本文利用温度依赖角分辨光电子能谱研究了双层Ruddlesden-Popper铱酸盐Sr $_3$ Ir $_2$ O $_7$。我们发现一个窄间隙相关绝缘体，与极化基态的光谱特征指示，惊人的相似，以前观察到的铜酸盐超导体的母体化合物。我们还观察到类似的行为为单层表弟Sr $_2$ IrO $_4$，表明强电子-玻色子耦合占主导地位的低能量激发这种异国情调的家庭的材料，并提供了一个微观之间的联系绝缘基态的完全不同的3D铜酸盐和5D铱酸盐。
英文摘要：
We investigate the bilayer Ruddlesden-Popper iridate Sr$_3$Ir$_2$O$_7$ by temperature-dependent angle-resolved photoemission. We find a narrow-gap correlated insulator, with spectral features indicative of a polaronic ground state, strikingly similar to that observed previously for the parent compounds of the cuprate superconductors. We additionally observe similar behaviour for the single-layer cousin Sr$_2$IrO$_4$, indicating that strong electron-boson coupling dominates the low-energy excitations of this exotic family of materials, and providing a microscopic link between the insulating ground states of the seemingly-disparate 3d cuprates and 5d iridates.
In this work we investigate temperature dependence of electronic structure of system with strong electronic correlations and strong electron-phonon interaction modeling cuprates in the frameworks of the three-band p-d-Holstein model by a polaronic version of the generalized tight binding (GTB) method. Within this approach the electronic structure is formed by polaronic quasiparticles constructed as excitations between initial and final polaronic multielectron states. Temperature effect is taken into account by occupation numbers of local excited polaronic states and variations in the magnitude…
The competition between antiferromagnetism and hole motion in two-dimensional Mott insulators lies at the heart of a doping-dependent transition from an anomalous metal to a conventional Fermi liquid. Condensed matter experiments suggest charge carriers change their nature within this crossover, but a complete understanding remains elusive. We observe such a crossover in Fermi-Hubbard systems on a cold-atom quantum simulator and reveal the transformation of multi-point correlations between spins and holes upon increasing doping at temperatures around the superexchange energy. Conventional obse…
Spectroscopic signatures of Kohn anomaly in a topological crystalline insulator
ETH Zurich（苏黎世联邦理工学院）；National Institute of Science Education and Research（国家科学教育与研究中心）；Homi Bhaba National Institute（霍米·巴巴国立研究所）；Max Planck Institute for the Physics of Complex Systems（马克斯·普朗克复杂系统物理研究所）；Institute of Physics, Polish Academy of Sciences（波兰科学院物理研究所）
The motion of doped electrons or holes in an antiferromagnetic lattice with strong on-site Coulomb interactions touches one of the most fundamental open problems in contemporary condensed matter physics. The doped charge may strongly couple to elementary spin excitations resulting in a dressed quasiparticle which is subject to confinement. This 'spin-polaron' possesses internal degrees of freedom with a characteristic 'ladder' excitation spectrum. Despite its fundamental importance for understanding high-temperature superconductivity, clear experimental spectroscopic signatures of these intern…
Frustrated Mott insulators such as transition metal dichalcogenides present an ideal platform for the experimental realization of externally tuned insulator-metal transition. In this paper, we present the first nonperturbative numerical investigation of the disorder-induced insulator-metal transition in a two-dimensional frustrated Mott insulator. Our approach is generic and captures the essential physics of Mott insulator-metal transition in geometrically frustrated lattices. For concreteness, we have compared our results with the experimental observations on copper (Cu) intercalated 1T-TaS2.…
Samarium hexaboride (SmB$_6$), a well-known Kondo insulator in which the insulating bulk arises from strong electron correlations, has recently attracted great attention owing to increasing evidence for its topological nature, thereby harboring protected surface states. However, corroborative spectroscopic evidence is still lacking, unlike in the weakly correlated counterparts, including Bi$_2$Se$_3$. Here we report results from planar tunneling that unveil the detailed spectroscopic properties of SmB$_6$. The tunneling conductance obtained on the (001) and (011) single crystal surfaces reveal…
