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Sample records for bedt-ttf

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

    NASA Astrophysics Data System (ADS)

    Graja, Andrzej; Olejniczak, Iwona; Barszcz, Bolesław; Schlueter, John

    2009-12-01

    Infrared and Raman investigations of two phases of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) based organic conductors with the same CF3CF2SO3- anion: β'-(BEDT-TTF)2CF3CF2SO3 and δ'-(BEDT-TTF)2CF3CF2SO3, are shortly reviewed and compared with the most typical infrared properties of the family of (BEDT-TTF)2RR'SO3 organic conductors, where R = SF5, CF3, and R' are CH2, CF2, CHF, CHFCF2, and CH2CF2. The role of the molecular structur and spatial organization of the counterions is discussed.

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

    NASA Astrophysics Data System (ADS)

    Graja, Andrzej; Olejniczak, Iwona; Barszcz, Bolesław; Schlueter, John A.

    2009-12-01

    Infrared and Raman investigations of two phases of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) based organic conductors with the same CF3CF2SO{3/-} anion: β'-(BEDT-TTF)2CF3CF2SO3 and δ'-(BEDT-TTF)2CF3CF2SO3, are shortly reviewed and compared with the most typical infrared properties of the family of (BEDT-TTF)2RR'SO3 organic conductors, where R = SF5, CF3, and R' are CH2, CF2, CHF, CHFCF2, and CH2CF2. The role of the molecular structur and spatial organization of the counterions is discussed.

  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. Facile synthesis of novel functionalized bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) derivatives.

    PubMed

    Liu, Shi-Xia; Dolder, Stefan; Pilkington, Melanie; Decurtins, Silvio

    2002-05-03

    An improved and efficient synthetic route to four functionalized bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) derivatives 2-5 is reported. Tetrathiolate 1 was readily prepared from 2,2'-bis(1,3,4,6-tetrathiapentalen-5-one) under carefully controlled conditions. Subsequent reaction of 1 with selected primary alkyl halides affords new functionalized BEDT-TTF derivatives in good yields.

  5. Electron phonon interaction in the organic superconductors αt-(BEDT-TTF) 2I 3 and β-(BEDT-TTF) 2IAuI

    NASA Astrophysics Data System (ADS)

    Ludwig, T.; Schweitzer, D.; Keller, H. J.

    1995-12-01

    A study of the low energetic modes in the resonance Raman spectra of the organic superconductors αt-(BEDT-TTF) 2I 3 (T c=8 K) and β-(BEDT-TTF) 2IAuI (T c=4 K) in the temperature range of 1.5 K-100 K was performed. In both materials, a vanishing of low energetic phonon bands (at 32 cm -1 and 42 cm -1 for αt-(BEDT-TTF) 2I 3 and at 27 cm -1 and 33 cm -1 for β-(BEDT-TTF) 2IAuI) is observed below T c. For the symmetric stretching mode of the I 3-Anions at 120 cm -1, no change below T c was found. The vanishing of the phonon bands is explained in the Balseiro-Falicov model of phonon-superconducting amplitude mode interaction due to a strong interaction of the superconducting gap and some phonon modes. In addition, measurements on α- and κ-(BEDT-TTF) 2I 3 are presented, indicating that the vanishing modes around 30 cm -1 are librational modes of the BEDT-TTF molecules.

  6. 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.

  7. Structural and electronic properties of α -(BEDT-TTF)2I3 , β -(BEDT-TTF)2I3 , and κ -(BEDT-TTF)2X3 (X = I, F, Br, Cl) organic charge transfer salts

    NASA Astrophysics Data System (ADS)

    Commeau, Benjamin; Geilhufe, R. Matthias; Fernando, Gayanath W.; Balatsky, Alexander V.

    2017-09-01

    (BEDT-TFF ) 2I3 charge transfer salts are reported to show superconductivity and pressure-induced quasi-two-dimensional Dirac cones at the Fermi level. By performing state of the art ab initio calculations in the framework of density functional theory, we investigate the structural and electronic properties of the three structural phases α , β , and κ . We furthermore report about the irreducible representations of the corresponding electronic band structures, symmetry of their crystal structure, and the origin of band crossings. Additionally, we discuss the chemically induced strain in κ -(BEDT-TTF ) 2I3 achieved by replacing the iodine layer with other halogens: fluorine, bromine, and chlorine. In the case of κ -(BEDT-TTF ) 2F3 , we identify topologically protected crossings within the band structure. These crossings are forced to occur due to the nonsymmorphic nature of the crystal. The calculated electronic structures presented here are added to the organic materials database (OMDB).

  8. Optical Properties of a Quantum Spin Liquid Candidate Material, κ-(BEDT-TTF)2Ag2(CN)3

    NASA Astrophysics Data System (ADS)

    Nakamura, Yuto; Hiramatsu, Takaaki; Yoshida, Yukihiro; Saito, Gunzi; Kishida, Hideo

    2017-01-01

    We investigated the electronic states of a quantum spin liquid candidate material, κ-(BEDT-TTF)2Ag2(CN)3, using optical methods. In reflectivity measurements, we observed the polarization dependence of electronic transitions, which reflects the crystal structure and anisotropic charge excitation. Raman scattering measurements revealed that the broad magnetic excitation mode is located below 600 cm-1. This spectral feature indicates the spin-liquid nature of the candidate material. The charge-sensitive molecular-vibrational modes observed in infrared and Raman spectra are broader than those of typical BEDT-TTF compounds, which indicate a possibility of dynamic charge fluctuation. By comparing the optical spectra of κ-(BEDT-TTF)2Ag2(CN)3 with a well-investigated spin-liquid candidate κ-(BEDT-TTF)2Cu2(CN)3, we found common optical properties of BEDT-TTF-based spin-liquid candidates. The dynamic fluctuations of charge on a BEDT-TTF dimer are independent of the arrangement of BEDT-TTF molecules and anion layers.

  9. Electron-phonon effects in the organic superconductor κ-(BEDT-TTF) 2Cu[N(CN) 2]Br

    NASA Astrophysics Data System (ADS)

    Eldridge, J. E.; Xie, Y.; Wang, Hau H.; Williams, Jack M.; Kini, A. M.; Schlueter, J. A.

    1996-01-01

    We report on room-temperature Raman measurements on κ-di[bis-ethylenedithiotetrathiafulvalene] copper dicyanamide bromide (κ-(BEDT-TTF) 2Cu[N(CN) 2]Br) and the isotopic analog 13C(6)-(BEDT-TTF) 2Cu[N(CN) 2]Br, in which the six central carbon atoms in the inner rings of the BEDT-TTF molecule are replaced with 13C, and assign the features to the symmetric intramolecular modes of vibration, by comparison with a recently published study on neutral BEDT-TTF. We then used these data to help us make a more definitive assignment that has been previously possible of the features in the low-temperature IR conductivity spectra of (BEDT-TTF) 2Cu[N(CN) 2]Br. It was also necessary to measure the low-temperature IR conductivity of additional isotopic analogs of BEDT-TTF, namely those containing 13C(6), 13C(2), 34S(8) and d(8). We found, as expected, that the spectra are dominated by the electron-phonon activated totally symmetric (A g) modes, but also that the nature of the strongest of these, ν3(A g), is changed dramatically in (BEDT-TTF) 2Cu[N(CN) 2]Br from what it is in neutral BEDT-TTF. We also found, unexpectedly, that one of the stronger IR features is most likely due to an activated non-totally-symmetric (B 3g) mode, instead of a normally IR-active mode, which had been previously assigned, and further that several other (B 3g) modes appear to be activated in the IR spectra.

  10. Ferroelectric properties of charge-ordered α -(BEDT-TTF ) 2I3

    NASA Astrophysics Data System (ADS)

    Lunkenheimer, P.; Hartmann, B.; Lang, M.; Müller, J.; Schweitzer, D.; Krohns, S.; Loidl, A.

    2015-06-01

    A detailed investigation of the out-of-plane electrical properties of charge-ordered α -(BEDT-TTF ) 2I3 provides clear evidence for ferroelectricity. Similar to multiferroic κ -(BEDT-TTF ) 2Cu[N (CN ) 2]Cl , the polar order in this material is ascribed to the occurrence of bond- and site-centered charge order. Dielectric response typical for relaxor ferroelectricity is found deep in the charge-ordered state. We suggest an explanation in terms of the existence of polar and nonpolar stacks of the organic molecules in this material, preventing long-range ferroelectricity. The results are discussed in relation to the formation or absence of electronic polar order in related charge-transfer salts.

  11. 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.

  12. Isotope effect in the organic superconductor β_H-(BEDT-TTF)2I3 where BEDT-TTF is bis (ethylenedithiotetrathiafulvalene)

    NASA Astrophysics Data System (ADS)

    Auban-Senzier, P.; Bourbonnais, C.; Jérome, D.; Lenoir, C.; Batail, P.; Canadell, E.; Buisson, J. P.; Lefrant, S.

    1993-03-01

    We have performed the simultaneous investigation of the isotope effect on the superconducting transition and on the Raman spectra in the organic superconductor β_H-(BEDT-TTF)2I3 (T_c = 8 K). For this purpose, we substitute ^{13}C for ^{12}C on the carbon sites of the central double bond of BEDT-TTF molecule. The isotope shifts measured by Raman experiments can be fairly well explained by standard molecular dynamics. However, the critical temperature is lowered by 0.2 K in the ^{13}C enriched material. We analyse the possible sources of this remarkable downward shift which leads to an isotope coefficient higher than the BCS value. The extended-Hückel calculations of the density of states for the two HOMO bands of β_H-(BEDT-TTF)2I3 do show that, within the framework of a weak coupling theory, its sizeable variation on the scale of ω_D cannot account for the observed isotope effect. On the other hand, we discuss how inelastic electronic scattering observed in resistivity measurements just above T_c can lead through a pair breaking mechanism to a sizeable increase of the isotope coefficient. Nous présentons une étude simultanée d'effet isotopique sur la transition supraconductrice et les spectres Raman dans le supraconducteur organique β_H-(BEDT-TTF)2I3 (T_c = 8 K). Pour cela, nous avons synthétisé le composé dans lequel les atomes de carbone de la double liaison centrale de la molécule BEDT-TTF sont substitués par l'isotope ^{13}C. Les déplacements isotopiques mesurés par spectroscopie Raman sont bien expliqués par la dynamique moléculaire standard. Cependant, la température critique est abaissée de 0.2 K dans le matériau enrichi en ^{13}C. Nous étudions les origines possibles de cet effet qui permet d'obtenir un coefficient isotopique supérieur à la valeur BCS. Des calculs de la densité d'états effectués par la méthode de Hückel étendue pour les deux bandes HOMO du composé montrent que, dans le cadre d'une théorie de couplage faible

  13. Metal-insulator transition in the dimerized organic conductor κ -(BEDT-TTF)2Hg (SCN )2Br

    NASA Astrophysics Data System (ADS)

    Ivek, Tomislav; Beyer, Rebecca; Badalov, Sabuhi; Čulo, Matija; Tomić, Silvia; Schlueter, John A.; Zhilyaeva, Elena I.; Lyubovskaya, Rimma N.; Dressel, Martin

    2017-08-01

    The organic charge-transfer salt κ -(BEDT-TTF)2Hg (SCN )2Br is a quasi-two-dimensional metal with a half-filled conduction band at ambient conditions. When cooled below T =80 K , it undergoes a pronounced transition to an insulating phase where the resistivity increases many orders of magnitude. In order to elucidate the nature of this metal-insulator transition, we have performed comprehensive transport, dielectric and optical investigations. The findings are compared with other dimerized κ -(BEDT-TTF) salts, in particular the Cl analog, where a charge-order transition takes place at TCO=30 K .

  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.

  15. Investigation of the superconducting gap structure in κ-(BEDT-TTF)2Cu(NCS)2 and κ-(BEDT-TTF)2Cu[N(CN)2]Br by means of thermal-conductivity measurements

    NASA Astrophysics Data System (ADS)

    Kühlmorgen, S.; Schönemann, R.; Green, E. L.; Müller, J.; Wosnitza, J.

    2017-10-01

    We report temperature-dependent thermal-conductivity, κ, measurements on the layered quasi-two-dimensional organic superconductors κ-(BEDT-TTF)2Cu(NCS)2 and κ-(BEDT-TTF)2Cu[N(CN)2]Br down to 160 mK. The results for κ-(BEDT-TTF)2Cu(NCS)2 may be consistent with a nodal superconducting (SC) gap structure as indicated by a non-negligible remnant linear contribution when κ/T \\propto T2 is extrapolated to T = 0 . For κ-(BEDT-TTF)2Cu[N(CN)2]Br, contrary to expectations, higher κ values are observed in the superconducting regime as compared to the normal, high-field state evidencing a dominant phonon contribution to κ in the superconducting state. The strong increase of κ in the normal state below T c for both samples indicates strong electron–phonon scattering. Our results highlight the need for thermal-conductivity measurements performed down to significantly lower temperatures to determine the symmetry of the SC gap.

  16. Organic superconductors revisited. STM imaging and DFT based simulations of the bc plane of κ-(BEDT-TTF)2Cu(NCS)2

    NASA Astrophysics Data System (ADS)

    Rohr, C.; Büttner, J. M.; Palitschka, F. A.; Kushch, N. D.; Kartsovnik, M. V.; Biberacher, W.; Gross, R.; Hermann, B. A.

    2009-05-01

    The surfaces of a ten years aged crystal and a freshly prepared κ-(BEDT-TTF)2Cu(NCS)2 crystal were compared by scanning tunneling microscopy (STM). The molecularly-resolved STM images of the bc plane of the crystals agree with each other and with the electronic contrast obtained by new density functional theory (DFT) based simulations. Even after ten years STM images of the molecular stacking of BEDT-TTF display a variation in brightness at the positions of different molecules. We attribute this symmetry breaking concerning the brightness in the STM images of the otherwise equivalent BEDT-TTF dimers to the electronic states of a relaxed surface.

  17. AC heat capacities of κ-(BEDT-TTF)2Cu2(CN)3 measured by microchip calorimeter

    NASA Astrophysics Data System (ADS)

    Muraoka, Y.; Yamashita, S.; Yamamoto, T.; Nakazawa, Y.

    2011-09-01

    Thermodynamic measurements of an organic spin liquid compound of κ-(BEDT-TTF)2Cu2(CN)3 where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene were performed by the ac calorimetry technique using a microchip device of TCG3880. This technique is effective to measure relative temperature and magnetic-field dependences of heat capacity for tiny single crystal samples less than 1μg. Broad hump structures in Cp vs T which are known as so-called 6 K anomaly were observed in κ-(BEDT-TTF)2Cu2(CN)3 and its deuterated compound. The hump temperatures are evaluated as 5.7 K in both compounds. This result demonstrates that the TCG3880 is useful for performing thermodynamic investigations of such kind of organic charge transfer complexes with much reduced sample quantity than the conventional techniques and that the existence of hump structure is intrinsic for κ-(BEDT-TTF)2Cu2(CN)3. The in-plane angular dependence of the magnetic field of 7 T applied parallel to the two dimensional layer is also studied and absence of in-plane anisotropy of the hump structure is discussed in both pristine and deuterated compounds.

  18. 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.

  19. Phase Competition and Superconductivity in κ-(BEDT-TTF)2X: Importance of Intermolecular Coulomb Interactions

    NASA Astrophysics Data System (ADS)

    Watanabe, Hiroshi; Seo, Hitoshi; Yunoki, Seiji

    2017-03-01

    We theoretically study the competition among different electronic phases in molecular conductors κ-(BEDT-TTF)2X. The ground-state properties of a 3/4-filled extended Hubbard model with the κ-type geometry are investigated by a variational Monte Carlo method. We find various competing phases: dimer-Mott insulator, polar charge-ordered insulator, 3-fold charge-ordered metal, and superconductivity, whose pairing symmetry is an "extended-s + dx2 - y2"-wave type. Our results show that the superconducting phase is stabilized not on the verge of the Mott metal-insulator transition but near charge order instabilities, clearly indicating the importance of the intradimer charge degree of freedom and the intermolecular Coulomb interactions, beyond the simple description of the half-filled Hubbard model.

