We study the interplay between Mott physics, driven by Coulomb repulsion U, and Hund physics, driven by Hund's coupling J, for a minimal model for Hund metals, the orbital-symmetric three-band Hubbard-Hund model (3HHM) for a lattice filling of 1/3. Hund-correlated metals are characterized by spin-orbital separation (SOS), a Hund's-rule-induced two-stage Kondo-type screening process, in which spin screening occurs at much lower energy scales than orbital screening. By contrast, in Mott-correlated metals, lying close to the phase boundary of a metal-insulator transition, the SOS window becomes negligibly small and the Hubbard bands are well separated. Using dynamical mean-field theory and the numerical renormalization group as real-frequency impurity solver, we identify numerous fingerprints distinguishing Hundness from Mottness in the temperature dependence of various physical quantities. These include ARPES-type spectra, the local self-energy, static local orbital and spin susceptibilities, resistivity, thermopower, and lattice and impurity entropies. Our detailed description of the behavior of these quantities within the context of a simple model Hamiltonian will be helpful for distinguishing Hundness from Mottness in experimental and theoretical studies of real materials.
We clarify the origin of the strikingly different spectroscopic properties of the chemically similar compounds NaOsO$_3$ and LiOsO$_3$. Our first-principle many-body analysis demonstrates that the highly sensitive physics of these two materials is controlled by their proximity to an adjacent Hund's-Mott insulating phase. In mildly correlated $5d$ oxides, this physics is triggered by the {\sl cooperative} action of intraorbital repulsion and Hund's exchange in half-filled $t_{2g}$ outer-shells. Small material-specific details hence result in an extremely sharp change of the electronic mobility,…
Mott-Hubbard and Hund electron correlations have been realized thus far in separate classes of materials. Here, we show that a single moiré homobilayer encompasses both kinds of physics in a controllable manner. We develop a microscopic multiband model that we solve by dynamical mean-field theory to nonperturbatively address the local many-body correlations. We demonstrate how tuning with twist angle, dielectric screening, and hole density allows us to switch between Mott-Hubbard and Hund correlated states in a twisted WSe$_2$ bilayer. The underlying mechanism is based on controlling Coulomb-i…
We point out the generic competition between the Hund's coupling and the spin-orbit coupling in correlated materials, and this competition leads to an electronic dilemma between the Hund's metal and the relativistic insulators. Hund's metals refer to the fate of the would-be insulators where the Hund's coupling suppresses the correlation and drives the systems into correlated metals. Relativistic Mott insulators refer to the fate of the would-be metals where the relativistic spin-orbit coupling enhances the correlation and drives the systems into Mott insulators. These contradictory trends are…
Motivated by the recent discovery of superconductivity in infinite-layer nickelates RE$_{1-δ}$Sr$_δ$NiO$_2$ (RE$=$Nd, Pr), we study the role of Hund's coupling $J$ in a quarter-filled two-orbital Hubbard model which has been on the periphery of the attention. A region of negative effective Coulomb interaction of this model is revealed to be differentiated from three- and five-orbital models in their typical Hund's metal active fillings. We identify distinctive regimes including four different correlated metals, one of which stems from the proximity to a Mott insulator while the other three, wh…
We study the ground state of the Hubbard model on a square lattice with two degenerate orbitals per site and at integer fillings as a function of onsite Hubbard repulsion $U$ and Hund's intra-atomic exchange coupling $J$. We use a variational slave-spin mean field (VSSMF) method which allows symmetry broken states to be studied within the computationally less intensive slave-spin mean field formalism, thus making the method more powerful to study strongly correlated electron physics. The results show that at half-filling, the ground state at smaller $U$ is a Slater antiferromagnet (AF) with su…
Ab initio Evidence for Strong Correlation Associated with Mott Proximity in Iron-based Superconductors
我们预测，发现的铁基超导体附近的d6配置（5 Fe 3d轨道填充6个电子）位于一个意想不到的大圆顶的相关电子物质在d5（即，半填充）的莫特绝缘体为中心的脚。这是基于多变量变分蒙特卡罗从头算低能量模型的结果推导的向下折叠。D5莫特接近延伸到随后出现的非相干金属，轨道微分由于莫特物理和洪德规则耦合，其次是反铁磁量子临界，根据现有的实验定量。
Interfaces between dissimilar correlated oxides can offer devices with versatile functionalities. In that respect, manipulating and measuring novel physical properties of oxide heterointerfaces are highly desired. Yet, despite extensive studies, obtaining direct information on their momentum-resolved electronic structure remains a great challenge. This is because most correlated interfacial phenomena appear within a few atomic layers from the interface, thus limiting the application of available experimental probes. Here, we utilize atomic-scale epitaxy and photoemission spectroscopy to demons…
The recent detailed study of quasi-one-dimensional iron-based ladders, with the $3d$ iron electronic density $n = 6$, has unveiled surprises, such as orbital-selective phases. However, similar studies for $n=6$ iron chains are still rare. Here, a three-orbital electronic Hubbard model was constructed to study the magnetic and electronic properties of the quasi-one-dimensional $n=6$ iron chain Ce$_2$O$_2$FeSe$_2$, with focus on the effect of doping. Specifically, introducing the Hubbard $U$ and Hund $J_{H}$ couplings and studying the model via the density matrix renormalization group, we report…
Spontaneous orbital-selective Mott transitions and the Jahn-Teller metal of A$_3$C$_{60}$
碱金属掺杂的富勒烯A $_3$ C $_{60}$是半填充的三轨道Hubbard系统，其在莫特绝缘体旁边显示出非常规的超导相。虽然这种配对被认为是由有效的负洪德耦合引起的，但在莫特跃迁附近的极不寻常的扬-泰勒金属，具有局域和巡回电子，还没有被理解。这种性质是一致的解释以前未被认识到的现象：自发过渡的多轨道系统与负Hund耦合到一个轨道选择性莫特状态。这种破缺态没有普通轨道矩，其特征在于依赖于轨道的两体算符（双占据）或依赖于轨道的动能，可以被视为奇频超导的对角阶版本。我们建议，最近发现的Jahn-Teller金属相Rb $_x$ Cs $_{3-x}$ C $_{60}$是这种新的物质状态的实验实现。
