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A Novel Strong Pairing Mechanism in High-TC Cuprates

F. A. Buot

Published Feb 20, 2025• 0 citations
Publisher

Abstract

In high-TC cuprates, the presence of parallel superconducting stripes or rivers of charge is well established experimentally. These also act as domain walls for the antiferromagnetic order. To readily explain the pattern of superconducting stripes near and at optimal doping levels, we propose a novel strong pairing mechanism, devoid of Coulomb repulsion, for high-TC cuprates. This new mechanism is based on the quantum entanglement and connement or degree of entanglement. Some quantum entanglement experiments with antiferromagnetic-chain links directly support our proposed entanglement pairing mechanism. Depending on doping levels, the triplet and singlet pairing can either exist independently, as a "lattice" of Bell basis states with unpolarized rivers of charge for underdoped regime, or as a mixed triplet-singlet or interacting Bell basis states with spatially alternating spin-polarized superconducting stripes of charge for overdoped range. Several spin resolved (SR)-ARPES experiments on the complex spin texture of cuprates are qualitatively interpreted in the light of our novel "lattice" of coupled triplet-singlet pairing leading to polarized rivers of charge in line with experimentally-found doping-level dependence. The resulting simple intuitive model suggests that entanglement is indeed a new strong pairing mechanism, devoid of Coulomb repulsion, leading to high-TC superconductivity and strange metal behavior above TC. Moreover, our model can possibly accommodate the Meissner effect, probably as superconducting plaquettes formed by "spokes" of antiferromagnetic-chain entanglement link.

