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Mielke, C. H.; Harrison, N.; Rickel, D.G.; Lacerda, A.; Vestal, R.M.; Montgomery, L. K.

doi:10.1103/physrevb.56.r4309

Cited by 54 publications

(42 citation statements)

References 28 publications

(17 reference statements)

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“…Figure 21 shows that a preferable value would be around 9.5 K. resistance between the superconducting and normal behaviour. This effect is seen over a restricted temperature range in a number of Cu-containing κ-phase salts [74,141,142]; it is most noticeable when the current is driven in the interplane direction [141,142]. A weaker effect can be observed when the current is driven in-plane, but is suppressed when the number of defects in the sample is reduced [143,144].…”

Section: The Superconducting Phase Diagrammentioning

confidence: 99%

Quasi-two-dimensional organic superconductors: A review

Singleton¹,

Mielke²

2002

Contemporary Physics

179

194

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Abstract. We present a review of quasi-two-dimensional organic superconductors. These systems exhibit many interesting phenomena, including reduced dimensionality, strong electron-electron and electron-phonon interactions and the proximity of antiferromagnetism, insulator states and superconductivity. Moreover, it has been possible to measure the electronic bands of many of the organics in great detail, in contrast to the situation in other well-known systems in which similar phenomena occur. We describe the crystal structure and normal-state properties of the organics, before presenting the experimental evidence for and against exotic superconductivity mediated by antiferromagnetic fluctuations. Finally, three instances of field-induced unconventional superconductivity will be described.

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Section: The Superconducting Phase Diagrammentioning

confidence: 99%

Quasi-two-dimensional organic superconductors: A review

Singleton¹,

Mielke²

2002

Contemporary Physics

179

194

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“…Shubnikov -de Haas experiments have established the existence of a well defined Fermi surface in these materials [2,3], demonstrating the Fermi liquid character of the low energy quasiparticles. Below T c , the low temperature 13 C-NMR spinlattice relaxation rate varies as T 3 [4][5][6], the electronic specific heat coefficient exhibits a magnetic field dependence γ ∝ B 1/2 [7] and the thermal conductivity κ is linear in T [8]; evidences for nodes of the SC gap function on the Fermi surface.…”

mentioning

confidence: 91%

“…In contrast, in organics, the magnetic coupling is frustrated, due to the underlying anisotropic triangular lattice [13]. In addition, their Fermi surface consists of two disconnected pieces [2,3]. Therefore, it is not at all obvious whether, despite these numerous similarities to cuprates, spin fluctuations can bring about superconductivity in the organics.…”

mentioning

confidence: 99%

Pairing due to Spin Fluctuations in Layered Organic Superconductors

1998

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I show that for a κ-type organic (BEDT-TTF)2X molecular crystal, a superconducting state with Tc ≈ 10 K and gap nodes on the Fermi surface can be caused by short-ranged antiferromagnetic spin fluctuations. Using a two-band description for the anti-bonding orbitals on a BEDT-TTF dimer of the κ-type salt, and an intermediate local Coulomb repulsion between two holes on one dimer, the magnetic interaction and the superconducting gap-function are determined self consistently within the fluctuation exchange approximation. The pairing interaction is predominantly caused by interband coupling and additionally affected by spin excitations of the quasi one-dimensional band.Electronic mechanisms for superconductivity are of conceptual interest on their own and allow, in principle, large superconducting (SC) transition temperatures since electronic energy scales easily exceed phononic energies. In addition to the copper-oxide based hightemperature superconductors, heavy fermion superconductors like UPt 3 and UBe 13 , and the ruthenate compound Sr 2 RuO 4 , organic superconductors are candidates for a pairing mechanism which originates in strong electronic correlations in the normal state.The organic molecular crystals κ-(BEDT-TTF) 2 X (in the following abbreviated as κ-(ET) 2 X), are very anisotropic quasi two-dimensional superconductors with transition temperatures up to around 10 K, depending on pressure and the ion X, which can, for example, be I 3 , Cu[N(CN) 2 ]Br or Cu(SCN) 2 [1]. Shubnikov -de Haas experiments have established the existence of a well defined Fermi surface in these materials [2,3], demonstrating the Fermi liquid character of the low energy quasiparticles. Below T c , the low temperature 13 C-NMR spinlattice relaxation rate varies as T 3 [4-6], the electronic specific heat coefficient exhibits a magnetic field dependence γ ∝ B 1/2 [7] and the thermal conductivity κ is linear in T [8]; evidences for nodes of the SC gap function on the Fermi surface. All these results suggest that superconductivity is caused by a highly anisotropic and likely non-phononic pairing interaction. An electronic mechanism is also supported by the absence of an isotope shift of T c due to the C=C and C-S phonon modes, as observed by 34 S and 13 C= 13 C isotope substitution in the central part of the ET-molecule [9].It has been pointed out earlier that many anomalous normal state properties of layered organics strongly suggest the important role of electronic correlations [10][11][12] and that some, but not all, of these anomalies are in striking similarity to cuprate superconductors [13]. Particularly magneto-transport, the thermoelectric power, and the uniform magnetic susceptibility display similar behavior. Another resemblance is their proximity to an antiferromagnetic (AF) state, even though, in organics, frustration and strong in-plane anisotropies demonstrate differences between both systems. Particularly, due to the, by now established, dominant d x 2 −y 2 order parameter component [14], high-temperature superconductivit...

