Quantum spin fluctuations and evolution of electronic structure in cuprates

Abstract

Correlation effects in CuO 2 layers give rise to a complicated landscape of collective excitations in high-T c cuprates. Their description requires an accurate account for electronic fluctuations at a very broad energy range and remains a challenge for the theory. Particularly, there is no conventional explanation of the experimentally observed "resonant" antiferromagnetic mode, which is often considered to be a mediator of superconductivity. Here we model spin excitations of the hole-doped cuprates in the paramagnetic regime and show that this antiferromagnetic mode is associated with electronic transitions between anti-nodal X and Y points of the quasiparticle band that is pinned to the Fermi level. We observe that upon doping of 7-12% the electronic spectral weight redistribution leads to the formation of a very stable quasiparticle dispersion due to strong correlation effects. The reconstruction of the Fermi surface results in a flattening of the quasiparticle band at the vicinity of the nodal MΓ/2 point, accompanied by a high density of charge carriers. Collective excitations of electrons between the nodal MΓ/2 and XM/2 points form the additional magnetic holes state in magnetic spectrum, which protects the antiferromagnetic fluctuation. Further investigation of the evolution of spin fluctuations with the temperature and doping allowed us to observe the incipience of the antiferromagnetic ordering already in the paramagnetic regime above the transition temperature. Additionally, apart from the most intensive low-energy magnetic excitations, the magnetic spectrum reveals less intensive collective spin fluctuations that correspond to electronic processes between peaks of the single-particle spectral function. arXiv:1806.05216v2 [cond-mat.str-el]

Dual parquet scheme for the two-dimensional Hubbard model: Modeling low-energy physics of high- Tc cuprates with high momentum resolution

“…Moreover, enhanced charge fluctuations support the picture that AF order breaks down due to the formation of a phase separated state 46 in which the holes form (maybe virtually) droplets in the AF background as predicted in Ref. 9. While in the latter paper only nonlocal fluctuations in the spin channel were taken into account, our dual parquet calculations allow to access the charge channel also, and the emergence of an increased charge sus- ceptibility at q = (0, 0) indeed provides a new and solid argument in favor of the phase separation picture.…”

Dual boson approach with instantaneous interaction

“…We have presented the Dual Boson approach with instantaneous interaction. By construction, this approach produces a susceptibility that satisfies the charge and spin conservation requirement 15,20,21,27,59 , and the Mermin-Wagner theorem. The instantaneous interaction assumption means that the method does not need an impurity solver that can handle retarded interactions, an important simplification that makes it more amendable to the simulation of multiband systems.…”

“…For the impurity model to also be at half-filling, we take µ = U /2. This choice of hybridization functions is useful, since the resulting form of the impurity action does not introduce higher-order terms in the Ward identities 20,21 . As we discuss below in Section II B, the impurity problem is solved numerically exactly and provides full frequency dependent local quantities such as the one-and two-particle Green's functions and fermion-fermion and fermion-boson vertices needed for the construction of the dual diagrams.…”

“…As shown in Ref. 21, this choice of the self-consistency condition follows from the invariance of the initial lattice problem with respect to the variation of the introduced hybridization functions, and it fulfills the Pauli principle. The sum over frequencies in the self-consistency condition corresponds to taking the equal-time component of the susceptibility 31 , so we can write…”

“…To address these situations, a simplification of the Dual Boson approach that does not require dynamic interactions in the impurity model has been introduced recently 21 . We use the fact that the dynamic interactions in Dual Boson are a priori free parameters in the Hubbard-Stratonovich decoupling that leads to the impurity model.…”