DYNAMIC DISORDER AT INTERMEDIATE TEMPERATURE AND ITS EFFECT ON THE MAGNETIC PROPERTIES OF THE ORGANIC SUPERCONDUCTOR κ-(BEDTTTF) 2 Cu[N(CN) 2 ]Br (original) (raw)
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OAJ Materials and Devices, 2018
We report investigations of the low temperature dc susceptibility and the magnetization on the layered organic superconductor k-(BEDT-TTF)2Cu[N(CN)2]Br near 80 K and the effect of disorder on the superconducting transition temperature Tc. The shielding effect (S) and the critical current density Jc were studied (with H parallel to the c axis of the crystal). Jc can be estimated by analysis of magnetic hysteresis measurement using the Bean model. For each temperature value, we observed two regimes in the critical current density Jc(H). Our results show that the magnetic properties of these compounds depend strongly on the cooling rate. The structural transformation which occurs at the vicinity of 80 K very strongly influences the physics of vortex lattice and the associated magnetic behavior. #organic_superconductor #critical_current #shielding_effect #magnetic_susceptibility #vortex_pinning
Superconducting state in the layered organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br
Synthetic Metals, 1999
We summarize the main features of the magnetic field-temperature phase diagram for the superconducting state of K-(BEDT-TIl?)#&~(CN)JBr. The initial temperature dependence of the real component of ac susceptibility for field parallel and perpendicular to the ac plane are markedly different. The out-of-plane penetration depth Ai, and the related superfluid density vary at low tempeartures as T'. Slow flux dynamics below the irreversibility line for the ac field perpendicular to the BEDT-TTF planes might be ascribed to a vortex-pair creation process. The characteristic relaxation time 5 ~10'~ s is thermally activated with an activation energy of about 300K.
Physical Review B, 2002
We report high-sensitivity ac susceptibility measurements of the penetration depth in the Meissner state of the layered organic superconductor-(BEDT-TTF) 2 Cu͓N(CN) 2 ͔Br. We have studied nominally pure single crystals from the two different syntheses and employed controlled cooling procedures in order to minimize intrinsic remnant disorder at low temperatures associated with the glass transition, caused by ordering of the ethylene moieties in BEDT-TTF molecule at T G ϭ75 K. We find that the optimal cooling procedures ͑slow cooling of Ϫ0.2 K/h or annealing for 3 days in the region of T G) needed to establish the ground state depend critically on the sample origin, indicating different relaxation times of terminal ethylene groups. We show that, in the ground state, the behavior observed for nominally pure single crystals from both syntheses is consistent with unconventional d-wave order parameter. The in-plane penetration depth in (T) is strongly linear, whereas the out-of-plane component out (T) varies as T 2. In contrast, the behavior of single crystals with long relaxation times observed after slow (Ϫ0.2 K/h) cooling is as expected for a d-wave superconductor with impurities ͓i.e., in (T)ϰ out (T)ϰT 2 ] or might be also reasonably well described by the s-wave model. Our results might reconcile the contradictory findings previously reported by different authors.
2018
H. El Ouaddi1,*, A. Tirbiyine1, A. Taoufik1, Y. Ait Ahmed1, A. Hafid1, M. Mamor2, H. Chaib3, A. Nafidi3, S. Snoussi4 1E.M.S, Research Laboratory, Faculty of Science, University Ibn Zoh, Agadir, Morocco 2M.S.I.S.M, Research Laboratory, Polydisciplinary Faculty, University Cadi Ayyad, Safi, Morocco 3L.P.M.C.N.E.R, Research Laboratory, Faculty of Science, University Ibn Zoh, Agadir, Morocco 4Laboratoire de Physique des Solides, UMR 8502, Université Paris-Sud, Bat.510, 91405 Orsay, France *E-mail: hassanelouaddi@gmail.com
Physical Review B, 2004
We give a theoretical analysis of published experimental studies of the effects of impurities and disorder on the superconducting transition temperature, Tc, of the organic molecular crystals κ-(BEDT-TTF)2X (where X=Cu[N(CN)2]Br and Cu(NCS)2 and BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene) and β-(BEDT-TTF)2X (for X=I3 and IBr2). The Abrikosov-Gorkov (AG) formula describes the suppression of Tc both by magnetic impurities in singlet superconductors, including s-wave superconductors and by non-magnetic impurities in a non-s-wave superconductor. We show that various sources of disorder (alloying anions, fast electron irradiation, disorder accidentally produced during fabrication and cooling rate induced disorder) lead to the suppression of Tc as described by the AG formula. This is confirmed by the excellent fit to the data, the fact that these materials are in the clean limit and the excellent agreement between the value of the interlayer hopping integral, t ⊥ , calculated from this fit and the value of t ⊥ found from angular-dependant magnetoresistance and quantum oscillation experiments. There are only two scenarios consistent with the current state of experimental knowledge. If the disorder induced by all of the four methods considered in this paper is, as seems most likely, non-magnetic then the pairing state cannot be s-wave. We show that published measurements of the cooling rate dependence of the magnetisation are inconsistent with paramagnetic impurities. Triplet pairing is ruled out by NMR and upper critical field experiments. Thus if the disorder is non-magnetic then this implies that l ≥ 2, in which case Occam's razor suggests that d-wave pairing is realised in both β-(BEDT-TTF)2X and κ-(BEDT-TTF)2X. However, particularly given the proximity of these materials to an antiferromagnetic Mott transition, it is possible that the disorder leads to the formation of local magnetic moments via some novel mechanism. Thus we conclude that either β-(BEDT-TTF)2X and κ-(BEDT-TTF)2X are d-wave superconductors or else they display a novel mechanism for the formation of localised moments, possibly related to the competition between the antiferromagnetic and superconducting grounds states. We suggest systematic experiments to differentiate between these two scenarios.
