arXiv subjects

Hairui Ding

Publications and source records attributed to Hairui Ding.

2 recordsLinked to original sources

arXiv2026

Domain-Direct Band Gaps: Classification and Material Realization

The conventional classification of direct band-gap semiconductors relies on point-like extrema in momentum space. Here, we introduce the concept of domain-direct band gaps, where the conduction-band minimum (CBM) and valence-band maximum (VBM) form extended manifolds in the Brillouin zone. We demonstrate this concept through the material realization of an extreme two-dimensional-two-dimensional (2D-2D) domain-direct band gap in twisted diamond. First-principles calculations show that both the CBM and VBM exhibit nearly flat 2D manifolds in the kx-ky plane with minimal energy variation (a few meV), yielding a direct band gap of 3.264 eV. In contrast, strong dispersion along the out-of-plane kz direction induces anisotropic carrier dynamics, with strongly suppressed in-plane Fermi velocities (down to about 10$^1$-10$^3$ m/s in certain directions) and much larger out-of-plane velocities (about 10$^6$ m/s). The nearly flat CBM and VBM manifolds enhance the joint density of states, leading to a pronounced optical absorption peak at the band gap onset. This new type of domain-direct gap, coupled with strong directional anisotropy, opens up opportunities for anisotropic optoelectronic applications. Our results establish domain-direct band gaps as a new class of semiconductors, demonstrating their feasibility in real materials.

cond-mat.mtrl-sci↗

arXiv2025

Nudged elastic band calculations of stacking and dislocation pathways in diamond

Diamond, the hardest natural crystal, has attracted significant attention for its plasticity, which is reported to be determined by its stacking faults. Studies mainly focused on one-dimensional linear pathways in stacking transitions, neglecting its transverse freedom on the main slip plane. However, in an actual stacking procedure, stacking faults can follow curve line along the slip plane rather than constrained to straight lines. In this study, using ab initio calculations, we mapped the {\gamma}-surface, defined as the landscape of generalized stacking fault energies, along the weakest direction of the {111} orientation in diamond. We then applied the Nudged Elastic Band (NEB) method to determine the minimum energy paths, finding significantly reduced stacking energy barriers compared to previous reports (for the glide-set, our energy barrier is only one-third of that for the traditional direct path). Our calculations reveal that the glide-set can round its high-energy peak, with a lower energy barrier within the entire stacking plane than the shuffle-set. By employing the NEB method, we have constructed the minimum energy path (MEP) for both the stacking and dislocation procedures. Our results provide new insights into the plasticity and stacking faults of diamond, advancing the understanding of superhard carbon material transition, especially the diamond under shear stress.

cond-mat.mtrl-sci↗