  20. Electrostatic Charge Carrier Injection into the Charge-Ordered Organic Material α-(BEDT-TTF)2I3

    NASA Astrophysics Data System (ADS)

    Kimata, Motoi; Ishihara, Takuma; Tajima, Hiroyuki

    2012-07-01

    We have fabricated a field effect transistor structure using the charge-ordered (CO) organic material α-(BEDT-TTF)2I3 to investigate the effects of electrostatic carrier injection. We have observed both n-type and bipolar behaviors in the CO state, whereas, previously, only n-type characteristics were reported. The present results indicate that the transfer characteristics for a negative gate voltage, i.e., hole transport characteristics, are highly dependent on the interface conditions between α-(BEDT-TTF)2I3 and the electrodes and/or gate insulator. In addition, the activation energy of the CO state is essentially independent of VSG. This result suggests the robustness of the CO state to electrostatic charge carrier injection.

  1. Nonlocal magnetoresistance measurements of the organic zero-gap conductor α -(BEDT-TTF ) 2I3

    NASA Astrophysics Data System (ADS)

    Kamiya, Takeshi; Kawasugi, Yoshitaka; Ara, Masato; Tada, Hirokazu

    2017-02-01

    We prepared nonlocal spin valves based on single crystals of an organic multilayered zero-gap conductor α -(BEDT-TTF ) 2I3 and succeeded in evaluating the spin-diffusion length (1.1 μm) and relaxation time (3 ns) at 2.5 K under a static pressure of 1.6 GPa using a polyethylene naphthalate as a substrate. Although α -(BEDT-TTF ) 2I3 includes heavy atoms, such as iodine, it exhibited a rather long spin-relaxation time comparable to that of graphene. The spin-orbit interaction (SOI) estimated on the basis of the experimental values of the spin-relaxation time and carrier lifetime (1.2 ps) was 90 mK. The long spin-relaxation time and small SOI evaluated for α -(BEDT-TTF ) 2I3 are considered to originate from its layered structure in which spin scattering induced by surface defects is suppressed. In addition, the inversion asymmetry, which generates an extra term in the equation for the SOI, might be reduced in layered structures. These findings provide guiding principles for materials design in organic spintronics.

  2. Organic Superconductor k-(BEDT-TTF)2Cu[N(CN)2]Br - A Tunable Electronic System across the Mott Transition -

    NASA Astrophysics Data System (ADS)

    Tokumoto, M.; Kinoshita, N.; Tanaka, Y.; Kinoshita, T.; Anzai, H.

    1998-03-01

    k-(BEDT-TTF)2Cu[N(CN)2]Br, is an organic superconductor with the highest Tc of 11.6K at ambient pressure (A. M. Kini et al., Inorg. Chem. 29, 2555 (1990)). We have reported a normal isotope effect,when all the hydrogen atoms of BEDT-TTF are replaced with deuterium, in other words, Tc was depressed by as much as 0.9 K (M. Tokumoto et al., J. Phys. Soc. Jpn. 60, 1426 (1991)), in contrast to the "inverse isotope effect" commonly observed in organic superconductors (K. Oshima, et al., Synth. Metals 27, A473 (1988)) . Recently, it was reported that the deuterated k-(BEDT-TTF)2Cu[N(CN)2]Br is of an insulating nature similar to k-(BEDT-TTF)2Cu[N(CN)2]Cl when cooled rapidly(Y. Nakazawa and K. Kanoda, Phys. Rev. B 53, R8875 (1996)). Here we report on the results of reexamination of the superconducting transition of deuterated k-(BEDT-TTF)2Cu[N(CN)2]Br by SQUID measurements with special attention to the cooling speed ranging from 10K/min to less than 0.01K/min. We observed a significant effect not only on the superconducting transition temperature Tc but also on the superconducting volume fraction.

  3. Experimental study of organic zero-gap conductor α-(BEDT-TTF)2I3.

    PubMed

    Tajima, Naoya; Kajita, Koji

    2009-04-01

    A zero-gap state with a Dirac cone type energy dispersion was discovered in the organic conductor α-(BEDT-TTF)2I3 under high hydrostatic pressures. This is the first two-dimensional (2D) zero-gap state discovered in bulk crystals with a layered structure. In contrast to the case of graphene, the Dirac cone in this system is highly anisotropic. The present system, therefore, provides a new type of massless Dirac fermion system with anisotropic Fermi velocity. This system exhibits remarkable transport phenomena characteristic to electrons on the Dirac cone type energy structure. The carrier density, written as n∝T(2), is a characteristic feature of the 2D zero-gap structure. On the other hand, the resistivity per layer (sheet resistance RS) is given as RS=h/e(2) and is independent of temperature. The effect of a magnetic field on samples in the zero-gap system was examined. The difference between zero-gap conductors and conventional conductors is the appearance of a Landau level called the zero mode at the contact points when a magnetic field is applied normal to the conductive layer. Zero-mode Landau carriers give rise to strong negative out-of-plane magnetoresistance.

  4. Dynamical Reduction of the Dimensionality of Exchange Interactions and the "Spin-Liquid" Phase of κ -(BEDT -TTF )2X

    NASA Astrophysics Data System (ADS)

    Powell, B. J.; Kenny, E. P.; Merino, J.

    2017-08-01

    We show that the anisotropy of the effective spin model for the dimer Mott insulator phase of κ -(BEDT -TTF )2X salts is dramatically different from that of the underlying tight-binding model. Intradimer quantum interference results in a model of coupled spin chains, where frustrated interchain interactions suppress long-range magnetic order. Thus, we argue, the "spin liquid" phase observed in some of these materials is a remnant of the Tomonaga-Luttinger physics of a single chain. This is consistent with previous experiments and resolves some outstanding puzzles.

  5. Quantum oscillations in coupled orbits networks of (BEDT-TTF) salts with tris(oxalato)metallate anions

    NASA Astrophysics Data System (ADS)

    Laukhin, Vladimir N.; Audouard, Alain; Fortin, Jean-Yves; Vignolles, David; Prokhorova, Tatyana G.; Yagubskii, Eduard B.; Canadell, Enric

    2017-01-01

    Band structure calculations relevant to bis-ethylenedithio-tetrathiafulvalene-based charge transfer salts containing tris(oxalato)metallate anions, with generic formula (BEDT-TTF)4A[M(C2O4)3].Solv, where A is a monovalent anion, M is a trivalent cation and Solv is a solvent, suggest that their Fermi surface is liable to achieve networks of compensated orbits coupled by magnetic breakdown. Even though this picture accounts for quantum oscillations spectra of a number of these compounds, puzzling results can be noticed in several cases, pointing to the possibility of Fermi surface reconstruction at low temperature.

  6. Universal inverse deuterium isotope effect on the Tc of BEDT-TTF-based molecular superconductors

    NASA Astrophysics Data System (ADS)

    Schlueter, J. A.; Kini, A. M.; Ward, B. H.; Geiser, U.; Wang, H. H.; Mohtasham, J.; Winter, R. W.; Gard, G. L.

    2001-04-01

    Deuterium substitution of the ethylene end groups of the ET [ET: BEDT-TTF or bis(ethylenedithio)tetrathiafulvalene] electron-donor molecule results in a 0.25 K increase in the superconducting transition temperature of three molecular superconductors derived from this molecule. Simplistically speaking, this change in Tc is in contradiction to that predicted by the electron-phonon coupling mechanism of the BCS theory. We suggest that the slight shortening of the C-D bond relative to the C-H bond, coupled with the recent findings of a large, negative uniaxial pressure derivative of Tc in κ-(ET) 2Cu(SCN) 2 and β ‧‧-(ET) 2SF 5CH 2CF 2SO 3, can explain this unique effect. Herein we report the first study of the effect of deuterium substitution on the superconducting transition temperature in a molecular-based superconductor in which the electron-donor molecules are packed in a β ‧‧ motif, viz., β ‧‧-(ET) 2SF 5CH 2CF 2SO 3. This compound is ideally suited for this study because it contains discrete (non-polymeric) anions, has a completely ordered structure, is indefinitely stable in air at room temperature, and is free from possible magnetic impurities. Substitution of the eight hydrogen atoms of the ET molecule by deuterium causes the Tc of β ‧‧-(ET) 2SF 5CH 2CF 2SO 3 to increase from 4.34±0.05 to 4.61±0.03 K. These values were determined by measuring several representative crystals from various parallel electrocrystallization experiments containing h 8- or d 8-ET that was prepared in parallel syntheses. This is the first example which demonstrates that the inverse (positive) isotope effect previously observed in κ-phase salts is also present in a β ‧‧-phase superconductor.

  7. Quantum criticality in an organic spin-liquid insulator κ-(BEDT-TTF)2Cu2(CN)3

    NASA Astrophysics Data System (ADS)

    Isono, Takayuki; Terashima, Taichi; Miyagawa, Kazuya; Kanoda, Kazushi; Uji, Shinya

    2016-11-01

    A quantum spin-liquid state, an exotic state of matter, appears when strong quantum fluctuations enhanced by competing exchange interactions suppress a magnetically ordered state. Generally, when an ordered state is continuously suppressed to 0 K by an external parameter, a quantum phase transition occurs. It exhibits critical scaling behaviour, characterized only by a few basic properties such as dimensions and symmetry. Here we report the low-temperature magnetic torque measurements in an organic triangular-lattice antiferromagnet, κ-(BEDT-TTF)2Cu2(CN)3, where BEDT-TTF stands for bis(ethylenedithio)tetrathiafulvalene. It is found that the magnetic susceptibilities derived from the torque data exhibit a universal critical scaling, indicating the quantum critical point at zero magnetic field, and the critical exponents, γ=0.83(6) and νz=1.0(1). These exponents greatly constrain the theoretical models for the quantum spin liquid, and at present, there is no theory to explain the values, to the best of our knowledge.

  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. Quantum criticality in an organic spin-liquid insulator κ-(BEDT-TTF)2Cu2(CN)3.

    PubMed

    Isono, Takayuki; Terashima, Taichi; Miyagawa, Kazuya; Kanoda, Kazushi; Uji, Shinya

    2016-11-14

    A quantum spin-liquid state, an exotic state of matter, appears when strong quantum fluctuations enhanced by competing exchange interactions suppress a magnetically ordered state. Generally, when an ordered state is continuously suppressed to 0 K by an external parameter, a quantum phase transition occurs. It exhibits critical scaling behaviour, characterized only by a few basic properties such as dimensions and symmetry. Here we report the low-temperature magnetic torque measurements in an organic triangular-lattice antiferromagnet, κ-(BEDT-TTF)2Cu2(CN)3, where BEDT-TTF stands for bis(ethylenedithio)tetrathiafulvalene. It is found that the magnetic susceptibilities derived from the torque data exhibit a universal critical scaling, indicating the quantum critical point at zero magnetic field, and the critical exponents, γ=0.83(6) and νz=1.0(1). These exponents greatly constrain the theoretical models for the quantum spin liquid, and at present, there is no theory to explain the values, to the best of our knowledge.

  10. Quantum criticality in an organic spin-liquid insulator κ-(BEDT-TTF)2Cu2(CN)3

    PubMed Central

    Isono, Takayuki; Terashima, Taichi; Miyagawa, Kazuya; Kanoda, Kazushi; Uji, Shinya

    2016-01-01

    A quantum spin-liquid state, an exotic state of matter, appears when strong quantum fluctuations enhanced by competing exchange interactions suppress a magnetically ordered state. Generally, when an ordered state is continuously suppressed to 0 K by an external parameter, a quantum phase transition occurs. It exhibits critical scaling behaviour, characterized only by a few basic properties such as dimensions and symmetry. Here we report the low-temperature magnetic torque measurements in an organic triangular-lattice antiferromagnet, κ-(BEDT-TTF)2Cu2(CN)3, where BEDT-TTF stands for bis(ethylenedithio)tetrathiafulvalene. It is found that the magnetic susceptibilities derived from the torque data exhibit a universal critical scaling, indicating the quantum critical point at zero magnetic field, and the critical exponents, γ=0.83(6) and νz=1.0(1). These exponents greatly constrain the theoretical models for the quantum spin liquid, and at present, there is no theory to explain the values, to the best of our knowledge. PMID:27841262

  11. Tetraalkyl- and dialkyl-substituted BEDT-TTF derivatives and their cation-radical salts : synthesis, structure, and properties.

    SciTech Connect

    Kini, A. M.; Parakka, J. P.; Geiser, U.; Wang, H.-H.; Rivas, F.; DiNino, E.; Thomas, S.; Dudek, J. D.; Williams, J. M.

    1999-01-01

    Tetraalkyl and dialkyl derivatives, where alkyl=ethyl and propyl, of the organic electron donor molecule bis(ethylenedithio)tetrathiafulvalene, BEDT-TTF or ET, have been synthesized via the Diels-Alder approach. Several cation-radical salts of these new donors have been prepared and structurally characterized, and found to contain donor molecules in nominally higher oxidation states (+1, +1.5 and +2) than the typically observed oxidation state of +0.5 in BEDT-TTF salts. The higher solubility of the tetraalkyl and dialkyl derivatives in solvents used for crystal growth is proposed as the principal reason for this finding. Surprisingly, X-ray crystallographic studies reveal that the alkyl groups in the neutral tetraethyl-ET as well as the oxidized tetraethyl-ET and diethyl-ET molecules in their cation-radical salts adopt axial configurations, rather than the expected equatorial configurations. Electrical properties of the cation-radical salts have been found to be either insulating or semiconducting, consistent with the higher oxidation states of the donor molecules in the salts and the crystal structures.

  12. Effect of Interband Fluctuation on Spin Susceptibility in Molecular Dirac Fermion System α-(BEDT-TTF)2I3

    NASA Astrophysics Data System (ADS)

    Matsuno, Genki; Kobayashi, Akito

    2017-01-01

    The nontrivial properties of interband spin fluctuations are studied by the random phase approximation in a Hubbard model describing the molecular conductor α-(BEDT-TTF)2I3, where wave functions are based on the four sublattices named A, A', B, and C in a two-dimensional BEDT-TTF molecular plane. It is found that the ferrimagnetic polarization observed by a recent NMR measurement emerges only if there exist cross terms among intra- and inter-band irreducible susceptibility matrix elements in the presence of the on-site Coulomb interaction U. It is also found that the nontrivial sign of the interband components of the spin susceptibility, being negative only for the B sublattice, is closely related to the characteristic phase structure of wave functions in the Dirac fermion system with multisublattices. The negative value of the spin susceptibility on the B sublattice observed in the experiment is associated with this negative interband susceptibility, which comes from the excitations in the gentle-slope region of the energy dispersion connecting the Dirac points with saddle points in the first Brillouin zone.

  13. Convenient synthesis of bis(benzo)-fused BEDT-TTF and higher homologues: new electron donor molecules for organic charge transfer salts and `molecular rulers`

    SciTech Connect

    Parakka, J.P.; Kini, A.M.; Williams, J.M.

    1996-10-01

    A convenient synthesis of bis(benzo)- and bis(naphtho)-fused bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) derivatives, employing the [4+2] cycloaddition reaction of oligo(1,3-dithiole-2,4, 5-trithione) with appropriate alkenes as a key step, is presented.

  14. LETTER TO THE EDITOR: Infrared studies of the organic superconductor κ-(BEDT- TTF)2Cu(SCN)2 under pressure

    NASA Astrophysics Data System (ADS)

    Klehe, A.-K.; McDonald, R. D.; Goncharov, A. F.; Struzhkin, V. V.; Mao, Ho-kwang; Hemley, R. J.; Sasaki, T.; Hayes, W.; Singleton, J.

    2000-04-01

    The organic superconductor icons/Journals/Common/kappa" ALT="kappa" ALIGN="TOP"/> -(BEDT-TTF)2 Cu(SCN)2 has been investigated at room temperature by polarized mid-infrared (600-7000 cm-1 ) reflectivity measurements at pressures of up to 1.7 GPa. The optical effective mass, m opt , decreases linearly with pressure, in contrast to the pressure dependence of the effective mass, m * , determined by magnetic quantum oscillation measurements (Caulfield J et al 1994 J. Phys.: Condens. Matter 6 2911-24; Caulfield J et al 1995 Synth. Met. 70 815-8). Most phonon modes are seen to exhibit a linear pressure dependence of 0.5-1% / GPa. The stronger pressure dependence of the central C = C mode of the BEDT-TTF molecule is discussed: it is thought to be due to the pressure dependence of the effective Coulomb repulsion in icons/Journals/Common/kappa" ALT="kappa" ALIGN="TOP"/> -(BEDT-TTF)2 Cu(SCN)2 . These measurements suggest that a change in the electron-electron interaction under pressure could be the relevant factor for the suppression of superconductivity under pressure in icons/Journals/Common/kappa" ALT="kappa" ALIGN="TOP"/> -(BEDT-TTF)2 Cu(SCN)2 .

