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We examine the cluster-size dependence of the cellular dynamical mean-field theory (CDMFT) applied to the two-dimensional Hubbard model. Employing the continuous-time quantum Monte Carlo method as the solver for the effective cluster model, we obtain CDMFT solutions for 4-, 8-, 12-, and 16-site clusters at a low temperature. Comparing various periodization schemes, which are used to construct the infinite-lattice quantities from the cluster results, we find that the cumulant periodization yields the fastest convergence for the hole-doped Mott insulator where the most severe size dependence is expected. We also find that the convergence is much faster around (0.0) and (&pgr;/2,&pgr;/2) than around (&pgr;,0) and (&pgr;,&pgr;). The cumulant-periodized self-energy seems to be close to its thermodynamic limit already for a 16-site cluster in the range of parameters studied. The 4-site results remarkably agree well with the 16-site results, indicating that the previous studies based on the 4-site cluster capture the essence of the physics of doped Mott insulators. [ABSTRACT FROM AUTHOR]

Topological insulators in the presence of a strong Coulomb interaction constitute novel phases of matter. Transitions between these phases can be driven by single-particle or many-body effects. On the basis of ab initio calculations, we identify a concrete material, i.e., Ca2PtO4, that turns out to be a hole-doped weak topological insulator. Interestingly, the Pt d orbitals in this material are relevant for the band inversion that gives rise to the topological phase. Therefore, Coulomb interactions should be of importance in Ca2PtO4. To study the influence of interactions on the weak topological insulating phase, we look at a toy model corresponding to a layer-stacked three-dimensional version of the Bernevig-Hughes-Zhang model with local interactions. For a low to intermediate interaction strength, we discover novel interaction-driven topological phase transitions between the weak topological insulator and two Dirac semimetal phases. The latter correspond to gapless topological phases. For strong interactions, the system eventually becomes a Mott insulator. [ABSTRACT FROM AUTHOR]

We investigate the role of electron-electron interaction in a two-band Hubbard model based on the Bernevig-Hughes-Zhang Hamiltonian exhibiting the quantum spin Hall (QSH) effect. By means of dynamical mean-field theory, we find that a system with topologically trivial noninteracting parameters can be driven into a QSH phase at finite interaction strength by virtue of local dynamical fluctuations. For very strong interaction, the system reenters a trivial insulating phase by going through a Mott transition. We obtain the phase diagram of our model by direct calculation of the bulk topological invariant of the interacting system in terms of its single-particle Green's function. [ABSTRACT FROM AUTHOR]

The dynamical mean-field theory is used to study the three-orbital model of the d³ compound SrRu2O6 both with and without explicitly including the O-p states. Depending on the size of the Hund's coupling J, at low to intermediate temperatures we find solutions corresponding to Mott or correlated covalent insulators. The latter can explain the experimentally observed absence of Curie susceptibility in the paramagnetic phase. At high temperatures, a single phase with smoothly varying properties is observed. d³ compound SrRu2O6 provides an ideal system to study the competition between the local moment physics and covalent bonding, since both effects are maximized, while SO interaction is found to play a minor role. [ABSTRACT FROM AUTHOR]

We present a detailed investigation of spectroscopic features located at the central metal ion of MnPc (where Pc represents phthalocyanine) on Ag(001) by means of scanning tunneling spectroscopy (STS) and first-principles theory. STS data taken close to the Fermi level reveal an asymmetric feature that cannot be fitted with a single Fano function representing a one-channel Kondo effect. Instead, our data indicate the existence of a second superimposed feature. Two potential physical origins, a second Kondo channel related to the dxz/yz orbitals, and a spectral feature of the dz2 orbital itself, are discussed. A systematic experimental and theoretical comparison of MnPc with CoPc and FePc indicates that the second feature observed on MnPc is caused by the dz2 orbital. This conclusion is corroborated by STM-induced dehydrogenation experiments on FePc and MnPc which in both cases result in a gradual shift towards more positive binding energies and a narrowing of the Kondo resonance. Theoretical analysis reveals that the latter is caused by the reduced hybridization between the d orbital and the substrate. Spatially resolved differential conductivity maps taken close to the respective peak positions show that the intensity of both features is highest over the central Mn ion, thereby providing further evidence against a second Kondo channel originating from the dxz/yz orbital of the central Mn ion. [ABSTRACT FROM AUTHOR]

