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It is shown that the dielectric relaxation in barrier coatings may be interpreted in terms of a ‘two-step’ continuous time random walk in one dimension. This was proved by comparison of the results using a normalised constant phase element whereby the evaluated coating parameters are in good agreement using both models. An analysis of the frequency dependence of the evaluated coating parameters suggests that the coating capacity calculated by means of a Young–Goehr impedance can be considered to represent a kind of border value for the normalised CPE—as well as for the random walk model. Comparing the results of electrochemical impedance spectroscopy and relaxation voltammetry one has to take into account the frequency dependence of the calculated coating parameters. Furthermore, an example is given which demonstrates that one can obtain equal results choosing the same frequency range and the same model using both techniques.

After a short introduction into the application of organic barrier coatings for corrosion protection the expectable parameters of the tested materials are discussed and the principle limitations are shown. Electrochemical impedance spectroscopy (EIS) is an already well known and also widely used technique, here only a very fundamental approach will be given. Relaxation voltammetry (RV) is a new electrochemical technology in the time domain. RV allows a two-step data interpretation: first a very direct and easy accessible extraction of the coating resistance and coating capacity from the raw data. Second, a much more detailed interpretation of electrochemical processes in the coating in terms of dielectric relaxation, diffusion and charge transfer is presented and discussed in this paper. Elektrochemische Untersuchungen von schutzenden organischen Barrierebeschichtungen – Grenzen der Technik mit Kleinsignalerregung Nach einer kurzen Einfuhrung in die Anwendung von Barrierebeschichtungen fur den Korrosionsschutz werden die zu erwartenden Parameter der untersuchten Materialien diskutiert und die grundsatzlichen Einschrankungen aufgezeigt. Elektrochemische Impedanzspektroskopie (EIS) ist eine schon gut bekannte und haufig angewendete Technik, weshalb hier nur die zugrunde liegenden Ansatze erklart werden. Relaxationsvoltammetrie (RV) ist eine neue elektrochemische Technologie in der Zeitdomane. RV erlaubt eine zweistufige Dateninterpretation: im ersten Schritt werden die leicht zuganglichen Beschichtungswiderstande und Kapazitaten aus den Rohdaten extrahiert. In einem zweiten Schritt wird eine wesentlich detailliertere Interpretation der elektrochemischen Prozesse in der Beschichtung auf der Basis von dielektrischer Relaxation, Diffusion und Ladungstransport in dieser Veroffentlichung vorgestellt und diskutiert.

The new π -electron donor bis(1.3-cylobutylenedithio)tetrathiafulvalene (1.3-CBDT-TTF), which is only slightly different in the periphery of the molecule with respect to the well-known donor BEDT-TTF, was synthesized. The molecular structure has been characterized and the electrochemical behavior of this new donor was investigated. New cation radical salts were prepared by electrocrystallization methods. The structures of (1.3-CBDT-TTF)I 2 , (1.3-CBDT-TTF) 2 [AuI 2 ], (1.3-CBDT-TTF) x (ReO 4 ) y and (1.3-CBDT-TTF) 2 PF 6 ·THF were characterized by X-ray analyses. The room temperature electrical resistivities of the radical salts are low and range between 0.5 and 5 Ω cm.

Seventeen different commercially available barrier coatings were investigated using relaxation voltammetry (RV). From the analysis of the potential transients over a wide relaxation range, it is concluded that the whole relaxation procedure can be described by the superposition of three elementary processes: a charge transfer, a dielectric relaxation and a diffusion process. The detailed analysis of the mathematical properties of the dielectric relaxation contribution leads to a Williams–Watts like transfer function: φ(t)=2 exp[−(λt)β]−exp[−2(λt)β], where φ(t) is the normalised transient decay for pure dielectric relaxation, λ a macroscopic (reciprocal) time constant and β=0.5. A ‘two-step’ continuous time random walk mechanism is proposed for the dielectric relaxation process. Furthermore, it is shown that for the coatings under investigation an ‘ideal behaviour’ is more the rule than the exception.