  15. The metal-insulator transition in the organic conductor β″-(BEDT-TTF)2Hg(SCN)2Cl

    NASA Astrophysics Data System (ADS)

    Li, Weiwu; Rose, Eva; Tran, Minh Vu; Hübner, Ralph; Łapiński, Andrzej; Świetlik, Roman; Torunova, Svetlana A.; Zhilyaeva, Elena I.; Lyubovskaya, Rimma N.; Dressel, Martin

    2017-08-01

    We explore the nature of the metal-insulator transition in the two-dimensional organic compound β″-(BEDT-TTF)2Hg(SCN)2Cl by x-ray, electrical transport, ESR, Raman, and infrared investigations. Magnetic and vibrational spectroscopy concurrently reveal a gradual dimerization along the stacking direction (a -b ) , setting in already at the crossover temperature of 150 K from the metallic to the insulating state. A spin gap of Δσ=47 meV is extracted. From the activated resistivity behavior below T = 55 K, a charge gap of Δρ=60 meV is derived. At TCO = 72 K, the C=C vibrational modes reveal the development of a charge-ordered state with a charge disproportionation of 2 δρ=0.34 e . In addition to a slight structural dimerization, charge-order causes stripes most likely perpendicular to the stacks.

  16. 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.

  17. Anion effects on electronic structure and electrodynamic properties of the Mott insulator κ -(BEDT-TTF ) 2Ag2(CN) 3

    NASA Astrophysics Data System (ADS)

    Pinterić, M.; Lazić, P.; Pustogow, A.; Ivek, T.; Kuveždić, M.; Milat, O.; Gumhalter, B.; Basletić, M.; Čulo, M.; Korin-Hamzić, B.; Löhle, A.; Hübner, R.; Sanz Alonso, M.; Hiramatsu, T.; Yoshida, Y.; Saito, G.; Dressel, M.; Tomić, S.

    2016-10-01

    The Mott insulator κ -(BEDT-TTF ) 2Ag2(CN) 3 forms a highly-frustrated triangular lattice of S =1 /2 dimers with a possible quantum-spin-liquid state. Our experimental and numerical studies reveal the emergence of a slight charge imbalance between crystallographically inequivalent sites, relaxor dielectric response, and hopping dc transport. In a broader perspective we conclude that the universal properties of strongly-correlated charge-transfer salts with spin liquid state are an anion-supported valence band and cyanide-induced quasidegenerate electronic configurations in the relaxed state. The generic low-energy excitations are caused by charged domain walls rather than by fluctuating electric dipoles. They give rise to glassy dynamics characteristic of dimerized Mott insulators, including the sibling compound κ -(BEDT-TTF)2Cu2 (CN )3.

  18. Fluctuation Spectroscopy Analysis Based on the Dutta-Dimon-Horn Model for the Charge-Glass System θ-(BEDT-TTF)2CsZn(SCN)4

    NASA Astrophysics Data System (ADS)

    Sato, Takuro; Miyagawa, Kazuya; Kanoda, Kazushi

    2016-12-01

    Glassy dynamics in the charge degrees of freedom in the organic conductor θ-(BEDT-TTF)2CsZn(SCN)4 is investigated through fluctuation spectroscopy. We observed the 1/f-type noise spectrum over the temperature range studied (20 < T < 300 K). The analysis of the data demonstrates that the DDH model, which assumes the 1/f noise to originate from the independent superposition of thermal activations over a range of energy gaps, explains the dynamics of the charge glass. The distribution of the energy gaps deduced from the analysis reveals that a gap of 0.3 eV dominates the glassy fluctuations in qualitative agreement with the strong-glass nature in θ-(BEDT-TTF)2CsZn(SCN)4.

  19. Insulator-metal transitions induced by electric field and photoirradiation in organic Mott insulator deuterated κ-(BEDT-TTF)2Cu[N(CN)2]Br.

    PubMed

    Sabeth, Farzana; Iimori, Toshifumi; Ohta, Nobuhiro

    2012-04-25

    The Mott insulator-metal transition induced by an external stimulus such as electric field, pressure, chemical doping, or photoirradiation has received considerable attention because of the potential use in new optoelectronic functional devices. Here we report an abrupt Mott insulator-metal transition observed as a current jump in a molecular-based Mott insulator, namely, deuterated κ-(BEDT-TTF)(2)Cu[N(CN)(2)]Br, where BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene, upon application of a pulsed voltage of certain magnitude (threshold voltage). Furthermore, the threshold voltage needed for the transition is shown to be reduced by photoirradiation. Thus, the Mott insulator-metal transition can be controlled by a combination of an external electric field and photoirradiation.

  20. Electric-field-induced intradimer charge disproportionation in the dimer-Mott insulator β'-(BEDT-TTF ) 2IC l2

    NASA Astrophysics Data System (ADS)

    Hattori, Yuma; Iguchi, Satoshi; Sasaki, Takahiko; Iwai, Shinichiro; Taniguchi, Hiromi; Kishida, Hideo

    2017-02-01

    Raman scattering spectra of the dimer-Mott insulator β'-(BEDT-TTF ) 2IC l2 [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene] under a static electric field are investigated. The application of the electric field induces two additional Raman peaks on both sides of the original peak position of the charge-sensitive Raman mode (ν2) in the spectra. At 10 kV/cm, the original peak almost disappears and only the newly emerging peaks are observed. The emergence of these peaks indicates the field-induced charge disproportionation within the dimer. The temporal change of the Raman signals with the inversion of the electric field suggests a macroscopic domain formation of the charge-disproportionate dimers. This picture is reinforced by the direct measurement of the polarization.

  1. Complete series of chiral paramagnetic molecular conductors based on tetramethyl-bis(ethylenedithio)-tetrathiafulvalene (TM-BEDT-TTF) and Chloranilate-bridged heterobimetallic honeycomb layers.

    PubMed

    Atzori, Matteo; Pop, Flavia; Auban-Senzier, Pascale; Clérac, Rodolphe; Canadell, Enric; Mercuri, Maria Laura; Avarvari, Narcis

    2015-04-06

    Electrocrystallization of enantiopure (S,S,S,S)- and (R,R,R,R)-tetramethyl-bis(ethylenedithio)-tetrathiafulvalene (TM-BEDT-TTF) donors, as well as the racemic mixture, in the presence of potassium cations and the tris(chloranilato)ferrate(III) [Fe(Cl2An)3](3-) paramagnetic anion afforded a complete series of chiral magnetic molecular conductors formulated as β-[(S,S,S,S)-TM-BEDT-TTF]3PPh4[K(I)Fe(III)(Cl2An)3]·3H2O (1), β-[(R,R,R,R)-TM-BEDT-TTF]3PPh4[K(I)Fe(III)(Cl2An)3]·3H2O (2), and β-[(rac)-TM-BEDT-TTF]3PPh4[K(I)Fe(III)(Cl2An)3]·3H2O (3). Compounds 1-3 are isostructural and crystallize in triclinic space groups (P1 for 1 and 2, P-1 for 3) showing a segregated organic-inorganic crystal structure, where anionic honeycomb layers obtained by self-assembling of the Λ and Δ enantiomers of the paramagnetic complex with potassium cations alternate with organic layers where the chiral donors are arranged in the β packing motif. Compounds 1-3 show a molecular packing strongly influenced by the topology of the inorganic layers and behave as molecular semiconductors with room-temperature conductivity values of ca. 3 × 10(-4) S cm(-1). The magnetic properties are dominated by the paramagnetic S = 5/2 [Fe(Cl2An)3](3-) anions whose high-spin character is confirmed by magnetic susceptibility measurements. The correlation between crystal structure and conducting behavior has been studied by means of tight-binding band structure calculations which support the observed conducting properties.

  2. Magnetothermopower study of the charge density wave state in a multiband organic conductor α - (BEDT - TTF)2KHg(SCN)4

    NASA Astrophysics Data System (ADS)

    Krstovska, Danica

    2017-02-01

    Magnetic field dependence of the thermopower and Nernst effect of the multiband organic conductor α - (BEDT - TTF)2KHg(SCN)4 is theoretically studied at low temperatures in the charge density wave (CDW) state, to fields of 30 T and several field directions. A theoretical model of quantum interlayer tunneling for the q1D charge carriers is used to probe the thermoelectric effects in the CDW state. The contribution from the q2D carriers is calculated by using the Boltzmann transport theory. The background components of the thermopower and Nernst effect as well as the quantum oscillations that originate from the closed Fermi surface orbits are analyzed. The model implies that in the CDW state, the properties of α - (BEDT - TTF)2KHg(SCN)4 are determined mostly by the orbits on the new open Fermi sheets. This is in accord with the previously reported CDW scenario of the low temperature state of α - (BEDT - TTF)2KHg(SCN)4 with imperfect nesting of the open Fermi surface sections.

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

    PubMed

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

    2015-01-01

    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 θ(21)-[(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 θ(21)-[(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 θ(21)-[(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

  4. 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.

  5. Anomalous thermal expansion of the organic superconductor κ-(BEDT-TTF) 2Cu[N(CN) 2]Br

    NASA Astrophysics Data System (ADS)

    Kund, M.; Müller, H.; Biberacher, W.; Andres, K.; Saito, G.

    1993-09-01

    High-resolution thermal expansion measurements on single crystals of the organic superconductor κ-(BEDT-TTF) 2Cu[N(CN) 2]Br were performed along all three principal directions in the temperature range from 4 to 300 K by means of capacitive dilatometry. Large anisotropies were observed which originate in the layer-type structure and the orthorhombic symmetry of this compound. At 80 K an anomalous and pronounced increase of the orthorhombic distortion of the conducting a-c plane is seen which correlates, together with a small observed thermal hysteresis, with an anomaly in the electrical resistivity. Here, the volume expansion coefficient β shows two subsequent jumps of approximately the same size ( Δβ = (22±4) × 10 -6 1/ K), but of opposite sign. We assume that a phase transition occurs at this temperature. A possible explanation for this is the interaction of donor libration modes with the polymeric anion through their terminal ethylenes via hydrogen bonds, leading in effect to an ethylene order-disorder transition.

  6. 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.

  7. Electron-transfer boat-vibration mechanism for superconductivity in organic molecules based on BEDT-TTF

    SciTech Connect

    Demiralp, E.; Dasgupta, S.; Goddard, W.A. III

    1995-08-09

    The highest T{sub c} organic superconductors all involve the organic molecule bis(ethylenedithio)tetrathiafulvalene (denoted as BEDT-TTF or ET) coupled with an appropriate acceptor. This leads to ET, ET{sup +}, or (ET){sub 2}{sup +} species in the crystal. Using ab initio Hartree-Fock calculations (6-31G** basis set), we show that ET deforms to a boat structure with an energy 28 meV (0.65 kcal/mol) lower than that of planar ET (D{sub 2} symmetry). On the other hand, ET{sup +} is planar. Thus, conduction in this system leads to a coupling between charge transfer and the boat deformation vibrational modes at 20 cm{sup -1} (ET) and 28 cm{sup -1} (ET{sup +}). We suggest that this electron-phonon coupling is responsible for the superconductivity and predict the isotope shifts ({delta}T{sub c}) for experimental tests of the electron-transfer boat-vibration (ET-BV) mechanism. The low frequency of this boat mode and its coupling to various lattice modes could explain the sensitivity of T{sub c} to defects, impurities, and pressure. We suggest that new higher temperature organic donors can be sought by finding modifications that change the frequency and stability of this boat distortion mode. 25 refs., 5 figs., 4 tabs.

  8. Isotope effect study of {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2}: Labeling in the anion

    SciTech Connect

    Kini, A.M.; Wang, H.H.; Schlueter, J.A.

    1995-12-31

    Since the initial discovery of organic superconductivity in 1979, a large number of organic superconductors have now been synthesized. However, the mechanism of electron-pairing in these novel superconductors has remained largely unresolved. Isotope effect studies constitute an important experimental tool for the investigation of whether or not the electron-pairing mechanism in organic superconductors is phonon-mediated, as in conventional superconductors. Recent isotope effect studies in the authors` laboratory, involving seven different isotopically labeled BEDT-TTF (or ET) derivatives, have demonstrated the following: (1) intramolecular phonon modes involving C{double_bond}C and C{single_bond}S stretching vibrations in the ET donor molecule are not the dominant mediators of electron-pairing, and (2) in {kappa}-(ET){sub 2}Cu(NCS){sub 2}, there exist two competing isotope effects--a normal mass effect, i.e., lowering of {Tc} upon isotopic labeling, when the ET molecular mass is increased by concurrent {sup 13}C and {sup 34}S labeling, in addition to an inverse isotope effect upon deuterium labeling in ET. It is of great interest to investigate if there is an isotope effect when the charge-compensating anions, which are also located within the non-conducting layer in the superconducting cation-radical salts, are isotopically labeled. The existence of an isotope effect when the anions are labeled would be indicative of electron-pairing with the mediation of vibrational frequencies associated with the anions. In this paper, the authors present the results of the first isotope effect study in which isotopic labeling in the anion portion of {kappa}-(ET){sub 2}Cu(NCS){sub 2} is carried out. The authors find no isotope effect when the carbon and nitrogen atoms of the thiocyanate groups in the anion are replaced with {sup 13}C and {sup 15}N isotopes.

  9. Three-quarter Dirac points, Landau levels, and magnetization in α -(BEDT-TTF ) 2I3

    NASA Astrophysics Data System (ADS)

    Kishigi, Keita; Hasegawa, Yasumasa

    2017-08-01

    The energies as a function of the magnetic field (H ) and the pressure are studied theoretically in the tight-binding model for the two-dimensional organic conductor α -(BEDT-TTF ) 2I3 , in which massless Dirac fermions are realized. The effects of the uniaxial pressure (P ) are studied by using the pressure-dependent hopping parameters. The system is semimetallic with the same area of an electron pocket and a hole pocket at P <3.0 kbar, where the energies (ɛD0 ) at the Dirac points locate below the Fermi energy (ɛF0 ) when H =0 . We find that at P =2.3 kbar the Dirac cones are critically tilted. In that case a type of band crossing occurs at "three-quarter" Dirac points; i.e., the dispersion is quadratic in one direction and linear in the other three directions. We obtain magnetic field dependencies of the Landau levels (ɛn) : ɛn-ɛD0∝(nH ) 4 /5 at P =2.3 kbar (three-quarter Dirac points) and | ɛn-ɛF0|∝(nH ) 2 at P =3.0 kbar (the critical pressure for the semimetallic state). We also study the magnetization as a function of the inverse magnetic field. We obtain two types of quantum oscillations. One is the usual de Haas-van Alphen (dHvA) oscillation, and the other is the unusual dHvA-like oscillation which is seen even in the system without the Fermi surface.

  10. Non-Fermi-liquid behavior of the organic superconductor κ-(BEDT-TTF)4Hg2.89Br8 probed by C13 NMR

    NASA Astrophysics Data System (ADS)

    Eto, Yoshihiro; Itaya, Megumi; Kawamoto, Atsushi

    2010-06-01

    An organic salt, κ-(BEDT-TTF)4Hg2.89Br8 exhibits superconductivity at 4.3 K under ambient pressure suggesting non-Fermi-liquid (NFL) behavior just above Tc . Whereas most organic superconductors are controlled by the bandwidth in the half-filled electron system, this salt realizes a carrier doping away from the half-filled electron system as well as high- Tc cuprates. In order to investigate the origin of NFL behavior, we assessed C13 -NMR measurements in this salt and observed the antiferromagnetic fluctuation as same as in an organic antiferromagnet κ-(BEDT-TTF)2Cu[N(CN)2]Cl with the gap structure. Application of pressure suppresses (T1T)-1 and shifts its maximum to lower temperatures with (T1T)-1 becoming constant above 2 GPa. These results suggest that applying pressure alters the electron system from NFL to FL state and that antiferromagnetic fluctuations contribute to the origin of NFL behavior.

