By combining density functional theory with low-energy effective Hamiltonian, we demonstrate strain-engineered electronic and topological properties of the recently synthesized two-dimensional (2D) bismuthene on SiC(0001) substrate. As bismuthene on SiC(0001) exhibits an indirect gap of 0.62 eV with nontrivial topology, we show that the band gap size can be further increased by an applied tensile strain, which follows a nearly linear fashion. Especially, with a tensile strain of 7%, the topological gap can be enhanced to an unprecedented value of 0.83 eV, originating from the different deformation potentials of the conduction band minimum principally contributed from p orbitals of Bi and valance band maximum from the hybridized states of Bi overlayer and SiC substrate. Moreover, we discuss the strength of spin–orbit coupling, in additional to the strain effect, in tuning the electronic structures and topological edge states. Our results suggest the promise of strain engineering in manipulating large-gap quantum spin Hall states on conventional semiconductor for practical dissipationless electronic transport and quantum information processing.

Recent years have witnessed a surge of research in twodimensional (2D) ferroelectric structures that may circumvent the depolarization effect in conventional perovskite oxide films. Herein, by first-principles calculations, we predict that an orthorhombic phase of lead(II) oxide, PbO, serves as a promising candidate for 2D ferroelectrics with good stability. With a semiconducting nature, 2D ferroelectric PbO exhibits intrinsic valley polarization, which leads to robust ferroelectricity with an in-plane spontaneous polarization of 2.4 × 10 −10 C/m and a Curie temperature of 455 K. Remarkably, we reveal that the ferroelectricity is strain-tunable, and ferroelasticity coexists in the PbO film, implying the realization of 2D multiferroics. The underlying physical mechanism is generally applicable and can be extended to other oxide films such as ferroelectric SnO and GeO, thus paving an avenue for future design and fabrication of functional ultrathin devices that are compatible with Si-based technology.

Quantum spin Hall to quantum anomalous Hall phase transition in monolayer jacutingaite (Pt2HgSe3) induced by chalogen (S, Se, Te) functionalization.

Two-dimensional (2D) quadrupole topological insulators, featured by topologically protected 0D corner modes, have recently attracted tremendous interest in condensed matter and materials physics. Herein, we construct a specific electric circuit made of capacitors and inductors forming a 2D Kekulé hexagonal lattice for quadrupole topological phase and corner modes. Trivial–nontrivial topological phase transition can be controlled by varying capacitance in the circuit, so that distinct topological edge states appear in 1D ribbons and corner states emerge in 0D flakes. We explore the field strength distribution and two-point impedance with respect to excitation frequency, and reveal that the topological corner resonance is robust against size of the LC network and randomness of the capacitors/inductors, a great benefit for experimental detection. Our results enrich the family of designer topoelectrical circuit as a flexible and tunable platform to achieve exotic quantum phases, which may have potential for future telecommunications, signal processing and quantum computing.

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