Testing electron-phonon coupling for the superconductivity in kagome metal CsV₃Sb₅

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Electron-phonon coupling (EPC) is fundamental to conventional superconductivity.
• The kagome metal CsV3Sb5 exhibits superconductivity intertwined with symmetry-breaking orders.
• Previous theoretical studies predicted weak EPC in CsV3Sb5, suggesting unconventional pairing.

Purpose of the Study:

• To experimentally determine the electron-phonon coupling (EPC) strength in CsV3Sb5.
• To investigate the role of EPC in the observed superconductivity and intertwined orders.
• To provide a microscopic understanding of the ground state in CsV3Sb5.

Main Methods:

• Angle-resolved photoemission spectroscopy (ARPES) using a 7-eV laser.
• Eliashberg function analysis to quantify EPC strength.
• Measurements on both pristine CsV3Sb5 and a Nb-doped variant, Cs(V0.93Nb0.07)3Sb5.

Main Results:

• Intermediate EPC strength (λ=0.45-0.6) was determined at 6 K for Sb 5p and V 3d bands in CsV3Sb5.
• This intermediate EPC can support a superconducting transition temperature comparable to experimental values.
• EPC on the V 3d-band significantly enhanced to λ~0.75 in Cs(V0.93Nb0.07)3Sb5 at 4.4 K.

Conclusions:

• The experimental findings suggest that conventional superconductivity mechanisms, driven by intermediate EPC, may play a role in CsV3Sb5.
• This challenges prior theoretical predictions of weak EPC and unconventional pairing.
• The results offer crucial insights into the complex pairing mechanisms in kagome superconductors.