Fermiology of Chiral Cadmium Diarsenide CdAs2, a Candidate for Hosting Kramers-Weyl Fermions

Abstract

Nonmagnetic chiral crystals are a new class of systems hosting Kramers-Weyl Fermions, arising from the combination of structural chirality, spin-orbit coupling (SOC), and time-reversal symmetry. These materials exhibit nontrivial Fermi surfaces with SOC-induced Chern gaps over a wide energy range, leading to exotic transport and optical properties. In this study, we investigate the electronic structure and transport properties of CdAs₂, a newly reported chiral material. We use synchrotron-based angle-resolved photoelectron spectroscopy (ARPES) and density functional theory (DFT) to determine the Fermiology of the (110)-terminated CdAs₂ crystal. Our results, together with complementary magnetotransport measurements, suggest that CdAs₂ is a promising candidate for novel topological properties protected by the structural chirality of the system. Our work sheds light on the details of the Fermi surface and topology for this chiral quantum material, providing useful information for engineering novel spintronic and optical devices based on quantized chiral charges, negative longitudinal magnetoresistance, and nontrivial Chern numbers.

Figure 1

Crystal structure and electronic band structure of bulk CdAs₂. (a) Optimized primitive (left) and conventional (right) unit cells of CdAs₂. (b) First Brillouin zone of the primitive cell. (c) Calculated electronic band structure without SOC effects. (d) Calculated electronic band structure including SOC effects. The Fermi level is set to zero and marked by a horizontal red dashed line. Cd and As atoms are represented by yellow and purple balls, respectively. The Kramers–Weyl nodes (d) are marked by yellow circles.

Figure 2

Characterization of the CdAs₂ single crystal. (a) High-resolution transmission electron microscopy (HR-TEM) image showing the crystalline structure of CdAs₂. (b) Small-area electron diffraction (SAED) pattern confirming the single crystal nature of CdAs₂, although the existence of elongated spots is a fingerprint of a slight mosaicity. (c) X-ray diffraction (XRD) pattern revealing the high quality of the crystal with sharp Bragg peaks. (d) Temperature-dependent magnetoresistance curve of CdAs₂ single crystal showing a linear dependence at low temperatures and a saturation behavior at high temperatures.

Figure 3

Top (left panel) and side (right panel) view of (2 × 1) (top panel) and (3 × 1) (bottom panel) supercell of (a) As–S1, (b) As–S2, (c) Cd–S1, and (d) Cd–S2, respectively. Lighter colors represent lower atoms for better visualization of surface atoms.

Figure 4

(a) Fermi surface of CdAs₂ showing the electron pockets of the conduction band at the Fermi level, covering several Brillouin zones. (b) Constant energy surface at 1 eV and (c) 2.35 eV below the Fermi level illustrating the valence band structure evolution at higher k-values. The measurements were carried out at 40 K using hν = 100 eV photons in horizontal polarization setups. On the constant energy cuts, the projection of the Wigner–Seitz cells were overlaid and high-symmetry points were marked.

Figure 5

Experimental band structure of bulk CdAs₂ along various high-symmetry directions. (a) ARPES repeated along the X–M–X path, showing a large view of the valence band structure. (b) Second derivative plot to aid the visualization of the states. (c) Zoomed-in view of part a near the Fermi level, highlighting the pockets belonging to the conduction band manifold. (d) ARPES valence band structure measured along the Z–M–Z path (negative k_x values). (e) Corresponding second derivative plot. The Z–M–Z path was also collected at positive k_x values and shown in part f along with the (g) second derivative. The valence band was also measured along the (h, i) P–X–P path and (j, k) Z–P direction.