Towards layer-selective quantum spin hall channels in weak topological insulator Bi4Br2I2

Abstract

Weak topological insulators, constructed by stacking quantum spin Hall insulators with weak interlayer coupling, offer promising quantum electronic applications through topologically non-trivial edge channels. However, the currently available weak topological insulators are stacks of the same quantum spin Hall layer with translational symmetry in the out-of-plane direction—leading to the absence of the channel degree of freedom for edge states. Here, we study a candidate weak topological insulator, Bi4Br2I2, which is alternately stacked by three different quantum spin Hall insulators, each with tunable topologically non-trivial edge states. Our angle-resolved photoemission spectroscopy and first-principles calculations show that an energy gap opens at the crossing points of different Dirac cones correlated with different layers due to the interlayer interaction. This is essential to achieve the tunability of topological edge states as controlled by varying the chemical potential. Our work offers a perspective for the construction of tunable quantized conductance devices for future spintronic applications.

Observation of Anomalous Planar Hall Effect Induced by One-Dimensional Weak Antilocalization

“…Bulk Bi 4 Br 4 is an ideal system with a strong anisotropy as its building block of the quasi-1D chains stacks with the vdW interaction. − , As shown in Figure a, Bi 4 Br 4 is made up of quasi-1D molecular chains extending along the b axis and possesses the monoclinic structure (space group: C2/m ) with a 107° angle between a and c axes. Due to the vdW interaction of the quasi-1D building block, the sample could be cleaved along both the a axis and the c axis to obtain the fresh (100) surface and (001) surface, respectively.…”

“…Experimentally, the bulk Bi 4 X 4 (X = I or Br) is the ideal system according to the large anisotropy, as its building block is the quasi-1D molecular chain stacking under the van der Waals force. − Due to the large SOI strength of Bi atoms and different stacking orders along the lattice c axis, abundant topological phases have been identified in this system with the 3D form, including weak topological insulator, second-order topological insulator, and topological trivial insulator. ,, The monolayer Bi 4 Br 4 is predicted to be a large-gap quantum spin Hall insulator with an atomic sharp topological nontrivial edge state, which has been consequently confirmed by scanning tunneling microscopy (STM) measurements. ,, This quasi-1D edge state is arranged in a 2D form ((100) surface) by stacking the monolayer Bi 4 Br 4 along the lattice c axis, where the anisotropic topological 2D surface state is expected to be realized under weak interlayer interaction. Due to the interchain coupling along the c axis, the (100) terrace topological surface states open about ∼10 meV gap with two gapless diagonal hinge states and make bulk Bi 4 Br 4 a second-order topological insulator, where the dispersion of the (100) surface along the k y direction is linear and there is barely no dispersion along k z direction. , Therefore, the quasi-1D edge state constructed 2D (100) surface states provide an ideal platform to investigate highly anisotropic electronic structure in 1D confinement.…”

Observation of Emergent Superconductivity in the Topological Insulator Ta2Pd3Te5 via Pressure Manipulation

“…Topological insulators (TIs) possess insulating bulk properties, enabling their edge states to act as conducting channels when backscattering is prohibited by time-reversal symmetry. − These materials boast remarkable features and facilitate unprecedented advancements, including anomalous Hall effect, − quantum valley Hall, , and Majorana zero modes. , Intricate and fantastic quantum states associated with these topological phases are robust against disturbances and decoherence, making them feasible for the promising implementation of TI-based quantum computation. − Moreover, the precise regulation of topological electronic states through external fields and pursuit of topological superconductivity in TI systems are essential prerequisites for realizing next-generation quantum devices, representing frontier focus within the domain of topological electronics. − …”