A simple electron counting model for half-Heusler surfaces.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Surface Science

Background:

• Heusler compounds are vital for topological and magnetic heterostructures.
• Understanding Heusler surface and interface atomic structures is critical for device performance.
• Surface reconstruction mechanisms in Heusler materials remain largely unexplored.

Purpose of the Study:

• To investigate the atomic and electronic structures of surface reconstructions on CoTiSb (001), a semiconducting half-Heusler.
• To determine the driving forces behind Heusler surface reconstruction.
• To develop a predictive model for Heusler surface properties.

Main Methods:

• Utilized molecular beam epitaxy (MBE) for material growth.
• Employed core-level and angle-resolved photoemission spectroscopy (ARPES) for electronic structure analysis.
• Applied scanning tunneling microscopy (STM) for atomic-scale imaging.
• Performed density functional theory (DFT) calculations for theoretical insights.

Main Results:

• Mapped the phase diagram of CoTiSb (001) surface reconstructions.
• Identified Sb-Sb dimers and Ti vacancies at low Sb coverage.
• Observed an Sb adlayer at high Sb coverage.
• Determined that charge neutrality and minimizing dangling bonds drive reconstruction, forming metallic surface states.

Conclusions:

• Developed a simple electron counting model explaining Heusler surface atomic and electronic structures.
• The model successfully explains experimental observations on CoTiSb (001) and predicts behavior in other Heusler materials like PtLuSb and NiMnSb.
• This framework aids in understanding and predicting surface properties of novel quantum materials.