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Sample records for bedt-ttf

  1. Low-temperature softening of some Raman modes in BEDT-TTF and d{sub 8}-BEDT-TTF.

    SciTech Connect

    Lin, Y.; Eldridge, J. E.; Williams, J. M.; Kini, A. M.; Wang, H. H.; Univ. of British Columbia

    1999-02-01

    We report the temperature-dependent frequencies of the strong features in the Raman spectra of neutral BEDT-TTF and d{sub 8}-BEDT-TTF. We note an unusual softening of the features due to the modes involving the C-H vibrations in the terminal ethylene groups, as well as one mode involving the central double-bonded carbon atoms. We relate these softenings to the increased bending of the neutral molecule at low temperatures.

  2. Assignment of the Raman spectra of some deuterated-BEDT-TTF superconductors.

    SciTech Connect

    Eldridge, J. E.; Wang, H. H.; Kini, A. M.; Schlueter, J. A.; Materials Science Division; Univ. of British Columbia

    2002-08-01

    We present the room-temperature Raman spectra of both the protonated and deuterated forms of kappa-(BEDT-TTF)2Cu[N(CN)2]Br, kappa-(BEDT-TTF)2Cu(NCS)2 and beta-(BEDT-TTF)2I3. Along with data for the neutral BEDT-TTF molecule these spectra are used to assign the many features in the spectra of the deuterated compounds.

  3. Bis(vinylenedithio)tetrathiafulvalene analogues of BEDT-TTF

    PubMed Central

    Demirtas, İlknur; Ozturk, Turan

    2015-01-01

    Summary This review aims to give an overview of the current status of our research on the synthesis of π-electron donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF, ET) analogues prepared from 1,8-diketones via a ring forming reaction. The new synthesized π-electron donors have vinyl moieties producing extended π-electron delocalization over the substituent phenyl rings at the peripheries. PMID:25977714

  4. Bis(vinylenedithio)tetrathiafulvalene analogues of BEDT-TTF.

    PubMed

    Ertas, Erdal; Demirtas, İlknur; Ozturk, Turan

    2015-01-01

    This review aims to give an overview of the current status of our research on the synthesis of π-electron donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF, ET) analogues prepared from 1,8-diketones via a ring forming reaction. The new synthesized π-electron donors have vinyl moieties producing extended π-electron delocalization over the substituent phenyl rings at the peripheries. PMID:25977714

  5. Vibrational spectra of two BEDT-TTF-based organic conductors : charge order.

    SciTech Connect

    Graja, A.; Olejniczak, I.; Barszcz, B.; Schlueter, J. A.; Materials Science Division; Polish Academy of Sciences

    2009-12-01

    Infrared and Raman investigations of two phases of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) based organic conductors with the same CF{sub 3}CF{sub 2}SO{sub 3}{sup -} anion: {beta}{prime}-(BEDT-TTF){sub 2}CF{sub 3}CF{sub 2}SO{sub 3} and {delta}{prime}-(BEDT-TTF){sub 2}CF{sub 3}CF{sub 2}SO{sub 3}, are shortly reviewed and compared with the most typical infrared properties of the family of (BEDT-TTF){sub 2}RR{prime}SO{sub 3} organic conductors, where R = SF{sub 5}, CF{sub 3}, and R{prime} are CH{sub 2}, CF{sub 2}, CHF, CHFCF{sub 2}, and CH{sub 2}CF{sub 2}. The role of the molecular structure and spatial organization of the counterions is discussed.

  6. A fourth polymorph in the family of BEDT-TTF salts with thiocyanatocuprate(I) anions: (BEDT-TTF){<_4}Cu{<_3}(NCS){<_5}.

    SciTech Connect

    Schlueter, J. A.; Geiser, U.; Wang, H. H.; Manson, J. L.

    2012-05-01

    A new crystallographic modification was found in the family of BEDT-TTF salts containing thiocyanatocuprate(I) anions. The cation radical salt crystallizes in the P{sup {bar 1}} space group with a = 8.2720(9) {angstrom}, b = 19.099(2) {angstrom}, c = 43.758(5) {angstrom}, {alpha} = 81.088(4){sup o}, {beta} = 87.253(4){sup o}, {gamma} = 83.790(4){sup o}, V = 6786.2(13) {angstrom}{sup 3} at 150 K. The BEDT-TTF radical cations pack in an {alpha}-type motif, but every four columns, there is a slip in the layer. Where this slip occurs, the stacks are coupled in a {beta}'' manner. The material exhibits semiconductive behavior with an activation energy of 0.13 eV above 250 K and 0.22 eV below. Packing motif of the (BEDT-TTF){sub 4}Cu{sub 3}(NCS){sub 5} structure.

  7. Tc of 11K Identified for the Third Polymorph of the (BEDT-TTF)(BEDT-TTF){<_2}Ag(CF{<_3}){<_4}(TCE) Organic Superconductor.

    SciTech Connect

    Kawamoto, T.; Mori, T.; Nakao, A.; Murakami, Y.; Schlueter, J. A.

    2012-01-01

    The crystal structure of the third polymorph of the organic superconductor (BEDT-TTF){sub 2}Ag(CF{sub 3}){sub 4}(TCE), where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene and TCE is 1,1,2-trichloroethane, has been investigated. The crystal consists of alternating stacks of two types of donor sheets, {Kappa}- and {alpha}-types. Although this structure is similar to the previously solved two-layered high-T{sub c} phase of (BEDT-TTF){sub 2}Ag(CF{sub 3}){sub 4}(TCE), the axis perpendicular to the conducting layer of the unit cell of the new phase is twice as large as that of the two-layered phase; thus, four layers form the repeating unit. Superconductivity is attributed to the {Kappa}-type conducting layer, because the {alpha}-type conducting layer is in an acentric charge-ordered state. The onset superconducting transition temperatures are approximately 11.0 and 9.5 K for the four-layered and two-layered phases, respectively.

  8. Successive transition of Josephson vortex ordering in κ-type BEDT-TTF superconductors

    NASA Astrophysics Data System (ADS)

    Ito, Hiroshi; Nakaharai, Shu; Ishiguro, Takehiko; Saito, Gunzi

    1996-12-01

    A magneto-oscillation of the susceptibility was observed in the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br under magnetic field applied parallel to the two-dimensional plane. The oscillation is understood in terms of the successive transition of Josephson vortex ordering.

  9. Analysis of Dirac Point in the Organic Conductor α-(BEDT-TTF)2I3

    NASA Astrophysics Data System (ADS)

    Suzumura, Yoshikazu

    2016-05-01

    The Dirac electron in the organic conductor α-(BEDT-TTF)2I3 under pressure is analyzed using a tight-binding model with nearest-neighbor transfer energies and four molecules per unit cell. By noting that the Dirac point between the first and second energy bands emerges or merges followed by the level crossing at a time-reversal invariant momentum (TRIM), an effective Hamiltonian is derived on the basis of these two wave functions at the TRIM, which have different parities associated with an inversion symmetry around the inversion center. We demonstrate that the Dirac point is determined by an intersection of two kinds of lines originating from the Hamiltonian described by symmetric and antisymmetric functions around the TRIM. The present method quantitatively gives a reasonable location of the Dirac point of α-(BEDT-TTF)2I3 in a wide pressure range.

  10. Charge ordering and superconductivity in {alpha}-(BEDT-TTF){sub 2}MHg(SCN){sub 4}.

    SciTech Connect

    Dressel, M.; Drichko, N.; Salameh, B.; Thoms, J.; Schlueter, J.; Merino, J.; Materials Science Division; Univ. Stuttgart; Ioffe Physico-Technical Inst.; Max-Planck-Inst. fur Festkorperforschung

    2002-11-01

    In the optical spectra of the non-superconducting salt {alpha}-(BEDT-TTF){sub 2}KHg(SCN){sub 4}4 a strong feature appears at frequencies of about 200 cm{sup -1} and temperatures below 200 K which indicates the opening of a pseudogap. This is in contrast to the superconducting {alpha}-(BEDT-TTF){sub 2}NH{sub 4}Hg(SCN){sub 4} which exhibits metallic-like optical properties down to 2 K. Based on exact diagonalisation calculations of the optical conductivity on an extended Hubbard model at quarter-filling we argue that the proximity of these salts to a charge ordering transition is responsible for the observed pseudogap. Our proposed scenario suggests that the different ground states, including superconductivity, are a consequence of the fluctuations associated with short range charge ordering which builds up close to the quantum phase transition.

  11. Positron lifetimes in TTF-TCNQ and κ-(BEDT-TTF) 2Cu(NCS) 2 single crystals

    NASA Astrophysics Data System (ADS)

    Ishibashi, Shoji; Tokumoto, Madoka; Kinoshita, Nobumori; Terada, Norio; Ihara, Hideo; Suzuki, Ryoichi; Ohdaira, Toshiyuki; Mikado, Tomohisa; Anzai, Hiroyuki

    1997-05-01

    Positron lifetimes in TTF-TCNQ (tetrathiafulvalene-tetracyanoquinodimethane) and κ-(BEDT-TTF) 2Cu(SCN) 2 (BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene) single crystals have been measured utilizing a pulsed variable-energy positron beam. The bulk positron lifetimes are 338 and 357 ps, respectively. The incident positron energy dependence of the lifetime is rather weak for both materials. Theoretical simulations have been also performed with several descriptions of the electronic wave functions and the electron-positron correlation. Results are compared with each other and the experiments.

  12. Strongly enhanced 1/f - noise level in {kappa}-(BEDT-TTF){sub 2}X salts.

    SciTech Connect

    Brandenburg, J.; Muller, J.; Wirth, S.; Schlueter, J. A.; Schweitzer, D.; Materials Science Division; Max-Planck-Inst.fur Chemical Physics of Solids; Goethe-Univ.; Univ. of Stuttgart

    2010-01-01

    Fluctuation spectroscopy has been used as an investigative tool to understand the scattering mechanisms of carriers and their low-frequency dynamics in quasi-two-dimensional organic conductors ?-(BEDT-TTF)2X. We report on the very high noise level in these systems as determined from Hooge's empirical law to quantify 1/f-type noise in solids. The value of the Hooge parameter ?H, i.e. the normalized noise level, of 105-107 is several orders of magnitude higher than values of ?Hnot, vert, similar10-2-10-3 typically found in homogeneous metals and semiconductors.

  13. Spin-current injection and detection in κ-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br

    SciTech Connect

    Qiu, Z. Hou, D.; Uruichi, M.; Uchida, K.; Yamamoto, H. M.; Saitoh, E.

    2015-05-15

    Spin-current injection into an organic semiconductor κ-(BEDT-TTF){sub 2}Cu[N(CN){sub 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 κ-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br film. Magnetic-field-angle dependence measurements indicate that the voltage signal is governed by the inverse spin Hall effect in κ-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br. We found that the voltage signal in the κ-(BEDT-TTF){sub 2}Cu[N(CN){sub 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.

  14. Probing the Mott physics in κ-(BEDT-TTF)₂X salts via thermal expansion.

    PubMed

    de Souza, Mariano; Bartosch, Lorenz

    2015-02-11

    In the field of interacting electron systems the Mott metal-to-insulator (MI) transition represents one of the pivotal issues. The role played by lattice degrees of freedom for the Mott MI transition and the Mott criticality in a variety of materials are current topics under debate. In this context, molecular conductors of the κ-(BEDT-TTF)2X type constitute a class of materials for unraveling several aspects of the Mott physics. In this review, we present a synopsis of literature results with focus on recent expansivity measurements probing the Mott MI transition in this class of materials. Progress in the description of the Mott critical behavior is also addressed. PMID:25603958

  15. Determining ethylene group disorder levels in {kappa}-(BEDT-TTF){sub 2}Cu[N(China){sub 2}]Br

    SciTech Connect

    Wolter, A. U. B.; Strack, Ch.; Lang, M.; Schweitzer, D.

    2007-03-01

    We present a detailed structural investigation of the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(China){sub 2}]Br at temperatures T from 9 to 300 K. Anomalies in the T dependence of the lattice parameters are associated with a glasslike transition previously reported at T{sub g}=77 K. From structure refinements at 9, 100, and 300 K, the orthorhombic crystalline symmetry, space group Pnma, is established at all temperatures. Further, we extract the T dependence of the occupation factor of the eclipsed conformation of the terminal ethylene groups of the BEDT-TTF molecule. At 300 K, we find 67(2)%, with an increase to 97(3)% at 9 K. We conclude that the glasslike transition is not primarily caused by configurational freezing-out of the ethylene groups.

  16. Searching for crystallographic superstructures in kappa-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br.

    SciTech Connect

    Wolter, A. U. B.; Feyerherm, R.; Dudzik, E.; Sullow, S.; Strack, Ch.; Lang, M.; Schweitzer, D.; Schlueter, J. A.; Materials Science Division; Inst Physcal Condensed Matter; Helmholtz-Centre Berlin for Materials and Energy; Leibniz Inst. Solid State Research; J. W. Goethe-Univ.; Univ. Stuttgart

    2010-01-01

    To resolve a superstructure formation previously reported for the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br, we present synchrotron x-ray diffraction experiments carried out at the MAGS beamline at BESSY, Helmholtz-Centre Berlin. Surprisingly, in our low temperature (28 K) experiments, when searching k-space at (h 0 3.5), h = 7, 8 and (h 0 0.5), h = 5, 7, for none of these spots we could detect scattering intensity associated to a superstructure formation, in contradiction to previous reports. Our data suggest that details of the structural properties of {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br - such as superstructure formation - sensitively depend on sample handling, e.g., cooling rates (in our case 4 K/min), or thermal cycling. A direct relationship between superstructure formation and terminal ethylene group ordering cannot be verified, disproving proposals put forth previously.

  17. First order vortex phase transition in the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2}

    SciTech Connect

    Inada, M.; Sasaki, T.; Nishizaki, T.; Kobayashi, N.; Yamada, S.; Fukase, T.

    1999-12-01

    The local magnetic induction is measured in the quasi-two dimensional organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2} by using a micro Hall probe. The small step is observed on the temperature dependence of the local magnetic induction. This result implies the existence of the first-order phase transition of the vortex system in this organic superconductor as is already reported in high-{Tc} oxide and other organic superconductors.

  18. Coulomb-induced pairing in a quarter-filled band model for κ-(BEDT-TTF)2X

    NASA Astrophysics Data System (ADS)

    de Silva, W. Wasanthi; Gomes, Niladri; Mazumdar, Sumit; Clay, R. Torsten

    κ -(BEDT-TTF)2X is a two dimensional organic charge transfer solid superconductor with a hole density of one half per (BEDT-TTF) molecule. With one hole per dimer of molecules, the material is frequently described using an effective 1 / 2 -filled band Hubbard model on an anisotropic triangular lattice. Within this effective model a metal to antiferromagnetic (AFM) semiconductor phase transition is found. Calculations beyond the mean field level, however, have shown absence of superconductivity within the model. We present the results of correlated-electron calculations on the κ-lattice for up to 64 BEDT-TTF molecules using the Constrained Path Monte Carlo (CPMC) and Path Integral Renormalization Group (PIRG) methods over a wide range of carrier density. We show that superconducting pair-pair correlations in this model are enhanced by electron-electron (e-e) interactions for d-wave pairing symmetry uniquely for hole density close to quarter-filling. Our results indicate that this enhancement of superconductivity is not related to the presence of AFM order, but to the strong tendency to spin-singlet formation in the quarter-filled band. Supported by DOE Grant DE-FG02-06ER46315 and NSF-CHE-151475.

  19. Spin dynamics of charge carriers in the process of their localization in {alpha}'-(BEDT-TTF){sub 2}IBr{sub 2} single crystals

    SciTech Connect

    Morgunov, R. B. Dmitriev, A. I.; Chernen'kaya, A. S.; Yakushi, K.; Yamamoto, K.; Tanimoto, Y.

    2010-11-15

    Sharp changes in the integral intensity and linewidth of the ESR spectrum that accompany the localization of the charge carriers have been revealed in {alpha}'-(BEDT-TTF){sub 2}IBr{sub 2} crystals. It has been found that the types of localization in two compounds under investigation are different: charge carriers in {beta}''-(BEDT-TTF){sub 4}NH{sub 4}[Cr(C{sub 2}O{sub 4}){sub 3}] are localized on irregular defects of the crystal lattice, whereas charge carriers in {alpha}'-(BEDT-TTF){sub 2}IBr{sub 2} are localized at the regular positions of the unit cell. The exchange narrowing of the ESR line and a sharp decrease in the dc and ac magnetic susceptibilities are observed in {alpha}'-(BEDT-TTF){sub 2}IBr{sub 2} at low temperatures T < 50 K. The dc and ac magnetic susceptibilities observed in {alpha}'-(BEDT-TTF){sub 2}IBr{sub 2} at high temperatures T > 50 K differ from each other, because the thermally activated hopping frequency of the charge carriers is higher than the frequency of the measuring UHF field of an ESR spectrometer.

  20. IR and raman spectra of {Beta}"-(BEDT-TTF){sub 2}RCH{sub 2}SO{sub 3} (R = SF{sub 5}, CF{sub 3}) : dimerization related to hydrogen bonding.

    SciTech Connect

    Olejniczak, I.; Barszcz, B.; Szutarska, A.; Graja, A.; Wojciechowski, R.; Schlueter, J. A.; Hata, A. N.; Ward, B. H.; Polish Academy of Sciences; Technical Univ. of Lodz

    2009-01-01

    The {Beta}''-(BEDT-TTF)2CF3CH2SO3 organic conductor has been synthesized by electrocrystallization. The crystal structure was determined by single-crystal X-ray diffraction and electronic properties examined. The polarized IR reflectance of {Beta}''-(BEDT-TTF)2SF5CH2SO3 and {Beta}''-(BEDT-TTF)2CF3CH2SO3, as well as Raman spectra of {Beta}''-(BEDT-TTF)2CF3CH2SO3 have been measured as a function of temperature. Both materials display charge-nonequivalence within the whole temperature range and unusual activation of vibronic modes with lowering the temperature. In particular, electron-molecular vibration coupling is involved in the activation of the v27 mode. The effect is discussed in terms of lattice dimerization involving hydrogen bonding between the anion layer and the conducting BEDT-TTF layer.

  1. Magnetocaloric Evidence for FFLO Superconductivity in κ-(BEDT-TTF)2Cu(NCS)2

    NASA Astrophysics Data System (ADS)

    Fortune, Nathanael; Agosta, Charles; Hannahs, Scott; Park, Ju-Hyun; Gu, Shuyao; Liang, Lucy; Schleuter, John

    We present new magnetocaloric and calorimetric measurements of the high field superconducting state in the layered structure superconductor κ - (BEDT-TTF)2Cu(NCS)2. The strongly field-orientation dependent phase transition between the low field superconducting state and high field superconducting states is first order and is nearly temperature independent, occurring at the Clogston-Chandrasakar paramagnetic limit Hp. Magnetocaloric measurements dT / dH as a function of magnetic field reveal that the system becomes strongly paramagnetic at the cross over from the low field to high field state. At lower temperatures, we are able to resolve small changes at the phase boundary due to the absorption/release of latent heat when increasing/decreasing field, indicating that the high field state is higher entropy than the low field state. These results provide strong new evidence for the formation of paramagnetic spin domains within an inhomogeneous FFLO superconducting state. They also allow us to rule out alternative explanations involving the formation of spin density waves within a homogenous superconducting state. A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement No. DMR-1157490 and the State of Florida.

  2. Giant magnetoresistance in organic superconductors {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2}

    SciTech Connect

    Zuo, F.; Schlueter, J.A.; Kelly, M.E.; Williams, J.M.

    1997-08-01

    In this letter, the authors report transport measurements with field and current parallel to the {alpha} axis (perpendicular to the conducting plane) in the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2}. The magnetoresistance displays a peak effect as a function of field and temperature with the peak fields increasing linearly with decreasing temperatures. The peak resistance is found to be greater than the normal state value extrapolated from both high and low field measurements. This is a first report of above normal resistance in a superconducting state. The results are in sharp contrast to the conventional dissipation mechanisms in the mixed state for anisotropic superconductors, as in the case of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. They propose a phenomenological model that the peak in the magnetoresistance is caused by a new scattering mechanism due to a strong coupling to the underlying crystal lattice of fluctuating vortices (vortex polarons). The model can semiquantitatively fit the data.

  3. Structure of bis(ethylenedithio)tetrathiafulvalenium dichlorocyanoselenate (2:1), (BEDT-TTF){sub 2}Cl{sub 2}SeCN

    SciTech Connect

    Geiser, U.; Schlueter, J.A.; Dudek, J.D.; Williams, J.M.

    1995-12-31

    The electron donor molecule BEDT-TTF has yielded approximately 50 superconductors to date. In addition, numerous other salts with a variety of electrical and magnetic properties have been discovered. Recently, the authors reported a semiconducting salt of BEDT-TTF with the novel T-shaped anion Br{sub 2}SeCN{sup {minus}2}. The crystallographic analysis of that salt revealed a near-centrosymmetric triclinic structure, except for the symmetry-breaking anion. On the basis of a Hamilton R-value test, the non-centrosymmetric space group P1 with ordered anions was preferred over centrosymmetric P{bar 1} with disordered anions. In this paper, the authors present the synthesis and crystal structure of the isostructural chlorine-analogue salt (BEDT-TTF){sub 2}Cl{sub 2}SeCN.

  4. Electronic and magnetic studies of {kappa}-(BEDT-TTF){sub 2}Hg(SCN){sub 2}Cl.

    SciTech Connect

    Yasin, S.; Rose, E.; Dumm, M.; Drichko, N.; Dressel, M.; Schlueter, J. A.; Zhilyaeva, E. I.; Torunova, S.; Lyubovskaya, R. N.

    2012-06-01

    DC resistivity and electron spin resonance (ESR) measurements have been performed on the two-dimensional organic conductor {kappa}-(BEDT-TTF){sub 2}Hg(SCN){sub 2}Cl. Due to electronic correlations, the compound undergoes a transition from a metallic to an insulating state at T{sub MI} = 34 K. The ESR parameters exhibit a drastic change below T{sub afm} = 27 K that evidences a magnetic phase transition. In this low-temperature state, we observe the characteristics of antiferromagnetic resonances in the angular dependence of the g-value.

  5. Mott criticality and multiferroicity in organic κ-(BEDT-TTF)2X salts

    NASA Astrophysics Data System (ADS)

    Lang, Michael

    2014-03-01

    Layered organic charge-transfer (CT) salts of the κ-(BEDT-TTF)2X family show a wealth of electronic phases resulting from the interplay of strong electron-electron correlations, reduced dimensions and magnetic frustration. Of particular interest has been the bandwidth-controlled Mott transition, separating an antiferromagnetic (afm) insulating state from a correlated metallic and superconducting state. Whereas the hydrogenated X = Cu[N(CN)2]Br salt is located on the metallic side, the deuterated variant, denoted κ-D8, is situated in splitting distance to the Mott transition, enabling the s-shaped transition line TMI to be crossed via temperature sweeps. The talk will address the following aspects: 1) Thermal expansion measurements on single crystalline κ-D8 reveal discontinuous changes of the lattice parameters on crossing the Mott transition line and a huge anomaly close to the second-order critical end point of TMI. By elaborating on a scaling theory, we found that (i) the latter effect is a consequence of an almost divergence of the Grüneisen parameter Γ at the finite- T critical end point, and (ii) that the expansivity data of are in excellent agreement with the Mott criticality lying within the 2D Ising universality class, at variance with results from conductivity measurements. Thermal expansion measurements under Helium-gas pressure are underway for providing thermodynamic information at variable pressure. 2) Surprisingly, for the isostructural X = Cu[N(CN)2]Cl salt, located close to the Mott transition on the insulating side, we found that besides the well-established afm order at TN ~ 27 K, the system also reveals a ferroelectric transition at TFE, making this material the first multiferroic CT salt. Most remarkably, the measurements reveal TFE ~TN , suggesting a close interrelation between both types of ferroic order. Work was supported by Deutsche Forschungsgemeinschaft through the Collaborative Research Centers TRR 49 and TRR 80.

