Quantum Oscillations in Topological Materials

Magnetic quantum oscillations play a key role in resolving the Fermi surfaces and electronic structures and confirming the prediction of topological materials. In type II Dirac semimetal XAl₃(X=V, Nb, Ta) [1], we measured the quantum oscillations in magnetization and determined the angular dependence of their Fermi surface cross-sectional areas, and reveals an excellent agreement with our first-principles calculations. As a result, the quantum oscillations support the existence of tilted Dirac cones with Dirac type-II nodes located at 100, 230, and 250 meV above the Fermi level for VAl₃, NbAl₃, and TaAl₃, respectively. We will further discuss the determination of Berry’s phase via quantum oscillations.

Similarly, topological Kondo insulator YbB12 revealed quantum oscillations in the insulating state [2]. We measured the torque magnetometry, electrical resistivity, and AC conductivity in YbB12 to map the trend of the quantum oscillations in both the low-field insulating and high-field metallic states [3]. The results uncovered possible magnetic-field-driven Lifshitz transitions in this topological Kondo insulator [4].

Studying quantum oscillations is also essential for the broad field of correlated quantum materials.  The first superconducting pyrochlore oxide Cd₂Re₂O₇ was proposed as a candidate for non-Abelian braiding, and the Weyl nodes can be moved by small temperature changes. The correct structure and the original mechanism of the structural transition have been debated for decades in Cd₂Re₂O₇. Our quantum oscillations resolved the issue by comparing the electronic structure models with the observed angular dependence of the FS orbits.  Moreover, we will discuss the Chern Fermi pocket of the recently discovered Kagome superconductor CsV₃Sb₅. Thanks to the extremely high magnetic field, we found the magnetic breakdown between the Chern orbits and the normal orbit. From the “spin-zero” effect, the Lande’ g factor is found to be as large as 14. The Berry curvature of the Chern Fermi pocket needs to be involved in generating large orbital moments.