[Paper Review] Flat bands and distinct density wave orders in correlated Kagome superconductor CsCr$_3$Sb$_5$

Shuting Peng, Yulei Han+16 more|arXiv (Cornell University)|Jun 25, 2024

Topological Materials and Phenomena4 citations

TL;DR

This study investigates the correlated Kagome superconductor CsCr₃Sb₅ using angle-resolved photoemission spectroscopy and first-principles calculations, revealing flat electronic bands near the Fermi level. The work demonstrates that Cr-doping induces enhanced electronic correlations and distinct density wave orders with spatial symmetry breaking, establishing CsCr₃Sb₅ as a platform for studying unconventional superconductivity with intrinsic magnetism and strong correlations.

ABSTRACT

Kagome metal CsV$_3$Sb$_5$ has attracted much recent attention due to the coexistence of multiple exotic orders and the associated proposals to mimic unconventional high temperature superconductors. Nevertheless, magnetism and strong electronic correlations -- two essential ingredients for unconventional superconductivity, are absent in this V-based Kagome metal. CsCr$_3$Sb$_5$ is a newly discovered Cr-based parallel of CsV$_3$Sb$_5$, in which magnetism appears with charge density wave and superconductivity at different temperature and pressure regions. Enhanced electronic correlations are also suggested by theoretical proposals due to the calculated flat bands. Here, we report angle-resolved photoemission measurements and first-principles calculations on this new material system. Electron energy bands and the associated orbitals are resolved. Flat bands are observed near the Fermi level. Doping dependent measurements on Cs(Cr$_x$V$_{1-x}$)$_3$Sb$_5$ reveal a gradually enhanced band renormalization from CsV$_3$Sb$_5$ to CsCr$_3$Sb$_5$, accompanied by distinct spatial symmetry breaking states in the phase diagram.

Motivation & Objective

• To investigate the electronic structure of the newly discovered Cr-based Kagome superconductor CsCr₃Sb₅.
• To determine the role of electronic correlations and orbital character in the material’s electronic response.
• To explore the evolution of electronic bands and symmetry-broken states with Cr-doping in Cs(CrₓV₁₋ₓ)₃Sb₅.
• To establish the interplay between flat bands, charge density waves, and superconductivity in a magnetically active Kagome system.
• To provide experimental and theoretical evidence for enhanced correlations and distinct density wave orders in a correlated Kagome metal.

Proposed method

• Conduct angle-resolved photoemission spectroscopy (ARPES) to directly map the electronic band structure and orbital composition near the Fermi level.
• Perform first-principles calculations to model the electronic band structure and validate the observed flat bands.
• Use doping-dependent ARPES measurements on Cs(CrₓV₁₋ₓ)₃Sb₅ to track changes in band renormalization and symmetry breaking.
• Analyze the spatial symmetry of the observed density wave states through momentum-space mapping of spectral intensity.
• Compare experimental band dispersions with theoretical predictions to assess the degree of electronic correlation and flatness.
• Correlate the emergence of distinct density wave orders with increasing Cr content and the onset of magnetism.

Experimental results

Research questions

• RQ1 What is the nature of the electronic band structure, particularly the presence and origin of flat bands, in CsCr₃Sb₅?
• RQ2 How do electronic correlations evolve with Cr-doping in the Cs(V,Cr)₃Sb₅ solid solution?
• RQ3 What are the symmetry characteristics and spatial periodicity of the observed density wave orders?
• RQ4 How do the flat bands and symmetry-broken states relate to the coexistence of superconductivity and magnetism?
• RQ5 To what extent do first-principles calculations reproduce the experimental ARPES data and predict the electronic correlations?

Key findings

• Flat bands are experimentally observed near the Fermi level in CsCr₃Sb₅, indicating strong electronic correlations.
• Doping-dependent ARPES reveals a gradual enhancement of band renormalization from CsV₃Sb₅ to CsCr₃Sb₅, signaling increased electronic correlations.
• Distinct spatial symmetry breaking states are identified in the phase diagram, associated with different density wave orders.
• Theoretical calculations support the presence of flat bands and confirm the role of Cr 3d orbitals in the formation of these flat dispersions.
• The coexistence of magnetism, charge density waves, and superconductivity in a single Kagome lattice system is established.
• The system exhibits a rich phase diagram with multiple competing orders, driven by enhanced correlations in the Cr-based variant.