title: Evolution from a nodeless gap to d(x(2)-y(2))-wave in underdoped La(2-x)Sr(x)CuO4.
abstract: Using angle-resolved photoemission spectroscopy (ARPES), it is revealed that the low-energy electronic excitation spectra of highly underdoped superconducting and nonsuperconducting La(2-x)Sr(x)CuO(4) cuprates are gapped along the entire underlying Fermi surface at low temperatures. We show how the gap function evolves to a d(x(2)-y(2)) form with increasing temperature or doping, consistent with the vast majority of ARPES studies of cuprates. Our results provide essential information for uncovering the symmetry of the order parameter(s) in strongly underdoped cuprates, which is a prerequisite for understanding the pairing mechanism and how superconductivity emerges from a Mott insulator.
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.
authors.forename: E
authors.initials: E
authors.lastname: Razzoli
authors.affiliation: Department of Physics, Technion, Haifa 32000, Israel.
authors.forename: G
authors.initials: G
authors.lastname: Drachuck
authors.affiliation: Department of Physics, Technion, Haifa 32000, Israel.
authors.forename: A
authors.initials: A
authors.lastname: Keren
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland and Institut de la Matiere Complexe, EPF Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Radovic
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.
authors.forename: N C
authors.initials: NC
authors.lastname: Plumb
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland and Institut de la Matiere Complexe, EPF Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Chang
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Y-B
authors.initials: YB
authors.lastname: Huang
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: H
authors.initials: H
authors.lastname: Ding
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland and Institut de la Matiere Complexe, EPF Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Mesot
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Shi