  6. Synthesis, crystal structure and physical properties of (BEDT-TTF)[Ni(tdas){sub 2}]: the first monomeric [Ni(tdas){sub 2}]{super -} monoanion, (BEDT-TTF = bis (ethylenedithio)tetrathiafulvalene; tdas = 1,2,5-thiadiazole-3,4-dithiolate).

    SciTech Connect

    Curreli, S.; Deplano, P.; Mercuri, M. L.; Pilia, L.; Serpe, A.; Schlueter, J. A.; Whited, M. A.; Geiser, U.; Coronado, E.; Gomez-Garcia, C. J.; Canadell, E.; Materials Science Division; Univ. de Valencia; Inorganica ed Analitica; Inst. de Ciencia de Materials de Barcelona

    2004-03-22

    We report the synthesis, structure, and physical properties of (BEDT-TTF)[Ni(tdas){sub 2}] [BEDT-TTF, or ET, is bis(ethylenedithio)tetrathiafulvalene; tdas is 1,2,5-thiadiazole-3,4-dithiolate], which is the first example of a salt containing monomeric [Ni(tdas){sub 2}]{sup -} monoanions. This salt, which crystallizes in the monoclinic space group P2{sub 1}/c with a = 17.2324(6) {angstrom}, b = 13.2740(5) {angstrom}, c = 10.9467(4) {angstrom}, {beta} = 96.974(2){sup o}, and V = 2485.5(2) {angstrom}{sup 3}, forms a layered structure. One layer contains dimerized BEDT-TTF electron donor molecules and isolated [Ni(tdas){sub 2}]{sup -} monoanions, while the second layer contains chains of [Ni(tdas){sub 2}]{sup -} monoanions. Conductivity measurements show that (BEDT-TTF)[Ni(tdas){sub 2}] has a semiconductor-to-semiconductor transition near 200 K, while magnetic measurements indicate that it is an S = 1/2 paramagnet with weak antiferromagnetic coupling. Reflectance spectra reveal bands in the near-infrared region (6.6 x 10{sup 3} and 10.6 x 10{sup 3} cm{sup -1}) which are typical of (BEDT-TTF){sub 2}{sup 2+} dimers. From these data, we can conclude that the unpaired electron lies on the [Ni(tdas){sub 2}]{sup -} anions. Tight-binding band structure calculations were used to analyze the electronic structure of this salt.

  7. Valence-band spectra of BEDT-TTF and TTF-based magnetic charge-transfer salts

    NASA Astrophysics Data System (ADS)

    Kurmaev, E. Z.; Moewes, A.; Chiuzbian, S. G.; Finkelstein, L. D.; Neumann, M.; Turner, S. S.; Day, P.

    2002-06-01

    The electronic structure of BEDT-TTF bis(ethylenedithio)tetrathiafulvalene, and TTF, tetrathiafulvalene, based ferrimagnetic insulating and paramagnetic semiconducting charge-transfer salts have been studied by x-ray emission spectroscopy (XES) and photoelectron spectroscopy (XPS). The counterions for the salts are the d-transition-metal complex anions [Cr(NCS)4(phen)]-, [Cr(NCS)4(Me2phen)]- and [Cr(NCS)4(isoq)2]- where Me2phen=4, 7-dimethyl-1, 10-phenanthroline, phen=1, 10-phenanthroline), and isoq=isoquinoline=C9H7N. The distribution of partial and total density of states was determined by comparing the XES spectra of the constituents (carbon and nitrogen Kα and Cr L2,3) with XPS valence-band spectra on the binding-energy scale. Splitting in the XPS N 1s and S 2p spectra was attributed to contributions from nonequivalent atoms, i.e., N in the NCS and phen based ligands, S in NCS and BEDT-TTF. Cr L-XES measured at the L2-threshold display an unusually high L2 to L3 intensity ratio, which is discussed in terms of Coster-Kronig transitions and a different excitation of L3 and L2 levels at the L2 threshold.

  8. Electrically induced phase transition in α -(BEDT-TTF)2I3 : Indications for Dirac-like hot charge carriers

    NASA Astrophysics Data System (ADS)

    Peterseim, T.; Ivek, T.; Schweitzer, D.; Dressel, M.

    2016-06-01

    The two-dimensional organic conductor α -(BEDT-TTF)2I3 undergoes a metal-insulator transition at TCO=135 K due to electronic charge ordering. We have conducted time-resolved investigations of its electronic properties in order to explore the field- and temperature-dependent dynamics. At a certain threshold field, the system switches from a low-conducting to a high-conducting state, accompanied by a negative differential resistance. Our time-dependent infrared investigations indicate that close to TCO, the strong electric field pushes the crystal into a metallic state with optical properties similar to the one for T >TCO . Well into the insulating state, however, at T =80 K , the spectral response evidences a completely different electronically induced high-conducting state. Applying a two-state model of hot electrons explains the observations by excitation of charge carriers with a high mobility. They resemble the Dirac-like charge carriers with a linear dispersion of the electronic bands found in α -(BEDT-TTF)2I3 at high pressure. Extensive numerical simulations quantitatively reproduce our experimental findings in all details.

  9. Microreflectance infrared study of electron-molecular vibrational coupling and lattice softness in BEDT-TTF salts

    SciTech Connect

    Ferraro, J.R.; Whangbo, Myung-Hwan; Wang, H.H.; Stout, P.

    1994-03-01

    Microreflectance infrared (MR-IR) spectra were obtained for several {beta}- and {kappa}-phase salts of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) and its deuterium analog d{sub 8}-ET by employing polarized and unpolarized light. The vibronic region of these MR-IR spectra provides information about the electron-molecular vibration (EMV) coupling, and the highest-frequency C-C-H bending vibration observed for an ET salt reflects the extent of its lattice softness. Under polarized light, the EMV coupling for an ET salt depends strongly upon how the light polarization vector is aligned with respect to the sample crystallographic axes. The lowest vibron frequency is indicative of increased EMV coupling.

  10. Different electronic transport regimes in the quasi-two-dimensional organic conductors {kappa}(BEDT-TTF){<_2}X.

    SciTech Connect

    Muller, J.; Brandenburg, J.; Schweitzer, D.; Schlueter, J. A.

    2012-05-01

    We study the low-frequency dynamical properties of correlated charge carriers in various of the quasi-two-dimensional organic charge-transfer salts {kappa}-(BEDT-TTF){sub 2}X by means of fluctuation (noise) spectroscopy. Close to the critical endpoint of the Mott metal-insulator transition, a pronounced increase of the 1/f-noise level accompanied by a substantial shift of spectral weight to low frequencies indicates a sudden increase of the time scale of the charge fluctuations. For the less correlated, more metallic materials, we find a crossover/transition from hopping transport of more-or-less localized carriers at elevated temperatures to a low-temperature regime, where a metallic coupling of the layers allows for coherent interlayer transport of delocalized electrons.

  11. Partial Dissolution of Charge Order Phase Observed in β-(BEDT-TTF)2PF6 Single Crystal Field Effect Transistor.

    PubMed

    Sakai, Masatoshi; Moritoshi, Norifumi; Kuniyoshi, Shigekazu; Yamauchi, Hiroshi; Kudo, Kazuhiro; Masu, Hyuma

    2016-04-01

    The effect of an applied gate electric field on the charge-order phase in β-(BEDT-TTF)2PF6 single-crystal field-effect transistor structure was observed at around room temperature by technical improvement with respect to sample preparation and electrical measurements. A relatively slight but systematic increase of the electrical conductance induced by the applied gate electric field and its temperature dependence was observed at around the metal-insulator transition temperature (TMI). The temperature dependence of the modulated electrical conductance demonstrated that TMI was shifted toward the lower side by application of a gate electric field, which corresponds to partial dissolution of the charge-order phase. The thickness of the partially dissolved charge order region was estimated to be several score times larger than the charge accumulation region. PMID:27451615

  12. Anomalous magnetic properties in the single-crystal {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2} superconductor

    SciTech Connect

    Zuo, F.; Schlueter, J.A.; Geiser, U.; Williams, J.M.

    1996-09-01

    Magnetization measurements have been performed on single crystals of the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu(SCN){sub 2} with the field parallel to the {ital a} axis (perpendicular to the conducting plane). At high temperatures, the magnetization {ital M} displays a power-law dependence on {ital H} with {ital M}{proportional_to}{ital H}{sup {alpha}} and {alpha}={minus}0.45{plus_minus}0.05. At low temperatures ({ital T}{le}7.5 K), an anomalous field dependence in {ital M}({ital H}) is observed. The irreversibility field determined from magnetic hysteresis loops displays a universal temperature dependence, i.e., from a high-temperature power-law dependence to a low-temperature exponential dependence. The results are qualitatively similar to the fishtail magnetization reported for the highly anisotropic oxide superconductors. {copyright} {ital 1996 The American Physical Society.}

  13. Coordination Chemistry of 2,2'-Bipyridyl- and 2,2':6',2″-Terpyridyl-Substituted BEDT-TTFs: Formation of a Supramolecular Capsule Motif by the Iron(II) Tris Complex of 2,2'-Bipyridine-4-thiomethyl-BEDT-TTF.

    PubMed

    Wang, Qiang; Martin, Lee; Blake, Alexander J; Day, Peter; Akutsu, Hiroki; Wallis, John D

    2016-09-01

    Molecules of tris(2,2'-bipyridine-4-thiomethyl-BEDT-TTF)iron(II) (BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene) assemble in pairs to form a novel supramolecular capsular structure in the solid state. Three BEDT-TTF residues from one complex lie in the three grooves between coordinated bipyridines of the other complex, and vice versa, to form a capsule with 3-fold rotational symmetry and an internal volume of ca. 160 Å(3). Further aspects of the coordination chemistry of this ligand, its 6-substituted isomer, and the 2,2':6'2″-terpyridyl-4'-thiomethyl-BEDT-TTF analogue are described. PMID:27517741

  14. Transport properties and structural features of the ambient-pressure superconductor {kappa}{sup '}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Cl

    SciTech Connect

    Zverev, V. N.; Manakov, A. I.; Khasanov, S. S.; Shibaeva, R. P.; Kushch, N. D.; Kazakova, A. V.; Buravov, L. I.; Yagubskii, E. B.; Canadell, E.

    2006-09-01

    The crystal structure and low-temperature transport properties of the recently synthesized {kappa}{sup '}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Cl radical cation salt are investigated. The crystals exhibit metallic conductivity and are ambient-pressure superconductors with critical temperature in the range (11.3-11.9) K. The crystals show some distinctions in structure as compared to that of the Mott insulator {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Cl: smaller size of the unit cell and deficiency in the occupancy of the copper positions. Anisotropy of superconducting properties as well as a nontrivial temperature dependence of the upper critical field were observed.

  15. Synthesis of racemic and chiral BEDT-TTF derivatives possessing hydroxy groups and their achiral and chiral charge transfer complexes

    PubMed Central

    Krivickas, Sara Jane; Hashimoto, Chiho; Yoshida, Junya; Ueda, Akira; Takahashi, Kazuyuki; Wallis, John D

    2015-01-01

    Summary Chiral molecular crystals built up by chiral molecules without inversion centers have attracted much interest owing to their versatile functionalities related to optical, magnetic, and electrical properties. However, there is a difficulty in chiral crystal growth due to the lack of symmetry. Therefore, we made the molecular design to introduce intermolecular hydrogen bonds in chiral crystals. Racemic and enantiopure bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) derivatives possessing hydroxymethyl groups as the source of hydrogen bonds were designed. The novel racemic trans-vic-(hydroxymethyl)(methyl)-BEDT-TTF 1, and racemic and enantiopure trans-vic-bis(hydroxymethyl)-BEDT-TTF 2 were synthesized. Moreover, the preparations, crystal structure analyses, and electrical resistivity measurements of the novel achiral charge transfer salt θ21-[(S,S)-2]3[(R,R)-2]3(ClO4)2 and the chiral salt α’-[(R,R)-2]ClO4(H2O) were carried out. In the former θ21-[(S,S)-2]3[(R,R)-2]3(ClO4)2, there are two sets of three crystallographically independent donor molecules [(S,S)-2]2[(R,R)-2] in a unit cell, where the two sets are related by an inversion center. The latter α’-[(R,R)-2]ClO4(H2O) is the chiral salt with included solvent H2O, which is not isostructural with the reported chiral salt α’-[(S,S)-2]ClO4 without H2O, but has a similar donor arrangement. According to the molecular design by introduction of hydroxy groups and a ClO4 − anion, many intermediate-strength intermolecular hydrogen bonds (2.6–3.0 Å) were observed in these crystals between electron donor molecules, anions, and included H2O solvent, which improve the crystallinity and facilitate the extraction of physical properties. Both salts are semiconductors with relatively low resistivities at room temperature and activation energies of 1.2 ohm cm with E a = 86 meV for θ21-[(S,S)-2]3[(R,R)-2]3(ClO4)2 and 0.6 ohm cm with E a = 140 meV for α'-[(R,R)-2]2ClO4(H2O), respectively. The variety of donor

  16. Proximity of Antiferromagnetism and d-wave superconductivity in κ-BEDT-TTF: A V-CPT study

    NASA Astrophysics Data System (ADS)

    Sahebsara, Peyman; Senechal, David

    2005-03-01

    The organic conductors κ-(BEDT-TTF)2X (X=Cu(NCS)2, Cu[N(CN)2]Br and Cu[N(CN)2]Cl) have attracted attention because the superconducting phase exists in the vicinity of an antiferromagntic insulating phase [1]. The salts with the first two substitutions are superconductors with critical temperature near 10K. The third one is a commensurate insulator, which transits to a superconducting phase at ambient pressure. We use the 2D, half-filled Hubbard model on a triangular lattice to describe these compounds. The ground state antiferromagnetism and superconductivity is investigated using variational cluster perturbation theory (V-CPT) [2-3]. The on-site repulsion U and the diagonal hopping t' are varied and a phase diagram of the κ-family of BEDT is obtained. [1] H. Kino and H. Fukuyama, J. Phys. Soc. Jpn. 65 (1996) 2158. [2] M. Potthoff, M. Aichorn and C. Dahnken, Phys. Rev. Lett. 91 (2003) 206402. [3] D. Senechal and A.-M. S. Tremblay, cond-mat/0410162

  17. Field-induced length changes in the spin-liquid candidate kappa{BEDT-TTF){<_2}Cu{<_2}(CN){<_3}.

    SciTech Connect

    Manna, R. S.; de Souza, M.; Schlueter, J. A.; Lang, M.; )

    2012-05-01

    Measurements of the coefficient of thermal expansion on the spin-liquid candidate {kappa}-(BEDT-TTF){sub 2}Cu{sub 2}(CN){sub 3} have revealed distinct and strongly anisotropic lattice effects around 6 K - a possible spin liquid instability. In order to study the effects of a magnetic field on the low-temperature spin-liquid state, dilatometric measurements have been conducted both as a function of temperature at B = const. and as a function of field at T = const. While the 6 K anomaly is found to be insensitive to magnetic fields B {le} 10 T, the maximum field applied, surprisingly strong B-induced effects are observed for magnetic fields applied along the in-plane b-axis. Above a threshold field of 0.5 T < B{sub c} {le} 1 T, a jump-like anomaly is observed in the b-axis lattice parameter. This anomaly, which is located at 8.7 K at B = 1 T, grows in size and shifts to lower temperatures with increasing the magnetic field. Although the anomaly bears resemblance to a first-order phase transition, the lack of hysteresis suggests otherwise.

  18. Vortex pinning in layered organic superconductors: {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br

    SciTech Connect

    Khizroev, S.; Zuo, F.; Alexandrakis, G.C.; Schlueter, J.A.; Geiser, U.; Williams, J.M.

    1996-04-01

    Magnetization studies on organic single-crystal superconductors of {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br with the field {ital H} parallel to the {ital b} axis (perpendicular to the conducting plane) show anomalous field and temperature dependence of vortex pinning in the mixed state. At high temperatures, the magnetization {ital M} decays with increasing field with a power-law dependence. The normalized relaxation rate {ital S}={ital d}(ln{ital M})/{ital d}(ln{ital t}) decreases monotonically with {ital H}. At low temperatures ({ital T}{lt}7 K), a change of sign in the curvature of {ital M}({ital H}) is observed, accompanied by a corresponding change in {ital S} as a function of {ital H}. Measurement of the irreversibility field {ital H}{sub rev} shows a universal power-law dependence of {ital H}{sub rev} on (1{minus}{ital T}/{ital T}{sub {ital c}}) in the temperature range investigated. We suggest that the magnetic anomaly observed is due to a dimensional crossover in the nature of vortex pinning. {copyright} {ital 1996 American Institute of Physics.}

  19. Mixed-state magnetoresistance in organic superconductors {kappa}{endash}(BEDT-TTF){sub 2}Cu(NCS){sub 2}

    SciTech Connect

    Zuo, F.; Schlueter, J.A.; Kelly, M.E.; Williams, J.M.

    1996-11-01

    We report transport measurements with field and current parallel to the {ital a} axis (perpendicular to the conducting plane) in the organic superconductor {kappa}{endash}(BEDT-TTF){sub 2}Cu(NCS){sub 2}. The magnetoresistance displays a peak effect as a function of field and temperature with the peak fields increasing linearly with decreasing temperatures. The peak resistance is found to be greater than the normal-state value extrapolated from both high- and low-field measurements. The results are in sharp contrast to the conventional dissipation mechanisms in the mixed state for anisotropic superconductors, as in the case of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. We propose a phenomenological model that the peak in the magnetoresistance is caused by a scattering mechanism due to a strong coupling to the underlying crystal lattice of fluctuating vortices (vortex polarons). The model can semiquantitatively fit the data. {copyright} {ital 1996 The American Physical Society.}

  20. Effects of Charge Fluctuations on Massless Dirac Fermions in Organic Conductor α-(BEDT-TTF)2I3

    NASA Astrophysics Data System (ADS)

    Kanao, Taro; Matsuura, Hiroyasu; Ogata, Masao

    2014-03-01

    A quasi-two-dimensional organic conductor α-(BEDT-TTF)2I3 has attracted much interest both for its charge ordering (CO) transition and for its remarkable transport properties at high pressure which appear when the transition suppressed. The latter has been revealed to be due to massless Dirac fermions (MDFs) at the Fermi energy, by measurements such as transport, NMR, and specific heat. Recently, the MDF phase has been re-examined, and some behaviors beyond non-interacting MDFs has been reported. In transport measurements, the resistivity shows a logarithmic increase at low temperatures. Also, NMR measurements show deviations from the non-interacting behaviors. The cause of these behaviors has not been clarified. Since the transition between the MDF phase and the CO phase is almost continuous, charge fluctuations are important there. As a cause of the behaviors above, we investigate effects of charge fluctuations using a minimal model for this system. We analyze this model by a self-consistent renormalization (SCR) theory, which can deal with effects of fluctuations precisely. On this basis, electric resistivity (or damping rate), specific heat, and one-particle density of states are calculated. Relevance to the experimental facts is discussed.

  1. Disorder-induced gap in the normal density of states of the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br.

    PubMed

    Diehl, Sandra; Methfessel, Torsten; Tutsch, Ulrich; Müller, Jens; Lang, Michael; Huth, Michael; Jourdan, Martin; Elmers, Hans-Joachim

    2015-07-01

    The local density of states (DOS) of the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br, measured by scanning tunneling spectroscopy on in situ cleaved surfaces, reveals a logarithmic suppression near the Fermi edge persisting above the critical temperature T(c). The experimentally observed suppression of the DOS is in excellent agreement with a soft Hubbard gap as predicted by the Anderson-Hubbard model for systems with disorder. The electronic disorder also explains the diminished coherence peaks of the quasi-particle DOS below T(c). PMID:26076168

  2. Magnetization Measurements in the 80 K Transformation for Deuterated Organic Superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br

    NASA Astrophysics Data System (ADS)

    El Ouaddi, H.; Tirbiyine, A.; Taoufik, A.; Ramzi, A.; Hafid, A.; Nafidi, A.; Chaib, H.; Senoussi, S.

    2013-02-01

    In this paper, we report systematic magnetic measurements on deuterated organic superconductor (κ-D8-Br)κ-(BEDT-TTF)2Cu[N(CN)2]Br. The irreversibility line Hirr(T) and the critical current density Jc were studied. Our results show the strong dependence of Hirr(T) and Jc on the cooling rate. The structural transformation which occurs at the vicinity of 80 K very strongly influences the physics of vortex lattice and the associated magnetic behavior. The irreversible magnetization becomes null at Hirr and vortices are not pinned; therefore they can displace more freely for an increase of the field or the temperature.

  3. Phase transitions in new BEDT-TTF κ-phase salts with hexacyanometalate anions [M(CN) 63- M=Co(III) and Fe(III)

    NASA Astrophysics Data System (ADS)

    Pierre Le Maguerè; Ouahab, Lahcène; Corian, Nathalie; Gómez-García, Carlos J.; Delhaès, Pierre; Even, Jacky; Bertault, Marcel

    1996-01-01

    The preparation, crystal structure determination and physical properties of the compounds formulated as κ-(BEDT-TTF) 4((C 2H 5) 4N)M(CN) 6.3H 2O (M= Co III and Fe III) are presented. Organic ET layers with packing of orthogonalized dimers containing charge carriers and inorganic octahedral hexacyanometalate anions with diamagnetic or paramagnetic transition metals coexist in the title compounds. Two phase transitions occuring respectively at 150 K and in the 230-260 K range have been evidenced by magnetic (SQUID and ESR), DSC measurements. However, preliminary X-Ray studies revealed a structural change around 240 K only.

  4. Reply to the ``Comment on `Electronic structure of insulating salts of the κ-(BEDT-TTF)2X family studied by low-temperature specific-heat measurements' ''

    NASA Astrophysics Data System (ADS)

    Nakazawa, Y.; Kanoda, K.

    1997-07-01

    The ac and dc susceptibility data of the identical sample of κ-(BEDT-TTF)2Cu[N(CN)2]Cl that we have used for the previous low-temperature specific-heat experiment [Phys. Rev. B 53, R8875 (1996)] is presented in order to reply to the preceding Comment. We observe neither appreciable depression of the magnetic transition temperature nor appearance of superconductive phase due to the grease effect in our experimental configuration, which excludes the interpretation of the specific-heat data speculated by Fortune and Sushko.

  5. Disorder-induced gap in the normal density of states of the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br

    NASA Astrophysics Data System (ADS)

    Diehl, Sandra; Methfessel, Torsten; Tutsch, Ulrich; Müller, Jens; Lang, Michael; Huth, Michael; Jourdan, Martin; Elmers, Hans-Joachim

    2015-07-01

    The local density of states (DOS) of the organic superconductor κ -(BEDT-TTF)2Cu[N(CN)2]Br, measured by scanning tunneling spectroscopy on in situ cleaved surfaces, reveals a logarithmic suppression near the Fermi edge persisting above the critical temperature {{T}\\text{c}} . The experimentally observed suppression of the DOS is in excellent agreement with a soft Hubbard gap as predicted by the Anderson-Hubbard model for systems with disorder. The electronic disorder also explains the diminished coherence peaks of the quasi-particle DOS below {{T}\\text{c}} .

  6. Zeeman-driven phase transition within the superconducting state of {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2}.