  11. Semimetallic and charge-ordered α -(BEDT-TTF)2I3: On the role of disorder in dc transport and dielectric properties

    NASA Astrophysics Data System (ADS)

    Ivek, Tomislav; Čulo, Matija; Kuveždić, Marko; Tutiš, Eduard; Basletić, Mario; Mihaljević, Branimir; Tafra, Emil; Tomić, Silvia; Löhle, Anja; Dressel, Martin; Schweitzer, Dieter; Korin-Hamzić, Bojana

    2017-08-01

    α -(BEDT-TTF)2I3 is a prominent example of charge ordering among organic conductors. In this work, we explore the details of transport within the charge-ordered as well as semimetallic phase at ambient pressure. In the high-temperature semimetallic phase, the mobilities and concentrations of both electrons and holes conspire in such a way to create an almost temperature-independent conductivity as well as a low Hall effect. We explain these phenomena as a consequence of a predominantly interpocket scattering which equalizes mobilities of the two types of charge carriers. At low temperatures, within the insulating charge-ordered phase two channels of conduction can be discerned: a temperature-dependent activation, which follows the mean-field behavior, and a nearest-neighbor-hopping contribution. Together with negative magnetoresistance, the latter relies on the presence of disorder. The charge-ordered phase also features a prominent dielectric peak which bears a similarity to relaxor ferroelectrics. Its dispersion is determined by free-electron screening and pushed by disorder well below the transition temperature. The source of this disorder can be found in the anion layers which randomly perturb BEDT-TTF molecules through hydrogen bonds.

  12. 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.

  13. 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.

  14. 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}.

  15. Non-fermi liquid behavior of the organic superconductor κ-(BEDT-TTF)4Hg2.89Br8 probed by 13C-NMR

    NASA Astrophysics Data System (ADS)

    Eto, Yoshihiro; Itaya, Megumi; Kawamoto, Atsushi

    2010-06-01

    We assessed 13C-NMR measurements in an organic salt, κ-(BEDT-TTF)4Hg2.89Br8, which exhibits superconductivity at 4.3 K under ambient pressure. We observed that (T1T)-1 of H // and ⊥ layer at ambient pressure increased as the temperature was decreased to 7 K, but decreased further at lower temperatures, suggesting that the decrease of (T1T)-1 was not due to the superconductive fluctuations, but due to the magnetism of the conduction electrons. Application of pressure suppresses (T1T)-1, with (T1T)-1 becoming constant above 2 GPa. These results suggest that applying pressure alters the electron system from a non-Fermi liquid (NFL) to a Fermi liquid (FL) state and that antiferromagnetic fluctuations contribute to the origin of NFL behavior. Whereas most organic conductors show Fermi liquid behavior, this salt is an organic superconductor that shows NFL behavior due to the antiferromagnetic fluctuations.

  16. Ground state in κ -(BEDT-TTF)2Hg(SCN)2Br studied by Raman Spectroscopy and Heat Capacity measurements

    NASA Astrophysics Data System (ADS)

    Hassan, N.; Turunova, S. A.; Zhilyaeva, E. I.; Lyubovskaya, R. N.; Drichko, N.

    Quasi-two-dimensional organic conductor κ -(BEDT-TTF)2Hg(SCN)2Br is a Mott insulator (Tc ~ 100 K) on a triangular lattice which makes it a potential spin liquid candidate. To elucidate its magnetic ground state we study heat capacity and Raman response of single crystals of this material. Our low temperature heat capacity measurements suggest a presence of a linear term in the temperature dependence, which might indicate the existence of gapless spinons. Vibrational Raman response indicates a presence of charge order fluctuations in the insulating state. The low-frequency Raman response is discussed in terms of fluctuations of ``paired electron crystal'' state. The work at IQM was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Material Sciences and Engineering, under Grant No. DEFG02-08ER46544.

  17. Inversion Symmetry and Wave-Function Nodal Lines of Dirac Electrons in Organic Conductor α-(BEDT-TTF)2I3

    NASA Astrophysics Data System (ADS)

    Piéchon, Frédéric; Suzumura, Yoshikazu

    2013-12-01

    By examining organic conductor alpha-(BEDT-TTF)_2I_3 which is described by a nearest neighbors tight-binding model it is shown that because of inversion symmetry, each component of a wave function (WF) exhibits nodal lines (NLs) in the Brillouin zone. In the absence of any band crossing, each NL connects two time reversal invariant momenta (TRIM) as partners. In the presence of a pair of Dirac points (band crossing), for each band that crosses and for each WF component there is a NL that connects the pair of Dirac points via a TRIM without partner. This second kind of NL leads to a discontinuous sign change for non vanishing components of the WF. Such a property is at the origin of the +/- pi Berry phase accumulated on a contour integral encircling one Dirac point. The results are examplified by numerical calculation of WFs components for the above conductor with a 3/4 filled band.

  18. Topological Domain Wall and Valley Hall Effect in Charge Ordered Phase of Molecular Dirac Fermion System α-(BEDT-TTF)2I3

    NASA Astrophysics Data System (ADS)

    Matsuno, Genki; Omori, Yukiko; Eguchi, Takaaki; Kobayashi, Akito

    2016-09-01

    The topological domain wall and valley Hall effect are theoretically investigated in the molecular conductor α-(BEDT-TTF)2I3. By using the mean-field theory in an extended Hubbard model, it is demonstrated under a cylinder boundary condition that a domain wall emerges in the charge ordered phase, and exhibits a topological nature near the phase transition to the massless Dirac Fermion phase. The topological nature is well characterized by the Berry curvature, which has opposite signs in two charge ordered phases divided by the domain wall, and gives rise to the valley Hall conductivity with opposite signs, enabling these phases to be distinguished. It is also found that the valley Hall conductivity in the tilted Dirac cones exhibits a characteristic double-peak structure as a function of chemical potential using the semi classical formalism.

  19. Metallic, insulating and superconducting states in κ-ET2X systems, where ET is the BEDT-TTF (bis(ethylenedithio)tetrathiafulvalene) molecule

    NASA Astrophysics Data System (ADS)

    Ivanov, Valery A.; Ugolkova, Elena A.; Zhuravlev, Mikhail Ye.

    1998-08-01

    An electronic structure and normal and superconducting properties are reviewed for layered organic materials on the basis of bis(ethylenedithio)tetrathiafulvalene molecule (BEDT-TTF, hereafter ET) with essential intraET electron and cross-dimer κ-packing in ET-plane. The metall-insulator phase transition is derived for realistic model of κ-ET2X salts. Based on the Fermi-surface topology and electron correlations the d-symmetry of superconducting order parameter is obtained with interplay between its nodes on the Fermi surface and superconducting phase characteristics. The results are in agreement with measured nonactivated temperature dependencies of NMR-relaxation rate of central carbon 13C spins in ET and superconducting specific heat.

  20. New BEDT-TTF/[Fe(C5O5)3]3- hybrid system: synthesis, crystal structure, and physical properties of a chirality-induced alpha phase and a novel magnetic molecular metal.

    PubMed

    Coronado, Eugenio; Curreli, Simona; Giménez-Saiz, Carlos; Gómez-García, Carlos J; Deplano, Paola; Mercuri, Maria Laura; Serpe, Angela; Pilia, Luca; Faulmann, Christophe; Canadell, Enric

    2007-05-28

    The paramagnetic and chiral anion [Fe(C5O5)3]3- (C5O52-=croconate) has been combined with the organic donor BEDT-TTF (=ET=bis(ethylenedithio)tetrathiafulvalene) to synthesize a novel paramagnetic semiconductor with the first chirality-induced alpha phase, alpha-(BEDT-TTF)5[Fe(C5O5)3].5H2O (1), and one of the few known paramagnetic molecular metals, beta-(BEDT-TTF)5[Fe(C5O5)3].C6H5CN (2). Both compounds present layers of BEDT-TTF molecules, with the alpha or beta packing modes, alternating with layers containing the high-spin S=5/2 Fe(III) anions and solvent molecules. In the alpha phase, the alternation of the chiral [Fe(C5O5)3]3- anions along the direction perpendicular to the BEDT-TTF chains induces an alternation of the tilt angle of the BEDT-TTF molecules, giving rise to the observed alpha phase. The alpha phase presents a semiconductor behavior with a high room-temperature conductivity (6 S.cm-1) and an activation energy of 116 meV. The beta phase presents a metallic behavior down to ca. 120 K, where a charge localization takes place with a reentrance to the metallic state below ca. 20 K followed by a metal-semiconductor transition at ca. 10 K. The magnetic properties are dominated by the paramagnetic S=5/2 [Fe(C5O5)3]3- anion with an extra Pauli-type paramagnetism in the metallic beta phase. The ESR spectra confirm the presence of the high-spin Fe(III)-containing anion and show a progressive localization in the organic sublattice along with an antiferromagnetic coupling below ca. 120 K that, in the metallic beta phase, could be at the origin of the transition from the metallic to the activated conductivity regime. The correlation between crystal structure and conductivity behavior has been studied by means of tight-binding band structure calculations which provide a rationalization of the charge distribution and conductivity results.

  1. 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.

  2. 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.

  3. Low-temperature Fermi surface of the organic conductor β″-(BEDT-TTF)(TCNQ)(1-x)(F1-TCNQ)x (x=0,0.05) from magnetooptical measurements

    NASA Astrophysics Data System (ADS)

    Kimata, M.; Oshima, Y.; Ohta, H.; Koyama, K.; Motokawa, M.; Yamamoto, H. M.; Kato, R.

    2007-01-01

    Magnetooptical measurements have been performed on the organic conductor β″ -(BEDT-TTF)(TCNQ) ( x=0 salt), and a related compound, β″-(BEDT-TTF)(TCNQ)0.95(F1-TCNQ)0.05 ( x=0.05 salt), to investigate their low-temperature Fermi surfaces (FSs). Although the room-temperature FS of both salts can be considered the same, our results indicate that the low-temperature FSs are completely different from each other. In the x=0 salt, the low-temperature FS consists of two very anisotropic quasi-two-dimensional (Q2D) FSs. Cross-sectional areas of anisotropic Q2D-FSs are very small, and correspond to 1-2% of the first Brillouin zone at room temperature. On the other hand, in the x=0.05 salt, only a pair of quasi-one-dimensional FSs exist at low temperature. Compared with the band calculation of x=0 salt, this Q1D-FS originates from the BEDT-TTF conducting layers. This result indicates that the two hump-like anomalies in the temperature dependence of resistivity at 80 and 20K , which are observed only in the x=0 salt, are related to the nesting of BEDT-TTF Q1D-FS. Hence, it is considered that anisotropic Q2D-FS pockets observed in the x=0 salt are generated by the imperfect nesting of Q1D-FS, and the density wave state may be formed in the x=0 salt at low temperatures.

  4. Pressure dependence of the metal-insulator transition in κ-(BEDT-TTF)2Hg(SCN)2Cl: optical and transport studies

    NASA Astrophysics Data System (ADS)

    Löhle, A.; Rose, E.; Singh, S.; Beyer, R.; Tafra, E.; Ivek, T.; Zhilyaeva, E. I.; Lyubovskaya, R. N.; Dressel, M.

    2017-02-01

    The two-dimensional organic conductor κ-(BEDT-TTF)2-Hg(SCN)2Cl exhibits a pronounced metal-insulator transition at {{T}\\text{CO}}=30 K. From the splitting of the molecular vibrations, the phase transition can be unambiguously assigned to charge-ordering with 2{δρ}=0.2e . We have investigated the pressure evolution of this behavior by temperature-dependent electrical transport measurements and optical investigations applying hydrostatic pressure up to 12 kbar. The data reveal a mean-field like down-shift of {{T}\\text{CO}}≤ft( p\\right) with a critical pressure of {{p}c}=0.7+/- 0.1 kbar and a metallic state above the suppression of the charge-ordered state; no traces of superconductivity could be identified down to T  =  1.5 K. As the charge order {δρ} sets in abruptly with decreasing temperature, its size remains unaffected by pressure. However, the fraction of charge imbalanced molecules decreases until it is completely absent above 1.6 kbar.

  5. Pressure dependence of the metal-insulator transition in κ-(BEDT-TTF)2Hg(SCN)2Cl: optical and transport studies.

    PubMed

    Löhle, A; Rose, E; Singh, S; Beyer, R; Tafra, E; Ivek, T; Zhilyaeva, E I; Lyubovskaya, R N; Dressel, M

    2017-02-08

    The two-dimensional organic conductor κ-(BEDT-TTF)2-Hg(SCN)2Cl exhibits a pronounced metal-insulator transition at [Formula: see text] K. From the splitting of the molecular vibrations, the phase transition can be unambiguously assigned to charge-ordering with [Formula: see text]. We have investigated the pressure evolution of this behavior by temperature-dependent electrical transport measurements and optical investigations applying hydrostatic pressure up to 12 kbar. The data reveal a mean-field like down-shift of [Formula: see text] with a critical pressure of [Formula: see text] kbar and a metallic state above the suppression of the charge-ordered state; no traces of superconductivity could be identified down to T  =  1.5 K. As the charge order [Formula: see text] sets in abruptly with decreasing temperature, its size remains unaffected by pressure. However, the fraction of charge imbalanced molecules decreases until it is completely absent above 1.6 kbar.

  6. The assignment of the normal modes of the BEDT-TTF electron-donor molecule using the infrared and Raman spectra of several isotopic analogs

    NASA Astrophysics Data System (ADS)

    Eldridge, J. E.; Homes, C. C.; Williams, Jack M.; Kini, A. M.; Wang, H. Hau

    1995-06-01

    Room-temperature infrared and Raman measurements on neutral bis(ethylenedithio) tetrathiafulvalene, abbreviated to BEDT-TTF, and four of its isotopic analogs are reported. The analogs are 13C(6) in which the central six carbon atoms are substituted with 13C; 13C(2) in which only the two central atoms are substituted and 34S(8) and d(8) in which all of the sulphur or all of the hydrogen atoms are substituted; respectively. The frequencies and frequency shifts of the Raman features and the infrared powder absorption features are measured. The polarized infrared reflectivity of a single crystal, and the intensities of the Raman features, help in assigning symmetries to certain resonances. By comparing these shifts to those calculated using a realistic valence force model the assigment of most of the in-plane fundamental intermolecular vibrational modes, and a few of the out-of-plane ethylene modes is achieved. The force constants are refined to produce excellent overall agreement between the measured and calculated frequencies and isotope shifts.

  7. Theory of coexisting CDW-SDW in (TMTTF)_2Br, (TMTSF)_2X and α-(BEDT-TTF)_2MHg(SCN)_4

    NASA Astrophysics Data System (ADS)

    Campbell, D. K.; Clay, R. Torsten; Ramasesha, S.; Mazumdar, S.

    1998-03-01

    Within conventional theories of spatial broken symmetries, CDW and SDW with same periodicities do not coexist. Recent X-ray scattering experiments on (TMTTF)_2Br and (TMTSF)_2PF6 have, however, determined that the 2kF SDWs in these systems are accompanied by 2kF CDWs (J.P. Pouget and S. Ravy, Synth. Metals 85, 1523 (1997)). Similar CDW-SDW coexistence has also been claimed in the α-(BEDT-TTF)_2MHg(SCN)4 (K. Miyagawa et al., Phys. Rev. B (1997)). We present a microscopic theory of coexisting CDW-SDW in these materials. We show that a complete understanding of the unconventional natures of the insulating phases in these materials is obtained only upon explicit inclusion of the strong Coulomb interactions between the holes on the organic molecules, the proper band-filling, lattice discreteness, and the anisotropic two-dimensional nature of the lattice within the starting Hamiltonian. Detailed exact and quantum Monte Carlo results are presented.

