Direct 3D mapping of the Fermi surface and Fermi velocity

Area of Science:

• Condensed Matter Physics
• Materials Science
• Surface Science

Background:

• Understanding the electronic structure of materials like tungsten is crucial for developing new electronic devices.
• Characterizing bulk and surface electronic properties provides insights into material behavior and potential applications.

Purpose of the Study:

• To perform a comprehensive mapping of tungsten's bulk electronic structure, including its Fermi surface and Fermi-velocity distribution.
• To investigate and characterize a novel surface state in tungsten and its impact on electronic properties.
• To explore the potential of high-Z bcc metals for hosting topologically non-trivial surface states.

Main Methods:

• Utilized a novel multidimensional photoemission data-recording technique combining full-field k-microscopy with time-of-flight parallel energy recording.
• Employed high-brilliance soft X-rays for rapid acquisition of 4D spectral function data across the bulk Brillouin zone.
• Performed spin-filtered momentum imaging to confirm the Dirac-like spin texture of the observed surface state.

Main Results:

• Achieved a full mapping of tungsten's bulk electronic structure and Fermi-velocity distribution in approximately 3 hours.
• Discovered a time-reversal-invariant surface state in a local bandgap, connecting hole and electron pockets.
• Confirmed the Dirac-like spin texture of the surface state and demonstrated the extraction of various electronic parameters from the 4D data.

Conclusions:

• The identified surface state plays a significant role in the electronic properties of tungsten, bridging otherwise separated electronic pockets.
• The advanced 4D photoemission technique enables efficient and comprehensive characterization of electronic structures.
• High-Z bcc metals with significant spin-orbit coupling are promising candidates for realizing topologically non-trivial surface states.