Identifying possible pairing states in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">Sr</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">RuO</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:math> by tunneling spectroscopy
Shu-Ichiro Suzuki, Masatoshi Sato, Yukio Tanaka
Abstract
We examine the tunneling spectroscopy of three-dimensional normal-$\mathrm{metal}/{\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ junctions as an experimental means to identify pairing symmetry in ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$. In particular, we consider three different possible pairing states in ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$: spin-singlet chiral $d$-wave, spin-triplet helical $p$-wave, and spin-nematic $f$-wave ones, all of which are consistent with recent nuclear-magnetic-resonance experiments [A. Pustogow et al., Nature (London) 574, 72 (2019)]. The Blonder-Tinkham-Klapwijk theory is employed to calculate the tunneling conductance, and the cylindrical two-dimensional Fermi surface of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ is properly taken into account as an anisotropic effective mass and a cutoff in the momentum integration. It is pointed out that the chiral $d$-wave pairing state is inconsistent with previous tunneling conductance experiments along the $c$ axis. We also find that the remaining candidates, the spin-triplet helical $p$-wave pairing state and the spin-nematic $f$-wave ones, can be distinguished from each other by the in-plane tunneling spectroscopy along the $a$ and $b$ axes.