A.E. Kovalev

The first ET salt with a metal complex anion containing a selenocyanate ligand, (ET)2TIlHg(SeCN)4 : synthesis, structure and properties

Synthesis of the first ET salt with a metal complex anion containing a selenocyanate ligand, α-(ET) 2 TlHg (SeCN) 4 , and its structure are reported. The temperature dependence of conductivity and thermopower in various crystallographic directions and the Shubnikov-de Haase oscillations have been studied. Distinctions of the bond length distributions in three crystallographically independent ET have been found, which may result in some charge localization in the radical-cation layer. A detailed comparison of the structure and properties of the compound obtained to its thiocyanate analog has been performed. It has been shown that in the α-(ET) 2 TlHg(SeCN) 4 salt there is no low-temperature phase transition characteristic of the α-(ET) 2 MHg(SCN) 4 compounds with M=K, Tl and Rb

Cyclotron resonance in the organic conductor (BEDO-TTF)2ReO4(H2O) in the millimeter wavelength band

Resonant microwave absorption in a (BEDO-TTF)2ReO4(H2O) organic conductor single crystal at a temperature of 1.9 K, a magnetic field of up to 70 kOe, and in the frequency band between 30 and 120 GHz has been studied. A spectral component due to the cyclotron resonance (CR) of two-dimensional charge carriers has been identified for ν⩾80 GHz and H⩾10 kOe. The effective mass m(ω) increases with the frequency from m≈0.8m0 at ν=80 GHz to m≈0.95m0 at ν=120 GHz. Measurements of the CR line position and FWHM as functions of frequency yield an independently determined imaginary part of the memory function M(ω), which controls the dynamic magnetoconductivity, and the relaxation time τ(ν=100 GHz)≈2.9×10−11 s, which is more than thirty times the value of this parameter in the low-frequency limit τ(ν→0). The anomalous behavior of the CR line position and FWHM is caused by the dispersion of both real and imaginary parts of M(ω), which are probably due to strong Fermi-liquid effects.

Influence of magnetic field on the electronic specific heat of the organic metal (BEDT-TTF)2KHg(SCN)4

Specific heat measurements of a single crystal of the organic metal (BEDT-TTF)2KHg(SCN)4 have been carried out at low temperatures and under a magnetic field of up to 14 T. A jump in the specific heat of about 0.1 J/mol·K, which corresponds to the antiferromagnetic phase transition, has been observed. The magnetic field is found to decrease the transition temperature at any field orientation. The strongest effect was found to take place in the field direction along the highly conducting ac plane.

Different types of angular magnetoresistance oscillations in the low- and high-temperature states of the organic conductor (BEDTTTF)2KHg(SCN)4

Abstract Angular oscillations of semi-classical magnetoresistance of (BEDTTTF) 2 KHg(SCN) 4 have been studied at different temperatures under a magnetic field rotated in various planes perpendicular to the highly conducting ac -plane. At temperatures above the phase transition, T > T p ≈ 8 K , the oscillations are attributed to the electron motion along the closed orbits of the Fermi surface cylinder. In contrast, the low-temperature oscillations are found to be associated with the existence of a specific plane determined most likely by the wave vector of the superstructure arising below T p .

Magnetoresistance oscillations in layered organic conductors (BEDT—TTF)2TlHg(XCN)4 with S = S and Se

Abstract Magnetoresistance anisotropy of (BEDT—TTF)2TlHg(XCN)4 with X =S and Se has been studied in magnetic fields up to 30 T. The magnetoresistance of the Se-containing salt is shown to be dominated by an extremely weakly warped Fermi surface cylinder. The behavior of the compound with X = S is more complicated. At fields below 20 T the magnetoresitance oscillations reveal a commensurate superstructure associated most likely with the antiferromagnetic phase transition. Higher fields, above 27 T, appear to suppress the magnetic order and restore the high-temperature electronic state.

Pressure-effect and anisotropy of resistivity in organic metal (ET)2TlHg(SCN)4

Abstract A influence of quasi-hydrostatic pressure on the conducting properties of the organic metal (ET) 2 TlHg(SCN) 4 was investigated. The low-temperature anomaly (T 3 Kbar so that the high-temperature metallic state is stabilized down to 1.3 K. Temperature dependencies of the resistance were studied for different cristallographical directions. It was established that there is a correlation between the resistance anisotropy and the presumed shape of Fermi surface.

Shubnikov-de haas oscillations in a new stable organic metal κ-(BETS)2C(CN)3

Abstract Shubnikov-de Haas oscillations in a new radical cation salt κ-(BETS) 2 C(CN) 3 have been studied in magnetic fields 7–14 T applied perpendicular to the highly conducting plane. The Fourier spectrum of the oscillations exhibits four prominent peaks, revealing a multiple-connected magnetic breakdown network of the electron orbits typical of the κ-type organic conductors. The obtained data are discussed in the framework of the full tight-binding band structure calculations. The cyclotron masses are considerably smaller than those found in κ-(BEDT-TTF) 2 X superconductors suggesting a lower role of many body interactions in the present compound.

Quantum and semiclassical oscillations in the organic metal, (BEDO-TTF)(2)Cl-x(H2O)(y)

We study quantum (Shubnikov-de Haas and de Haas-van Alphen) oscillations and angular oscillations of the reluctance in the organic quasi-two-dimensional metal (BO)2Clx(H2O)y. We show that the Fermi surface in this compound consists of a slightly corrugated cylinder with its axis perpendicular to the conducting plane. The cross section of the cylinder in this plane is a perfect circle of radius kF≃3×107 cm−1. The effective carrier mass associated with this cylinder is m*=(1.65–2.0) m0 in the conducting plane, while the Dingle temperature is TD=3–4 K.

Comparative torque studies of α-(BEDT-TTF)2MHg(SCN)4 (M = K, Tl, NH4)

Abstract We report comparative studies of oscillatory (de Haas-van Alphen effect) and steady (anisotropy of the static susceptibility) torque in the quasi-two-dimensional organic metals α-(BEDT-TTF) 2 MHg(SCN) 4 (M = K, Tl, NH 4 ). The measurements were carried out with a torque-magnetometer in magnetic fields up to 28 T and temperatures between 0.4 and 4.2 K. Up to the highest fields, no anomalous behaviour of the steady or oscillatory torque is observed in the NH 4 salt. In contrast the K and Tl salts undergo a phase transition the so-called “kink transition” at around 23 and 26 T respectively. These two compounds show very similar behaviour. For Θ ≤ 60° where Θ is the angle between the magnetic field and the normal to the conducting planes the phase transition is characterized by a strong increase in the oscillation amplitude. For Θ ≥ 60°, the kink transition can no longer be clearly seen but up to the highest fields, several anomalies appear together with strong hysteresis of the steady torque.

Galvanomagnetic properties of the new organic metal ET2TlHg(S0.45Se0.55CN)4

Magnetoresistance and magnetic torque have been studied in the single crystals of the mixed complex (ET)2TlHg(S0.45Se0.55CN)4. The quantum oscillations (Shubnikov-de Haas and de Haas-van Alphen) have been observed and investigated in details in this compound. The behavior of these oscillations is close to that in the complex (ET)2TlHg(SeCN)4 but is characterized by a stronger carrier scattering induced by the disordered positions of the S and Se atoms in the anion.