    SciTech Connect

    Wright, J. A.; Green, E.; kuhns, P.; Reyes, A.; Brooks, J.; Schlueter, J.; Kato, R.; Yamamoto, H.; Kobayashi, M.; Brown , S. E.

    2011-08-16

    {sup 13}C nuclear magnetic resonance measurements were performed on {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2}, with the external field placed parallel to the quasi-2D conducting layers. The absorption spectrum is used to determine the electronic spin polarization M{sub s} as a function of external field H at a temperature T = 0.35 K. A discontinuity in the derivative dM{sub s}/dH at an applied field of H{sub s} = 213 {+-} 3 kOe is taken as evidence for a Zeeman-driven transition within the superconducting state and stabilization of inhomogeneous superconductivity.

  7. Optical investigations of the superconducting energy gap in b00-(BEDT-TTF)2SF5CH2CF2SO3

    SciTech Connect

    Kaiser, S.; Yasin, S.; Drichko, N.; Dressel, M.; Room, T.; Huvonen, D.; Nagel, U.; Gard, G. L.; Schlueter, J. A.

    2012-01-01

    The organic salt {beta}''-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} is a two-dimensional metal with a quarter-filled conduction band. In the metallic state the optical conductivity evidences interaction of the charge carriers with charge-order fluctuations that become stronger as temperature decreases. In the superconducting phase below T{sub c} {approx} 5K, indications of the superconducting gap with 2{Delta} {approx} 12 cm{sup -1} are observed in the optical spectrum, corresponding to 2{Delta}/k{sub B}T{sub c} {approx} 3.3. Its temperature and magnetic field dependences are also consistent with predictions by the BCS theory of a weakly coupled superconductor. The conductivity ratio {sigma}{sub 1}(T = 1.75 K)/{sigma}{sub 1}(10 K) indicates the opening of the superconducting gap in {beta}''-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}.

  8. 1/f noise in the quasi-two-dimensional organic conductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Cl.

    SciTech Connect

    Mueller, J.; Brandenburg, J.; Schlueter, J. A.; Materials Science Division; Goethe Univ.; Max Planck Inst. for Chemical Physics of Solids

    2009-01-01

    Resistance noise spectroscopy is applied to bulk single crystals of the quasi-two-dimensional organic conductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Cl both under moderate-pressure and at ambient-pressure conditions. When pressurized, the system can be shifted to the inhomogeneous coexistence region of antiferromagnetic insulating and superconducting phases, where percolation effects dominate the electronic fluctuations [J. Moeller et al., Phys. Rev. Lett. 102, 047004 (2009)]. Independent of the pressure conditions, at higher temperatures we observe generic 1/f{alpha}-type spectra, typical for this class of quasi-two-dimensional organic charge-transfer salts. The magnitude of the electronic noise is extremely enhanced compared to typical values of homogeneous semiconductors or metals. This indicates that a highly inhomogeneous current distribution may be an intrinsic property of organic charge-transfer salts. The temperature dependence of the nearly 1/f spectra can be very well described by a generalized random fluctuation model [P. Dutta, P. Dimon, and P. M. Horn, Rev. Lett. 43, 646 (1979)]. We find that the number of fluctuators and/or their coupling to the electrical resistance depend on the temperature. The phenomenological model explains a pronounced peak structure in the low-frequency noise at around 100 K, which is not observed in the resistivity itself, in terms of the thermally activated conformational degrees of freedom of the BEDT-TTF molecules ethylene endgroups.

  9. Coulomb enhancement of superconducting pair-pair correlations in a 3/4 -filled model for κ -(BEDT-TTF)2X

    NASA Astrophysics Data System (ADS)

    De Silva, W. Wasanthi; Gomes, N.; Mazumdar, S.; Clay, R. T.

    2016-05-01

    We present the results of precise correlated-electron calculations on the monomer lattices of the organic charge-transfer solids κ -(BEDT-TTF) 2X for 32 and 64 molecular sites. Our calculations are for band parameters corresponding to X =Cu[N (CN) 2]Cl and Cu2(CN) 3, which are semiconducting antiferromagnetic and quantum spin liquid, respectively, at ambient pressure. We have performed our calculations for variable electron densities ρ per BEDT-TTF molecule, with ρ ranging from 1 to 2. We find that d -wave superconducting pair-pair correlations are enhanced by electron-electron interactions only for a narrow carrier concentration about ρ =1.5 , which is precisely the carrier concentration where superconductivity in the charge-transfer solids occurs. Our results indicate that the enhancement in pair-pair correlations is not related to antiferromagnetic order, but to a proximate hidden spin-singlet state that manifests itself as a charge-ordered state in other charge-transfer solids. Long-range superconducting order does not appear to be present in the purely electronic model, suggesting that electron-phonon interactions also must play a role in a complete theory of superconductivity.

  10. Quasi-two-dimensional spin-split Fermi-liquid behavior of {kappa}-(BEDT-TTF){sub 2}I{sub 3} in strong magnetic fields

    SciTech Connect

    Harrison, N.; Mielke, C.H.; Rickel, D.G.; Wosnitza, J.; Qualls, J.S.; Brooks, J.S.; Balthes, E.; Schweitzer, D.; Heinen, I.; Strunz, W.

    1998-10-01

    Measurements of both the magnetization and magnetotransport of {kappa}-(BEDT-TTF){sub 2}I{sub 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 {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{endash}de Haas (SdH) effect but clearly visible also for the de Haas{endash}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. thinsp {copyright} {ital 1998} {ital The American Physical Society}

  11. Origin of the glass-like dynamics in molecular metals κ-(BEDT-TTF)2X: implications from fluctuation spectroscopy and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Müller, Jens; Hartmann, Benedikt; Rommel, Robert; Brandenburg, Jens; Winter, Stephen M.; Schlueter, John A.

    2015-08-01

    We have studied the low-frequency dynamics of the charge carriers in different organic charge-transfer salts κ-(BEDT-TTF)2X with polymeric anions X by using resistance noise spectroscopy. Our aim is to investigate the structural, glass-like transition caused by the conformational degrees of freedom of the BEDT-TTF molecules’ terminal ethylene groups. Although of fundamental importance for studies of the electronic ground-state properties, the phenomenology of the glassy dynamics has been minimally investigated and its origin is not understood. Our systematic studies of fluctuation spectroscopy of various different compounds reveal a universal, pronounced maximum in the resistance noise power spectral density related to the glass transition. The energy scale of this process can be identified with the activation energy of the glass-like ethylene endgroup structural dynamics as determined from thermodynamic and NMR measurements. For the first time for this class of ‘plastic crystals’, we report a typical glassy property of the relaxation time, namely a Vogel-Fulcher-Tammann law, and are able to determine the degree of fragility of the glassy system. Supporting ab initio calculations provide an explanation for the origin and phenomenology of the glassy dynamics in different systems in terms of a simple two-level model, where the relevant energy scales are determined by the coupling of the ethylene endgroups to the anions.

  12. Surface superstructures of quasi-one-dimensional organic conductor β-(BEDT-TTF)2PF6 crystal studied by scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Shigekawa, H.; Miyake, K.; Miyauchi, A.; Ishida, M.; Oigawa, H.; Nannichi, Y.; Yoshizaki, R.; Mori, T.

    1995-12-01

    Two kinds of superstructures were found at ~280 K by scanning tunneling microscopy on the crystal surface of β-(BEDT-TFF)2PF6, a quasi-one-dimensional organic conductor with a metal-insulator phase transition at ~297 K. One has a structural modulation which is perpendicular to the one-dimensional conductive axis, similar to that previously observed on a TTF-TCNQ crystal surface. The other has a twofold periodicity along the one-dimensional conductive axis, as expected from the theory. Under the assumption that the former is an intermediate structure caused by the interaction between neighboring one-dimensional molecular chains, superstructures which have been observed in BEDT-TTF compounds could be explained well.

  13. Superconductivity and fluctuating magnetism in quasi-two-dimensional {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br probed with implanted muons.

    SciTech Connect

    Lancaster, T.; Blundel, S. J.; Pratt, F. L.; Schlueter, J. A.; Materials Science Division; Rutherford Appleton Lab.; Oxford Univ.

    2011-01-19

    A muon-spin relaxation ({mu}{sup +}SR) investigation is presented for the molecular superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br. Evidence is found for low-temperature phase separation throughout the bulk of the material, with only a fraction of the sample showing a superconducting signal, even for slow cooling. Rapid cooling reduces the superconducting fraction still further. For the superconducting phase, the in-plane penetration depth is measured to be {lambda}{parallel} = 0.47(1) {micro}m, and evidence is seen for a vortex decoupling transition in applied fields above 40 mT. The magnetic fluctuations in the normal state produce a precipitous drop in relaxation rate above 100 K, and we discuss the possible causes for the unusual relaxation that we observe for T > T{sub c}.

  14. Phase transition and lattice distortion in the proposed spin-liquid system {kappa}-(BEDT-TTF){sub 2}Cu{sub 2}(CN){sub 3}.

    SciTech Connect

    Lang, M.; Manna, R. S.; de Souza, M.; Bruhl, A.; Schlueter, J. A.; Materials Science Division; Goethe-Univ.

    2010-01-01

    We report measurements of the uniaxial coefficients of thermal expansion {alpha}{sub i} and the specific heat C on the spin-liquid candidate {kappa}-(BEDT-TTF){sub 2}Cu{sub 2}(CN){sub 3}. We observe anomalous and strongly anisotropic in-plane expansivities, implying (i) distinct T-induced b-c lattice distortions and (ii) an increase in the ratio of the hopping amplitudes t{prime}/t upon cooling into the low-temperature regime. Most importantly, the {alpha}{sub i} data reveal clear evidence for a second-order phase transition around 6 K, accompanied by distinct lattice effects. By using a Grueneisen-scaling Ansatz, we are able to extract the corresponding anomaly to the specific heat. Estimates of the entropy indicate that spin degrees of freedom alone cannot account for the phase transition anomaly, suggesting that charge degrees of freedom are involved.

  15. Magnetic-field induced crossover of superconducting percolation regimes in the layered organic Mott system {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Cl.

    SciTech Connect

    Mueller, J.; Brandenberg, J.; Schlueter, J. A.; Materials Science Division; Max Planck Inst. for Chemical Physics of Solids

    2009-01-01

    Fluctuation spectroscopy is used to investigate the organic bandwidth-controlled Mott system {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Cl. We find evidence for percolative-type superconductivity in the spatially inhomogeneous coexistence region of antiferromagnetic insulating and superconducting states. When the superconducting transition is driven by a magnetic field, percolation seems to be dominated by instable superconducting clusters upon approaching T{sub c}(B) from above, before a 'classical' type of percolation is resumed at low fields, dominated by the fractional change of superconducting clusters. The 1/f noise is resolved into Lorentzian spectra in the crossover region, where the action of an individual fluctuator is enhanced, pointing to a mesoscopic phase separation.

  16. Temperature dependence of structural and electronic properties of the spin-liquid candidate {kappa}-(BEDT-TTF){sub 2}Cu{sub 2}(CN){sub 3}.

    SciTech Connect

    Jeschke, H. O.; de Souze, M.; Valenti, R.; Manna, R. S.; Lang, M.; Schlueter, J. A.

    2012-01-01

    We investigate the effect that the temperature dependence of the crystal structure of a two-dimensional organic charge-transfer salt has on the low-energy Hamiltonian representation of the electronic structure. For that, we determine the crystal structure of {kappa}-(BEDT-TTF){sub 2}Cu{sub 2}(CN){sub 3} for a series of temperatures between T=5 and 300 K by single crystal X-ray diffraction and analyze the evolution of the electronic structure with temperature by using density functional theory and tight binding methods. We find a considerable temperature dependence of the corresponding triangular lattice Hubbard Hamiltonian parameters. We conclude that even in the absence of a change of symmetry, the temperature dependence of quantities like frustration and interaction strength can be significant and should be taken into account.

  17. Role of layer packing for the electronic properties of the organic superconductor (BEDT-TTF ) 2Ag (CF3)4(TCE )

    NASA Astrophysics Data System (ADS)

    Altmeyer, Michaela; Valentí, Roser; Jeschke, Harald O.

    2015-06-01

    The charge-transfer compound (BEDT-TTF ) 2Ag (CF3)4(TCE ) crystallizes in three polymorphs with different alternating layers: While a phase with a κ packing motif has a low superconducting transition temperature of Tc=2.6 K , two phases with higher Tc of 9.5 and 11 K are multilayered structures consisting of α' and κ layers. We investigate these three systems within density functional theory and find that the α' layer shows different degrees of charge order for the two κ -α' systems and directly influences the electronic behavior of the conducting κ layer. We discuss the origin of the distinct behavior of the three polymorphs and propose a minimal tight-binding Hamiltonian for the description of these systems based on projective molecular Wannier functions.

  18. Structural disorder and its effect on the superconducting transition temperature in the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br

    SciTech Connect

    Su, X.; Zuo, F.; Schlueter, J.A.; Kelly, M.E.; Williams, J.M.

    1998-06-01

    In this paper, we report direct evidence of a structural transition in the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br near 80 K and the effect of disorder on the superconducting transition temperature. By cooling the sample from above 80 K, the interlayer magnetoresistance displays a bumplike feature, which increases sharply with increasing cooling rate. The rapidly cooled sample has a much larger resistivity and a lower transition temperature, which decreases linearly with increasing resistivity near the transition temperature. We propose that rapid cooling quenches the sample into a disordered state. Localized moments in the disordered state reduce the superconducting transition temperature. {copyright} {ital 1998} {ital The American Physical Society}

  19. Interlayer magnetoresistance in the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br near the superconducting transition

    SciTech Connect

    Zuo, F.; Schlueter, J.A.; Williams, J.M.

    1999-07-01

    In this paper, we report transport measurements of interlayer magnetoresistance with field parallel and perpendicular to the current direction in the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br. For H{parallel}J, the isothermal magnetoresistance R(H) displays a peak effect as a function of field. While the magnetoresistance at small field can be fitted to stacked Josephson junction model, the negative magnetoresistance is not consistent with quasiparticle tunneling model with a simple mean field gap. The origin for the peak effect remains unresolved. For H{perpendicular}J, R(H) increases monotonically with increasing field. Large magnetoresistance for H{perpendicular}J is consistent with the layered structure of the organic compounds. {copyright} {ital 1999} {ital The American Physical Society}

  20. Effects of inhomogeneity on the interlayer magnetoresistance in the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br

    SciTech Connect

    Zuo, F.; Su, X.; Zhang, P.; Schlueter, J.A.; Kelly, M.E.; Williams, J.M.

    1998-03-01

    In this paper, we compare the interlayer transport in the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br on samples of different inhomogeneities in terms of resistive transition width {Delta}T. For field parallel to the current, H{parallel}I, in the direction perpendicular to the layers, the isothermal magnetoresistance R(H) displays a peak effect as a function of field for high quality samples. The peak effect decreases gradually with increasing {Delta}T and it disappears completely for the sample with {Delta}T{gt}2 K. The results demonstrate clearly that the peak in R(H) in the interlayer direction is intrinsic to the layered structure in this compound. {copyright} {ital 1998} {ital The American Physical Society}

  1. Structural and electronic control of the metal to insulator transition and local orderings in the θ-(BEDT-TTF)2X organic conductors.

    PubMed

    Alemany, Pere; Pouget, Jean-Paul; Canadell, Enric

    2015-11-25

    A first-principles density functional theory (DFT) study of [Formula: see text]-(BEDT-TTF)2X molecular conductors with X  =  I3, CsCo(SCN)4 (ambient pressure, 7.5 kbar and 10 kbar), CsZn(SCN)4, TlCo(SCN)4, RbCo(SCN)4 and RbZn(SCN)4 (220 K and 90 K) is reported. It is shown that these salts exhibit three different types of band structure each of them associated with a different physical behavior. In contrast with previous proposals it is found that the key electronic parameter behind the differences in the band structures is the intrastack transfer integral, t c . A new mechanism for the metal to insulator transition in the [Formula: see text]-(BEDT-TTF)2MM'(SCN)4 ([Formula: see text], Tl; [Formula: see text], Co) salts is proposed, where an order-disorder structural transition of the ethylenedithio groups doubling the periodicity along the stack direction drives the system into an electronically pseudo-1D system along the interstack direction that is subject to a 4k F charge localization of holes. The structural rearrangement is such that the holes are not distributed equally between the two donors; the larger hole density is associated with the B donors which establish the strongest hydrogen bonds with the anion layers. A detailed microscopic description of how disorder of the ethylenedithio groups, the θ dihedral angle and the electronic structure intermingle and lead to the unusual phase diagram of these salts is presented. In this framework the role of pressure and uniaxial strain in controlling the physical behavior of these salts is discussed. PMID:26510211

  2. Structural and electronic control of the metal to insulator transition and local orderings in the θ-(BEDT-TTF)2X organic conductors

    NASA Astrophysics Data System (ADS)

    Alemany, Pere; Pouget, Jean-Paul; Canadell, Enric

    2015-11-01

    A first-principles density functional theory (DFT) study of θ -(BEDT-TTF)2X molecular conductors with X  =  I3, CsCo(SCN)4 (ambient pressure, 7.5 kbar and 10 kbar), CsZn(SCN)4, TlCo(SCN)4, RbCo(SCN)4 and RbZn(SCN)4 (220 K and 90 K) is reported. It is shown that these salts exhibit three different types of band structure each of them associated with a different physical behavior. In contrast with previous proposals it is found that the key electronic parameter behind the differences in the band structures is the intrastack transfer integral, t c . A new mechanism for the metal to insulator transition in the θ -(BEDT-TTF)2MM‧(SCN)4 (\\text{M}=\\text{Rb} , Tl; {{\\text{M}}\\prime}=\\text{Zn} , Co) salts is proposed, where an order-disorder structural transition of the ethylenedithio groups doubling the periodicity along the stack direction drives the system into an electronically pseudo-1D system along the interstack direction that is subject to a 4k F charge localization of holes. The structural rearrangement is such that the holes are not distributed equally between the two donors; the larger hole density is associated with the B donors which establish the strongest hydrogen bonds with the anion layers. A detailed microscopic description of how disorder of the ethylenedithio groups, the θ dihedral angle and the electronic structure intermingle and lead to the unusual phase diagram of these salts is presented. In this framework the role of pressure and uniaxial strain in controlling the physical behavior of these salts is discussed.

  3. Lattice vibrations of the charge-transfer salt κ -(BEDT-TTF)2Cu2(CN )3: Comprehensive explanation of the electrodynamic response in a spin-liquid compound

    NASA Astrophysics Data System (ADS)

    Dressel, M.; Lazić, P.; Pustogow, A.; Zhukova, E.; Gorshunov, B.; Schlueter, J. A.; Milat, O.; Gumhalter, B.; Tomić, S.

    2016-02-01

    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 of copper and linkage isomerism in the anion structure cause a loss of symmetry, frustration, disorder, and domain formation. Our findings consistently explain the temperature and polarization-dependent THz and infrared measurements, reinforce the understanding of dielectric properties, and have important implications for the quantum spin-liquid state, which should be treated beyond two-dimensional, purely electronic models.

  4. Pressure-dependent optical investigations of α -(BEDT-TTF)2I3 : Tuning charge order and narrow gap towards a Dirac semimetal

    NASA Astrophysics Data System (ADS)

    Beyer, R.; Dengl, A.; Peterseim, T.; Wackerow, S.; Ivek, T.; Pronin, A. V.; Schweitzer, D.; Dressel, M.

    2016-05-01

    Infrared optical investigations of α -(BEDT-TTF)2I3 have been performed in the spectral range from 80 to 8000 cm-1 down to temperatures as low as 10 K by applying hydrostatic pressure. In the metallic state, T >135 K, we observe a 50% increase in the Drude contribution as well as the mid-infrared band due to the growing intermolecular orbital overlap with pressure up to 11 kbar. In the ordered state, T

  5. Intrinsic vs. extrinsic inelastic scattering contributions in kappa-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br - transport measurements under hydrostatic pressure.

    SciTech Connect

    Strack, C.; Akinci, C.; Paschenko, V.; Wolf, B.; Uhrig, E.; Assmus, W.; Schreuer, J.; Wiehl, L.; Schlueter, J.; Wosnitza, J.; Schweitzer, D.; Lang , M.; Materials Science Division; J.W. Goethe-Universitat Frankfurt; Inst.fur Festkorperphysik; Univ. Stuttgart

    2006-12-05

    Interlayer-resistivity measurements have been performed on a variety of single crystals of the quasi-two-dimensional organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br. These crystals, which have been synthesized along two somewhat different routes, reveal strongly sample-dependent resistivity profiles: while the majority of samples shows a more or less pronounced {rho}(T) maximum around 90 K with a semiconducting behavior above, some crystals remain metallic at all temperatures T {le} 300 K. In the absence of significant differences in the crystals' structural parameters and chemical compositions, as proved by high-resolution X-ray and electron-probe-microanalysis, these results indicate that real structure phenomena, i.e. disorder and/or defects, may strongly affect the inelastic scattering. Comparative resistivity measurements under He-gas pressure on two crystals with strongly differing {rho}(T) profiles indicate that these additional, sample-dependent scattering contributions are characterized by an extraordinarily strong pressure response which is highly non-monotonous as a function of temperature. No correlations have been found between the strength of these scattering contributions and other characteristic properties such as the glass transition at T{sub g} = 77 K, the temperature T* {approx} 40 K, where the temperature dependence of the resistivity changes rather abruptly, or the superconducting transition temperature T{sub c}.

  6. Anisotropy of the competing superconducting and magnetic states in quasi-2D organic conductor κ-(BEDT-TTF)2Cu[N(CN)2]Br: An elastic investigation

    NASA Astrophysics Data System (ADS)

    Fournier, D.; Poirier, M.; Truong, K. D.

    2007-03-01

    Ultrasonic measurements performed on the quasi-2D organic conductor κ-(BEDT-TTF)2Cu[N(CN)2]Br reveal a phase separation between superconductivity and magnetism in the vicinity of the Mott transition line. We report here longitudinal (L) and transverse (T) ultrasonic velocity measurements propagating perpendicularly to the highly conducting planes; a magnetic field up to 18 Tesla could be applied along the same direction to differentiate the superconducting phase from the magnetic one. The huge velocity dip observed between 30 and 40 K and associated to a compressibility increase driven by the electronic degrees of freedom is not observed for T-waves polarized along [001]; this implies that only magnetic fluctuations associated to 1D sheets of the Fermi surface can couple to the ultrasonic waves. Around Tc= 12 K, both the temperature profile and the amplitude of the elastic anomalies are highly dependent on the wave polarization. A magnetic field investigation of these anomalies not only establishes the anisotropic character of the superconducting anomaly, but it reveals also the onset of a magnetic transition below 15 K over the same temperature range as the superconducting one. These anomalies likely favor a multi-component superconducting order parameter.

  7. In-place ESR microwave conductivity measurements and electronic band structure studies of the organic superconductor {beta}{double_prime}-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}

    SciTech Connect

    Wang, H.H.; VanZile, M.L.; Schlueter, J.A.

    1999-07-01

    The electronic structure of the organic superconductor {beta}{double_prime}-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} (BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene) was characterized with the use of electron spin resonance (ESR) spectroscopy and electronic band structure calculations. The room-temperature ESR line width is 24--27 G in the plane of a donor molecule layer (i.e., in the ab-plane) and {approximately} 32 G along the normal to this plane (i.e., along the c*-direction). The ab-plane anisotropy of the microwave conductivity was extracted for the first time from the ESR Dysonian line shape analysis. The in-plane conductivity varies sinusoidally, is maximal along the interstack direction (b-axis), and is minimal along the donor stack direction ({alpha}-axis). The Fermi surfaces of the title compound consist of a 2D hole pocket and a pair of 1D wavy lines. The directions for the in-plane conductivity maximum and minimum are in excellent agreement with the electronic band structure calculated for {beta}{double_prime}-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}, and the origin of the in-plane conductivity anisotropy lies in the one-dimensional part of the Fermi surface. This is the first time that an organic conductor shows Dysonian ESR line shape due to its 2D and strongly metallic nature, yet the 1D character is revealed simultaneously through the in-plane conductivity anisotropy.

