Magnetic Field-Induced Lattice Effects in a Quasi-2D Organic Conductor Close to the Mott Metal-Insulator Transition

We present ultra-high-resolution dilatometric studies in magnetic fields on a quasi-two-dimensional organic conductor $\kappa$-(D8-BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br, which is located close to the Mott metal-insulator (MI) transition. The obtained thermal expansion coefficient, $\alpha(T)$, reveals two remarkable features: (i) the Mott MI transition temperature $T_{MI}$ = (13.6 $\pm$ 0.6)\,K is insensitive to fields up to 10\,T, the highest applied field; (ii) for fields along the interlayer \emph{b}-axis, a magnetic-field-induced (FI) phase transition at $T_{FI}$ = (9.5 $\pm$ 0.5)\,K is observed above a threshold field $H_c \sim$ 1 T, indicative of a spin reorientation with strong magneto-elastic coupling.Comment: 5 pages, 4 figure

BEDT-TTF radical salts: organic metals and superconductors

A review of the structural, electronic and superconducting properties of some BEDT-TTF-radical salts is given

Structural aspects of organic superconductors

Some physical properties of the organic superconductors with the highest transition temperatures are presented. In addition the influence of small structural changes on the superconducting transition temperature is discussed. Finally bulk superconductivity in polycrystalline pressed pellets of organic metals is reported

First-order electronic phase transition in α\alpha-(BEDT-TTF)2_2I3_3 revealed by temperature-dependent generalized ellipsometry

The nature of correlation-driven metal-insulator transitions remains a longstanding puzzle in solid-state physics. While some theories suggest a second-order character, various experimental observations in these materials indicate first-order phase transitions. Despite considerable progress over the last decades in understanding the underlying driving mechanisms of metal-insulator transitions, in particular the phase coexistence remains poorly understood on a microscopic scale. Here, we employ Mueller matrix spectroscopic and temperature-dependent ellipsometry to determine the anisotropic dielectric functions of the two-dimensional charge-transfer salt $\alpha$-(BEDT-TTF)$_2$I$_3$ across its charge-order metal-insulator transition. Our results offer valuable insights into temperature-dependent changes of the dielectric functions along the different crystallographic axes. Furthermore, we apply an effective-medium approximation to quantify the correlation between the metal-to-insulator transition and the volume fraction of the metallic phase embedded within the insulating phase. Through this comprehensive approach, generalized ellipsometry unravels the nature of the correlation-driven metal-insulator transition

The anisotropy of conductivity of n-type germanium in strong d.c. fields

The electric conductivity of n-type germanium at large d.c. field intensities has been measured in three directions of symmetry of the cubic lattice. From these data the repopulation of valleys of the conduction band has been determined. Measurements were done with three materials of different purity. The variation of repopulation between these materials can be explained qualitatively by the influence of Coulomb scattering at ionized impurities. The data are compared with those of Nathan and theoretical data of Franz and Reik et al. The relations of these data to those of the current component perpendicular to the field direction (Sasaki et al.) are also given

Energy relaxation and intervalley relaxation of hot electrons in n-type germanium

The average current density in n-type germanium subjected to superimposed strong ac and weak dc electric fields was both measured and calculated for frequencies of 9 and 35 GHz. Repopulation relaxation of the conduction band valleys and energy relaxation were taken into account. Experimental and theoretical result agree qualitatively

Electronic interactions between polycyclic arenes in cyclophanes

The π-π interaction between polycyclic arenes and the effects of orientation were studied in [2.2]-, [3.3]-, and [3.2]naphthalenophanes, [2]naphthaleno[2]paracyclophanes, and syn- and anti[2.2](2,7)fluorenophane by electron absorption and emission spectroscopy as well as by optically detected magnetic resonance (ODMR) of the excited triplet state. The π-π interaction in the excited singlet and triplet state was found to be highest if a maximal number of sixmembered rings of the interacting arenes in a parallel orientation are completely eclipsed. Similarly, the π-π interaction between the nonbonding nitrogen electron pair and the aromatic π electrons was investigated in isomeric etheno-bridged naphthalenopyridinophanes and an anthracenopyridinophane; in these pyridinophanes, the pyridine rings are fixed perpendicularly above different sites of the naphthalene and anthracene units, respectively

Anisotropic chemical shifts and spin rotation constants of 15N from liquid and solid state NMR: Nitrobenzene

The study of the 15N spin-lattice relaxation time T1 in nitrobenzene at 14 and 32 MHz from −10 to 60°C showed that at 32 MHz relaxation due to anisotropic chemical shift is predominant. At low frequencies, the relaxation is caused mainly by spin rotation and at low temperature also by intermolecular dipole-dipole interaction. From the powder spectrum in solid nitrobenzene, the principal elements of the shielding tensor σ were obtained: σxx = −273 ± 10 ppm, σyy = +94 ± 10 ppm, and σzz = +156 ± 10 ppm relative to liquid nitrobenzene, Δσ = σ xx - ½(σ yy + σ zz) = -398 ± 20ppm. From the almost axially symmetric σ -tensor, the spin rotation constants were calculated: C‖ = 11.4 ± 1.5 kHz and C⊥ = 1.35 ± 0.5 kHz, where C‖ is the component parallel to the twofold axis of the molecule. These values for Δσ and the spin rotation constants are in excellent agreement with those obtained by analysis of the relaxation data. A comparison of anisotropic chemical shifts and spin rotation constants for 15N and 13C in isoelectronic compounds is given