We compute the correlated electronic structure of stacked $1T$-TaS$_2$ bilayers using the $GW$ + EDMFT method. Depending on the surface termination, the semi-infinite uncorrelated system is either band-insulating or exhibits a metallic surface state. For realistic values of the onsite and intersite interactions, a Mott gap opens in the surface state, but this gap is smaller than the gap originating from the bilayer structure. Our results are consistent with recent scanning tunneling spectroscopy measurements for different terminating layers, and with our own photoemission measurements, which indicate the coexistence of spatial regions with different gaps in the electronic spectrum.
We propose the concept of "hybridization-switching induced Mott transition" which is relevant to a broad class of ABO$_3$ perovskite materials including BiNiO$_3$ and PbCrO$_3$ which feature extended $6s$ orbitals on the A-site cation (Bi or Pb), and A-O covalency induced ligand holes. Using {\it ab initio} electronic structure and slave rotor theory calculations, we show that such systems exhibit a breathing phonon driven A-site to oxygen hybridization-wave instability which conspires with strong correlations on the B-site transition metal ion (Ni or Cr) to induce a Mott insulator. These Mott…
The time-dependent Mott transition in a periodic Anderson model with off-site, nearest-neighbor hybridization is studied within the framework of nonequilibrium self-energy functional theory. Using the two-site dynamical-impurity approximation, we compute the real-time dynamics of the optimal variational parameter and of different observables initiated by sudden quenches of the Hubbard-U and identify the critical interaction. The time-dependent transition is orbital selective, i.e., in the final state, reached in the long-time limit after the quench to the critical interaction, the Mott gap ope…
The heavy fermion state with Kondo-hybridization (KH), usually manifested in f-electron systems with lanthanide or actinide elements, was recently discovered in several 3d transition metal compounds without f-electrons. However, KH has not yet been observed in 4d/5d transition metal compounds, since more extended 4d/5d orbitals do not usually form flat bands that supply localized electrons appropriate for Kondo pairing. Here, we report a doping- and temperature-dependent angle-resolved photoemission study on 4d Ca2-xSrxRuO4, which shows the signature of KH. We observed a spectral weight transf…
We study a model for photovoltaic energy collection consisting of a Mott insulating layer in presence of acoustic phonons, coupled to two wide-band fermion leads at different chemical potentials and driven into a nonequilibrium steady state by a periodic electric field. We treat electron correlations with nonequilibrium dynamical mean-field theory (DMFT) using the so-called auxiliary master equation approach as impurity solver and include dissipation by acoustic phonons via the Migdal approximation. For a small hybridization to the leads, we obtain a peak in the photocurrent as a function of t…
Orbital-selective Mottness Driven by Geometric Frustration of Interorbital Hybridization in Pr4Ni3O10
Tsinghua University（清华大学）；ShanghaiTech University（上海科技大学）；Songshan Lake Materials Laboratory（松山湖材料实验室）；Yale University（耶鲁大学）；Diamond Light Source（钻石光源）；University of Oxford（牛津大学）；Lanzhou University（兰州大学）；Shanghai Advanced Research Institute, Chinese Academy of Sciences（中国科学院上海高等研究院）；University of Science and Technology of China（中国科学技术大学）；SLAC National Accelerator Laboratory（斯坦福直线加速器中心）；Hefei National Laboratory（合肥国家实验室）
Mott-Derived Local Moments and Kondo Hybridization in a d-electron Kagome lattice
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所凝聚态物理国家实验室）；University of Chinese Academy of Sciences（中国科学院大学）；State Key Laboratory of Low Dimensional Quantum Physics, Department of Physics, Tsinghua University（清华大学物理系低维量子物理国家重点实验室）；National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University（南京大学固体微结构物理全国重点实验室及物理学院）；Technical Institute of Physics and Chemistry, Chinese Academy of Sciences（中国科学院化学物理研究所）
We study the structural, electronic and vibrational properties of single-layer 1TNbSe$_2$ from first principles. Within the generalized gradient approximation, the 1T polytype is highly unstable with respect to the 2H. The DFT+U method improves the stability of the 1T phase, explaining its detection in experiments. A charge density wave occurs with a $\sqrt{13}\times\sqrt{13}~R30^{\circ}$ periodicity, in agreement with STM data. At $U=0$, the David-star reconstruction displays a flat band below the Fermi level with a marked d$_{z^2-r^2}$ orbital character of the central Nb. The Hubbard interac…
There is increasing recognition that the multiorbital nature of the 3d electrons is important to the proper description of the electronic states in the normal state of the iron-based superconductors. Earlier studies of the pertinent multiorbital Hubbard models identified an orbital-selective Mott phase, which anchors the orbital-selective behavior seen in the overall phase diagram. An important characteristics of the models is that the orbitals are kinetically coupled -- i.e. hybridized -- to each other, which makes the orbital-selective Mott phase especially nontrivial. A U(1) slave-spin meth…