Field dependence of the Hall effect in the organic superconductors κ-(BEDT-TTF)2Cu[N(CN)2]Cl1 − xBrx
Synthetic Metals, 1998
Hall voltage versus magnetic field curves were found to be nonlinear and to have temperature-dependent shape in the organic superconductors K-(BEDT-TTF) 2Cu [ N (CN) 2 ] CI1 _ A3r~ (BEDT-TTF = bis (ethylenedithio) tetrathiafutvalene). Close relation between the shape of the curves and structural anomalies in the salts was disclosed. The nonlinearity is assigned to magnetic ordering, causing or accompanying structural transformation. Changes of the Hall effect field dependence were used together with magnetic viscosity phenomena to plot a phase diagram of the salts. The main lines of the diagram could be traced through all compositions, irrespective of their resistance behavior. The results cast doubt on the decisive role of purely electronic instabilities in phase transformations in the material and are discussed in relation to the origin of magnetic order.
Acta Crystallographica Section B Structural Science, 1995
Anion Disorder in the 115-118 K Structures of the Organic Superconductors KL-(BEDT-TTF)2Cu(CF3)4(C2H3CI3) and KL-(BEDT-TTF)2Ag(CFa)4(C2HaCI 3) [BEDT-TTF-3,4;3',4'-Bis(ethylenedithio)-2,2',5,5'-tetrathiafulvalene]
Magnetic quantum oscillations in the organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br
Journal of Experimental and Theoretical Physics Letters, 1997
The interlayer magnetoresistance of the organic superconductor-͑BEDT-TTF͒ 2 Cu͓N͑CN͒ 2 ͔Br is measured at ambient pressure and under pressures of up to 12.5 kbar. In addition to the slow Shubnikov-de Haas oscillations with a frequency of Ӎ150 T observed at Pу5 kbar, rapid oscillations attributed to the magnetic breakdown orbit enveloping an area equal to 100% of the area of the Brillouin zone are found to emerge above Bϭ 20 T. The latter oscillations are observed at ambient pressure as well as under pressures of up to 9 kbar.
Microscopic Theory of Organic Superconductors
Journal of Superconductivity, 2000
A microscopic theory of organic superconductors based on the concept of partial electron dielectrization is developed from first principles. Self-consistent equations for the superconducting order parameter (⌬) and insulating order parameter (D) are derived using a Green's function technique and equation of motion method. The theory is applied to explain the experimental results in the two-dimensional organic superconductor k-(BEDT-TTF) 2 Cu(NCS) 2 . The present model explains coexistence of spin density wave (SDW) state and superconductivity state in the system. The behavior of superconducting order parameter (⌬), insulating order parameter (D), specific heat, density of state, free energy, and critical field is also studied for the system k-(BEDT-TTF) 2 Cu(NCS) 2 .
Diamagnetic properties of the organic superconductor κ-(BEDT-TTF)2Cu(NCS)2
Synthetic Metals, 1990
The static magnetization of a ~-(BEDT-TTF)2Cu(NCS): single crystal has been measured with an RF-SQUID magnetometer in the temperature range 2 K ~< T ~< 11 K in the external magnetic fields 0.1 Oe ~< H ~< 40 Oe. The obtained results are discussed within the critical state model. The lower critical field, H~I, and the critical current of magnetization, Jc, in the conducting plane are evaluated considering demagnetization effects. The temperature dependence of H~I is found to be linear down to 2 K with dH~l/dT =-21.50e K-l and H~I(0) ~-160 Oe. The deviation from the known BCS behaviour might be connected with the strong temperature dependence of the mean free path in the compound. An exponential temperature dependence of Jc is obtained below 6 K: Jc(T) = Jc0 exp(-~T), with Jc0 ~ 10s A cm-2 and ~ ~ 0.43 K-1.