The angular dependent magnetoresistance in alpha-(BEDT-TTF)_2KHg(SCN)_4

In spite of extensive experimental studies of the angular dependent magnetoresistance (ADMR) of the low temperature phase (LTP) of alpha-(BEDT-TTF)_2KHg(SCN)_4 about a decade ago, the nature of LTP remains elusive. Here we present a new study of ADMR of LTP in alpha-(ET)_2 salts assuming that LTP is unconventional charge density wave (UCDW). In the presence of magnetic field the quasiparticle spectrum in UCDW is quantized, which gives rise to striking ADMR in UCDW. The present model appears to account for many existing ADMR data of alpha-(BEDT-TTF)_2KHg(SCN)_4 remarkably well.Comment: 6 pages, 4 figure

Anisotropic charge dynamics in the quantum spin-liquid candidate κ\kappa-(BEDT-TTF)2_2Cu2_2(CN)3_3

We have in detail characterized the anisotropic charge response of the dimer Mott insulator $\kappa$-(BEDT-TTF)$_2$\-Cu$_2$(CN)$_3$ by dc conductivity, Hall effect and dielectric spectroscopy. At room temperature the Hall coefficient is positive and close to the value expected from stoichiometry; the temperature behavior follows the dc resistivity $\rho(T)$. Within the planes the dc conductivity is well described by variable-range hopping in two dimensions; this model, however, fails for the out-of-plane direction. An unusually broad in-plane dielectric relaxation is detected below about 60 K; it slows down much faster than the dc conductivity following an Arrhenius law. At around 17 K we can identify a pronounced dielectric anomaly concomitantly with anomalous features in the mean relaxation time and spectral broadening. The out-of-plane relaxation, on the other hand, shows a much weaker dielectric anomaly; it closely follows the temperature behavior of the respective dc resistivity. At lower temperatures, the dielectric constant becomes smaller both within and perpendicular to the planes; also the relaxation levels off. The observed behavior bears features of relaxor-like ferroelectricity. Because heterogeneities impede its long-range development, only a weak tunneling-like dynamics persists at low temperatures. We suggest that the random potential and domain structure gradually emerge due to the coupling to the anion network.Comment: 14 pages, 13 figure

Interplay between the glassy transition and granular superconductivity in organic materials

It is known that some (BEDT-TTF)2X layered organic superconductors undergo a glassy transition near 80 K. Our purpose is to exploit quenched disorder to get new insights on both the superconducting state (T < 12 K) and the glassy transition by studying the superconducting properties as functions of annealing time (ta) and temperature (Ta) around 80 K. The main results on the fully deuterated kappa-(BEDT-TTF)2Cu[N(CN)2]Br compound are: 1) The data can be described by a percolation cluster model. 2) At short time scales, the clusters grow with ta following a power law. 3) At large time scales the clusters grow toward a thermodynamic state following a stretched exponential law in (1 - exp(-(t/tau)beta)with beta varying from about 0.5 to 1 in our Ta range (65 - 110 K). 4) The relaxation time follows an Arrhenius law tau(T)=tau0exp(U/T) with U around 2660 K and 1/tau0 around 2x1013 s-1. 5) The asymptotic magnetization fits with a scaling law with Tg around 55K and n around 3.2. The results are consistent with a Ising spin-glass-like model.Comment: 17 pages; 4 figure

Theory of c-axis Josephson tunneling in d-wave superconductors

The temperature and angular dependence of the c-axis Josephson current and the superfluid density in layered d-wave superconductors are studied within the framework of an extended Ambegaokar-Baratoff formalism. In particular, the effects of angle-dependent tunneling matrix elements and Andreev scattering at grain boundaries are taken into account. These lead to strong corrections of the low-temperature behavior of the plasma frequency and the Josephson current. Recent c-axis measurements on the cuprate high-temperature superconductors HgBa_2CaCu_{1+\delta} and Bi_2Sr_2CaCu_2O_{8+\delta} can therefore be interpreted to be consistent with a d-wave order parameter.Comment: Revtex, 4 pages with 4 eps figures, to appear in PRB R

Modalities of self-organized charge response in low dimensional systems

We present modalities of self-organized charge response in low dimensional systems, like diverse organic and quantum spin systems, studied by the low-frequency (10 mHz – 1 MHz) dielectric spectroscopy. Density wave structures with the order of commensurability N = 4 can be recognized as phasons in a random impurity potential, whereas those with N = 3 can be viewed as topological defects like charge domain wall pairs in the background domain structure

(Data set) Distinction of charge transfer and Frenkel excitons in pentacene traced via infrared spectroscopy

Data from the publication are given in Origin format with Figure codes. More data are available upon request

Single-particle and spin-density wave charge dynamics in (TMTSF)2PF6 and (TMTSF)2AsF6 : A comparative overview

We present the results of DC and AC (100 mHz - 1MHz) electrical transport measurements in low and high electric fields performed in the spin-density wave (SDW) state of the Bechagaards salts (TMTSF)2PF6 and (TMTSF)2AsF6. We argue that a degree of complex structure of the SDW ground state which is unfolded in a particular experiment depends strongly on the chosen experimental probe and the crystal measured

In-plane and out-of-plane superfluid density of the layered organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br

The anisotropic magnetic penetration depth λb and λac, where t = T/Tc, in the layered organic superconductor [MATH] (abbreviated as [MATH]) are obtained from AC susceptibility data. We find λb(0)= 133 µm, consistent with earlier results and [MATH], which is new. Also, assuming λac(0) ≈ 1 µm, we obtain [MATH]. The observed power laws are consistent with the ones expected in d-wave superconductivity