O. A. Bogdanova

New BETS based molecular conductors with bromomercurate anions

Five BETS-based salts with different bromomercurate anions have been isolated. Some of these compounds ungergo the M-I transition with the temperature decrease, the others behave as metals. Among them a salt of nonstoichiometric composition BETS 4 Hg 2.84 Br 8 has been found with κ-type packing of organic layers.

Infrared spectra of conducting BEDSe-TTF charge-transfer salts with halide mercurate anions

Abstract We report on the studies of single crystal reflectance spectra (650–6500 cm −1 ) of four conducting radical cation salts formed by the organic donor, bis(ethylenediseleno) tetrathiafulvalene (BETSe-TTF) and mercury halide anions, Hg 3 Br 8 , HgBr 4 , Hg 2 I 6 and HgCl 4 . Additionally, infrared (IR) and Fourier transform near infrared (FT-NIR) Raman spectra of neutral BEDSe-TTF were measured. Electronic bands are analysed using a Drude–Lorentz dielectric function. Vibrational bands, mainly those related to the coupling of electrons with internal vibrations of BEDSe-TTF, are discussed. Considerable differences between IR spectra of the studied salts are mainly due to different charge of BEDSe-TTF cations.

Optical properties of a new organic metal (BEDO-TTF)5[CsHg(SCN)4]2

Abstract Polarized reflectance and optical conductivity spectra of single crystals of a new organic conductor based on the BEDO molecule, BEDO 5 [CsHg(SCN) 4 ] 2 , were investigated in the 600–6500 cm −1 and 9000–40 000 cm −1 range for the three principal axis at 300 K. Quasi-two-dimensional character of the conducting electronic system was established. The parameters of electronic system were obtained using the Drude model. The conducting bands of the investigated conductor appeared to be narrower than those of the recently investigated superconductor with the analogous structure, (BEDO-TTF) 2 ReO 4 (H 2 O). An assignment of the vibrational features for all the investigated polarizations was proposed.

BEDT-TTF, BEDO-TTF, and BEDSe-TTF salts with metal containing anions

Abstract The synthesis of new BEDO-TTF and BEDSe-TTF based salts with metal containing anions [HgX 3 ] − , [HgX 4 ] 2− , [Hg 3 X 8 ] 2− (X = Cl, Br, I), [Hg 3.5 I 9 ] 2− , [KHg(SCN) 4 ] − , [NH 4 Hg(SCN) 4 ] 2− , and [Pt(CN) 4 ] 2− is discussed. Most of the BEDO-TTF salts behave as metals down to 4 K. Among BEDSe-TTF salts only (BEDSe-TTF) 4 Hg 3 Br 8 TCE is a metal with the metal-insulator transition at 193 K.

Electron and electron-phonon effects in the quasi-two-dimensional molecular conductor θ-(BETS)4HgBr4(C6H5Cl): Optical studies at 300–15 K

This paper reports on a study of the polarized reflectance and optical conductivity spectra of the quasi-two-dimensional molecular conductor θ-(BETS)4HgBr4(C6H5Cl) within the 700–6500-cm−1 region at 300–15 K and within the 9000–40 000 cm−1 region at 300 K performed along two principal directions in the crystal plane parallel to the conducting layers of the BETS molecules. The IR spectra obtained at 300 K follow a close-to-Drude behavior, with strong broad features (1200–1400 cm−1) due to electron-vibrational (vibronic) coupling (VC) superposed on the high Drude background. As the temperature is lowered in the range 180–80 K, in the spectra there appears a Lorentz term with ωt=2900 cm−1, as well as three additional VC-induced bands in the 800–1180-cm−1 region, which disappear as the temperature is decreased further. The results obtained indicate the existence of unstable structural distortions along the two principal directions in the crystal, which are accompanied by the formation of a commensurate charge-density wave.