The room temperature (300 K) electronic structure of pulsed laser deposited LaNi_{x}V_{1-x}O_{3} thin films have been demonstrated. The substitution of early-transition metal (TM) V in LaVO_{3} thin films with late-TM Ni leads to the decreasing in out-of-plane lattice parameter. Doping of Ni does not alter the formal valence state of Ni and V in LaNi_{x}V_{1-x}O_{3} thin films, divulging the absence of carrier doping into the system. The valence band spectrum is observed to comprise of incoherent structure owing to the localized V 3d band along with the coherent structure at Fermi level. With …
We have measured the reflectivity spectra of the barium iridate $9R$ BaIrO$_3$, the crystal structure of which consists of characteristic Ir$_3$O$_{12}$ trimers. In the high-temperature phase above the transition temperature $T_c\simeq180$ K, we find that the optical conductivity involves two temperature-dependent optical transitions with an ill-defined Drude response. These features are reminiscent of the optical spectra in the organic dimer Mott insulators, implying a possible emergence of an unusual electronic state named trimer Mott insulator in BaIrO$_3$, where the carrier is localized on…
How a Mott insulator develops into a weakly coupled metal upon doping is a central question to understanding various emergent correlated phenomena. To analyze this evolution and its connection to the high-$T_c$ cuprates, we study the single-particle spectrum for the doped Hubbard model using cluster perturbation theory on superclusters. Starting from extremely low doping, we identify a heavily renormalized quasiparticle dispersion that immediately develops across the Fermi level, and a weakening polaronic side band at higher binding energy. The quasiparticle spectral weight roughly grows at tw…
Spectroscopic evidence for a molecular orbital Kondo insulator
University of California, Berkeley（加州大学伯克利分校）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Stanford University（斯坦福大学）；SLAC National Accelerator Laboratory（SLAC国家加速器实验室）；National Synchrotron Radiation Research Center（台湾国家同步辐射研究中心）；University of Washington（华盛顿大学）；National Institute of Standards and Technology (NIST)（美国国家标准与技术研究院）
Electric pulse induced electronic patchwork in the Mott insulator GaTa$_{4}$Se$_{8}$
继最近发现的绝缘体到金属的转变由电场诱导的GaTa $_{4}$ Se $_{8}$，我们进行了详细的扫描隧道显微镜/光谱研究的原始（绝缘）和过渡（导电）晶体的这种窄间隙莫特绝缘体。光谱图表明，原始样品是空间均匀的绝缘体，而过渡样品揭示了在纳米尺度上的复杂的电子图案，由金属和超绝缘补丁沉浸在原始绝缘矩阵。令人惊讶的是，这两种补丁都伴随着强烈的局部地形膨胀，从而证明了在这种金属-绝缘体过渡中涉及的强电子-晶格耦合。最后，利用一个强大的电场产生的STM隧道结，我们证明了可能性，即使在室温下，局部的金属-绝缘体转变。
By combining scanning tunneling microscopy/spectroscopy and first-principles calculations, we systematically study the local electronic states of magnetic dopants V and Cr in the topological insulator (TI) Sb2Te3. Spectroscopic imaging shows diverse local defect states between Cr and V, which agree with our first-principle calculations. The unique spectroscopic features of V and Cr dopants provide electronic fingerprints for the co-doped magnetic TI samples with the enhanced quantum anomalous Hall effect. Our results also facilitate the exploration of the underlying mechanism of the enhanced q…
Correlated states emerge in low-dimensional systems owing to enhanced Coulomb interactions. Elucidating these states requires atomic scale characterization and delicate control capabilities. In this study, spectroscopic imaging-scanning tunneling microscopy was employed to investigate the correlated states residing in the one-dimensional electrons of the monolayer and bilayer MoSe2 mirror twin boundary (MTB). The Coulomb energies, determined by the wire length, drive the MTB into two types of ground states with distinct respective out-of-phase and in-phase charge orders. The two ground states …