The Fermi surface (FS) of the new organic metal (BEDT-TTF)4[ Ni(dto)2] has been investigated by de Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) experiments. In both quantum oscillations with two different frequencies Fα = 634 T and Fβ = 4245 T are observed. These results confirm the calculated FS, which consists of one-dimensional and two-dimensional parts separated by a small energy gap. It is shown that the temperature and field dependence of the oscillation amplitudes can be well described by standard Lifshitz-Kosevich theory considering the magnetic breakdown by the so-called coupled network model. Beatings of the oscillation amplitudes are observed by field-dependent dHvA and SdH experiments. They can be explained by a slightly warped FS showing that this material represents a quasi–two-dimensional electronic system. The observed beating nodes in the dHvA and SdH signals appear at different magnetic fields. This fact is discussed in terms of additional scattering mechanisms.

High-resolution specific-heat measurements of the organic superconductor kappa-(BEDT-TTF)(2)-Cu[N(CN)(2)]Br in the superconducting ( B = 0) and normal ( B = 14 T) states show a clearly resolvable anomaly at T(c) = 11.5 K and an electronic contribution, C(es), which can be reasonably well described by strong-coupling BCS theory. Most importantly, C(es) vanishes exponentially in the superconducting state which gives evidence for a fully gapped order parameter.

In this paper, we report transport measurements of the interlayer magnetoresistance with field, H, parallel to the current, J, in the organic superconductor κ-(bis(ethylenedithio)-tetrathiafulvalene (ET))2I3. The isothermal magnetoresistance R(H) displays a peak as a function of field for 1>T/Tc≥0.4. At lower temperatures T/Tc

The anisotropic magnetic penetration depth lambda /sub b/(t) and lambda /sub ac/(t), where t=T/T/sub c/, in the layered organic superconductor kappa -(BEDT-TTF)/sub 2/CuN(CN)/sub 2/Br (abbreviated as kappa -ET-Br) are obtained from AC susceptibility data. We find lambda /sub b/(0)=133 mu m, consistent with earlier results and Delta lambda /sub b/(t)= lambda /sub b/(t)- lambda /sub b/(0) varies as t/sup 2/, which is new. Also, assuming lambda /sub ac/(0) approximately=1 mu m, we obtain Delta lambda /sub ac/(t) varies as t. The observed power laws are consistent with the ones expected in d-wave superconductivity.

ac susceptibility measurements are reported for single crystals of the layered organic superconductor $\ensuremath{\kappa}{\ensuremath{-}(\mathrm{B}\mathrm{E}\mathrm{D}\mathrm{T}\ensuremath{-}\mathrm{T}\mathrm{T}\mathrm{F})}_{2}\mathrm{Cu}[\mathrm{N}(\mathrm{CN}{)}_{2}]\mathrm{Br}.$ The value of the out-of-plane penetration depth ${\ensuremath{\lambda}}_{b}(0)$ was found to be 133 $\ensuremath{\mu}\mathrm{m},$ consistent with earlier results. The temperature dependence of the in-plane superfluid density, with the value of in-plane component ${\ensuremath{\lambda}}_{\mathrm{ac}}(0)$ of the order of 1 $\ensuremath{\mu}\mathrm{m},$ is strongly linear in T, whereas the out-of-plane superfluid density varies as ${T}^{2}$ at low temperatures. The observed behavior is fully consistent with the one expected for d-wave superconductivity.

A comparison of the temperature dependant reflectivity spectra of the organic superconductor κ-(h 8 -BEDT-TTF) 2 Cu[N(CN) 2 ]Br and κ-(d 8 -BEDT-TTF) 2 Cu[N(CN) 2 ]Br on rapid cooling is presented. κ-(d 8 -BEDT-TTF) 2 Cu[N(CN) 2 ]Br is on the border of a superconductor—magnetic-insulator transition. On rapid cooling, the low temperature ground state is a purely magnetic phase. The reflectivity spectra then are very similar as for κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl which has an antiferromagnetic ground state. It is proposed that localized charge carriers contribute to the mid-infrared reflectivity of the low temperature magnetic phase of κ-(d 8 -BEDT-TTF) 2 Cu[N(CN) 2 ]Br.

