Topological frequency shift of quantum oscillation in CaFeAsF

Taichi Terashima,Shinya Uji,Teng Wang,Gang Mu

doi:10.1038/s41535-022-00431-z

Abstract

Guo, Alexandradinata, et al. have recently proposed that quantum-oscillation frequencies from Dirac/Weyl fermions exhibit a negative shift proportional to T2 because of the energy dependence of the effective mass peculiar to a linear band-dispersion. We have measured Shubnikov–de Haas oscillation in CaFeAsF up to T = 9 K. The frequency of the α Dirac electron exhibits a negative shift with increasing T, while that of the β Schrödinger hole does not. For T ⩾ 5 K where β is negligible, the α-frequency shift is proportional to T2 and its rate agrees with the theoretical prediction within experimental accuracy. At lower temperatures, the shifts of α and β deviate from theoretical expectations, which we ascribe to the inaccuracy in the frequency determination due to unfavorable interference between frequencies. Our results confirm that the topological frequency shift can be utilized to identify Dirac/Weyl fermions when quantum-oscillation frequencies can be determined accurately.

Highlights

Dirac or Weyl fermions in topological semimetals can in principle be identified by detecting the Berry phase in quantum-oscillation measurements[11,12]
We focus on Shubunikov-de Haas (SdH)
The Fermi surface in CaFeAsF is composed of a pair of α Dirac electron cylinders and a β Shrödinger hole cylinder[14]

Summary

INTRODUCTION

Quantum oscillation arising from Landau quantization of electron motion in magnetic fields is a powerful tool to investigate electronic structures of metals. Since the Onsager relation[3] and LifshitzKosevich formula[4] to interpret the quantum oscillation were established in 1950s, it has been used to determine the Fermi surface of elemental metals[5] and heavy fermions[6,7], high-Tc cuprates[8], and so on. Dirac or Weyl fermions in topological semimetals can in principle be identified by detecting the Berry phase in quantum-oscillation measurements[11,12]. We note that the phase of fundamental quantum oscillation is the same between normal fermions with a negative Rs,[1] and Dirac fermions with a positive Rs,[1]. Guo, Alexandradinata, et al (hereafter GAM et al after the three corresponding authors) proposed a new approach[16] They pointed out that quantum-oscillation frequency from Dirac/Weyl pockets should exhibit a characteristic temperature dependence. 4β mÃ ∂E ; dependence of the α and β frequencies and to compare them to the GAM model

(2) RESULTS

Experimental results and analysis

DISCUSSION

METHODS