Sanghyun Ji | Searcharxiv

arXiv2023

Fermi surface magnetization of Fe-doped NbSb$_2$ investigated by magnetic quantum oscillations

Magnetic quantum oscillations (MQOs) have been widely used as a tool for probing Fermi surfaces. The shape and topology of the Fermi surface and the related physical parameters, such as the cyclotron mass and relaxation time, can be verified by carefully analyzing the frequency, amplitude, and phase of MQOs. In particular, phase analysis, from which we can obtain the Berry phase, has received much attention with the growing interest in the topology of condensed matter physics. Here, beyond the conventional uses of MQOs, we show that MQOs can be used to determine the Fermi surface magnetization. We doped dilute magnetic element Fe into the Dirac semimetal NbSb$_2$ to only introduce magnetism without changing the shape of the Fermi surface. We observed a phase shift in magnetically doped Fe-NbSb$_2$, which is in contrast to the lack of a phase shift in pristine NbSb$_2$ and nonmagnetic Bi-doped NbSb$_2$, indicating the strong exchange interaction between doped magnetic impurities and Fermi surface electrons. We estimated the Fermi surface magnetization introduced by magnetic Fe doping from the phase shift. This work demonstrates not only how tiny magnetic impurities can significantly change the Fermi surface magnetization but also how the Fermi surface magnetization can be investigated by phase analysis of MQOs.

cond-mat.mes-hall↗

arXiv2021

Orbit topology analysed from $π$ phase shift of magnetic quantum oscillations in three-dimensional Dirac semimetal

With the emergence of Dirac fermion physics in the field of condensed matter, magnetic quantum oscillations (MQOs) have been used to discern the topology of orbits in Dirac materials. However, many previous researchers have relied on the single-orbit Lifshiftz-Kosevich formula, which overlooks the significant effect of degenerate orbits on MQOs. Since the single-orbit LK formula is valid for massless Dirac semimetals with small cyclotron masses, it is imperative to generalize the method applicable to a wide range of Dirac semimetals, whether massless or massive. This report demonstrates how spin-degenerate orbits affect the phases in MQOs of three-dimensional massive Dirac semimetal, NbSb$_2$. With varying the direction of the magnetic field, an abrupt $π$ phase shift is observed due to the interference between the spin-degenerate orbits. We investigate the effect of cyclotron mass on the $π$ phase shift and verify its close relation to the phase from the Zeeman coupling. We find that the $π$ phase shift occurs when the cyclotron mass is 1/2 of the electron mass, indicating the effective spin gyromagnetic ratio is $g_s$ = 2. Our approach is not only useful for analysing MQOs of massless Dirac semimetals with a small cyclotron mass, but also can be used for MQOs in massive Dirac materials with degenerate orbits, especially in topological materials with a sufficiently large cyclotron mass. Furthermore, this method provides a useful way to estimate the precise $g_s$ value of the material.

cond-mat.mes-hall↗