Q=0 collective modes originating from the low-lying Hg-O band in the superconducting HgBa2CuO4+\delta

TL;DR

This paper proposes that low-energy collective modes in HgBa2CuO4+delta originate from hybridized Hg-O states, offering an alternative to orbital current explanations and aligning with experimental observations.

Contribution

It introduces a multi-orbital model showing a Q=0 collective mode from Hg-O states, providing a new explanation for pseudogap phenomena in cuprates.

Findings

Identification of a Hg-O hybridized band near the Fermi level.

Prediction of a Q=0 collective mode in the spin-excitation spectrum.

Suggestion of magnetic order development in the Hg-O layer.

Abstract

Motivated by the recent discovery of two Q\sim0 collective modes [Y. Li et al., Nature 468, 283 (2010); ibid Nat. Phys. 8, 404 (2012)] in the single-layer HgBa2CuO4+\delta, which are often taken as evidence of the orbital current origin of a pseudogap, we examine an alternative and assumption-free scenario constrained by first-principle calculations. We find that in addition to the common CuO2 band, a hybridized Hg-O state is present in the vicinity of the Fermi level, and that it contributes to the low-energy ground state of this system. We calculate the spin-excitation spectrum based on the random-phase-approximation in the superconducting state using a two band model and show that a collective mode in the multi-orbital channel arises at Q=0. This mode splits in energy, yet remains at Q\sim0 as the pseudogap develops breaking both translational and time-reversal symmetries in the spin-channel, and thus gap out the electrnic states. The observations of the dynamical mode and static moment in the pseudogap state are in good accord with experimental observations. A verifiable prediction of this proposal is the development of magnetic order also in the Hg-O layer. Detection of Hg-O band via optical study, or magnetic moment in the Hg-O layer will be tests of this calculation.