{
  "id": "2012.07103",
  "version": "v2",
  "published": "2020-12-13T17:05:56.000Z",
  "updated": "2021-03-29T17:01:50.000Z",
  "title": "Giant thermopower and power factor in magic angle twisted bilayer graphene at low temperature",
  "authors": [
    "S. S. Kubakaddi"
  ],
  "categories": [
    "cond-mat.mes-hall",
    "cond-mat.mtrl-sci"
  ],
  "abstract": "The in-plane phonon-drag thermopower $S^g$, diffusion thermopower $S^d$ and the power factor $PF$ are theoretically investigated in twisted bilayer graphene (tBLG) as a function of twist angle $\\theta$, temperature $T$ and electron density $n_s$ in the region of low $T$ (1-20 K). As $\\theta$ approaches magic angle $\\theta_m$, the $S^g$ and $S^d$ are found to be strongly enhanced, which is manifestation of great suppression of Fermi velocity ${\\nu_F}^*$ of electrons in moire flat band near $\\theta_m$. This enhancement decreases with increasing $\\theta$ and $T$. In the Bloch- Gruneisen (BG) regime, it is found that $S^g \\sim {\\nu_F}^{* -2}$, $T^3$ and ${n_s}^{-1/2}$. As $T$ increases, the exponent $\\delta$ in $S^g \\sim T^\\delta$, changes from 3 to nearly zero and a maximum $S^g$ value of $\\sim$ 10 mV/K at $\\sim$ 20 K is estimated. $S^g$ is larger (smaller) for smaller $n_s$ in low (high) temperature region. On the other hand, $S^d$, taken to be governed by Mott formula, $\\sim {\\nu_F}^{* -1}$, $T$ and ${n_s}^{-1/2}$ and $S^d<<S^g$ for $T > \\sim$ 2 K. The power factor $PF$ is also found to be strongly $\\theta$ dependent and very much enhanced. Consequently, possibility of a giant figure of merit is discussed.In tBLG, $\\theta$ acts as a strong tuning parameter of both $S^g$ and $S^d$ and $PF$ in addition to $T$ and $n_s$. Our results are qualitatively compared with the measured out-of-plane thermopower in tBLG.",
  "revisions": [
    {
      "version": "v2",
      "updated": "2021-03-29T17:01:50.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "magic angle twisted bilayer graphene",
      "power factor",
      "giant thermopower",
      "low temperature",
      "in-plane phonon-drag thermopower"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}