Dirac fermions attract considerable interest for several years and tremendous efforts are devoted to unveil the Dirac/Weyl semimetallic state in real crystalline systems. The behavior of Dirac fermions under strong correlations and in the proximity of other ordered states is under particular scrutiny as robust experimental signatures are scarce. α-(BEDT-TTF)₂I₃ constitutes a superior model in this regard because the Dirac state occurs next to an electronically ordered ground state enabling us to investigate and deliberately vary the exotic properties in correlated Dirac fermions. The charge-ordered insulator gradually evolves to a metal when pressure is applied, and at low temperatures the electronic bands form tilted Dirac-like cones. Here, we present systematic low-temperature infrared experiments on α-(BEDT-TTF)₂I₃ in an extended pressure range. A metallic state with a frequency-independent optical conductivity indicates the coexistence of the trivial and massless Dirac electrons. We discover the opening of an energy gap due to correlated Dirac fermions at the boundary to the insulating state; it is gradually suppressed when pressure increases. The unique possibility of tuning the correlated Dirac state provides unprecedented insight into this novel electronic state and yields information relevant for Dirac electron systems in general.

狄拉克费米子几年来引起了人们的极大兴趣，并付出了巨大的努力来揭示真实晶体系统中的狄拉克/魏尔半金属态。狄拉克费米子在强相关性和其他有序状态附近的行为受到特别的审查，因为缺乏可靠的实验信号。α-（BEDT-TTF）₂ I ₃在这方面，我们构成了一个卓越的模型，因为狄拉克状态紧挨着电子有序基态发生，这使我们能够研究并故意改变相关狄拉克费米子的外来性质。当施加压力时，电荷排序的绝缘体逐渐演化为金属，并且在低温下，电子带形成倾斜的狄拉克型圆锥体。在这里，我们目前对α-（BEDT-TTF）₂ I _3进行系统的低温红外实验在更大的压力范围内。具有与频率无关的光导率的金属状态表明平凡的和无质量的狄拉克电子共存。我们发现由于边界处的狄拉克费米子与绝缘态相关而导致的能隙的打开。当压力增加时，它逐渐被抑制。调整相关狄拉克状态的独特可能性为这种新颖的电子状态提供了空前的洞察力，并产生了与狄拉克电子系统相关的信息。