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Anomalous hyperfine coupling and nuclear magnetic relaxation in Weyl semimetals

机译：Weyl半金属中的异常超精细耦合和核磁弛豫

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摘要

The electron-nuclear hyperfine interaction shows up in a variety of phenomena including, e.g., NMR studies of correlated states and spin decoherence effects in quantum dots. Here we focus on the hyperfine coupling and the NMR spin relaxation time T_1 in Weyl semimetals. Since the density of states in Weyl semimetals varies with the square of the energy around the Weyl point, a naive power counting predicts a 1/T_1T ～ E~4 scaling, with E the maximum of temperature (T) and chemical potential. By carefully investigating the hyperfine interaction between nuclear spins and Weyl fermions, we find that while its spin part behaves conventionally, its orbital part diverges unusually, with the inverse of the energy around the Weyl point. Consequently, the nuclear spin relaxation rate scales in a graphenelike manner as 1/T_1T ～ E~2 ln(E/ω_0), with ω_0 the nuclear Larmor frequency. This allows us to identify an effective hyperfine coupling constant, which is tunable by gating or doping. This is relevant for the decoherence effect in spintronics devices and double quantum dots, where hyperfine coupling is the dominant source of spin-blockade lifting.
机译：电子-核超精细相互作用表现在多种现象中，包括例如相关状态的NMR研究和量子点中的自旋退相干效应。在这里，我们专注于Weyl半金属的超精细耦合和NMR自旋弛豫时间T_1。由于Weyl半金属中的状态密度随Weyl点附近能量的平方而变化，因此，通过初始功率计数可预测1 / T_1T〜E〜4的缩放比例，其中E为温度（T）和化学势的最大值。通过仔细研究核自旋与Weyl费米子之间的超精细相互作用，我们发现，尽管其自旋部分具有常规行为，但其轨道部分却异常地发散，其能量与Weyl点周围的能量成反比。因此，核自旋弛豫速率以类似于石墨烯的方式缩放为1 / T_1T〜E〜2 ln（E /ω_0），ω_0为核拉莫尔频率。这使我们能够确定有效的超精细耦合常数，该常数可以通过选通或掺杂来调节。这与自旋电子器件和双量子点中的退相干效应有关，其中超精细耦合是自旋封锁解除的主要来源。

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  • 来源
    《Physical review》 |2016年第24期|245141.1-245141.6|共6页
  • 作者

    Zoltan Okvatovity; Ferenc Simon; Balazs Dora;

  • 作者单位

    Department of Theoretical Physics and BME-MTA Exotic Quantum Phases Research Group, Budapest University of Technology and Economics, Budapest 1111, Hungary;

    Department of Physics and MTA-BME Lenduelet Spintronics Research Group (PROSPIN), Budapest University of Technology and Economics, Budapest 1111, Hungary;

    Department of Theoretical Physics and BME-MTA Exotic Quantum Phases Research Group, Budapest University of Technology and Economics, Budapest 1111, Hungary;

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