Field-Induced Superconductivity in a Spin-Ladder Cuprate

Schön, J. H.; Dorget, M.; Beuran, F. C.; Xu, Xiang; Arushanov, E.; Laguës, M.; Cavellin, C. Deville

doi:10.1126/science.1064204

Cited by 30 publications

(15 citation statements)

References 27 publications

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“…It is expected that hole doping to two-leg spin ladders will lead to the superconductivity due to that effective attraction between extra holes may arise from the magnetic interactions (11). In fact, hole-doped spin ladders of copper-oxide-based materials have been reported, which exhibited superconducting transitions by chemical doping and under high pressure (12)(13)(14), or in the field-effecttransistor configuration (15).…”

Section: Partially Charged [Ni(dmit) 2 ]mentioning

confidence: 99%

Two Polymorphs of (Anilinium)(18-Crown-6)[Ni(dmit)2]: Structure and Magnetic Properties

Nishihara

Akutagawa

Hasegawa

et al. 2002

Journal of Solid State Chemistry

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Section: Partially Charged [Ni(dmit) 2 ]mentioning

confidence: 99%

Two Polymorphs of (Anilinium)(18-Crown-6)[Ni(dmit)2]: Structure and Magnetic Properties

Nishihara

Akutagawa

Hasegawa

et al. 2002

Journal of Solid State Chemistry

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confidence: 99%

“…This clearly confirms the above value for J cyc . One might speculate that such a sizeable cyclic spin exchange term will have significant consequences for superconductivity in the doped spin ladders [15,16] since magnetic and pairing correlations are considered as closely related phenomena [17].We study an isolated two-leg S=1/2 ladder characterized by an antiferromagnetic Heisenberg Hamiltonian with an additional cyclic spin exchange term: where J ⊥ and J denote the rung and leg couplings, the index i refers to the rungs, and l, r label the two legs. The cyclic permutation operator P 1234 for 4 spins on a plaquette is given by:…”

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confidence: 99%

Cyclic spin exchange in cuprate spin ladders

et al. 2002

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We investigate the influence of a cyclic spin exchange Jcyc on the one-and two-triplet excitations of an undoped two-leg S=1/2 ladder, using the density matrix renormalization group (DMRG). The dispersion of the S=0 two-triplet bound state is dramatically reduced by Jcyc due to a repulsion between triplets on neighboring rungs. In (La,Ca)14Cu24O41 a consistent description of both the spin gap and the S=0 bound state requires Jcyc/J ⊥ ≈ 0.20-0.27 and J/J ⊥ ≈ 1.25-1.35. With these coupling ratios the recently developed dynamical DMRG yields an excellent description of the entire S=0 excitation spectrum observed in the optical conductivity, including the continuum contribution.PACS numbers: 75.10. Jm, 75.40.Gb, 75.40.Mg, 74.72.Jt, 75.30.Et The antiferromagnetic parent compounds of the high-T c cuprates are thought to be the best representatives of the two-dimensional S=1/2 square-lattice Heisenberg model. Understanding their magnetic properties is of utmost importance due to the intimate relationship of magnetic correlations and high-T c superconductivity. Recently, the question how to set up a minimal model which accounts for these magnetic properties has been readdressed. High-resolution inelastic neutron scattering experiments performed on the two-dimensional S=1/2 antiferromagnet La 2 CuO 4 [1] exhibit a magnon dispersion at the zone boundary which cannot be obtained within a nearest-neighbor Heisenberg model. It has been argued that the inclusion of a cyclic spin exchange term of about 20% would reproduce this dispersion [2]. This cyclic spin exchange emerges as a correction to the nearestneighbor Heisenberg Hamiltonian in order t 4 /U 3 from a t/U -expansion of the one-band Hubbard model [3]. It is expected to be the dominant correction within a more realistic three-band description of the CuO 2 -planes because there the cyclic permutation of 4 spins on a plaquette can take place without double occupancy [4,5]. Similar cyclic spin exchange processes have proven to be significant in other systems, e.g. in cuprate spin chains a ferromagnetic 2-spin cyclic exchange is responsible for the unusually strong exchange anisotropy [6].Cuprate spin ladders offer an alternative approach to decide about the existence and potential implications of a cyclic spin exchange term. They are composed of the same corner-sharing Cu-O plaquettes as the 2D cuprates, thus similar exchange couplings are expected for all spin products. In fact the inclusion of a cyclic spin exchange has been suggested in order to explain the smallness of the ladder spin gap observed in (La,Ca) 14 Cu 24 O 41 [7][8][9]. However, it is impossible to extract a unique set of coupling parameters or even to settle the existence of a cyclic spin exchange term from an analysis of the spin gap only. Here, the optical conductivity σ(ω) [10,11] can provide the missing information. Magnetic excitations can be observed in σ(ω) via the simultaneous excitation of a phonon [12,13]. In (La,Ca) 14 Cu 24 O 41 , two peaks in σ(ω) were identified as S=0 bound states of tw...