A new magneto-quantum oscillation (QO) frequency F0=13.2 T is observed in the normal conducting state of the strong two-dimensional (2D) organic superconductor κ-(BEDT-TTF)2I3. Such a frequency is neither predicted by band-structure calculations nor yet observed in Shubnikov–de Haas experiments on any κ-structured material of the BEDT-TTF family. An oscillatory structure with the same frequency is observed in the anomalous damping of the QO amplitudes of the known frequencies F2=570 T and F3=3883 T. These damping effects are restricted to the magnetic field orientation perpendicular to the conducting (b,c)-planes (i.e., Θ=0°), high fields B>12 T and low temperatures T

We report on Shubnikov{de Haas and de Haas{van Alphen measurements of an organic metal based on the molecular donor bis(ethylenedioxy)-tetrathiavulvalene (= BEDO-TTF) and the anion Cl with H2O molecules. The observed single oscillation frequency perfectly follows the two-dimensional de- pendence F = F0=cos with F0 = (4890 20) T. The Fermi-surface area of 50% of the rst Brillouin zone proves a quarter-lled band, i.e., a 2:1 stoichiometry of the BEDO-TTF donor with respect to the anion. The apparent discrepancy to X-ray data which give a 1:1 ratio between BEDO-TTF and Cl is understood by replacement of H2O molecules with (H3O) + ions. The proposed stoichiometry therefore is (BEDO-TTF) + (H5O2) + (Cl )2. The cyclotron eective mass is mc =( 1 :54 0:05)me=cos when deduced from the temperature dependence of the fundamental oscillation amplitude, but strongly reduced when extracted from higher harmonics. This and the strong harmonic content of the oscillations signals an in- fluence of the two-dimensional electronic structure and can be qualitatively understood by applying the concept of magnetic interaction to the eect of the oscillatory chemical potential.

Measurements of both the magnetization and magnetotransport of $\ensuremath{\kappa}{\ensuremath{-}(\mathrm{B}\mathrm{E}\mathrm{D}\mathrm{T}\ensuremath{-}\mathrm{T}\mathrm{T}\mathrm{F})}_{2}{\mathrm{I}}_{3}$ (BEDT-TTF is bisethylenedithio-tetrathiafulvalene) in magnetic fields extending to 60 T at 0.4 K and 20 T at 35 mK are reported. Strong eddy currents observed in the magnetization are found to exhibit critical currentlike behavior. This might be connected with the breakdown of the quantum Hall effect, as proposed previously for $\ensuremath{\alpha}$-phase salts. The strong two dimensionality leads to an apparent fall of the effective mass together with an overall suppression of the amplitude of the magnetic quantum oscillations at high magnetic fields or very low temperatures. These effects are more pronounced for the Shubnikov--de Haas (SdH) effect but clearly visible also for the de Haas--van Alphen (dHvA) oscillations. The apparent fall of the effective mass and the deviations of the dHvA signal from the behavior predicted by the standard Lifshitz-Kosevich theory can quantitatively be explained by the influence of chemical-potential oscillations on the wave form in a two-dimensional, spin-split Fermi liquid. The much stronger deviations from the conventional behavior in the transport data hint to an additional mechanism unique to the SdH effect.

A new electrochemical method is presented to measure the properties of barrier coatings. This technique is called relaxation voltammetry (RV). The new developed electronic device combines electrometer type accuracy in measuring current under experimental conditions with an adequate high sampling rate. The former is necessary to determine the coating resistance the latter is required to get access to the coating capacity. The verification of the accuracy of this new method is done by measuring dummy cells with known resistors and capacitors. The values of these components are in the same order of magnitude as they can be obtained by the investigation of coated metals.

