Kubakaddi S S
Department of Physics, Karnatak University, Dharwad-580 003, Karnataka, India.
J Phys Condens Matter. 2015 Nov 18;27(45):455801. doi: 10.1088/0953-8984/27/45/455801. Epub 2015 Oct 22.
A theory of low-temperature phonon-drag thermopower S(g) in three-dimensional (3D) Dirac semimetals has been developed considering screened electron-phonon deformation potential coupling. Numerical investigations of S(g), in the boundary scattering regime for phonons, are made in 3D Dirac semimetal Cd3As2, as a function of temperature T and electron concentration n e. S(g) is found to increase rapidly for about T < 1 K and nearly levels off for higher T. It is also seen that S(g) increases (decreases) with decreasing n e at lower (higher) T (<2 K). A screening effect is found to be very significant, strongly affecting T and n e dependence for about <1 K and becoming negligible at higher temperature. In the Bloch-Gruneisen (BG) regime the power laws S(g) ~ T(8) (T(4)) and S(g) ~ n(e)(-5/3)(n(e)(-1/3) with (without) screening are obtained. These laws with respect to T and n e are, respectively, characteristics of 3D phonons and Dirac 3D electrons. Comparison with diffusion thermopower S(d) shows that S (g) dominates (and is much greater than) S(d) for about T > 0.2 K. Herring's law S(g) μ p ~ T (-1), relating phonon limited mobility μ p and S(g) in the BG regime, is shown to be valid in 3D Dirac semimetals. The results obtained here are compared with those in 3D semiconductors, low-dimensional semiconductor heterojunctions and graphene. We conclude that n e-dependent measurements, rather than T-dependent ones, provide a clearer signature of the 3D Dirac semimetal phase.
考虑到屏蔽电子 - 声子形变势耦合，已经建立了一种关于三维（3D）狄拉克半金属中低温声子拖拽热功率S(g)的理论。在3D狄拉克半金属Cd3As2中，针对声子的边界散射区域，对S(g)进行了数值研究，研究其作为温度T和电子浓度ne的函数。发现S(g)在T < 1 K左右迅速增加，而在较高温度时几乎趋于平稳。还可以看到，在较低（较高）温度（<2 K）下，S(g)随着ne的减小而增加（减小）。发现一种屏蔽效应非常显著，在T < 1 K左右强烈影响T和ne的依赖性，而在较高温度下可忽略不计。在布洛赫 - 格律恩森（BG）区域，得到了有（无）屏蔽时的幂律S(g) ~ T(8)（T(4)）和S(g) ~ n(e)(-5/3)（n(e)(-1/3)）。这些关于T和ne的定律分别是3D声子和狄拉克3D电子的特征。与扩散热功率S(d)的比较表明，在T > 0.2 K左右，S(g)占主导（且远大于）S(d)。在BG区域中，将声子限制迁移率μp与S(g)相关联的赫林定律S(g) μ p ~ T (-1)在3D狄拉克半金属中被证明是有效的。将这里得到的结果与3D半导体、低维半导体异质结和石墨烯中的结果进行了比较。我们得出结论，与温度相关的测量相比，与电子浓度相关的测量能更清晰地体现3D狄拉克半金属相的特征。
