Interwoven atypical quantum states in CeLiBi${}_2$

Abstract

We report the discovery of CeLiBi${}_2$, the first example of a material in the tetragonal Ce$T{X}_2$ ($T$ = transition metal; $X$ = pnictogen) family wherein an alkali cation replaces the typical transition metal. Magnetic susceptibility and neutron powder diffraction measurements are consistent with a crystal-field $\hat{I}{“}_6$ ground state Kramers doublet that orders antiferromagnetically below $T_N=3.4$ K with an incommensurate propagation wave vector $\mathbf{k}=(0,0.0724(4),0.5)$ that generates a nanometric modulation of the magnetic structure. The best model of the ordered state is an elliptical cycloid with Ce moments primarily residing in the $ab$ plane. This is highly unusual, as all other $\hat{I}{“}_6$ Ce$T{X}_2$ members order ferromagnetically. Further, we observe an atypical hard-axis metamagnetic transition at $2$ T in magnetostriction, magnetization, and resistivity measurements. CeLiBi${}_2$ is a rare example of a highly conductive material with dominant skew scattering leading to a large anomalous Hall effect. Quantum oscillations with five frequencies arise in magnetostriction and magnetic susceptibility data to $T=30$ K and $\hat{I}{¼}_{0}H=55$ T, which indicate small Fermi pockets of light carriers with effective masses as low as 0.07$m_e$. Density functional theory calculations indicate that square-net Dirac-like Bi$-p$ bands are responsible for these ultralight carriers. Together, our results show that CeLiBi${}_2$ enables multiple atypical magnetic and electronic properties in a single clean material.

16 pages, 10 figures