The topological materials have attracted much attention recently. While three-dimensional topological insulators are becoming abundant, two-dimensional topological insulators remain rare, particularly in natural materials. ZrTe5 has host a long-standing puzzle on its anomalous transport properties; its underlying origin remains elusive. Lately, ZrTe5 has ignited renewed interest because it is predicted that single-layer ZrTe5 is a two-dimensional topological insulator and there is possibly a topological phase transition in bulk ZrTe5. However, the topological nature of ZrTe5 is under debate as some experiments point to its being a three-dimensional or quasi-two-dimensional Dirac semimetal. Here we report high-resolution laser-based angle-resolved photoemission measurements on ZrTe5. The electronic property of ZrTe5 is dominated by two branches of nearly-linear-dispersion bands at the Brillouin zone center. These two bands are separated by an energy gap that decreases with decreasing temperature but persists down to the lowest temperature we measured (~2 K). The overall electronic structure exhibits a dramatic temperature dependence; it evolves from a p-type semimetal with a hole-like Fermi pocket at high temperature, to a semiconductor around ~135 K where its resistivity exhibits a peak, to an n-type semimetal with an electron-like Fermi pocket at low temperature. These results indicate a clear electronic evidence of the temperature-induced Lifshitz transition in ZrTe5. They provide a natural understanding on the underlying origin of the resistivity anomaly at ~135 K and its associated reversal of the charge carrier type. Our observations also provide key information on deciphering the topological nature of ZrTe5 and possible temperature-induced topological phase transition.
The Landau-Lifshitz/Looyenga dielectric mixture expression and its self-similar fractal nature
本文从谱密度表示法的角度讨论了混合介质的介电常数。推导出用于预测介电性质的不同表示[Tuncer E 2005 J. Phys. Condens.事项17 L125]。为了说明该表示的强度并证实所提出的假设，选择Landau-Lifshitz/Looyenga表达式，并提取混合物的结构信息。最近开发的数值方法来解决逆积分变换和建议的经验缩放介电常数表达式估计的谱密度函数的Landau-Lifshitz/Looyenga表达式。在模拟中，夹杂物相的浓度q是变化的。不同夹杂物浓度组成的混合物的估计的谱函数显示出相似的谱密度函数，由一对钟形分布组成，具有重合的峰位置。因此，我们认为，巧合是一个自相似的分形性质的混合物拓扑（结构）的考虑Landau-Lifshitz/Looyenga表达式的一个绝对说明。因此，光谱没有改变显着增加填料浓度水平-表现出自相似的光谱密度函数为不同的浓度水平。我们的结论是，因此，Landau-Lifshitz/Looyenga表达式适用于复杂的复合系统，其结构中有层次的顺序，这证实了文献中的发现。
Signature of an Ultrafast Photo-Induced Lifshitz Transition in the Nodal-Line Semimetal ZrSiTe
在这里，我们报告的超快光学光谱研究的半金属ZrSiTe。我们的测量结果表明，与该家族的其他化合物相反，电子激发的突然注入导致$A_{1g}$声子模式的强相干响应，该声子模式动态地修改Zr和Te原子与Si层之间的距离。“冻结声子”DFT计算，其中能带结构被计算为沿着声子模式坐标的核位置的函数，表明沿着该模式的大位移显著改变材料的电子结构，迫使能带接近甚至穿过费米能。时域响应的不相干部分揭示了对于大于$3.43 \times 10^{17}$ cm $^{-3}$的激发密度，低通量下的延迟电子响应不连续地演变成瞬时响应。这种突然变化的电子激发的耗散通道是一个超快的Lifshitz过渡，我们暂时关联到一个对称性保持$A_{1g}$声子模式驱动的费米表面的拓扑结构的变化表示。
Lifshitz Transition and Nontrivial H-Doping Effect in Cr-based Superconductor KCr$_3$As$_3$H$_x$
本文报道了掺氢铬基超导体KCr $_3$ As $_3$ H $_x$的第一性原理研究。结果表明KCr $_3$ As $_3$ H为顺磁基态.电子结构由两个准一维费米面和一个3D费米面组成，主要由Cr-d $_{z^2}$，d $_{x^2-y^2}$和d $_{xy}$轨道贡献.裸电子磁化率显示了一个以$Γ$为中心的虚峰，表明可能存在铁磁自旋涨落。在适度空穴掺杂时，系统经历Lifshitz转变，这可以增强系统的Q1 D特征。Bader电荷分析和电子局域化函数揭示了KCr $_3$ As $_3$ H中氢的强成键性质，这导致了KCr $_3$ As $_3$ H中的非平凡电子掺杂.
Observation of Iso-Symmetric Structural and Lifshitz Transitions in Quasi-one-dimensional CrNbSe$_5$
Michigan State University（密歇根州立大学）；Ames National Laboratory（艾姆斯国家实验室）；Iowa State University（爱荷华州立大学）；University of South Carolina（南卡罗来纳大学）；Harvard University（哈佛大学）
Magnetic field-induced non-trivial Lifshitz transition in TaCo2Te2
South China University of Technology（华南理工大学）；Saha Institute of Nuclear Physics, A CI of Homi Bhabha National Institute（萨哈核物理研究所，霍米·巴巴国立学院）；Shenzhen Technology University（深圳技术大学）；Southern University of Science and Technology（南方科技大学）
Signatures of a Quantum Griffiths Phase close to an Electronic Nematic Quantum Phase Transition
在量子临界点附近，淬火无序可以导致量子格里菲思相，伴随着一个奇异的幂律标度与连续变化的动力学指数，在零温度极限发散。在这里，我们研究了铁基超导体FeSe $_{0.89}$ S $_{0.11}$中的一个量子临界点。我们报告了一个不寻常的交叉的磁阻等温线在非超导正常状态，其特点是在一个大的温度范围内连续变化的动力学指数。我们解释我们的结果中的量子格里菲斯相位所造成的硒和S原子的局部分布的结果的dielectric岛。在低温下，格里菲斯相被掩盖的费米液相的出现，由于一个强大的nematoelastic耦合和Lifshitz转变，改变了费米表面的拓扑结构。
Pressure-induced Lifshitz and quantum phase transitions in electron-doped cuprate superconductor
Center for High Pressure Science & Technology Advanced Research（高压科学前沿中心）；Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；Shanghai Key Laboratory of Material Frontiers Research in Extreme Environments, Shanghai Advanced Research in Physical Sciences（极端环境材料前沿研究上海市重点实验室，上海物理科学研究院）；Maryland Quantum Materials Center, Department of Physics, University of Maryland（马里兰大学量子材料中心，物理学系）
