Cascade of correlated electron states in a kagome superconductor CsV3Sb5 (2103.03118v1)

Abstract: The kagome lattice of transition metal atoms provides an exciting platform to study electronic correlations in the presence of geometric frustration and nontrivial band topology, which continues to bear surprises. In this work, using spectroscopic imaging scanning tunneling microscopy, we discover a cascade of different symmetry-broken electronic states as a function of temperature in a new kagome superconductor, CsV3Sb5. At a temperature far above the superconducting transition Tc ~ 2.5 K, we reveal a tri-directional charge order with a 2a0 period that breaks the translation symmetry of the lattice. As the system is cooled down towards Tc, we observe a prominent V-shape spectral gap opening at the Fermi level and an additional breaking of the six-fold rotation symmetry, which persists through the superconducting transition. This rotation symmetry breaking is observed as the emergence of an additional 4a0 unidirectional charge order and strongly anisotropic scattering in differential conductance maps. The latter can be directly attributed to the orbital-selective renormalization of the V kagome bands. Our experiments reveal a complex landscape of electronic states that can co-exist on a kagome lattice, and provide intriguing parallels to high-Tc superconductors and twisted bilayer graphene.

• The paper reveals a hierarchical emergence of symmetry-broken electronic states, starting with a tri-directional 2a₀ charge order above Tc and evolving to a unidirectional order near Tc.
• It employs spectroscopic imaging to correlate V-shaped spectral gaps and anisotropic scattering with theoretical band calculations and ARPES data.
• The work highlights implications for nematic ordering and potential topological superconductivity, suggesting novel routes for unconventional pairing mechanisms.

Cascade of Correlated Electron States in a Kagome Superconductor CsV$_3$Sb$_5$

The paper "Cascade of correlated electron states in a kagome superconductor CsV$_3$Sb$_5$" investigates the emergence of symmetry-broken electronic states in the novel kagome superconductor, CsV$_3$Sb$_5$. Employing spectroscopic imaging scanning tunneling microscopy (SI-STM), the authors uncover significant insights into the correlated electron phenomena driven by geometric frustrations and nontrivial band topology on the kagome lattice.

Key Findings

The research delineates a sequential manifestation of electronic states with broken symmetry as a function of temperature. The primary observations are:

1. Tri-Directional Charge Order: At temperatures significantly above the superconducting transition temperature, $T_c \sim 2.5 \text{K}$, there exists a 2$\mathbf{a}_0$ period charge order that disrupts the translation symmetry of the lattice.
2. Progression Towards Superconductivity: As the system is cooled closer to $T_c$, a V-shaped spectral gap appears at the Fermi level, along with a rotational symmetry-breaking, manifesting as a unidirectional charge order with a 4$\mathbf{a}_0$ period.
3. Anisotropic Scattering: The anisotropic scattering in differential conductance maps is attributed to the orbital-selective renormalization of the vanadium kagome bands.
4. Consistency Across Experimental Techniques: The spectral features identified via dI/dV spectra align with theoretical band structure calculations and empirical ARPES maps.

Implications

This work illustrates the prolific complexity of electronic states on a kagome lattice and draws parallels to phenomena observed in high-$T_c$ superconductors and twisted bilayer graphene systems. The coexistence of superconductivity with a state exhibiting intrinsically broken rotational symmetry may have profound implications on the superconducting order parameter within this class of materials, signaling potential unconventional pairing mechanisms.

Theoretical and Practical Impacts:

• Nematic Ordering: The observed anisotropic features suggest a significant nematic electronic order, a higher-order symmetry breaking known to influence the electronic properties in condensed matter systems.
• Topological Superconductivity: Given the non-trivial band topology of CsV$_3$Sb$_5$, the prospect of uncovering intrinsic topological superconductivity and associated Majorana modes presents a fertile ground for further exploration.

Future Research Directions

The paper outlines critical areas for future exploration. The relationship between different symmetry-broken phases needs more elucidation through detailed temperature-, energy-, and doping-dependent studies. Additionally, probing for potential topological superconductivity and Majorana modes in these materials would further enrich understanding and technological exploitation of exotic superconducting states.

Conclusively, this research marks a noteworthy advancement in the understanding of correlated and topological phenomena in kagome systems, setting a precedent for further inquiries into their potential applications in quantum materials.