A new electrochemical method was established to measure the properties of barrier coatings. This technique is called relaxation voltammetry (RV) and is based on very sensitive current measurement and relatively high sample rates at the initial decay of the relaxation signal. The verification of the accuracy of this new method is done by measuring dummy cells with known resistors and capacitors. These results are compared with and confirmed by electrochemical impedance spectroscopy (EIS). The swelling and water uptake of two typical commercial organic coatings for corrosion protection are investigated and the RV and EIS data are discussed.

The electronic system of the organic superconductor κ-(BEDT-TTF) 2 I 3 (BEDT-TTF = bis(ethylenedithiolo)tetrathiafulvalene) is identified as extremely two-dimensional (2D). The topology of the Fermi surface (FS) was investigated by means of Shubnikov-de Haas (SdH) as well as de Haas-van Alphen (dHvA) experiments focusing on the verification of the 2D character of the system. This two-dimensionality specially takes effect as soon as the magnetic field is oriented exactly perpendicular to the conducting planes (i.e. Θ = 0°). Under such conditions strong anomalous damping effects in the field and temperature dependence of quantum oscillation amplitudes are observed. These anomalous damping effects are discussed in terms of the occurrence of quasi-particle excitations with fractional statistics (QPFS) which may only occur in extremely 2D systems at high magnetic fields and low temperatures (i.e., only when ħω C ≫ k B T ). Taking up these requirements, the aim of this work is to quantify the extreme two-dimensionality of the electronic system of κ-(BEDT-TTF) 2 I 3 and to show that the observed damping effects in fact are determined by the ratio ħω C / k B T . These facts may support the interpretation of the observed damping effects of quantum oscillation amplitudes at high magnetic fields, low temperatures and Θ = 0° as generated by the possible occurrence of such QPFS.

We report de Haas-van Alphen (dHvA) measurements of the high-Tc modification (Tc = 7 - 8 K) and Shubnikov-de Haas results of the low-Tc modification (Tc ≈ 1:4 K) of the organic superconductor β-(BEDT-TTF)2I3. In the high-Tc phase we find a single closed two-dimensional orbit with a dHvA frequency F0 = (3815±10) T and a 1/cosθ dependence as expected for a quasi two-dimensional system (where θ is the angle between the magnetic field and the direction normal to the conducting planes). The effective cyclotron mass is mc = (4:2±0:2)me. The dHvA signal shows a beating pattern caused by the three-dimensional warping of the Fermi cylinder. The inter-plane transfer integral estimated from the maximum beating frequency ΔF is t⊥/eF ≈ 1/175. At the angles where the beating disappears, i.e., ΔF ≈ 0, the oscillations have a harmonic content which is much larger than expected from the Lifshitz-Kosevich formula. In the low-Tc phase weak SdH oscillations with a frequency of FSdH ≈ 110 T and an effective cyclotron mass mc ≈ 1:0me is found. These results suggest a possible reconstruction of the Fermi surface in the low-Tc phase.

Polarized reflectivity spectra of single crystals of (BEDO-TTF) 2 ReO 4 (H 2 O) (BEDO-TTF = bis(ethylenedioxy)tetrathiafulvalene) were measured in the spectral range from 500 to 8500 cm −1 at six temperatures between 300 and 20 K. The polarization of the incident radiation was arranged parallel and perpendicular to the stacking axis of the donor molecules. The temperaturedependent reflectivity and the optical conductivity are presented. Changes at the metal-metal phase transition at 213 K and the metalsemiconductor phase transition at 35 K are discussed. The Drude parameters of the conduction electrons were obtained by fitting the reflectance data with a DrudeLorentz model, indicating that both phase transitions are accompanied by an abrupt change of the relaxation constant of the free charge carriers. Both phase transitions have an effect on the vibrational spectra and possible changes of the crystal structure at the phase transitions are discussed.