  8. In-plane ESR microwave conductivity measurements and electronic band structure studies of the organic superconductor, {beta}'-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}.

    SciTech Connect

    Wang, H. H.; VanZile, M. L.; Schlueter, J. A.; Geiser, U.; Kini, A. M.; Sche, P. P.; Koo, H.-J.; Whangbo, M.-H.; Nixon, P. G.; Winter, R. W.; Gard, G. L.; Chemistry; North Carolina State Univ.; Portland State Univ.

    1999-07-01

    The electronic structure of the organic superconductor {beta}''-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} (BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene) was characterized with the use of electron spin resonance (ESR) spectroscopy and electronic band structure calculations. The room-temperature ESR line width is 24-27 G in the plane of a donor molecule layer (i.e., in the ab-plane) and {approx}32 G along the normal to this plane (i.e., along the c*-direction). The ab-plane anisotropy of the microwave conductivity was extracted for the first time from the ESR Dysonian line shape analysis. The in-plane conductivity varies sinusoidally, is maximal along the interstack direction (b-axis), and is minimal along the donor stack direction (a-axis). The Fermi surfaces of the title compound consist of a 2D hole pocket and a pair of 1D wavy lines. The directions for the in-plane conductivity maximum and minimum are in excellent agreement with the electronic band structure calculated for {beta}''-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}, and the origin of the in-plane conductivity anisotropy lies in the one-dimensional part of the Fermi surface. This is the first time that an organic conductor shows Dysonian ESR line shape due to its 2D and strongly metallic nature, yet the 1D character is revealed simultaneously through the in-plane conductivity anisotropy.

  9. New ambient pressure organic superconductors:. alpha. -(BEDT-TTF) sub 2 (NH sub 4 )Hg(SCN) sub 4 ,. beta. m-(BEDO-TTF) sub 3 Cu sub 2 (NCS) sub 3 , and. kappa. -(BEDT-TTF) sub 2 Cu(N(CN) sub 2 )Br

    SciTech Connect

    Wang, H.H.; Beno, M.A.; Carlson, K.D.; Geiser, U.; Kini, A.M.; Montgomery, L.K.; Thompson, J.E.; Williams, J.M.

    1990-01-01

    More than one hundred and twenty conducting salts based on the organic donor-molecule BEDT-TTF are known, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene (abbreviated herein as ET). Several of the early salts possessed tetrahedral and octahedral anions, such as (ET){sub 2}ClO{sub 4}(TCE), (ET){sub 2}PF{sub 6}, (ET){sub 2}ReO{sub 4}, and (ET){sub 2}BrO{sub 4}. The perchlorate salt is metallic to 1.4 K,{sup 1} and the perrenate derivative was the first ET based organic superconductor ({Tc} 2 K, 4.5 kbar). Since the discovery of ambient pressure superconductivity in {beta}-(ET){sub 2}I{sub 3} ({Tc} 1.4 K),{sup 5} other isostructural {beta}-(ET){sub 2}X salts have been prepared with higher {Tc}'s. A structure-property correlation for the {beta}-type salts has been reviewed in this volume; it predicts that {Tc}'s higher than 8K are possible if {beta}-salts with linear anions longer than I{sub 3}{sup {minus}} can be synthesized. During the search for new linear anions, a variety of compounds with discovered with polymeric anions. The report of superconductivity in {kappa}-(ET){sub 4}Hg{sub 3}X{sub 8} (X = Cl, {Tc} 5.4 K 29 kbar and X = Br, {Tc} 4.3 K ambient pressure and 6.7 K 3.5 kbar) and {kappa}-(ET){sub 2}Cu(NCS){sub 2} ({Tc} 10.4 K) further stimulated the search for novel polymeric anions. A general synthetic strategy for preparing new salts containing polymeric anions is to couple a coordinatively unsaturated neutral transition metal halide/pseudohalide with a simple halide or pseudohalide during an electrocrystallization synthesis. In this article, the authors discuss three new ambient pressure organic superconductors with novel polymeric anions, {alpha}-(ET){sub 2}(NH{sub 4})Hg(SCN){sub 4}, {beta}m-(BO){sub 3}Cu{sub 2}(NCS){sub 3} and {kappa}-(ET){sub 2}Cu(N(CN){sub 2})Br. 48 refs., 8 figs., 2 tabs.

  10. Experimental and semiempirical method to determine the Pauli-limiting field in quasi-two-dimensional superconductors as applied to κ-(BEDT-TTF)2Cu(NCS)2: strong evidence of a FFLO state

    SciTech Connect

    Agosta, C. C.; Jin, J.; Coniglio, W. A.; Smith, B. E.; Cho, K.; Mihut, I.; Martin, C.; Tozer, S. W.; Murphy, T. P.; Palm, E. C.; Schlueter, J. A.; Kurmoo, M.

    2012-01-01

    We present upper critical field data for {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2} with the magnetic field close to parallel and parallel to the conducting layers. We show that we can eliminate the effect of vortex dynamics in these layered materials if the layers are oriented within 0.3-inch of parallel to the applied magnetic field. Eliminating vortex effects leaves one remaining feature in the data that corresponds to the Pauli paramagnetic limit (H{sub p}). We propose a semiempirical method to calculate the H{sub p} in quasi-2D superconductors. This method takes into account the energy gap of each of the quasi-2D superconductors, which is calculated from specific-heat data, and the influence of many-body effects. The calculated Pauli paramagnetic limits are then compared to critical field data for the title compound and other organic conductors. Many of the examined quasi-2D superconductors, including the above organic superconductors and CeCoIn{sub 5}, exhibit upper critical fields that exceed their calculated H{sub p} suggesting unconventional superconductivity. We show that the high-field low-temperature state in {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2} is consistent with the Fulde-Ferrell-Larkin-Ovchinnikov state.

  11. Anisotropic magnetoresistance in the organic superconductor {beta}{sup {double_prime}}-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}

    SciTech Connect

    Su, X.; Zuo, F.; Schlueter, J.A.; Williams, J.M.; Nixon, P.G.; Winter, R.W.; Gard, G.L.

    1999-02-01

    In this paper, we report transport measurements of interlayer magnetoresistance with field parallel and perpendicular to the current direction in an all organic superconductor {beta}{sup {double_prime}}-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}. For H{parallel}I, the isothermal magnetoresistance R(H) at low temperatures (T{le}T{sub c}) displays a peak effect as a function of field. For H{perpendicular}I, R(H) increases monotonically with increasing field. The results are very analogous to the interlayer magnetoresistance in {kappa}-(BEDT-TTF){sub 2}X compounds. The observation of the peak effect or negative magnetoresistance in different systems for H{parallel}I{perpendicular} plane suggests that it is intrinsic to the layered organic superconductors. For H{perpendicular}I, the large positive magnetoresistance is in a general agreement with a two band model for charge transport. {copyright} {ital 1999} {ital The American Physical Society}

  12. High-Temperature Charge and Structure Anomalies in β''-(BEDT-TTF)4[(H3O)Ga(C2O4)3]•C6H5NO2

    NASA Astrophysics Data System (ADS)

    Ihara, Yoshihiko; Futami, Yosuke; Kawamoto, Atsushi

    2016-01-01

    We have performed specific heat, X-ray diffraction, electron spin resonance (ESR), and NMR experiments on the organic superconductor β''-(BEDT-TTF)4[(H3O)Ga(C2O4)3]•C6H5NO2 (β''-Ga) salt at high temperatures to reveal the origin of the resistivity minimum observed around 100 K. Since splitting of the Raman spectrum was observed at a charge-sensitive vibration mode, the anomaly around 100 K has been ascribed to a charge instability with fractional charge imbalance. In addition, another charge instability was detected at 8.5 K in a previous NMR experiment. The origin of these anomalies observed at different temperatures should be investigated to uncover the electronic state in which superconductivity occurs. Our results suggest that the β''-Ga salt undergoes a thermodynamic charge transition at TCO = 90 K, which has a different origin from the charge instability observed at 8.5 K in the NMR experiment. We discuss the possible connection between these charge instabilities by comparing the present results with those obtained for other BEDT-TTF salts with two charge-ordering transitions.

  13. In-plane superfluid density and microwave conductivity of the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br: Evidence for d-wave pairing and resilient quasiparticles

    NASA Astrophysics Data System (ADS)

    Milbradt, S.; Bardin, A. A.; Truncik, C. J. S.; Huttema, W. A.; Jacko, A. C.; Burn, P. L.; Lo, S.-C.; Powell, B. J.; Broun, D. M.

    2013-08-01

    We report the in-plane microwave surface impedance of a high-quality single crystal of κ-(BEDT-TTF)2Cu[N(CN)2]Br. In the superconducting state, we find three independent signatures of d-wave pairing: (i) a strong, linear temperature dependence of superfluid density; (ii) deep in the superconducting state the quasiparticle scattering rate Γ˜T3; and (iii) no BCS coherence peak is observed in the quasiparticle conductivity. Above Tc, the Kadowaki-Woods ratio and the temperature dependence of the in-plane conductivity show that the normal state is a Fermi liquid below ≃23 K, yet resilient quasiparticles dominate the transport up to ≃50 K.

  14. Modification of local electronic state by BEDT-STF doping to κ -(BEDT-TTF)2Cu[N (CN ) 2]Br salt studied by 13C NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Kobayashi, T.; Ihara, Y.; Kawamoto, A.

    2016-03-01

    We present the results of site-selective 13C NMR spectroscopy on an organic superconductor κ -(BEDT-TTF)2Cu[N (CN ) 2]Br (κ -Br) doped with BEDT-STF molecules. We reveal microscopically the modulation of the local electronic state caused by the BEDT-STF doping from the 13C NMR measurement on two types of samples, which are 13C enriched κ -Br doped with naturally abundant BEDT-STF molecules, and natural κ -Br doped with 13C enriched BEDT-STF molecules. The results of the nuclear spin-lattice relaxation rate 1 /T1 measured both in the normal and superconducting state suggest that the potential disorder at the BEDT-STF sites scatters antiferromagnetic interaction and superconducting Cooper pairs.

  15. Lattice effects and entropy release at the low-temperature phase transition in the spin-liquid candidate kappa-(BEDT-TTF){sub 2}Cu{sub 2}(CN){sub 3}.

    SciTech Connect

    Manna, R. S.; de Souza, M.; Bruhl, A.; Schlueter, J. A.; Lang, M.; Materials Science Division; Goethe-Univ.

    2010-01-08

    The spin-liquid candidate {kappa}-(BEDT-TTF){sub 2}Cu{sub 2}(CN){sub 3} has been studied by measuring the uniaxial expansion coefficients {alpha}{sub i}, the specific heat, and magnetic susceptibility. Special emphasis was placed on the mysterious anomaly around 6K - a potential spin-liquid instability. Distinct and strongly anisotropic lattice effects have been observed at 6K, clearly identifying this feature as a second-order phase transition. Owing to the large anomalies in {alpha}{sub i}, the application of Grueneisen scaling has enabled us to determine the corresponding specific heat contribution and the entropy release. Comparison of the latter with available spin models suggests that spin degrees of freedom alone cannot account for the phase transition. Scenarios, involving charge degrees of freedom, are discussed.

  16. Static and dynamic interaction between π and d electrons in organic superconductor β″-(BEDT-TTF)4[(H3O ) Fe (C2O4)3] .C6H5Br studied by 13C NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Ihara, Y.; Futami, Y.; Kawamoto, A.; Matsui, K.; Goto, T.; Sasaki, T.; Benmansour, S.; Gómez-García, C. J.

    2016-08-01

    We present the results of 13C NMR experiments in an organic superconductor with localized Fe spins β″-(BEDT-TTF) 4[(H3O ) Fe (C2O4)3] .C6H5Br . We reveal the antiferromagnetic coupling between Fe d spins and π spins, which creates an exchange field antiparallel to the external field direction at the π electrons. In addition to the static effects of Fe spins, we show from the nuclear spin-lattice relaxation rate measurement that the magnetic fluctuations generated by Fe spins are suppressed at low temperatures and high magnetic fields. These conditions are suitable to stabilize the field-induced superconductivity by the field compensation mechanism. After the suppression of Fe-spin dynamics by a magnetic field of 19 T, we observed the underlying π -electron contribution. We discuss a possible anomaly in the π -electron system.

  17. Charge transport in charge-ordered layered crystals θ-(BEDT-TTF)2MZn(SCN)4 (M=Cs,Rb) : Effects of long-range Coulomb interaction and the Pauli exclusion principle

    NASA Astrophysics Data System (ADS)

    Takahide, Yamaguchi; Kimata, Motoi; Hazama, Kaori; Terashima, Taichi; Uji, Shinya; Konoike, Takako; Yamamoto, Hiroshi M.

    2010-06-01

    We have measured the current-voltage (I-V) characteristics, dielectric properties, and magnetoresistances of insulating layered organic crystals θ-(BEDT-TTF)2MZn(SCN)4 (M=Cs,Rb) , in which electron-electron Coulomb interactions are considered to induce charge ordering. The in-plane I-V characteristics follow the power law with a large exponent that exceeds 10 in the low-temperature limit. The nonlinear I-V characteristics are attributed to electric field induced unbinding of pairs of an electron and a hole that are thermally excited and attracted to each other due to two-dimensional long-range Coulomb interaction. The temperature and frequency dependences of the in-plane dielectric constant for M=Cs are explained by the polarization of the electron-hole bound pairs, consistently with the I-V characteristics. The large dielectric anisotropy ( ≈100 at 0.6 K) observed for M=Cs suggests two-dimensional long-range Coulomb interaction, which is also consistent with the explanation of the nonlinear I-V curves. The organic crystals have a large positive magnetoresistance ratio, e.g., ≈10000% for M=Cs in a magnetic field of 10 T at 0.1 K. The magnetoresistance is nearly independent of the magnetic field orientation despite the highly two-dimensional charge transport, indicating that it is electron-spin related. The magnetoresistance may be caused by magnetic field induced parallel alignment of spins of mobile and localized electrons, both in the highest occupied molecular orbital of a BEDT-TTF molecule, and by the resulting suppression of conduction due to the Pauli exclusion principle.

  18. Synthesis, characterization, and physical properties of two new magnetic organic metals, [BEDT-TTF]{sub 4}[C(CN){sub 2}CONH{sub 2}]CuX{sub x} (X = Cl and Br{sub 0.77}Cl{sub 0.22})

    SciTech Connect

    Wang, H.H.; Geiser, U.; Kumar, S.K.

    1995-12-31

    Two new BEDT-TTF based charge transfer salts, [BEDT-TTF]{sub 4}[C(CN){sub 2}CONH{sub 2}]CuX{sub 2} (X = Cl and Br{sub 0.77}Cl{sub 0.22}) have been synthesized and characterized with use of X-ray diffraction, Energy Dispersive Spectroscopy (EDS), and Raman spectroscopy. ESR spectroscopy reveals that the anion layer contains 3% of paramagnetic Cu(II) species which exhibit Curie-Weiss behavior with a Weiss constant of {theta} = {minus}2.8 K. Both compounds are metallic below 150 K. AC susceptibility, RF penetration depth, and RF impedance measurements under pressure do not reveal signals of superconductivity.

  19. Localization of conduction electrons and the magnetic properties of the molecular metals {beta}''-(BEDT-TTF){sub 4}NH{sub 4}[M(C{sub 2}O{sub 4}){sub 3}] . DMF (M = Cr{sup 3+}, Fe{sup 3+})

    SciTech Connect

    Morgunov, R. B. Shibaeva, R. P.; Yagubskii, E. B.; Kato, T.; Tanimoto, Y

    2006-01-15

    Quasi-two-dimensional organic metals {beta}''-(BEDT-TTF){sub 4}NH{sub 4}[M(C{sub 2}O{sub 4}){sub 3}] . DMF containing the oxalate complexes of Cr{sup 3+} or Fe{sup 3+} ions between the conducting organic layers of the BEDT-TTF molecules are studied by EPR spectroscopy, and the contributions of these metallic complexes, conduction electrons, and non-equilibrium lattice defects to the magnetic susceptibility are determined. An analysis of the temperature dependence of the magnetic susceptibility and the EPR line shape has revealed partial localization of conduction electrons at T < 20 K in the crystals with Cr{sup 3+} ions. The size of the localization region is close to the size of an individual BEDT-TTF molecule. The localization effect weakens as nonequilibrium defects disappear during long-term storage at room temperature. The localization of conduction electrons is found to be accompanied by the appearance of weak antiferromagnetic interaction between the Cr{sup 3+} ions at T < 20 K, which disappears when Fe{sup 3+} ions substitute for Cr{sup 3+} ions.

  20. Sudden slowing down of charge carrier dynamics at the Mott metal-insulator transition in κ-(D8-BEDT-TTF)2Cu[N(CN)2]Br

    NASA Astrophysics Data System (ADS)

    Brandenburg, Jens; Müller, Jens; Schlueter, John A.

    2012-02-01

    We investigate the dynamics of correlated charge carriers in the vicinity of the Mott metal-insulator (MI) transition in the quasi-two-dimensional organic charge-transfer salt κ-(D8-BEDT-TTF)2Cu[N(CN)2]Br by means of fluctuation (noise) spectroscopy. The observed 1/f-type fluctuations are quantitatively very well described by a phenomenological model based on the concept of non-exponential kinetics. The main result is a correlation-induced enhancement of the fluctuations accompanied by a substantial shift of spectral weight to low frequencies in the vicinity of the Mott critical endpoint. This sudden slowing down of the electron dynamics, observed here in a pure Mott system, may be a universal feature of MI transitions. Our findings are compatible with an electronic phase separation in the critical region of the phase diagram and offer an explanation for the not yet understood absence of effective mass enhancement when crossing the Mott transition.

  1. Sudden slowing down of charge carrier dynamics at the Mott metal-insulator transition in kappa-(D{sub 8}-BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br.

    SciTech Connect

    Brandenburg, J.; Muller, J.; Schlueter, J. A.

    2012-02-01

    We investigate the dynamics of correlated charge carriers in the vicinity of the Mott metal-insulator (MI) transition in the quasi-two-dimensional organic charge-transfer salt {kappa}-(D{sub 8}-BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br by means of fluctuation (noise) spectroscopy. The observed 1/f-type fluctuations are quantitatively very well described by a phenomenological model based on the concept of non-exponential kinetics. The main result is a correlation-induced enhancement of the fluctuations accompanied by a substantial shift of spectral weight to low frequencies in the vicinity of the Mott critical endpoint. This sudden slowing down of the electron dynamics, observed here in a pure Mott system, may be a universal feature of MI transitions. Our findings are compatible with an electronic phase separation in the critical region of the phase diagram and offer an explanation for the not yet understood absence of effective mass enhancement when crossing the Mott transition.

  2. Structure and magnetotransport properties of the new quasi-two-dimensional molecular metal {beta} Double-Prime -(BEDT-TTF){sub 4}H{sub 3}O[Fe(C{sub 2}O{sub 4}){sub 3}] {center_dot} C{sub 6}H{sub 4}Cl{sub 2}

    SciTech Connect

    Zorina, L. V.; Prokhorova, T. G.; Simonov, S. V. Khasanov, S. S.; Shibaeva, R. P.; Manakov, A. I.; Zverev, V. N.; Buravov, L. I.; Yagubskii, E. B.

    2008-02-15

    The {beta} Double-Prime -(BEDT-TTF){sub 4}A{sup I}[M{sup III}(C{sub 2}O{sub 4}){sub 3}] {center_dot} G(A{sup I}=NH{sub 4}{sup +}, H{sub 3}O{sup +}, K{sup +}, Rb{sup +}; M{sup III}=Fe, Cr; G = 'guest' solvent molecule) family of layered molecular conductors with magnetic metal oxalate anions exhibits a pronounced dependence of the conducting properties on the type of neutral solvent molecules introduced into the complex anion layer. A new organic dichlorobenzene (C{sub 6}H{sub 4}Cl{sub 2})-containing conductor of this family, namely, {beta} Double-Prime -(BEDT-TTF){sub 4}H{sub 3}O[Fe(C{sub 2}O{sub 4}){sub 3}] {center_dot} C{sub 6}H{sub 4}Cl{sub 2}, is synthesized. The structure of the synthesized single crystals studied by X-ray diffraction is characterized by the following parameters: a = 10.421(1) A, b= 19.991(2) A, c= 35.441(3) A, {beta} = 92.87(1) Degree-Sign , V= 7374(1) A{sup 3}, space groupC2/c, and Z = 4. In the temperature range 0.5 and 2-300 K, the conductivity of the crystals is metallic without changing into a superconducting state. The magnetotransport properties of the crystals are examined in magnetic fields up to 17 T at T = 0.5 K. In fields higher than 10 T, Shubnikov-de Haas oscillations are detected, and the Fourier spectrum of these oscillations contains two frequencies with maximum amplitudes of about 80 and 375 T. The experimental results are compared with the related data obtained for other phases of this family. The possible structural mechanisms of the effect of a guest solvent molecule on the transport properties of the {beta} Double-Prime -(BEDT-TTF){sub 4}A{sup I}[M{sup III}(C{sub 2}O{sub 4}){sub 3}] {center_dot} G crystals are analyzed.

  3. Structure and magnetotransport properties of the new quasi-two-dimensional molecular metal {beta}''-(BEDT-TTF){sub 4}H{sub 3}O[Fe(C{sub 2}O{sub 4}){sub 3}] . C{sub 6}H{sub 4}Cl{sub 2}

    SciTech Connect

    Zorina, L. V. Prokhorova, T. G.; Simonov, S. V. Khasanov, S. S.; Shibaeva, R. P.; Manakov, A. I.; Zverev, V. N.; Buravov, L. I.; Yagubskii, E. B.

    2008-02-15

    The {beta}''-(BEDT-TTF){sub 4}A{sup I}[M{sup III}(C{sub 2}O{sub 4}){sub 3}] . G(A{sup I}=NH{sub 4}{sup +}, H{sub 3}O{sup +}, K{sup +}, Rb{sup +}; M{sup III}=Fe, Cr; G = 'guest' solvent molecule) family of layered molecular conductors with magnetic metal oxalate anions exhibits a pronounced dependence of the conducting properties on the type of neutral solvent molecules introduced into the complex anion layer. A new organic dichlorobenzene (C{sub 6}H{sub 4}Cl{sub 2})-containing conductor of this family, namely, {beta}''-(BEDT-TTF){sub 4}H{sub 3}O[Fe(C{sub 2}O{sub 4}){sub 3}] . C{sub 6}H{sub 4}Cl{sub 2}, is synthesized. The structure of the synthesized single crystals studied by X-ray diffraction is characterized by the following parameters: a = 10.421(1) A, b= 19.991(2) A, c= 35.441(3) A, {beta} = 92.87(1){sup o}, V= 7374(1) A{sup 3}, space groupC2/c, and Z = 4. In the temperature range 0.5 and 2-300 K, the conductivity of the crystals is metallic without changing into a superconducting state. The magnetotransport properties of the crystals are examined in magnetic fields up to 17 T at T = 0.5 K. In fields higher than 10 T, Shubnikov-de Haas oscillations are detected, and the Fourier spectrum of these oscillations contains two frequencies with maximum amplitudes of about 80 and 375 T. The experimental results are compared with the related data obtained for other phases of this family. The possible structural mechanisms of the effect of a guest solvent molecule on the transport properties of the {beta}''-(BEDT-TTF){sub 4}A{sup I}[M{sup III}(C{sub 2}O{sub 4}){sub 3}] . G crystals are analyzed.

