Fingerprinting triangular-lattice antiferromagnet by excitation gaps

${\mathrm{CeCd}}_3{\mathrm{As}}_3$ is a rare-earth triangular-lattice antiferromagnet with large interlayer separation. Our field-dependent heat capacity measurements at dilution fridge temperatures allow us to trace the field evolution of the spin-excitation gaps throughout the antiferromagnetic and paramagnetic regions. The distinct gap evolution places strong constraints on the microscopic pseudospin model, which, in return, yields a close quantitative description of the gap behavior. This analysis provides crucial insights into the nature of the magnetic state of ${\mathrm{CeCd}}_3{\mathrm{As}}_3$, with a certainty regarding its stripe order and low-energy model parameters that sets a compelling paradigm for exploring and understanding the rapidly growing family of the rare-earth-based triangular-lattice systems.

Figure 1

Open symbols are $T_N$ and $T_U$ vs in-plane field $H$ from the heat capacity data in Figs. 2 and 2; solid circles are $C/T$ values at 100 mK, and lines are guides to the eye. A crossover (XO) region between $T_N$ and $T_U$ is highlighted. Inset: sketch of the stripe-$\mathbf{x}$ AF phase in zero and finite field (see text).

Figure 2

Specific heat $C/T$ vs $T$ shows (a) the nonmonotonic field dependence of $T_N$ for $H<3.5$ T, (b) the emergence of $T_U$ and the XO region for $H>3.5$ T (lines are guides to the eye), (c) the low-$T$ dependence of $C/T$ away from and at the QCP together with the fits from Eqs. (1) and (2) (lines).

Figure 3

$\mathrm{\Delta }$ vs $H$ obtained using Eqs. (1) and (2) (symbols). The excitation spectrum gaps at the ordering vector $Y$ (${\mathrm{\Delta }}_{\mathrm{Y}}$) and complimentary $M$ point (${\mathrm{\Delta }}_{\mathrm{M}}$) for the parameters of the model (3) discussed in text. Inset: Brillouin zone with the $Y$ and $M$ points for the stripe phase in Fig. 1.