[Paper Review] Nodal superconductivity and superconducting domes in the topological Kagome metal CsV3Sb5

Chenglong Zhao, Lu-Yun Wang+12 more|arXiv (Cornell University)|Feb 16, 2021

Topological Materials and Phenomena78 citations

TL;DR

The paper reports nodal superconductivity in CsV3Sb5 and reveals two superconducting domes under pressure, indicating unconventional pairing in this Kagome vanadium compound.

ABSTRACT

Recently superconductivity was discovered in the Kagome metal AV3Sb5 (A = K, Rb, and Cs), which has an ideal Kagome lattice of vanadium. These V-based superconductors also host charge density wave (CDW) and topological nontrivial band structure. Here we report the ultralow-temperature thermal conductivity and high pressure resistance measurements on CsV3Sb5 with Tc = 2.5 K, the highest among AV3Sb5. A finite residual linear term of thermal conductivity at zero magnetic field and its rapid increase in fields suggest nodal superconductivity. By applying pressure, the Tc of CsV3Sb5 increases first, then decreases to lower than 0.3 K at 11.4 GPa, showing a clear first superconducting dome peaked around 0.8 GPa. Above 11.4 GPa, superconductivity re-emerges, suggesting a second superconducting dome. Both nodal superconductivity and superconducting domes point to unconventional superconductivity in this V-based superconductor. While our finding of nodal superconductivity puts a strong constrain on the pairing state of the first dome, which should be related to the CDW instability, the superconductivity of the second dome may present another exotic pairing state in this ideal Kagome lattice of vanadium.

Motivation & Objective

• Investigate the superconducting state of CsV3Sb5 with ultralow-temperature thermal conductivity.
• Explore how external pressure affects Tc and superconducting phases.
• Determine whether superconductivity is conventional or unconventional in this V-based Kagome system.

Proposed method

• Measure ultralow-temperature thermal conductivity and its field dependence.
• Perform high-pressure resistance measurements up to beyond 11 GPa.
• Identify residual linear term in thermal conductivity to infer nodal behavior.
• Track Tc as a function of pressure to map superconducting domes.

Experimental results

Research questions

• RQ1 Is superconductivity in CsV3Sb5 nodal or fully gapped?
• RQ2 How does applying pressure modify Tc and the superconducting state?
• RQ3 Do multiple superconducting domes appear under pressure, and what do they imply about pairing mechanisms?
• RQ4 What is the relationship between superconductivity and CDW instability in CsV3Sb5?

Key findings

• CsV3Sb5 exhibits a finite residual linear term in thermal conductivity at zero field, and its rapid field-induced increase suggests nodal superconductivity.
• Tc reaches 2.5 K, the highest among AV3Sb5 compounds.
• Under pressure, Tc first increases, then decreases to below 0.3 K at 11.4 GPa, indicating a first superconducting dome (peaked near 0.8 GPa).
• Above 11.4 GPa, superconductivity re-emerges, indicating a second superconducting dome.