  4. Magnetic field, frequency and temperature dependence of complex conductance of ultrathin La1.65Sr0.45CuO4/La2CuO4 films and the organic superconductors κ-(BEDT-TTF)2Cu[N(CN)2]Br

    SciTech Connect

    V. A. Gasparov; Bozovic, I.; He, Xi; Dubuis, G.; Pavuna, D.; Kushch, N. D.; Yagubskii, E. B.; Schlueter, J. A.

    2015-09-01

    In this study, we used atomic-layer molecular beam epitaxy (ALL-MBE) to synthesize bilayer films of a cuprate metal (La1.65Sr0.45CuO4) and a cuprate insulator (La2CuO4), in which interface superconductivity occurs in a layer that is just one-half unit cell thick. We have studied the magnetic field and temperature dependence of the complex sheet conductance, σ(ω), of these films, and compared them to κκ-(BEDT-TTF)2Cu[N(CN)2]Br single crystals. The magnetic field H was applied both parallel and perpendicular to the 2D conducting layers. Experiments have been carried out at frequencies between 23 kHz and 50 MHz using either two-coil mutual inductance technique, or the LC resonators with spiral or rectangular coils. The real and the imaginary parts of the mutual-inductance M(T,ω) between the coil and the sample were measured and converted to complex conductivity. For H perpendicular to the conducting layers, we observed almost identical behavior in both films and κ-Br single crystals: (i) the transition onset in the inductive response, Lk–1(T) occurs at a temperature lower by 2 K than in Re σ(T), (ii) this shift is almost constant with magnetic field up to 8 T; (iii) the vortex diffusion constant D(T) is exponential due to pinning of vortex cores. These results can be described by the extended dynamic theory of the Berezinski–Kosterlitz–Thouless (BKT) transition and dynamics of bound vortex–antivortex pairs with short separation lengths.

  5. Magnetic field, frequency and temperature dependence of complex conductance of ultrathin La1.65Sr0.45CuO4/La2CuO4 films and the organic superconductors κ-(BEDT-TTF)2Cu[N(CN)2]Br

    DOE PAGESBeta

    V. A. Gasparov; Bozovic, I.; He, Xi; Dubuis, G.; Pavuna, D.; Kushch, N. D.; Yagubskii, E. B.; Schlueter, J. A.

    2015-09-01

    In this study, we used atomic-layer molecular beam epitaxy (ALL-MBE) to synthesize bilayer films of a cuprate metal (La1.65Sr0.45CuO4) and a cuprate insulator (La2CuO4), in which interface superconductivity occurs in a layer that is just one-half unit cell thick. We have studied the magnetic field and temperature dependence of the complex sheet conductance, σ(ω), of these films, and compared them to κκ-(BEDT-TTF)2Cu[N(CN)2]Br single crystals. The magnetic field H was applied both parallel and perpendicular to the 2D conducting layers. Experiments have been carried out at frequencies between 23 kHz and 50 MHz using either two-coil mutual inductance technique, or themore » LC resonators with spiral or rectangular coils. The real and the imaginary parts of the mutual-inductance M(T,ω) between the coil and the sample were measured and converted to complex conductivity. For H perpendicular to the conducting layers, we observed almost identical behavior in both films and κ-Br single crystals: (i) the transition onset in the inductive response, Lk–1(T) occurs at a temperature lower by 2 K than in Re σ(T), (ii) this shift is almost constant with magnetic field up to 8 T; (iii) the vortex diffusion constant D(T) is exponential due to pinning of vortex cores. These results can be described by the extended dynamic theory of the Berezinski–Kosterlitz–Thouless (BKT) transition and dynamics of bound vortex–antivortex pairs with short separation lengths.« less

  6. Novel ET-coordinated copper(I) complexes: syntheses, structures, and physical properties (ET = BEDT-TTF = Bis(ethylenedithio)tetrathiafulvalene).

    PubMed

    Kanehama, Ryo; Umemiya, Masamichi; Iwahori, Fumiyasu; Miyasaka, Hitoshi; Sugiura, Ken-ichi; Yamashita, Masahiro; Yokochi, Yasukata; Ito, Hiroshi; Kuroda, Shin-ichi; Kishida, Hideo; Okamoto, Hiroshi

    2003-11-01

    New molecular charge-transfer complexes of bis(ethylenedithio)tetrathiafulvalene (ET), (ET)Cu(2)Br(4) (1), (ET)(2)Cu(6)Br(10) (2), (ET)(2)[Cu(4)Br(6)ET] (3), (ET)(2)Cu(2)Br(4) (4), (ET)(2)Cu(3)Br(7)(H(2)O) (5), and (ET)(2)Cu(6)Br(10)(H(2)O)(2) (6), have been synthesized by diffusing reaction of ET and Cu(II)Br(2). Their crystal structures and physical properties have been investigated. X-ray analyses revealed that ET molecules coordinated to the copper ions with the sulfur atoms of the ethylenedithio groups in all compounds. The Cu-S distances are found in the range 2.268(5)-2.417(8) A, being close to the typical Cu(I)-S coordination bond distances. Strong d-pi interactions between d-electrons of the copper ions and pi-electrons of the ET molecules can be expected through the Cu-S coordination bonds. ET molecules behave as trans-bidentate ligands bonding to two different copper ions in 1 and 3, as cis-bidentate ligands in 2, 5, and 6, and as monodentate ligands in 4. In the crystal structure of 3, there are two types of ET molecules in the crystal structure, where the first type is a trans-bidentate ligand and the second forms a stacking structure by itself. Compounds 1, 2, 4, and 6 show semiconducting behavior down to low temperature (sigma(RT) = 1.6 x 10(-2) S cm(-1) and E(a) = 122 meV for 1, sigma(RT) = 2.1 S cm(-1) and E(a) = 21 meV for 2, sigma(RT) = 5.4 x 10(-4) S cm(-1) and E(a) = 239 meV for 4, and sigma(RT) = 5.1 x 10(-2) S cm(-1) and E(a) = 207 meV for 6). On the other hand, in 3, a metal-like region is observed along the b-axis and c-axis, due to the contribution of stacked ET molecules, and a metal-semiconductor transition occurs at 280 and 270 K, respectively. Also, 5 exhibits metallic conductivity in the temperature ranges 240-300 and 200-300 K along the b-axis and c-axis, respectively, despite the oxidation state of ET with 2+. PMID:14577786

  7. 80 K anomaly and its effect on the superconducting and magnetic transition in deuterated {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Br

    SciTech Connect

    Su, X.; Zuo, F.; Schlueter, J.A.; Kini, A.M.; Williams, J.M.

    1998-08-01

    In this paper, we report careful transport and magnetic measurements on single crystals of deuterated {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br. By cooling the sample at different rates, it is found that cooling through 80K has a dramatic effect on the normal state metal-insulator transition and the superconducting transition temperatures. In-plane resistivity depends strongly on the cooling rate for temperatures below 80K, above which all resistivity curves cooled at different rates converge. By comparing it with the nondeuterated salt and the quasi-1D Bechgaard salt, we speculate that 80K corresponds to a structural phase transition in the anion chain. Fast cooling through 80K will freeze the high temperature magnetic phase to low temperatures and the presence of local magnetic moments suppresses the superconducting T{sub c}. {copyright} {ital 1998} {ital The American Physical Society}

  8. Evidence of Andreev bound states as a hallmark of the FFLO phase in κ-(BEDT-TTF)2Cu(NCS)2

    NASA Astrophysics Data System (ADS)

    Mayaffre, H.; Krämer, S.; Horvatić, M.; Berthier, C.; Miyagawa, K.; Kanoda, K.; Mitrović, V. F.

    2014-12-01

    Superconductivity is a quantum phenomenon arising, in its simplest form, from the pairing of fermions with opposite spin into a state with zero net momentum. Whether superconductivity can occur in fermionic systems with an unequal number of two species distinguished by spin or flavour presents an important open question in condensed-matter physics or quantum chromodynamics. In condensed matter the imbalance between spin-up and spin-down electrons that form the Cooper pairs is induced by the magnetic field. Such an imbalanced system can lead to exotic superconductivity in which pairs acquire finite momentum. This momentum leads to a spatially inhomogeneous state consisting of periodically alternating `normal' and `superconducting' regions. Here, we establish that the hallmark of this state is the appearance of spatially localized and spin-polarized quasiparticles forming the so-called Andreev bound states (ABS). These are detected through our nuclear magnetic resonance (NMR) measurements.

  9. Inhomogeneous 1H NMR spin-lattice relaxation in the organic superconductor kappa-(BEDT-TTF)2Cu[N(CN)2]Br

    NASA Astrophysics Data System (ADS)

    Gezo, Joseph Christopher

    The two-dimensional superconductors based on the organic molecule "ET" have been an active area of research since their discovery over two decades ago. The member of this family with the highest critical temperature, kappa-(ET)2Cu[N(CN)2]Br ( Tc=11.7 K), has seen renewed interest since the observation of an anomalous Nernst signal by Nam et al in 2007 [51]. A similar effect was seen earlier by Ong's group in some of the high-temperature cuprate superconductors by [78,84]. This is interpreted to be evidence of a picture of superconductivity in which the resistive transition is driven by thermal fluctuations in the phase of the superconducting order parameter. Below Tc, these fluctuations take the form of bound vortex-antivortex pairs that have no long-range effect on the phase. At Tc, they undergo a Kosterlitz-Thouless unbinding transition; the unbound vortices destroy long-range phase coherence. Previously reported proton NMR measurements on this material have shown a high sensitivity to vortex motion, but reported no interesting behavior above the phase transition [15,25,42]. In this thesis, we revisit the 1H NMR properties of kappa-(ET)2Cu[N(CN)2]Br, paying specific attention to the spin-lattice relaxation, to look for some fingerprint of the phenomenon observed by Nam et al.

  10. Enhanced T{sub c} in the first dual layered molecular superconductor.

    SciTech Connect

    Schlueter, J. A.; Wiehl, L.; Park, H.; de Souza, M.; Lang, M.; Koo, H.-J.; Whangbo, M.-H.; Materials Science Division; Goethe-Univ. Frankfurt; Kyung Hee Univ.; North Carolina State Univ.

    2010-07-02

    Single-crystal X-ray diffraction has shown that the high-critical-temperature (T{sub c}) phase of the filamentary molecular superconductor (BEDT-TTF){sub 2}Ag(CF{sub 3}){sub 4}(1,1,2-trichloroethane) [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene] contains layers of BEDT-TTF radical cations with alternating {kappa}- and {alpha}'-type packing motifs. This molecule-based superconductor with dual BEDT-TTF packing motifs has a T{sub c} five times higher than that of its polymorph that contains only {kappa}-type packing.

  11. Competition entre supraconductivite et magnetisme au voisinage de la transition de Mott dans le conducteur organique quasi-bidimensionnel k-(BEDT-TTF)2copper[N(CN)2]bromine

    NASA Astrophysics Data System (ADS)

    Fournier, David

    Les conducteurs organiques quasi-bidimensionnels kappa-ET2X presentent d'importantes similitudes avec les SCHT telles qu'une phase isolant de Mott, un regime de pseudogap et un etat supraconducteur. L'etude de leurs proprietes apparait donc complementaire. Parmi les interrogations persistantes concernant la physique de ces systemes, l'origine du (ou des) processus exotique d'appariement, responsable de la supraconductivite est le sujet suscitant l'interet le plus marque dans la communaute. L'hypothese d'un mecanisme lie a la proximite d'un etat antiferromagnetique est privilegiee. Une etape importante dans la resolution de cette problematique est l'identification de la symetrie du parametre d'ordre. D'apres de nombreux travaux sur les systemes fortement correles, la sonde ultrasonore, de par sa sensibilite aux excitations de quasiparticule a basse temperature, est consideree comme particulierement adaptee a l'etude de cette propriete. Cependant, son emploi necessite l'utilisation d'un compose metallique a basse temperature et completement supraconducteur. Le compose metallique organique kappa-ET 2Cu[N(CN)2]Br presente toutes les caracteristiques necessaires a l'etude de cette propriete. En effet, il est situe loin de la transition du premier ordre de Mott et est completement supraconducteur. De facon surprenante, ce systeme semble se coupler fortement avec le reseau ce qui augmente significativement la sensibilite de cette sonde aux proprietes du gaz electronique. Cependant, des difficultes techniques importantes, liees a la nature intrinseque de ce materiau, doivent etre surmontees pour proceder a des mesures suivant differentes polarisations. La presente etude a profondement modifie notre comprehension de ce systeme. En effet, ces mesures ont permis de constater que le kappa-ET2Cu[N(CN)2]Br est un compose qui est situe en bordure de la zone de coexistence entre la supraconductivite et le magnetisme, ce qui constitue un resultat totalement inattendu. De plus, la variation judicieuse du cycle thermique s'est averee etre equivalente a une modification de la pression chimique. Cette derniere est modifiee par l'intermediaire d'une relaxation structurale autour de 85 K appelee la transition de verre d'ethylenes. Cela nous a permis de suivre l'evolution de cette coexistence en s'approchant de la transition de premier ordre, et ainsi de statuer sur la competition entre la supraconductivite et le magnetisme ainsi que sur l'existence d'une separation de phase d'ordre macroscopique. De plus, nous avons observe une anisotropie similaire sur les mesures de vitesse ultrasonore entre le regime de pseudogap et la supraconductivite. Ce resultat tend a confirmer l'existence d'une physique commune entre le regime de pseudogap et l'etat supraconducteur. Le regime de pseudogap, encore meconnu a ce jour, est probablement relie a des fluctuations antiferromagnetiques, dont l'origine pourrait etre un emboitement de la surface de Fermi quasi-unidimensionnelle de ce compose, ou bien relie a la proximite de la physique de Mott. Enfin, l'analyse de la symetrie du parametre d'ordre supraconducteur, qui est probablement de type s+d, tend a demontrer que les processus de couplage interplan sont d'une importance cruciale. L'approche theorique de Hubbard purement 2D dans le plan conducteur semble donc insuffisante pour la recherche du mecanisme d'appariement.

  12. Number of organic superconductors grows

    SciTech Connect

    Maugh, T.H. II

    1983-11-11

    Work leading to the development of tetramethyltetraselenafulvalene (TMTSF) salts and bis(ethylenedithiolo)tetrathiafulvalene (BEDT-TTF) compounds is reviewed and the superconducting properties of these compounds are described. The outlook for additional organic superconducting compounds is discussed.

  13. DC and high-frequency conductivity of the organic metals {beta}"-(BEDT-TFF){sub 2}SF{sub 5}RSO{sub 3} (R=CH{sub 2}CF{sub 2} and CHF).

    SciTech Connect

    Glied, M.; Yasin, S.; Kaiser, S.; Drichko, N.; Dressel, M.; Schlueter, J. A.; Materials Science Division; Univ. Stuttgart

    2009-01-01

    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}''-(d8-BEDT-TTF)2SF5CH2CF2SO3 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.

  14. Evidence for charge order in organic superconductors obtained by vibrational spectrosocopy.

    SciTech Connect

    Drichko, N.; Kaiser, S.; Sun, Y.; Clauss, C.; Dressel, M.; Mori, H.; Schlueter, J.; Zhyliaeva, E. I.; Torunova, S. A.; Lyubovskaya, R. N.; Materials Science Division; Univ. of Stuttgart; Ioffe Physico-Technical Inst.; Univ. of Tokyo; Russian Academy of Science

    2009-01-01

    We study charge disproportionation in few quasi-two-dimensional BEDT-TTF-based compounds by following the temperature dependence of a charge-sensitive vibration v{sub 27}(B{sub 1u}) of BEDT-TTF molecule. While in a charge ordered insulator {theta}-(BEDT-TTF){sub 2}RbZn(SCN){sub 4} a difference between charge on the lattice sites is as high as 0.6e, a small charge disproportionation of 0.15-0.2e is found in two metallic compounds that become superconducting at low temperatures {beta}{double_prime}-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} and {beta}-(EDT-TTF){sub 4}[Hg{sub 3}I{sub 8}]{sub (1-x)}. In contrast to these, a pure metallic {beta}{double_prime}-(BEDT-TTF){sub 2}SO{sub 3}CHFSF{sub 5} does not show any presence of charge disproportionation. This study suggests a correlation between a slight charge disproportionation in the metallic state and superconductivity.

  15. Pressure dependence of the conduction-electron-spin-resonance linewidth of the α and β phases of di-bis(ethylene- diothiolo)tetrathiafulvalene triiodide

    NASA Astrophysics Data System (ADS)

    Forró, L.; Sekretarczyk, G.; Krupski, M.; Schweitzer, D.; Keller, H.

    1987-02-01

    We report conduction-electron-spin-resonance linewidth (ΔH) measurements of the α and β phases of the organic conductor di-bis(ethylenediothiolo)tetrathiafulvalene triiodide [(BEDT-TTF)2I3] in the 80-300 K temperature range under applied pressures of up to 5 kbar. ΔH increases under pressure in contrast to the predictions of the Elliot formula for the spin relaxation in metals. The pressure derivative d(lnΔH)/dP is -5.5+/-1%/kbar and 9.8+/-1%/kbar for the α and β phases of (BEDT-TTF)2I3 respectively.

  16. Near constancy of the pressure dependence of Tc across families of organic and fullerene superconductors

    NASA Astrophysics Data System (ADS)

    Crespi, Vincent H.; Cohen, Marvin L.

    1996-01-01

    Pressure strongly depresses the superconducting transition temperature Tc of both the doped fullerenes and the β-ET[(BEDT-TTF)nXm, (BEDT-TTF)=bis(ethylenedithio)tetrathiofulvalene)] organic superconductors. An outstanding puzzle in these materials is the weak variation dTc/dP across families of compounds with large variations in Tc. This property has been used to argue against phonon-induced pairing. However, closer examination of the volume dependence of Tc reveals that the weak variation of dTc/dP is consistent with moderate (but not weak) electron-phonon coupling.

  17. Possible Frohlich superconductivity in strong magnetic fields.

    SciTech Connect

    Mielke, C. H.; Harrison, N.; Ardavan, A.; Goddard, P.; Singleton, J.; Narduzzo, A.; Montgomery, Lawrence; Balicas, L.; Brooks, J. S.; Tokumoto, M.

    2001-01-01

    A brief review of some of the arguments pointing towards the possibility of organic conductors of the form {alpha}-(BEDT-TTF)&J3g(SCN)4 (where M=K, T1 and Rb) being candidates for Frohlich superconductivity is given.

  18. BEDT-TFF salts with fluorinated sulfonate anions.

    SciTech Connect

    Geiser, U.; Schlueter, J. A.; Kini, A. M.; Wang, H. H.; Ward, B. H.; Mohtasham, J.; Gard, G. L.; Portland State Univ.

    2003-01-01

    A number of layered conducting BEDT-TTF, bis(ethylenedithio)tetrathiafulvalene, salts with heavily fluorinated organosulfonate anions have been prepared and characterized. Of particular interest are the salts containing SF{sub 5}RSO{sub 3}{sup -} anions, where R is a partially fluorinated aliphatic backbone. While structurally similar --the {beta}' packing type predominates--the ground state of these salts varies from superconducting in the case of {beta}'-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} [1] to insulating. Many of the salts with insulating ground states are metallic at room temperature, but charge localization and disproportionation over crystallographically non-equivalent sites occurs at low temperature. The organosulfonate group exhibits a propensity to bind to lithium ions, thus ternary salts incorporating Li+ into the complex anion layer are often found. The fluorophilic effect in organofluorine compounds may be exploited to form salts where the conducting BEDT-TTF layers are separated by extremely bulky anion bilayers. The crystal structure of one such system, (BEDT-TTF){sub 3}[(CF{sub 3}){sub 2}CFC{sub 2}H{sub 4}SO{sub 3}]{sub 4}(H{sub 5}O{sub 2}){sub 2}, is described here.

  19. Ab initio pseudopotential band calculation of organic conductors

    SciTech Connect

    Ishibashi, Shoji; Kohyama, Masanori

    1999-12-01

    The authors have calculated the band structures of organic conductors TTF-TCNQ and {beta}-(BEDT-TTF){sub 2}I{sub 3} using the ab initio plane-wave pseudopotential method within the local-density approximation (LDA). The Fermi-surface shape and the origin of bands near the Fermi level are investigated for each compound.

  20. Angle-dependent evolution of the Fulde-Ferrell-Larkin-Ovchinnikov state in an organic superconductor.

    SciTech Connect

    Beyer, R.; Bergk, B.; Schlueter, J. A.; Wosnitza, J.

    2012-01-01

    We report magnetic-field and angular-dependent high-resolution specific-heat measurements of the organic superconductor {beta}{double_prime}-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}. When the magnetic field is aligned precisely within the conducting BEDT-TTF layer, at low temperatures a clear upturn of the upper critical field beyond the Pauli limit of 9.73 T is observed, hinting at the emergence of a Fulde-Ferrell-Larkin-Ovchinnikov state. This upturn disappears when the field is oriented out of plane by more than {approx}0.5 deg. For smaller out-of-plane angles, the specific-heat anomaly at T{sub c} sharpens and a second peaky phase transition appears within the superconducting state.

  1. Overview of organic superconductors

    SciTech Connect

    Mori, Hatsumi . Nagoya Division)

    1994-01-10

    Organic materials which are usually used for insulators, were shown to be an electrical conductor by H. Akamatsu, H. Inokuchi, and Y. Matsunaga in 1954. Moreover, J.P. Ferraris et al. showed that TTF [center dot] TCNQ was stably metallic down to around 60 K in 1973. Because of a low dimensionality of organic compound, however, a stabilization of an electronic state and a destabilization of a periodic lattice constructed a charge density wave which led a metal-insulator transition (a Peierls transition). After overcoming this low dimensionality, D. Jerome et al. discovered the first organic superconductor, (TMTSF)[sub 2] PF[sub 6] ([Tc] = 0.9 K (12kbar)) in 1980. Then with the resisting up of [Tc] constantly, the superconductor [kappa]-(BEDT-TTF)[sub 2](NCS)[sub 2] ([Tc] = 10.4 K) was found in 1987 and the [Tc] of [kappa]-(BEDT-TTF)[sub 2]Cu[N(CN)[sub 2

  2. Relation between geometry and charge transfer in low-dimensional organic salts

    SciTech Connect

    Umland, T.C.; Allie, S.; Kuhlmann, T.; Coppens, P.

    1988-11-03

    The Cambridge Data Base has been used to examine the relation between charge transfer and geometry in salts containing the TCNQ (tetracyanoquinodimethanide) anion and the TTF (tetrathiofulvalene), TSF (tetraselenofulvalene), and BEDT-TTF (bis(ethylenedithio)tetrathiofulvalene) cations. The correlation is based on either a bond length ratio or a bond length difference function and is calculated both for an extended data set, including charge transfers based on stoichiometry, and on a more restricted set based on neutral molecules and experimentally measured charge transfers. A two-parameter linear least-squares fit is found to be adequate; inclusion of a third (quadratic) coefficient does not give a significant improvement with the data available. The bond length difference function tends to give somewhat smaller standard deviations in predictions based on the derived equations. The curves for BEDT-TTF are not significantly different from those for the larger TTF set of entries.