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“…The ladder compounds are conceptually important because they provide the only known superconducting copper oxide without a square lattice. The hypothesis that the ladder compounds are anisotropic two-dimensional systems appears difficult to sustain in view of the discovery reported in [4]. Furthermore, the resistivity at optimal doping (when T c is the highest) is linear with temperature [4].…”

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confidence: 99%

“…[4,5] in the current issue of science -applying a similar technique to two very different materials-drastically alter the perception that planar cuprates are the only route to high temperature superconductivity.Schön et al use a field-effect device introduced in previous investigations to transform insulating compounds into metals [6]. On page 2430, they show that copper oxide materials with a ladder structure (panel B in the first figure) can be superconducting [4], even without the high pressure applied in previous studies of related compounds. Even more spectacularly, they report on page 2432 that the T c of a noncuprate molecular materials, C 60 (panel C in the first figure), known before to superconduct at 52 K upon hole doping [7], can be raised by hole doping with intercalated CHBr 3 to 117 K [5], not far from the cuprate record.…”

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confidence: 99%

The Race to Beat the Cuprates

Dagotto

2001

Science

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Superconductors are materials that lose all electrical resistance below a specific temperature, known as the critical temperature (T c ). Large-scale applications, for example, in superconducting cables, require materials with high (ideally room temperature) T c 's, but most superconductors have very low T c 's, typically a few kelvin or less. The discovery of a layered copper oxide (cuprate) with a T c of 38 K (see panel A in the first figure) in 1986 [1] raised hopes that high temperature superconductivity might be within reach. By 1993, cuprate T c 's of 133 K at ambient pressure had been achieved [2,3], but efforts to further increase cuprate T c 's have not been fruitful. Two reports by Schön et al. [4,5] in the current issue of science -applying a similar technique to two very different materials-drastically alter the perception that planar cuprates are the only route to high temperature superconductivity.Schön et al. use a field-effect device introduced in previous investigations to transform insulating compounds into metals [6]. On page 2430, they show that copper oxide materials with a ladder structure (panel B in the first figure) can be superconducting [4], even without the high pressure applied in previous studies of related compounds. Even more spectacularly, they report on page 2432 that the T c of a noncuprate molecular materials, C 60 (panel C in the first figure), known before to superconduct at 52 K upon hole doping [7], can be raised by hole doping with intercalated CHBr 3 to 117 K [5], not far from the cuprate record. Simple extrapolations suggest that the T c could be increased even further, effectively ending the dominance of cuprates in the high-T c arena.The idea behind the studies is conceptually simple. Field-effect doping exploits the fact that under a strong, static electric field, charge (electrons or holes) will accumulate at the surface of the material, effectively modifying the electronic density in that region. This is necessary to stabilize superconductors away from nominally insulating compositions. The dielectric portion of the field-effect device must be able to sustain electric fields large enough to induce a sufficient number of holes per atom or molecule for the material under study to become superconducting. In addition, the interface with the studied material must be as perfect as possible. Doping through a field-effect device [4,5] avoids imperfections that cause the system to deviate locally from its average properties. Such imperfections are inevitably induced by chemical doping. Disorder has not been seriously considered by most cuprate high-T c theorists, but its important role is slowly emerging. Some phase diagrams of cuprates may have to be redrawn when doping is introduced through a field-effect device [8].

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Field-Induced Superconductivity in a Spin-Ladder Cuprate

Cited by 30 publications

References 27 publications

Two Polymorphs of (Anilinium)(18-Crown-6)[Ni(dmit)2]: Structure and Magnetic Properties

Two Polymorphs of (Anilinium)(18-Crown-6)[Ni(dmit)2]: Structure and Magnetic Properties

Cyclic spin exchange in cuprate spin ladders

The Race to Beat the Cuprates

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