  8. First-principles investigation of local structure deformation induced by x-ray irradiation in κ -(BEDT-TTF ) 2Cu [N (CN) 2 ] Br

    NASA Astrophysics Data System (ADS)

    Kang, Lijing; Akagi, Kazuto; Hayashi, Kouichi; Sasaki, Takahiko

    2017-06-01

    We investigated the local structure deformation induced by x-ray irradiation in an organic molecular conductor κ -(BEDT-TTF ) 2Cu [N (CN) 2 ] Br using density-functional-theory (DFT-) based first-principles calculations. Our results demonstrate that the structure change due to x-ray excitation can be predicted by introducing a core hole at specific light atoms of the anion molecules with an infinite lifetime. The formation of a bond-shifted structure triggered by a double excitation was expected as a possible irreversible molecular defect leading to permanent irradiation damage. The calculated change in molecular vibration spectra after irradiation was consistent with the experimental results, and some different vibration modes by further irradiation were also predicted. The calculated local density of states indicates that the bond-shifted structure in the anion layer causes local potential modulation to the carriers (holes) in the cation layer. The introduced potential disorder for the carriers could increase the resistivity due to a localization effect that has been observed experimentally so far.

  9. 13C-NMR studies of the paramagnetic and charge-ordered states of the organic superconductor β''-(BEDT-TTF)3Cl2·2H2O under pressure

    NASA Astrophysics Data System (ADS)

    Nagata, Sanato; Ogura, Takashi; Kawamoto, Atsushi; Taniguchi, Hiromi

    2011-07-01

    β''-(BEDT-TTF)3Cl2·2H2O [BEDT-TTF: b̲is-(e̲thylened̲it̲hio)t̲etrat̲hiaf̲ulvalene] is superconductive under pressures, whereas the salt exhibits metal-insulator (MI) transition under ambient pressure. The insulator phase in the salt was examined using the charge density wave (CDW) phase that was obtained from band calculation. The charge-ordered (CO) state was recently proposed as the insulator phase of the salt, and the mechanism of superconductivity intermediated by charge fluctuation was suggested. We accessed 13C-NMR on β''-(BEDT-TTF)3Cl2·2H2O at ambient pressure and under pressure up to 1.6 GPa. At ambient pressure, the NMR spectrum changed at approximately 100 K. Three isolated peaks appeared at low temperatures, suggesting that the CO state exists below 100 K, and spin-gap behavior was observed. By analyzing the chemical shift, the charges on the three sites were estimated as ˜+0.4e, ˜+0.6e, and ˜+1.0e. The ratio of peak intensity and unsymmetrical peak position suggest the CO state with some symmetry breaking. When pressure is applied, the splitting of the NMR peaks in the CO state is reduced. The salt finally exhibits superconductivity at 1.6 GPa, spin-gap behavior observed at (T1T)-1 below 1.3 GPa suddenly disappears, whereas the NMR spectrum predicts that charge disproportionation coexists with superconductivity. The suppression of the spin-singlet formation observed in (T1T)-1 at 1.6 GPa suggests the metallic state with the charge disproportionation and the CO instability with some symmetry breaking.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. The current-density dependence U(J) of the activation energy for the motion of Abrikosov vortices in the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Cl{sub 0.5}Br{sub 0.5}

    SciTech Connect

    Primenko, A.E.; Kuznetsov, V.D.; Metlushko, V.V.

    1995-02-01

    The authors have investigated the thermally activated motion of flux in the organic superconductor {kappa}-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Cl{sub 0.5}Br{sub 0.5} over a wide range of current densities J, and have obtained the dependence of the activation energy U for this motion on current density. 21 refs., 2 figs.

  16. 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.

  17. Unconventional quantum fluid at high magnetic fields in the marginal charge-density-wave system α-(BEDT-TTF)2MHg(SCN)4 (M=K and Rb)

    NASA Astrophysics Data System (ADS)

    Harrison, N.; Singleton, J.; Bangura, A.; Ardavan, A.; Goddard, P. A.; McDonald, R. D.; Montgomery, L. K.

    2004-04-01

    Single crystals of the organic charge-transfer salts α-(BEDT-TTF)2MHg(SCN)4 have been studied using Hall-potential measurements (M=K) and magnetization experiments (M=K, Rb). The data show that two types of screening currents occur within the high-magnetic-field, low-temperature charge-density wave (CDWx) phases of these salts in response to time-dependent magnetic fields. The first, which gives rise to the induced Hall potential, is a free current (jfree), present at the surface of the sample. The time constant for the decay of these currents is much longer than that expected from the sample resistivity. The second component of the current appears to be magnetic (jmag), in that it is a microscopic, quasiorbital effect; it is evenly distributed within the bulk of the sample upon saturation. To explain these data, we propose a simple model invoking a new type of quantum fluid comprising a CDW coexisting with a two-dimensional Fermi-surface pocket which describes the two types of current. The model and data are able to account for the body of previous experimental data which had generated apparently contradictory interpretations in terms of the quantum Hall effect or superconductivity.

  18. 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 PAGES

    V. A. Gasparov; Bozovic, I.; He, Xi; ...

    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

  19. 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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    We used atomic-layer molecular beam epitaxy (ALL-MBE) to synthesize bilayer films of a cuprate metal (La1.65Sr0.45CuO4, LSCO) and a cuprate insulator (La2CuO4, LCO), 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 κ-(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 Reσ(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.

  20. Comparison of the crystal and electronic structures of three 2:1 salts of the organic donor molecule BEDT-TTF with pentafluorothiomethylsulfonate anions SF{sub 5}CH{sub 2}SO{sub 3}{sup {minus}}, SF{sub 5}CHFSO{sub 3}{sup {minus}}, and SF{sub 5}CF{sub 2}SO{sub 3}{sup {minus}}

    SciTech Connect

    Ward, B.H.; Schlueter, J.A.; Geiser, U.

    2000-02-01

    Salts of the donor molecule, bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET), with pentafluorothiomethylsulfonate (SF{sub 5}CX{sub 2}SO{sub 3}{sup {minus}}, X = H or F) anions have been prepared. Three phases, {beta}{double_prime}-(ET){sub 2}SF{sub 5}CH{sub 2}SO{sub 3}{beta}{prime}-(ET){sub 2}SF{sub 5}CF{sub 2}SO{sub 3} and {beta}{double_prime}-(ET){sub 2}SF{sub 5}CHFSO{sub 3} (A,B, and C respectively) were obtained by electrocrystallization with the corresponding LiSF{sub 5}CX{sub 2}SO{sub 3} electrolytes. The structures of these salts were determined by single-crystal X-ray diffraction, and their physical properties were examined by electrical resistivity measurements as well as by ESR and Raman spectroscopy. The A,C and B salts are considerably different in their crystal structures, physical properties, and electronic structures despite the similarity in the structures of SF{sub 5}CX{sub 2}SO{sub 3}{sup {minus}}(X = H,F) anions. The A salt has two kinds of ET donor molecules with considerably different charge densities. The electronic structure of C has both one-dimensional (1D) and two-dimensional (2D) Fermi surfaces which are similar to those found in the organic superconductor A. The ESR data for the B salt indicate that it opens a spin gap below 45 K. The differences in the physical properties of the three salts were analyzed by calculating the HOMO-HOMO interaction energies between nearest-neighbor ET molecules in their donor molecule layers.

  1. 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.

  2. Coexistence of magnetic and delocalized electrons in hybrid molecular materials: The series of organic-inorganic radical salts (BEDT-TTF){sub 8}[XW{sub 12}O{sub 40}](solv){sub n} (X = 2(H{sup +}), B{sup III}, Si{sup IV}, Cu{sup II}, Fe{sup III}; solv=H{sub 2}O, CH{sub 3}CN)

    SciTech Connect

    Gomez-Garcia, C.J.; Gimenez-Saiz, C.; Triki, S.

    1995-08-02

    The synthesis, crystal structure and physical properties of the new series {alpha}{sub 1} and {alpha}{sub 2} of radical salts made with bis (ethylenedithio) tetrathiafulvalene (BEDT-TTF or ET) and Keggin polyoxoanions are reported. The structure of the {alpha}{sub 1}-ET{sub 8}[XW{sub 12}O{sub 40}] (X=Co{sup II}, Cu{sup II}, 2(H{sup +}) and Fe{sup III}) series consists of alternating layers of the organic donor and the Keggin polyoxometalates. The organic layers contain three crystallographically independent molecules that form two different parallel stacks alternating in the [101] direction. The structure of the {alpha}{sub 2}-ET{sub 8}[XW{sub 12}O{sub 40}] (X=Co{sup II}, Cu{sup II}, 2(H{sup +}), Fe{sup III} and B{sup III}) series is similar to that of the {alpha}{sub 1} phase but the organic layers contain only two crystallographically independent molecules. In both {alpha} phases the Keggin polyanions form closed packed pseudohexagonal layers. Both crystal structures suggest the presence of two types of differently charged stacks: a dimerized one with almost neutral ET molecules, and an eclipsed one formed by almost ionized ET molecules. This inhomogeneous charge distribution is confirmed by Raman spectroscopy. Conductivity measurements show that all compounds are semiconductors, in agreement with the band structure EHT calculations. Magnetic measurements indicate the presence of antiferromagnetic interactions in the organic sublattice with the presence of a strong Curie tail and confirm the electronic distribution in the two kinds of stacks. ESR spectra of the salts with dimagnetic anions complete these results and for the radical salts with paramagnetic anions indicate that both sublattices coexist but do not interact significantly.

  3. Preparation and properties of double-bridged BEDT-TTF dimer and its perchlorate salt

    NASA Astrophysics Data System (ADS)

    Tachikawa, T.; Izuoka, A.; Kumai, R.; Sugawara, T.; Sugawara, Y.

    1992-04-01

    A novel twin donor with double ethylene bridges ( 1) was synthesized and perchlorate salt of its cation radical was prepared. The salt showed a metallic temperature dependence of conductivity from room temperature down to about 100 K. In the salt the donor molecule takes a V-shape conformation and a donor packing shows a unique three dimensional arrangement. A bridging thia-crown moiety may play an important role in determining the conformation and the arrangement of the donor.

  4. Systematic investigation of electronic structure in BEDT-TTF based organic superconductors with Tc above 10 K; [kappa]-(BEDT-TTF)[sub 2]X (X = Cu(NCS)[sub 2], Cu[N(CN)[sub 2

    SciTech Connect

    Nakamura, Toshikazu; Nobutoki, Tomoko; Miyamoto, Masao; Tsubokura, Yuichi; Tsuchiya, Ryota; Takahashi, Toshihiro ); Kanoda, Kazushi ); Saito, Gunzi )

    1994-06-01

    The electronic structure of the title superconductors has been investigated by electrical resistivity, complex susceptibility, and electron paramagnetic resonance (EPR) measurements. The superconducting properties (pressure dependence of Tc, magnetic penetration depth, upper critical field, and so on) of these three salts are similar to each other, while transport properties in the normal state have shown a large variety in the temperature dependence. In order to clarify the electronic structure in the normal state, the EPR parameters, the spin susceptibility ([Chi][sub spin]), and the linewidth ([Delta]H[sub pp]), are compared. An anomalous temperature dependence of the g-value has been observed below 150 K in the Cu(NCS)[sub 2] and Cu(CN)[N(CN)[sub 2

  5. Pressure studies on a low-resistance variant of the quasi-2D organic superconductor κ-(BEDT-TTF) 2Cu[N(CN) 2]Br

    NASA Astrophysics Data System (ADS)

    Lang, M.; Strack, Ch.; Akinci, C.; Wolf, B.; Schlueter, J. A.; Wosnitza, J.; Schweitzer, D.

    2005-04-01

    Measurements of the interlayer resistivity, ρ⊥( T), under hydrostatic pressure have been performed on a low (LR)- and high (HR)-resistance variant of the title organic superconductor. While the HR sample, synthesized according to the standard procedure, shows a semimetallic-like ρ( T) behavior at high temperatures followed by the pronounced maximum around 90 K, the LR crystal, which is the result of a somewhat modified synthesis route, remains metallic for T⩽300 K. Common to both variants is, however, an almost abrupt change in ρ(T) around T*=40 K, consistent with a density-wave-type instability, which below T≈12 K coexists with superconductivity, and a ρ∝ AT2 dependence for T⩽T⩽T0. While T* and Tc are sample independent, the values for A and T0 were found to differ markedly between both variants, inconsistent with the T2 dependence originating from coherent Fermi-liquid excitations.

  6. 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.

  7. Electron-phonon coupling in {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2} organic superconductor studied by Raman scattering spectroscopy.

    SciTech Connect

    Pedron, D.

    1998-07-31

    Low frequency Raman data for {kappa}-(ET){sub 2}Cu(NCS){sub 2}(T{sub c} = 10.4 K) are reported. Measurements have been performed in a wide range of temperatures (1.5-100 K) and frequency hardening related to the superconducting transition has been observed for all the low-lying coupled phonons. The measured relative frequency shifts are lower than those previously reported for {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br (T{sub c} = 11.67 K), but the behavior of the two systems is similar and indicates a significant strength of the intermolecular electron-photon coupling. The effects of isotopic substitutions ({sup 13}C{sub 4} {sup 34}S{sub 8} and {sup 2}H{sub 8}) in ET molecules on the low frequency Raman active phonons of {kappa}-(ET{sub 2}Cu(NCS){sub 2}) are also reported. They give the first direct experimental confirmation to the suggested lattice softening induced by deuteration.

  8. 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.

  9. Dielectric Properties of Organic Charge-Transfer Salts

    NASA Astrophysics Data System (ADS)

    Fischer, J. K. H.; Lunkenheimer, P.; Krohns, S.; Manna, R. S.; Hartmann, B.; Schubert, H.; Lang, M.; Müller, J.; Schlueter, J. A.; Mézière, C.; Batail, P.; Loidl, A.

    The BEDT-TTF-based charge-transfer salts have attracted considerable attention due to their often intriguing dielectric properties. An example is κ-(BEDT-TTF)2Cu[N(CN)2]Cl. It was recently found to exhibit multiferroicity, for which a new electric-dipole driven mechanism was proposed. The polar moment in this system was suggested to arise from the dimerization of the BEDT-TTF molecules, combined with charge order. Another interesting recent example is α-(BEDT-TTF)2I3, which shows the signature of relaxor-ferroelectric behavior. Here, we will present an overview of the dielectric properties of the above systems and provide new results on κ-(BEDT-TTF)2Hg(SCN)2Cl, which also seems to show relaxor-ferroelectric behavior in its charge-ordered state. In addition, we present measurements of δ-(EDT-TTF-CONMe2)2Br. This compound lacks dimerization, but exhibits charge order already at room temperature.

  10. A facile route to aromatic ring-annelated bis(ethylenedithio) tretrathiafluvalene derivatives

    SciTech Connect

    Parakka, J.P.; Kini, A.M.; Williams, J.M.

    1996-12-31

    The synthesis of bis(benzo)- and bis(naphtho)-fused derivatives of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) is easily achieved by employing the (4+2) cycloaddition reaction of oligo(1,3-dithiole-2,4,5-trithione) with appropriate olefins as the key step.

  11. An International Conference on Organic Superconductors Held in South Lake Tahoe, California on May 20-24, 1990

    DTIC Science & Technology

    1990-11-30

    8217 per telecon Dr. Mark Ross . Dist Spcak 6 Naval Research Laboratory/code 6112. Su.ca VHG 12/17/90 - Stanford University, Stanford, CA 94305 Wi~iamA...Government purposes. I I I AN ELECTRONIC BAND STRUCTURE CALCULATION FOR P-(BEDT-TTF)213 M. Weger*, J. Kubler **, D. Schweitzer@, C. Sommers# *Racah Institute

  12. 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.

  13. A statistical model for the intrinsically broad superconducting to normal transition in quasi-two-dimensional crystalline organic metals.

    SciTech Connect

    Singleton, J.; Harrison, N.; Mielke, C. H.; Schlueter, J. A.; Materials Science Division; LANL; Univ. of Oxford

    2001-11-05

    Although quasi-two-dimensional organic superconductors such as {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2} (BEDT-TTF{triple_bond}bis(ethylene-dithio)tetrathiafulvalene) seem to be very clean systems, with apparent quasiparticle mean free paths of several thousand angstroms, the superconducting transition is intrinsically broad (e.g. {approx}1 K wide for {Tc}{approx}10 K). We propose that this is due to the extreme anisotropy of these materials, which greatly exacerbates the statistical effects of spatial variations in the potential experienced by the quasiparticles. Using a statistical model, we are able to account for the experimental observations. A parameter {bar x}, which characterizes the spatial potential variations, may be derived from Shubnikov-de Haas oscillation experiments. Using this value, we are able to predict a transition width which is in good agreement with that observed in megahertz penetration-depth measurements on the same sample.

