Optical Investigations of the Electrical Anisotropy of α- and β- (BEDT-TTF)<sub>2</sub>I<sub>3</sub>

Koch, B.; Geserich, Hans Peter; Ruppel, Wolfgang; Schweitzer, Dieter; Dietz, Klaus; Keller, Heimo J.

doi:10.1080/00268948508075183

Cited by 47 publications

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“…The reflectivity for both polarizations is plotted in figure 5a. The results of our polarized reflection measurements confirm earlier observations [20,[24][25][26][27][28]. In agreement with the dc and microwave conductivity data the reflectivity in the b direction is significantly higher compared to E II a.…”

Section: Introductionsupporting

confidence: 81%

“…The broad transition is much less pronounced in the a direction, but apart from the absolute value the far-infrared (FIR) behavior shows the same features in the perpendicular direction. In the visible spectral range a strong dispersion appears near 20000 cm-I in the a direction, and it is assigned to molecular excitations of the tri-iodine anions [24,26].…”

Section: Introductionmentioning

confidence: 99%

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Field and frequency dependent transport in the two-dimensional organic conductor α-(BEDT-TTF)2I3

et al. 1994

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Abstract. -The title compound undergoes a metal-insulator phase transition of unknown origin at TMI = 135 K. We studied the electrodynamic response of Q-(BEDT-TTFhh in a wide range of frequency, covering microwave and millimeter wave frequencies as weIl as the optical spectral range, and found a frequency dependent conductivity up to 1000 cm-1 in the low temperature phase. This is accompanied be a non-linear transport with a smooth onset at about 10 V fcm. Our X-ray studies show no indication of superstructure reflections and clearly rule out the formation of a charge density wave ground state. The lack of a temperature dependence in the millimeter wave conductivity between 20 K and 100 K makes hopping transport unlikely.

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Section: Introductionsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Field and frequency dependent transport in the two-dimensional organic conductor α-(BEDT-TTF)2I3

et al. 1994

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“…The conductivity obtained after a Kramer-Kronig analysis is displayed in Figure 2. In agreement with the spectra reported for a-(BEDT-TTFhI 3 [12] the conductivity perpendicular to the BEDT~TTF molecular stacks is greater than that parallel to the stacks. The overall shapes of the conductivity differ from those of a-(BEDT-TT FhI3 mainly because of the much higher d.c. conductivity to which our infrared conductivities extrapolate.…”

Section: Introductionsupporting

confidence: 80%

The infrared optical properties of the α-phase organic superconductor, α-(BEDT - TTF)2 (NH4Hg(NCS)4)

et al. 1993

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The title compound is the only known organic superconductor (Tc = 0.8 K) with an a-phase crystal structure, in which the conducting plane contains single BEDT-TT F molecules with alternating orientation, rather than the pairs of molecules found in the higher Tc Ie-phase compounds. We have measured the polarized reflectivity of protonated and deuterated ., from 80 cm-1 to 8000 cm-l , at temperatures between 6.5 K and 300 K. The overall shape of these spectra are discussed. The optical conductivity obtained after a Kramers-Kronig analysis shows no maximum in the mid-infrared as known from the compounds of the Ie-phase due to the lack of dimerization of the BEDT-TTF molecules. This causes an accentuation of the far-infrared intraband conductivity. The vibrational features are assigned and discussed. INTRODUCTIONEven if the first popular BEDT-TTF (bia--(ethylenedithio) tetrathiafulvalene) radical ion salt was a- , no superconductivity in an a-phase crystal of this familiy was found. Various efforts to observe ambient pressure superconductivity in an a-phase BEDT-TTF salt like a-(BEDT-TTFhI 3 or related components a-(BEDT-TTFhAuI2 have failed: Doping of a-(BE-DT-TTFhI 3 ·with iodine does not cause a partial supression of the metal-insulator transition at 135 K and superconducting behaviour at T ~ 3 K as reported [2], but only gives a slight rise of the high-frequency conductivity in the insulating phase after extreme doping of several hours [3].

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“…Detailed discussions of the ambient-pressure optical properties have been reported previously by several groups. 3,18,19,33,[45][46][47][48][49] In Fig. 8 the optical reflectivity of α-(BEDT-TTF) 2 I 3 is displayed in the far and mid infrared (80 to 8000 cm −1 ) for both polarizations parallel and perpendicular to the a-axis; the plots correspond to the raw data taken off the diamond-to-sample interface at different temperatures as indicated.…”

Section: 63mentioning

confidence: 99%

“…Although the infrared optical properties of α-(BEDT-TTF) 2 I 3 have been measured repeatedly, 3,18,19,33,[45][46][47][48][49] to our knowledge no pressure and temperature-dependent optical studies have been reported by now that allow to follow the suppression of charge order and explore the properties of the occurring zero-gap state. Using our recently developed piston pressure cell for infrared measurements 50 we thus have performed comprehensive optical experiments on α-(BEDT-TTF) 2 I 3 that reveal the influence of pressure on the charge disproportionation and the suppression of the optical gap towards the zero-gap state.…”

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Pressure-dependent optical investigations ofα−(BEDT-TTF)2I3: Tuning charge order and narrow gap towards a Dirac semimetal

et al. 2016

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Infrared optical investigations of α-(BEDT-TTF)2I3 have been performed in the spectral range from 80 to 8000 cm −1 down to temperatures as low as 10 K by applying hydrostatic pressure. In the metallic state, T > 135 K, we observe a 50% increase in the Drude contribution as well as the mid-infrared band due to the growing intermolecular orbital overlap with pressure up to 11 kbar. In the ordered state, T < TCO, we extract how the electronic charge per molecule varies with temperature and pressure: Transport and optical studies demonstrate that charge order and metalinsulator transition coincide and consistently yield a linear decrease of the transition temperature TCO by 8 − 9 K/kbar. The charge disproportionation ∆ρ diminishes by 0.017 e/kbar and the optical gap ∆ between the bands decreases with pressure by -47 cm −1 /kbar. In our high-pressure and low-temperature experiments, we do observe contributions from the massive charge carriers as well as from massless Dirac electrons to the low-frequency optical conductivity, however, without being able to disentangle them unambiguously.

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Optical Investigations of the Electrical Anisotropy of α- and β- (BEDT-TTF)₂I₃

Cited by 47 publications

References 1 publication

Field and frequency dependent transport in the two-dimensional organic conductor α-(BEDT-TTF)2I3

Field and frequency dependent transport in the two-dimensional organic conductor α-(BEDT-TTF)2I3

The infrared optical properties of the α-phase organic superconductor, α-(BEDT - TTF)2 (NH4Hg(NCS)4)

Pressure-dependent optical investigations ofα−(BEDT-TTF)2I3: Tuning charge order and narrow gap towards a Dirac semimetal

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Optical Investigations of the Electrical Anisotropy of α- and β- (BEDT-TTF)2I3

Cited by 47 publications

References 1 publication

Field and frequency dependent transport in the two-dimensional organic conductor α-(BEDT-TTF)2I3

Field and frequency dependent transport in the two-dimensional organic conductor α-(BEDT-TTF)2I3

The infrared optical properties of the α-phase organic superconductor, α-(BEDT - TTF)2 (NH4Hg(NCS)4)

Pressure-dependent optical investigations ofα−(BEDT-TTF)2I3: Tuning charge order and narrow gap towards a Dirac semimetal

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Optical Investigations of the Electrical Anisotropy of α- and β- (BEDT-TTF)₂I₃