Anomalies in the temperature evolution of the Dirac states in a topological crystalline insulator SnTe

TL;DR

This study investigates how temperature variations affect the Dirac surface states in the topological crystalline insulator SnTe, revealing anomalies linked to structural changes and highlighting the role of anharmonicity and strain in topological robustness.

Contribution

It provides the first detailed experimental and theoretical analysis of temperature-induced anomalies in Dirac states of SnTe, emphasizing the influence of structural and anharmonic effects on topological properties.

Findings

Bulk bands shift with temperature, approaching and receding from the Fermi level.

Surface Dirac slopes vary with temperature, indicating changes in electronic structure.

Dirac state intensity diminishes at high temperatures due to complex structural effects.

Abstract

Discovery of topologically protected surface states, believed to be immune to weak disorder and thermal effects, opened up a new avenue to reveal exotic fundamental science and advanced technology. While time-reversal symmetry plays the key role in most such materials, the bulk crystalline symmetries such as mirror symmetry preserve the topological properties of topological crystalline insulators (TCIs). It is apparent that any structural change may alter the topological properties of TCIs. To investigate this relatively unexplored landscape, we study the temperature evolution of the Dirac fermion states in an archetypical mirror-symmetry protected TCI, SnTe employing high-resolution angle-resolved photoemission spectroscopy and density functional theory studies. Experimental results reveal a perplexing scenario; the bulk bands observed at 22 K move nearer to the Fermi level at 60 K and again shift back to higher binding energies at 120 K. The slope of the surface Dirac bands at 22 K becomes smaller at 60 K and changes back to a larger value at 120 K. Our results from the first-principles calculations suggest that these anomalies can be attributed to the evolution of the hybridization physics with complex structural changes induced by temperature. In addition, we discover drastically reduced intensity of the Dirac states at the Fermi level at high temperatures may be due to complex evolution of anharmonicity, strain, etc. These results address robustness of the topologically protected surface states due to thermal effects and emphasize importance of covalency and anharmonicity in the topological properties of such emerging quantum materials.