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“…In the absence of SOC, but retaining inversion symmetry, ∆ eff ∼ 0, and I α is expected to vanish at all fields. Nonetheless, F α oscillations are observed in κ-phase salts, often with I α I β in ET salts [40,42,43] and I α I β in Se-based BETS salts [44][45][46]. Assuming that ∆ eff arises primarily from SOC, we expect the ratio of breakdown fields…”

mentioning

confidence: 97%

Importance of spin-orbit coupling in layered organic salts

2017

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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, 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 controversial field-induced behaviour 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.Layered organic materials have long served as ideal systems for studying complex physical phenomena such as the interplay between charge and spin order, unconventional superconductivity, and, exotic phases emerging from strong electronic correlations [1][2][3][4]. In these systems, high compressibility and synthetic versatility allows fine tuning of the underlying interactions via physical and chemical pressure, thus providing access to many different ground states. For example, significant evidence has recently emerged for a quantum spin liquid (QSL) state in a number of triangular-lattice organics,However, the appearance of very small energy gaps, and field-induced anomalies in the former material remain essentially unexplained. Likewise, interest has recently grown in the α-phase materials α-(ET) 2 I 3 [10] and α-(BETS) 2 I 3 [11]. The former material has been argued to form, under pressure, a zero gap semimetal (ZGS) with the Fermi energy located at the intersection of a pair of tilted Dirac cones [10,12,13]. However, the low-energy electronic and magnetic response shows significant departure from theoretical expectations for simple Dirac systems [14,15]. An unexplored aspect is the effect of spin-orbit coupling (SOC) in these systems.For (inorganic) magnetic insulators, strong SOC may generate large anisotropic magnetic interactions, associated with exotic spin-liquid states discussed e.g. for the iridates and α-RuCl 3 [16][17][18][19][20][21][22]. In weakly correlated systems such as BiSb, Bi 2 Te 3 , etc. [23][24][25][26], SOC tends to open a gap in the bulk, and may lead to nontrivial band topology and associated exotic edge states. Such effects have rarely been considered for the organic ET salts, as the light C, S, H atoms provide only moderate SOC. Nonetheless, it is known that SOC plays a dominant role in the spin relaxation of graphene [27][28][29] and organic-based semiconductors [30], and may be relatively enhanced for orbitally degenerate systems [31]. Indeed, in this work, we argue, despite a weak relative magnitude, that SOC is relevant for the low-energy properties in selected (representative) organic salts. We discuss as primary examples, the α-phase Dirac semimetals, and κ-phase...

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Fermi-surface topology ofκ−(BEDT−TTF)

Cited by 54 publications

References 28 publications

Quasi-two-dimensional organic superconductors: A review

Quasi-two-dimensional organic superconductors: A review

Pairing due to Spin Fluctuations in Layered Organic Superconductors

Importance of spin-orbit coupling in layered organic salts

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