Interwoven atypical quantum states in CeLiBi$_2$

TL;DR

CeLiBi$_2$ is a novel tetragonal Ce$TX_2$ compound exhibiting unique magnetic ordering, an elliptical cycloid structure, and ultralight carriers with a large anomalous Hall effect, revealing complex intertwined magnetic and electronic phenomena.

Contribution

This study reports the discovery and characterization of CeLiBi$_2$, the first in its family with alkali cation substitution, showing unusual magnetic and electronic properties not seen in related compounds.

Findings

Antiferromagnetic order below 3.4 K with incommensurate wave vector.

Unusual elliptical cycloid magnetic structure with in-plane Ce moments.

Presence of ultralight carriers and a large anomalous Hall effect.

Abstract

We report the discovery of CeLiBi$_2$, the first example of a material in the tetragonal Ce$TX_2$ ($T$ = 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 $\Gamma_6$ ground state Kramers doublet that orders antiferromagnetically below $T_N = 3.4$ K with an incommensurate propagation wave vector ${\bf{k}} = (0, 0.0724(4), 0.5)$ 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 $\Gamma_6$ Ce$TX_2$ 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 $\mu_0H = 55$ 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.