We present de Haas-van Alphen (dHvA) measurements of the isostructural quasi-two-dimensional (quasi-2D) organic superconductors β-(BEDT-TTF) 2 IBr 2 and β H -(BEDT-TTF) 2 I 3 with superconducting transition temperatures of T c ≃ 2.5 K and T c ≃ 7 K, respectively. For both salts almost the same dHvA frequency and a beating behavior of the dHvA signal are found which reflect the similarity of the Fermi surface (FS) topology in both materials. The FS can be well described by a slightly corrugated quasi-2D cylinder. The corresponding overlap integral t⊥ between the highly conducting organic layers could be determined with high precision. t⊥ is larger for β H -(BEDT-TTF) 2 I 3 although this salt has the larger interlayer distance. The effective cyclotron masses are very similar in both materials (m c 4 m e ). On the other hand, the observed spin-splitting zeros suggest a rather large difference and large absolute values of the conduction electron g-factor which seems to reflect the importance of electron-electron interactions in the β-phase salts.

In this communication we describe the fabrication and characterization of thin films of the radical cation salts α-, αt-(BEDT-TTF)2I3 and (BEDO-TTF)2.4I3. Thin films of these compounds were made by evaporation of the salts in high vacuum onto several substrates. They were characterized by X-ray diffraction, scanning electron microscopy, infrared absorption, Raman scattering, de-conductivity measurements and magnetically modulated microwave absorption. Depending on the temperature of the substrate and the evaporation rate, the films of α-(BEDT-TTF)2I3 exhibit different degrees of microcrystallinity which under the right conditions can be strongly reduced to obtain relatively smooth, completely covering films. Additionally such films have a high degree of orientation with respect to the substrate plane. The conversion into films of the superconducting αt-phase is possible and the high orientation is maintained. Due to grain boundaries, the dcconductivity is thermally activated, but the single grains are superconducting. The best results in the fabrication of smooth, completely covering films were obtained with (BEDO-TTF)2.4I3 on NaCl single crystals. Here the orientation of the donor molecule with respect to the substrate plane is different from the one found in the (BEDT-TTF)2I3 salts.

We report on a systematic study of the thermodynamic superconducting properties on high-quality crystals of the quasi-two-dimensional (quasi-2D) organic superconductor $\ensuremath{\kappa}$-${(\mathrm{B}\mathrm{E}\mathrm{D}\mathrm{T}\ensuremath{-}\mathrm{T}\mathrm{T}\mathrm{F})}_{2}$${\mathrm{I}}_{3}$. Low-field magnetization measurements served to determine the lower critical field ${B}_{c1}$. Just below ${T}_{c}=3.5$ K, down to \ensuremath{\sim} 3 K, ${B}_{c1}$ perpendicular (\ensuremath{\perp}) to the highly conducting BEDT-TTF layers is found to be strongly suppressed below the sensitivity limit of the instrumental resolution. This might be an indication for single-vortex fluctuations expected for a strongly 2D superconductor. The critical field ${B}_{c2}^{*}$ determined by ac-susceptibility measurements is found to be related to an irreversibility line. The temperature and frequency dependences of ${B}_{c2}^{*}$ are consistent with well-established flux-creep models. The upper critical field ${B}_{c2\ensuremath{\perp}}$ extracted from magnetization measurements is consistent with specific-heat data. For both principal field orientations a crossover of the critical-field slopes $|\frac{d{B}_{c2}}{\mathrm{dT}}|$ towards a shallow tail close to ${T}_{c}$ is observed. Apparent discrepancies of the thermodynamic critical fields for parallel and perpendicular field orientation are found, indicating either a strongly reduced ${B}_{c1\ensuremath{\parallel}}$ or ${B}_{c2\ensuremath{\parallel}}$.

