Silvia Tomic

• Institute of Physics

One of the most fascinating aspects of condensed matter is its ability to conduct electricity, which is particularly pronounced in conventional metals such as copper or silver. Such behavior stems from a strong tendency of valence electrons to delocalize in a periodic potential created by ions in the crystal lattice of a given material. In many adv...

Among transition metal oxides, manganites have attracted significant attention because of colossal magnetoresistance (CMR)—a magnetic field-induced metal–insulator transition close to the Curie temperature. CMR is closely related to the ferromagnetic (FM) metallic phase which strongly competes with the antiferromagnetic (AFM) charge ordered (CO) ph...

Effects of magnesium (Mg²⁺) ions on the stability and structural properties of double-stranded DNA are vitally important for DNA folding and functional behavior. Complementing our previous study on highly hydrated thin films of DNA with sodium counterions, with no buffer (pH ≈ 6) and surrounded with Mg²⁺ cations, here we use Fourier transform infra...

This review provides a perspective on recent developments and their implications for our understanding of novel quantum phenomena in the physics of two-dimensional organic solids. We concentrate on the phase transitions and collective response in the charge sector, the importance of coupling of electronic and lattice degrees of freedom and stress a...

Here, the first accurate study is presented of the room-temperature and 100 K structures of one of the first organic spin liquids,-(BEDT-TTF) 2 Ag 2 (CN) 3. It is shown that the monoclinic structure determined previously is only the average one. It is shown that the exact structure presents triclinic symmetry with two non-equivalent dimers in the u...

Here, the first accurate study is presented of the room-temperature and 100 K structures of one of the first organic spin liquids, κ-(BEDT-TTF)2Ag2(CN)3. It is shown that the monoclinic structure determined previously is only the average one. It is shown that the exact structure presents triclinic symmetry with two non-equivalent dimers in the unit...

This review provides a perspective on recent developments and their implications for our understanding of novel quantum phenomena in the physics of two-dimensional organic solids. We concentrate on the phase transitions and collective response in the charge sector, the importance of coupling of electronic and lattice degrees of freedom and stress a...

We report on the electrodynamic properties of the single crystalline lead-substituted M-type barium hexaferrite, Ba _0.3 Pb _0.7 Fe _12 O _19 , performed in the broad frequency range including radio-frequency, terahertz and sub-terahertz bands, which are particularly important for the development of microelectronic devices. We demonstrate how chang...

We investigate the dc resistivity and Hall effect of the quasi-two-dimensional organic materials κ–(ET)2X, where X=Ag2(CN)3 and B(CN)4 and compare them with the results for X=Cu2(CN)3. All three compounds are considered to be quantum-spin-disordered Mott insulators. Despite high similarities in chemical composition and crystal structure, large diff...

The Widom line identifies the locus in the phase diagram where a supercritical gas crosses over from gas-like to a more liquid-like behavior. A similar transition exists in correlated electron liquids, where the interplay of Coulomb repulsion, bandwidth and temperature triggers between the Mott insulating state and an incoherent conduction regime....

Organic layered charge-transfer salts κ -(BEDT-TTF) 2 X form highly frustrated lattices of molecular dimers in which strong correlations give rise to Mott insulating states situated close to the metal-to-insulator phase boundary. The salts κ -(BEDT-TTF) 2 Cu 2 (CN) 3 and κ -(BEDT-TTF) 2 Ag 2 (CN) 3 have been considered as prime candidates for a qua...

We present here the first accurate determination of the exact structure of κ-(BEDT-TTF)2Cu2(CN)3. Not only did we show that the room temperature structure used over the last twenty years was incorrect, but we were also able to correctly and precisely determine it. The results of our work provide evidence that the structure presents a triclinic symm...

The Widom line identifies the locus in the phase diagram where a supercritical gas crosses over from gas-like to a more liquid-like behavior. A similar transition exists in correlated electron liquids, where the interplay of Coulomb repulsion, bandwidth and temperature triggers between the Mott insulating state and an incoherent conduction regime....

