Thermally driven phase transitions in freestanding low-buckled silicene, germanene, and stanene

Journal Article · Wed May 31 00:00:00 EDT 2023 · Physical Review Materials

DOI:https://doi.org/10.1103/physrevmaterials.7.054008· OSTI ID:1975732

Davis, John M. ^[1]; Orozco-Galvan, Gustavo S. ^[2]; Barraza-Lopez, Salvador ^[2]

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1. University of Arkansas, Fayetteville, AR (United States); University of Arkansas
2. University of Arkansas, Fayetteville, AR (United States)

Low-buckled silicene, germanene, and stanene are group-IV graphene allotropes. They form a honeycomb lattice out of two interpenetrating (A and B) triangular sublattices that are vertically separated by a small distance Δ_z. The atomic numbers Z of silicon, germanium, and tin are larger than that of carbon (Z_C = 6), making them the first experimentally viable two-dimensional topological insulators. Those materials have a twice-energy-degenerate atomistic structure characterized by the buckling direction of the B sublattice with respect to the A sublattice [whereby the B atom either protrudes above (Δ_z > 0) or below (Δ_z < 0) the A atoms], and the consequences of that energy degeneracy on their elastic and electronic properties have not been reported thus far. Here, we uncover ferroelastic, bistable behavior on silicene, which turns into an average planar structure at about 600 K. Furthermore, the creation of electron and hole puddles obfuscates the zero-temperature spin-orbit coupling (SOC)-induced band gaps at temperatures as low as 200 K, which may discard silicene as a viable two-dimensional topological insulator for room-temperature applications. Germanene, on the other hand, never undergoes a low-buckled-to-planar two-dimensional transformation, becoming amorphous at around 675 K instead, and preserving its SOC-induced band gap despite band broadening. Stanene undergoes a transition onto a crystalline three-dimensional structure at about 300 K, preserving its SOC-induced electronic band gap up to that temperature. Unlike what is observed in silicene and germanene, stanene readily develops a higher-coordinated structure with a high degree of structural order. Furthermore, the structural phenomena are shown to have far-reaching consequences for the electronic and vibrational properties of those two-dimensional topological insulators.

• Research Organization: University of Arkansas, Fayetteville, AR (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: SC0022120
• OSTI ID: 1975732
• Journal Information: Physical Review Materials, Journal Name: Physical Review Materials Journal Issue: 5 Vol. 7; ISSN 2475-9953
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
Electrical properties
Electrical properties of membranes
Ferroelasticity
Mechanical properties of membranes
Phase transitions
Spin-orbit coupling
Structural properties
Thermal properties
Thermomechanical effects
Topological materials