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Ambient Pressure Superconductivity in the   -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl Single Crystals

ISCOM’2005. Ambient Pressure Superconductivity in the   -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl Single Crystals. E.B. Yagubskii, N.D. Kushch, A.V. Kazakova, L.I. Buravov Institute of Problems of Chemical Physics of RAS, Chernogolovka, Moscow District, 142432 Russia.

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Ambient Pressure Superconductivity in the   -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl Single Crystals

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  1. ISCOM’2005 Ambient Pressure Superconductivity in the -(BEDT-TTF)2Cu[N(CN)2]Cl Single Crystals E.B. Yagubskii, N.D. Kushch, A.V. Kazakova, L.I. Buravov Institute of Problems of Chemical Physics of RAS, Chernogolovka, Moscow District, 142432 Russia • Isostructural radical cation salts -(BEDT-TTF)2Cu[N(CN)2]X, where X = Cl (-Cl), Br (-Br): structure and transport properties (TC = 11.6 K for -Br at P = 0 and 12.8 K for -Cl at 0.3 kbars;the Argonne group, Inorg. Chem., 1990, 29, 2555, 3272) • Synthesis of the crystals of-(BEDT-TTF)2Cu[N(CN)2]Cl (-Cl) • The structural distinctions between -Cl and -Cl crystals • Metallic conductivity and superconductivity of-Cl at ambient pressure • Upper critical magnetic fields: HC2(T)dependencies • Summary V.N. Zverev, A.I. Manakov, S.S. Khasanov, R.P. Shibaeva Institute of Solid State Physics of RAS, Chernogolovka, Moscow District, 142432 Russia Chernogolovka 2005

  2. b Conducting BEDT-TTF layer a Anion layer c -type BEDT-TTF layer Institute of Problems of Chemical Physics Institute of Solid State Physics Crystal Structure of Radical Cation Salts -(BEDT-TTF)2Cu[N(CN)2]X, where X = Cl (-Cl), Br (-Br)

  3. Metal Superconductor Institute of Problems of Chemical Physics Institute of Solid State Physics Resistivity behavior of -(BEDT-TTF)2X salts, where X = Cu[N(CN)2]Cl, Cu[N(CN)2]Br Temperature–pressure phase diagram of -(BEDT-TTF)2Cu[N(CN)2]Cl (P. Limelette et al., PRL,2003, 91, 016401)

  4. Institute of Problems of Chemical Physics Institute of Solid State Physics Synthesis of -(BEDT-TTF)2Cu[N(CN)2]Cl (-Cl)and  -(BEDT-TTF)2Cu[N(CN)2]Cl (-Cl) -Cl, the standard method (H. Wang et al.,Chem Mater., 1992, 4, 247): electro-oxidation of BEDT-TTF under constant current (0.1–0.5 A/cm2), solvent: 1,1,2-trichloroethane (TCE)+10 vol% absolute ethanol, electrolyte: a) CuCl + PPh4[N(CN)2]; b) CuCl + NaN(CN)2 +18-crown-6 ether; c) CuCl + PPh4[N(CN)2] + N(hexyl)4Cl; d) Cu[N(CN)2] +N(hexyl)4Cl. -Cl:electro-oxidation of BEDT-TTF under constant current (0.3 – 0.5 A, 0.9–1.5 A/cm2) in the presence of Cu[N(CN)2]2, solvent TCE + 10 vol% of 96% ethanol. For Mn[N(CN)2]2 as electrolyte, the crystals of the salt with a paramagnetic {Mn[N(CN)2]3} anion, (BEDT-TTF)2[Mn(dca)3], were obtained. In the case of Cu[N(CN)2]2 the crystals of '-Cl salt were formed together with the (BEDT-TTF)2CuCl2 ones as a minor product.

  5. Institute of Problems of Chemical Physics Institute of Solid State Physics Structural Data for the Single Crystals of κ-(BEDT-TTF)2Cu[N(CN)2]Cl 1 – the crystal of Mott insulator -Cl (data from U. Geiser et al., Physica C, 1991, 194, 475) 2 – the crystal of Mott insulator -Cl obtained by us 3 – the crystal of superconductor -Cl

  6. Institute of Problems of Chemical Physics Institute of Solid State Physics The temperature dependencies of longitudinal (J||(ac)) and transverse (J||b) resistance for -Cl crystal The electroresistance was measured by a four-probe technique at alternating current (20 Hz). The samples: thin plates with 1×0.3×0.02 mm characteristic sizes. The surface was oriented along the conducting layers (theac plane). Two contacts were made to each of two opposite sample surfaces with conducting graphite paste. Sample resistance was measured when current was applied both parallel (J||(ac)) and perpendicular (J||b) to conducting layers. The value of the current was not higher than 10A.