The Mott insulator $\beta'$-EtMe$_3$Sb[Pd(dmit)$_2$]$_2$ belongs to a class of charge transfer solids with highly-frustrated triangular lattice of $S=1/2$ molecular dimers and a quantum-spin-liquid ground state. Our experimental and {\it ab initio} theoretical studies show the fingerprints of strong correlations and disorder, important role of cati...

The Mott insulator $\beta'$-EtMe$_3$Sb[Pd(dmit)$_2$]$_2$ belongs to a class of charge transfer solids with highly-frustrated triangular lattice of $S=1/2$ molecular dimers and a quantum-spin-liquid ground state. Our experimental and ab initio theoretical studies show the fingerprints of strong correlations and disorder, important role of cation-dim...

The organic charge-transfer salt $\kappa$-(BEDT-TTF)$_{2}$Hg(SCN)$_{2}$Br is a quasi two-dimensional metal with a half-filled conduction band at ambient conditions. When cooled below $T=80$ K it undergoes a pronounced transition to an insulating phase where the resistivity increases many orders of magnitude. In order to elucidate the nature of this...

We report the temperature and magnetic field dependence of transport properties in epitaxial films of the manganite La$_{1-x}$Ca$_{x}$MnO$_{3}$ in the overdoped region of the phase diagram for $x > 0.5$, where a charge--ordered (CO) and an antiferromagnetic (AF) phase are present. Resistivity, magnetoresistance and angular dependence of magnetoresi...

We report the temperature and magnetic field dependence of transport properties in epitaxial films of the manganite La1 −xCaxMnO3 in the overdoped region of the phase diagram for x > 0.5, where a charge–ordered (CO) and an antiferromagnetic (AF) phase are present. Resistivity, magnetoresistance and angular dependence of magnetoresistance were measu...

\alpha$-(BEDT-TTF)$_2$I$_3$ is a prominent example of charge ordering among organic conductors. In this work we explore the details of transport within the charge-ordered as well as semimetallic phase at ambient pressure. In the high-temperature semimetallic phase, the mobilities and concentrations of both electrons and holes conspire in such a way...

Utilizing Fourier transform infrared spectroscopy we have investigated the vibrational spectrum of thin dsDNA films in order to track the structural changes upon addition of magnesium ions. In the range of low magnesium concentration ([magnesium]/[phosphate] = [Mg]/[P] < 0.5), both the red shift and the intensity of asymmetric PO2 stretching band d...

The Mott insulator $\kappa$-(BEDT-TTF)$_2$Ag$_2$(CN)$_3$ forms a highly-frustrated triangular lattice of $S=1/2$ dimers with a possible quantum-spin-liquid state. Our experimental and numerical studies reveal the emergence of a slight charge imbalance between crystallographically inequivalent sites, relaxor dielectric response and hopping dc transp...

The Mott insulator $\kappa$-(BEDT-TTF)$_2$Ag$_2$(CN)$_3$ forms a highly-frustrated triangular lattice of $S=1/2$ dimers with a possible quantum-spin-liquid state. Our experimental and numerical studies reveal the emergence of a slight charge imbalance between crystallographically inequivalent sites, relaxor dielectric response and hopping dc transp...

The dimer Mott insulator κ−(BEDT-TTF)2Cu2(CN)3 exhibits unusual electrodynamic properties. Numerical investigations of the electronic ground state and the molecular and lattice vibrations reveal the importance of the Cu2(CN)3− anion network coupled to the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) molecules: The threefold cyanide coordination...

The dimer Mott insulator $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ exhibits unusual electrodynamic properties. Numerical investigations of the electronic ground state and the molecular and lattice vibrations reveal the importance of the Cu$_2$(CN)$_3^-$ anion network coupled to the BEDT-TTF molecules: The threefold cyanide coordination of copper and li...

In conventional ferroelectrics the polarization is induced either by the relative displacement of positive and negative ions due to a lattice distortion or by the collective alignment of permanent electric dipoles. Strongly correlated materials with the inversion-symmetry-broken ground states feature electronic ferroelectricity, a phenomenon which...

