Photoemission spectra of massless Dirac fermions on the verge of exciton condensation

Orthorhombic-to-Monoclinic Phase Transition of Ta2NiSe5 Induced by the Bose-Einstein Condensation of Excitons

Using the band structure calculation and mean-field analysis of the derived three-chain Hubbard model with phonon degrees of freedom, we discuss the origin of the orthorhombic-to-monoclinic phase transition of the layered chalcogenide Ta$_2$NiSe$_5$. We show that the Bose-Einstein condensation of excitonic electron-hole pairs cooperatively induces the instability of the phonon mode at momentum $q\rightarrow 0$ in the quasi-one-dimensional Ta-NiSe-Ta chain, resulting in the structural phase transition of the system. The calculated single-particle spectra reproduce the deformation of the band st…

固体Ta2Pd3Te5基态中激子的光电子发射

Exciton photoemission from a ground state of a solid Ta2Pd3Te5

本文利用轨道选择性角分辨光电子能谱在Ta2Pd3Te5基态中直接观测到激子光电子发射，证实其能量低于价带顶并揭示波函数的尺寸与奇宇称，为相干激子应用和奇异量子相研究开辟新途径。

Comment on "Identification of different electron screening behavior between the bulk and surface of (Ga,Mn)As [Phys. Rev. Lett. 107, 187203 (2011)]"

In a recent Letter [Phys. Rev. Lett. 107, 187203 (2011)], Fujii et al. reported Mn 2p photoelectron emission spectra for (Ga,Mn)As recorded using hard x-rays. Due to the enhanced bulk sensitivity, hard-x-ray spectra reveal an extra "low-binding-energy peak", which is absent in surface-sensitive spectra recorded using soft x-rays. Based on Anderson-impurity-model calculations, Fujii et al. assigned the low-binding-energy peak to a cd6L2 final state, and related the variations in its intensity to variations in the As 4p-Mn 3d hybridization strength V. We show here that the definition of the char…

光谱学特征揭示体态磁性拓扑绝缘体中的持久激子凝聚

Spectroscopic signatures of persistent exciton condensation in a bulk magnetic topological insulator

本研究通过时间分辨光电子能谱在磁性拓扑绝缘体MnBi$_2$Te$_4$中观察到微秒级寿命的激子凝聚态光谱特征，表明该材料是研究光致多体态与拓扑磁性相互作用的理想平台。

Tuning across the BCS-BEC crossover in the multiband superconductor Fe$_{1+y}$Se$_x$Te$_{1-x}$ : An angle-resolved photoemission study

The crossover from Bardeen-Cooper-Schrieffer (BCS) superconductivity to Bose-Einstein condensation (BEC) is difficult to realize in quantum materials because, unlike in ultracold atoms, one cannot tune the pairing interaction. We realize the BCS-BEC crossover in a nearly compensated semimetal Fe$_{1+y}$Se$_x$Te$_{1-x}$ by tuning the Fermi energy, $ε_F$, via chemical doping, which permits us to systematically change $Δ/ ε_F$ from 0.16 to 0.5 were $Δ$ is the superconducting (SC) gap. We use angle-resolved photoemission spectroscopy to measure the Fermi energy, the SC gap and characteristic chang…

Bose-Einstein condensation of strongly correlated electrons and phonons in cuprate superconductors

The long-range Froehlich electron-phonon interaction has been identified as the most essential for pairing in high-temperature superconductors owing to poor screening, as is now confirmed by optical, isotope substitution, recent photoemission and some other measurements. I argue that low energy physics in cuprate superconductors is that of superlight small bipolarons, which are real-space hole pairs dressed by phonons in doped charge-transfer Mott insulators. They are itinerant quasiparticles existing in the Bloch states at low temperatures as also confirmed by continuous-time quantum Monte-Ca…

过渡金属碳化物（MXenes）的鲁棒高温拓扑激子绝缘体

Robust high-temperature topological excitonic insulator of transition-metal carbides (MXenes)

本文提出“宇称阻挫”机制解释拓扑激子绝缘体罕见的原因，并通过第一性原理计算证明单层MXenes可实现室温鲁棒拓扑激子凝聚，为寻找新材料和探究拓扑与多体效应相互作用提供了新平台。

光诱导激子凝聚体表现出BEC-BCS渡越的特征

Signatures of a light-induced exciton condensate exhibiting BEC-BCS crossover

本研究利用时间分辨角分辨光电子能谱，在单层MnBi₂Te₄中证实光诱导非平衡激子凝聚体及其BEC-BCS渡越的特征，确立其为相关研究的模型系统。

量子受限1$T$-TiSe$_2$电荷密度波的载流子密度调控

Carrier-Density Control of the Quantum-Confined 1$T$-TiSe$_2$ Charge-Density-Wave

本研究利用角分辨光电子能谱与理论计算，发现钾吸附可在低温相1$T$-TiSe$_2$表面诱导二维电子气并实现电荷密度波的量子受限，通过调控载流子密度可抵消激子凝聚的电子能量增益且保留长程结构序，为低维激子相关多体态调控提供了范例。

电子-声子耦合在激子绝缘体候选材料Ta2NiSe5中的作用

Role of electron-phonon coupling in excitonic insulator candidate Ta2NiSe5

本研究利用高分辨率同步辐射X射线衍射和角分辨光电子能谱技术，揭示了激子绝缘体候选材料Ta2NiSe5中的电子-声子耦合效应，结合第一性原理与模型计算构建了最小晶格模型，并提出了一种超越还原论方法的通用框架来分离库仑与电子-声子耦合效应，为研究具有交织序的关联系统提供了新视角。