Dependence of Tc on hydrostatic pressure in β″-(ET)2SF5CH2CF2SO3 and κ-(ET)2Cu(NCS)2

Sadewasser, Sascha; Looney, C.; Schilling, J. S.; Schlueter, John A.; Williams, Jack M.; Nixon, Paul; Winter, R.; Gard, Gary L.

doi:10.1016/s0038-1098(97)00398-0

Cited by 21 publications

(17 citation statements)

References 13 publications

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“…17 In previous hydrostaticpressure studies up to about 2.3 kbar, dT c /dp ϭϪ1.34 K/kbar was determined by use of ac-susceptibility measurements. 4 This fits with thermal-expansion results that gave a similar initial hydrostatic-pressure dependence of T c . 18 For this material no other pressure-dependent properties have been reported so far.…”

Section: Introductionsupporting

confidence: 83%

“…The decrease of the superconducting transition temperature T c with applied pressure is extraordinarily large and may reach up to dT c /dpϷϪ3.8 K/kbars for the 2D organic superconductor -(BEDT-TTF) 2 Cu(NCS) 2 , where BEDT-TTF stands for bisethylenedithio-tetrathiafulvalene ͑or ET for short͒. 3,4 The origin of the strong pressure effect on T c in organic superconductors is not fully understood, but phenomenologically it is caused either by a decreasing density of states at the Fermi level as a result of an increasing electronic bandwidth or by a reduced interaction potential between the Cooper pairs. Both effects lead to a reduced coupling strength causing T c ϰexp(Ϫ1/) to decrease.…”

Section: Introductionmentioning

confidence: 99%

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Pressure-induced insulating state in an organic superconductor

et al. 2003

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The electronic-transport properties of the quasi-two-dimensional organic superconductor ␤Љ-(BEDT-TTF) 2 SF 5 CH 2 CF 2 SO 3 , 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 the rapid reduction of the superconducting transition temperature T c (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.

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Section: Introductionsupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Pressure-induced insulating state in an organic superconductor

et al. 2003

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“…In both cases, the superconducting transition is sharp, and the in-plane dc conductivity is on the order of 300 ⍀ Ϫ1 cm Ϫ1 near 10 K. The pressure dependence of T c is typical of that of many ET salts (dT c /dPϭ1.34 K/kbar͒. 13 An estimate of the 300 K microwave conductivity via ESR shows an anisotropy of b / a Ϸ1.4 in the conducting plane. 14,15 Analogous to other ␤Љ compounds, 16 electronic band-structure calculations predict a Fermi surface ͑FS͒ consisting of a pair of one-dimensional ͑1D͒ electronic bands and a two-dimensional ͑2D͒ hole pocket, which is 14.8% of the first Brillouin zone ͑FBZ͒.…”

Section: Introductionmentioning

confidence: 87%

Optical properties ofβ″−(ET)2SF5

et al. 1999

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We report the polarized infrared and optical reflectance of ␤Љ-(ET) 2 SF 5 CH 2 CF 2 SO 3 as a function of temperature. This fully organic superconductor displays weakly metallic behavior over the entire temperature range of our investigation. The electronic properties present several unusual features including the lack of a conventional free carrier ͑Drude͒ response at low temperature, infrared localization phenomena, and an unexpected temperature dependence of the oscillator strength. Similar behavior is observed in other ␤ and ␤Љ superconductors above T c , suggesting that this class of compounds is very close to a metal˜insulator transition where electronic correlations are important and the Drude response carries very little spectral weight. Vibronic features increase in intensity with decreasing temperature in the infrared, as expected. The temperature dependence of key anion vibrational modes are discussed in terms of intermolecular hydrogen bonding within the anion pocket. ͓S0163-1829͑99͒04330-1͔

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“…Comparative Raman studies on on deuterated and undeuterated κ-(BEDT-TTF) 2 Cu(NCS) 2 may also be interpreted in this way [35]. It might also be possible to simulate the size and direction of change of T c experienced upon deuteration from the anisotropic compressibility [24,36] of κ-(BEDT-TTF) 2 Cu(NCS) 2 , and the strongly anisotropic uniaxial pressure dependence of its superconducting transition temperature [37,38,39]. However, neither of these explanations can shed any light on the very obvious relationship between the details of the Fermi-surface shape and T c , shown by our data (Figures 2 and 3).…”

Section: F(p)/f(0)mentioning

confidence: 99%

Comparison of the normal-state properties of -(BEDT-TTF)₂Cu(NCS)₂and its deuterated analogue in high magnetic fields and under high hydrostatic pressures

Biggs

Klehe²,

Singleton³

et al. 2002

J. Phys.: Condens. Matter

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Abstract. Details of the Fermi-surface topology of deuterated κ-(BEDT-TTF) 2 Cu(NCS) 2 have been measured as a function of pressure, and compared with equivalent measurements of the undeuterated salt. We find that the superconducting transition temperature is much more dramatically suppressed by increasing pressure in the deuterated salt. It is suggested that this is linked to pressure-induced changes in the Fermi-surface topology, which occur more rapidly in the deuterated salt than in the undeuterated salt as the pressure is raised. Our data suggest that the negative isotope effect observed on deuteration is due to small differences in Fermi-surface topology caused by the isotopic substitution.

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Dependence of Tc on hydrostatic pressure in β″-(ET)2SF5CH2CF2SO3 and κ-(ET)2Cu(NCS)2

Cited by 21 publications

References 13 publications

Pressure-induced insulating state in an organic superconductor

Pressure-induced insulating state in an organic superconductor

Optical properties ofβ″−(ET)2SF5

Comparison of the normal-state properties of -(BEDT-TTF)₂Cu(NCS)₂and its deuterated analogue in high magnetic fields and under high hydrostatic pressures

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Dependence of Tc on hydrostatic pressure in β″-(ET)2SF5CH2CF2SO3 and κ-(ET)2Cu(NCS)2

Cited by 21 publications

References 13 publications

Pressure-induced insulating state in an organic superconductor

Pressure-induced insulating state in an organic superconductor

Optical properties ofβ″−(ET)2SF5

Comparison of the normal-state properties of -(BEDT-TTF)2Cu(NCS)2and its deuterated analogue in high magnetic fields and under high hydrostatic pressures

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Product

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Comparison of the normal-state properties of -(BEDT-TTF)₂Cu(NCS)₂and its deuterated analogue in high magnetic fields and under high hydrostatic pressures