Crossover of the pairing symmetry from $s$- to $d$-wave in iron pnictide superconductors

Abstract

One of the major themes in the physics of condensed matter is unconventional superconductivity in correlated electronic systems. The symmetry structure of Cooper pairs is thought to be the key to the understanding of the pairing mechanism of their superconductivity. In iron pnictide superconductors, the precise symmetry of the order parameter as well its evolution with doping remains highly controversial. There is no general consensus on the nature of pairing in iron-based superconductors leaving the perspectives ranging from $s^{++}$ wave, to $s^{\pm }$, and $d$ wave. Here we show that doping induced a sudden change of the pairing symmetry from the $s^{++}$- to $d$-wave in the BaFe${}_{2-x}$Ni${}_x$As${}_2$ system with an $s^{\pm }$ state near the crossover boundary at $x=0.15$. The presence of the $s^{\pm }$ state is of particular scientific interest because an intermediate phase breaks the pairing symmetry when the $s$- and $d$-wave phases come together to interfere. For $x<$ 0.15, the temperature dependence of the London penetration depth, lower critical field, and specific heat in the superconducting (SC) state provides strong evidence for a two-band $s$-wave order parameter. Upon doping for $x>$ 0.15, we find the temperature and magnetic-field contributions to the specific heat in $T^2$ and $\sqrt{H}$, respectively, indicating line nodes in the SC gap. These findings thus clarify the symmetry nature as well as the evolution of the SC order parameter with doping in pnictide superconductors.

arXiv comment20 pages, 3 figures

References in corpus (19)

• Fermi surface nesting induced strong pairing in iron-based superconductors
• Nematic spin correlations in the tetragonal state of uniaxial strained BaFe2-xNixAs2
• Universal heat conduction in the iron-arsenide superconductor KFe2As2 : Evidence of a d-wave state
• s+is State with Broken Time Reversal Symmetry in Fe-Based Superconductors
• Doping dependence of heat transport in the iron-arsenide superconductor Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$: from isotropic to strongly $k$-dependent gap structure
• Change of pairing symmetry in the iron-based superconductor KFe2As2
• Inter-pocket pairing and gap symmetry in Fe-based superconductors with only electron pockets
• Mechanism for a Pairing State with Time-Reversal Symmetry Breaking in Iron-Based Superconductors
• Band and momentum dependent electron dynamics in superconducting $\mathrm{Ba}(\mathrm{F}{\mathrm{e}}_{1-\mathrm{x}}\mathrm{C}{\mathrm{o}}_{\mathrm{x}}{)}_2\mathrm{A}{\mathrm{s}}_2$ as seen via electronic Raman scattering
• Domain walls and their experimental signatures in s+is superconductors
• Incommensurate spin fluctuations in hole-overdoped superconductor KFe2As2
• Large anisotropic uniaxial pressure dependencies of Tc in single crystalline Ba(Fe0.92Co0.08)2As2
• Volovik effect in the $\pm$s-wave state for the iron-based superconductors
• Suppression of superconductivity by Neel-type magnetic fluctuations in the iron pnictides
• Measurement of a Sign-Changing Two-Gap Superconducting Phase in Electron-Doped Ba(Fe_{1-x}Co_x)_2As_2 Single Crystals using Scanning Tunneling Spectroscopy
• Three-dimensional nodal superconducting gap in single crystals Ba(Fe${}_{1-x}$Ni${}_x$)${}_2$As${}_2$
• Thermodynamics of d-wave superconductors in a magnetic field
• Nodeless superconductivity in the presence of spin-density wave in pnictide superconductors: The case of BaFe${}_{2-x}$Ni${}_x$As${}_2$
• Gap Anisotropy in Iron-Based Superconductors: A Point-Contact Andreev Reflection Study of BaFe${}_{2-x}$Ni${}_x$As${}_2$ Single Crystals

Cited by in corpus (1)

• Probing the pairing symmetry in the over-doped Fe-based superconductor Ba_0.35Rb_0.65Fe_2As_2 as a function of hydrostatic pressure