Observation of unoccupied states of SnTe(111) using pump-probe ARPES measurement

Persistence of Structural Distortion and Bulk Band Rashba Splitting in SnTe above Its Ferroelectric Critical Temperature

“…By looking at our ARPES measurements, we identify the S 1 and S 2 surface states as the candidate for the linear dispersion in the occupied states that has been interpreted as a topological surface state in previous studies. In light of the study of Plekhanov and co-workers, our observation of the persistence of local rhombohedral lattice distortions above T c therefore excludes the possible existence of topological surface states at high temperature on the (111) surface, at odds with recent time-resolved ARPES studies . Our new results therefore require a reassessment of these observations.…”

“…In light of the study of Plekhanov and co-workers, 44 our observation of the persistence of local rhombohedral lattice distortions above T c therefore excludes the possible existence of topological surface states at high temperature on the (111) surface, at odds with recent time-resolved ARPES studies. 49 Our new results therefore require a reassessment of these observations. We have characterized the band structure of SnTe(111) using high-energy resolution ARPES measurements with unprecedented quality.…”

Direct Probe of the Ferromagnetic Proximity Effect at the Interface of SnTe/Fe Heterostructure by Polarized Neutron Reflectometry

“…Because the mirror symmetry of crystals is the origin of TCIs’ surface states, it is especially important to evaluate the crystal distortion of the (110) plane, which ensures the topological surface state, and the (001), which is the surface of our sample. Though we did not perform detailed structural analyses on the SnTe sample in this study yet, a crystal deformation of ϵ ∥ ∼ 10 –3 would be expected because, in our previous study, almost the same degree of the crystal deformation was detected in a SnTe layer similarly grown on a CdTe template. This is consistent with Sulich et al, who point out the possibility of a gap opening at an in-plane strain ϵ ∥ ∼ 10 –3 .…”

“…According to a theoretical study by Plekhanov et al, the lattice distortion of this magnitude would not induce the gap opening in the Dirac band of the surface state; therefore, the magnetic proximity effect should not be affected. Actually, at least the Dirac cone is observed with such a degree of strain by time- and angle-resolved photoemission spectroscopy, although it is difficult to determine whether a small gap has opened up or not. In any case, QAHE is considered feasible if the magnetic gap exceeds the structural gap even if it exists.…”

Ferroic Berry Curvature Dipole in a Topological Crystalline Insulator at Room Temperature

“…TCIs are a class of topological quantum materials whose topological surface states are protected by mirror symmetry, unlike TIs, in which time-reversal symmetry protects their states. The topological surface state in a TCI allows an abundant physical nature as in TIs, and this nature can be controlled by mechanical strain, structural distortion, impurity doping, and temperature. − However, progress in the quest for the above-mentioned intriguing physical nature in TCIs has lagged behind that of TIs, and indeed, pioneering research on TCIs has been mainly limited to photoelectron spectroscopy − and scanning tunnelling microscopy. − The rock-salt structure IV–VI materials, Pb 1– x Sn x Te (PST), are a family of TCIs ,, (see Figure a) and host four massive or massless Dirac cones on their (001) surfaces that reflect ferroelectric displacements of atoms at the surfaces. ,, In line with the physics of the BCD, it is envisaged that the ferroelectric structural transition of PST gives rise to structural distortion that renders the BCD tunable and switchable for the following reason. Under the ferroelectric distortion, the mirror symmetry in PST breaks, resulting in opening gaps of the Dirac cones located perpendicular to the direction of ferroelectric distortion (Figure b,c).…”