Interwoven atypical quantum states in CeLiBi2

We report the discovery of CeLiBi2, the first example of a material in the tetragonal CeTX2 (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 Γ6 ground-state Kramers doublet that orders antiferromagnetically below TN=3.4 K with an incommensurate propagation wave vector 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 Γ6CeTX2 members order ferromagnetically. Further, we observe an atypical hard-axis metamagnetic transition at 2 T in magnetostriction, magnetization, and resistivity measurements. CeLiBi2 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 μ0H=55 T, which indicate small Fermi pockets of light carriers with effective masses as low as 0.07me. Density functional theory calculations indicate that square-net Dirac-like Bi-p bands are responsible for these ultralight carriers. Together, our results show that CeLiBi2 enables multiple atypical magnetic and electronic properties in a single clean material.