Spin excitations and flat electronic bands in a Cr-based kagome superconductor

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Kagome lattice materials are of interest for unique quantum states.
• Flat bands (FBs) arise from quantum interference and can lead to emergent orders when tuned to the chemical potential.
• Direct evidence of FBs at the chemical potential and their role in bulk materials is lacking.

Purpose of the Study:

• Investigate the role of flat bands in the emergent low-temperature order of the kagome metal superconductor CsCr3Sb5.
• Provide direct evidence for flat bands at the Fermi level in this material.
• Determine the origin of the low-temperature magnetic excitations.

Main Methods:

• Angle-resolved photoemission spectroscopy (ARPES)
• Resonant inelastic X-ray scattering (RIXS)
• Density functional theory (DFT) calculations

Main Results:

• The low-energy electronic structure of CsCr3Sb5 is dominated by flat bands at the Fermi level.
• Low-energy magnetic excitations were observed, correlating with flat band shifts across the low-temperature transition.
• These findings suggest a magnetic origin for the low-temperature order.

Conclusions:

• The kagome flat bands in CsCr3Sb5 are situated at the Fermi level.
• The observed magnetic excitations support a magnetic origin for the low-temperature emergent order.
• Kagome flat bands likely play a crucial role in the emergence of this order.