title: Direct evidence for a pressure-induced nodal superconducting gap in the Ba0.65Rb0.35Fe2As2 superconductor.
abstract: The superconducting gap structure in iron-based high-temperature superconductors (Fe-HTSs) is non-universal. In contrast to other unconventional superconductors, in the Fe-HTSs both d-wave and extended s-wave pairing symmetries are close in energy. Probing the proximity between these very different superconducting states and identifying experimental parameters that can tune them is of central interest. Here we report high-pressure muon spin rotation experiments on the temperature-dependent magnetic penetration depth in the optimally doped nodeless s-wave Fe-HTS Ba0.65Rb0.35Fe2As2. Upon pressure, a strong decrease of the penetration depth in the zero-temperature limit is observed, while the superconducting transition temperature remains nearly constant. More importantly, the low-temperature behaviour of the inverse-squared magnetic penetration depth, which is a direct measure of the superfluid density, changes qualitatively from an exponential saturation at zero pressure to a linear-in-temperature behaviour at higher pressures, indicating that hydrostatic pressure promotes the appearance of nodes in the superconducting gap.
authors.affiliation: Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen, Switzerland.
authors.forename: Z
authors.initials: Z
authors.lastname: Guguchia
authors.affiliation: Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Amato
authors.affiliation: School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: J
authors.initials: J
authors.lastname: Kang
authors.affiliation: Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen, Switzerland.
authors.forename: H
authors.initials: H
authors.lastname: Luetkens
authors.affiliation: Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen, Switzerland.
authors.forename: P K
authors.initials: PK
authors.lastname: Biswas
authors.affiliation: Leibniz-Institut für Festkörper- und Werkstoffforschung (IFW) Dresden, D-01171 Dresden, Germany.
authors.forename: G
authors.identifier: http://orcid.org/0000-0002-7722-6599
authors.initials: G
authors.lastname: Prando
authors.affiliation: Physik-Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
authors.forename: F
authors.initials: F
authors.lastname: von Rohr
authors.affiliation: Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-422 Wroclaw, Poland.
authors.forename: Z
authors.initials: Z
authors.lastname: Bukowski
authors.affiliation: Department of Physics, Tbilisi State University, Chavchavadze 3, GE-0128 Tbilisi, Georgia.
authors.forename: A
authors.initials: A
authors.lastname: Shengelaya
authors.affiliation: Physik-Institut der Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
authors.forename: H
authors.initials: H
authors.lastname: Keller
authors.affiliation: Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen, Switzerland.
authors.forename: E
authors.initials: E
authors.lastname: Morenzoni
authors.affiliation: School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Rafael M
authors.initials: RM
authors.lastname: Fernandes
authors.affiliation: Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen, Switzerland.
authors.forename: R
authors.initials: R
authors.lastname: Khasanov