1,368 research outputs found

    Electron localization near Mott transition in organic superconductor κ\kappa-(BEDT-TTF)2_{2}Cu[N(CN)2]_{2}]Br

    Full text link
    The effect of disorder on the electronic properties near the Mott transition is studied in an organic superconductor κ\kappa-(BEDT-TTF)2_{2}Cu[N(CN)2_{2}]Br, which is systematically irradiated by X-ray. We observe that X-ray irradiation causes Anderson-type electron localization due to molecular disorder. The resistivity at low temperatures demonstrates variable range hopping conduction with Coulomb interaction. The experimental results show clearly that the electron localization by disorder is enhanced by the Coulomb interaction near the Mott transition.Comment: 5 pages, 4 figure

    Magnetic and Electronic Phase Diagram and Superconductivity in the Organic Superconductors k-(BEDT-TTF)2X

    Get PDF
    The magnetic susceptibility of the organic superconductors κ\kappa-(h8 or d8-ET)2_{2}XX, X=X = Cu(NCS)2_{2} and Cu[N(CN)2_{2}]Br has been studied. A metallic phase below T=T^{*} = 37 \sim 38 K for X=X = Cu[N(CN)2_{2}]Br and 46 \sim 50 K for X=X = Cu(NCS)2_{2} has an anisotropic temperature dependence of the susceptibility and the charge transport. Partial charge-density-wave or charge fluctuation is expected to coexist with the metallic phase instead of the large antiferromagnetic fluctuation above TT^{*}. The phase diagram and the superconductivity of κ\kappa-(ET)2_{2}XX are discussed in connection with this phase.Comment: 5 pages, 4figures, REVTeX, references are corrected, accepted for pubication in Phys. Rev.

    Imaging phase separation near the Mott boundary in the correlated organic superconductors κ\kappa-(BEDT-TTF)2_{2}X

    Get PDF
    Electronic phase separation consisting of the metallic and insulating domains with 50 -- 100 μ\mum in diameter is found in the organic Mott system κ\kappa-[(hh8-BEDT-TTF)1x_{1-x}(dd8-BEDT-TTF)x_{x}]2_{2}Cu[N(CN)2_{2}]Br by means of scanning micro-region infrared spectroscopy using the synchrotron radiation. The phase separation appears below the critical end temperature 35 -- 40 K of the first order Mott transition. The observation of the macroscopic size of the domains indicates a different class of the intrinsic electronic inhomogeneity from the nano-scale one reported in the inorganic Mott systems such as High-TcT_{c} copper and manganese oxides.Comment: 4 pages, 3 figure

    Low temperature vortex liquid states induced by quantum fluctuations in the quasi two dimensional organic superconductor kappa-(BEDT-TTF)_{2} Cu(NCS)_{2}

    Get PDF
    We report the transport properties in the vortex liquid states induced by quantum fluctuations at low temperature in the layered organic superconductor kappa-(BEDT-TTF)_{2} Cu(NCS)_{2}. A steep drop of the resistivity observed below about 1 K separates the liquid state into two regions. In the low resistance state at lower temperature, a finite resistivity with weak temperature dependence persists down to 100 mK at least. The finite resistivity in the vortex state at T ~= 0 K indicates the realization of quantum vortex liquid assisted by the strong quantum fluctuations instead of the thermal one. A possible origin for separating these liquid states is a remnant vortex melting line at the original position, which is obscured and suppressed by the quantum fluctuations. A non-linear behavior of the in-plane resistivity appears at large current density in only the low resistance state, but not in another vortex liquid state at higher temperature, where the thermal fluctuations are dominant. The transport properties in the low resistance state are well understood in the vortex slush concept with a short-range order of vortices. Thus the low resistance state below 1 K is considered to be a novel quantum vortex slush state.Comment: 7 pages, 5 figure

    Relaxor ferroelectricity induced by electron correlations in a molecular dimer Mott insulator

    Full text link
    We have investigated the dielectric response in an antiferromagnetic dimer-Mott insulator beta'-(BEDT-TTF)2ICl2 with square lattice, compared to a spin liquid candidate kappa-(BEDT-TTF)2Cu2(CN)3. Temperature dependence of the dielectric constant shows a peak structure obeying Curie-Weiss law with strong frequency dependence. We found an anisotropic ferroelectricity by pyrocurrent measurements, which suggests the charge disproportionation in a dimer. The ferroelectric actual charge freezing temperature is related to the antiferromagnetic interaction, which is expected to the charge-spin coupled degrees of freedom in the system.Comment: 5 pages, 4 figures, to be published in Phys. Rev.

    Optical probe of carrier doping by X-ray irradiation in organic dimer Mott insulator κ\kappa-(BEDT-TTF)2_{2}Cu[N(CN)2]_{2}]Cl

    Get PDF
    We investigated the infrared optical spectra of an organic dimer Mott insulator κ\kappa-(BEDT-TTF)2_{2}Cu[N(CN)2_{2}]Cl, which was irradiated with X-rays. We observed that the irradiation caused a large spectral weight transfer from the mid-infrared region, where interband transitions in the dimer and Mott-Hubbard bands take place, to a Drude part in a low-energy region; this caused the Mott gap to collapse. The increase of the Drude part indicates a carrier doping into the Mott insulator due to irradiation defects. The strong redistribution of the spectral weight demonstrates that the organic Mott insulator is very close to the phase border of the bandwidth-controlled Mott transition.Comment: 4 pages, 4 figure

    Phase separation in the vicinity of the surface of κ\kappa-(BEDT-TTF)2_2Cu[N(CN)2_2]Br by fast cooling

    Full text link
    Partial suppression of superconductivity by fast cooling has been observed in the organic superconductor κ\kappa-(BEDT-TTF)2_2Cu[N(CN)2_2]Br by two means: a marked sample size effect on the magnetic susceptibility and direct imaging of insulating regions by scanning microregion infrared reflectance spectroscopy. Macroscopic insulating regions are found in the vicinity of the crystalline surface after fast cooling, with diameters of 50--100 μ\mum and depths of a few μ\mum. The very large in-plane penetration depth reported to date (\sim 24--100 μ\mum) can be explained by the existence of the insulating regions.Comment: Several rhetoric alternations to avoid misleadings. 6 pages, 3 figures. to be publihsed in Phys. Rev.

    Mott transition and superconductivity in the strongly correlated organic superconductor κ\kappa-(BEDT-TTF)2_{2}Cu[N(CN)2]_{2}]Br

    Get PDF
    The magnetic field effect on the phase diagram of the organic Mott system κ\kappa-(BEDT-TTF)2_{2}Cu[N(CN)2_{2}]Br in which the bandwidth was tuned by the substitution of deuterated molecules was studied by means of the resistivity measurements performed in magnetic fields. The lower critical point of the first-order Mott transition, which ended on the upper critical field Hc2H_{\rm c2}-temperature plane of the superconductivity, was determined experimentally in addition to the previously observed upper critical end point. The lower critical end point moved to a lower temperature with the suppression of TcT_{\rm c} in magnetic fields and the Mott transition recognized so far as the SS-shaped curve reached T=T = 0 when H>Hc2H > H_{\rm c2} in the end.Comment: 5 pages, 4 figure
    corecore