Yeh, N.-C. and Teague, M. L. and Wu, R. T.-P. and Feng, Z. J. and Chu, H. and Moehle, A. M. (2013) Scanning Tunneling Spectroscopic Studies of the Low-Energy Quasiparticle Excitations in Cuprate Superconductors. Journal of Superconductivity and Novel Magnetism, 26 (1). pp. 65-70. ISSN 1557-1939. http://resolver.caltech.edu/CaltechAUTHORS:20120724-143259985
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We report scanning tunneling spectroscopic (STS) studies of the low-energy quasiparticle excitations of cuprate superconductors as a function of magnetic field and doping level. Our studies suggest that the origin of the pseudogap (PG) is associated with competing orders (COs), and that the occurrence (absence) of PG above the superconducting (SC) transition T_c is associated with a CO energy Δ_(CO) larger (smaller) than the SC gap Δ_(SC). Moreover, the spatial homogeneity of Δ_(SC) and Δ_(CO) depends on the type of disorder in different cuprates: For optimally and under-doped YBa_2Cu_3O_(7−δ) (Y-123), we find that Δ_(SC) < Δ_(CO) and that both Δ_(SC) and Δ(CO) exhibit long-range spatial homogeneity, in contrast to the highly inhomogeneous STS in Bi_2Sr_2CaCu_2O_(8+x) (Bi-2212). We attribute this contrast to the stoichiometric cations and ordered apical oxygen in Y-123, which differs from the non-stoichiometric Bi-to-Sr ratio in Bi-2212 with disordered Sr and apical oxygen in the SrO planes. For Ca-doped Y-123, the substitution of Y by Ca contributes to excess holes and disorder in the CuO_2 planes, giving rise to increasing inhomogeneity, decreasing Δ_(SC) and Δ_(CO), and a suppressed vortex-solid phase. For electron-type cuprate Sr_(0.9)La_(0.1)CuO_2 (La-112), the homogeneous Δ_(SC) and Δ_(CO) distributions may be attributed to stoichiometric cations and the absence of apical oxygen, with Δ_(CO) < Δ_(SC) revealed only inside the vortex cores. Finally, the vortex-core radius (ξ_(halo)) in electron-type cuprates is comparable to the SC coherence length ξ_(SC), whereas ξ_(halo) ∼ 10ξ_(SC) in hole-type cuprates, suggesting that ξ_(halo) may be correlated with the CO strength. The vortex-state irreversibility line in the magnetic field versus temperature phase diagram also reveals doping dependence, indicating the relevance of competing orders to vortex pinning.
|Additional Information:||© 2012 Springer Science+Business Media, LLC. Received: 30 April 2012; Accepted: 25 June 2012; Published online: 15 July 2012. Original paper for the Proceedings of ICSM2012, Istanbul (April 29–May 4). We acknowledge funding provided by NSF Grant #DMR0907251, by the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center with support of the Gordon and Betty Moore Foundation, and by the Kavli Nanoscience Institute with support of the Kavli Foundation. ZJF acknowledges the support from China Scholarship Council during his visit to Caltech.|
|Group:||Institute for Quantum Information and Matter, IQIM|
|Subject Keywords:||Cuprate superconductivity; Pseudogap; Competing orders; Quasiparticle excitations; Scanning tunneling spectroscopy|
|Official Citation:||Yeh, N. C., M. L. Teague, et al. (2013). "Scanning Tunneling Spectroscopic Studies of the Low-Energy Quasiparticle Excitations in Cuprate Superconductors." Journal of Superconductivity and Novel Magnetism 26(1): 65-70.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||25 Jul 2012 20:21|
|Last Modified:||14 Feb 2013 22:51|
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