Quantum phase transitions in magnetism and superconductivity: emergent spin topology seen with neutrons

Abstract

Magnetic spins and charges interact strongly in high-temperature superconductors. New physics emerges as layers of copper oxide are tuned towards the boundary of the superconducting phase. As the pseudogap increases the characteristic spin excitation energy decreases. We show that our well-annealed YBa2Cu3O6+x (YBCO6+x) single crystals are orthorhombic and superconducting but not antiferromagnetically ordered. Near the critical concentration for superconductivity for x = 0.35 the spins fluctuate on two energy scales, one a relaxational spin response at ~2 meV and the other a slow central mode that is resolution-limited in energy (<0.08 meV) but broad in momentum. The gradual formation on cooling of a central mode over a range of momenta suggests that the spin ground state from which coherent superconducting pairing emerges may be quantum disordered. We show that YBCO6.35 adopts a homogeneous state that consists of highly-organized frozen sub-critical three-dimensional spin correlations. The continuous spin evolution indicates that a single quantum state occurs in contrast to claims from site-based probes that lightly doped YBCO undergoes a transition to antiferromagnetic Bragg order followed by a sharp transition to a cluster glass phase. For x = 0.35, where Tc = 18 K is reduced to 1/5 of Tcmax, the spin ground state is reached without a sharp transition and consists of short correlations extending over only 8 Angstrom between cells and 42 Angstrom within the planes. Polarized neutrons show the angular spin distribution to be isotropic unlike the AF insulator. Since moment is conserved we interpret this as evidence for hole-induced spin rotations rather than decay.

Review of spin response in cuprate superconductors YBCO underdoped to suppress Tc based on talk at International Conference on Neutron Scattering, Sydney, Australia, Nov 27-Dec 2, 2005 6 pages 6 figures

References in corpus (11)

• Theory of Two-Dimensional Quantum Heisenberg Antiferromagnets with a Nearly Critical Ground State
• Two-Dimensional Geometry of Spin Excitations in the High Temperature Superconductor YBa2Cu3O6+x
• One-dimensional nature of the magnetic fluctuations in YBa${}_2$Cu${}_3$O${}_{6.6}$
• From incommensurate to dispersive spin-fluctuations: The high-energy inelastic spectrum in superconducting YBa2Cu3O6.5
• Dynamic Stripes and Resonance in the Superconducting and Normal Phases of YBa2Cu3O6.5 Ortho-II Superconductor
• Electronic phase separation in lightly-doped La${}_{2-x}$Sr${}_x$CuO${}_4$
• Nanoscopic coexistence of magnetism and superconductivity in YBa2Cu3O6+x detected by MuSR
• Delocalized fermions in underdoped cuprates
• Central mode and spin confinement near the boundary of the superconducting phase in YBa2Cu3O6.353 (Tc=18 K)
• Spin-glass phase of cuprates
• Low-temperature nodal-quasiparticle transport in lightly doped YBa_{2}Cu_{3}O_{y} near the edge of the superconducting doping regime

Cited by in corpus (4)

• Spin dynamics near the critical doping in weakly-superconducting underdoped YBa2Cu3O6.35 (Tc=18K)
• Magnetic field resonantly enhanced free spins in underdoped YBa${}_2$Cu${}_3$O${}_{6+x}$
• Antiferromagnetic correlations near the lower edge of superconducting dome in YBCO6+x
• Separation of magnetic and superconducting behaviour in YBCO6.33 (Tc=8.4 K)