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Three-dimensional Dirac cone carrier dynamics in Na_3Bi and Cd_3As_2

机译:Na_3Bi和Cd_3As_2中的三维Dirac锥载流子动力学

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摘要

Optical measurements and band structure calculations are reported on three-dimensional Dirac materials. The electronic properties associated with the Dirac cone are identified in the reflectivity spectra of Cd_3As_2 and Na_3Bi single crystals. In Na_3Bi, the plasma edge is found to be strongly temperature dependent due to thermally excited free carriers in the Dirac cone. The thermal behavior provides an estimate of the Fermi level E_f = 25 meV and the z-axis Fermi velocity v_z = 0.3 eV A associated with the heavy bismuth Dirac band. At high energies above the Γ-point Lifshitz gap energy, a frequency- and temperature-independent €_2 indicative of Dirac cone interband transitions translates into an ab-plant Fermi velocity of 3 e V A. The observed number of IR phonons rules out the P6_3/mmc space-group symmetry but is consistent with the P3cl candidate symmetry. A plasmaron excitation is discovered near the plasmon energy that persists over a broad range of temperature. The optical signature of the large joint density of states arising from saddle points at Γ is strongly suppressed in Na_3Bi, consistent with band structure calculations that show the dipole transition-matrix elements to be weak due to the very small s-orbital character of the Dirac bands. In Cd_3As_2, a distinctive peak in reflectivity due to the logarithmic divergence in €_1 expected at the onset of Dirac cone interband transitions is identified. The center frequency of the peak shifts with temperature quantitatively consistent with a linear dispersion and a carrier density of n = 1.3 × 10~(17) cm~(-3). The peak width gives a measure of the Fermi-velocity anisotropy of 10%, indicating a nearly spherical Fermi surface. The line shape gives an upper bound estimate of 7 meV for the potential fluctuation energy scale.
机译:在三维狄拉克材料上报道了光学测量和能带结构计算。在Cd_3As_2和Na_3Bi单晶的反射光谱中确定了与狄拉克锥相关的电子性质。在Na_3Bi中,由于狄拉克锥中的热激发自由载流子,等离子体边缘受温度影响很大。热行为提供了费米能级E_f = 25 meV和z轴费米速度v_z = 0.3 eV A与重铋迪拉克带相关的估计。在高于Γ点Lifshitz间隙能量的高能量下,指示狄拉克锥带间跃迁的与频率和温度无关的€_2转换为3e V A的绝对植物费米速度。观察到的IR声子数排除了P6_3 / mmc空间组对称性,但与P3cl候选对称性一致。在等离子激元能量附近发现了等离子体激元激发,该等离子体激元能在很宽的温度范围内持续存在。 Na_3Bi中强烈抑制了由Γ处的鞍点引起的大联合态密度的光学特征,这与能带结构计算相符,该带结构计算表明,由于狄拉克的s轨道特性很小,偶极跃迁矩阵元素很弱乐队。在Cd_3As_2中,确定了由于狄拉克锥锥带间跃迁的出现而期望的€_1的对数发散所导致的反射率的独特峰值。峰的中心频率随温度的变化与线性色散和载流子密度n = 1.3×10〜(17)cm〜(-3)定量一致。峰宽表示费米速度各向异性为10%,表明费米表面接近球形。线形给出了潜在波动能标度的7 meV的上限估计。

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  • 来源
    《Physical review》 |2016年第8期|085121.1-085121.13|共13页
  • 作者单位

    Department of Physics, University of Maryland at College Park, College Park, Maryland 20742, USA,Center for Nanophysics and Advanced Materials, University of Maryland at College Park, College Park, Maryland 20742, USA;

    Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA;

    Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA;

    Department of Physics, University of Maryland at College Park, College Park, Maryland 20742, USA,Center for Nanophysics and Advanced Materials, University of Maryland at College Park, College Park, Maryland 20742, USA;

    Department of Physics, University of Maryland at College Park, College Park, Maryland 20742, USA,Center for Nanophysics and Advanced Materials, University of Maryland at College Park, College Park, Maryland 20742, USA;

    Department of Physics, University of Maryland at College Park, College Park, Maryland 20742, USA,Center for Nanophysics and Advanced Materials, University of Maryland at College Park, College Park, Maryland 20742, USA;

    Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA;

    Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA;

    Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA;

    Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan;

    Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan,Institute of Physics, Academia Sinica, Taipei 11529, Taiwan;

    Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546,Department of Physics, National University of Singapore, Singapore 117542;

    Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA;

    Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA;

    Department of Physics, University of Maryland at College Park, College Park, Maryland 20742, USA,Center for Nanophysics and Advanced Materials, University of Maryland at College Park, College Park, Maryland 20742, USA;

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