Dramatic Plasmon Response to the Charge-Density-Wave Gap Development in 1T−TiSe2

Band splitting and enhanced charge density wave modulation in Mn-implanted CsV3Sb5

“…In addition, the excitation process is also similar to the exciton-insulator excitation in 1T-TiSe 2 and Ta 2 NiSe 5 . 48–51 Such a kind of excitation state implies that the Coulomb shielding of electron–hole pairs becomes weaker in Mn-doped samples, which decreases the carrier concentration.…”

Exciton insulator in a moiré lattice

“…来研究激子凝聚，那么是否有体系能够存在无衰减的激子呢？人们通过理论发现 [1,3,4] ，等离激元软化 [8,9] ，量子输运 [10,11] ，增大压强 [12] 及红外光谱 [13] 等做了丰富的研 究，然而这些材料关于激子凝聚的实验支撑还未出现 [14,15] 。在探索无衰减的激子 过程中，人们发现了另外一个途径，如果能够将电子和空穴空间上分置到相邻的 双层量子阱结构中，中间通过介电材料隔开防止电子空穴复合，当中间层厚度足 够薄以至于电子空穴的相互吸引能量远远超过电子空穴各自在层中的动能时，这 样一个由电子空穴吸引相互作用占主导的体系便有可能会自发形成激子。人们最 开始在双层砷化镓量子阱中实现了这样的电子空穴双层结构 [16][17][18] ，然而为了抑制 其电子空穴的动能需要施加纵向的磁场，当双层砷化镓都处于最低朗道能级的半 填充时， 体系自发形成电子空穴对 (其中一层需要做粒子-空穴转换 (图 1(b) [6] ))。 并且该体系能够通过一系列电输运的测量方法观察到激子超流的现象，比如完美 的库伦拖拽(perfect Coulomb drag) ，量子化的拖拽霍尔电阻，零耗散的回流电流 (counter-flow current) ，约瑟夫森型的隧穿电流等 [17][18][19] 。相比于 1T-TaSe 2 , WTe 2 等材料体系，电子空穴双层体系具有更丰富的实验现象，因此成为研究激子绝缘 体的重要分支。近年来二维材料体系的发展对该领域的研究也有显著的促进作用 [20,21] 。比如在石墨烯-氮化硼-石墨烯结构中，当氮化硼厚度约为 3nm 时，两层石 墨烯中的电子空穴可以通过相互吸引形成激子 [22,23] ，并且该体系通过栅极电压可 以很容易调控各自的载流子浓度，研究者们甚至可以观察到 BEC 到 BCS 的转变 [24] 。然而这类双层体系都需要外加磁场产生朗道平带来抑制载流子的动能，那么 是否有办法无需外加磁场也可以产生平带呢？这就是本文主要讨论到的问题，我 们将展示利用莫尔平带在双层体系中实现无磁场情况下的激子绝缘体。…”

Ultrafast Condensed Matter Physics at Attoseconds

“…Theoretical studies also predict the role of shift vector on the time-and angle-dependent emissions of HHG dynamics. [123,124] (iii) For exciton dynamics, on the other hand, the high temporal resolution of ATAS/ATRS can well separate the time scale of exciton formation/melting (∼ fs) and lattice dynamics (∼ ps), [125] which would contribute to determine the competition mechanism between excitonic insulator and CDW in 1T-TiSe2 and Ta2NiSe5, [126][127][128][129] and even to estimate the time scale of exciton condensation. [130] More interestingly, the recently discovered Kagome materials 𝐴V3Sb5 (𝐴 = K, Rb, or Cs), [131][132][133] where the flat band, Dirac cone and van Hove singularity coexist, have displayed the rich phase diagrams including the novel charge phases (CDW, pair density wave and electronic nematicity [134][135][136] ), the topology and anomalous Hall effects, [137,138] the double-peak domain of superconductivity, [139,140] and antiferromagnet.…”