We report results on the fabrication of thin films of the organic radical cation salt (BEDO-TTF)2.4I3. The title compound is an organic metal with a room temperature dc-conductivity of 180 – 360 S/cm. On amorphous substrates as quartz glass and silicon wafers ( Si SiO 2 ), we found one or more orientations of the crystalline material with respect to the substrate plane. On NaCl there is only a single, very strong Bragg reflection, which is due to the very good, substrate-induced orientation of the film. Scanning electron microscopy reveals growth of grains on the quartz glass substrates, whereas on NaCl large smooth areas with 1 to 10 μm edge size are observed. The dc-conductivity shows a slightly activated behaviour with an activation energy of 20 meV and a room temperature value of 1 S/cm.

κ-(BEDT-TTF)2I3 is an extreme case of an electronically two-dimensional (2D) organic metal with a superconducting transition at around 4 K. In magnetic fields up to 27 T the field, angular and the temperature dependence of de Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) oscillation amplitudes were investigated. From the temperature dependence of the oscillation amplitudes the cyclotron effective massm* was investigated using Lifshitz-Kosevich formula (LK) and the surprising result is, thatm* appears to be magnetic field dependent as soon as the magnetic field is applied exactly perpendicular to the conducting planes so that the cyclotron orbit lies within those planes (i.e. Θ=0o) but field independent at Θ≠0o. It is shown that the LK formula can satisfactorily be used for the interpretation of all data obtained at Θ≠0o but not in the case where Θ=0o. An explanation of the anomalous data at Θ=0o can furthermore neither be given satisfactorily by the descriptions of magneto-quantum oscillations in 2D electronic systems nor by the occurrence of magnetic interaction effects (MI). Tentatively, the observed smaller oscillation amplitudes in κ-(BEDT-TTF)2I3 at Θ=0o above 12 T and below 1 K compared to the standard LK theory will be discussed in terms of a loss in the number of fermions by the occurrence of quasiparticles with fractional statistics.

The Fermi surfaces (FS) and effective masses of the organic superconductors (BEDO-TTF) 2 ReO 4 (H 2 O) ( 1 ) and κ-(BEDT-TTF) 2 I 3 ( 2 ) were investigated by SdH- and dHvA-measurements in magnetic fields up to 27T in the temperature range from 0.5K to 4.2K. In 1 two small closed pockets (0.7% and 1.5% of the first Brillouin zone [FBZ] are observed corresponding very well with two cross-sectional areas of the FS obtained for a hole and an electron pocket from tight binding calculations. In contrast to 1 in 2 two relatively large closed sections (13% and 85% of the FBZ) of the FS are observed, again confirming the tight binding calculations. For 2 in magnetic fields above 12T the effective mass for the larger orbit, as obtained from the temperature dependence of the SdH-oscillation amplitudes, is magnetic field dependent as long as the field is arranged perpendicular to the conducting planes. In contrast, from dHvA-measurements — which were performed by turning the magnetic field by 27° with respect to the SdH-experiments — the observed effective mass is field independent (m ∗ = 3.9m O ). We suppose that the occurrence of particles with fractional statistics at temperatures below 1K and in fields above 12T might be the reason for the observed field dependence of the effective mass in the SdH investigations.

Crystalline films of αt-(BEDT-TTF)2I3 were produced by annealing amorphous films of (BEDT-TTF)2I3 in an I2 gas atmosphere of 90°C. The I2 atmosphere was used in order to reduce the loss of iodine in the films, which has been a major problem so far. Low field microwave absorption shows an onset of superconductivity around 8 K providing the success of this new technique.

High-resolution specific-heat measurements of the organic superconductor kappa-(BEDT-TTF)(2)-Cu[N(CN)(2)]Br in the superconducting ( B = 0) and normal ( B = 14 T) states show a clearly resolvable anomaly at T(c) = 11.5 K and an electronic contribution, C(es), which can be reasonably well described by strong-coupling BCS theory. Most importantly, C(es) vanishes exponentially in the superconducting state which gives evidence for a fully gapped order parameter.

