1206.4292 (Tanmoy Das)

Q=0 collective modes originating from the low-lying Hg-O band in the
superconducting HgBa$_2$CuO$_{4+δ}$    [PDF]

Tanmoy Das

Motivated by the recent discovery of two Q=0 collective modes [Y. Li {\it et al.}, Nature {\bf 468}, 283 (2010); {\it ibid} Nat. Phys. {\bf 8}, 404 (2012)] in the single-layer HgBa$_2$CuO$_{4+\delta}$, which is often taken as an evidence of orbital current origin of pseudogap, we examine an alternative and assumption-free scenario constrained by first-principle calculations. We find that in addition to the common CuO$_2$ 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 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=0 as a static magnetic moment develops in both bands in the pseudogap regime breaking both translational and time-reversal symmetries in the spin-channel. The observations of dynamical mode and static moment in the pseudogap state are in good accord with experimental observations.

View original: http://arxiv.org/abs/1206.4292