Emergence of large quantum oscillation frequencies in thin flakes of the kagome superconductor CsV$_{3}$Sb$_{5}$

TL;DR

This study reveals large quantum oscillation frequencies and small effective masses in thin flakes of CsV₃Sb₅, indicating high-velocity carriers and orbital-selective band modifications, crucial for understanding its electronic properties.

Contribution

It provides the first unambiguous detection of new high-frequency quantum oscillations in thin CsV₃Sb₅ flakes and links these to orbital-selective band structure changes.

Findings

Discovery of large quantum oscillation frequencies in thin flakes

Observation of small cyclotron effective masses (~0.1 m_e)

Evidence for orbital-selective modifications in the band structure

Abstract

Kagome metals AV$_3$Sb$_5$~(A = K, Rb, Cs) are recently discovered platforms featuring an unusual charge-density-wave (CDW) order and superconductivity. The electronic band structure of a kagome lattice can host both flat bands as well as Dirac-like bands, offering the possibility to stabilize various quantum states. Here, we probe the band structure of CsV$_3$Sb$_5$ via Shubnikov-de Haas quantum oscillations on both bulk single crystals and thin flakes. Although our frequency spectra are broadly consistent with the published data, we unambiguously reveal the existence of new frequencies with large frequencies ranging from $\sim$2085~T to $\sim$2717~T in thin flakes when the magnetic field is along the $c$-axis. These quasi-two-dimensional frequencies correspond to $\sim$52\% to 67\% of the CDW-distorted Brillouin zone volume. The Lifshitz-Kosevich analysis further uncovers surprisingly small cyclotron effective masses, of the order of $\sim$0.1~$m_e$, for these frequencies. Consequently, a large number of high-velocity carriers exists in the thin flake of CsV$_3$Sb$_5$. Comparing with our band structure calculations, we argue that an orbital-selective modification of the band structure is active. Our results provide indispensable information for understanding the fermiology of CsV$_3$Sb$_5$, paving a way for understanding how an orbital-selective mechanism can become an effective means to tune its electronic properties.