DOI
10.20944/preprints202502.1587.v1

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•Oct 1, 2021•0 citations
In high-TC cuprates, the presence of parallel superconducting stripes or rivers of charge is well established experimentally. These also act as domain walls for the antiferromagnetic order. To readily explain the pattern of superconducting stripes near and at optimal doping levels, we propose a novel strong pairing mechanism, devoid of Coulomb repulsion, for high-TC cuprates. This new mechanism is based on the quantum entanglement and connement or degree of entanglement. Some quantum entanglement experiments with antiferromagnetic-chain links directly support our proposed entanglement pairing mechanism. Depending on doping levels, the triplet and singlet pairing can either exist independently, as a "lattice" of Bell basis states with unpolarized rivers of charge for underdoped regime, or as a mixed triplet-singlet or interacting Bell basis states with spatially alternating spin-polarized superconducting stripes of charge for overdoped range. Several spin resolved (SR)-ARPES experiments on the complex spin texture of cuprates are qualitatively interpreted in the light of our novel "lattice" of coupled triplet-singlet pairing leading to polarized rivers of charge in line with experimentally-found doping-level dependence. The resulting simple intuitive model suggests that entanglement is indeed a new strong pairing mechanism, devoid of Coulomb repulsion, leading to high-TC superconductivity and strange metal behavior above TC. Moreover, our model can possibly accommodate the Meissner effect, probably as superconducting plaquettes formed by "spokes" of antiferromagnetic-chain entanglement link.
We demonstrate that entanglement and confinement hole pairing (ECHP) is a precise physics of the entanglement framework of the RVB theory of high-Tc cuprates. Our novel strong ECHP mechanism explains the entire phase diagram of both electron and hole-doped cuprates, notably the linearly decreasing T* at the pseudogap but with "T*-singularity" at the peak of the superconducting (SC) dome, the Tc=T* at the optimum doping and the rest of the overdoped regions of the SC dome, the duality of the spin gap and strange metal phase, the presence of the parallel superconducting stripes in the CuO plane (spin-polarized and spin-unpolarized channels), and the linear-T resistivity of the strange metal phase above the overdoped regions of the SC dome. This also explains the experimental spin textures of the cuprates. We refer to our new ECHP model as a resonating entanglement and confinement hole pair (RECHP) theory. Based on RECHP theory, we were able to provide a conceptual and comprehensive semiquantitative explanation of the entire phase diagram, thus providing the sought-after pairing mechanism responsible for the entire phase diagram of high-T_{C} cuprates.
Abstract In quantum materials, the electronic interaction and the electron-phonon coupling are, in general, two essential ingredients, the combined impact of which may drive exotic phases. Recently, an anomalously strong electron-electron attraction, likely mediated by phonons, has been proposed in one-dimensional copper-oxide chain Ba2−xSrxCuO3+δ. Yet, it is unclear how this strong near-neighbor attraction V influences the superconductivity pairing in the system. Here we perform accurate many-body calculations to study the extended Hubbard model with on-site Coulomb repulsion U > 0 and near-neighbor attraction V < 0 that could well describe the cuprate chain and likely other similar transition-metal materials with both strong correlations and lattice effects. We find a rich quantum phase diagram containing an intriguing Tomonaga-Luttinger liquid phase — besides the spin density wave and various phase separation phases — that can host dominant spin-triplet pairing correlations and divergent superconductive susceptibility. Upon doping, the spin-triplet superconducting regime can be further broadened, offering a feasible mechanism to realize p-wave superconductivity in realistic cuprate chains.
Abstract Resonant interactions associated with the emergence of a bound state constitute one of the cornerstones of modern many-body physics. Here we present a Feshbach perspective on the origin of strong pairing in Fermi-Hubbard type models. We perform a theoretical analysis of interactions between spin-polaron charge carriers in doped Mott insulators, modeled by a near-resonant two-channel scattering problem, and report evidence for Feshbach-type interactions in the dx2−y2{d}_{{x}^{2}-{y}^{2}}dx2−y2​ d x 2 − y 2 channel, consistent with the established phenomenology of cuprates. Existing experimental and numerical results on hole-doped cuprates lead us to conjecture the existence of a light, long-lived, low-energy excited state of two holes, which enables near-resonant interactions. To put our theory to a test we suggest to use coincidence angle-resolved photoemission spectroscopy (cARPES), pair-tunneling measurements or pump-probe experiments. The emergent Feshbach resonance among spin-polarons could also underlie superconductivity in other doped antiferromagnetic Mott insulators highlighting its potential as a unifying strong-coupling pairing mechanism rooted in quantum magnetism.
Resonant interactions associated with the emergence of a bound state constitute one of the cornerstones of modern many-body physics, ranging from Kondo physics, BEC-BCS crossover, to tunable interactions at Feshbach resonances in ultracold atoms or 2D semiconductors. Here we present a Feshbach perspective on the origin of strong pairing in Fermi-Hubbard type models. We perform a theoretical analysis of interactions between charge carriers in doped Mott insulators, modeled by a near-resonant two-channel scattering problem, and find strong evidence for Feshbach-type interactions in the dx2−y2d_{x^2-y^2}dx2−y2​ channel that can support strong pairing, consistent with the established phenomenology of cuprates. Existing experimental and numerical results on hole-doped cuprates lead us to conjecture the existence of a light, long-lived, low-energy excited state of two holes with bipolaron character in these systems, which enables near-resonant interactions and can thus provide a microscopic foundation for theories of high-temperature superconductivity involving strong attraction, as assumed e.g. in BEC-BCS crossover scenarios. To put our theory to a direct test we suggest to use coincidence angle-resolved photoemission spectroscopy (cARPES), pair-tunneling measurements or less direct pump-probe experiments. The emergent Feshbach resonance we propose could also underlie superconductivity in other doped antiferromagnetic Mott insulators, as recently proposed for bilayer nickelates, highlighting its potential as a unifying strong-coupling pairing mechanism rooted in quantum magnetism.
We generalize the condition under which a quantum material exhibiting a pseudogap phase is a precursor to a superconducting (SC) dome. The result reveals the non-analytic T* as a function of doping. A well-known example is the high-Tc cuprates. Essentially, the SC dome is generated under two conditions: (1) that the pseudogap T* is a decreasing function of doping, due to the decrease in size of extended pairing of doped holes with doping, and most importantly, (2) that the rate of configurational-ordering parameter is an increasing function of doping as a result of the decrease in extended length of the disordered pairs. The theory behind these hinges on a novel strong entanglement and confinement hole pairing (ECHP) mechanism that unravels the microscopic features of the entire phase diagram of both electron and hole-doped high-Tc cuprates, recently discussed in the by Buot et al. The ECHP configurational ordering (CO) at the underdoped and overdoped regions qualitatively agrees with spin texture experiments, and strongly suggests that strange metal phase can only occur in the overdoped region, in agreement with experiments.
In quantum materials, the electronic interaction and the electron-phonon coupling are in general two essential ingredients, the combined impact of which may drive exotic phases. Recently, an anomalously strong electron-electron attraction, mediated by phonons, has been unveiled in one-dimensional (1D) copper-oxide chain compound. Yet it is unclear how this strong near-neighbor (NN) attraction VVV influences the superconductivity pairing. In this work, we employ the density-matrix renormalization group (DMRG) method to study this experiment-relevant extended Hubbard model with on-site Coulomb repulsion U>0U>0U>0 and NN attraction V<0V<0V<0, relevant for the 1D cuprate chain and likely other similar transition-metal materials. We find this extended ttt-UUU-VVV model hosts a rich quantum phase diagram consisting of the spin density wave phase, phase separation phases, the Tomonaga-Luttinger liquid (TLL) phase, and especially an intriguing TLL regime with divergent superconducting susceptibility and dominant spin-triplet pair correlations. Upon doping, such a spin-triplet pairing regime can be further broadened in the parameter space and extends to larger UUU. Our results show robust triplet pairing induced by attractive interaction VVV, offering a feasible mechanism to realize ppp-wave superconductivity in 1D cuprates.