Motivated by recent photoemission and pump-probe experiments, we report determinant Quantum Monte Carlo simulations of hybridization fluctuations in the half-filled periodic Anderson model. A tentative phase diagram is constructed based solely on hybridization fluctuation spectra and reveals a crossover regime between an unhybridized selective Mott state and a fully hybridized Kondo insulating state. This intermediate phase exhibits nonlocal hybridization fluctuations and consequentially the so-called "band bending" and a direct hybridization gap as observed in angle-resolved photoemission spe…
Theory of doped Mott insulators is revisited in the light of recent understanding on the singular self-energy structure of the single-particle Green's function. The unique pole structure in the self-energy induces the high-temperature superconductivity in the anomalous part, while it generates Mott gap and pseudogap in the normal part. Here, we elucidate that fractionalization of electrons, which is exactly hold in the Mott insulator in the atomic limit, more generally produces the emergent Mott-gap fermion and dark (hidden) fermions. It does not require any spontaneous symmetry breaking. The …
The effect of interorbital hopping on the orbital selective Mottness in a two-band correlation system is investigated by using the dynamical mean-field theory with the Lanczos method as impurity solver. We construct the phase diagram of the two-orbital Hubbard model with interorbital hopping ($t_{12})$, where the orbital selective Mott phases (OSMP) show different evolution trends. We find that the negative interorbital hopping ($t_{12}<0$) can enhance the OSMP regime upon tuning the effective bandwidth ratio. On the contrary, for the cases with positive interorbital hopping ($t_{12}>0$), the …
Combination of low-dimensionality and electron correlation is vital for exotic quantum phenomena such as the Mott-insulating phase and high-temperature superconductivity. Transition-metal dichalcogenide (TMD) 1T-TaS2 has evoked great interest owing to its unique nonmagnetic Mott-insulator nature coupled with a charge-density-wave (CDW). To functionalize such a complex phase, it is essential to enhance the CDW-Mott transition temperature TCDW-Mott, whereas this was difficult for bulk TMDs with TCDW-Mott < 200 K. Here we report a strong-coupling 2D CDW-Mott phase with a transition temperature on…
The vicinity of a Mott insulating phase has constantly been a fertile ground for finding exotic quantum states, most notably the high Tc cuprates and colossal magnetoresistance manganites. The layered transition metal dichalcogenide 1T-TaS2 represents another intriguing example, in which the Mott insulator phase is intimately entangled with a series of complex charge-density-wave (CDW) orders. More interestingly, it has been recently found that 1T-TaS2 undergoes a Mott-insulator-to-superconductor transition induced by high pressure, charge doping, or isovalent substitution. The nature of the M…
If a material with an odd number of electrons per unit cell turns out to be insulating, Mott localisation may be invoked as an explanation. This is widely accepted for the layered compound 1T-TaS2, which has a low-temperature insulating phase comprising charge order clusters with 13 unpaired orbitals each. But if the stacking of layers doubles up the unit cell to include an even number of orbitals, the nature of the insulating state is ambiguous. Here, scanning tunnelling microscopy (STM) reveals two distinct terminations of the charge order in 1T-TaS2, the sign of such a double-layer stacking…
Tuning the electronic properties of a matter is of fundamental interest in scientific research as well as in applications. Recently, the Mott insulator-metal transition has been reported in a pristine layered transition metal dichalcogenides 1T-TaS$_2$, with the transition triggered by an optical excitation, a gate controlled intercalation, or a voltage pulse. However, the sudden insulator-metal transition hinders an exploration of how the transition evolves. Here, we report the strain as a possible new tuning parameter to induce Mott gap collapse in 1T-TaS$_2$. In a strain-rich area, we find …
Ambipolar doping-induced surface in-gap state on Mott-insulating Ca$_2$RuO$_4$
Institute for Solid State Physics, The University of Tokyo（东京大学固体物理研究所）；Roma Tre University（罗马第三大学）；CNR-SPIN（意大利国家研究委员会自旋电子学研究所）；Dipartimento di Fisica ”E.R. Caianiello”, Università di Salerno（萨莱诺大学E.R. Caianiello物理学系）；Physik-Institut, Universität Zürich（苏黎世大学物理研究所）
We combined optical spectroscopy and first principles electronic structure calculations to reveal the charge gap in the polar magnet Fe$_2$Mo$_3$O$_8$. Iron occupation on the octahedral site draws the gap strongly downward compared to the Zn parent compound, and subsequent occupation of the tetrahedral site creates a narrow resonance near the Fermi energy that draws the gap downward even further. This resonance is a many-body effect that emanates from a flat valence band in a Mott-like state due to screening of the local moment - similar to expectations for a Zhang-Rice singlet, except that he…
We investigate the low-temperature charge-density-wave (CDW) state of bulk TaS$_2$ with a fully self-consistent DFT+U approach, over which the controversy has remained unresolved regarding the out-of-plane metallic band. By examining the innate structure of the Hubbard U potential, we reveal that the conventional use of atomic-orbital basis could seriously misevaluate the electron correlation in the CDW state. By adopting a generalized basis, covering the whole David star, we successfully reproduce the Mott insulating nature with the layer-by-layer antiferromagnetic order. Similar consideratio…
