Triangular lattice, with each site coordinating with six neighbors, is one most common network in two-dimensional (2D) limit. Manifestations of peculiar properties in the lattice, including magnetic frustration and quantum spin liquid, have been restricted to single-orbital tight-binding (TB) model so far, while the orbital degree of freedom is largely overlooked. Here, by combining TB modeling with first-principles calculations, we demonstrate the rich electronic structures of triangular lattice with multiple $(p_{x}, p_{y}, p_{z})$
(
p
x
,
p
y
,
p
z
)
orbitals. Type I/II Dirac point, quadratic nodal point and nodal-loops are observed, and the topological phase diagram is mapped out by manipulating the horizontal mirror symmetry, spin-orbit coupling and energy position of relevant orbitals. Remarkably, we show that large-gap quantum spin Hall phase (∼0.2 eV) can be realized in experimentally achievable systems by growing indium monolayer on a series of semiconducting substrates, such as C/Si/Ge(111) and SiC(0001) surfaces, and the proposed materials capture the TB parameter space well. Our work not only provides physical insights into the orbital physics in 2D lattices, but also sheds light on the integration of novel quantum states with conventional semiconductor technology for potential applications, such as dissipationless interconnects for electronic circuits.
The 60NiTi (Ni60wt%–Ti40wt%) intermetallic is a hard-to-process material. Understanding of hot deformation behavior is crucial for the hot working of 60NiTi. This work studied hot deformation behavior and corresponding microstructure of the hot isostatic pressed 60NiTi in the temperature range of 900 °C–1050 °C and at strain rates of 0.1, 0.01, and 0.001 s-1 through a hot compression test. The flow stress and microstructure were susceptible to the hot deformation parameters. The flow stress decreased with the increase in deformation temperature and decrease in strain rate. Work hardening occurred at a small strain, then followed by softening; finally, near-dynamic equilibrium was achieved between work hardening and softening. A constitutive equation was developed to describe the effects of strain rate and temperature on flow stress. Simulation of hot deformation via the finite element method revealed the workpiece’s inhomogeneous deformation. The deformation occurred mainly in the center area of the cylindrical sample, resulting in high stress and strain concentrations in this region and causing the equiaxial grains to be compressed into prolate grains. This work can provide guidance for the hot working, such as forging and hot rolling, of 60NiTi.
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