Robust cross-chain surface interstitial electronic states and doping-enhanced superconductivity in monolayer $M_2$N ($M$= Ti, Zr, Hf) electrides

Abstract

The exploration of electrides holds great promise for advancing both fundamental physics and chemistry, owing to their unique characteristics arising from loosely bound interstitial anionic electrons. Here we report a class of cross-chain electrides, distinguished by two distinct anionic electron subchannels forming alternating chains in real space. Through structural symmetry analysis and first-principles calculations, we identify two-dimensional $M_2$N ($M$ = Ti, Zr, Hf) materials as prototypical systems exhibiting these unique features. The anionic electron channels on the upper and lower surfaces of these materials display a vertically alternating pattern, with their projected bands revealing momentum-dependent splitting behavior in the reciprocal space, protected by a crystal symmetry operation $\mathcal{O}$. Notably, the cross-chain electride characteristic in the $M_2$N monoalyers is independent of the layer number and remains robust on the upper and lower surfaces of layered structures, presenting a pronounced and robust surface interstitial electronic state. Additionally, we have explored the superconductivity of these systems, and found that both Ti${}_2$N and Zr${}_2$N are intrinsic superconductors with superconducting transition temperatures below 1.0 K. Further results show that appropriate hole doping can significantly enhance their superconducting transition temperatures and can induce the Hf${}_2$N monolayer to exhibit superconductivity. Our findings provide valuable insights into the design and tuning of novel electrides with enhanced superconducting properties, offering another pathway for deeply understanding the interplay between electride behavior and superconductivity in novel materials.

8 Pages, 7 figures

References in corpus (17)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• High-mobility transport anisotropy and linear dichroism in few-layer black phosphorus
• Optimized norm-conserving Vanderbilt pseudopotentials
• Controlling magnetism in 2D CrI3 by electrostatic doping
• Altermagnetism: spin-momentum locked phase protected by non-relativistic symmetries
• On the origin of magnetic anisotropy in two dimensional CrI${}_3$
• Accurate Measurement of the Cleavage Energy of Graphite
• Discovery of two-dimensional anisotropic superconductivity at KTaO${}_3$ (111) interfaces
• Two-dimensional superconductivity at the surfaces of KTaO3 gated with ionic liquid
• Superconductivity in Li6P electride
• Spin chirality fluctuation in two-dimensional ferromagnets with perpendicular anisotropy
• Anomalous Dirac Plasmons in 1D Topological Electrides
• As-Li electrides under high pressure: superconductivity, plastic, and superionic states
• Anisotropic two-dimensional screening at the surface of black phosphorus
• X-type stacking in cross-chain antiferromagnets
• Switchable Atomically Thin 2D Electrides from First-principles Prediction
• Two-dimensional non-van der Waals niobium nitride nanosheets with high-temperature two-gap superconductivity