Spin-current injection and detection in strongly correlated organic conductor

Spin-current injection into an organic semiconductor $\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$ film induced by the spin pumping from an yttrium iron garnet (YIG) film. When magnetization dynamics in the YIG film is excited by ferromagnetic or spin-wave resonance, a voltage signal was found to appear in the $\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$ film. Magnetic-field-angle dependence measurements indicate that the voltage signal is governed by the inverse spin Hall effect in $\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$. We found that the voltage signal in the $\rm{\kappa\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$/YIG system is critically suppressed around 80 K, around which magnetic and/or glass transitions occur, implying that the efficiency of the spin-current injection is suppressed by fluctuations which critically enhanced near the transitions

DC and high-frequency conductivity of the organic metals beta"-(BEDT-TTF)2SF5RSO3 (R = CH2CF2 and CHF)

The temperature dependences of the electric-transport properties of the two-dimensional organic conductors beta"-(BEDT-TTF)2SF5CH2CF2SO3, beta"-(d8-BEDT-TTF)2SF5CH2CF2SO3, and beta"-(BEDT-TTF)2SF5CHFSO3 are measured by dc methods in and perpendicular to the highly-conducting plane. Microwave measurements are performed at 24 and 33.5 GHz to probe the high-frequency behavior from room temperature down to 2 K. Superconductivity is observed in beta"-(BEDT-TTF)2SF5CH2CF2SO3 and its deuterated analogue. Although all the compounds remain metallic down to low-temperatures, they are close to a charge-order transition. This leads to deviations from a simple Drude behavior of the optical conductivity which become obvious already in the microwave range. In beta"-(BEDT-TTF)2SF5CH2CF2SO3, for instance, charge fluctuations cause an increase in microwave resistivity for T < 20 K which is not detected in dc measurements. beta"-(BEDT-TTF)2SF5CHFSO3 exhibits a simple metallic behavior at all frequencies. In the dc transport, however, we observe indications of localization in the perpendicular direction.Comment: 8 pages, 9 figure

Ground state and finite temperature behavior of 1/4-filled band zigzag ladders

We consider the simplest example of lattice frustration in the 1/4-filled band, a one-dimensional chain with next-nearest neighbor interactions. For this zigzag ladder with electron-electron as well as electron-phonon interactions we present numerical results for ground state as well as thermodynamic properties. In this system the ground state bond distortion pattern is independent of electron-electron interaction strength. The spin gap in the ground state of the zigzag ladder increases with the degree of frustration. Unlike in one-dimension, where the spin-gap and charge ordering transitions can be distinct, we show that in the ladder they occur simultaneously. We discuss spin gap and charge ordering transitions in 1/4-filled materials with one, two, or three dimensional crystal structures. We show empirically that regardless of dimensionality the occurrence of simultaneous or distinct charge and magnetic transitions can be correlated with the ground state bond distortion pattern.Comment: 12 pages, 8 eps figure

Charge-ordering in θ\theta -(BEDT-TTF)2_{2}MM′^\prime (SCN)4_{4} [ M = Cs, Rb, Tl, M′^\prime = Zn, Co]

Vibrational spectra, x-ray scattering and electrical resistivity of $\theta$-(BEDT-TTF)$_{2}$MM$^\prime$(SCN)$_{4}$, [ M = Cs, Rb, Tl, M$^\prime$ = Zn, Co] were measured in various temperature ranges. Vibrational spectra with the aid of x-ray scattering manifested charge disproportionation and charge ordering in their low-temperature phases. Except $\theta$-(BEDT-TTF)$_{2}$CsM$^\prime$(SCN)$_{4}$, the orthorhombic form provided a horizontal stripe. On the other hand, monoclinic $\theta$-(BEDT-TTF)$_{2}$TlZn(SCN)$_{4}$ provided a diagonal stripe. The electronic state of the high-temperature phase is discussed based on the line shape of the Raman spectrum. Key words. Charge-ordering, BEDT-TTF, Raman spectroscopy, infrared spectroscopy

Charge disproportionate state of BEDT-TTFβ′′\beta '' – salts

We studied C=C stretching bands of $\beta''$-(ET)$_{3}$(ReO$_{4})_{2}$ and $\beta$-(ET)$_{4}$M(CN)$_{4}$H$_{2}$O (M=Pt, Pd and Ni) at the low temperatures below 300 K in order to verify the inhomogeneous charge distributions. A drastic spectral change was observed for $\beta ''$-(ET)$_{3}$(ReO$_{4})_{2}$ at 80 K, below which the system falls into the charge ordered state. On the other hand, a continuous spectral change was observed for $\beta ''$-(ET)$_{4}$Ni(CN)$_{4}$H$_{2}$O and $\beta ''$-(ET)$_{4}$Pd(CN)$_{4}$H$_{2}$O. $\nu$$_{2}$ for M=Ni and Pd exhibited a doublet, suggesting an inhomogeneous charge distributions. $\nu$$_{2}$ for M=Pt did not show a peak splitting, while C=C bands for the deuterium analogue exhibited a behaviour similar to those for M=Ni. Key words. Molecular conductors – organic conductors – ET salts – vibrational spectra – structural analyses – charge ordered state – mean-field calculations–isotope effect

Isotope Effect on Metal-Insulator Transition of (EDO-TTF)2XF6(X=P,As) with Multi-Instability of Metallic State

The partially deuterated 4,5-ethylenedioxy-tetrathiafulvalene-d2 (EDO-TTF-d2) was synthesized from the undeuterated EDO-TTF-d0. The single crystals of (EDO-TTF-d2)2XF6 (X = P, As) were prepared by the conventional electrocrystallization technique. The deuterium contents of EDO-TTF-d2 itself and the radical cation salts were 99% D by mass spectral analysis. The magnetic susceptibility measurement revealed that (EDO-TTF-d2)2XF6 undergoes a metal–insulator transition at 2–3 K higher temperature than the undeuterated salts. In infrared and Raman spectra, significant isotope shifts were observed not only on C–H vibrational modes but also on TTF-skeletal modes. The assignment of experimental bands was performed on the basis of normal-mode analysis at B3LYP/6-31G(d,p) level of theory