  14. Ferroelectric charge order enhanced by magnetic frustration in dimer Mott insulators

    NASA Astrophysics Data System (ADS)

    Gomi, Hiroki; Inagaki, Takeshi J.; Takahashi, Akira

    2016-01-01

    We investigate the effect of magnetic frustration on the dielectric properties of dimer Mott insulators. We adopt the two-dimensional quarter-filled extended Hubbard model for κ -(BEDT -TTF )2X with an additional coupling with the dimer lattice motions, and numerically obtain the ground state. In the parameter range for strong magnetic frustration, an interdimer bond-length alternation mode that lifts the quasidegeneracy of classical spin configurations is strongly coupled to the electron system; this alternation mode occurs even with an extremely small electron-lattice coupling constant. Furthermore, the bond-length alternation induces in the dimers electric dipoles, which align along the same direction. A dimer Mott insulator phase with the ferroelectric charge order is obtained in the region. These results are consistent with the relaxorlike dielectric anomaly in κ -(BEDT-TTF ) 2Cu2(CN) 3 .

  15. History of crystalline organic conductor

    NASA Astrophysics Data System (ADS)

    Murata, Keizo

    2017-05-01

    A brief view of crystalline organic conductor is presented. Since the discovery of TTF-TCNQ (tetrathiafulvalene-tetracyanoquinodimethane) in the mid 1970’s, pressure has been an indispensable tool to develop the physics of this field. From the aspect of charge transfer salt, TTF-TCNQ and its family was specified with partial charge transfer, two chain one-dimensional (1D) system, charge density wave (CDW) and commensurability. On the other hand, in (TMTSF)2X family (TMTSF: tetramethyltetraselenafulvalene, X: electron acceptor such as PF6, ClO4), complete charge transfer, one chain system, spin density wave (SDW), field-induced SDW, quantum Hall effect, superconductivity were discussed. Further, together with pressure itself, cooling rate was noticed to be important for low temperature properties. Recently, coming back to TTF-TCNQ family, i.e., HMTSF-TCNQ, whether or not field-induced CDW, instead of field-induced SDW, and quantum Hall effect is present was discussed (HMTSF: hexamethylene-tetraselenafulvalene). Whether or not the Fermiology in (TMTTF)2X under pressure is similar to that of (TMTSF)2X is discussed as well. In (BEDT-TTF)2X, new aspect of macroscopic polarization of α-(BEDT-TTF)2I3 related to charge order is described. At the end, in contrast to the charge transfer salts, non-charge transfer salt, that is, single component conductor is presented as a new possible example of Dirac cone, which was deeply studied by many researchers in α-(BEDT-TTF)2I3, together with the theoretical calculation of its magnetic susceptibility (BEDT-TTF: bisethylenedithia-tetrathiafulvalene).

  16. Vibrational studies of {sup 13}C- and {sup 34}S-labelled bis(ethylenedithio)tetrathiafulvalene (ET) donor molecule

    SciTech Connect

    Ferraro, J.R.; Kini, A.M.; Williams, J.M.; Stout, P.

    1994-06-01

    FT-IR and FT-Raman studies of {sup 13}C- and {sup 34}S-labelled bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF or ET) electron-donor molecules were made and the results presented herein. Assignments for fundamental vibrations in ET were verified. Spectral data confirms that ET has no center-of-symmetry, and that the data can be reconciled by a D-type point group with only slight interactions occurring between the 4 molecules per unit cell.

  17. 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.

  18. Raman scattering in an anisotropic triangular spin lattice system

    NASA Astrophysics Data System (ADS)

    Kishida, Hideo; Nakamura, Yuto; Mizukoshi, Kazushi; Yoshida, Yukihiro; Saito, Gunzi

    Spin-disordered quantum phases in an anisotropic triangular spin lattice system, κ-(BEDT-TTF)2B(CN)4, were recently reported. In this compound, the ratio of the two transfer integrals, t' / t , reaches 1.44 at 298 K and 1.80 at 100 K. Its optical conductivity in the infrared region is anisotropic. The temperature dependence of the optical anisotropy correlates with that of t' / t . From the experimentally evaluated optical anisotropy, we expect that the values of t' / t are larger than 1.80 in the lower temperature region. For this compound, we observe the polarization-dependent broad Raman scattering signals below 600 cm-1 at 10 K. In such a wavenumber region, we have observed the magnetic Raman signals in triangular spin lattice systems such as κ-(BEDT-TTF)2X and β'-type Pd(dmit)2 salts. By comparison with them, we discuss the origin of the Raman signals observed for κ-(BEDT-TTF)2B(CN)4.

  19. 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).

  20. 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.

  1. Polarization selectivity of charge localization induced by a 7-fs nearly single-cycle light field in an organic metal

    NASA Astrophysics Data System (ADS)

    Kawakami, Y.; Yoneyama, Y.; Amano, T.; Itoh, H.; Yamamoto, K.; Nakamura, Y.; Kishida, H.; Sasaki, T.; Ishihara, S.; Tanaka, Y.; Yonemitsu, K.; Iwai, S.

    2017-05-01

    Polarization selectivity of light-field-induced charge localization was investigated in an organic metal α -(BEDT-TTF ) 2I3 with a triangular lattice. Dependences of transient reflectivity spectra on polarizations of the 7-fs pump and probe lights indicate that a short-range charge order (CO) is induced efficiently from the metallic phase for the pump polarization perpendicular to the 1010-type CO axis. A numerical solution of a time-dependent Schrödinger equation clarified that the 1010 CO is induced by field-induced re-distribution of charges cooperating with competing intersite Coulomb repulsions in the triangular lattice.

  2. 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.

  3. 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.

  4. 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.

  5. Near-degeneracy of extended s +dx2-y2 and dx y order parameters in quasi-two-dimensional organic superconductors

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    The symmetry of the superconducting order parameter in quasi-two-dimensional bis-ethylenedithio-tetrathiafulvalene (BEDT-TTF) organic superconductors is a subject of ongoing debate. We report ab initio density-functional-theory calculations for a number of organic superconductors containing κ -type layers. Using projective Wannier functions, we derive the parameters of a common low-energy Hamiltonian based on individual BEDT-TTF molecular orbitals. In a random-phase approximation spin-fluctuation approach, we investigate the evolution of the superconducting pairing symmetry within this model, and we point out a phase transition between extended s +dx2-y2 and dx y symmetry. We discuss the origin of the mixed order parameter and the relation between the realistic molecule description and the widely used dimer approximation. Based on our ab initio calculations, we position the investigated materials in the obtained molecule model phase diagram, and we simulate scanning tunneling spectroscopy experiments for selected cases. Our calculations show that many κ -type materials lie close to the phase-transition line between the two pairing symmetry types found in our calculation, possibly explaining the multitude of contradictory experiments in this field.

  6. Anisotropic superconductivity in β-(BDA-TTP)2SbF6: STM spectroscopy

    NASA Astrophysics Data System (ADS)

    Nomura, K.; Muraoka, R.; Matsunaga, N.; Ichimura, K.; Yamada, J.

    2009-03-01

    We have investigated the gap symmetry in the superconducting phase of β-(BDA-TTP)2SbF6 with use of the scanning tunneling microscope (STM). The tunneling spectra obtained on the conducting surface show a clear superconducting gap structure. Its functional form is of V-shaped similarly to κ-(BEDT-TTF)2X and suggests the anisotropic superconducting gap with line nodes. For lateral surfaces the shape of tunneling spectra varies from the U-shape with relatively large gap to the V-shape with small gap depending on the tunneling direction alternately twice between directional angle 0 and π. From the analysis of conductance curve taking the k dependence of the tunneling probability into account, it is found that the gap has maximum near the a* and c* axes and the nodes appear along near a*+c* and the a-c* directions. These indicate that the d like superconducting pair is formed in this system as the case of κ-(BEDT-TTF)2X. This node direction is consistent with the theoretical prediction based on the spin fluctuation mechanism. However, the zero-bias conductance peak has not been observed yet.

  7. N-Type Superconductivity in an Organic Mott Insulator Induced by Light-Driven Electron-Doping.

    PubMed

    Suda, Masayuki; Takashina, Naoto; Namuangruk, Supawadee; Kungwan, Nawee; Sakurai, Hidehiro; Yamamoto, Hiroshi M

    2017-09-01

    The presence of interface dipoles in self-assembled monolayers (SAMs) gives rise to electric-field effects at the device interfaces. SAMs of spiropyran derivatives can be used as photoactive interface dipole layer in field-effect transistors because the photochromism of spiropyrans involves a large dipole moment switching. Recently, light-induced p-type superconductivity in an organic Mott insulator, κ-(BEDT-TTF)2 Cu[N(CN)2 ]Br (κ-Br: BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene) has been realized, thanks to the hole carriers induced by significant interface dipole variation in the spiropyran-SAM. This report explores the converse situation by designing a new type of spiropyran monolayer in which light-induced electron-doping into κ-Br and accompanying n-type superconducting transition have been observed. These results open new possibilities for novel electronics utilizing a photoactive SAMs, which can design not only the magnitude but also the direction of photoinduced electric-fields at the device interfaces. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Tuning Correlations in Low-Dimensional Electron Systems: Fermi liquid versus non-Fermi-liquid behavior in organic conductors

    NASA Astrophysics Data System (ADS)

    Dressel, Martin

    2012-02-01

    While the electronic properties of cuprates can be modified by electron or hole doping, organic conductors provide the opportunity to tune the strength of electronic correlations more directly. Varying the bandwidth by (physical or chemical) pressure, the κ-phase BEDT-TTF compounds cross over from a Fermi liquid to a Mott insulator by increasing effective correlations. We systematically investigate the electronic transport properties in organic conductors by dc resistivity and optical measurements in order to extract the temperature and frequency-dependent scattering rate 1/τ= A(kBT)^2 + B(φ)^2. We find corresponding temperature and frequency ranges in which the parabolic behaviors are observed. For the first time, we can quantitatively relate the two prefactors (A/B=56) and their enhancement as correlations increase upon approaching the Mott transition. Conceptually low-dimensional organic conductors are also good candidates for quantum criticality because often an ordered state is located next to a metallic state when the system is tuned by pressure. Interestingly both are found, order in the spin as well as in the charge sector. Fermi-liquid behavior observed in the metallic state seems to be limited to certain regions of the phase diagram with non-Fermi-liquid properties evolving as the ordered phase is approached. It is not clear whether these deviations from Fermi liquid behavior are actually a signature of quantum criticality.[4pt] [1] M. Dressel, Quantum criticality in organic conductors? Fermi-liquid versus non-Fermi-liquid behavior, J. Phys.: Condens. Matter 23, 293201 (2011).[2] S. Yasin, M. Dumm, B. Salameh, P. Batail, C. M'ezi'ere and M. Dressel, Transport studies at the Mott transition of the two-dimensional organic metal κ-(BEDT-TTF)2Cu[N(CN)2]BrxCl1-x, Eur. Phys. J. B 79, 383 (2011).[3] M. Dumm, D. Faltermeier, N. Drichko and M. Dressel, Bandwidth-controlled Mott transition in κ-(BEDT-TTF)2Cu[N(CN)2]BrxCl1-x: Optical studies of correlated

  9. Importance of spin-orbit coupling in layered organic salts

    NASA Astrophysics Data System (ADS)

    Winter, Stephen M.; Riedl, Kira; Valentí, Roser

    2017-02-01

    We investigate the spin-orbit coupling (SOC) effects in α - and κ -phase BEDT-TTF and BEDT-TSF organic salts. Contrary to the assumption that SOC in organics is negligible due to light C, S, and H atoms, we show the relevance of such an interaction in a few representative cases. In the weakly correlated regime, SOC manifests primarily in the opening of energy gaps at degenerate band touching points. This effect becomes especially important for Dirac semimetals such as α -(ET) 2I3 . Furthermore, in the magnetic insulating phase, SOC results in additional anisotropic exchange interactions, which provide a compelling explanation for the puzzling field-induced behavior of the quantum spin-liquid candidate κ -(ET) 2Cu2(CN) 3 . We conclude by discussing the importance of SOC for the description of low-energy properties in organics.

  10. 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.

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

    PubMed

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

    2013-12-02

    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-T(c) cuprate superconductors a fluctuating superconducting state persists to temperatures significantly above T(c). 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.

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

    PubMed

    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.

  13. LETTER TO THE EDITOR: Mixed order parameters, accidental nodes and broken time reversal symmetry in organic superconductors: a group theoretical analysis

    NASA Astrophysics Data System (ADS)

    Powell, B. J.

    2006-11-01

    We present a group theoretical analysis of several classes of organic superconductor. We predict that highly frustrated organic superconductors, such as κ-(ET)2Cu2(CN)3 (where ET is BEDT-TTF, bis(ethylene-dithio)tetrathiafulvalene) and β'-[Pd(dmit)2]2X, undergo two superconducting phase transitions, the first from the normal state to a d-wave superconductor and the second to a d+id state. We show that the monoclinic distortion of κ-(ET)2Cu(NCS)2 means that the symmetry of its superconducting order parameter is different from that of orthorhombic κ-(ET)2Cu[N(CN)2]Br. We propose that β'' and θ phase organic superconductors have dxy+s order parameters.

  14. Efros-Shklovskii Coulomb gap in the absence of disorder

    NASA Astrophysics Data System (ADS)

    Rademaker, Louk; Mahmoudian, Samiyeh; Ralko, Arnaud; Fratini, Simone; Dobrosavljevic, Vladimir

    2015-03-01

    Certain models of frustrated electron systems have been shown to self-generate glassy behavior, in the absence of disorder. Possible candidate materials contain quarter-filled triangular lattices with long-range Coulomb interactions, as found in the θ-family of organic BEDT-TTF crystals. In disordered insulators with localized electronic states, the so-called Coulomb glass, the single particle excitation spectrum displays the well-known Efros-Shklovskii gap. The same excitation spectrum is investigated in a class of models that display self-generated electronic glassiness, showing pseudogap formation related to the Efros-Shklovskii Coulomb gap. Our study suggests universal characteristics of all electron glasses, regardless of disorder.

  15. Glassy Dynamics in Geometrically Frustrated Coulomb Liquids without Disorder

    NASA Astrophysics Data System (ADS)

    Mahmoudian, Samiyeh; Rademaker, Louk; Ralko, Arnaud; Fratini, Simone; Dobrosavljević, Vladimir

    2015-07-01

    We show that introducing long-range Coulomb interactions immediately lifts the massive ground state degeneracy induced by geometric frustration for electrons on quarter-filled triangular lattices in the classical limit. Important consequences include the stabilization of a stripe-ordered crystalline (global) ground state, but also the emergence of very many low-lying metastable states with amorphous "stripe-glass" spatial structures. Melting of the stripe order thus leads to a frustrated Coulomb liquid at intermediate temperatures, showing remarkably slow (viscous) dynamics, with very long relaxation times growing in Arrhenius fashion upon cooling, as typical of strong glass formers. On shorter time scales, the system falls out of equilibrium and displays the aging phenomena characteristic of supercooled liquids above the glass transition. Our results show remarkable similarity with the recent observations of charge-glass behavior in ultraclean triangular organic materials of the θ -(BEDT -TTF )2 family.

  16. Glassy Dynamics in Geometrically Frustrated Coulomb Liquids without Disorder.

    PubMed

    Mahmoudian, Samiyeh; Rademaker, Louk; Ralko, Arnaud; Fratini, Simone; Dobrosavljević, Vladimir

    2015-07-10

    We show that introducing long-range Coulomb interactions immediately lifts the massive ground state degeneracy induced by geometric frustration for electrons on quarter-filled triangular lattices in the classical limit. Important consequences include the stabilization of a stripe-ordered crystalline (global) ground state, but also the emergence of very many low-lying metastable states with amorphous "stripe-glass" spatial structures. Melting of the stripe order thus leads to a frustrated Coulomb liquid at intermediate temperatures, showing remarkably slow (viscous) dynamics, with very long relaxation times growing in Arrhenius fashion upon cooling, as typical of strong glass formers. On shorter time scales, the system falls out of equilibrium and displays the aging phenomena characteristic of supercooled liquids above the glass transition. Our results show remarkable similarity with the recent observations of charge-glass behavior in ultraclean triangular organic materials of the θ-(BEDT-TTF)(2) family.

