${\mathrm{CeAu}}_2\mathrm{Bi}$: A new nonsymmorphic antiferromagnetic compound

Here, we report the structural and electronic properties of ${\mathrm{CeAu}}_2\mathrm{Bi}$, a new heavy-fermion compound crystallizing in a nonsymmorphic hexagonal structure $\left(P63/mmc\right)$. The ${\mathrm{Ce}}^{3+}$ ions form a triangular lattice which orders antiferromagnetically below $T_N=3.1\mathrm{K}$ with a magnetic hard axis along the $c$ axis. Under applied pressure, $T_N$ increases linearly at a rate of $0.07\mathrm{K}/\mathrm{kbar}$, indicating that the Ce $f$ electrons are fairly localized. In fact, heat capacity measurements provide an estimate of 150(10) $\mathrm{mJ}/\mathrm{mol}{\mathrm{K}}^2$ for the Sommerfeld coefficient. The crystal-field scheme obtained from our thermodynamic data points to a ground state with a dominantly $|j_z=\pm 1/2\rangle$ character, which commonly occurs in systems with a hard $c$ axis. Finally, electronic band structure calculations and symmetry analysis in $k$ space reveal that ${\mathrm{CeAu}}_2\mathrm{Bi}$ hosts symmetry-protected crossings at $k_z=\pi$ in the paramagnetic state.

Figure 1

(a) Hexagonal structure of ${\mathrm{CeAu}}_2\mathrm{Bi},a=4.887\left(1\right)\AA$ and $c=9.375\left(1\right)\AA$. (b) A $c$-axis view of the crystalline structure of ${\mathrm{CeAu}}_2\mathrm{Bi}$ displaying the triangular lattice formed by ${\mathrm{Ce}}^{3+}$ ions.

Figure 2

(a) $\chi \left(T\right)$ at ${\mu }_{0}H=0.1$ T. The top inset shows a zoomed-in view of $\chi \left(T\right)$ in the low-temperature range. The bottom insets show ${(\chi -{\chi }_0)}^{-1}$ as a function of temperature. (b) $M$ as a function of applied magnetic field. The solid red lines are fits using a CEF mean-field model.

Figure 3

(a) Specific heat measurements for ${\mathrm{CeAu}}_2\mathrm{Bi}$ and ${\mathrm{LaAu}}_2\mathrm{Bi}$. The insets show $C_p/T$ as a function of $T^2$. The solid line is an extrapolation of the fit used to extract the Sommerfeld coefficient. (b) Magnetic specific heat and entropy of ${\mathrm{CeAu}}_2\mathrm{Bi}$. The solid red line is a fit using a CEF mean-field model. (c) Specific heat behavior as a function of temperature of ${\mathrm{CeAu}}_2\mathrm{Bi}$ for several applied magnetic fields.

Figure 4

(a) $\rho \left(T\right)$ for ${\mathrm{CeAu}}_2\mathrm{Bi}$ and ${\mathrm{LaAu}}_2\mathrm{Bi}$. The inset shows the low-temperature behavior of the ${\mathrm{CeAu}}_2\mathrm{Bi}$ resistivity for several applied magnetic fields. (b) $\rho \left(T\right)$ of ${\mathrm{CeAu}}_2\mathrm{Bi}$ for different applied pressures. The insets show the low-temperature range of the resistivity for several applied pressures and the temperature-pressure phase diagram, respectively.

Figure 5

(a) Electronic band structure of ${\mathrm{CeAu}}_2\mathrm{Bi}$. (b) Zoom-in view of the electronic structure for $k_z=\pi$. Two bands with opposite $R\text{−}z$ eigenvalues (red and blue) intersect forming a line (green), which intersects the chemical potential (gray plane) at the two points where the Fermi surfaces of the individual bands (black circles) intersect (see text for details). (c) Density of states and (d) Fermi surface of ${\mathrm{CeAu}}_2\mathrm{Bi}$.