title: Extending universal nodal excitations optimizes superconductivity in Bi2Sr2CaCu2O8+delta.
abstract: Understanding the mechanism by which d wave superconductivity in the cuprates emerges and is optimized by doping the Mott insulator is one of the major outstanding problems in condensed-matter physics. Our high-resolution scanning tunneling microscopy measurements of the high-transition temperature (Tc) superconductor Bi2Sr2CaCu2O8+delta show that samples with different Tc values in the low doping regime follow a remarkably universal d wave low-energy excitation spectrum, indicating a doping-independent nodal gap. We demonstrate that Tc instead correlates with the fraction of the Fermi surface over which the samples exhibit the universal spectrum. Optimal Tc is achieved when all parts of the Fermi surface follow this universal behavior. Increasing the temperature above Tc turns the universal spectrum into an arc of gapless excitations, whereas overdoping breaks down the universal nodal behavior.
authors.affiliation: Joseph Henry Laboratories and Department of Physics, Princeton University, Princeton, NJ 08544, USA.
authors.forename: Aakash
authors.initials: A
authors.lastname: Pushp
authors.forename: Colin V
authors.initials: CV
authors.lastname: Parker
authors.forename: Abhay N
authors.initials: AN
authors.lastname: Pasupathy
authors.forename: Kenjiro K
authors.initials: KK
authors.lastname: Gomes
authors.forename: Shimpei
authors.initials: S
authors.lastname: Ono
authors.forename: Jinsheng
authors.initials: J
authors.lastname: Wen
authors.forename: Zhijun
authors.initials: Z
authors.lastname: Xu
authors.forename: Genda
authors.initials: G
authors.lastname: Gu
authors.forename: Ali
authors.initials: A
authors.lastname: Yazdani