Exploring the phase diagram of InAs/GaSb/InAs trilayer quantum wells

We study topological insulators based on InAs/GaSb/InAs trilayer quantum wells with different InAs thicknesses ranging from 8.0 to 13.5 nm to experimentally ascertain the phase diagram in this material system. Gate-voltage and temperature-dependent transport measurements reveal distinct transport signatures between samples designed from the trivial-insulating, the topological-insulating, up to the semimetallic phase. Two-carrier transport together with pronounced Van Hove singularities are observable only for the samples grown in the topological-insulating phase and if camelback-like dispersions are present in the hybridized valence or conduction band. The different shaping and the amount of Van Hove singularities in our samples deliver information about a turning point inside the topological-insulating phase. Temperature-dependent measurements allow to further confirm the gap energy values for the trivial- and topological-insulating samples. Furthermore, the indirect inverted gaps are found to be more temperature insensitive in comparison to the trivial gap.