Dynamics of orbital degrees of freedom probed via isotope $^{121,123}$ Sb nuclear quadrupole moments in Sb-substituted iron-pnictide superconductors

T. Kouchi; K. Yoshinaga; T. Asano; S. Nishioka; M. Yashima; H. Mukuda; A. Iyo; T. Kawashima; S. Miyasaka

doi:10.1103/PhysRevB.108.014507

paper

Dynamics of orbital degrees of freedom probed via isotope $^{121, 123}$ Sb nuclear quadrupole moments in Sb-substituted iron-pnictide superconductors

arXiv:2307.05112 · doi:10.1103/PhysRevB.108.014507

Abstract

Isotope $^{121, 123}$ Sb nuclei with large electric quadrupole moments are applied to investigate the dynamics of orbital degrees of freedom in Sb-substituted iron(Fe)-based compounds. In the parent compound LaFe(As $_{0.6}$ Sb $_{0.4}$ )O, the nuclear spin relaxation rate $^{121, 123} (T_{1}^{- 1})$ at $^{121, 123}$ Sb sites was enhanced at structural transition temperature ( $T_{s} \sim$ 135 K), which is higher than Néel temperature ( $T_{N} \sim$ 125 K). The isotope ratio $^{123} (T_{1}^{- 1}) /^{121} (T_{1}^{- 1})$ indicates that the electric quadrupole relaxation due to the dynamical electric field gradient at Sb site increases significantly toward $T_{s}$ . It is attributed to the critically enhanced nematic fluctuations of stripe-type arrangement of Fe- $3 d_{x z}$ (or $3 d_{y z}$ ) orbitals. In the lightly electron-doped superconducting (SC) compound LaFe(As $_{0.7}$ Sb $_{0.3}$ )(O $_{0.9}$ F $_{0.1}$ ), the nematic fluctuations are largely suppressed in comparison with the case of the parent compound, however, it remains a small enhancement below 80 K down to the $T_{c}$ ( $\sim$ 20 K). The results indicate that the fluctuations from both the spin and orbital degrees of freedom on the $3 d_{x z}$ (or $3 d_{y z}$ ) orbitals can be seen in lightly electron-doped SC state of LaFeAsO-based compounds. We emphasize that isotope $^{121, 123}$ Sb quadrupole moments are sensitive local probe to identify the dynamics of orbital degrees of freedom in Fe-pnictides, which provides with a new opportunity to discuss the microscopic correlation between the superconductivity and both nematic and spin fluctuations simultaneously even in the polycrystalline samples.

arXiv comment7 pages, 4 figures and 1 supplemental file

Dynamics of orbital degrees of freedom probed via isotope 121,123 Sb nuclear quadrupole moments in Sb-substituted iron-pnictide superconductors

Abstract

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Dynamics of orbital degrees of freedom probed via isotope $^{121, 123}$ Sb nuclear quadrupole moments in Sb-substituted iron-pnictide superconductors