Evidence for Itinerant Ferromagnetic Flat Bands Producing Large Transverse Responses

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Flat electronic bands emerge from wavefunction interference, potentially leading to novel correlated phenomena when crossing the Fermi energy (EF).
• Previous discoveries of itinerant flat bands at EF typically involved systems without symmetry breaking.
• Symmetry-broken systems with flat bands at EF offer unique platforms for studying novel phases and spontaneous responses.

Purpose of the Study:

• To experimentally and theoretically investigate the existence and properties of itinerant ferromagnetic flat bands in a stacked honeycomb-kagome lattice.
• To explore the potential of these flat bands in driving novel electronic phenomena and responses.
• To assess the material GdCo5 as a platform for spintronic and thermoelectric applications.

Main Methods:

• Theoretical modeling of electronic band structures.
• Angle-resolved photoemission spectroscopy (ARPES) to probe electronic states.
• Magneto-thermoelectric measurements to characterize transport properties.

Main Results:

• Experimental and theoretical evidence for itinerant ferromagnetic flat bands formed by spin-polarized d-electron orbitals in GdCo5.
• Identification of multiple topological flat bands at the Fermi energy (EF) with significant Berry curvature.
• Observation of large transverse responses, including a gigantic anomalous Nernst effect, yielding high transverse thermoelectric conductivity at room temperature.

Conclusions:

• The discovery of itinerant ferromagnetic flat bands in GdCo5, even with broken symmetry, provides a new avenue for exploring exotic electronic phases.
• The observed large Berry curvature and significant transverse thermoelectric effects highlight the potential of these flat bands for spintronic and thermoelectric devices.
• This research opens up possibilities for designing and utilizing materials with engineered itinerant magnetic flat bands for advanced technological applications.