Pressure dependence of the conduction-electron-spin-resonance linewidth of the $α$ and $β$ phases of di-bis(ethylene- diothiolo)tetrathiafulvalene triiodide. Forró, L., Sekretarczyk, G., Krupski, M., Schweitzer, D., & Keller, H. Physical Review B, 35(5):2501-2504, 1987.
Pressure dependence of the conduction-electron-spin-resonance linewidth of the $α$ and $β$ phases of di-bis(ethylene- diothiolo)tetrathiafulvalene triiodide [link]Website  abstract   bibtex   
We report conduction-electron-spin-resonance linewidth (M) measurements of the a and P phases of the organic conductor di-bis(ethylenediothiolo)tetrathiafulvalene triiodide [(BEDT-TTF)213] in the 80-300-K temperature range under applied pressures of up to 5 kbar. hH in-creases under pressure in contrast to the predictions of the Elliot formula for the spin relaxation in metals. The pressure derivative d(ln~)/dP is — 5.5~ 1%/kbar and 9.8+ 1%/kbar for the a and P phases of (BEDT-TTF)213, respectively. The conduction-electron-spin-resonance (CESR) line-width (hH) of metals is connected to the scattering rate (r ') of electrons and to the spin-orbit coupling by the El-liot formula AH (hg) r '/y, where Ag =g — 2.0023 measures the spin-orbit coupling, and y is the electron gyromagnetic ratio. However, this relation fails to give the right magnitude and temperature dependence of the CESR linewidth of quasi-one-dimensional (QlD) organic metals. For example, in the case of tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) hH is three or-ders of magnitude lower than expected from the known scattering time and spin-orbit interaction, and it increases on decreasing temperature although z ' is decreasing as measured in resistivity. Several diA'erent interpretations of the CESR linewidth in QlD conductors have been put forward in the last ten years. The common point of these theories is that symme-try restrictions due mainly to the 1D character of the elec-tron band states limit the spin-orbit scattering in these ma-terials. In order to reproduce the temperature dependence of DH 1D fluctuations, interchain scatterings or libronic modes 5 have been evoked. The bis(ethylenediothiolo) tetrathiafulvalene (BEDT-TTF) molecule with monovalent anions or iodine com-plexes forms conducting salts which are less one dimen-sional than the compounds of the TTF-TCNQ or (TMTSF)2A' families (where TMTSF represents tetra-methyltetraselenafulvalene). For example, in the a and P modifications of (BEDT-TTF) zl3, abbreviated a-, P-(BEDT-TTF)2I3, the side-by-side interaction of the BEDT-TTF molecules is comparable to the face-to-face interaction. The room-temperature conductivity (o) is 20 (0 cm) ' and within a factor of 2 it is isotropic in the a-b plane for both compounds, while in the c' direction a is 0.02 (0 cm) ' for tt-(BEDT-TTF)zl3 and 0.1 (f1 cm) ' for P-(BEDT-TTF)zls. The efect of this quasi-two-dimensional (Q2D) character of the electronic structure on the spin-relaxation rate initiated the present study. In this Communication we will discuss the pressure dependence of the ESR linewidth of the a-and P-(BEDT-TTF)2I& since ambient pressure results have already been reported by several groups. We have performed our pressure-and temperature-dependent ESR measurements at the A' band using a high-pressure apparatus, which works at pressures up to 5 kbar and at temperatures from 80 to 350 K. ' The ap-paratus contains a cylindrical corundum resonator directly coupled to the waveguide by a matching corundum wedge. The pressure chamber in which the resonantor is placed is made of nonmagetic beryllium bronze. The temperature of the system was controlled by a nitrogen vapor flux pumped through a heat exchanger disposed outside the pressure chamber. In this work the pressure medium was petroleum ether. The samples of a-,P-(BEDT-TTF)zls were prepared by electrocrystallization described previously. One single crystal of typical dimensions 3 x 2 x 0.1 mm 3 of P-(BEDT-TTF)2I3 was enough for the pressure-dependent ESR measurements, but ten aligned single crystals of a-(BEDT-TTF)zls of dimensions 3 x 2x 0.2 mms were need-ed to have a satisfactory signal-to-noise ratio. The results reported here correspond to sample orientation in which the line shape was Lorentzian and did not change with pressure at 300 K. Below 150 K the line shape of the P-(BEDT-TTF)21s is Dysonian. Corrections in the linewidth due to the Dysonian line shape have not been done since even in the extreme skin depth case the correction is less than the experimental inaccuracy.
