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• 1. [Article] Specific heat and critical fields of the organic superconductor β″–(BEDT-TTF)2SF5CH2CF2SO3

  We report on specific-heat, magnetization, and ac-susceptibility measurements of β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃, an organic superconductor with Tc=4.5 K, where BEDT-TTF stands for bis(ethylenedithio)-tetrathiafulvalene. ...

  Citation × Citation Citation Abstract Copy Title: Specific heat and critical fields of the organic superconductor β″–(BEDT-TTF)2SF5CH2CF2SO3 Author: Wanka, S., Hagel, J., Beckmanm, D., Wosnitza, J., Schlueter, J. A., Williams, Jack M., Nixon, P. G., Winter, Rolf Walter, Gard, Gary L. Year: 1998 We report on specific-heat, magnetization, and ac-susceptibility measurements of β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃, an organic superconductor with Tc=4.5 K, where BEDT-TTF stands for bis(ethylenedithio)-tetrathiafulvalene. The jump of the specific heat C at Tc and the exact form of the specific heat difference between C in the superconducting (B=0 T) and in the normal (B=3.5 T) state can be well described by BCS theory with strong coupling. We estimate an electron-phonon coupling parameter λ≈1.1. From measurements of C in magnetic fields we extract the upper critical field Bc₂(T). Low-field dc-magnetization measurements were used to determine the temperature dependence of the lower critical field Bc₁. From Tc down to ~3 K the characteristic suppression of Bc1(T) below the sensitivity limit is observed. Title: Specific heat and critical fields of the organic superconductor β″–(BEDT-TTF)2SF5CH2CF2SO3 Author: Wanka, S., Hagel, J., Beckmanm, D., Wosnitza, J., Schlueter, J. A., Williams, Jack M., Nixon, P. G., Winter, Rolf Walter, Gard, Gary L. Year: 1998 We report on specific-heat, magnetization, and ac-susceptibility measurements of β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃, an organic superconductor with Tc=4.5 K, where BEDT-TTF stands for bis(ethylenedithio)-tetrathiafulvalene. The jump of the specific heat C at Tc and the exact form of the specific heat difference between C in the superconducting (B=0 T) and in the normal (B=3.5 T) state can be well described by BCS theory with strong coupling. We estimate an electron-phonon coupling parameter λ≈1.1. From measurements of C in magnetic fields we extract the upper critical field Bc₂(T). Low-field dc-magnetization measurements were used to determine the temperature dependence of the lower critical field Bc₁. From Tc down to ~3 K the characteristic suppression of Bc1(T) below the sensitivity limit is observed. Close

• 2. [Article] Shubnikov–de Haas effect in the superconducting state of an organic superconductor

  We report the observation of Shubnikov–de Haas (SdH) oscillations in the mixed state of the organic superconductor β″-(BEDT-TTF)₂SF₅CH₂CF₂SO₃ (Tc≈4.4K). At low temperatures the SdH oscillations persist ...

  Citation × Citation Citation Abstract Copy Title: Shubnikov–de Haas effect in the superconducting state of an organic superconductor Author: Wosnitza, J., Wanka, S., Hagel, J., Häussler, R., Löhneysen, H. v., Schlueter, J. A., Geiser, U., Nixon, P. G., Winter, Rolf Walter, Gard, Gary L. Year: 2000 We report the observation of Shubnikov–de Haas (SdH) oscillations in the mixed state of the organic superconductor β″-(BEDT-TTF)₂SF₅CH₂CF₂SO₃ (Tc≈4.4K). At low temperatures the SdH oscillations persist clearly below the upper critical field Bc₂(0)≈3.6 T almost down to the field where the resistivity vanishes. Rather unusually, no additional damping of the SdH-signal amplitude — as well as of the de Haas–van Alphen amplitude — is observed in the superconducting state. This indicates that the damping in the vortex state of this quasi-two-dimensional superconductor is different in character to that observed for most three-dimensional materials. Title: Shubnikov–de Haas effect in the superconducting state of an organic superconductor Author: Wosnitza, J., Wanka, S., Hagel, J., Häussler, R., Löhneysen, H. v., Schlueter, J. A., Geiser, U., Nixon, P. G., Winter, Rolf Walter, Gard, Gary L. Year: 2000 We report the observation of Shubnikov–de Haas (SdH) oscillations in the mixed state of the organic superconductor β″-(BEDT-TTF)₂SF₅CH₂CF₂SO₃ (Tc≈4.4K). At low temperatures the SdH oscillations persist clearly below the upper critical field Bc₂(0)≈3.6 T almost down to the field where the resistivity vanishes. Rather unusually, no additional damping of the SdH-signal amplitude — as well as of the de Haas–van Alphen amplitude — is observed in the superconducting state. This indicates that the damping in the vortex state of this quasi-two-dimensional superconductor is different in character to that observed for most three-dimensional materials. Close

• 3. [Article] Coherent vs Incoherent Interlayer Transport in Layered Metals

  The magnetic-field, temperature, and angular dependence of the interlayer magnetoresistance of two different quasi-two-dimensional (2D) organic superconductors is reported. For k -BEDT-TTF)₂I₃, where BEDTTTF ...

