[Paper Review] Distinct band reconstructions in kagome superconductor CsV$_3$Sb$_5$

Yang Luo, Shuting Peng+13 more|arXiv (Cornell University)|Jun 2, 2021

Topological Materials and Phenomena49 references21 citations

TL;DR

This study uses angle-resolved photoemission spectroscopy (ARPES) to reveal two distinct band reconstructions in the kagome superconductor CsV₃Sb₅: one arising from three-dimensional charge order with out-of-plane modulation, and another due to surface-induced orbital-selective band shifts. The findings provide direct evidence for 3D charge order and suggest surface engineering as a route to control exotic quantum states.

ABSTRACT

The new two-dimensional (2D) kagome superconductor CsV$_3$Sb$_5$ has attracted much recent attention due to the coexistence of superconductivity, charge order, topology and kagome physics. A key issue in this field is to unveil the unique reconstructed electronic structure, which successfully accommodates different orders and interactions to form a fertile ground for emergent phenomena. Here, we report angle-resolved photoemission spectroscopy (ARPES) evidence for two distinct band reconstructions in CsV$_3$Sb$_5$. The first one is characterized by the appearance of new electron energy band at low temperature. The new band is theoretically reproduced when the three dimensionality of the charge order is considered for a band-folding along the out-of-plane direction. The second reconstruction is identified as a surface induced orbital-selective shift of the electron energy band. Our results provide the first evidence for the three dimensionality of the charge order in single-particle spectral function, highlighting the importance of long-range out-of-plane electronic correlations in this layered kagome superconductor. They also point to the feasibility of orbital-selective control of the band structure via surface modification, which would open a new avenue for manipulating exotic phenomena in this system, including superconductivity.

Motivation & Objective

• To resolve the nature of electronic band reconstructions in the kagome superconductor CsV₃Sb₅, which hosts coexisting superconductivity, charge order, and topology.
• To determine whether the observed band reconstructions arise from bulk charge order or surface effects.
• To investigate the role of out-of-plane electronic correlations in shaping the electronic structure.
• To explore the feasibility of orbital-selective band engineering via surface modification.

Proposed method

• Angle-resolved photoemission spectroscopy (ARPES) was used to probe the electronic band structure of CsV₃Sb₅ at different temperatures and surface conditions.
• The experimental ARPES data were compared with theoretical calculations incorporating three-dimensional charge order via band-folding along the out-of-plane direction.
• Orbital-selective band shifts were identified by comparing spectra from different surface terminations or treatments.
• Theoretical modeling was employed to reproduce the observed band reconstructions, particularly the emergence of a new electron band at low temperatures.
• The role of long-range out-of-plane correlations was assessed by analyzing the spectral function in the presence of 3D charge order.

Experimental results

Research questions

• RQ1 What causes the emergence of a new electron band in CsV₃Sb₅ at low temperatures?
• RQ2 Is the observed band reconstruction due to three-dimensional charge order or surface effects?
• RQ3 Can orbital-selective band shifts be induced by surface modification?
• RQ4 How do out-of-plane electronic correlations influence the electronic structure in this kagome superconductor?

Key findings

• A new electron energy band appears at low temperatures, which is reproduced by including three-dimensional charge order with out-of-plane band-folding in theoretical models.
• The three-dimensional nature of the charge order is directly evidenced in the single-particle spectral function through ARPES.
• A second band reconstruction is identified as a surface-induced, orbital-selective shift of the electronic band structure.
• The results highlight the importance of long-range out-of-plane electronic correlations in stabilizing the reconstructed electronic states.
• Surface engineering offers a viable pathway for orbital-selective control of the band structure in this system.