We investigate the effect of strong electronic correlation on the massless Dirac fermion system, $\alpha$-(BEDT-TTF)$_2$I$_3$, under pressure. In this organic salt, one can control the electronic correlation by changing pressure and access the quantum critical point between the massless Dirac fermion phase and the charge ordering phase. We theoretically study the electronic structure of this system by applying the slave-rotor theory and find that the Fermi velocity decreases without creating a mass gap upon approaching the quantum critical point from the massless Dirac fermion phase. We show that the pressure-dependence of the Fermi velocity is in good quantitative agreement with the results of the experiment where the Fermi velocity is determined by the analysis of the Shubnikov-de Haas oscillations in the doped samples. Our result implies that the massless Dirac fermion system exhibits a quantum phase transition without creating a mass gap even in the presence of strong electronic correlations.

中文翻译：

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有机无质量狄拉克费米子系统 α-(BEDT-TTF)2I3 在压力下的量子相变

我们在压力下研究了强电子相关性对无质量狄拉克费米子系统 $\alpha$-(BEDT-TTF)$_2$I$_3$ 的影响。在这种有机盐中，人们可以通过改变压力来控制电子相关性，并访问无质量狄拉克费米子相和电荷有序相之间的量子临界点。我们通过应用从动转子理论从理论上研究了该系统的电子结构，发现费米速度在从无质量狄拉克费米子相接近量子临界点时会降低而不会产生质量间隙。我们表明，费米速度的压力依赖性与实验结果具有良好的定量一致性，其中费米速度是通过分析掺杂样品中的 Shubnikov-de Haas 振荡来确定的。