Perspective on the phase diagram of cuprate high-temperature superconductors

Rybicki, Damian; Jurkutat, Michael; Reichardt, Steven; Kapusta, Cz.; Haase, Jürgen

doi:10.1038/ncomms11413

Cited by 123 publications

(138 citation statements)

References 69 publications

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“…[14] further, such that we can quantitatively determine the hole contents of the Cu 3d(x 2 − y 2 ) and O 2p σ orbitals for all cuprates. This includes, in particular, the hole/electron distribution in the parent compounds, where we find that the inherent Cu 2+ hole is shared between Cu 3d(x 2 − y 2 ) and O 2p σ depending on the material chemistry, as suggested recently [15]. Thus, we can relate the hole content of both orbitals quantitatively to the critical temperature.…”

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confidence: 72%

Distribution of electrons and holes in cuprate superconductors as determined from17OandCu63nuclear magnetic resonance

et al. 2014

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The distribution of electrons and holes in the CuO2 plane of the high-temperature superconducting cuprates is determined with nuclear magnetic resonance through the quadrupole splittings of 17 O and 63 Cu. Based on new data for single crystals of electron-doped Pr2−xCexCuO4(x=0, 0.05, 0.10, 0.15) as well as Nd2−xCexCuO4 (x=0, 0.13) the changes in hole contents n d of Cu 3d(x 2 − y 2 ) and np of O 2pσ orbitals are determined and they account for the stoichiometrically doped charges, similar to hole-doped La2−xSrxCuO4. It emerges that while n d + 2np = 1 in all parent materials as expected, n d and np vary substantially between different groups of materials. Doping holes increases predominantly np, but also n d . To the contrary, doping electrons predominantly decreases n d and only slightly np. However, np for the electron doped systems is higher than that in hole doped La1.85Sr0.15CuO4. Cuprates with the highest maximum Tcs appear to have a comparably low n d while, at the same time, np is very high. The rather high oxygen hole content of the Pr2CuO4 and Nd2CuO4 with the low n d seems to make them ideal candidates for hole doping to obtain the highest Tc. The high-temperature superconducting cuprates (HTSCs) emerge from insulating antiferromagnetic parent materials, the essential unit of which is the CuO 2 plane. It is formed, in first approximation, by Cu 2+ (3d 9 ) and O 2− (2p 6 ), with the half-filled Cu 3d(x 2 − y 2 ) orbital hybridized with four O 2p σ orbitals, so that a near square planar arrangement of Cu and O follows. Charge neutrality is provided by layers between CuO 2 planes, the chemistry of which can be varied widely. By changing the average charge state of the layers, e.g., by doping them, electrons are added or removed from the CuO 2 plane. These additional electrons or holes destroy the Cu-based antiferromagnetism. Above a certain doping level superconductivity can emerge with a maximum critical transition temperature T c at optimal average doping, and it decreases nearly parabolically as the doping departs from the optimal value. The highest T c 's vary widely among different materials, and it is not quite clear which material parameters affect this behavior. Therefore, the knowledge of the microscopic distribution of charges in the CuO 2 plane is of great interest for a better understanding of the doping process.A local probe like nuclear magnetic resonance (NMR) can yield vital information about the doping process since a change in the hole or electron content in the Cu 3d(x 2 − y 2 ) or O 2p σ orbitals changes the electric field gradients (EFGs) experienced by the 63,65 Cu (I = 3 2) and 17 O (I = 5 2) nuclei through the electric quadrupole interaction that splits the nuclear resonances for Cu and O into 2I lines in a high magnetic field. Their frequencies are given by ν n = ν 0 ± nν Q : the central line (n = 0) is in leading order unaffected by the quadrupole interaction that causes an angular dependent quadrupole splitting ν Q for the 2I − 1 satellite transitions (n = 1 for Cu and n = 1, ...

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confidence: 72%

Distribution of electrons and holes in cuprate superconductors as determined from17OandCu63nuclear magnetic resonance

et al. 2014

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“…Finally, we would like to discuss the findings in view of the NMR phase diagram [34] that was suggested recently. We do not observe an immediate trend relating T c to the NMR shifts in Figure 7.…”

Section: Discussionmentioning

confidence: 86%

“…The degree of covalency of the planar Cu-O bond, i.e., the hole distribution between Cu and O that is set by material chemistry and is related to the charge transfer gap, was shown to set the maximum T c and superfluid density [33,34]. In Figure 8c, the La 2−x Sr x CuO 4 family, having the lowest O hole content and the lowest maximum T c , is limited to a very narrow window of K = 1.35 -1.40% such that doping and increasing temperature only affect an increase in K ⊥ .…”

Section: Discussionmentioning

confidence: 99%

“…Signal intensity issues have not been properly addressed with most experiments adding to uncertainties. Perhaps the strongest evidence, however, that the observed NMR signals do represent the bulk properties is the fact that the quadrupole splittings measured with NMR account for the average chemical doping [32][33][34].…”

