High-pressure is utilized to realize new 2D layered structures in PdSe₂ with high-mobility transport anisotropy for photovoltaic applications.

Emerging two-dimensional (2D) noble-metal dichalcogenide (NMDC) PdX₂ (X = S and Se) materials crystallize in an unusual orthorhombic structure (2O phase) with unique pentagons and PdX₄ planar squares as building blocks, and have attracted tremendous attention in recent years for their novel physical and chemical properties, as well as promising applications in the future. Motivated by the attractive properties and encouraging applications of PdX₂ materials, we explore the 2O phase NMDC material PdSSe using particle swarm optimization algorithms combined with first-principles calculations. We not only uncover three stable low-energy bulk phases, but also predict two polymorphs of the 2D monolayer exfoliated from the bulk phases, exhibiting mechanical, dynamic, and thermal stabilities. Due to its novel puckered pentagonal structure, the PdSSe monolayer exhibits flexible mechanical properties with anisotropic Young's modulus and Poisson's ratio. The bandgaps of the two polymorphs of the 2D pentagonal PdSSe monolayer are 2.10 and 2.06 eV, and their band-edges perfectly straddle the redox potential of water. Furthermore, these materials possess excellent light absorption in the visible and ultraviolet regions, and the absorption coefficients reach the order of 10⁶ cm⁻¹. More importantly, the predicted materials exhibit highly desirable carrier mobilities and anisotropy, which can promote the separation of the photogenerated electrons and holes, and effectively reduce the probability of recombination, thus remarkably promoting photocatalytic water splitting. These excellent properties enable PdSSe monolayers as candidate materials for promising applications in high-performance optoelectronic and nanoelectronic devices. The predicted unconventional properties of PdSSe not only supply a meaningful complement to the fascinating NMDC materials of PdSe₂ and PdS₂, but also will attract extensive interest from a wide audience to explore unanticipated properties and design new functional devices based on PdSSe.

Recently, signatures of superconductivity with critical temperature from 20 to 30 K have been reported in pressured trilayer nickelate La₄Ni₃O₁₀ through a pressure-induced structure transition. Here we explore the evolution of electronic structures and electronic correlations in different phases of La₄Ni₃O₁₀ under corresponding pressure regions, by using density functional theory (DFT) combined with dynamical mean-field theory (DMFT). Similar to bilayer superconductor La₃Ni₂O₇, the electronic bands in superconducting La₄Ni₃O₁₀ are dominated by Ni-3 d x 2 − y 2 and 3 d z 2 orbits near the Fermi level, in contrast, the inner Ni–O plane in La₄Ni₃O₁₀ generates a doublet hole-pocket Fermi surfaces around the Brillouin-zone corner, meanwhile one branch of the Ni- 3 d z 2 bands is pushed very close above the Fermi level, which can induce an electron pocket through small electron doping. The DFT+DMFT simulations suggest that the electronic correlations only give minor modification to the Fermi surfaces, meanwhile the Ni- 3 d z 2 and 3 d x 2 − y 2 states on outer Ni–O layers have considerable greater mass enhancements than on the inner layer. The sensitiveness of electronic structure under doping and unique layer dependence of correlation suggest a distinct superconducting mechanism with respect to bilayer La₃Ni₂O₇. Based on the DFT and DFT+DMFT simulations, we eventually derive a trilayer effective tight-binding model, which can produce rather precise electronic bands and Fermi surfaces, hence can serve as an appropriate model to further study the superconducting mechanism and paring symmetry in trilayer La₄Ni₃O₁₀.