Electronic band structure of a nodal line semimetal candidate ErSbTe

TL;DR

ErSbTe is investigated as a heavier Lanthanide member of the LnSbTe family to understand how spin–orbit coupling and 4f magnetism shape topological band structure. The study combines bulk thermodynamic and transport measurements with ARPES and first-principles calculations (with and without SOC) to map the electronic structure and assess symmetry protections. It finds a nonsymmorphic symmetry–protected nodal line along X–R with a Dirac crossing near the Fermi level, and SOC-induced gaps along certain directions, notably Γ–M, while magnetic ordering occurs at two close antiferromagnetic transitions around 1.9 K and 1.75 K. The work highlights the delicate balance between symmetry, SOC, and magnetism in governing topological states in ErSbTe and positions this material as a benchmark for topology in magnetic LnSbTe compounds.

Abstract

The LnSbTe family is well known for hosting a plethora of intriguing characteristics stemming from its crystalline symmetry, magnetic structure, 4f electronic correlations and spin orbit coupling (SOC) phenomena. In this paper, we have systematically studied the bulk electrical and thermodynamic properties and electronic structure of the nodal line semimetal candidate ErSbTe using angle resolved photoemission spectroscopy (ARPES) corroborated with first principles based theoretical band structure calculations with and without considering the effect of SOC, a critical factor dictating the band degeneracy which depends on the choice of the Ln atom. Corroborative temperature dependent susceptibility, electrical resistivity and thermodynamic measurements, coherently exhibit paramagnetic to antiferromagnetic phase transition approximately at 1.94 K, and another sharp anomaly at 1.75 K. The zero field cooled resistivity measurement does not show the characteristic hump like feature in the other LnSbTe materials. The electronic band structure of ErSbTe, exhibits a diamond shaped Fermi surface. Along the high symmetry direction GX, electronic bands are projected to cross over the Fermi energy, necessitated by the nonsymmorphic symmetry of the system. The other crossing along this direction is gapped, which evolves along the momentum space reaching its maximum along the GM direction.

Figures (4)

• Figure 1: Crystal structure, electronic band structure, thermodynamic, magnetic and transport properties of ErSbTe. (a) Crystal structure of ErSbTe, containing 2D square planar Sb square-net and zigzag Er-Te layers. Electronic band structure (b) without and (c) with the spin--orbit coupling (SOC) along high symmetry directions of corresponding Brillouin zone presented on (b). Temperature dependencies of the (e) inverse magnetic susceptibility (f) electrical resistivity measured in magnetic fields of 0 and 9 T, and (g) specific heat of ErSbTe single crystals. The solid red line in panel (e) represents the Curie-Weiss fit. Upper inset in panel (e) depicts the magnetic susceptibility measured at the lowest temperatures measured in zero-field-cooled and field-cooled regimes (solid blue circles and open green diamonds, respectively); Lower inset in panel (e) presents the field dependence of the magnetization measured at 1.74 K with an increasing (open black squares) and decreasing (solid blue circles) magnetic field. The inset in panel (g) depicts the low-temperature specific heat data.
• Figure 2: Fermi surface (FS) and constant energy contour (CEC) maps of ErSbTe. (a) Experimentally observed Fermi surface map and (b) CEC maps at different binding energies (mentioned at each subplot) of ErSbTe at an incident photon energy of 95 eV, the surface Brillouin zone is marked with a blue-dashed square and all the high symmetry points ($\overline{\Gamma}$, $\overline{\text{M}}$ and $\overline{\text{X}}$) are also indicated. (c) FS and CECs obtained from incident photon energy of 85 eV (measured at the respective binding energy positions). The ARPES measurements were performed at Stanford Synchrotron Radiation Lightsource (SSRL) endstation 5-2 at a temperature of 12 K.
• Figure 3: Electronic structure along the $\overline{\Gamma}$--$\overline{\text{X}}$ direction. (a) Electronic dispersion map along $\overline{\text{X}}$--$\overline{\Gamma}$--$\overline{\text{X}}$ direction measured with incident photon energy of 35 eV, (b) the theoretically calculated surface projected band structure along $\overline{\Gamma}$--$\overline{\text{X}}$. (c) Magnified view of the dispersion map in the vicinity of $\overline{\text{X}}$ high symmetry point (indicated with the box in the panel (a)), (d) second derivative of Fig. (c). The broken pink (orange) lines act as guide for the eyes indicating bands $\beta$$(\alpha)$, converging to form the Dirac point. The ARPES dispersion maps were collected at beam line 5--2 in SSRL at a temperature of 12 K.
• Figure 4: ARPES band dispersions along the $\overline{\Gamma}$--$\overline{\text{M}}$ and $\overline{\text{M}}$--$\overline{\text{X}}$ directions. (a) Cuts parallel to the $\overline{\Gamma}$--$\overline{\text{M}}$ high symmetry direction. (b) second derivative of (a). (c) Band dispersion along the $\overline{\text{M}}$--$\overline{\text{X}}$ direction and (d) its second derivative. The measurements were performed at beamline 5--2 in SSRL at a temperature of 12 K.