Temperature dependence of infrared reflectance spectra of BEDO5[CsHg(SCN)4]2

Polarized reflectivity spectra of a new organic conductor BEDO 5 [CsHg(SCN) 4 ] 2 were measured in the spectral range of 700-6500cm -1 at 300-10 K. An anisotropy of temperature behavior of optical conductivity in the conducting plane was observed, it shows metallic character for the direction perpendicular to BEDO stacks and non-metallic behavior for the direction parallel to BEDO stacks, where a growth of a broad band at near 4000 cm -1 testifies for the appearance of an energy gap. Fitting by the Drude-Lorentz model points on an existence of a low-frequency energy gap. The gaps may appear due to dimerisation of BEDO molecules in the stacks at low temperatures.

De Haas-van Alphen oscillations in the quasi-two-dimensional organic metal (BEDO-TTF)5[CsHg(SCN)4]2

The magnetization oscillations in the quasi-two-dimensional organic metal (BEDO-TTF)5[CsHg(SCN)4]2 are thoroughly investigated over a wide range of magnetic field directions at different temperatures down to 0.4 K. The results obtained are in good agreement with the shape and sizes of the Fermi surface calculated from the x-ray diffraction data. Apart from the fundamental frequencies, the combination frequencies are found in the magnetization oscillation spectrum. It is demonstrated that these combination frequencies are governed by the motion of charge carriers along the real closed orbits inside the network of magnetic breakdown orbits formed under the action of the magnetic field. It is uniquely established that the combination frequencies previously revealed in the magnetoresistance oscillation spectrum of the same metal are associated with the quantum interference effect. The angular dependences of the oscillation amplitude exhibit minima, which are explained by the spin splitting of the Landau levels.

Recovery of the metallic state and quantum oscillations in a dielectric salt of the (ET)8[Hg4X12(C6H5Y)2] family at X = Y = Br under compression

The quasi-two-dimensional organic conductor (ET)8[Hg4Br12(C6H5Br)2] (ET is bis(ethylenedithio)tetrathiafulvalene) undergoes a metal-insulator phase transition at T ∼ 170 K. It has been shown that a pressure of 8 kbar suppresses this transition and holds a metallic state to liquid-helium temperatures. Shubnikov—de Haas quantum oscillations with the single frequency F = 215 T have been observed in a magnetic field up to 15 T. The properties of this salt are compared to the properties of the (ET)8[Hg4Cl12(C6H5Cl)2] salt of the same family. Time annealing provides an important effect on the conducting properties of the salt under investigation.

Quantum oscillations in a novel organic quasi-two-dimensional (BEDO-TTF) 5 [RbHg(SCN) 4 ] 2 metal

Quantum magnetization and magnetoresistance oscillations are detected in the quasi-two-dimensional organic metal (BEDO-TTF)5[RbHg(SCN)4]2 for the first time. The magnetization oscillation spectrum corresponds to a calculated Fermi surface provided that a magnetic breakdown is realized. The magnetoresistance oscillation spectrum contains additional frequencies, one of which can unambiguously be related to quantum interference. An analysis of the angular dependence of the magnetoresistance oscillation amplitude indicates that the many-body interactions in this metal are weak.

Transport, Magnetic and Optical Properties of a Quasi-Two-Dimensional Organic Metal Based on BEDO-TTF (Bis-(Ethylenedioxy) Tetrathiafulvalene)

Polarized reflectivity spectra, tight binding band structure calculations as well as magnetoresistance and magnetization measurements have been carried out for the new quasi-two-dimensional organic conductor β″-(BEDO-TTF)5[CsHg(SCN)4]2. Polarized reflectivity and optical conductivity spectra have shown that at low temperatures this salt exhibits metallic behaviour in the direction perpendicular to the BEDO-TTF stacks, but non-metallic behaviour in the direction parallel to the stacks. It is supposed that the non-metallic behaviour is due to the dimerization of BEDO-TTF molecules in the stacks at low temperatures. Tight binding calculations suggest that the Fermi surface can be described as containing two contributions: a closed two-dimensional portion associated with holes and a open, pseudo-one-dimensional portion associated with electrons. Shubnikov-de Haas and de Haas-van Alphen oscillations have shown that some frequencies of their complicated Furie spectra are in good agreement with the calculated Fermi surface. The other frequencies of the spectra can be well understood in the frame of the quantum interference effect.