Measurements of AC magnetic susceptibility in kappa -(BEDT-TTF)/sub 2/CuN(CN)/sub 2/Br show that the b-axis penetration depth below T/sub c/ exhibits behaviour different from that observed in the ac plane, which exhibits the T-linear dependence. In agreement with earlier measurements, a leading quadratic temperature dependence is found at low temperatures. The temperature dependence of the out-of-plane superfluid density is shown to best agree with a model of d-wave superconducting layers coupled by coherent Josephson tunneling.

We report a detailed characterization of the magnetism and AC transport in single crystals of the organic conductor kappa-(BEDT-TTF)_2-Cu[N(CN)_2]Cl by means of magnetic anisotropy measurements and low-frequency dielectric spectroscopy. Magnetic anisotropy obeys Curie-Weiss law with negative Curie-Weiss temperature in the temperature range 300 K - 70 K. An antiferromagnetic transition with concomitant canted antiferromagnetic state is established at 22 K. A large hysteresis in the spin-flop transition and magnetic field reversal of the weak ferromagnetic magnetization are documented for the first time. A broad dielectric relaxation mode of moderate strength(\Delta\epsilon~3 10^3) emerges at 32 K, and weakens with temperature. The mean relaxation time, much larger than that expected for single-particle excitations, is thermally activated in a manner similar to the DC conductivity and saturates below 22 K. These features suggest the origin of the broad relaxation as an intrinsic property of the weak ferromagnetic ground state. We propose a charged domain wall in a random ferromagnetic domain structure as the relaxation entity. We argue that the observed features might be well described if Dzyaloshinsky-Moriya interaction is taken into account. A Debye relaxation with similar temperature dependence was also observed and seems to be related to an additional ferromagnetic-like, most probably, field-induced phase. We tentatively associate this phase, whose tiny contribution was sample dependent, with a Cu^{;2+}; magnetic subsystem.

We summarize the main features of the magnetic field-temperature phase diagram for the superconducting state of κ-(BEDTTTF) 2 Cu[N(CN) 2 ]Br. The initial temperature dependence of the real component of ac susceptibility for field parallel and perpendicular to the ac plane are markedly different. The out-of-plane penetration depth λ b and the related superfluid density vary at low tempeartures as T 1 . Slow flux dynamics below the irreversibility line for the ac field perpendicular to the BEDT-TTF planes might be ascribed to a vortex-pair creation process. The characteristic relaxation time τ >10 −4 s is thermally activated with an activation energy of about 300K.

We summarize the main features of the low frequency dielectric relaxation observed below 30K in the weak ferromagnetic state of κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl. The observed width of the relaxation process is somewhat broader than for a Debye process and has a moderate strength of about 3.10 3 . The mean relaxation time, which is much larger than expected for single particle excitations, is thermally activated in a manner similar to the dc conductivity and saturates below the antiferromagnetic phase transition. A charged domain wall in a random ferromagnetic domain structure is proposed as the relaxation entity.

(BEDT-TTF) 4 [Ni(dto) 2 ] was investigated from 0.3 cm -1 to 8000 cm -1 with various optical techniques. On the background that quantum oscillation experiments are in good agreement with band structure calculations, the optical properties show some surprising aspects. While the MIR spectra are similar to those of other metallic BEDT-TTF materials, a sharp pseudo-gap feature and a very narrow Drude peak develop in the FIR at low temperatures.

We present dc-magnetization and ac-susceptibility measurements of the organic superconductors κ-(ET) 2 X with X = I 3 , Cu(NCS) 2 , and Cu[N(CN) 2 ]Br. For all investigated materials the lower critical field perpendicular to the highly conducting planes, B cl ⊥ , tends to zero already 0.5 K below T c . This might be an indication for fluctuation effects of single vortices expected for 2D superconductors. Pinning effects lead to an apparent increase of B cl towards lower temperatures and they play an important role for the temperature and frequency dependence of the irreversibility field B irr determined by ac-susceptibility.