[论文解读] Competing superconductivity and charge-density wave in Kagome metal CsV3Sb5: evidence from their evolutions with sample thickness

Boqin Song, Xinran Kong+13 more|arXiv (Cornell University)|May 19, 2021

Topological Materials and Phenomena参考文献 11被引用 25

一句话总结

这项研究展示了 CsV3Sb5 的 Tc 与 TCDW 在厚度上的相反演化关系，为超导性与 CDW 竞争提供了有力证据，约在 60 nm 处实现从三维到二维的临界跨越，解释了 CDW 的趋势。

ABSTRACT

Recently superconductivity and topological charge-density wave (CDW) were discovered in the Kagome metals $A$V$_3$Sb$_5$ ($A$ = Cs, Rb, and K), which have an ideal Kagome lattice of vanadium. Here we report resistance measurements on thin flakes of CsV$_3$Sb$_5$ to investigate the evolution of superconductivity and CDW with sample thickness. The CDW transition temperature ${\it T}_{ m CDW}$ decreases from 94 K in bulk to a minimum of 82 K at thickness of 60 nm, then increases to 120 K as the thickness is reduced further to 4.8 nm (about five monolayers). Since the CDW order in CsV$_3$Sb$_5$ is quite three-dimensional (3D) in the bulk sample, the non-monotonic evolution of ${\it T}_{ m CDW}$ with reducing sample thickness can be explained by a 3D to 2D crossover around 60 nm. Strikingly, the superconducting transition temperature ${\it T}_{ m c}$ shows an exactly opposite evolution, increasing from 3.64 K in the bulk to a maximum of 4.28 K at thickness of 60 nm, then decreasing to 0.76 K at 4.8 nm. Such exactly opposite evolutions provide strong evidence for competing superconductivity and CDW, which helps us to understand these exotic phases in $A$V$_3$Sb$_5$ Kagome metals.

研究动机与目标

• Investigate how superconductivity and CDW evolve with sample thickness in CsV3Sb5.
• Identify whether superconductivity and CDW compete by comparing their thickness dependencies.
• Understand the dimensional crossover and its impact on CDW formation.
• Establish experimental evidence using thin flakes to connect structural dimensionality with electronic phases.

提出的方法

• Fabricate CsV3Sb5 thin flakes via an Al2O3-assisted exfoliation method.
• Perform four-probe resistance measurements on devices under varying temperatures.
• Determine thickness with Atomic Force Microscopy (AFM) and confirm sample integrity during preparation.
• Extract TCDW from resistance vs. temperature data and Tc from 10% resistance drop criteria.
• Apply perpendicular magnetic fields to map the upper critical field Hc2(T) and fit with Ginzburg-Landau theory.

实验结果

研究问题

• RQ1 How do Tc and TCDW change as CsV3Sb5 is thinned from bulk to a few nanometers?
• RQ2 Is there evidence that superconductivity and CDW compete in CsV3Sb5 across thicknesses?
• RQ3 What mechanism explains the non-monotonic evolution of TCDW with thickness?
• RQ4 Does a dimensional crossover (3D to 2D) around 60 nm account for CDW behavior?

主要发现

• TCDW decreases from 94 K in bulk to 82 K at 60 nm, then increases to 120 K at 4.8 nm (five monolayers).
• Tc increases from 3.64 K in bulk to 4.28 K at 60 nm, then drops to 0.76 K at 4.8 nm.
• Hc2(0) for the 60 nm sample is about 1.78 T, inferred from GL fits.
• Superconducting transitions become sharper as thickness decreases.
• The opposite evolutions of Tc and TCDW with thickness provide strong evidence for competing superconductivity and CDW in CsV3Sb5.