Core Concepts

Chiral pair density wave order that breaks time-reversal symmetry is detected in KV3Sb5 and CsV3Sb5, with residual Fermi arcs observed as candidate Bogoliubov Fermi states.

Abstract

The content describes the experimental observation of chiral kagome superconductivity modulations with residual Fermi arcs in the materials KV3Sb5 and CsV3Sb5 using normal and Josephson scanning tunneling microscopy. Key highlights:

- The superconducting gap in these materials exhibits a U-shaped profile with flat residual in-gap states.
- The superconducting gap shows chiral 2a × 2a spatial modulations, with the chirality tunable by magnetic field. These modulations align with the observed chiral 2a × 2a pair-density modulations detected through Josephson tunneling.
- Quasiparticle interference imaging of the in-gap zero-energy states reveals segmented Fermi arcs, which are linked to the reconstructed vanadium d-orbital states within the charge order.
- The residual Fermi arcs are explained as candidate Bogoliubov Fermi states, resulting from the partial suppression of the d-orbital states through an interorbital 2a × 2a pair density wave (PDW) order.
- The observed PDW order is differentiated from impurity-induced gap modulations, and it demonstrates the fundamental space-momentum correspondence inherent in finite-momentum-paired superconductivity.

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Stats

Superconductivity involving finite-momentum pairing can lead to spatial-gap and pair-density modulations, as well as Bogoliubov Fermi states within the superconducting gap.
The superconducting gap in KV3Sb5 and CsV3Sb5 exhibits a U-shaped profile with flat residual in-gap states.
The superconducting gap shows chiral 2a × 2a spatial modulations, with the chirality tunable by magnetic field.
The chiral 2a × 2a pair-density modulations are observed through Josephson tunneling.

Quotes

"We observe a U-shaped superconducting gap with flat residual in-gap states."
"This gap shows chiral 2a × 2a spatial modulations with magnetic-field-tunable chirality, which align with the chiral 2a × 2a pair-density modulations observed through Josephson tunnelling."
"These findings demonstrate a chiral pair density wave (PDW) that breaks time-reversal symmetry."

Key Insights Distilled From

by Hanbin Deng,... at **www.nature.com** 08-21-2024

Deeper Inquiries

The observed chiral kagome superconductivity modulations and residual Fermi arcs in KV3Sb5 and CsV3Sb5 are closely tied to the materials' electronic structure and the underlying mechanisms of superconductivity. In these materials, the chiral 2a × 2a spatial modulations in the superconducting gap indicate the presence of a chiral pair density wave (PDW) that breaks time-reversal symmetry. This PDW order is significant as it demonstrates a unique form of superconductivity involving finite-momentum pairing, leading to spatial-gap and pair-density modulations. The flat residual in-gap states and U-shaped superconducting gap observed suggest unconventional superconductivity in these materials. Furthermore, the segmented arcs in the residual Fermi arcs can be linked to the reconstructed vanadium d-orbital states within the charge order, indicating a complex interplay between different electronic states in these materials.

To further investigate the interplay between the chiral PDW order, charge order, and the emergence of Bogoliubov Fermi states in materials like KV3Sb5 and CsV3Sb5, additional experimental techniques could be employed. Techniques such as angle-resolved photoemission spectroscopy (ARPES) could provide valuable insights into the electronic band structure and Fermi surface topology of these materials. Scanning tunneling spectroscopy (STS) combined with magnetic field manipulation could help elucidate the magnetic-field-tunable chirality of the chiral superconducting modulations. Moreover, inelastic neutron scattering could be utilized to probe the spin excitations and magnetic correlations in these materials, shedding light on the role of spin degrees of freedom in the observed phenomena.

Beyond KV3Sb5 and CsV3Sb5, other systems based on kagome lattice structures could exhibit similar phenomena related to unconventional superconductivity. Materials such as herbertsmithite (ZnCu3(OH)6Cl2) and volborthite (Cu3V2O7(OH)2·2H2O) are examples of kagome lattice compounds that have shown exotic magnetic and electronic properties, making them potential candidates for exploring chiral superconductivity and related phenomena. Investigating these systems could provide further insights into the role of geometric frustration, strong electron correlations, and topological effects in driving unconventional superconductivity. Understanding the behavior of correlated electron systems in kagome lattice materials could pave the way for the discovery of new quantum states of matter and the development of novel superconducting technologies.

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