Local Observations of Orbital Diamagnetism and Excitation in Three-Dimensional Dirac Fermion Systems Bi${}_{1-x}$Sb${}_x$

Abstract

Dirac fermions display a singular response against magnetic and electric fields. A distinct manifestation is large diamagnetism originating in the interband effect of Bloch bands, as observed in bismuth alloys. Through ${}^{209}$Bi NMR spectroscopy, we extract diamagnetic orbital susceptibility inherent to Dirac fermions in the semiconducting bismuth alloys Bi${}_{1-x}$Sb${}_x$ ($x=0.08-0.16$). The ${}^{209}$Bi hyperfine coupling constant provides an estimate of the effective orbital radius. In addition to the interband diamagnetism, Knight shift includes an anomalous temperature-independent term originating in the enhanced intraband diamagnetism under strong spin-orbit coupling. The nuclear spin-lattice relaxation rate $1/T_1$ is dominated by orbital excitation and follows cubic temperature dependence in the extensive temperature range. The result demonstrates the robust diamagnetism and low-lying orbital excitation against the small gap opening, whereas $x$-dependent spin excitation appears at low temperatures.

10 pages, 4 figures

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Cited by in corpus (2)

• Site-dependent Local Spin Susceptibility and Low-energy Excitation in a Weyl Semimetal WTe${}_2$
• Robust orbital diamagnetism of correlated Dirac fermions in chiral Ising universality class