  3. Crystal structure analysis under uniaxial strain at low temperature using a unique design of four-axis x-ray diffractometer with a fixed sample

    SciTech Connect

    Kondo, Ryusuke; Kagoshima, Seiichi; Harada, Jimpei

    2005-09-15

    For the purpose of crystal structure analysis under uniaxial strain at low temperatures, we developed a pressure cell for uniaxial compression and a unique design of an x-ray diffractometer wherein both the x-ray source and the detector are capable of two-axial rotation with a fixed sample. This arrangement is advantageous to crystal structure analyses under extreme conditions that require a large and heavy apparatus. Using the present diffractometer, we performed the crystal structure analyses of the organic conductor, {alpha}-(BEDT-TTF){sub 2}I{sub 3} (BEDT-TTF denotes bis(ethylene)dithio-tetrathiafulvalene), under uniaxial strain and ambient pressure, and at room and low temperatures, and obtained results that were qualitatively consistent with those of resistivity measurements.

  4. Photoinduced melting and charge order in quarter-filled organic conductors: Itinerant electron systems with competing interactions

    NASA Astrophysics Data System (ADS)

    Yonemitsu, Kenji; Maeshima, Nobuya; Tanaka, Yasuhiro; Miyashita, Satoshi

    2009-02-01

    Photoinduced charge dynamics in one- and two-dimensional organic conductors are studied theoretically in extended Peierls-Hubbard models. For quasi-one-dimensional (EDO-TTF)2PF6, photoinduced change in the charge order pattern from (0110) to (1010) is accompanied by probe-energy-dependent oscillations of conductivity. This is caused by coexistence of charge order and delocalized electrons. For quasi-two-dimensional α-(BEDT-TTF)2I3 and θ-(BEDT-TTF)2RbZn(SCN)4, photoinduced melting of the horizontal-stripe charge order proceeds easier in the α-type salt than in the θ-type salt. This is because the charge order in the θ-type salt is more strongly stabilized by electron-phonon interactions.

  5. Antiferromagnetic fluctuations in a quasi-two-dimensional organic superconductor detected by Raman spectroscopy.

    SciTech Connect

    Drichko, Natalia; Hackl, Rudi; Schlueter, John A.

    2015-10-15

    Using Raman scattering, the quasi-two-dimensional organic superconductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br (T-c = 11.8 K) and the related antiferromagnet kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl are studied. Raman scattering provides unique spectroscopic information about magnetic degrees of freedom that has been otherwise unavailable on such organic conductors. Below T = 200 K a broad band at about 500 cm(-1) develops in both compounds. We identify this band with two-magnon excitation. The position and the temperature dependence of the spectral weight are similar in the antiferromagnet and in the metallic Fermi liquid. We conclude that antiferromagnetic correlations are similarly present in the magnetic insulator and the Fermi-liquid state of the superconductor.

  6. Radical salts of TTF derivatives with the metal-metal bonded [Re 2Cl 8] 2- anion

    NASA Astrophysics Data System (ADS)

    Reinheimer, Eric W.; Galán-Mascarós, José R.; Gómez-García, Carlos J.; Zhao, Hanhua; Fourmigué, Marc; Dunbar, Kim R.

    2008-11-01

    Four new salts of the radical cations of TMTSF (tetramethyltetraselenafulvalene), TMTTF (tetramethyltetrathiafulvalene), BEDT-TTF (bisethylenedithiotetrathia-fulvalene) (ET) and o-Me 2TTF ( o-4,4'-dimethyltetrathiafulvalene) with the metal-metal bonded dianion [Re 2Cl 8] 2- were synthesized, and their structures and physical properties investigated. The structures of these semiconducting salts feature one-dimensional stacking of the donor molecules interleaved with [Re 2Cl 8] 2- anions and interstitial solvent molecules.

  7. Charge disproportionation, everywhere!

    NASA Astrophysics Data System (ADS)

    Takahashi, T.; Hiraki, K.; Moroto, S.; Tajima, N.; Takano, Y.; Kubo, Y.; Satsukawa, H.; Chiba, R.; Yamamoto, H. M.; Kato, R.; Naito, T.

    2005-12-01

    Charge disproportionation (CD) recently observed in many organic conductors is reviewed. CD is closely related to the charge ordering (CO) but is observed even when no long range CO is established. In a θ -phase BEDT-TTF salt, (BEDT-TTF){2}RbZn(SCN){4}, an extremely slow dynamics of CD has been observed above T_MI. A similar phenomenon is also observed in the Cs-analog, (BEDT-TTF){2}CsZn(SCN){4}. However, a spin-singlet ground state without CD is suggested in this salt at low temperatures. It is shown that α -(BETS){2}I{3} exhibits CD at low temperatures, as in α -(BET-TTF){2}I{3}. Recently, an abnormal line broadening has been observed in 13C-NMR of (TMTSF){2}FSO{3} under pressure as well as in 77Se-NMR of λ-(BETS){2}FeCl{4} in a high field. We expect that both are very likely caused by a large CD among the organic molecular sites. The current investigation is a part of a Grant-in-Aid for Scientific Research on Priority Areas of Molecular Conductors (No. 15073221) from the Ministry of Education, Culture, Sports, Science and Technology, Japan, and the “Japan-Korea Joint Research Project” from Japan Society for the Promotion of Science (03-01-8) and Korea Science and Engineering Foundation (F01-2003-000-20023-0).

  8. Quantum Hall effect in multilayered massless Dirac fermion systems with tilted cones

    NASA Astrophysics Data System (ADS)

    Tajima, Naoya; Yamauchi, Takahiro; Yamaguchi, Tatsuya; Suda, Masayuki; Kawasugi, Yoshitaka; Yamamoto, Hiroshi M.; Kato, Reizo; Nishio, Yutaka; Kajita, Koji

    2013-08-01

    A massless Dirac fermion ststem was realized in α-(BEDT-TTF)2I3 [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene] under high pressure. In contrast to graphene, this is the first bulk (multilayered) massless Dirac fermion material. Another important difference from graphene is that this system has highly tilted Dirac cones. In this case, conventional chiral symmetry is broken under a magnetic field. Here we experimentally addressed the following question: Is the Landau level structure of the system with tilted Dirac cones the same as that of graphene [conventional two-dimensional (2D) Dirac fermion system] under a magnetic field? The answer is yes. We succeeded in injecting holes into α-(BEDT-TTF)2I3 under high pressure. The detection of Shubnikov-de Haas oscillations whose phase was modified by Berry's phase π is direct evidence that this system is truly a 2D Dirac fermion system. In addition, we revealed the energy diagram of this device and characterized the multilayered quantum Hall effect.

  9. Attractive mechanical properties of a lightweight highly sensitive bi layer thermistor: polycarbonate/organic molecular conductor

    NASA Astrophysics Data System (ADS)

    Laukhina, E.; Lebedev, V.; Rovira, C.; Laukhin, V.; Veciana, J.

    2016-03-01

    The paper covers some of the basic mechanical characteristics of a recently developed bi layer thermistor: polycarbonate/(001) oriented layer of organic molecular conductor α’-(BEDT-TTF)2IxBr3-x, were BEDT-TTF=bis(ethylenedithio)tetrathiafulvalen. The nano and macro mechanical properties have been studied in order to use this flexible, low cost thermistor in sensing applications by proper way. The nano-mechanical properties of the temperature sensitive semiconducting layer of α’-(BEDT-TTF)2IxBr3-x were tested using nanoindentation method. The value of Young's modulus in direction being perpendicular to the layer plan was found as 9.0 ±1.4 GPa. The macro mechanical properties of the thermistor were studied using a 5848 MicroTester. The tensile tests showed that basic mechanical characteristics of the thermistor are close to those of polycarbonate films. This indicates a good mechanical strength of the developed sensor. Therefore, the thermistor can be used in technologies that need to be instrumented with highly robustness lightweight low cost temperature sensors. The paper also reports synthetic details on fabricating temperature sensing e-textile. As the temperature control is becoming more and more important in biomedical technologies like healthcare monitoring, this work strongly contributes on the ongoing research on engineering sensitive conducting materials for biomedical applications.

  10. Raman studies of low-dimensional conductors and superconductors

    NASA Astrophysics Data System (ADS)

    Lin, Yuankun

    Using a Fourier Raman spectrometer equipped with an infrared laser, together with cryogenics, three types of materials have been investigated as a function of temperature in this thesis. The first is the investigation of organic materials including kappa-(BEDT-TTF)2Cu(NCS)2 (T c = 10.4 K), kappa-(BEDT-TTF)2Cu(N(CN)2)Br (Tc = 11.6 K), alphat-(BEDT-TTF) 2I3 (Tc = 8 K) and beta-(BEDT-TTF) 2AuI2 (Tc = 5 K) which become superconductors at low temperature. The second is the study of the first organic conductor TTF-TCNQ which behaves in exactly the opposite way by becoming an insulator at low temperature. The third is the study of the strontium-doped lanthanum copper oxide superconductors with higher transition temperature. For BEDT-TTF based organic superconductors, the electron-phonon coupling is very strong. The frequencies and intensities of three strongest features (nu3 (Ag), nu9 (A g) and nu60 (B3g) modes) in the Raman spectra have been analyzed as a function of temperature. The frequencies of some modes are observed to soften in the temperature range where antiferromagnetic spin fluctuations have been observed, providing evidence of interactions between the phonons and the magnetism. The nu3 g (B3g) mode is observed to be very unusual in many ways, such as having an inverse isotope frequency shift. Below Tc this mode exhibits an increase of 2.2 cm -1in kappa-(BEDT-TTF)2Cu(N(CN)2)Br (T c = 11.6 K) and a decrease of 1.7 cm-1in alpha t-(BEDT-TTF)2I3 (Tc = 8 K). This is the highest frequency phonon in any material to be affected by superconductivity. For TTF-TCNQ, many new lines are observed at temperatures below 150 K as the fluctuating charge-densitywave occurs. The intensity of these lines increases with decreasing temperature. These new lines are assigned according to the deuterium-isotope frequency shifts. In the fluctuating charge-density-wave phase the Frohlich electron-phonon interaction is the probable cause of the appearance of Raman-forbidden scattering

  11. Scaling theory of the mott transition and breakdown of the Grüneisen scaling near a finite-temperature critical end point.

    PubMed

    Bartosch, Lorenz; de Souza, Mariano; Lang, Michael

    2010-06-18

    We discuss a scaling theory of the lattice response in the vicinity of a finite-temperature critical end point. The thermal expansivity is shown to be more singular than the specific heat such that the Grüneisen ratio diverges as the critical point is approached, except for its immediate vicinity. More generally, we express the thermal expansivity in terms of a scaling function which we explicitly evaluate for the two-dimensional Ising universality class. Recent thermal expansivity measurements on the layered organic conductor κ-(BEDT-TTF)2X close to the Mott transition are well described by our theory. PMID:20867311

  12. Bandwidth tuning triggers interplay of charge order and superconductivity in two-dimensional organic materials.

    SciTech Connect

    Kaiser, S.; Dressel, M.; Sun, Y.; Greco, A.; Schlueter, J. A.; Gard, G. L.; Drichko, N.; Materials Science Division; Univ. Stuttgart; UNR-CONICET; Portland State Univ.; Ioffe Physico-Technical Inst.

    2010-11-09

    We observe charge-order fluctuations in the quasi-two-dimensional organic superconductor {beta}{double_prime}-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}, both by means of vibrational spectroscopy, locally probing the fluctuating charge order, and by investigating the in-plane dynamical response by infrared reflectance spectroscopy. The decrease of the effective electronic interaction in an isostructural metal suppresses both charge-order fluctuations and superconductivity, pointing to their interplay. We compare the results of our experiments with calculations on the extended Hubbard model.

  13. Dielectric spectroscopy on organic charge-transfer salts.

    PubMed

    Lunkenheimer, P; Loidl, A

    2015-09-23

    This topical review provides an overview of the dielectric properties of a variety of organic charge-transfer salts, based on both, data reported in literature and our own experimental results. Moreover, we discuss in detail the different processes that can contribute to the dielectric response of these materials. We concentrate on the family of the 1D (TMTTF)2 X systems and the 2D BEDT-TTF-based charge-transfer salts, which in recent years have attracted considerable interest due to their often intriguing dielectric properties. We will mainly focus on the occurrence of electronic ferroelectricity in these systems, which also includes examples of multiferroicity. PMID:26325011

  14. Comparison among superconducting models for β″-ET 4[(H 3O)Fe(C 2O 4) 3]·C 6H 5Br single crystals by scanning tunnelling spectroscopy

    NASA Astrophysics Data System (ADS)

    Gambardella, A.; Di Capua, R.; Salluzzo, M.; Vaglio, R.; Affronte, M.; del Pennino, U.; Curreli, S.; Giménez-Saiz, C.; Gómez-García, C. J.; Coronado, E.

    2008-12-01

    Single crystals of the novel superconductor β″-(BEDT-TTF) 4[(H 3O)Fe(C 2O 4) 3]·C 6H 5Br charge-transfer salt were studied using a scanning tunnelling microscope. The measured samples have an onset critical temperature of about 4.0 K. Features often reported on similar compounds were observed in the tunnelling spectra at 1.4 K. STS spectra are compared with several models for the superconducting density of states. Our analysis evidences inhomogeneous superconductivity and indicates that the presence of a magnetic layer into the sample plays a role in determining the superconducting spectroscopic features.

  15. Collective excitations in layered organic conductors

    NASA Astrophysics Data System (ADS)

    Bonačić Lošić, Ž.; Bjeliš, A.; Županović, P.

    2010-06-01

    We apply the dielectric formalism within random phase approximation (RPA) and G0W0 approximation to the tight-binding multi-band systems with the three-dimensional long-range Coulomb interaction in order to calculate the one-particle spectral function for TTF-TCNQ, and to investigate dielectric properties of quasi-two-dimensional conductor ‧-(BEDT-TTF)2SF5CH2CF2SO3. In the model with two one-dimensional electron bands per donor and acceptor chains, appropriate for TTF-TCNQ, the RPA dielectric response comprises a low energy collective mode due to the strong coupling between the plasmon and the dipolar modes, together with the mode at order of magnitude higher energies. The first mode is responsible for the absence of low-energy quasi-particles and the appearance of broad dispersion at low energies in the spectral function. The wide structure at higher energies is due the second mode. These results are in the qualitative agreement with the ARPES data. In the model with two conducting bands, one one-dimensional and the other two-dimensional, which can be applied to ‧-(BEDT-TTF)2SF5CH2CF2SO3, the coupling between the plasmon and the dipolar mode leads to the appearance of the low energy collective mode perpendicular to the stacks, while the low energy dipolar mode persists along the stacks, as is observed in optical measurements.

  16. Quasiparticles and Fermi liquid behaviour in an organic metal

    PubMed Central

    Kiss, T.; Chainani, A.; Yamamoto, H.M.; Miyazaki, T.; Akimoto, T.; Shimojima, T.; Ishizaka, K.; Watanabe, S.; Chen, C.-T.; Fukaya, A.; Kato, R.; Shin, S.

    2012-01-01

    Many organic metals display exotic properties such as superconductivity, spin-charge separation and so on and have been described as quasi-one-dimensional Luttinger liquids. However, a genuine Fermi liquid behaviour with quasiparticles and Fermi surfaces have not been reported to date for any organic metal. Here, we report the experimental Fermi surface and band structure of an organic metal (BEDT-TTF)3Br(pBIB) obtained using angle-resolved photoelectron spectroscopy, and show its consistency with first-principles band structure calculations. Our results reveal a quasiparticle renormalization at low energy scales (effective mass m*=1.9 me) and ω2 dependence of the imaginary part of the self energy, limited by a kink at ~50 meV arising from coupling to molecular vibrations. The study unambiguously proves that (BEDT-TTF)3Br(pBIB) is a quasi-2D organic Fermi liquid with a Fermi surface consistent with Shubnikov-de Haas results. PMID:23011143

  17. Theory of the β-Type Organic Superconductivity under Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Suzuki, Takeo; Onari, Seiichiro; Ito, Hiroshi; Tanaka, Yukio

    2011-09-01

    We study theoretically the shift of the superconducting transition temperature (Tc) under uniaxial compression in β-type organic superconductors, β-(BEDT-TTF)2I3 and β-(BDA-TTP)2X (X=SbF6, AsF6), in order to clarify the electron correlation, the spin frustration, and the effect of dimerization. The transfer integrals are calculated by the extended Hückel method assuming the uniaxial strain, and the superconducting state mediated by the spin fluctuation is solved using Eliashberg's equation with the fluctuation--exchange approximation. The calculation is carried out on both the dimerized (one-band) and nondimerized (two-band) Hubbard models. We have found that (i) the behavior of Tc in β-(BEDT-TTF)2I3 with a stronger dimerization is well reproduced by the dimer model, while that in weakly dimerized β-BDA-TTP salts is rather well reproduced by the two-band model, and (ii) the competition between the spin frustration and the effect induced by the fluctuation is important in these materials, which causes the nonmonotonic shift of Tc against uniaxial compression.

  18. Silk/nano-material hybrid: properties and functions

    NASA Astrophysics Data System (ADS)

    Steven, Eden; Lebedev, Victor; Laukhina, Elena; Laukhin, Vladimir; Alamo, Rufina G.; Rovira, Concepcio; Veciana, Jaume; Brooks, James S.

    2014-03-01

    Silk continues to emerge as a material of interest in electronics. In this work, the interaction between silk and conducting nano-materials are investigated. Simple fabrication methods, physical, electronic, thermal, and actuation properties are reported for spider silk / carbon nanotube (CNT-SS) and Bombyx mori / (BEDT-TTF)-based organic molecular conductor hybrids (ET-S). The CNT-SS fibers are produced via water and shear assisted method, resulting in fibers that are tough, custom-shapeable, flexible, and electrically conducting. For ET-S bilayer films, a layer transfer technique is developed to deposit linked crystallites of (BEDT-TTF)2I3 molecular conductor onto silk films, generating highly piezoresistive semi-transparent films. In both cases, the hybridization allows us to gain additional functions by harnessing the water-dependent properties of silk materials, for example, as humidity sensor and electrical current- or water-driven actuators. SEM, TEM, FT-IR, and resistance measurements under varying temperature, strain, and relative humidity reveal the synergistic interactions between the bio- and nano-materials. E.S. is supported by NSF-DMR 1005293.

  19. Quest for the quantum limit in three dimensional metals

    SciTech Connect

    Brooks, J.S.; Qualls, J.S.; Engel, L.W.

    1996-11-01

    The purpose of this work is to exploit ultra-high, flux compression type magnetic fields to achieve magnetic energies which are on the same or greater scale of the electronic structure in metallic systems. Under such conditions a metal. may become an insulator, may acquire a completely new electronic structure, or may develop novel configurations of electronic order. In this paper we consider experiments on quasi-two dimensional molecular conductors in both non-destructive pulsed fields to 60 T and in destructive flux compression fields to 700 T at low temperatures. New results on the molecular conductors {alpha}-(BEDT-TTF) {sub 2}NH{sub 4}Hg(SCN){sub 4} and (TMTSF){sub 2}ClO{sub 4} are discussed in experiments up to 60 T at low temperatures, and preliminary results on {alpha}-(BEDT-TTF){sub 2}NH{sub 4}Hg(SON){sub 4} in the 700 T MC1 series flux compression generators are presented. We argue that true direct dc electrical transport measurements in these materials at low temperatures up to 700 T appear to be within reach.

  20. Magnetic imaging of interlayer Josephson vortices.

    SciTech Connect

    Kirtley, J. A.

    1999-01-15

    The authors have magnetically imaged interlayer Josephson vortices emerging parallel to the planes of single crystals of the organic superconductor {kappa}-(BEDT-TTF){sub 2} Cu(NCS){sub 2}, and the single layer cuprate high-T{sub c} superconductors Tl{sub 2}Ba{sub 2}CuO{sub 6+{delta}} (Tl-2201) and (Hg,Cu)Ba{sub 2}CuO{sub 6+{delta}} (Hg-1201), using a scanning Superconducting Quantum Interference Device (SQUID) microscope. These images provide a direct measurement of the interlayer penetration depth, which is approximately 63 {micro}m for {kappa}-(BEDT-TTF){sub 2} Cu(NCS){sub 2}, 18 {micro}m for Tl-2201 and 8 {micro}m for Hg-1201. The lengths for the cuprates are about a factor of 10 larger than originally predicted by the interlayer tunneling model for the mechanism of superconductivity in layered compounds, indicating that this mechanism alone cannot account for the high critical temperatures in these materials.

  1. Highly sensitive multi-layer pressure sensor with an active nanostructured layer of an organic molecular metal

    NASA Astrophysics Data System (ADS)

    Laukhin, V.; Lebedev, V.; Laukhina, E.; Rovira, C.; Veciana, J.

    2016-03-01

    This work addresses to the modern technologies that need to be instrumented with lightweight highly sensitive pressure sensors. The paper presents the development of a new plain flexible thin pressure sensor using a nanostructured layer of the highly sensitive organic piezoresistive metal β-(BEDT-TTF)2I3 as an active component; BEDT-TTF=bis (ethylenedithio)tetrathiafulvalene. The original construction approach permits one to operate the developed sensor on the principle of electrical resistance variations when its piezoresistive layer is elongated under a pressure increase. The pressure sensing element and a set of gold electrodes were integrated into one compact multi-layer design. The construction was optimized to enable one generic design for pressure ranges from 1 to 400 bar. The pressure tests showed that the sensor is able to control a small pressure change as a well definite electrical signal. So the developed type of the sensors is very attractive as a new generation of compact, lightweight, low-cost sensors that might monitor pressure with a good level of measurement accuracy.

  2. Recent developments in the determination of the amplitude and phase of quantum oscillations for the linear chain of coupled orbits

    NASA Astrophysics Data System (ADS)

    Audouard, Alain; Fortin, Jean-Yves

    2014-04-01

    De Haas-van Alphen oscillations are studied for Fermi surfaces (FS) illustrating the model proposed by Pippard in the early sixties, namely the linear chain of orbits coupled by magnetic breakdown. This FS topology is relevant to many multiband quasi-two-dimensional (q-2D) organic metals such as κ-(BEDT-TTF)2Cu(NCS)2 and θ-(BEDT-TTF)4CoBr4(C6H4Cl2) which are considered in detail. Whereas the Lifshits-Kosevich model only involves a first order development of field- and temperature-dependent damping factors, second order terms may have significant contribution to the Fourier components amplitude for such q-2D systems at high magnetic field and low temperature. The strength of these second order terms depends on the relative value of the involved damping factors, which are in turns strongly dependent on parameters such as the magnetic breakdown field, effective masses and, most of all, effective Lande factors. In addition, the influence of field-dependent Onsager phase factors on the oscillation spectra is considered.

  3. Exotic Quantum Phases and Phase Transitions of Strongly Interacting Electrons in Low-Dimensional Systems

    NASA Astrophysics Data System (ADS)

    Mishmash, Ryan V.

