shubnikov-de Haas and de Haas-van Alphen Measurements