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1. Luminescence Properties of Defects in GaN: Solved and Unsolved Problems

   https://doi.org/10.3390/solids6030052  

   Reshchikov, Michael A (September 2025, Solids)

   Chai, Lucy (Ed.)

   Gallium Nitride (GaN) is a wide-bandgap semiconductor that has revolutionized optoelectronic applications, enabling blue/white light-emitting devices and high-power electronics. Point defects in GaN strongly influence its optical and electronic properties, producing both beneficial and detrimental effects. This review provides a comprehensive update on the current understanding of point defects in GaN and their impact on photoluminescence (PL). Since our earlier review (Reshchikov and Morkoç, J. Appl. Phys. 2005, 97, 061301), substantial progress has been made in this field. PL bands associated with major intrinsic and extrinsic defects in GaN are now much better understood, and several defects in undoped GaN (arising from unintentional impurities or specific growth conditions) have been identified. Notably, the long-debated origin of the yellow luminescence band in GaN has been resolved, and the roles of Ga and N vacancies in the optical properties of GaN have been revised. Zero-phonon lines have been discovered for several defects. Key parameters, such as electron- and hole-capture coefficients, phonon energies, electron–phonon coupling strength, thermodynamic charge transition levels, and the presence of excited states, have been determined or refined. Despite these advances, several puzzles associated with PL remain unsolved, highlighting areas for future investigation. 

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2. Computational Discovery of a Novel Yttrium Silicide as an Ambient Pressure Superconductor

   https://doi.org/10.1002/andp.202500210  

   Tao, Shuo; Sun, Ying; Zhu, Li (November 2025, Annalen der Physik)

   Abstract Metal silicides have garnered significant attention due to their diverse crystalline structures, tunable electronic properties, and potential applications in superconducting devices. While numerous rare‐earth metal silicides (REMSs) demonstrate superconductivity at ambient pressure, the known yttrium silicide phases exhibit extremely low superconducting critical temperatures ( K), limiting their practical applications. Through comprehensive crystal structure prediction and first‐principles calculations, the discovery of a novel ‐ phase that exhibits superconductivity with a of 8.4 K at ambient pressure is reported. This is significantly higher than any previously reported binary yttrium silicide. This electron‐phonon coupling calculations reveal that the unique dumbbell silicon network in this structure plays a crucial role in mediating strong electron‐phonon interactions, with a coupling parameter . This finding expands the fundamental understanding of structure‐property relationships in metal silicides and highlights the potential of yttrium silicides as promising candidates for next‐generation superconducting electronics, including quantum circuits and superconducting qubits. 

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3. Intersystem crossing and exciton–defect coupling of spin defects in hexagonal boron nitride

   https://doi.org/10.1038/s41524-021-00525-5  

   Smart, Tyler J.; Li, Kejun; Xu, Junqing; Ping, Yuan (December 2021, npj Computational Materials)

   null (Ed.)

   Abstract Despite the recognition of two-dimensional (2D) systems as emerging and scalable host materials of single-photon emitters or spin qubits, the uncontrolled, and undetermined chemical nature of these quantum defects has been a roadblock to further development. Leveraging the design of extrinsic defects can circumvent these persistent issues and provide an ultimate solution. Here, we established a complete theoretical framework to accurately and systematically design quantum defects in wide-bandgap 2D systems. With this approach, essential static and dynamical properties are equally considered for spin qubit discovery. In particular, many-body interactions such as defect–exciton couplings are vital for describing excited state properties of defects in ultrathin 2D systems. Meanwhile, nonradiative processes such as phonon-assisted decay and intersystem crossing rates require careful evaluation, which competes together with radiative processes. From a thorough screening of defects based on first-principles calculations, we identify promising single-photon emitters such as Si VV and spin qubits such as Ti VV and Mo VV in hexagonal boron nitride. This work provided a complete first-principles theoretical framework for defect design in 2D materials. 

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4. Respective Roles of Electron-Phonon and Electron-Electron Interactions in the Transport and Quasiparticle Properties of SrVO3

   https://doi.org/10.1103/PhysRevLett.133.186501  

   Abramovitch, David J; Mravlje, Jernej; Zhou, Jin-Jian; Georges, Antoine; Bernardi, Marco (October 2024, Physical Review Letters)

   The spectral and transport properties of strongly correlated metals, such as SrVO3 (SVO), are widely attributed to electron-electron (𝑒−𝑒) interactions, with lattice vibrations (phonons) playing a secondary role. Here, using first-principles electron-phonon (𝑒-ph) and dynamical mean field theory calculations, we show that 𝑒-ph interactions play an essential role in SVO: they govern the electron scattering and resistivity in a wide temperature range down to 30 K, and induce an experimentally observed kink in the spectral function. In contrast, the 𝑒−𝑒 interactions control quasiparticle renormalization and low temperature transport, and enhance the 𝑒-ph coupling. We clarify the origin of the near 𝑇2 temperature dependence of the resistivity by analyzing the 𝑒−𝑒 and 𝑒-ph limited transport regimes. Our work disentangles the electronic and lattice degrees of freedom in a prototypical correlated metal, revealing the dominant role of 𝑒-ph interactions in SVO. 

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5. Exciton dispersion and exciton–phonon interaction in solids by time-dependent density functional theory

   https://doi.org/10.1063/5.0137326  

   Liu, Junyi; Lu, Gang; Zhang, Xu (January 2023, The Journal of Chemical Physics)

   Understanding, predicting, and ultimately controlling exciton band structure and exciton dynamics are central to diverse chemical and materials problems. Here, we have developed a first-principles method to determine exciton dispersion and exciton–phonon interaction in semiconducting and insulating solids based on time-dependent density functional theory. The first-principles method is formulated in planewave bases and pseudopotentials and can be used to compute exciton band structures, exciton charge density, ionic forces, the non-adiabatic coupling matrix between excitonic states, and the exciton–phonon coupling matrix. Based on the spinor formulation, the method enables self-consistent noncollinear calculations to capture spin-orbital coupling. Hybrid exchange-correlation functionals are incorporated to deal with long-range electron–hole interactions in solids. A sub-Hilbert space approximation is introduced to reduce the computational cost without loss of accuracy. For validations, we have applied the method to compute the exciton band structure and exciton–phonon coupling strength in transition metal dichalcogenide monolayers; both agree very well with the previous GW-Bethe–Salpeter equation and experimental results. This development paves the way for accurate determinations of exciton dynamics in a wide range of solid-state materials. 

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