    Experiments on strongly correlated quasi-two-dimensional electronic materials---for example, the high-temperature cuprate superconductors and the putative quantum spin liquids kappa-(BEDT-TTF)2Cu2(CN)3 and EtMe3Sb[Pd(dmit)2]2---routinely reveal highly mysterious quantum behavior which cannot be explained in terms of weakly interacting degrees of freedom. Theoretical progress thus requires the introduction of completely new concepts and machinery beyond the traditional framework of the band theory of solids and its interacting counterpart, Landau's Fermi liquid theory. In full two dimensions, controlled and reliable analytical approaches to such problems are severely lacking, as are numerical simulations of even the simplest of model Hamiltonians due to the infamous fermionic sign problem. Here, we attempt to circumvent some of these difficulties by studying analogous problems in quasi-one dimension. In this lower dimensional setting, theoretical and numerical tractability are on much stronger footing due to the methods of bosonization and the density matrix renormalization group, respectively. Using these techniques, we attack two problems: (1) the Mott transition between a Fermi liquid metal and a quantum spin liquid as potentially directly relevant to the organic compounds kappa-(BEDT-TTF)2Cu 2(CN)3 and EtMe3Sb[Pd(dmit)2] 2 and (2) non-Fermi liquid metals as strongly motivated by the strange metal phase observed in the cuprates. In both cases, we are able to realize highly exotic quantum phases as ground states of reasonable microscopic models. This lends strong credence to respective underlying slave-particle descriptions of the low-energy physics, which are inherently strongly interacting and also unconventional in comparison to weakly interacting alternatives. Finally, working in two dimensions directly, we propose a new slave-particle theory which explains in a universal way many of the intriguing experimental results of the triangular lattice organic spin

  4. Mott metal-insulator transition on compressible lattices.

    PubMed

    Zacharias, Mario; Bartosch, Lorenz; Garst, Markus

    2012-10-26

    The critical properties of the finite temperature Mott end point are drastically altered by a coupling to crystal elasticity, i.e., whenever it is amenable to pressure tuning. Similar as for critical piezoelectric ferroelectrics, the Ising criticality of the electronic system is preempted by an isostructural instability, and long-range shear forces suppress microscopic fluctuations. As a result, the end point is governed by Landau criticality. Its hallmark is, thus, a breakdown of Hooke's law of elasticity with a nonlinear strain-stress relation characterized by a mean-field exponent. Based on a quantitative estimate, we predict critical elasticity to dominate the temperature range ΔT*/T(c)≃8%, close to the Mott end point of κ-(BEDT-TTF)(2)X. PMID:23215206

  5. Magnetic field induced lattice effects in a quasi-two-dimensional organic conductor close to the Mott metal-insulator transition

    NASA Astrophysics Data System (ADS)

    de Souza, Mariano; Brühl, Andreas; Strack, Christian; Schweitzer, Dieter; Lang, Michael

    2012-08-01

    We present ultra-high-resolution dilatometric studies in magnetic fields on a quasi-two-dimensional organic conductor κ-(D8-BEDT-TTF)2Cu[N(CN)2]Br, which is located close to the Mott metal-insulator (MI) transition. The obtained thermal expansion coefficient, α(T), reveals two remarkable features: (i) the Mott MI transition temperature TMI=(13.6±0.6) K is insensitive to fields up to 10 T, the highest applied field; (ii) for fields along the interlayer b axis, a magnetic field induced (FI) phase transition at TFI=(9.5±0.5) K is observed above a threshold field Hc˜1 T, indicative of a spin reorientation with strong magnetoelastic coupling.

  6. Synthesis, Crystal Structures and Physical Properties of TTF-Based Conducting Charge Transfer Salts with Anions Containing Selenocyanate Ligands

    NASA Astrophysics Data System (ADS)

    Turner, Scott S.; Le Pévelen, Delphine; Day, Peter; Prout, Keith

    2002-11-01

    Three new charge transfer salts of tetrathiafulvalene (TTF)-based donors with selenocyanate-metal complex anions have been synthesized. The salts have been characterized as BEDT-TTF 4[Cr(NCSe) 6]·CH 2Cl 2, II, TTF 3[Cr(NCSe) 4phen] 2, III and BEDT-TTF 2[Cr(NCSe) 4phen]·CH 2Cl 2, IV, where phen=1,10'-phenanthroline and BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene. At 120 K, II crystallizes in the P2 1/ m space group with a= 10.454(1), b= 31.990(1), c= 12.339(1) Å, β= 113.163(2)°, V= 3793.8Å 3, Z= 4 and at 240 K in the same space group with a= 10.530(1), b=32.122(1), c= 12.396(1) Å, β=113.186(3)°, V=3854.2 Å 3, Z=4. At 240 K III crystallizes in the C2/ c space group, a=38.9272(5), b=11.2992(1), c=15.2540(3) Å, β=106.8877(6)°, V=6420.1 Å 3, Z=8. The structure of IV has been solved in the Poverline1 space group with a=8.7629(3), b=11.7977(4), c=26.6031(9), α=81.697(2), β=87.858(3), γ=74.8471(14), V=2626.8 Å 3, Z=2. All of the salts have numerous S·Se close atomic contacts between donors and acceptors but there is no magnetic exchange between ions, as previously seen in closely related salts such as TTF[Cr(NCS) 4phen] and (donor)[ M(NCS) 4(isoquinoline) 2], where M=Cr, Fe and donor=TTF, BEDT-TTF or TMTTF (tetramethyltetrathiafulvalene). Indeed, II and IV are paramagnetic semiconductors whereas III is a paramagnetic insulator. The absence of long-range magnetic order is discussed in terms of structure-function relations since there are no π-stacking interactions between donor and acceptor, which are seen in all of the bulk magnets of this type where the donor spin is magnetically coupled to the anion. The synthesis and crystal structure of the starting material, [(C 4H 9) 4N] 3[Cr(NCSe) 6], I, is also reported; it crystallizes in the Poverline1 space group with a=12.220(1), b=12.814(1), c=13.008(1) Å, α=99.608(6), β=114.028(5), γ=92.637(6)°, V=1819.5 Å 3, Z=2.

  7. Realistic Parameters for the Description of Organic Metals

    NASA Astrophysics Data System (ADS)

    Dolfen, Andreas; Koch, Erik; Blum, Volker; Cano-Cortés, Laura; Merino, Jaime

    2009-03-01

    In molecular crystals correlation effects are often significant. For a non-perturbative description of the full Coulomb interaction we have therefore to resort to a model description in terms of generalized Hubbard models. The derivation of parameters for such models is crucial for realistic simulations. While hopping parameters are easily derived from density-functional theory (DFT) the Coulomb parameters pose a significant problem due to screening processes. We decompose their contributions into intra- and inter-molecular parts. The intra-molecularly screened Coulomb parameters are treated within DFT whereas the inter-molecular corrections are evaluated using classical electrostatics with DFT-derived polarizabilities and the distributed-dipole approach in combination with a Ewald summation. Even for simple lattices of polarizable point dipoles we find intriguing screening phenomena. As realistic applications we discuss the one- and two-dimensional organic metals TTF-TCNQ and θ-(BEDT-TTF)2I3.

  8. Organic superconductors: The Bechgaard salts and relatives

    NASA Astrophysics Data System (ADS)

    Brown, S. E.

    2015-07-01

    Organic conductors were originally considered a route to achieving high temperature superconductivity. While that goal could not be met, what came to be was a class of materials in which the interplay between correlations and dimensionality, and sometimes geometric frustration, lead to a spectacular diversity of phases and phenomena that are tuned by magnetic field, pressure, and temperature. Highlighted here are the physical properties of the superconducting and normal states of the first family of organic superconductors, the quasi-one dimensional Bechgaard salts (TMTSF)2X, as well as the quasi-two dimensional compounds κ -(BEDT-TTF)2X. In both cases, the preponderance of experiments indicate that the superconductivity is nodal. As well, the importance of correlations is evident in the temperature/pressure phase diagrams, and the influence of low-energy magnetic fluctuations over the normal state properties above the superconducting transition temperature is substantial.

  9. Coulomb Interaction Effect in Weyl Fermions with Tilted Energy Dispersion in Two Dimensions

    NASA Astrophysics Data System (ADS)

    Isobe, Hiroki; Nagaosa, Naoto

    2016-03-01

    Weyl fermions with tilted linear dispersions characterized by several different velocities appear in some systems including the quasi-two-dimensional organic semiconductor α -(BEDT -TTF )2I3 and three-dimensional WTe2 . The Coulomb interaction between electrons modifies the velocities in an essential way in the low-energy limit, where the logarithmic corrections dominate. Taking into account the coupling to both the transverse and longitudinal electromagnetic fields, we derive the renormalization group equations for the velocities of the tilted Weyl fermions in two dimensions, and found that they increase as the energy decreases and eventually hit the speed of light c to result in the Cherenkov radiation. Especially, the system restores the isotropic Weyl cone even when the bare Weyl cone is strongly tilted and the velocity of electrons becomes negative in certain directions.

  10. Coulomb interaction effect in tilted Weyl fermion in two dimensions

    NASA Astrophysics Data System (ADS)

    Isobe, Hiroki; Nagaosa, Naoto

    Weyl fermions with tilted linear dispersions characterized by several different velocities appear in some systems including the quasi-two-dimensional organic semiconductor α-(BEDT-TTF)2I3 and three-dimensional WTe2. The Coulomb interaction between electrons modifies the velocities in an essential way in the low energy limit, where the logarithmic corrections dominate. Taking into account the coupling to both the transverse and longitudinal electromagnetic fields, we derive the renormalization group equations for the velocities of the tilted Weyl fermions in two dimensions, and found that they increase as the energy decreases and eventually hit the velocity of light c to result in the Cherenkov radiation. Especially, the system restores the isotropic Weyl cone even when the bare Weyl cone is strongly tilted and the velocity of electrons becomes negative in certain directions.

  11. Quantum melting of magnetic order in an organic dimer Mott-insulating system

    NASA Astrophysics Data System (ADS)

    Naka, Makoto; Ishihara, Sumio

    2016-05-01

    Quantum entanglement effects between the electronic spin and charge degrees of freedom are examined in an organic molecular solid, termed a dimer Mott-insulating system, in which molecular dimers are arranged in a crystal as fundamental units. A low energy effective model includes an antisymmetric exchange interaction, as one of the dominant magnetic interactions. This interaction favors a 90 deg spin configuration, and competes with the Heisenberg-type exchange interaction. Stabilities of the magnetic ordered phases are examined by using the spin-wave theory, as well as the Schwinger-boson theory. It is found that the spin-charge interaction promotes an instability of the long-range magnetic ordered state around a parameter region where two spin-spiral phases are merged. Implication for the quantum spin liquid state observed in κ -(BEDT-TTF)2Cu2 (CN) 3 is discussed.

  12. Superconducting fluctuations in organic molecular metals enhanced by Mott criticality

    PubMed Central

    Nam, Moon-Sun; Mézière, Cécile; Batail, Patrick; Zorina, Leokadiya; Simonov, Sergey; Ardavan, Arzhang

    2013-01-01

    Unconventional superconductivity typically occurs in materials in which a small change of a parameter such as bandwidth or doping leads to antiferromagnetic or Mott insulating phases. As such competing phases are approached, the properties of the superconductor often become increasingly exotic. For example, in organic superconductors and underdoped high-Tc cuprate superconductors a fluctuating superconducting state persists to temperatures significantly above Tc. By studying alloys of quasi-two-dimensional organic molecular metals in the κ-(BEDT-TTF)2X family, we reveal how the Nernst effect, a sensitive probe of superconducting phase fluctuations, evolves in the regime of extreme Mott criticality. We find strong evidence that, as the phase diagram is traversed through superconductivity towards the Mott state, the temperature scale for superconducting fluctuations increases dramatically, eventually approaching the temperature at which quasiparticles become identifiable at all. PMID:24292063

  13. Field-Induced Metal-Insulator Transition in a Two-Dimensional Organic Superconductor

    SciTech Connect

    Wosnitza, J.; Wanka, S.; Hagel, J.; Lo''hneysen, H. v.; Qualls, J. S.; Brooks, J. S.; Balthes, E.; Schlueter, J. A.; Geiser, U.; Mohtasham, J.

    2001-01-15

    The quasi-two-dimensional organic superconductor {beta}''-( BEDT-TTF){sub 2}SF{sub 5} CH{sub 2}CF {sub 2}SO{sub 3} (T{sub c}{approx}4.4 K) shows very strong Shubnikov--de Haas (SdH) oscillations which are superimposed on a highly anomalous steady background magnetoresistance, R{sub b} . Comparison with de Haas--van Alphen oscillations allows a reliable estimate of R{sub b} which is crucial for the correct extraction of the SdH signal. At low temperatures and high magnetic fields insulating behavior evolves. The magnetoresistance data violate Kohler's rule, i.e., cannot be described within the framework of semiclassical transport theory, but converge onto a universal curve appropriate for dynamical scaling at a metal-insulator transition.

  14. Shubnikov--de Haas effect in the superconducting state of an organic superconductor

    SciTech Connect

    Wosnitza, J.; Wanka, S.; Hagel, J.; Ha''ussler, R.; Lo''hneysen, H. v.; Schlueter, J. A.; Geiser, U.; Nixon, P. G.; Winter, R. W.; Gard, G. L.

    2000-11-01

    We report the observation of Shubnikov--de Haas (SdH) oscillations in the mixed state of the organic superconductor {beta}''-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} (T{sub c}{approx}4.4K). At low temperatures the SdH oscillations persist clearly below the upper critical field B{sub c2}(0){approx}3.6T almost down to the field where the resistivity vanishes. Rather unusually, no additional damping of the SdH-signal amplitude -- as well as of the de Haas--van Alphen amplitude -- is observed in the superconducting state. This indicates that the damping in the vortex state of this quasi-two-dimensional superconductor is different in character to that observed for most three-dimensional materials.

  15. Coulomb Interaction Effect in Weyl Fermions with Tilted Energy Dispersion in Two Dimensions.

    PubMed

    Isobe, Hiroki; Nagaosa, Naoto

    2016-03-18

    Weyl fermions with tilted linear dispersions characterized by several different velocities appear in some systems including the quasi-two-dimensional organic semiconductor α-(BEDT-TTF)_{2}I_{3} and three-dimensional WTe_{2}. The Coulomb interaction between electrons modifies the velocities in an essential way in the low-energy limit, where the logarithmic corrections dominate. Taking into account the coupling to both the transverse and longitudinal electromagnetic fields, we derive the renormalization group equations for the velocities of the tilted Weyl fermions in two dimensions, and found that they increase as the energy decreases and eventually hit the speed of light c to result in the Cherenkov radiation. Especially, the system restores the isotropic Weyl cone even when the bare Weyl cone is strongly tilted and the velocity of electrons becomes negative in certain directions. PMID:27035318

  16. Electronic structure of a dual-layered organic charge transfer salt

    NASA Astrophysics Data System (ADS)

    Jeschke, Harald; Altmeyer, Michaela; Valenti, Roser

    2015-03-01

    We examine the electronic properties of polymorphs of (BEDT-TTF)2Ag(CF3)4(TCE) (1,1,2-trichloroethane) within density functional theory (DFT). While a phase with low superconducting transition temperature Tc = 2 . 6 K exhibits a κ packing motif, two high Tc phases are layered structures consisting of α' and κ packed layers. We determine the electronic structures and discuss the influence of the insulating α' layer on the conducting κ layer. We find that the stripes of high and low charge in the α' layer correspond to a stripe pattern of hopping parameters in the κ layer. This finding is the basis for studying the effect of the different underlying Hamiltonians on the superconducting properties. Research funded within DFG Transregio 49.

  17. Phase-change memory function of correlated electrons in organic conductors

    NASA Astrophysics Data System (ADS)

    Oike, H.; Kagawa, F.; Ogawa, N.; Ueda, A.; Mori, H.; Kawasaki, M.; Tokura, Y.

    2015-01-01

    Phase-change memory (PCM), a promising candidate for next-generation nonvolatile memories, exploits quenched glassy and thermodynamically stable crystalline states as reversibly switchable state variables. We demonstrate PCM functions emerging from a charge-configuration degree of freedom in strongly correlated electron systems. Nonvolatile reversible switching between a high-resistivity charge-crystalline (or charge-ordered) state and a low-resistivity quenched state, charge glass, is achieved experimentally via heat pulses supplied by optical or electrical means in organic conductors θ -(BEDT-TTF)2X . Switching that is one order of magnitude faster is observed in another isostructural material that requires faster cooling to kinetically avoid charge crystallization, indicating that the material's critical cooling rate can be useful guidelines for pursuing a faster correlated-electron PCM function.

  18. Development of an optical time-resolved measurement system under high-pressure and low-temperature with a piston-cylinder pressure cell

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Satoshi; Kino, Yohei; Nakagawa, Koichi; Nakagawa, Daisuke; Yamada, Jun-ichi; Toda, Yasunori

    2016-04-01

    To perform the femtosecond pump-probe spectroscopy under high pressure and low temperature, we constructed a measurement system with a piston cylinder type pressure cell installing an optical fiber bundle. The applied pressure was achieved to 6 kbar and the cell was cooled down to 15 K. Several demonstrations revealed that broadening and change of polarization of pulse (duration of ˜120 fs) owing to the dispersions in the fiber bundle are much small indicating that those have little influence on the measurement of carrier relaxation dynamics. In the measurements of κ-(BEDT-TTF)2Cu(NCS)2 under 1.3 kbar at 43 K, we have successfully detected the polarization anisotropy of the carrier relaxation dynamics and estimated the decay time in the same way as the normal measurement.

  19. Thermodynamic Evidence of d-Wave Superconductivity of the Organic Superconductor λ-(BETS)2GaCl4

    NASA Astrophysics Data System (ADS)

    Imajo, Shusaku; Kanda, Naoki; Yamashita, Satoshi; Akutsu, Hiroki; Nakazawa, Yasuhiro; Kumagai, Hiroya; Kobayashi, Takuya; Kawamoto, Atsushi

    2016-04-01

    Low-temperature heat capacity of the organic superconductor λ-(BETS)2GaCl4 in a temperature range between 0.6 and 10 K was measured for a single crystal sample by relaxation calorimetry technique. The contribution of electronic heat capacity in the superconducting state shows T2 dependence at lower temperature that indicates the existence of quasi-particle excitations from the line-nodal gap structure of d-wave pairing. The recovery of the electronic heat capacity coefficient, γ by magnetic field shows H1/2 dependence that is consistent with the picture of line-nodal superconductor. In spite of the different packing from typical organic superconductors κ-(BEDT-TTF)2X, the λ-type BETS salt also shows a feature of d-wave symmetry pairing.

  20. Thermal-transport Studies of Quantum Spin Liquids

    NASA Astrophysics Data System (ADS)

    Yamashita, Minoru

    2011-03-01

    Quantum spins, coupling antiferromagnetically on a 2D triangular lattice, cannot simultaneously satisfy all interactions. This frustrated situation is expected to give rise to mysterious fluid-like states of spins without long- range order, so called quantum spin liquid (QSL). The ground state of QSL and its exotic phenomena, such as fractionalized excitation with an artificial gauge field, have been extensively discussed for decades, yet to be identified by lack of any real materials. This is why the recent discoveries of materials possessing an ideal 2D triangular lattice have spurred a great deal of interest. To understand the nature of QSL, knowledge of the low-lying excitation, particularly the presence/absence of an excitation gap, is of primary importance. We employ thermal transport measurements on newly discovered QSL candidates, κ -(BEDT-TTF)2 Cu 2 (CN)3 and EtMe 3 Sb[Pd(dmit)2 ]2 , and report that the two organic insulators possess different QSLs characterized by different elementary excitations. In κ -(BEDT-TTF)2 Cu 2 (CN)3, heat transport is thermally activated in low temperatures, suggesting presence of a spin gap in this QSL. In stark contrast, in EtMe 3 Sb[Pd(dmit)2 ]2, a sizable temperature-linear term of thermal conductivity is clearly resolved in the zero-temperature limit, showing gapless excitation with long mean free path (~ 1 ,000 lattice distances), analogous to excitations near the Fermi surface in normal metals. These results are consistent with theoretical suggestions including 2D gapless spinons with a Fermi surface. This work was done in collaboration with N. Nakata, Y. Senshu, M. Nagata, Y. Kasahara, S. Fujimoto, T. Shibauchi, Y. Matsuda, T. Sasaki, N. Yoneyama, N. Kobayashi, H. M. Yamamoto and R. Kato.

  1. Coexistence of ferromagnetism and metallic conductivity in a molecule-based layered compound.

    PubMed

    Coronado, E; Galán-Mascarós, J R; Gómez-García, C J; Laukhin, V

    2000-11-23

    Crystal engineering--the planning and construction of crystalline supramolecular architectures from modular building blocks--permits the rational design of functional molecular materials that exhibit technologically useful behaviour such as conductivity and superconductivity, ferromagnetism and nonlinear optical properties. Because the presence of two cooperative properties in the same crystal lattice might result in new physical phenomena and novel applications, a particularly attractive goal is the design of molecular materials with two properties that are difficult or impossible to combine in a conventional inorganic solid with a continuous lattice. A promising strategy for creating this type of 'bi-functionality' targets hybrid organic/inorganic crystals comprising two functional sub-lattices exhibiting distinct properties. In this way, the organic pi-electron donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) and its derivatives, which form the basis of most known molecular conductors and superconductors, have been combined with molecular magnetic anions, yielding predominantly materials with conventional semiconducting or conducting properties, but also systems that are both superconducting and paramagnetic. But interesting bulk magnetic properties fail to develop, owing to the discrete nature of the inorganic anions. Another strategy for achieving cooperative magnetism involves insertion of functional bulky cations into a polymeric magnetic anion, such as the bimetallic oxalato complex [MnIICrIII(C2O4)3]-, but only insoluble powders have been obtained in most cases. Here we report the synthesis of single crystals formed by infinite sheets of this magnetic coordination polymer interleaved with layers of conducting BEDT-TTF cations, and show that this molecule-based compound displays ferromagnetism and metallic conductivity. PMID:11100721

  2. Coexistence of ferromagnetism and metallic conductivity in a molecule-based layered compound

    NASA Astrophysics Data System (ADS)

    Coronado, Eugenio; Galán-Mascarós, José R.; Gómez-García, Carlos J.; Laukhin, Vladimir

    2000-11-01

    Crystal engineering-the planning and construction of crystalline supramolecular architectures from modular building blocks-permits the rational design of functional molecular materials that exhibit technologically useful behaviour such as conductivity and superconductivity, ferromagnetism and nonlinear optical properties. Because the presence of two cooperative properties in the same crystal lattice might result in new physical phenomena and novel applications, a particularly attractive goal is the design of molecular materials with two properties that are difficult or impossible to combine in a conventional inorganic solid with a continuous lattice. A promising strategy for creating this type of `bi-functionality' targets hybrid organic/inorganic crystals comprising two functional sub-lattices exhibiting distinct properties. In this way, the organic π-electron donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) and its derivatives, which form the basis of most known molecular conductors and superconductors, have been combined with molecular magnetic anions, yielding predominantly materials with conventional semiconducting or conducting properties, but also systems that are both superconducting and paramagnetic. But interesting bulk magnetic properties fail to develop, owing to the discrete nature of the inorganic anions. Another strategy for achieving cooperative magnetism involves insertion of functional bulky cations into a polymeric magnetic anion, such as the bimetallic oxalato complex [MnIICrIII(C2O4)3]-, but only insoluble powders have been obtained in most cases. Here we report the synthesis of single crystals formed by infinite sheets of this magnetic coordination polymer interleaved with layers of conducting BEDT-TTF cations, and show that this molecule-based compound displays ferromagnetism and metallic conductivity.