Section: Frequencies Shifts and Splittingsmentioning

confidence: 99%

“…With the new understanding of the cuprate phase diagram in terms of NMR that has two charge components (at Cu and O) [34], we decided to take a closer look at all available Cu shift data, which led us eventually to introduce a new, contrasting NMR shift phenomenology that will be discussed below. [27,41].…”

Section: Failure Of the Single Fluid Modelmentioning

confidence: 99%

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Contrasting Phenomenology of NMR Shifts in Cuprate Superconductors

2017

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Nuclear magnetic resonance (NMR) shifts, if stripped of their uncertainties, must hold key information about the electronic fluid in the cuprates. The early shift interpretation that favored a single-fluid scenario will be reviewed, as well as recent experiments that reported its failure. Thereafter, based on literature shift data for planar Cu, a contrasting shift phenomenology for cuprate superconductors is developed, which is very different from the early view while being in agreement with all published data. For example, it will be shown that the hyperfine scenario used up to now is inadequate as a large isotropic shift component is discovered. Furthermore, the changes of the temperature dependences of the shifts above and below the superconducting transitions temperature proceed according to a few rules that were not discussed before. It appears that there can be substantial spin shift at the lowest temperature if the magnetic field is perpendicular to the CuO 2 plane, which points to a localization of spin in the 3d(x 2 − y 2 ) orbital. A simple model is presented based on the most fundamental findings. The analysis must have new consequences for theory of the cuprates.

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Gate‐Tunable Electrical Transport in Thin 2M‐WS₂ Flakes

Che

Deng

Fang

et al. 2019

Adv Elect Materials

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discovered metastable phase. It has the highest intrinsic T c of 8.9 K among all the TMDs. [5] Its crystal structure has a symmetry of a monoclinic space group C2/m. The crystal structure of 2M-WS 2 has a different stacking order along the c-axis, compared with the known T d -WTe 2 or 1T′-MoTe 2 , where "2" indicates the number of monolayers in each unit cell and "M" represents the monoclinic lattice. [6] Furthermore, the theoretical calculation indicates that hole and electron pockets coexist at the Fermi surface of 2M-WS 2 and this material owns a possible topological surface state. [6] As a newly discovered superconductor in TMDs, little has been known about the properties of 2M-WS 2 . To understand the superconducting state as well as other electronic states, the phase diagram is very important and helpful. As we know, T c can be fine-tuned by the carrier density of the materials. [6] Traditionally, to modulate the carrier density, researchers need to fabricate a series of electrondoped and/or hole-doped samples. Fortunately, electrochemical gating has been employed as an effective way to dope carriers over a wide range. [7] The detailed tuning by lithium intercalation through the charge density wave and superconductivity phase in 1T-TaS 2 classified the universality of the quantum critical point. [8] Furthermore, electrochemical gating can induce the reversible structure transformation. A tristate phase transformation was realized in SrCoO 3−x by using an electric field to control the insertion and extraction of oxygen and hydrogen ions that were electrolyzed from H 2 O. [9] So, upon applying proper gate voltage (V g ), ions in the dielectric electrolyte can be effectively controlled to accumulate on the surface of material or intercalate into the material, thus tuning its electronic states.In this article, we selected the new metastable phase 2M-WS 2 as a model to systematically modulate the carrier density and explore its transport properties by gate-controlled Li-ion intercalation. Primary 2M-WS 2 is a superconductor with a T c of 8.9 K; when the Li-ion polymer gel was dropped on the sample, flake sample underwent a phase transition from a superconductor to an insulator, which is induced by the Li-ion intercalation. The corresponding carrier density changed from 9.05 × 10 21 to −6.04 × 10 20 cm −3 . Interestingly, the process of phase transition is reversible with the intercalation and deintercalation of lithium ions. In particular, our complete phase diagram for the first time provides fresh insights into the relations between the superconducting state and various other electronic states.2M-WS 2 is a metastable phase among TMDs that was first reported in our previous paper. [5] It owns a layered structure with monoclinic space group C2/m, in which each atomic Electrolyte gating has been employed as an effective way to modulate the electronic properties of transition metal dichalcogenides (TMDs) by carrier doping over a wide range. Here, the carrier density of a new metastable phase of TMD material 2M-WS...

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Perspective on the phase diagram of cuprate high-temperature superconductors

Cited by 123 publications

References 69 publications

Distribution of electrons and holes in cuprate superconductors as determined from17OandCu63nuclear magnetic resonance

Distribution of electrons and holes in cuprate superconductors as determined from17OandCu63nuclear magnetic resonance

Contrasting Phenomenology of NMR Shifts in Cuprate Superconductors

Gate‐Tunable Electrical Transport in Thin 2M‐WS₂ Flakes

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Perspective on the phase diagram of cuprate high-temperature superconductors

Cited by 123 publications

References 69 publications

Distribution of electrons and holes in cuprate superconductors as determined from17OandCu63nuclear magnetic resonance

Distribution of electrons and holes in cuprate superconductors as determined from17OandCu63nuclear magnetic resonance

Contrasting Phenomenology of NMR Shifts in Cuprate Superconductors

Gate‐Tunable Electrical Transport in Thin 2M‐WS2 Flakes

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Gate‐Tunable Electrical Transport in Thin 2M‐WS₂ Flakes