Search for: All records

This study explores the electronic and structural properties of the kagome metal CsV3Sb5 under uniaxial pressures up to 20 GPa, utilizing first-principles calculations based on experimental crystallographic data provided by Tsirlin et al., SciPost Phys. 12, 049 (2022). At ambient pressure, the electronic band structure exhibits multiple Dirac points, van Hove singularities (VHSs), and flat bands near the Fermi level, which progressively shift closer to the Fermi level with increasing pressure. Remarkably, two additional Dirac-like crossings emerge above 4.9 GPa, moving ∼25 meV below the Fermi level at 20 GPa. Concurrently, the VHS crosses the Fermi level as pressure increases to 9.8 GPa, highlighting a dynamic evolution of the electronic structure under high pressure conditions. The Fermi surface evolution under pressure reveals quasi-2D pockets, including a deformed cylindrical pocket centered at the Γ-point and a hexagonal pocket at the Brillouin zone boundary. Notably, the cylindrical pocket splits into two semi-spherical pockets above 4.9 GPa. Phonon calculations indicate lattice dynamical instability at ambient pressure, as evidenced by negative phonon frequencies, but stabilization occurs above 4.9 GPa, where all phonon modes become positive. These findings provide crucial insights into the pressure-induced modifications in the electronic and structural properties of CsV3Sb5, advancing the understanding of kagome-based quantum materials and their emergent phenomena. 

This study investigates the electronic structure of the vanadium-based kagome metal YV6Sn6 using magnetoresistance (MR) and torque magnetometry. The MR exhibits a nearly linear, non-saturating behavior, increasing by up to 55% at 35 T but shows no evidence of Shubnikov–de Haas oscillations. In contrast, the torque signal, measured up to 41.5 T, reveals clear de Haas–van Alphen (dHvA) oscillations over a wide frequency range, from a low frequency of Fα ∼20 T to high frequencies between 8 and 10 kT. Angular and temperature-dependent dHvA measurements were performed to probe the Fermi surface parameters of YV6Sn6. The dHvA frequencies display weak angular dependence, and the effective mass, determined by fitting the temperature-dependent data to the Lifshitz–Kosevich formula, is 0.097 mo, where mo represents the free electron mass. To complement the experimental findings, we computed the electronic band structure and Fermi surface using density functional theory. The calculations reveal several notable features, including multiple Dirac points near the Fermi level, flatbands, and Van Hove singularities. Two bands cross the Fermi level, contributing to the Fermi surface, with theoretical frequencies matching well with the observed dHvA frequencies. These combined experimental and theoretical insights enhance our understanding of the electronic structure of YV6Sn6 and provide a valuable framework for studying other vanadium- and titanium-based kagome materials. 

This work presents a detailed study of the electronic structure, phonon dispersion, Z2 invariant calculation, and Fermi surface of the newly discovered kagome superconductor CsV3Sb5, using density functional theory. The phonon dispersion in the pristine state reveals two negative modes at the M and L points of the Brillouin zone, indicating lattice instability. CsV3Sb5 transitions into a structurally stable 2 × 2 × 1 charge density wave (CDW) phase, confirmed by positive phonon modes. The electronic band structure shows several Dirac points near the Fermi level, with a narrow gap opening due to spin–orbit coupling (SOC), although the effect of SOC on other bands is minimal. In the pristine phase, this material exhibits a quasi-2D cylindrical Fermi surface, which undergoes reconstruction in the CDW phase. We calculated quantum oscillation frequencies using Onsager’s relation, finding good agreement with experimental results in the CDW phase. To explore the topological properties of CsV3Sb5, we computed the Z2 invariant in both pristine and CDW phases, resulting in a value of (ν0; ν1ν2ν3) = (1; 000), suggesting the strong topological nature of this material. Our detailed analysis of phonon dispersion, electronic bands, Fermi surface mapping, and Z2 invariant provides insights into the topological properties, CDW order, and unconventional superconductivity in AV3Sb5 (A = K, Rb, and Cs). 

This work presents the evolution of the electronic properties of kagome superconductor CsV3Sb5 under pressure. The magnetoresistance under high fields of 43 T showed clear Shubnikov–de Haas (SdH) oscillations with multiple frequencies up to 2000 T. With the application of pressure, we observed a sudden change in SdH oscillations with the disappearance of the high-frequency signal near the critical pressure Pc1 ∼ 0.7 GPa. We argue that this change could be due to a reconstruction of the Fermi surface (FS) in CsV3Sb5. To interpret our experimental data, we computed the electronic band structures and FS of CsV3Sb5 using ab initio density functional theory. Our results indicate that both the electronic bands and FS of CsV3Sb5 are highly sensitive to external pressure. The deformation of FS pockets with increasing pressure qualitatively explains our experimental observations. The pressure-driven FS instability in CsV3Sb5 may induce changes in its electronic states, such as superconductivity, charge density wave, nontrivial topology, and more. Therefore, these results are invaluable for gaining insights into these electronic states in CsV3Sb5, as well as in other kagome materials.