II-VI materials such as HgTe and CdTe have gained attention for their potential in topological insulator (TI) applications due to their strong spin-orbit coupling and inverted band structures. HgTe/CdTe quantum wells exhibit quantized edge states with conductance values precisely matching the theoretical prediction of e^2/h per spin channel at cryogenic temperatures (~10 K). These edge states are robust against backscattering, making them ideal for low-power spintronic devices. Recent experiments demonstrated a Hall conductance plateau at ν = ±1/2 in HgTe-based TIs under magnetic fields up to 12 T, confirming their topological nature.
The integration of II-VI TIs into hybrid heterostructures has unlocked new functionalities in quantum computing and sensing platforms. For example, coupling HgTe TIs with superconducting Nb electrodes induced Majorana zero modes (MZMs) at temperatures below 2 K, paving the way for fault-tolerant quantum computing devices. The measured zero-bias conductance peaks exhibited a quantized value of 2e^2/h, consistent with MZM predictions. Additionally, the use of electrostatic gating enabled precise control over the Fermi level within ±10 meV, enhancing device tunability and reproducibility across multiple fabrication runs (>90% yield).
Scalability remains a challenge for II-VI TI-based devices due to material inhomogeneities and fabrication complexities at the nanoscale level (<100 nm). Advanced epitaxial growth techniques like molecular beam epitaxy (MBE) have achieved defect densities below ~10^8 cm^-2 in HgTe/CdTe heterostructures grown on lattice-matched substrates such as ZnCdTe or GaAs(111)B surfaces; this represents an improvement by an order-of-magnitude compared-to previous methods (<10^9 cm^-2). Furthermore,the development-of strain engineering protocols has minimized interfacial dislocations by up-to-50%, ensuring high-quality interfaces critical-for maintaining topological properties over large areas (>1 mm^2).
Theoretical investigations using density functional theory (DFT) combined-with tight-binding models-have predicted novel-II VI-based-TIs-with enhanced stability-and higher transition temperatures (>300 K). For instance,CdSe/ZnSe superlattices were identified-as promising candidates-for room-temperature-TIs due-to their robust-band inversion-induced-by strain effects (~3% lattice mismatch). Experimental validation-is ongoing,but preliminary results indicate-the presence-of protected-edge states-at temperatures-above-200 K,significantly advancing-the field-towards practical applications-in electronics-and spintronics.
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