Angle-Resolved Spectroscopy of Positronium Emission from a Cu(110) Surface

Area of Science:

• Atomic and surface physics
• Quantum mechanics
• Materials science

Background:

• Positronium (Ps) affinity for metals (A_Ps) is crucial for understanding positron interactions with surfaces.
• Direct time-of-flight (TOF) measurements of A_Ps are limited by the short triplet state lifetime of Ps (142 ns).

Purpose of the Study:

• To develop a high-precision method for measuring the affinity of positronium atoms for metal surfaces.
• To overcome the limitations imposed by the short lifetime of positronium's triplet state.

Main Methods:

• Conversion of emitted ground-state positronium into long-lived Rydberg states to extend time-of-flight.
• Precision time-of-flight (TOF) measurements of Rydberg-state positronium emitted from a Cu(110) surface.
• Comparison of experimental results with theoretical calculations using density functional theory (DFT) with generalized gradient approximations.

Main Results:

• Experimental measurement of A_Ps for Cu(110) at 128 K yielded (-2.476 ± 0.010_stat ± 0.013_syst) eV.
• Theoretical DFT calculations predicted A_Ps for Cu(110) at 128 K to be (-2.545 ± 0.010_num ± 0.010_syst) eV.
• The developed method enables significantly more precise measurements of positronium affinity.

Conclusions:

• The Rydberg-state conversion technique dramatically enhances the precision of positronium affinity measurements.
• Experimental results show good agreement with advanced theoretical calculations, validating the method.
• This precision opens avenues for refining density functional theory for positron-matter interactions.