Spin dynamics in the normal and superconducting states of YBa2Cu3O6+x

Shifting of the magnetic-resonance peak to lower energy in the superconducting state of underdoped YBa 2 Cu 3 O 6.8

“…This peak also occurs in Imχ in addition to another contribution which stands in the normal state [1,3]. However, this part of Imχ is so reduced with increased doping [3,4] that it becomes hardly detectable [4,6,7] in fully oxydized samples.The origin of this magnetic resonance has been extensively discussed, especially in itinerant magnetism descriptions [8,9,10,11,12,13,14]. Beyond all the different hypotheses in these approaches, one can basically consider that an enhancement of the electronic spin susceptibility arises at a specific energy due to the opening of the SC gap.…”

“…However, the behaviour of the resonance peak in the underdoped regime remains unclear. So far, only short reports of a previous investigation at x ≃ 0.83 [2,3] have emphasized that crucial point.In this letter, we establish that, for an underdoped sample exhibiting a T C = 82 K, the magnetic resonance peak is shifted to E r = 34 meV. This energy leads to a resonance energy and T C ratio which is almost the same as in optimally doped and overdoped samples, E r /k B T C = 4.9 ± 0.2.…”

“…Second, in the SC state, when going from the weakly-doped regime x ≃ 0.5 to fully oxidized sample x ≃ 1[3], Imχ is gradually restricted to a smaller energy range. It is shifted to higher energies with increasing x by a doping dependant energy gap [1,2,3,4], called spin-gap. In optimally doped samples and overdoped samples (x ≥ 0.94), it is now well established that a strong sharp magnetic peak appears around 40 meV, called resonance by J. Rossat-Mignod et al [1] for its first evidence.…”

“…They have been experimentally evidenced by the persistence of spin fluctuations in the metallic state of cuprates. Especially, inelastic neutron scattering (INS) experiments have allowed to investigate the wavevector, energy and the doping dependencies of the imaginary part of the generalized magnetic susceptibility (Imχ) on a unique sample of YBa 2 Cu 3 O 6+x (YBCO) in its metallic state [1,2,3]. First, Imχ is still located at the antiferromagnetic (AF) wavevector, Q AF = (1/2, 1/2, q l ) ≡ (π, π).…”

Coexistence of magnetism and superconductivity in at−Jbilayer

“…This state possesses the merit of explaining the resonance peak at 41 meV obtained in neutron scattering experiments 6,20,21,22 . In this paper we consider also this pairing symmetry in the search for most stable ground state in bilayers.…”