Discovery of unconventional chiral charge order in kagome superconductor KV3Sb5 (2012.15709v3)

Abstract: Intertwining quantum order and nontrivial topology is at the frontier of condensed matter physics. A charge density wave (CDW) like order with orbital currents has been proposed as a powerful resource for achieving the quantum anomalous Hall effect in topological materials and for the hidden phase in cuprate high-temperature superconductors. However, the experimental realization of such an order is challenging. Here we use high-resolution scanning tunnelling microscopy (STM) to discover an unconventional charge order in a kagome material KV3Sb5, with both a topological band structure and a superconducting ground state. Through both topography and spectroscopic imaging, we observe a robust 2x2 superlattice. Spectroscopically, an energy gap opens at the Fermi level, across which the 2x2 charge modulation exhibits an intensity reversal in real-space, signaling charge ordering. At impurity-pinning free region, the strength of intrinsic charge modulations further exhibits chiral anisotropy with unusual magnetic field response. Theoretical analysis of our experiments suggests a tantalizing unconventional chiral CDW in the frustrated kagome lattice, which can not only lead to large anomalous Hall effect with orbital magnetism, but also be a precursor of unconventional superconductivity.

• The paper reveals a chiral charge-density-wave order in KV3Sb5 using STM, identifying a 2×2 modulation with an energy gap from -23 meV to +29 meV.
• The study integrates STM measurements with theoretical models to quantify an anomalous Hall conductivity of 310 Ω⁻¹cm⁻¹ and orbital magnetism of ~0.11 μB per V atom.
• The findings suggest a connection between unconventional CDW order and topological superconductivity, paving the way for advances in quantum materials and spintronics.

Unconventional Chiral Charge Order in Kagome Superconductor KVSb

The paper discusses the identification and implications of an unconventional chiral charge-density-wave (CDW) order in the kagome superconductor KVSb$_3$. Employing high-resolution scanning tunneling microscopy (STM), the paper identifies an unusual 2×2 superlattice charge modulation pattern in the system. This finding is particularly crucial as the order is interlinked with the unconventional topology of KVSb$_3$, exhibiting the potential for new kinds of electronic phases in quantum materials.

The research outlines the discovery of a robust 2×2 superlattice modulation via STM topography and spectroscopy, which presents an energy gap at the Fermi level. This gap, stretching from -23 meV to +29 meV, has been observed to disappear at 80K, indicating a connection to CDW order. Moreover, the paper detects chiral anisotropy in the charge modulation pattern, suggesting unconventional CDW characteristics possibly leading to a significant anomalous Hall effect, a haLLMark of topologically nontrivial systems.

Theoretical analysis within the paper indicates that this discovered CDW order, likely arising due to interactions at the van Hove singularities of the electronic structure, is of chiral nature. This order manifests an unusual magnetic field response, reinforcing the hypothesis of time-reversal symmetry breaking in the CDW order parameters. The research further connects these characteristics to the system’s superconductive state, suggesting underlying topological mechanisms in play.

Numerical Results and Theoretical Implications

The integration of theoretical models reveals that the chiral CDW order opens a substantial topological energy gap at Dirac cones, imparting a giant anomalous Hall conductivity of 310 $\Omega^{-1}$cm$^{-1}$, consistent with experimental observations. The investigation highlights that the Berry curvature field induced by this CDW order contributes to notable orbital magnetism, quantified at approximately 0.11 $\mu_B$ per V atom. Such contributions are pivotal for understanding transport anomalies and magnetic behaviors observed in KVSb$_3$ at lower temperatures.

Moreover, the paper explores the complexity of the kagome lattice geometry—a point of theoretical interest due to its inherent frustration and potential for hosting exotic quantum phases. The interplay between geometry, electronic correlations, and band topology in KVSb$_3$ has been meticulously analyzed, suggesting that similar lattice-induced phenomena might exist in other materials, with implications for quantum computing and information science applications.

Future Directions and Experimental Prospects

This paper sets a foundation for further exploration of chiral orders in similar systems and their potential links to unconventional superconductivity. Given the strong coupling between CDW and superconductivity, future research could explore new forms of Cooper pairing mechanisms, investigating the potential emergence of chiral Majorana modes in engineered atomic layers.

Additionally, understanding the switching of chirality under magnetic field applications opens avenues for exploring new device concepts in spintronics. Subsequent experimental work ought to focus on single-defected regions and extend into atomically-thin layers to uncover other related, yet unexplored, quantum phenomena.

In summary, the uncovering of unconventional chiral charge order in KVSb$_3$ elucidates the potential for new correlated electronic phenomena in kagome superconductors, providing substantive evidence for intertwining quantum order with nontrivial topology. This paper's insights could guide future research in quantum materials, advancing foundational understanding and technological innovation in quantum electronic systems.