We combine low energy muon spin rotation (LE-$μ$SR) and soft-X-ray angle-resolved photoemission spectroscopy (SX-ARPES) to study the magnetic and electronic properties of magnetically doped topological insulators, (Bi,Sb)$_2$Te$_3$. We find that one achieves a full magnetic volume fraction in samples of (V/Cr)$_x$(Bi,Sb)$_{2-x}$Te$_3$ at doping levels x $\gtrsim$ 0.16. The observed magnetic transition is not sharp in temperature indicating a gradual magnetic ordering. We find that the evolution of magnetic ordering is consistent with formation of ferromagnetic islands which increase in number …
Spectroscopic signatures of persistent exciton condensation in a bulk magnetic topological insulator
Stanford University（斯坦福大学）；Aarhus University（奥胡斯大学）；Università degli Studi di Trieste（的里雅斯特大学）；Elettra - Sincrotrone Trieste S.C.p.A.（Elettra-的里雅斯特同步辐射中心）；Tohoku University（东北大学）；Technical University of Denmark（丹麦技术大学）
By using variational wave functions and quantum Monte Carlo techniques, we investigate the interplay between electron-electron and electron-phonon interactions in the two-dimensional Hubbard-Holstein model. Here, the ground-state phase diagram is triggered by several energy scales, i.e., the electron hopping $t$, the on-site electron-electron interaction $U$, the phonon energy $ω_0$, and the electron-phonon coupling $g$. At half filling, the ground state is an antiferromagnetic insulator for $U \gtrsim 2g^2/ω_0$, while it is a charge-density-wave (or bi-polaronic) insulator for $U \lesssim 2g^…
We report electrical (angular magneto-resistance, and Hall), thermal (heat capacity) and spectroscopic (Raman, x-ray photo electron, angle resolved photo electron) characterization of bulk Bi2Se3 topological insulator, which is being is grown by self flux method through solid state reaction from high temperature (950C) melt and slow cooling (2C/hour) of constituent elements. Bi2Se3 exhibited metallic behaviour down to 5K. Magneto transport measurements revealed linear up to 400% and 30% MR at 5K under 14 Tesla field in perpendicular and parallel field direction respectively. We noticed that th…
Topological insulators are a class of band insulators with non-trivial topology, a result of band inversion due to the strong spin-orbit coupling. The transition between topological and normal insulator can be realized by tuning the spin-orbit coupling strength, and has been observed experimentally. However, the impact of chemical disorders on the topological phase transition was not addressed in previous studies. Herein, we report a systematic scanning tunneling microscopy/spectroscopy and first-principles study of the topological phase transition in single crystals of In doped Bi$_2$Se$_3$. …
Electronic localization on the structural inhomogeneities formed due to Bi and Te deficiency in the MBE grown films of AFM topological insulator MnBi2Te4: Evidence from spectroscopic ellipsometry and infrared studies
We investigate electron transport through an antidot embedded in a narrow strip of two-dimensional topological insulator. We focus on the most generic and experimentally relevant case with broken axial spin symmetry. Spin-non-conservation allows additional scattering processes which change the transport properties profoundly. We start from an analytical model for noninteracting transport, which we also compare with a numerical tight-binding simulation. We then extend this model by including Coulomb repulsion on the antidot, and we study the transport in the Coulomb-blockade limit. We investiga…
The pseudogap, d-wave superconductivity and electron-boson coupling are three intertwined key ingredients in the phase diagram of the cuprates. Sr$_2$IrO$_4$ is a 5d-electron counterpart of the cuprates in which both the pseudogap and a d-wave instability have been observed. Here, we report spectroscopic evidence for the presence of the third key player in electron-doped Sr$_2$IrO$_4$: electron-boson coupling. A kink in nodal dispersion is observed with an energy scale of ~50 meV. The strength of the kink changes with doping, but the energy scale remains the same. These results provide the fir…