We present the measurements of the magnetotransport properties of the spin liquid candidate κ-(BEDT-TTF)2Cu2(CN)3. The temperature dependencies of dc resistivity and Hall coefficient RH as well as magnetoresistance at fixed temperatures in magnetic fields up to 5 T suggest that the charge transport takes place via 2D variable range hopping among lo...

The electrodynamic response of the organic spin-liquid candidate $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ has been measured in an extremely wide energy range ($10^{-13}$ to 2 eV) as a function of temperature (5 to 300 K). Below the Mott gap, excitations from the un-gapped spinon continuum cause a considerable contribution to the infrared conductivity,...

We have in detail characterized the anisotropic charge response of the dimer Mott insulator $$\kappa${}\text{$-${}}(\text{BEDT-TTF}{)}_{2}{\mathrm{Cu}}_{2}(\text{CN}{)}_{3}$ 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 temp...

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 $\...

The Mott insulator κ-(BEDT-TTF)2Cu[N(CN)2]Cl consists of molecular dimers arranged on an anisotropic triangular lattice. At low temperatures a pronounced dielectric anomaly is observed, and eventually a canted antiferromagnetic ground state forms. Optical spectroscopy clearly rules out charge imbalance and the existence of quantum electric dipoles...

We overview the state of knowledge regarding the symmetry of the superconducting order parameter in layered organic superconductors based on κ-(BEDT-TTF). A remnant intrinsic disorder at low temperatures in nominally pure single crystals emerges as one of decisive key ingredients that inuences the value and the temperature dependence of the penetra...

The effect of magnesium ion Mg2+ on the dielectric relaxation of semidilute DNA aqueous solutions has been studied by means of dielectric spectroscopy in the 100 Hz- 100 MHz frequency range. De Gennes-Pfeuty-Dobrynin semidilute solution correlation length is the pertinent fundamental length scale for sufficiently low concentration of added salt, de...

Electric-field-dependent pulse measurements are reported in the charge-ordered state of α-(BEDT-TTF)2I3. At low electric fields up to about 50 V/cm only negligible deviations from Ohmic behavior can be identified with no threshold field. At larger electric fields and up to about 100 V/cm a reproducible negative differential resistance is observed w...

The Mott insulator \kappa-(BEDT-TTF)2Cu[N(CN)2]Cl consists of molecular dimers arranged on an anisotropic triangular lattice and develops a canted antiferromagnetic ground state. It has recently been suggested that this system features purely electronic ferroelectricity which requires an electric dipole moment. Optical spectroscopy clearly rules ou...

Electric-field-dependent pulse measurements are reported in the charge-ordered state of alpha-(BEDT-TTF)2I3. At low electric fields up to about 50 V/cm only negligible deviations from Ohmic behavior can be identified with no threshold field. At larger electric fields and up to about 100 V/cm a reproducible negative differential resistance is observ...

Utilizing infrared vibrational spectroscopy we have investigated dimerized two-dimensional organic salts in order to search for possible charge redistribution that might cause electronic dipoles and ferroelectricity: the quantum spin liquid \kappa-(BEDT-TTF)2Cu2(CN)3, the antiferromagnetic Mott insulator \kappa-(BEDT-TTF)2$Cu[N(CN)2]Cl, and the sup...

We overview the study of biopolyelectrolytes by dielectric spectroscopy technique by primarily focusing on the case of repulsive regime of intersegment interactions mediated by univalent counterions. Two observed dielectric relaxations in 100 Hz–100 MHz frequency range due to diffusive motion of counterions are related to polyelectrolyte structural...

We report a detailed characterization of an unique 3-fold commensurate insulating state in single crystals of the organic π – inorganic d hybrid Cu(DMe-DCNQI)2 systems with deuterated and partially deuterated DCNQI ring, by means of low-frequency dielectric spectroscopy. A broad relaxation mode of strength ∆ε ≈ 103-104 centred at ν0 ≈ 1-10 kHz is o...

