Nematic transition and highly two-dimensional superconductivity in BaTi${}_2$Bi${}_2$O revealed by ${}^{209}$Bi-nuclear magnetic resonance/nuclear quadrupole resonance measurements

Abstract

In this Rapid Communication, a set of ${}^{209}$Bi-nuclear magnetic resonance (NMR)/nuclear quadrupole resonance (NQR) measurements has been performed to investigate the physical properties of superconducting (SC) BaTi${}_2$Bi${}_2$O from a microscopic point of view. The NMR and NQR spectra at 5~K can be reproduced with a non-zero in-plane anisotropic parameter $\eta$, indicating the breaking of the in-plane four-fold symmetry at the Bi site without any magnetic order, i.e., `the electronic nematic state'. In the SC state, the nuclear spin-lattice relaxation rate divided by temperature, $1/T_{1}T$, does not change even below $T_{\mathrm{c}}$, while a clear SC transition was observed with a diamagnetic signal. This observation can be attributed to the strong two-dimensionality in BaTi${}_2$Bi${}_2$O. Comparing the NMR/NQR results among BaTi${}_2$$Pn$${}_2$O ($Pn$ = As, Sb, and Bi), it was found that the normal and SC properties of BaTi${}_2$Bi${}_2$O were considerably different from those of BaTi${}_2$Sb${}_2$O and BaTi${}_2$As${}_2$O, which might explain the two-dome structure of $T_{\mathrm{c}}$ in this system.

5 pages, 6 figures

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