MATERIALS SCIENCE COLLOQUIUM

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ABSTRACT: In hole-doped cuprates, superconductivity occurs where antiferromagnetic ordering and charge carrier mobility are mutually frustrated. A contentious question has been: what sorts of correlations emerge to reduce the frustration and how do they relate to the superconductivity? In the system La_2-xBa_xCuO₄, we observe the formation of charge and spin stripes that order when a structural transition leads to suitable anisotropy of the CuO₂ planes [1]. At x=1/8, where stripe ordering is strongest, bulk superconductivity is suppressed; nevertheless, evidence for 2D superconductivity is observed [2]. This is an intriguing situation, as the coexistence of locally antiferromagnetic order with superconductivity appears to require an intertwining of the order parameters [3]. At x=0.095, we observe robust superconductivity below 32 K [4]; however, the spin fluctuations are essentially gapless, with no obvious magnetic resonance below Tc. This may require a spatial modulation of the pair wave function. These experiments provide valuable insights into the intimate relationships among spins, charges, and pairing in the cuprates.

1. M. Hücker et al., Phys. Rev. B 83, 104506 (2011).
2. Q. Li et al., Phys. Rev. Lett. 99, 067001 (2007); J.M. Tranquada et al., Phys. Rev. B 78, 174529 (2008).
3. E. Berg et al., New J. Phys. 11, 115004 (2009).
4. J.S. Wen et al., arXiv:1009.0031; arXiv:1111.5383