The hole distribution in Sr14Cu24O41 is studied by low-temperature polarization-dependent O K near-edge x-ray absorption fine-structure measurements and state-of-the-art electronic structure calculations that include core-hole and correlation effects in a mean-field approach. Contrary to all previous analysis, based on semiempirical models, we show...

The hole distribution in Sr$_{14}$Cu$_{24}$O$_{41}$ is studied by low temperature polarization dependent O K Near-Edge X-ray Absorption Fine Structure measurements and state of the art electronic structure calculations that include core-hole and correlation effects in a mean-field approach. Contrary to all previous analysis, based on semi-empirical...

Structural properties of Na-DNA and Na-HA aqueous solutions can be quantified using dielectric spectroscopy in the frequency range 100 Hz–100 MHz. Two relaxation modes are typically detected that can be attributed to diffusive motion of polyion counterions. The overall study as a function of polyion length, concentration and added salt concentratio...

We quantified the Manning free (uncondensed) counterions fraction θ for dilute aqueous solutions of rodlike polyions: 150 bp DNA fragments, in the presence of a very low concentration of monovalent salt c(salt)<0.05 mM. Conductivity measurements of these solutions for DNA base pair concentration range 0.015≤c≤8 mM were complemented by fluorescence...

We have measured the in-plane and out-of-plane resistivities of the organic superconductor β-(BEDT-TTF)2AuI2 with disorder introduced by x-ray irradiation. [Here BEDT-TTF is bis(ethylenedithio)- tetrathiafulvalene]. For defect concentrations less than 0.15% per mole, Matthiessen’s rule is obeyed at all temperatures and a T2 term in the resistivity...

We report on the anisotropic response, the charge and lattice dynamics of normal and charge-ordered phases with horizontal stripes in single crystals of the organic conductor alpha-(BEDT-TTF)2I3 determined by dc resistivity, dielectric and optical spectroscopy. An overdamped Drude response and a small conductivity anisotropy observed in optics is c...

We quantified the Manning free (uncondensed) counterions fraction $\theta$ for dilute solutions of rod-like polyions - 150bp DNA fragments, in very low salt $<0.05$mM. Conductivity measurements of aqueous DNA solutions in the concentration range $0.015\leq c \leq 8$~mM (bp) were complemented by fluorescence correlation spectroscopy (FCS) measuremen...

We report a study of DNA (150 bp fragments) conformations in very low added salt $<0.05$mM, across wide DNA concentration range $0.0015\leq c \leq 8$~mM (bp). We found an intermediate DNA conformation in the region $0.05 < c < 1$~mM, by means of fluorescence correlation spectroscopy (FCS) and UV-absorbance measurements. FCS detected that in this re...

Dielectric spectroscopy is used to investigate fundamental length scales describing the structure of hyaluronic acid sodium salt (Na-HA) semidilute aqueous solutions. In salt-free regime, the length scale of the relaxation mode detected in MHz range scales with HA concentration as c(HA)(-0.5) and corresponds to the de Gennes-Pfeuty-Dobrynin correla...

The charge response of a charge-ordered state in the organic conductor α-(BEDT-TTF)2I3 is characterized by dc resistivity, dielectric and optical spectroscopy in different crystallographic directions within the two-dimensional conduction layer. Two dielectric modes are detected. The large mode is related to the phasonlike excitation of the 2k(F) bo...

Dielectric spectroscopy is used to investigate fundamental length scales describing the structure of hyaluronic acid sodium salt (Na-HA) semidilute aqueous solutions. In salt-free regime, the length scale of the relaxation mode detected in MHz range scales with HA concentration as $c_\mathrm{HA}^{-0.5}$ and corresponds to the de Gennes-Pfeuty-Dobry...

The charge transport in the copper-oxygen chain/ladder layers of (La,Y)y(Sr,Ca)14-yCu24O41 is investigated along two crystallographic directions in the temperature range from 50 K to 700 K and for doping levels from y ~= 6 (number of holes nh < 1) to y = 0 (number of holes nh = 6). A crossover from a one-dimensional hopping transport along the chai...

