Topological states on the gold surface.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Chemistry

Background:

• Gold surfaces exhibit unique electronic states, historically termed Shockley surface states.
• These states are crucial for benchmarking advanced spectroscopic techniques like ARPES and scanning tunnelling spectroscopy.
• The understanding of these states is foundational in surface science and electronic properties of metals.

Purpose of the Study:

• To re-evaluate the nature of Shockley surface states on gold.
• To investigate the potential topological origin of these surface electronic states.
• To confirm the presence and characteristics of topologically derived surface states (TDSSs) in noble metals.

Main Methods:

• Theoretical band structure calculations to define Z2-type invariants for gold.
• Angle-resolved photoemission spectroscopy (ARPES) measurements.
• Experimental detection of the dispersion of unoccupied surface states.

Main Results:

• Shockley surface states on gold can be accurately described as topologically derived surface states (TDSSs) of a topological insulator.
• Z2-type invariants were successfully defined for gold, characterizing it as a topological insulator.
• ARPES measurements confirmed the existence and dispersion of these TDSSs, including unoccupied states.
• Similar TDSSs were identified on the surfaces of silver, copper, platinum, and palladium.

Conclusions:

• The long-known Shockley surface states on gold and other noble metals possess a topological origin.
• This reinterpretation as TDSSs provides a new quantum mechanical framework for understanding these ubiquitous surface electronic states.
• The findings unify the understanding of surface states across different noble metals under the paradigm of topological insulators.