  Citation × Citation Citation Abstract Copy Title: Coherent vs Incoherent Interlayer Transport in Layered Metals Author: Gard, Gary L., Wosnitza, J., Hagel, J., Qualls, J. S., Brooks, J. S., Balthes, E., Schweitzer, D., Schlueter, J. A., Geiser, U., Mohtasham, Javid, Winter, Rolf Walter Year: 2002 The magnetic-field, temperature, and angular dependence of the interlayer magnetoresistance of two different quasi-two-dimensional (2D) organic superconductors is reported. For k -BEDT-TTF)₂I₃, where BEDTTTF is bisethylenedithio-tetrathiafulvalene, we find a well-resolved peak in the angle-dependent magnetoresistance at Q590°(field parallel to the layers). This clear-cut proof for the coherent nature of the interlayer transport is absent for β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃. This and the nonmetallic behavior of the magnetoresistance suggest an incoherent quasiparticle motion for the latter 2D metal. Title: Coherent vs Incoherent Interlayer Transport in Layered Metals Author: Gard, Gary L., Wosnitza, J., Hagel, J., Qualls, J. S., Brooks, J. S., Balthes, E., Schweitzer, D., Schlueter, J. A., Geiser, U., Mohtasham, Javid, Winter, Rolf Walter Year: 2002 The magnetic-field, temperature, and angular dependence of the interlayer magnetoresistance of two different quasi-two-dimensional (2D) organic superconductors is reported. For k -BEDT-TTF)₂I₃, where BEDTTTF is bisethylenedithio-tetrathiafulvalene, we find a well-resolved peak in the angle-dependent magnetoresistance at Q590°(field parallel to the layers). This clear-cut proof for the coherent nature of the interlayer transport is absent for β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃. This and the nonmetallic behavior of the magnetoresistance suggest an incoherent quasiparticle motion for the latter 2D metal. Close

• 4. [Article] Enhanced magnetic quantum oscillations in the mixed state of a two-dimensional organic superconductor

  We report on de Haas–van Alphen (dHvA) oscillations observed in the mixed state of the organic superconductor β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃ (BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene) utilizing ...

  Citation × Citation Citation Abstract Copy Title: Enhanced magnetic quantum oscillations in the mixed state of a two-dimensional organic superconductor Author: Wosnitza, J., Hagel, J., Meeson, P. J., Bintley, D., Schlueter, J. A., Mohtasham, Javid, Winter, Rolf Walter, Gard, Gary L. Year: 2003 We report on de Haas–van Alphen (dHvA) oscillations observed in the mixed state of the organic superconductor β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃ (BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene) utilizing the field-modulation technique and torque magnetometry. At low temperatures (30 mK), the dHvA signal persists down to 1.4 T well below the upper critical field Bc2≈3.6T. Contrary to most theoretical predictions and previous experimental findings, no additional damping of the dHvA-oscillation amplitude, but a reduced damping of the dHvA signal is found. This highly unusual effect might indicate a reduced quasiparticle scattering rate or an additional oscillatory contribution in the superconducting state. Title: Enhanced magnetic quantum oscillations in the mixed state of a two-dimensional organic superconductor Author: Wosnitza, J., Hagel, J., Meeson, P. J., Bintley, D., Schlueter, J. A., Mohtasham, Javid, Winter, Rolf Walter, Gard, Gary L. Year: 2003 We report on de Haas–van Alphen (dHvA) oscillations observed in the mixed state of the organic superconductor β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃ (BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene) utilizing the field-modulation technique and torque magnetometry. At low temperatures (30 mK), the dHvA signal persists down to 1.4 T well below the upper critical field Bc2≈3.6T. Contrary to most theoretical predictions and previous experimental findings, no additional damping of the dHvA-oscillation amplitude, but a reduced damping of the dHvA signal is found. This highly unusual effect might indicate a reduced quasiparticle scattering rate or an additional oscillatory contribution in the superconducting state. Close

• 5. [Article] Pressure-induced insulating state in an organic superconductor

  The electronic-transport properties of the quasi-two-dimensional organic superconductor β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃, where BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene, have been investigated ...

  Citation × Citation Citation Abstract Copy Title: Pressure-induced insulating state in an organic superconductor Author: Gard, Gary L., Mohtasham, Javid, Schlueter, J. A., Pfleiderer, C., Wosnitza, J., Hagel, J. Year: 2003 The electronic-transport properties of the quasi-two-dimensional organic superconductor β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃, where BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene, have been investigated in magnetic fields up to 15 T and under hydrostatic pressure up to about 14 kbars. Shubnikov–de Haas data reveal a nonmonotonic pressure dependence of the holelike Fermi surface, a roughly linear increase of the electron g factor, and an approximately linear decrease of the cyclotron effective mass. By assuming that the latter reflects the pressure-induced reduction of the superconducting coupling parameter λ the rapid reduction of the superconducting transition temperature Tc(p) can be reasonably well described by the modified McMillan equation. Above about 12 kbars the material becomes insulating with an activated resistive behavior. This first-order metal-insulator transition has a hysteresis of about 3 kbars. This unexpected behavior is assumed to be of structural origin, although clear changes of electronic band-structure properties precede the phase transition. Title: Pressure-induced insulating state in an organic superconductor Author: Gard, Gary L., Mohtasham, Javid, Schlueter, J. A., Pfleiderer, C., Wosnitza, J., Hagel, J. Year: 2003 The electronic-transport properties of the quasi-two-dimensional organic superconductor β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃, where BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene, have been investigated in magnetic fields up to 15 T and under hydrostatic pressure up to about 14 kbars. Shubnikov–de Haas data reveal a nonmonotonic pressure dependence of the holelike Fermi surface, a roughly linear increase of the electron g factor, and an approximately linear decrease of the cyclotron effective mass. By assuming that the latter reflects the pressure-induced reduction of the superconducting coupling parameter λ the rapid reduction of the superconducting transition temperature Tc(p) can be reasonably well described by the modified McMillan equation. Above about 12 kbars the material becomes insulating with an activated resistive behavior. This first-order metal-insulator transition has a hysteresis of about 3 kbars. This unexpected behavior is assumed to be of structural origin, although clear changes of electronic band-structure properties precede the phase transition. Close