Field induced density wave in a kagome superconductor (2501.13260v1)

Abstract: On the kagome lattice, electrons benefit from the simultaneous presence of band topology, flat electronic bands, and van Hove singularities, forming competing or cooperating orders. Understanding the interrelation between these distinct order parameters remains a significant challenge, leaving much of the associated physics unexplored. In the kagome superconductor KV3Sb5, which exhibits a charge density wave (CDW) state below T = 78 K, we uncover an unpredicted field-induced phase transition below 6 K. The observed transition is marked by a hysteretic anomaly in the resistivity, nonlinear electrical transport, and a change in the symmetry of the electronic response as probed via the angular dependence of the magnetoresistivity. These observations surprisingly suggest the emergence of an unanticipated broken symmetry state coexisting with the original CDW. To understand this experimental observation, we developed a theoretical minimal model for the normal state inside the high-temperature parent CDW phase where an incommensurate CDW order emerges as an instability sub-leading to superconductivity. The incommensurate CDW emerges when superconducting fluctuations become fully suppressed by large magnetic fields. Our results suggest that, in kagome superconductors, quantum states can either coexist or are nearly degenerate in energy, indicating that these are rich platforms to expose new correlated phenomena.

• The paper demonstrates a field-induced incommensurate charge density wave in KV3Sb5, marked by hysteretic resistivity and symmetry breaking at ~30 T.
• It employs temperature-dependent resistance and angular magnetoresistance analyses to uncover electronic reconstruction under high magnetic fields.
• The study advances our understanding of competing quantum phases in kagome superconductors, offering a framework for exploring magnetic field-induced orders.

Field-Induced Density Wave in a Kagome Superconductor KV3Sb5

This paper presents a thorough investigation into the emergence of a field-induced density wave phase in the kagome superconductor KV3Sb5. Recognized for hosting a confluence of band topology, flat electronic bands, and van Hove singularities, kagome lattices facilitate rich electronic behaviors, including competing and coexisting order parameters. The charge density wave (CDW) state within these materials, particularly in AV3Sb5, has been a focus due to its contributions to time-reversal symmetry breaking and possible loop current phases. This paper broadens our understanding by uncovering a novel magnetic field-induced broken symmetry state in KV3Sb5, marking a significant step toward decoding the complex electronic interactions within kagome lattice systems.

The paper revolves around the interplay between charge density waves and superconductivity in KV3Sb5. The authors document the discovery of a new phase transition in this compound below 6 K induced by magnetic fields approximately 30 T, identified via transport anomalies such as a hysteretic change in resistivity and nonlinear I-V characteristics. The authors suggest that these phenomena indicate the emergence of an incommensurate CDW state that coexists with the original CDW formed at lower magnetic fields.

A systematic experimental approach was executed to elucidate the properties of this transition. The authors utilized mechanically exfoliated KV3Sb5 flakes and conducted temperature-dependent resistance measurements, confirming the presence of metallic transport and the CDW transition around 77 K. Upon application of high magnetic fields, a distinct hysteretic anomaly in resistivity was observed near 30 T, manifesting the emergence of the field-induced transition. The robustness of this transition was affirmed by tracking its temperature and angular dependence, revealing the critical role of symmetry alterations in the magnetoresistance response.

The angular dependence of the magnetoresistivity was instrumental in signaling modifications in the electronic symmetry. Initial low-field resistance measurements demonstrated four-fold symmetry, which transitioned into two-fold symmetry under high magnetic fields deeply suggesting an electronic reconstruction of the Fermi surface.

To comprehend the microscopic basis for the observed phase transition, a minimal theoretical model was developed. This model proposes that the field-induced state is an incommensurate CDW brought forth by magnetic field suppression of superconducting fluctuations and the dominant superconducting phase at low fields. Such insights offer an intriguing parallel with observed behaviors in other strongly correlated systems like cuprates and transition metal dichalcogenides, highlighting the layered multistability of electronic interactions in these quantum materials.

The implications of this paper are numerous both on practical and theoretical fronts. Practically, these findings propel further experimental explorations into high-field behaviors of kagome systems, potentially influencing the development of electronic material applications where control over electronic phases is desired. Theoretically, it supports the notion of kagome systems as fertile grounds for uncovering new quantum phenomena and serves as a template for understanding field-induced orders in other strongly correlated materials. Moreover, the possibility of additional magnetic field-induced phases, as suggested by this research, calls for continued exploration using high magnetic fields.

In summary, the revelations concerning the field-induced density wave in KV3Sb5 impart significant advancement in the paper of kagome superconductors, underscoring their intricate phase dynamics and potential for future research into novel quantum fields. The paper makes notable strides in describing how quantum states can coexist or manifest near energy analogous conditions, providing fresh insights into the manipulation and control of quantum materials under extreme conditions.