@article{
 title = {Pressure dependence of the conduction-electron-spin-resonance linewidth of the $α$ and $β$ phases of di-bis(ethylene- diothiolo)tetrathiafulvalene triiodide},
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 year = {1987},
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 pages = {2501-2504},
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 abstract = {We report conduction-electron-spin-resonance linewidth (M) measurements of the a and P phases of the organic conductor di-bis(ethylenediothiolo)tetrathiafulvalene triiodide [(BEDT-TTF)213] in the 80-300-K temperature range under applied pressures of up to 5 kbar. hH in-creases under pressure in contrast to the predictions of the Elliot formula for the spin relaxation in metals. The pressure derivative d(ln~)/dP is — 5.5~ 1%/kbar and 9.8+ 1%/kbar for the a and P phases of (BEDT-TTF)213, respectively. The conduction-electron-spin-resonance (CESR) line-width (hH) of metals is connected to the scattering rate (r ') of electrons and to the spin-orbit coupling by the El-liot formula AH (hg) r '/y, where Ag =g — 2.0023 measures the spin-orbit coupling, and y is the electron gyromagnetic ratio. However, this relation fails to give the right magnitude and temperature dependence of the CESR linewidth of quasi-one-dimensional (QlD) organic metals. For example, in the case of tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) hH is three or-ders of magnitude lower than expected from the known scattering time and spin-orbit interaction, and it increases on decreasing temperature although z ' is decreasing as measured in resistivity. Several diA'erent interpretations of the CESR linewidth in QlD conductors have been put forward in the last ten years. The common point of these theories is that symme-try restrictions due mainly to the 1D character of the elec-tron band states limit the spin-orbit scattering in these ma-terials. In order to reproduce the temperature dependence of DH 1D fluctuations, interchain scatterings or libronic modes 5 have been evoked. The bis(ethylenediothiolo) tetrathiafulvalene (BEDT-TTF) molecule with monovalent anions or iodine com-plexes forms conducting salts which are less one dimen-sional than the compounds of the TTF-TCNQ or (TMTSF)2A' families (where TMTSF represents tetra-methyltetraselenafulvalene). For example, in the a and P modifications of (BEDT-TTF) zl3, abbreviated a-, P-(BEDT-TTF)2I3, the side-by-side interaction of the BEDT-TTF molecules is comparable to the face-to-face interaction. The room-temperature conductivity (o) is 20 (0 cm) ' and within a factor of 2 it is isotropic in the a-b plane for both compounds, while in the c' direction a is 0.02 (0 cm) ' for tt-(BEDT-TTF)zl3 and 0.1 (f1 cm) ' for P-(BEDT-TTF)zls. The efect of this quasi-two-dimensional (Q2D) character of the electronic structure on the spin-relaxation rate initiated the present study. In this Communication we will discuss the pressure dependence of the ESR linewidth of the a-and P-(BEDT-TTF)2I& since ambient pressure results have already been reported by several groups. We have performed our pressure-and temperature-dependent ESR measurements at the A' band using a high-pressure apparatus, which works at pressures up to 5 kbar and at temperatures from 80 to 350 K. ' The ap-paratus contains a cylindrical corundum resonator directly coupled to the waveguide by a matching corundum wedge. The pressure chamber in which the resonantor is placed is made of nonmagetic beryllium bronze. The temperature of the system was controlled by a nitrogen vapor flux pumped through a heat exchanger disposed outside the pressure chamber. In this work the pressure medium was petroleum ether. The samples of a-,P-(BEDT-TTF)zls were prepared by electrocrystallization described previously. One single crystal of typical dimensions 3 x 2 x 0.1 mm 3 of P-(BEDT-TTF)2I3 was enough for the pressure-dependent ESR measurements, but ten aligned single crystals of a-(BEDT-TTF)zls of dimensions 3 x 2x 0.2 mms were need-ed to have a satisfactory signal-to-noise ratio. The results reported here correspond to sample orientation in which the line shape was Lorentzian and did not change with pressure at 300 K. Below 150 K the line shape of the P-(BEDT-TTF)21s is Dysonian. Corrections in the linewidth due to the Dysonian line shape have not been done since even in the extreme skin depth case the correction is less than the experimental inaccuracy.},
 bibtype = {article},
 author = {Forró, László and Sekretarczyk, G and Krupski, M and Schweitzer, D. and Keller, H},
 journal = {Physical Review B},
 number = {5}
}
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