The charge response in the barium vanadium sulfide (BaVS3) single crystals is characterized by dc resistivity and low frequency dielectric spectroscopy. A broad relaxation mode in MHz range with huge dielectric constant ~= 10^6 emerges at the metal-to-insulator phase transition TMI ~= 67 K, weakens with lowering temperature and eventually levels of...

Dielectric spectroscopy is used to investigate fundamental length scales of 146 bp short-fragment (nucleosomal) dilute Na-DNA solutions. Two relaxation modes are detected: the high- and the low-frequency mode. Dependence of the corresponding length scales on the DNA and on the (uni-valent) salt concentration is studied in detail, being different fr...

Methods for direct (without the use of the Kramers–Kronig relations) measuring the dielectric response (dynamic conductivity and permittivity) spectra of dielectrics, conductors, and superconductors in the terahertz frequency range (0.03–1.5 THz) are described. The methods are realised by using BWO (backward-wave oscillator) spectrometers developed...

The “chain-ladder” compounds with formula (Sr/La/Ca)14Cu24O41 exhibit a rather complex crystallographic structure due to their composite character. These materials consist of an alternating stacking of two distinct types of layers forming interpenetrated subsystems [1]. One subsystem is formed of (Sr/La/Ca)2Cu2O3 layers with a ladder-like structure...

The electrical resistivity along the high-conductivity axis has been measured at pressures up to 9 kbar in the novel organic conductor (2,5 DM-DCNQI)2Cu. Deviations from the usual linear behaviour of the conductivity under pressure at room temperature have been observed. Moreover, at lower temperatures metal-to-insulator phase transitions have been...

We report a study of the transverse magnetoresistance in the spin-density-wave state of the organic conductor (TMTSF)2NO3 at ambient pressure, in fields up to 37 T. For field along the lowest conductivity axis (c*), two series of quantum oscillations, with temperature-independent frequencies of 63 T and 248 T, respectively, are observed in the 2-12...

We report the first transport characterization of a unique commensurate spin-density wave state of the organic charge insulator (TMTTF)2 Br. An additional anomaly in d.c. resistivity is observed at 22 K, above the SDW transition temperature Tc = 12.5 K. Non-Ohmic current-voltage characteristics with sharp threshold fields of the order of 1-10 V/cm...

The charge response in the barium vanadium sulfide (BaVS3) single crystals is characterized by dc resistivity and low frequency dielectric spectroscopy. A broad relaxation mode in MHz range with huge dielectric constant ~= 10^6 emerges at the metal-to-insulator phase transition TMI ~= 67 K, weakens with lowering temperature and eventually levels of...

Among known Bechgaard and Fabre salts (TMTSF)2NO3 is unique since it never becomes superconducting even under pressure. Also, though (TMTSF)2NO3 undergoes the spin density wave (SDW) transition, the low temperature transport is semimetallic and gapless. We propose: a) the absence of the superconductivity is due to the inverse symmetry breaking asso...

We report on a detailed characterization of complex dielectric response of Na-DNA aqueous solutions by means of low-frequency dielectric spectroscopy (40 Hz-110 MHz). Results reveal two broad relaxation modes of strength 20<Deltaepsilon(LF)<100 and 5<Deltaepsilon(HF)<20, centered at 0.5 kHz<nu(LF)<70 kHz and 0.1 MHz<nu(HF)<15 MHz. The characteristi...

Among many Bechgaard salts, TMTSF2NO3 exhibits very anomalous low temperature properties. Unlike conventional spin density wave (SDW), TMTSF2NO3 undergoes the SDW transition at $\T_SDW\approx 9.5$ K and the low temperature quasiparticle excitations are gapless. Also, it is known that TMTSF2NO3 does not exhibit superconductivity even under pressure,...

The fundamental length scales in semidilute Na-DNA aqueous solutions have been investigated by dielectric spectroscopy. The low- and the high-frequency relaxation modes are studied in detail. The length scale of the high-frequency relaxation mode at high DNA concentrations can be identified with the de Gennes-Pfeuty-Dobrynin correlation length of p...