  3. Mott metal-insulator transition induced by utilizing a glasslike structural ordering in low-dimensional molecular conductors

    NASA Astrophysics Data System (ADS)

    Hartmann, Benedikt; Müller, Jens; Sasaki, Takahiko

    2014-11-01

    We utilize a glasslike structural transition in order to induce a Mott metal-insulator transition in the quasi-two-dimensional organic charge-transfer salt κ -(BEDT-TTF)2Cu [N (CN)2Br ]. In this material, the terminal ethylene groups of the BEDT-TTF molecules can adopt two different structural orientations within the crystal structure, namely eclipsed (E) and staggered (S) with the relative orientation of the outer C-C bonds being parallel and canted, respectively. These two conformations are thermally disordered at room temperature and undergo a glasslike ordering transition at Tg˜75 K. When cooling through Tg, a small fraction that depends on the cooling rate remains frozen in the S configuration, which is of slightly higher energy, corresponding to a controllable degree of structural disorder. We demonstrate that, when thermally coupled to a low-temperature heat bath, a pulsed heating current through the sample causes a very fast relaxation with cooling rates at Tg of the order of several 1000 K /min . The freezing of the structural degrees of freedom causes a decrease of the electronic bandwidth W with increasing cooling rate, and hence a Mott metal-insulator transition as the system crosses the critical ratio (W/U ) c of bandwidth to on-site Coulomb repulsion U . Due to the glassy character of the transition, the effect is persistent below Tg and can be reversibly repeated by melting the frozen configuration upon warming above Tg. Both by exploiting the characteristics of slowly changing relaxation times close to this temperature and by controlling the heating power, the materials can be fine-tuned across the Mott transition. A simple model allows for an estimate of the energy difference between the E and S state as well as the accompanying degree of frozen disorder in the population of the two orientations.

  4. Novel Quantum Criticality in Two Dimensional Topological Phase transitions

    NASA Astrophysics Data System (ADS)

    Cho, Gil Young; Moon, Eun-Gook

    2016-01-01

    Topological quantum phase transitions intrinsically intertwine self-similarity and topology of many-electron wave-functions, and divining them is one of the most significant ways to advance understanding in condensed matter physics. Our focus is to investigate an unconventional class of the transitions between insulators and Dirac semimetals whose description is beyond conventional pseudo relativistic Dirac Hamiltonian. At the transition without the long-range Coulomb interaction, the electronic energy dispersion along one direction behaves like a relativistic particle, linear in momentum, but along the other direction it behaves like a non-relativistic particle, quadratic in momentum. Various physical systems ranging from TiO2-VO2 heterostructure to organic material α-(BEDT-TTF)2I3 under pressure have been proposed to have such anisotropic dispersion relation. Here, we discover a novel quantum criticality at the phase transition by incorporating the long range Coulomb interaction. Unique interplay between the Coulomb interaction and electronic critical modes enforces not only the anisotropic renormalization of the Coulomb interaction but also marginally modified electronic excitation. In connection with experiments, we investigate several striking effects in physical observables of our novel criticality.

  5. Conductors with small Fermi energies and small gap energies

    SciTech Connect

    Thorn, R.J.

    1993-09-01

    If the Fermi energy is of the order of meV`s, the usual treatment of the density of free electrons is not valid, but use can be made of an averaged density of states that depends weakly on temperature, so that the temperature variation of the conductivity can be expressed by the equation: {sigma} {congruent} CT{sup (1-s)} 1n{l_brace}[(exp({beta}E{sub f}) + 1)/2][exp({minus}{beta}(E{sub g} {minus} E{sub f})) + 1)]{r_brace} in which E{sub f} is the Fermi energy, E{sub g} is the top of the energy gap for thermal activation, s is the exponent of the temperature-dependent scattering. This equation serves to define a class of solids consisting of a microcomposite with a narrow conduction band for which E{sub f} of the order of ceV`s or less and a thermal activated conduction for which E{sub g} is of the order of ceV`s. It describes quantitatively the conductivity, {sigma}(T;{Delta}, for YBa{sub 2}Cu{sub 3}O{sub 7-{Delta}} and {sigma}(T;p) as the hydrostatic pressure p is varied for {kappa}-(BEDT-TTF){sub 2}CuN(CN){sub 2}Br.

  6. Design strategies for the preparation of polymeric organic superconductors. Final report, 1 October 1992-29 February 1996

    SciTech Connect

    Spangler, C.W.; Reynolds, J.R.

    1996-06-17

    Several copolymers were synthesized in which the known superconducting precursor bis-ethylenedithiot etrathiafulvalene, BEDT-TTF (`ET`), was incorporated as a formal repeat unit into aliphatic and aromatic polyesters as well as an aliphatic polyurethane. These polymers could be cast as optically quality thin films. All polymers could be oxidized to either monocation or dication forms in solution with antimony pentachloride, in which all the ET subunits had been oxidized. Et subunits could also be attached as pendant groups on a poly (methyl methacrylate) backbone with up to 60% incorporation. All of the polymers were thermally stable to above 200 degrees C, and were fully characterized by both DSC, TGA and GPC. Cyclic voltammetry clearly showed that the incorporated ET subunits were electroactive, with two redox peaks showing the successive formation of the radical cation and dication peaks. Room temperature DC conductivities for the polymer films before and after oxidative doping were obtained, with conductivities of the oxidized films generally falling between 10(exp {minus}6) to 10(exp {minus}4) S/cm. Several attempts to incorporate TTF subunits into copolymer formulations proved to generally unsuccessful, although this research is continuing.

  7. NMR Studies of Novel Electronic Phases in Low Dimensional Molecular Solids at High Pressure and Low Temperature

    NASA Astrophysics Data System (ADS)

    Brown, Stuart

    2013-03-01

    Molecular superconductors are known for anisotropic electronic band structure, correlations, and a sensitivity to mechanical or chemical pressure which acts to control the relative strength of the respective kinetic and potential energies. Modest pressures, of order 1 GPa are commonly used to continuously tune from a Mott insulating ground state to a superconducting state, and NMR has been particularly successful in identifying the orders involved, and the nature of the excitations in the various phases encountered. The family of quasi-two dimensional systems κ-(BEDT-TTF)2X (e.g., X=Cu(NCS)2, Cu[N(CN)2]Cl) includes a line of first order phase transitions separating the Mott and superconducting phases, with the superconducting state exhibiting signatures for line nodes associated with an order parameter sign-change over the Fermi surface. The pressure/temperature phase diagram of the quasi-one dimensional materials (TMTSF)2X, X=PF6, ClO4,...) includes more phases, as a consequence of effective 1/4-filling and a substantial density wave susceptibility. The SC ground state is singlet, and there is evidence for a sign-change of the order parameter over the Fermi surface. The high-conductivity normal state exhibits properties associated with two-dimensional spin fluctuations, with signatures in the relaxation rate, as well as transport that are reminiscent of behaviors observed in other correlated superconductors. Supported by the NSF under grant no. DMR-1105531

  8. Trifluoromethylmetallate anions as components of molecular charge transfer salts and superconductors.

    SciTech Connect

    Schlueter, J. A.

    1998-10-14

    Whereas polymeric and common inorganic anions frequently deprive the synthetic chemist of a chance to modify a charge transfer salt's structure through anion alterations, discrete organometallic anions provide a vast opportunity to probe the structure/property correlations of a material through rational synthetic methods. We have recently undertaken a research effort aimed at the crystallization of conducting charge transfer salts which possess modifiable, organometallic anions as the charge compensating entities. This research has been richly rewarded with the discovery of a new family of bis(ethylenedithio) tetrathiafulvalene (BEDT-TTF or ET) based molecular superconductors. Herein is presented a summary of over twenty {kappa}(ET){sub 2}M(CF{sub 3}){sub 4}(1,1,2-trihaloethane) (M = Cu, Ag, Au) superconducting salts. Three new related salts are also reported: (ET){sub 2} [trans-Ag(CF{sub 3}),(CN){sub 2}], {kappa}{sub L}(BEDT-TSF){sub 2}Ag(CF{sub 3}){sub 4}(TCE), and {kappa}{sub L}(ET){sub 2}Ag(CF{sub 3}){sub 3}Cl(TCE).

  9. Spin-zero anomaly in the magnetic quantum oscillations of a two-dimensional metal.

    SciTech Connect

    Wosnitza, J.; Gvozdikov, V. M.; Hagel, J.; Meeson, P. J.; Schlueter, J. A.; Ignatchick, O.; Winter, R. W.; Gard, G. L.; Davis, H.; Bergk, B.; Materials Science Division; Technische Univ. Dresden; Max-Planck Inst. Phys. Complex Systems; Univ. Bristol; Portland State Univ.

    2008-01-01

    We report on an anomalous behavior of the spin-splitting zeros in the de Haas-van Alphen (dHvA) signal of a quasi-two-dimensional organic superconductor. The zeros as well as the angular dependence of the amplitude of the second harmonic deviate remarkably from the standard Lifshitz-Kosevich (LK) prediction. In contrast, the angular dependence of the fundamental dHvA amplitude as well as the spin-splitting zeros of the Shubnikov-de Haas (SdH) signal follow the LK theory. We can explain this behavior of the dHvA signal by small chemical-potential (CP) oscillations and find a very good agreement between theory and experiment. A detailed wave-shape analysis of the dHvA oscillations corroborates the existence of an oscillating CP. We discuss the absence of the above spin-zero effect in the SdH signal and argue that in {beta}{double_prime}-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} it can be explained by an incoherent variable range hopping interlayer transport which is insensitive to the small CP oscillations.

  10. An organic thyristor.

    PubMed

    Sawano, F; Terasaki, I; Mori, H; Mori, T; Watanabe, M; Ikeda, N; Nogami, Y; Noda, Y

    2005-09-22

    Thyristors are a class of nonlinear electronic device that exhibit bistable resistance--that is, they can be switched between two different conductance states. Thyristors are widely used as inverters (direct to alternating current converters) and for the smooth control of power in a variety of applications such as motors and refrigerators. Materials and structures that exhibit nonlinear resistance of this sort are not only useful for practical applications: they also provide systems for exploring fundamental aspects of solid-state and statistical physics. Here we report the discovery of a giant nonlinear resistance effect in the conducting organic salt theta-(BEDT-TTF)2CsCo(SCN)4, the voltage-current characteristics of which are essentially the same as those of a conventional thyristor. This intrinsic organic thyristor works as an inverter, generating an alternating current when a static direct-current voltage is applied. Whereas conventional thyristors consist of a series of diodes (their nonlinearity comes from interface effects at the p-n junctions), the present salt exhibits giant nonlinear resistance as a bulk phenomenon. We attribute the origin of this effect to the current-induced melting of insulating charge-order domains, an intrinsically non-equilibrium phenomenon in the sense that ordered domains are melted by a steady flow. PMID:16177784

  11. Novel Quantum Criticality in Two Dimensional Topological Phase transitions

    PubMed Central

    Cho, Gil Young; Moon, Eun-Gook

    2016-01-01

    Topological quantum phase transitions intrinsically intertwine self-similarity and topology of many-electron wave-functions, and divining them is one of the most significant ways to advance understanding in condensed matter physics. Our focus is to investigate an unconventional class of the transitions between insulators and Dirac semimetals whose description is beyond conventional pseudo relativistic Dirac Hamiltonian. At the transition without the long-range Coulomb interaction, the electronic energy dispersion along one direction behaves like a relativistic particle, linear in momentum, but along the other direction it behaves like a non-relativistic particle, quadratic in momentum. Various physical systems ranging from TiO2-VO2 heterostructure to organic material α-(BEDT-TTF)2I3 under pressure have been proposed to have such anisotropic dispersion relation. Here, we discover a novel quantum criticality at the phase transition by incorporating the long range Coulomb interaction. Unique interplay between the Coulomb interaction and electronic critical modes enforces not only the anisotropic renormalization of the Coulomb interaction but also marginally modified electronic excitation. In connection with experiments, we investigate several striking effects in physical observables of our novel criticality. PMID:26791803

  12. Importance of C-H-donor and C-H-anion contact interactions for the crystal packing, the lattice softness and the superconducting transition temperatures of organic conducting salts

    SciTech Connect

    Whangbo, M.-H.; Novoa, J.J.; Jung, D. . Dept. of Chemistry); Williams, J.M.; Kinj, A.M.; Wang, H.H.; Geiser, U.; Beno, M.A.; Carlson, K.D. )

    1990-01-01

    The organic donor molecule BEDT-TTF and its analogs 2--4 have yielded a number of ambient-pressure superconducting salts. What structural and electronic factors govern the magnitudes of their superconducting transition temperature {Tc} has been a topic of intense studies. Examination of the band electronic structures of closely related superconducting salts shows, that the magnitudes of their {Tc}'s are primarily determined by the softness of their crystal lattices. The crystal packing and the lattice softness of organic donor salts are strongly influenced by the donor{hor ellipsis}donor and donor{hor ellipsis}anion contact interactions involving the donor-molecule C-H bonds. In the present work, we briefly review the electronic structures of some representative organic salt superconductors and discuss the softness of their crytsal lattices on the basis of the interaction energies calculated for the C-H{hor ellipsis}donor and C-H{hor ellipsis}anion contact interactions. 34 refs., 14 figs., 8 tabs.

  13. Proceedings of the 9th International Symposium on Foundations of Quantum Mechanics in the Light of New Technology

    NASA Astrophysics Data System (ADS)

    Ishioka, Sachio; Fujikawa, Kazuo

    2009-06-01

    phenomena. Dynamical magnetoelectric effects in multiferroics / Y. Tokura. Exchange-stabilization of spin accumulation in the two-dimensional electron gas with Rashba-type of spin-orbit interaction / H. M. Saarikoski, G. E. W. Bauer. Electronic Aharonov-Casher effect in InGaAs ring arrays / J. Nitta, M. Kohda, T. Bergsten. Microscopic theory of current-spin interaction in ferromagnets / H. Kohno ... [et al.]. Spin-polarized carrier injection effect in ferromagnetic semiconductor / diffusive semiconductor / superconductor junctions / H. Takayanagi ... [et al.]. Low voltage control of ferromagnetism in a semiconductor P-N junction / J. Wunderlich ... [et al.].Measurement of nanosecond-scale spin-transfer torque magnetization switching / K. Ito ... [et al.]. Current-induced domain wall creep in magnetic wires / J. Ieda, S. Maekawa, S. E. Barnes. Pure spin current injection into superconducting niobium wire / K. Ohnishi, T. Kimura, Y. Otani. Switching of a single atomic spin induced by spin injection: a model calculation / S. Kokado, K. Harigaya, A. Sakuma. Spin transfer torque in magnetic tunnel junctions with synthetic ferrimagnetic layers / M. Ichimura ... [et al.]. Gapless chirality excitations in one-dimensional spin-1/2 frustrated magnets / S. Furukawa ... [et al.] -- Dirac fermions in condensed matter. Electronic states of graphene and its multi-layers / T. Ando, M. Koshino. Inter-layer magnetoresistance in multilayer massless dirac fermions system [symbol]-(BEDT-TTF)[symbol]I[symbol] / N. Tajima ... [et al.]. Theory on electronic properties of gapless states in molecular solids [symbol]-(BEDT-TTF)[symbol]I[symbol] / A. Kobayashi, Y. Suzumura, H. Fukuyama. Hall effect and diamagnetism of bismuth / Y. Fuseya, M. Ogata, H. Fukuyama. Quantum Nernst effect in a bismuth single crystal / M. Matsuo ... [et al.] -- Quantum dot systems. Kondo effect and superconductivity in single InAs quantum dots contacted with superconducting leads / S. Tarucha ... [et al.]. Electron transport

  14. Systematic analytical and numerical studies of highly correlated electron systems

    NASA Astrophysics Data System (ADS)

    Tsai, Shan-Wen

    Strong electron correlations in condensed matter systems give rise to a wide range of striking physical properties, producing phenomena as varied as high temperature superconductivity, metal-insulator transitions and the integer and fractional quantum Hall effects. Quantum critical systems also exhibit strong correlations between a large number of degrees of freedom. In this thesis we study these complicated systems using a combination of analytical and numerical approaches. We perform systematic investigations, which adds to the robustness of our results. We develop a new method, based on the density-matrix renormalization-group (DMRG) algorithm combined with finite-size scaling analysis, to study critical behavior in quantum spin chains and extract critical exponents. Accurate results are obtained for spin-1/2 antiferromagnetic chains and the spin-1 chain at the critical point separating the Haldane and the dimerized phases. Disorder in a system can change its properties drastically. Plateau transitions in the integer quantum Hall effect provide the clearest example of quantum critical behavior in a disordered system. We provide analytical proof that the Chalker-Coddington model, which is used to describe the plateau transitions, is quantum critical. Starting from a field theory based on this model, equivalent to a non-Hermitian supersymmetric spin chain, we prove quantum criticality by a Lieb-Schultz-Mattis type theorem. This approach was motivated by numerical results obtained using the DMRG/finite-size scaling method. Our generalized LSM theorem also applies to the spin quantum Hall effect, which can appear in disordered d-wave superconductors with broken time-reversal symmetry. The last part of the thesis is a renormalization-group study of two dimensional interacting electron systems. We obtain results relevant to high-temperature superconductors and also to the family of kappa - (BEDT - TTF)2X organic superconductors. At half filling, the fully nested

  15. Soft x-ray emission and absorption studies of semiconductors and organic molecular solids

    NASA Astrophysics Data System (ADS)

    Stagarescu, Cristian B.

    A combination of soft x-ray absorption (SXA) and soft x-ray emission (SXE) spectroscopy with tunable synchrotron radiation was developed and used to study the bulk electronic structure of semiconductors and organic superconductors. Soft x-ray emission measures the chemically and orbitally resolved partial density of occupied electronic states (PDOS) while in absorption the partial density of unoccupied states is measured. Due to their high technological relevance, there has been a renewed interest in the electronic properties of the wide band-gap nitride semiconductors GaN, AlN, InN and their alloys. The valence- and conduction-band partial densities of states of GaN and AlN were measured and found in good agreement with theoretical results. In the AlxGa1-xN (0 ≤ x ≤ 1) alloy system, N 2p → 1s emission measurements allowed the motion of the elementally resolved bulk valence-band maximum to be monitored as a function of the Al content. In the same system, conclusive experimental evidence for the presence of N 2p-Ga 3d hybridized states was provided by the evolution of a N 2p emission feature situated below the bottom of the valence-band. with the Ga content. In the related oxide semiconductor CdO, the existence of O 2p-Cd 4d hybridized states was verified and their energy position was measured by recording emission from O 2 p states. The issue of identifying contributions of non-equivalent chemical sites to the electronic structure of a complex, organic solid was approached using a combination of SXA and SXE with tunable excitation energy. Two organic superconductors based on the bis-ethylenedithio-tetrathiafulvalene (BEDT-TTF, or ET) molecule, kappa-ET 2Cu[N(CN)2]Br and kappa-ET2Cu(SCN)2 were investigated. The bulk C 2p occupied and unoccupied PDOS of kappa-ET2Cu[N(CN)2]Br and kappa-ET 2Cu(SCN)2 were measured and found to be quite similar, reflecting mostly contributions from the common conductive ET layers. Dependence of the C 2p → 1s emission spectra on

  16. PREFACE: Superconducting materials Superconducting materials

    NASA Astrophysics Data System (ADS)

    Charfi Kaddour, Samia; Singleton, John; Haddad, Sonia

    2011-11-01

    and by invited authors selected by the editor. We are grateful to IUPAP, ICTP and the European Office of Aerospace Research and Development, Air Force Office of Scientific Research, United States Air Force Laboratory. We would like to acknowledge the authors for their careful work, and finally we thank Dr L Smith the publisher of Journal of Physics: Condensed Matter for her patience and help. Superconducting materials contents Raman spectrum in the pseudogap phase of the underdoped cuprates: effect of phase coherence and the signature of the KT-type superconducting transitionTao Li and Haijun Liao Pressure effects on Dirac fermions in α-(BEDT-TTF)2I3Takahiro Himura, Takao Morinari and Takami Tohyama Effect of Zn doping in hole-type 1111 phase (Pr, Sr)FeAsOXiao Lin, Chenyi Shen, Chen Lv, Jianjian Miao, Hao Tan, Guanghan Cao and Zhu-An Xu Superconductivity and ferromagnetism in EuFe2(As1 - xPx)2*Guanghan Cao, Shenggao Xu, Zhi Ren, Shuai Jiang, Chunmu Feng and Zhu'an Xu OInhomogeneous superconductivity in organic conductors: the role of disorder and magnetic fieldS Haddad, S Charfi-Kaddour and J-P Pouget

  17. Proceedings of the 9th International Symposium on Foundations of Quantum Mechanics in the Light of New Technology

    NASA Astrophysics Data System (ADS)

    Ishioka, Sachio; Fujikawa, Kazuo

    2009-06-01

    phenomena. Dynamical magnetoelectric effects in multiferroics / Y. Tokura. Exchange-stabilization of spin accumulation in the two-dimensional electron gas with Rashba-type of spin-orbit interaction / H. M. Saarikoski, G. E. W. Bauer. Electronic Aharonov-Casher effect in InGaAs ring arrays / J. Nitta, M. Kohda, T. Bergsten. Microscopic theory of current-spin interaction in ferromagnets / H. Kohno ... [et al.]. Spin-polarized carrier injection effect in ferromagnetic semiconductor / diffusive semiconductor / superconductor junctions / H. Takayanagi ... [et al.]. Low voltage control of ferromagnetism in a semiconductor P-N junction / J. Wunderlich ... [et al.].Measurement of nanosecond-scale spin-transfer torque magnetization switching / K. Ito ... [et al.]. Current-induced domain wall creep in magnetic wires / J. Ieda, S. Maekawa, S. E. Barnes. Pure spin current injection into superconducting niobium wire / K. Ohnishi, T. Kimura, Y. Otani. Switching of a single atomic spin induced by spin injection: a model calculation / S. Kokado, K. Harigaya, A. Sakuma. Spin transfer torque in magnetic tunnel junctions with synthetic ferrimagnetic layers / M. Ichimura ... [et al.]. Gapless chirality excitations in one-dimensional spin-1/2 frustrated magnets / S. Furukawa ... [et al.] -- Dirac fermions in condensed matter. Electronic states of graphene and its multi-layers / T. Ando, M. Koshino. Inter-layer magnetoresistance in multilayer massless dirac fermions system [symbol]-(BEDT-TTF)[symbol]I[symbol] / N. Tajima ... [et al.]. Theory on electronic properties of gapless states in molecular solids [symbol]-(BEDT-TTF)[symbol]I[symbol] / A. Kobayashi, Y. Suzumura, H. Fukuyama. Hall effect and diamagnetism of bismuth / Y. Fuseya, M. Ogata, H. Fukuyama. Quantum Nernst effect in a bismuth single crystal / M. Matsuo ... [et al.] -- Quantum dot systems. Kondo effect and superconductivity in single InAs quantum dots contacted with superconducting leads / S. Tarucha ... [et al.]. Electron transport

  18. Preface

    NASA Astrophysics Data System (ADS)

    Batail, Patrick

    2004-04-01

    with p _π-p_π overlap interactions between frontier orbitals of the precursors is today a very active field of research reaching out in field of molecular magnetic materials. Also, the materials chemistry of single component molecular metals and the development of strategies for the chemical control of band filling in molecular metals are areas of intense research. Considerable progress reported in first principle-based electronic structure calculations for large complex systems and band structure calculations of molecular metals should diffuse promptly in the molecular materials community. On the physics side, recent advances in understanding the localization-delocalization-charge ordering competition in low dimensional systems of strongly correlated electrons, and their formulation at ISCOM'03 in a language and format accessible to experimentalists and materials scientists, carries a great many promises for significant developments in the conception of novel molecular superconductors. The physics of one- and two-dimensional molecular metals and superconductors was a strong component of ISCOM'03 with very diverse complementary experimental approaches including transport, uniaxial and isotropie high pressures and high magnetic fields studies, thermal conductivity, STM. Two dimensional conductors have proved to be prototype materials for the study of interacting electron gases through the phenomenon of Mott localization exhibited in some BEDT-TTF salts. Applications of angle-resolved photo-emission investigations have been reported and emerge as a very promising area for future developments. Coupled to quantum chemistry calculations the latter carry along an enormous potential, as exemplified by the wealth of information delivered on the nature of the chemical bonding and electronic structure of molecular solids. The reports of superconductivity induced by a large magnetic field in RETS salts containing magnetic anions have shown how organic materials have brought the