  17. Unconventional superconductors under a rotating magnetic field. II. Thermal transport

    NASA Astrophysics Data System (ADS)

    Vorontsov, A. B.; Vekhter, I.

    2007-06-01

    We present a microscopic approach to the calculations of thermal conductivity in unconventional superconductors for a wide range of temperatures and magnetic fields. Our work employs the nonequilibrium Keldysh formulation of the quasiclassical theory. We solve the transport equations using a variation of the Brandt-Pesch-Tewordt method that accounts for the quasiparticle scattering on vortices. We focus on the dependence of the thermal conductivity on the direction of the field with the respect to the nodes of the order parameter, and discuss it in the context of experiments aiming to determine the shape of the gap from such anisotropy measurements. We consider quasi-two-dimensional Fermi surfaces with vertical line nodes and use our analysis to establish the location of gap nodes in heavy-fermion CeCoIn5 and the organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 .

  18. Two-dimensional magnetic quantum oscillations observed in an organic metal

    SciTech Connect

    Hagel, J.; Wanka, S.; Wosnitza, J.; Balthes, E.; Schlueter, J. A.; Kini, A. M.; Geiser, U.; Mohtasham, J.; Winter, R. W.; Gard, G. L.

    2000-07-24

    The de Haas-van Alphen (dHvA) signal of the organic superconductor {beta}{double_prime}-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} shows an inverse-sawtooth wave form which proves the existence of an ideal two-dimensional (2D) Fermi surface. The dHvA wave shape can almost perfectly be described by a 2D theory assuming a constant chemical potential. This either implies the existence of the predicted quasi-one-dimensional band with an exceptionally large density of states or the chemical potential may be pinned due to localized states near the Fermi energy.

  19. Highly Mobile Metastable State of He-4 Thin Films: A Glass Transition by Mechanical Perturbation?

    NASA Astrophysics Data System (ADS)

    Minoguchi, Tomoki

    2017-06-01

    Solid layers of helium on graphite surface are known to go into a highly mobile state (HMS) once the solid layer is enforced to slip on the substrate. The HMS collapses to the stable inert state with the lifetime extending over 10^4 s. In this paper, we suggest that the HMS is a structural glass by showing the similarities between the present system and an organic conductor named BEDT-TTF. The latter was recently discovered to be an electronic glass if the cooling rate is rapid enough across the freezing temperature (Wigner crystal formation temperature). We then address a novel annealing process promoted by a local condensate which should be seen for the present He-4 case as the condensation fraction grows in the liquid overlayer.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Scaling Theory of the Mott Transition and Breakdown of the Gr"uneisen Scaling Near a Finite-Temperature Critical End Point

    NASA Astrophysics Data System (ADS)

    Bartosch, Lorenz

    2012-02-01

    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 Gr"uneisen 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.[2mm] [1] Lorenz Bartosch, Mariano de Souza, and Michael Lang, Physical Review Letters 104, 245701 (2010).

  5. Valley-selective Landau-Zener oscillations in semi-Dirac p -n junctions

    NASA Astrophysics Data System (ADS)

    Saha, K.; Nandkishore, R.; Parameswaran, S. A.

    2017-07-01

    We study transport across p -n junctions of gapped two-dimensional semi-Dirac materials: nodal semimetals whose energy bands disperse quadratically and linearly along distinct crystal axes. The resulting electronic properties—relevant to materials such as TiO2/VO2 multilayers and α -(BEDT-TTF)2I3 salts—continuously interpolate between those of mono- and bilayer graphene as a function of propagation angle. We demonstrate that tunneling across the junction depends on the orientation of the tunnel barrier relative to the crystalline axes, leading to strongly nonmonotonic current-voltage characteristics, including negative differential conductance in some regimes. In multivalley systems, these features provide a natural route to engineering valley-selective transport.

  6. Highly Mobile Metastable State of He-4 Thin Films: A Glass Transition by Mechanical Perturbation?

    NASA Astrophysics Data System (ADS)

    Minoguchi, Tomoki

    2017-01-01

    Solid layers of helium on graphite surface are known to go into a highly mobile state (HMS) once the solid layer is enforced to slip on the substrate. The HMS collapses to the stable inert state with the lifetime extending over 10^4 s. In this paper, we suggest that the HMS is a structural glass by showing the similarities between the present system and an organic conductor named BEDT-TTF. The latter was recently discovered to be an electronic glass if the cooling rate is rapid enough across the freezing temperature (Wigner crystal formation temperature). We then address a novel annealing process promoted by a local condensate which should be seen for the present He-4 case as the condensation fraction grows in the liquid overlayer.

  7. 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.

  8. Mott Metal-Insulator Transition on Compressible Lattices

    NASA Astrophysics Data System (ADS)

    Zacharias, Mario; Bartosch, Lorenz; Garst, Markus

    2012-10-01

    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*/Tc≃8%, close to the Mott end point of κ-(BEDT-TTF)2X.

  9. Experimental evaluation of the electron{endash}intramolecular-vibration coupling constants of tetramethyltetrathiafulvalene

    SciTech Connect

    Meneghetti, M.; Toffoletti, A.; Pasimeni, L.

    1996-12-01

    The relevant electron-intramolecular vibrations coupling constants of tetramethyltetrathiafulvalene (TMTTF) have been experimentally obtained. The determination was possible studying the optical properties of dimers of TMTTF{sup +} in polymethyl-methacrylate films on the basis of a Holstein-Hubbard dimer model. Electron paramagnetic resonance measurements of the singlet-triplet energy gap of the dimers made possible the calculation of the coupling constants without the need for absolute values of the optical spectra and the knowledge of structural parameters. The values of the coupling constants show differences with previously reported values for TMTTF or related molecules like TTF and bis-ethylenedithio-TTF (BEDT-TTF). {copyright} {ital 1996 The American Physical Society.}

  10. 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.

  11. 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.

  12. Plaquette chirality patterns for robust zero-gap states in α-type organic conductor

    NASA Astrophysics Data System (ADS)

    Piéchon, Frédéric; Suzumura, Yoshikazu; Morinari, Takao

    2015-04-01

    Dirac electrons with a zero-gap state (ZGS) in organic conductor α-(BEDT- TTF)2I3 result from a fine tuning of the seven nearest neighbors transfer integrals (a1,a2,a3,b1,b2,b3,b4) between the four molecules of the unit cell. In this work we show that for given moduli |a11,...|b41, the possibility of having Dirac electron with a ZGS at 3/4 (or 1/4) filling strongly depends on the specific configurations of signs of the seven transfer integral. More precisely it is possible to classify the sign configurations into essentially four classes determined by χa = sign(a2a3) and χb = sign(b1b2b3b4). Using extended numerics, we show that for both weak and large inhomogeneity in the moduli, the class (χa,χb) = (—, —) is the most favorable to find Dirac electrons with ZGS at 3/4 (or 1/4) filling. For the class (χa,χb) = (+, +) in the opposite case, we never found any ZGS at either 1/4 or 3/4 filling. The last two classes given by (χa,χb) = (+, —) and (χa,χb) = (—, +) corresponding to an intermediate situation; they allow for ZGS at 3/4 (resp. 1/4) filling but are much less favorable than class (χa, χb) = (—, —). As a matter of fact, all previous numerical studies of Dirac electrons and ZGS in α-(BEDT-TTF)2I3 correspond to class (χa,χb) = (—, +).

  13. Staggered Flux State in Two-Dimensional Hubbard Models

    NASA Astrophysics Data System (ADS)

    Yokoyama, Hisatoshi; Tamura, Shun; Ogata, Masao

    2016-12-01

    The stability and other properties of a staggered flux (SF) state or a correlated d-density wave state are studied for the Hubbard (t-t'-U) model on extended square lattices, as a low-lying state that competes with the dx2 - y2-wave superconductivity (d-SC) and possibly causes the pseudogap phenomena in underdoped high-Tc cuprates and organic κ-BEDT-TTF salts. In calculations, a variational Monte Carlo method is used. In the trial wave function, a configuration-dependent phase factor, which is vital to treat a current-carrying state for a large U/t, is introduced in addition to ordinary correlation factors. Varying U/t, t'/t, and the doping rate (δ) systematically, we show that the SF state becomes more stable than the normal state (projected Fermi sea) for a strongly correlated (U/t ≳ 5) and underdoped (δ ≲ 0.16) area. The decrease in energy is sizable, particularly in the area where Mott physics prevails and the circular current (order parameter) is strongly suppressed. These features are consistent with those for the t-J model. The effect of the frustration t'/t plays a crucial role in preserving charge homogeneity and appropriately describing the behavior of hole- and electron-doped cuprates and κ-BEDT-TTF salts. We argue that the SF state does not coexist with d-SC and is not a "normal state" from which d-SC arises. We also show that a spin current (flux or nematic) state is never stabilized in the same regime.

  14. 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.

  15. Large-N theory of the Sp(N) Heisenberg quantum antiferromagnet on an anisotropic triangular lattice

    NASA Astrophysics Data System (ADS)

    Chung, Chung-Hou; Marston, Brad

    2000-03-01

    The magnetic properties of the two-dimensional layered organic superconductors κ-(BEDT-TTF)_2X are modeled by a spin-1/2 Heisenberg quantum antiferromagnet on an anisotropic triangular lattice. The phase diagram is ascertained by means of a large-N expansion of the Sp(N) generalization of the physical SU(2) \\cong Sp(1) Heisenberg magnet.(S. Sachdev and N. Reed, Int. J. Mod. Phys. B5), 219 (1991). The phase diagram is presented in the two-dimensional parameter space of J_1/J_2, the ratio of the nearest to next-nearest neighbor Heisenberg exchange, and the ratio nb / N, which sets the strength of the quantum fluctuations. At large nb / N (equivalent to the large-spin limit of the physical SU(2) model) quantum effects are small, the ground states break global Sp(N) spin-rotational symmetry, and exhibit magnetic long-range-order (LRO). At small nb / N, however, quantum fluctuations overwhelm the tendency to order and there is only short-range magnetic order (SRO). The LRO and SRO phases can be further classified into two types depending on the size of the anisotropy: (i) ground states with commensurate, collinear, spin correlations; and (ii) ground states with incommensurate, coplanar, spin correlations. Finite-N corrections due to a Berry's phase term modify the character of the SRO phases, leading in the case of the commensurate state to spin-Peierls order and the confinement of spinons.

  16. Charge Ordered Insulator without Magnetic Order Studied by Correlator Projection Method

    NASA Astrophysics Data System (ADS)

    Hanasaki, Kota; Imada, Masatoshi

    2005-10-01

    The Hubbard model with additional intersite interaction ‘V’ (the extended Hubbard model) is investigated by the correlator projection method (CPM). CPM is a newly developed numerical method that combines the equation-of-motion approach and the dynamical mean-field theory. Using this method, properties of the extended Hubbard Model at quarter filling are discussed with special emphasis on the metal-insulator transition induced by electron-electron correlations. As we increase the interaction, a metal-insulator transition to a charge ordered insulator with antiferromagnetic order occurs at low temperatures, but a metal-insulator transition to a charge ordered insulator without magnetic symmetry breaking occurs at intermediate temperatures. Here, the magnetic order is found to be confined to low temperatures because of the smallness of the exchange coupling Jeff. The present results are in sharp contrast to the Hatree--Fock approximation whereas they are in agreement with the experimental results on quarter-filled materials with strong correlations such as organic BEDT-TTF conductors.

  17. NMR evidence of a high field phase transition in κ-(ET)Cu(NCS)2

    NASA Astrophysics Data System (ADS)

    Wright, Jeffrey; Clark, W. C.; Prettner, Elizabeth; Kuhns, Phil; Reyes, Arneil; Brooks, J. S.; Schlueter, John; Brown, Stuart

    2010-03-01

    The anisotropic electronic properties of the organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 make it an excellent candidate for inhomogeneous superconductivity (FFLO state) when the magnetic field is applied in-plane, so as to avoid orbital suppression of the superconductivity. Results of various previous measurements have been interpreted as supporting the existence of an FFLO state for fields B˜21-22T. In this work, ^13C NMR measurements were used to probe the hyperfine fields in the range of B=14-27T and T=0.5-1.6K. A sharp peak in the relaxation rate 1/T1(B) at B˜22T signals a phase transition associated with a turn-on of spin susceptibility, while evolution the spectrum with field indicate the system remains superconducting at higher fields. Additionally, only small variations of the hyperfine fields are observed for external fields B=14-20T, and we discuss this observation in relation to the superconducting order parameter symmetry.

  18. Calorimetric Measurements of Magnetic-Field-Induced Inhomogeneous Superconductivity Above the Paramagnetic Limit

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

    We report the first magnetocaloric and calorimetric observations of a magnetic-field-induced phase transition within a superconducting state to the long-sought exotic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state, first predicted over 50 years ago. Through the combination of bulk thermodynamic calorimetric and magnetocaloric measurements in the organic superconductor κ -(BEDT -TTF )2Cu (NCS )2 as a function of temperature, magnetic field strength, and magnetic field orientation, we establish for the first time that this field-induced first-order phase transition at the paramagnetic limit Hp is a transition to a higher-entropy superconducting phase, uniquely characteristic of the FFLO state. We also establish that this high-field superconducting state displays the bulk paramagnetic ordering of spin domains required of the FFLO state. These results rule out the alternate possibility of spin-density wave ordering in the high-field superconducting phase. The phase diagram determined from our measurements—including the observation of a phase transition into the FFLO phase at Hp—is in good agreement with recent NMR results and our own earlier tunnel-diode magnetic penetration depth experiments but is in disagreement with the only previous calorimetric report.

  19. Calorimetric Measurements of Magnetic-Field-Induced Inhomogeneous Superconductivity Above the Paramagnetic Limit.

    PubMed

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

    2017-06-30

    We report the first magnetocaloric and calorimetric observations of a magnetic-field-induced phase transition within a superconducting state to the long-sought exotic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state, first predicted over 50 years ago. Through the combination of bulk thermodynamic calorimetric and magnetocaloric measurements in the organic superconductor κ-(BEDT-TTF)_{2}Cu(NCS)_{2} as a function of temperature, magnetic field strength, and magnetic field orientation, we establish for the first time that this field-induced first-order phase transition at the paramagnetic limit H_{p} is a transition to a higher-entropy superconducting phase, uniquely characteristic of the FFLO state. We also establish that this high-field superconducting state displays the bulk paramagnetic ordering of spin domains required of the FFLO state. These results rule out the alternate possibility of spin-density wave ordering in the high-field superconducting phase. The phase diagram determined from our measurements-including the observation of a phase transition into the FFLO phase at H_{p}-is in good agreement with recent NMR results and our own earlier tunnel-diode magnetic penetration depth experiments but is in disagreement with the only previous calorimetric report.

  20. 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).

  1. de Haas-van Alphen studies and Fermi surface properties of organic superconductors (ET)[sub 2]X

    SciTech Connect

    Wosnitza, J. . Physikalisches Inst.); Crabtree, G.W.; Williams, J.M.; Wang, H.H.; Carlson, K.D.; Geiser, U. )

    1993-04-01

    de Haas-van Alphen (dHvA) measurements of organic superconductors (ET)[sub 2]X, where ET stands for bis(ethylene)dithiotetrathiafulvalene (or BEDT-TTF) and X = IBr[sub 2], (NH[sub 4])Hg(SCN)[sub 4] and Cu(NCS)[sub 2] are reported. The strong two-dimensionality of the Fermi surface (FS) is clearly seen by the perfect 1/cos([Theta])-behavior of the dHvA frequency. The distinctive kind of beating and the angular dependence of the dHvA signal in [beta]-(ET)[sub 2]IBr[sub 2] gives clear evidence for a lightly corrugated structure of the FS. Due to the nearly cylinder-shape of the FS the bare band structure effective mass, m[sub b], also shows a 1/cos([Theta])-dependence which is responsible for spin splitting zeros at certain angles. At these points, where the fundamental amplitude of the dHvA signal is vanishing, m[sub b] could exactly be determined and by comparison with the independently measured cyclotron effective mass the electron-phonon coupling constant could be estimated. 17 refs, 5 figs.

