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arXiv 2102.09917cond-mat.str-elcond-mat.mes-hall
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三维Dirac费米子系统Bi $_{1-x}$ Sb $_x$的轨道抗磁性和激发的局域观测

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

Yukihiro Watanabe, Masashi Kumazaki, Hiroki Ezure, Takao Sasagawa, Robert Cava, Masayuki Itoh, Yasuhiro Shimizu

摘要:

狄拉克费米子对磁场和电场表现出奇异的响应。一个明显的表现是大的抗磁性起源于布洛赫带的带间效应,如在铋合金中观察到的。通过$^{209}$ Bi NMR谱,我们提取了半导体铋合金Bi $_{1-x}$ Sb $_x$($x = 0.08 - 0.16$)中狄拉克费米子固有的抗磁轨道磁化率。$^{209}$ Bi超精细耦合常数提供了有效轨道半径的估计。除了带间抗磁性外,奈特位移还包括一个与温度无关的反常项,它起源于强自旋轨道耦合下增强的带内抗磁性。核自旋-晶格弛豫速率$1/T_1$主要受轨道激发的影响,并在很宽的温度范围内遵循立方温度依赖性。结果表明,在小的能隙开口下,存在强的抗磁性和低轨道激发,而在低温下出现$x$依赖的自旋激发。

英文摘要:

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.

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