Inspired by the physics of rare earth nickelates, we study the photoemission (PES) and resonant inelastic X-ray scattering (RIXS) spectra of a correlated electron system with two types of insulating sublattices. Sublattice A is characterized by a hybridization gap and a low-spin state, while sublattice B features a Mott gap and a local magnetic moment. We show how the coupling of these two qualitatively different insulating states affects the dynamics of photo-induced charge carriers and how the nonequilibrium states manifest themselves in the PES and RIXS signals. In particular, we find that …
The ground-state orbital occupancy of the Ru$^{4+}$ ion in Ca$_{2-x}$La$_x$RuO$_4$ [x=0, 0.05(1), 0.07(1) and 0.12(1)] was investigated by performing X-ray absorption spectroscopy (XAS) in the vicinity of the O K edge as a function of angle between the incident beam and the surface of the crystals. A minimal model of the hybridization between the O 2p states probed at the K edge and the Ru 4d orbitals was used to analyze the XAS data, allowing the ratio of hole occupancies $n_{xy}/n_{yz,zx}$ to be determined as a function of doping and temperature. For the samples displaying a low-temperature …
The localization-delocalization transition is at the heart of strong correlation physics. Recently, there is great interest in multiorbital systems where this transition can be restricted to certain orbitals, leading to an orbital-selective Mott phase (OSMP). Theoretically, the OSMP is widely studied for kinetically decoupled orbitals, but the effect of interorbital hopping remains unclear. Here, we show how nonlocal interorbital hopping leads to local hybridization in single-site dynamical mean-field theory (DMFT). Under fairly general circumstances, this implies that, at zero temperature, th…
Distinguishing and controlling the extent of Mottness is important for materials where the energy scales of the onsite Coulomb repulsion U and the bandwidth W are comparable. Here we report the ultrafast electronic dynamics of 1T-TaS$_2$ by ultrafast time- and angle-resolved photoemission spectroscopy. A comparison of the electron dynamics for the newly-discovered intermediate phase (I-phase) as well as the low-temperature commensurate charge density wave (C-CDW) phase shows distinctive dynamics. While the I-phase is characterized by an instantaneous response and nearly time-resolution-limited…
1T-TaS$_2$ is a charge-density-wave (CDW) compound with a Mott-insulating ground state. The metallic state obtained by doping, substitution or pulsed charge injection is characterized by an emergent CDW domain wall network, while single domain walls can be found in the pristine Mott state. Here we study whether and how the single walls become metallic. Tunneling spectroscopy reveals partial suppression of the Mott gap and the presence of in-gap states strongly localized at the domain-wall sites. Using the real-space dynamical mean field theory description of the strongly correlated quantum-par…
1T-TaS$_2$ undergoes successive phase transitions upon cooling and eventually enters an insulating state of mysterious origin. Some consider this state to be a band insulator with interlayer stacking order, yet others attribute it to Mott physics that support a quantum spin liquid state.Here, we determine the electronic and structural properties of 1T-TaS$_2$ using angle-resolved photoemission spectroscopy and X-Ray diffraction. At low temperatures, the 2$π$/2c-periodic band dispersion, along with half-integer-indexed diffraction peaks along the c axis, unambiguously indicates that the ground …
Electron-phonon-driven charge density waves can in some circumstances allow electronic correlations to become predominant, driving a system into a Mott insulating state. New insights into both the Mott state and preceding charge density wave may result from observations of the coupled dynamics of their underlying degrees of freedom. Here, tunneling injection of single electrons into the upper Hubbard band of the Mott charge-density-wave material 1T-TaS2 reveals extraordinarily narrow electronic excitations which couple to amplitude mode phonons associated with the charge density wave's periodi…
Realization of a Wigner-Mott insulator in 6R-TaS$_2$ superconductor
Beijing National Center for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所（北京凝聚态物理国家研究中心））；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；Hefei National Laboratory（合肥国家实验室）；Department of Physics, Boston College（波士顿学院物理系）
In the framework of cluster perturbation theory for the 2D Hubbard and Hubbard-Holstein models at low hole doping we have studied the effect of local and short-range correlations in strongly correlated systems on the anomalous features in the electronic spectrum by investigating the fine structure of quasiparticle bands. Different anomalous features of spectrum are obtained as the result of intrinsic properties of strongly correlated electron and polaron bands in the presence of short-range correlations. Particularly, features similar to the electron-like Fermi-pockets of cuprates at hole dopi…
Discovery of a hybridization-wave electronic order in a van der Waals Kondo lattice
University of Chinese Academy of Sciences（中国科学院大学）；Chinese Academy of Sciences（中国科学院）；University of Science and Technology of China（中国科学技术大学）；Nanjing University（南京大学）；Beijing Institute of Technology（北京理工大学）