  2. de Haas-van Alphen studies and Fermi surface properties of organic superconductors (ET){sub 2}X

    SciTech Connect

    Wosnitza, J.; Crabtree, G.W.; Williams, J.M.; Wang, H.H.; Carlson, K.D.; Geiser, U.

    1993-04-01

    de Haas-van Alphen (dHvA) measurements of organic superconductors (ET){sub 2}X, where ET stands for bis(ethylene)dithiotetrathiafulvalene (or BEDT-TTF) and X = IBr{sub 2}, (NH{sub 4})Hg(SCN){sub 4} and Cu(NCS){sub 2} are reported. The strong two-dimensionality of the Fermi surface (FS) is clearly seen by the perfect 1/cos({Theta})-behavior of the dHvA frequency. The distinctive kind of beating and the angular dependence of the dHvA signal in {beta}-(ET){sub 2}IBr{sub 2} gives clear evidence for a lightly corrugated structure of the FS. Due to the nearly cylinder-shape of the FS the bare band structure effective mass, m{sub b}, also shows a 1/cos({Theta})-dependence which is responsible for spin splitting zeros at certain angles. At these points, where the fundamental amplitude of the dHvA signal is vanishing, m{sub b} could exactly be determined and by comparison with the independently measured cyclotron effective mass the electron-phonon coupling constant could be estimated. 17 refs, 5 figs.

  3. Electronic structure of some β-(C10H8S8)2X compounds as studied by infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Jacobsen, C. S.; Tanner, D. B.; Williams, Jack M.; Geiser, U.; Wang, H. H.

    1987-06-01

    Polarized reflectance measurements have been made on two isostructural conducting compounds of bis(ethylenedithio)tetrathiafulvalene [BEDT-TTF or ET, (C10H8S8)]: β-(ET)2AuI2 and β-(ET)2I2Br. The former is superconducting at ambient pressure with Tc=5 K, whereas the latter retains normal-metal conductivity to low temperatures. The reflectance measurements, made at temperatures of approximately 30 and 300 K, spanned 80 cm-1 (0.01 eV) through 33 000 cm-1 (~4 eV); they were made for polarization along the ET molecular stacking axis and transverse to it in the sheets or layers of ET molecules. Band-structure parameters determined from the plasmon frequencies imply that the anisotropy is rather low for organic conductors, with t~=0.22 eV and t⊥~=0.09 eV for β-(ET)2AuI2 t~=0.18 eV and t⊥~=0.07 eV for β-(ET)2I2Br. At 300 K, the spectra differ substantially from the expectations of simple one-electron models, suggesting that both electron-phonon and electron-electron interactions play important roles in the electronic structure of these materials. At low temperatures, the materials display basically metallic characteristics, yet deviate significantly from simple Drude-model behavior. At 30 K, no effect attributable to superconducting fluctuations could be observed.

  4. Rational design of organic superconductors through the use of the large, discrete molecular anions M(CF{sub 3}){sub 4}{sup -}(M = Cu, Ag, Au) and SO{sub 3}CF{sub 2}CH{sub 2}SF{sub 5}{sup -}

    SciTech Connect

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

    1996-10-01

    A new approach to synthesis of organic superconductors has recently been pioneered which involves the use of large discrete molecular anions as the charge-compensating entities in these charge transfer salts. The organic electron-donor molecule bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) has been electrocrystallized with the novel organometallic M(CF{sub 3}){sub 4}{sup -} (M=Cu, Ag, Au) anions in a variety of 1,1,2-trihaloethane solvents. Over 20 organic superconductors have been synthesized which can be described by (ET){sub 2}M(CF{sub 3}){sub 4}(1,1,2- trihaloethane). These solvated salts are shown to have highly anisotropic physical properties which can be tuned via modifications of each of their three molecular components: ET electron donor molecule, M(CF{sub 3}){sub 4}{sup -} anion, and neutral 1,1,2- trihaloethane solvent molecule. Superconductivity has also been observed in an ET salt containing the discrete SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}{sup -} anion with onset temperature near 5.2 K.

  5. Pairing symmetries in a Hubbard model on an anisotropic triangular lattice

    NASA Astrophysics Data System (ADS)

    Watanabe, Tsutomu; Yokoyama, Hisatoshi; Tanaka, Yukio; Inoue, Jun-ichiro

    2007-10-01

    To consider the paring symmetry formed in organic compounds κ-(BEDT-TTF)2X, we study the half-filled-band Hubbard model on an anisotropic triangular lattice (t in two bond directions and t‧ in the other), using an optimization VMC method. As trial states, we adopt a coexisting state of an antiferromagnetic (AF) order and the dx2-y2 -wave RVB gap, in addition to the d + id- and d + d-wave gap states. In these states, we take account of the effect of band (or Fermi surface) renormalization. Magnetic Mott transitions occur, and a regime of robust superconductivity could not be found, in contrast with our previous study. In the insulating regime, the coexisting state in which an AF order prevails is always the lowest-energy state up to remarkably large t‧/t (≲1.3), whereas a dxy-wave RVB state becomes predominant when t‧/t exceeds this value. In the insulating regime, the effective Fermi surface, determined by the renormalized value t˜‧ / t , is markedly renormalized into different directions according to t‧/t; for t‧/t ≲ 1.3, it approaches that of the square lattice (t˜‧ / t = 0) , whereas for t‧/t ≳ 1.3, it becomes almost one-dimensional (t˜‧ / t≫ 1) .

  6. Temperature dependence of the magnetic moment relaxation rate of the organic superconductor x-(BEDT-TFF){sub 2}Cu[N(CN){sub 2}]Cl{sub 0.5}Br{sub 0.5}

    SciTech Connect

    Primenko, A.E.; Kuznetsov, V.D.; Metlushko, V.V.; Mendeleev, D.V.; Kushch, N.D.; Yagubskii, E.B.

    1994-06-01

    The authors have investigated relaxation of the residual magnetic moment of x-(BEDT-TTF){sub 2}Cu[N(CN){sub 2}]Cl{sub 0.5}Br{sub 0.5}, an organic superconductor, in the temperature range 2.4 to 9.5 K. In these investigations, they observed that the reduced relaxation rate S=d 1n P{sub m}/dt ln t remains constant for T/T{sub c} < 0.7, and then increases rapidly with T. They also determined the temperature dependence of the critical current density in zero magnetic field. In comparing the functions s(T) and J{sub c}(T) for this superconductor with their counterparts for single-crystal high-temperature superconductors, they have found that their behavior is most analogous to that of s(T) and J{sub c}(T) for YBaCuO. Using the relaxation curves, they have calculated the current-voltage characteristics E(J), which are well-described by a power law function of the type E{proportional_to}J{sup n}. 15 refs., 7 figs.

  7. Critical Behavior in Doping-Driven Metal-Insulator Transition on Single-Crystalline Organic Mott-FET.

    PubMed

    Sato, Yoshiaki; Kawasugi, Yoshitaka; Suda, Masayuki; Yamamoto, Hiroshi M; Kato, Reizo

    2017-02-08

    We present the carrier transport properties in the vicinity of a doping-driven Mott transition observed at a field-effect transistor (FET) channel using a single crystal of the typical two-dimensional organic Mott insulator κ-(BEDT-TTF)2CuN(CN)2Cl (κ-Cl). The FET shows a continuous metal-insulator transition (MIT) as electrostatic doping proceeds. The phase transition appears to involve two-step crossovers, one in Hall measurement and the other in conductivity measurement. The crossover in conductivity occurs around the conductance quantum e(2)/h, and hence is not associated with "bad metal" behavior, which is in stark contrast to the MIT in half-filled organic Mott insulators or that in doped inorganic Mott insulators. Through in-depth scaling analysis of the conductivity, it is found that the above carrier transport properties in the vicinity of the MIT can be described by a high-temperature Mott quantum critical crossover, which is theoretically argued to be a ubiquitous feature of various types of Mott transitions.

  8. Assignment of the in-plane molecular vibrations of the electron-donor molecule BDT-TTP based on polarized Raman and infrared spectra, in which BDT-TTP is 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene

    NASA Astrophysics Data System (ADS)

    Ouyang, J.; Yakushi, K.; Kinoshita, T.; Nanbu, N.; Aoyagi, M.; Misaki, Y.; Tanaka, K.

    2002-06-01

    Infrared and Raman spectra of 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TTP) and 1,3,4,6-tetrathiapentalene-2,5-dione (TTP-DO) are reported. The vibrational modes of TTP-DO are assigned with the aid of the depolarization ratio of solution Raman spectra, polarized reflection spectra and polarized Raman spectra. A D2h symmetry is assumed for the BDT-TTP molecule and its in-plane fundamental vibrations are assigned with the aid of the polarization ratio and the correlation with TTP-DO, tetrathiafulvalene (TTF), tetramethyltetrathiafulvalene (TMTTF) and bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF). Normal coordinate calculation with a modified internal valence force field was carried out for the in-plane fundamental vibrations of TTP-DO and BDT-TTP. Ab initio calculations of the normal modes of BDT-TTP 0 and BDT-TTP + are compared with the empirical analysis.

  9. 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

  10. 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.

  11. Novel Quantum Criticality in Two Dimensional Topological Phase transitions.

    PubMed

    Cho, Gil Young; Moon, Eun-Gook

    2016-01-21

    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.

  12. Photoinduced Enhancement of Anisotropic Charge Correlations on Triangular Lattices with Trimers

    NASA Astrophysics Data System (ADS)

    Yonemitsu, Kenji

    2017-02-01

    To explore nontrivial photoinduced modulations of charge correlations, we theoretically study photoinduced dynamics in quarter-filled extended Hubbard models with competing intersite repulsive interactions on triangular lattices with trimers, where the end points are crystallographically equivalent. The exact diagonalization method is used and the time-dependent Schrödinger equation is numerically solved during and after photoexcitation. Time-averaged double occupancy and intersite density-density correlations can be interpreted as due to effective on-site and intersite repulsive interactions, respectively, relative to transfer energies. In the case where the intersite repulsive interactions compete with each other, the anisotropy of their effective interactions can be enhanced with the help of the trimers, irrespective of whether the trimers are linear or bent. In particular, in the case where the arrangement of the trimers is close to that in α-(bis[ethylenedithio]-tetrathiafulvalene)2I3 [α-(BEDT-TTF)2I3] in the metallic phase, the effective on-site repulsion is enhanced relative to the transfer energies. The relevance of this theoretical finding to the experimentally observed optical freezing of charge motion is discussed.

  13. Breakdown of Hooke's law of elasticity at the Mott critical endpoint in an organic conductor.

    PubMed

    Gati, Elena; Garst, Markus; Manna, Rudra S; Tutsch, Ulrich; Wolf, Bernd; Bartosch, Lorenz; Schubert, Harald; Sasaki, Takahiko; Schlueter, John A; Lang, Michael

    2016-12-01

    The Mott metal-insulator transition, a paradigm of strong electron-electron correlations, has been considered as a source of intriguing phenomena. Despite its importance for a wide range of materials, fundamental aspects of the transition, such as its universal properties, are still under debate. We report detailed measurements of relative length changes ΔL/L as a function of continuously controlled helium-gas pressure P for the organic conductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl across the pressure-induced Mott transition. We observe strongly nonlinear variations of ΔL/L with pressure around the Mott critical endpoint, highlighting a breakdown of Hooke's law of elasticity. We assign these nonlinear strain-stress relations to an intimate, nonperturbative coupling of the critical electronic system to the lattice degrees of freedom. Our results are fully consistent with mean-field criticality, predicted for electrons in a compressible lattice with finite shear moduli. We argue that the Mott transition for all systems that are amenable to pressure tuning shows the universal properties of an isostructural solid-solid transition.

  14. Breakdown of Hooke’s law of elasticity at the Mott critical endpoint in an organic conductor

    PubMed Central

    Gati, Elena; Garst, Markus; Manna, Rudra S.; Tutsch, Ulrich; Wolf, Bernd; Bartosch, Lorenz; Schubert, Harald; Sasaki, Takahiko; Schlueter, John A.; Lang, Michael

    2016-01-01

    The Mott metal-insulator transition, a paradigm of strong electron-electron correlations, has been considered as a source of intriguing phenomena. Despite its importance for a wide range of materials, fundamental aspects of the transition, such as its universal properties, are still under debate. We report detailed measurements of relative length changes ΔL/L as a function of continuously controlled helium-gas pressure P for the organic conductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl across the pressure-induced Mott transition. We observe strongly nonlinear variations of ΔL/L with pressure around the Mott critical endpoint, highlighting a breakdown of Hooke’s law of elasticity. We assign these nonlinear strain-stress relations to an intimate, nonperturbative coupling of the critical electronic system to the lattice degrees of freedom. Our results are fully consistent with mean-field criticality, predicted for electrons in a compressible lattice with finite shear moduli. We argue that the Mott transition for all systems that are amenable to pressure tuning shows the universal properties of an isostructural solid-solid transition. PMID:27957540

  15. Spin susceptibility of Andreev bound states

    NASA Astrophysics Data System (ADS)

    Rosemeyer, B. M.; Vorontsov, Anton B.

    2016-10-01

    We calculate the electronic spin susceptibility and spin-lattice relaxation rate in a singlet superconductor near a pair-breaking surface, or in a domain wall of the order parameter. We directly link the presence of high-density Andreev bound states in the inhomogeneous region, combined with coherence factors, to the enhancement of the susceptibility above the normal state's value for certain q vectors. Besides the dominant peak at ferromagnetic vector q =0 , we find significant enhancement of antiferromagnetic correlations at vectors q ≲2 kf , with q along the domain wall in an S -wave superconductor, and across the domain wall in D -wave (nodes along the wall). These features are destroyed by applying a moderate Zeeman field that splits the zero-energy peak. We solve Bogoliubov-de Gennes equations in momentum space and discuss the deviation of our results from the lattice models investigated previously. Large enhancement of the spin-lattice relaxation rate T1-1 at the domain wall provides a clear signature of the quasiparticle bound states, and is in good agreement with recent experiment in organic superconductor κ -(BEDT-TTF ) 2Cu (NCS) 2 .

  16. Universal scaling law for the condensation energy across a broad range of superconductor classes

    NASA Astrophysics Data System (ADS)

    Kim, J. S.; Tam, G. N.; Stewart, G. R.

    2015-12-01

    One of the goals in understanding any new class of superconductors is to search for commonalities with other known superconductors. The present work investigates the superconducting condensation energy, U , in the iron based superconductors (IBSs), and compares their U with a broad range of other distinct classes of superconductor, including conventional BCS elements and compounds and the unconventional heavy fermion, S r2Ru O4 ,L i0.1ZrNCl ,κ -(BEDT-TTF)2Cu (NCS )2 , and optimally doped cuprate superconductors. Surprisingly, both the magnitude and Tc dependence (U ∝Tc3.4 ±0.2 ) of U are—contrary to the previously observed behavior of the specific heat discontinuity at Tc, Δ C —quite similar in the IBS and BCS materials for Tc>1.4 K. In contrast, the heavy fermion superconductors' U vs Tc are strongly (up to a factor of 100) enhanced above the IBS/BCS while the cuprate superconductors' U are strongly (factor of 8) reduced. However, scaling of U with the specific heat γ (or Δ C ) brings all the superconductors investigated onto one universal dependence upon Tc. This apparent universal scaling U / γ ∝Tc2 for all superconductor classes investigated, both weak and strong coupled and both conventional and unconventional, links together extremely disparate behaviors over almost seven orders of magnitude for U and almost three orders of magnitude for Tc. Since U has not yet been explicitly calculated beyond the weak coupling limit, the present results can help direct theoretical efforts into the medium and strong coupling regimes.

  17. Pseudogap and singlet formation in organic and cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Merino, J.; Gunnarsson, O.

    2014-06-01

    -energy excitations determining the pseudogap have suppressed d-wave pairing, indicating that the pseudogap can be related to breaking very short-range d-wave pairs. Geometrical frustration on the anisotropic triangular lattice relevant to κ-(BEDT-TTF)2X leads to a switch in the character of the ground state of the cluster at intermediate hopping ratios t'/t˜0.7. Electron doping of the frustrated square lattice destroys the pseudogap, in agreement with photoemission experiments on cuprates, due to a larger Schrieffer-Wolff exchange coupling, JK, and a stronger cluster-bath coupling for the antinodal point.

  18. 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

  19. 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

  20. 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