M. V. Kartsovnik

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.

de Haas-van Alphen oscillations and angular magnetoresistance oscillations in the organic metal κ-(BETS)2GaCl4

Quantum de Haas-van Alphen oscillations and semiclassical angular magnetoresistance oscillations are observed in the quasi-two-dimensional organic metal κ-(BETS)2GaCl4. The behavior of these oscillations attests to the existence of two cylindrical Fermi surface sheets with axes perpendicular to the conducting plane. The cross-sectional areas of these cylinders in the conducting plane are equal to about 20 and 100% of the corresponding cross section of the Brillouin zone. It is shown that the many-particle interaction can be suppressed significantly in this compound.

On the possibility of a radical decrease in the strength of many-body interactions in the organic metal α-(BETS)2 KHg(SCN)4

Behavior of the de Haas-van Alphen (dHvA) oscillations depending on the angle between the magnetic field direction and the perpendicular to conducting layers in the quasi-two-dimensional organic metal α-(BETS)2 KHg(SCN)4 was studied in detail. The angular dependence of the dHvA oscillation amplitude exhibits a series of minima (at ±43.2°, ±64.6°, and ±72.0°) related to the “zero spin” effect, through which it is possible to estimate the splitting factor. An analysis of this value suggests that many-body interactions in the compound studied are either absent or at least radically weakened.

Possible weakening of the many-body interactions in the organic quasi-two-dimensional metal α-(BETS)2NH4Hg(SCN)4

The behavior of the de Haas-van Alphen oscillations in the organic quasi-two-dimensional metal α-(BETS)2NH4Hg(SCN)4 is comprehensively studied as a function of the angle between the magnetic-field direction and the normal to the conducting layers in it. The angular dependence of the oscillation amplitude has minima at angles of ±40° and ±62°, which are caused by the spin zero effect. The positions of these minima suggest that the electron-phonon and electron-electron interactions in this metal are significantly weakened.

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.

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.

Fermi surface in the new organic quasi-two-dimensional metal alpha-(BETS)(2)TlHg(SeCN)(4)

Quantum oscillations of de Haas-van Alphen and Shubnikov-de Haas and semiclassical angular oscillations of the magnetoresistance have been observed in the quasi-two-dimensional organic metal α-(BETS)2TlHg(SeCN)4. The quantum oscillations are connected with the cylindrical part of the Fermi surface. The angular oscillations are associated with the carrier motion on both the cylindrical part and quasi-planar sheets of the Fermi surface. The values of the Dingle temperature, TD ≈ 2–3 K, and the effective mass, m* ≈ 1.03m0, have been defined. The possibility of the weakening of multibody interactions has been shown in this 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.