NOVEL MAGNETISM IN A MODEL CUPRATE SUPERCONDUCTOR

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Date/Time:Thursday, 01 Sep 2011 - Saturday, 03 Sep 2011
Location:Room 5 PHYSICS
Phone:515-294-5630
Channel:Condensed Matter Physics
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Martin Greven

Univeristy of Minnesota, Minneapolis, USA

Magnetic correlations might cause the superconductivity in the cuprates and are generally believed to be antiferromagnetic. Following our success in growing sizable crystals of the structurally simple compound HgBa_2CuO_(4+delta) [1], we used polarized neutron diffraction to demonstrate the universal existence of a novel type of magnetic order in superconducting samples [2]. Unlike antiferromagnetism, this order does not break the lattice translational symmetry. Our inelastic neutron scattering measurements confirmed the existence of the well-known magnetic resonance at the antiferromagnetic point [3] and to led to the insight that the resonance energy is universally related to the superconducting gap in several families of unconventional superconductors [4]. These experiments also resulted in the discovery of several excitations branches that appear to be fundamental collective modes associated with the novel magnetic order [5]. This pseudogap magnetism is consistent with a particular type of order involving circulating charge currents and with the notion that the phase diagram of the cuprates is controlled by an underlying quantum critical point [6].

[1] X. Zhao et al., Adv. Mat. 18, 3243 (2006); N. Barišić et al., Phys. Rev. B 78, 054518 (2008).
[2] Y. Li et al., Nature 455, 372 (2008).
[3] G. Yu et al., Phys. Rev. B 81, 064518 (2010).
[4] G. Yu et al., Nature Physics 5, 873 (2009).
[5] Y. Li et al., Nature 468, 283 (2010) and unpublished results.
[6] C. Varma, Nature 468, 184 (2010).