Magneto-arpes Reveals Momentum-Dependent Symmetry Breaking in CsV Sb, Confirming Exotic Charge Density Order

The interplay of complex electronic states in materials often leads to unusual properties, and recent studies of the kagome superconductor CsV₃Sb₅ suggest a particularly intricate arrangement of charge ordering and broken symmetries. Jianwei Huang, Zheng Ren, Hengxin Tan, and colleagues at Rice University and the Weizmann Institute of Science now demonstrate how an external magnetic field dramatically alters the electronic structure of this material, revealing a momentum-dependent response that breaks established symmetries. Using a technique called magneto-ARPES, the team observed that specific bands associated with vanadium orbitals broaden in the presence of a magnetic field, selectively breaking rotational symmetry, while antimony-based electron pockets elongate. These findings pinpoint the origin of time-reversal symmetry breaking linked to the vanadium bands and reveal fluctuations in symmetry extending beyond the temperature at which charge ordering occurs, offering a new method for controlling and understanding intertwined electronic orders in materials.

Magnetic Field Tunes Fermi Surface Topology

Researchers investigated the electronic structure of CsV₃Sb₅, a material displaying intriguing charge density wave (CDW) behaviour and potential topological properties. Their core discovery centres on how an external magnetic field alters the material’s Fermi surface and electronic spectrum, distorting it particularly around key points and breaking its original symmetry. They also observed that the magnetic field causes momentum-selective broadening of spectral features, meaning certain regions of the Fermi surface respond more strongly than others, and that the Fermi pocket around a high-symmetry point becomes elongated and rotates when a magnetic field is applied. These changes in the Fermi surface and electronic spectrum indicate a breaking of both rotational and mirror symmetry within the material’s electronic structure. To understand these observations, the researchers combined experimental data with theoretical modelling, including a model based on the material’s kagome lattice structure and simulations of angle-resolved photoemission spectroscopy (ARPES). This combined approach provides insights into the underlying mechanisms driving the observed phenomena and paves the way for further exploration of its potential applications.

Tunable Magneto-ARPES Reveals Kagome Superconductor Response

Scientists pioneered a new technique, magneto-ARPES, to investigate the electronic structure of CsV₃Sb₅, a kagome superconductor. This technique allows probing how the material responds to magnetic fields during ARPES measurements, a previously challenging area due to unpredictable effects on photoelectron trajectories. By implementing an in situ tunable out-of-plane magnetic field, the team carefully calibrated the system, demonstrating that even small magnetic fields are sufficient to observe measurable effects. The team meticulously addressed potential artifacts arising from the magnetic field’s influence on photoelectrons, identifying and correcting for effects such as constant energy contour rotation, emission angle contraction, and momentum broadening. This careful analysis allowed for accurate measurements of the material’s electronic structure under magnetic fields, and by comparing Fermi surface maps measured with and without a magnetic field, they observed clear evolution of the electronic spectra, focusing on specific energy levels where key bands are well separated.

Momentum-Selective Broadening Reveals Kagome Superconductor Order

Scientists have demonstrated a novel method for investigating intertwined electronic orders in materials using magneto-ARPES. This work focuses on CsV₃Sb₅, a kagome superconductor exhibiting charge density wave (CDW) order, and reveals a momentum-selective response of its electronic structure to applied magnetic fields. Experiments show that bands associated with vanadium orbitals exhibit selective spectral broadening that breaks rotational symmetry and is sensitive to the direction of the magnetic field, disappearing above the CDW transition temperature. Detailed analysis of the electronic structure reveals that the antimony-dominated electron pocket at the centre of the Brillouin zone becomes elongated under an applied field, an effect that persists even above the CDW transition temperature.

The team meticulously corrected for effects caused by the magnetic field, ensuring accurate measurements of the field-dependent electronic structure. Further investigation of constant energy contours revealed that applying a magnetic field weakens one branch of specific contours, while the other remains sharp, demonstrating a clear magneto-dichroic effect. This selective spectral broadening, observed through momentum distribution curves, is consistent with theoretical simulations.

Kagome Superconductor Responds to Magnetic Fields

This research demonstrates a detailed understanding of the electronic behaviour within the kagome superconductor CsV₃Sb₅, revealing how magnetic fields interact with its complex electronic structure. Scientists utilized magneto-ARPES to observe momentum-selective responses to applied magnetic fields, identifying distinct behaviours within different electron orbitals. Specifically, bands associated with vanadium orbitals exhibit spectral broadening that breaks rotational symmetry when a magnetic field is applied, an effect observed even above the temperature at which charge order develops, while antimony-dominated electron pockets elongate under the influence of the field. These findings illuminate the origin of time-reversal symmetry breaking linked to the vanadium bands at the onset of charge ordering, while the field-induced rotational symmetry breaking associated with antimony orbitals suggests fluctuations extending beyond the ordered state. This work establishes a novel method for disentangling intertwined electronic orders within materials by tuning them in momentum space, offering a new avenue for exploring complex quantum materials.