The quasi-one-dimensional cuprates (La,Y,Sr,Ca)14Cu24O41, consisting of spin-chains and spin-ladders, have attracted much attention, mainly because they represent the first superconducting copper oxide with a non-square lattice. Theoretically, in isolated hole-doped two-leg ladders, superconductivity is tightly associated with the spin gap, althoug...

The most comprehensive charge response study of the intrinsically hole doped, spin-chain and spin-ladder composites is overviewed. Results of dc and electric-field-dependent resistivity, low frequency dielectric, and optical spectroscopy in all crystallographic directions are used to build phase diagrams of the underdoped materials (hole count=6-y...

The anisotropic and non-linear transport properties of the quasi one-dimensional organic conductor (TMTSF) 2 PF 6 have been studied by dc, radiofrequency, and microwave methods. Microwave experiments along all three axes reveal that collective transport, which is considered to be the fingerprint of the spin-density-wave condensate, also occurs in t...

The charge response of the ladders in Sr14-xCaxCu24O41 is characterized by dc resistivity, low frequency dielectric, and optical spectroscopy in all three crystallographic directions. The collective charge-density wave screened mode is observed in the direction of the rungs for x=0 , 3, and 6, in addition to the mode along the legs. For x=8 and 9,...

The anisotropic and non-linear transport properties of the quasi one-dimensional organic conductor (TMTSF)_2PF_6 have been studied by dc, radiofrequency, and microwave methods. Microwave experiments along all three axes reveal that collective transport, which is considered to be the fingerprint of the spin-density-wave condensate, also occurs in th...

It has been recently established that the superconductivity (SC) in j-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br is extremely sensitive to the cooling procedure through 100–70 K, where the ethylene groups attached to the BEDT-TTF molecules order with very slow relaxation times (the glass transition). In particular, the superconductivity in the annealed samples is...

Highly sensitive ac susceptibility measurements were performed in order to resolve the controversy regarding the symmetry of the superconducting order parameter in kappa-BEDT-TTF materials. The experimentally obtained superfluid density behaviour qualitatively contradicts s-wave symmetry theoretical predictions, but disagrees also quantitatively wi...

The charge response in the spin chain and ladder compound Sr_14-xCa_xCu_24O_41 is characterized by dc resistivity, low-frequency dielectric spectroscopy and optical spectroscopy. We identify an insulator-to-insulator phase transition below which a charge-density wave (CDW) develops in the ladder arrays. Calcium doping suppresses this phase with the...

Transport and low-frequency optical reflection measurements (180–380 GHz) are reported for the quasi-three-dimensional conducting alloy Cu[(2,5(CH3)2–DCNQI)0.70(2,5(CD3)2–DCNQI)0.30]2 between room temperature and 35 K. The optical properties of the system are strongly anisotropic. It is metallic down to 60 K where a Mott–Peierls phase transition o...

The charge response in the spin chain and/or ladder compound Sr14-xCaxCu24O41 is characterized by dc resistivity, low-frequency dielectric spectroscopy and optical spectroscopy. We identify a phase transition below which a charge-density wave (CDW) develops in the ladder arrays. Calcium doping suppresses this phase with the transition temperature d...

The characterization of charge response in the spin chain and/or ladder compound Sr14-xCaxCu24O41 was presented. The characterization was done by using dc resistivity, low-frequency dielectric spectroscopy and optical spectroscopy. A suppression of the charge-density-wave state was found in the compound by calcium doping.

We show that the spin chain/ladder compound La3Sr3Ca8Cu24O41 is an insulator with hopping transport along the chains. In the temperature range 35 280 K, dc conductivity sigmadc(T) follows Mott's law of variable-range hopping conduction; the frequency dependence has the form sigma(nu,T)=sigmadc(T)+A(T)nus, where s&ap;1. The conduction mechanism chan...

