Effective action, magnetic excitations, and quantum fluctuations in lightly doped single-layer cuprates

Abstract

We consider the extended two-dimensional t-tЈ-tЉ-J model at zero temperature. Parameters of the model corresponds to doping by holes. Using the low doping effective action, we demonstrate that the system can: ͑1͒ preserve the long-range collinear antiferromagnetic order, ͑2͒ lead to a spin spiral state ͑static or dynamic͒, and ͑3͒ lead to the phase-separation instability. We show that at parameters of the effective action corresponding to the single-layer cuprate La 2−x Sr x CuO 4 , the spin spiral ground state is realized. We derive properties of magnetic excitations and calculate quantum fluctuations. Quantum fluctuations destroy the static spin spiral at the critical doping x c Ϸ 0.11. This is the point of the quantum phase transition to the spin-liquid state ͑dynamic spin spiral͒. The state is still double degenerate with respect to the direction of the dynamic spiral, so this is a "directional nematic." The superconducting pairing exists throughout the phase diagram and is not sensitive to the quantum phase transition. We also compare the calculated neutron-scattering spectra with experimental data.

Fermi surface reconstruction by dynamic magnetic fluctuations and spin-charge separation near anO(3)quantum critical point

“…[30][31][32][33] The static magnetic order vanishes within this doping range, as also confirmed by nuclear magnetic resonance (NMR) wipeout 34,35 and recently confirmed by muon spin rotation (μSR) data. 36 The reduction of the static magnetic moment has been calculated within a low-energy effective theory, 37 and a QCP around x ≈ 0.11 is predicted, close to the experimental value x ≈ 0.09 observed in YBa 2 Cu 3 O y . 33,38,39 It is then intriguing to ask whether the topological LP is related to this magnetic QCP, especially how the change of magnetic excitations can influence the electronic properties.…”

“…On the other side of the QCP, deep inside the AF phase, the hole interaction with a magnetic field is described by pseudospin 40,41 and this interaction implies a partial SCS. 37 Evolution of the spin cloud when approaching the QCP from the AF phase is not clear at present.…”

“…This is the meaning of SCS in the magnetically ordered phase, although it is better to say partial SCS since there is a local part of the interaction with the external magnetic field and there is a nonlocal part of the interaction; see the discussion in Ref. 37. This kind of SCS differs from what is called SCS in one-dimensional systems with no magnetic ordering where the interaction remains local, s · B, with one quasiparticle (spinon) carrying spin and another quasiparticle (holon) carrying charge.…”

Quasielastic neutron scattering from two-dimensional antiferromagnets at a finite temperature

“…There is no doubt that the magnetic QCP observed in YBa 2 Cu 3 O y is of a more complex nature than just a simple O(3) QCP, see a discussion in Ref. 10. Nevertheless, it is clear that generically Eq.…”

“…Furthermore, it is incommensurate, mainly due to the contribution of charge degrees of freedom, which certainly complicates a theoretical analysis of magnetic properties, see Ref. 10. Moreover, both compounds, YBa 2 Cu 3 O 6.45 and La 1.9 Sr 0.1 CuO 4 are superconducting at low enough temperatures.…”