  7. Institute of Problems of Chemical Physics Institute of Solid State Physics Temperature dependencies for longitudinal (ас) and transverse (b) resistivities as well as the resistivity anisotropy (b/ас) for -Cl crystal The resistivities (b and ас) were calculated by the modified Montgomery method (L.I. Buravov, Sov. Phys. Tech. Phys., 1989, 34, 464). b / ac= 200 – 400 (at 300 K), b / ac= 1000 – 1400 (at 15 K).

  8. Institute of Problems of Chemical Physics Institute of Solid State Physics Superconducting transition in -(BEDT-TTF)2Cu[N(CN)2]Cl (-Cl) detected by the temperature dependencies of resistance and dynamic susceptibility ( in insert) The Tc = 11.5 K at ambient pressure for -Clcorrelates with the Tc of -Cl under pressure of 0.5 kbars as it follows from the pressure dependence of Tc for the -Cl, studied by Argonne group (J.M. Williams et al., Inorg. Chem., 1990, 29, 3272)

  9. Institute of Problems of Chemical Physics Institute of Solid State Physics Influence of external magnetic field on superconducting transition in -Cl when the current is applied parallel to conducting layers, Jac, and the magnetic field is applied perpendicular to them, Hb

  10. Institute of Problems of Chemical Physics Institute of Solid State Physics Influence of externalmagnetic field on superconducting transition in -Clwhen the current is applied perpendicular to conducting layers, Jb, and the magnetic field is applied parallel to them, Hac

  11. Institute of Problems of Chemical Physics Institute of Solid State Physics Influence of external magnetic field on superconducting transition in -Cl when the current and magnetic field are applied perpendicular to conducting layers, JHb

  12. Institute of Problems of Chemical Physics Institute of Solid State Physics Temperature dependencies of Hc2 for the external magnetic field orientations both parallel to conducting layers (Hac) and perpendicular to them (Hb) when the current was applied perpendicular to conducting layers (Jb) and there was no broadening of a superconducting transition All the points except one were obtained from the curve R(T) at fixed values of the field H. The last point in the lower curve was obtained from the curve R(H) at the fixed temperature T = 1.2 K. At Н||b the dHc2/dT derivative is close to zeroat Т = Тс(0). When magnetic field is along the(ас) plane, the derivative is finite and equal to dHc2 /dT Tc(0) = -1.36 T/K.

  13. Institute of Problems of Chemical Physics Institute of Solid State Physics Summary • For the first time the '-(BEDT-TTF)2Cu[N(CN)2]Сl ('-Сl) salt, which exhibits metallic conductivity and is ambient pressure superconductor, was obtained. • The '-Cl crystals showed some distinctions in structure as compared to that of the Mott insulator -Сl: smaller size of the unit cell and deficiency ( 6%) of the occupancy of Cu positions. An incomplete population of Cu positions can testify that Cu2+ is present along with Cu+ in anion sheets of '-Сl. The appearance of superconductivity in the '-Сl crystals at ambient pressure is probably due to the effect of “chemical compression”. • The temperature dependencies of upper critical magnetic fields for '-Сl crystals were studied and it was found that the curves have positive curvature for the external magnetic field applied both parallel and perpendicular to BEDT-TTF conducting layers.

  14. Institute of Problems of Chemical Physics Institute of Solid State Physics CONTRIBUTION N.D. Kushch, A.V. Kazakova – synthesis of crystals Institute of Problem of Chemical Physics, Chernogolovka L.I. Buravov – measurements of resistence Institute of Problem of Chemical Physics, Chernogolovka V.N. Zverev, A.I. Manakov  study of resistivity anisotropy and с2(Т) dependencies Institute of Solid State Physics, Chernogolovka R.P. Shibaeva, S.S. Khasanov  study of crystal structure Institute of Solid State Physics, Chernogolovka

  15. Institute of Problems of Chemical Physics Institute of Solid State Physics Temperature dependencies of the interlayer () and intralayer () resistivity of -Cl, calculated by modified Montgomery method, in the range of superconducting transition.Magnetic field (H) was applied perpendicular to the conducting layers, Hb

  16. Institute of Problems of Chemical Physics Institute of Solid State Physics Influence of magnetic field on superconducting transition when the current and the magnetic field are applied parallel to conducting layers, JHac

  17. Institute of Problems of Chemical Physics Institute of Solid State Physics The curves of superconducting transitions for the same '-Сl crystal when the current is applied parallel to conducting layers (Jac) and perpendicular to them (Jb)

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