We overview low frequency dielectric spectroscopy and non-linear dc electrical transport in single crystals of a member of copper-DCNQI charge-transfer salt with N = 3 commensurate charge density wave. Broad relaxation mode of moderate strength weakens and becomes narrower with decreasing temperature. Threshold electrical field diverges, concomitan...

In a small range of pressure, superconductivity (SC) and Spin Density Wave (SDW) states are shown to coexist in the Bechgaard salt (TMTSF)2PF6 and the Fabre salt (TMTTF)2BF4. In (TMTSF)2PF6, a precise investigation of the (P,T) phase diagram has led us to demonstrate the coexistence of the two phases with a superconducting critical temperature whic...

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 cz 4 can be recognized as phasons in a random impurity potential, whereas those with N...

The electrodynamic response of the spin-ladder compound Sr14-xCaxCu24O41(x=0,3,9) has been studied from radio frequencies up to the infrared. At temperatures below 250 K a pronounced absorption peak appears around 12 cm-1 in Sr14Cu24O41 for the radiation polarized along the chains/ladders (E||c). In addition a strongly temperature-dependent dielect...

We report high-sensitivity AC susceptibility measurements of the penetration depth in the Meissner state of the layered organic superconductor kappa-(BEDT-TTF)2Cu[N(CN)2]Br. We have studied nominally pure single crystals from the two different syntheses and employed controlled cooling procedures in order to minimize intrinsic remnant disorder at lo...

The phase diagram of the organic superconductor (TMTSF)2PF6has been revisited using transport measurements with an improved control of the applied pressure. We have found a 0.8 kbar wide pressure domain below the critical point (9.43 kbar, 1.2 K) for the stabilisation of the superconducting ground state featuring a coexistence regime between spin d...

The electrodynamic response of the spin-ladder compound Sr14-xCaxCu24O41(x=0,3,9) has been studied from radio frequencies up to the infrared. At temperatures below 250 K a pronounced absorption peak appears around 12cm-1 in Sr14Cu24O41 for the radiation polarized along the chains/ladders (E‖c). In addition a strongly temperature-dependent dielectri...

The present state of knowledge in the ®eld of layered organic superconductors based on j-(BEDT-TTF) is reviewed. Normal and ground states inside the temperature versus pressure phase diagram are discussed. The question of un-conventional versus conventional superconducting pairing is addressed. Ó 2001 Elsevier Science B.V. All rights re-served.

We report a detailed characterization of an unique 2- and 4-fold commensurate charge density wave (CDW) state in single crystals of the organic conductor (2.5(OCH3)2DCNQI)2Li by means of low-frequency (0.1 Hz-1 MHz) dielectric spectroscopy. We show that in addition to the narrow Debye-like relaxation mode of strength Δɛ≈ 10 7 with Arrhenius-like re...

Electric-field-dependent measurements are reported in the low-temperature state of the organic conductors Cu[2,5(CD3)(2)-DCNQI](2) and Cu[(2,5(CH3)(2)-DCNQI)(0.70)(2,5(CD3)(2)-DCNQI)(0.30)](2) With N=3 commensurate CDW. We correlate observed features of the electric conduction below and above threshold field with the temperature evolution of the N=...

We overview complex conductivity measurements (20Hz - 1MHz) in low-dimensional organic systems kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl, and deuterated Cu-DCNQI and its alloys, with commensurate density wave ground states. We discuss the obtained results in comparison with those for the incommensurate density waves, like in (TMTSF)(2)PF6, in which the pha...

We present an experimental study of the pressure-temperature phase diagram of the organic conductor (DM-DCNQI)2Cu. We show that it is possible to suppress the ambient pressure metallic phase by applying pressure - even as low as 100 bar. On increasing the pressure, the metal-insulator transition temperature increases and its strong first-order char...

We report a detailed characterization of quantum Hall effect (QHE) influence on the linear and non-linear resistivity tensor in FISDW phases of the organic conductor (TMTSF)2PF6. We show that the behavior at low electric fields, observed for nominally pure single crystals with different values of the resistivity ratio, is fully consistent with a th...