We employ density functional theory plus dynamical mean field theory and identify the physical origin of why two layers of SrVO3 on a SrTiO3 substrate are insulating: the thin film geometry lifts the orbital degeneracy, which in turn triggers a first-order Mott-Hubbard transition. Two layers of SrVO3 are just at the verge of a Mott-Hubbard transition and hence ideally suited for technological applications of the Mott-Hubbard transition: the heterostructure is highly sensitive to strain, electric field, and temperature. A gate voltage can also switch between metal (on) and insulator (off), so that a transistor with ideal on-off switching properties is realized. [ABSTRACT FROM AUTHOR]

We propose an unexplored class of absorbing materials for high-efficiency solar cells: heterostructures of transition-metal oxides. In particular, LaVO3 grown on SrTiO3 has a direct band gap ~1.1 eV in the optimal range as well as an internal potential gradient, which can greatly help to separate the photogenerated electron-hole pairs. Furthermore, oxide heterostructures afford the flexibility to combine LaVO3 with other materials such as LaFeO3 in order to achieve even higher efficiencies with band-gap graded solar cells. We use density-functional theory to demonstrate these features. [ABSTRACT FROM AUTHOR]

In the context of realistic calculations for strongly correlated materials with d or f electrons the efficient computation of multi-orbital models is of paramount importance. Here we introduce a set of invariants for the SU(2)-symmetric Kanamori Hamiltonian, which allows us to massively speed up the calculation of the fermionic trace in hybridization-expansion continuous-time quantum Monte Carlo algorithms. We show that by exploiting this set of good quantum numbers the study of the orbital-selective Mott transition in systems with up to seven correlated orbitals becomes feasible. [ABSTRACT FROM AUTHOR]

The recent discovery of AV3Sb5 (A=K,Rb,Cs) has uncovered an intriguing arena for exotic Fermi surface instabilities in a kagome metal. Among them, superconductivity is found in the vicinity of multiple van Hove singularities, exhibiting indications of unconventional pairing. We show that the sublattice interference mechanism is central to understanding the formation of superconductivity in a kagome metal. Starting from an appropriately chosen minimal tight-binding model with multiple van Hove singularities close to the Fermi level for AV3Sb5, we provide a random phase approximation analysis of superconducting instabilities. Nonlocal Coulomb repulsion, the sublattice profile of the van Hove bands, and the interaction strength turn out to be the crucial parameters to determine the preferred pairing symmetry. Implications for potentially topological surface states are discussed, along with a proposal for additional measurements to pin down the nature of superconductivity in AV3Sb5. [ABSTRACT FROM AUTHOR]

We study the resistivity of three-dimensional semimetals with linear dispersion in the presence of on-site electron-electron interaction. The well-known quadratic temperature dependence of the resistivity of conventional metals is turned into an unusual T6 behavior. An analogous change affects the thermal transport, preserving the linearity in T of the ratio between thermal and electrical conductivities. These results hold from weak coupling up to the nonperturbative region of the Mott transition. Our findings yield a natural explanation for the hitherto not understood large exponents characterizing the temperature dependence of transport experiments on various topological semimetals. [ABSTRACT FROM AUTHOR]

We clarify the origin of the strikingly different spectroscopic properties of the chemically similar compounds NaOsO3 and LiOsO3. 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. Although 5d oxides are mildly correlated, we show that the cooperative action of intraorbital repulsion and Hund's exchange becomes the dominant physical mechanism in these materials if their t2g shell is half filled. Small material specific details hence result in an extremely sharp change of the electronic mobility, explaining the surprisingly different properties of the paramagnetic high-temperature phases of the two compounds. [ABSTRACT FROM AUTHOR]

The Rashba effect is fundamental to the physics of two-dimensional electron systems and underlies a variety of spintronic phenomena. It has been proposed that the formation of Rashba-type spin splittings originates microscopically from the existence of orbital angular momentum (OAM) in the Bloch wave functions. Here, we present detailed experimental evidence for this OAM-based origin of the Rashba effect by angle-resolved photoemission (ARPES) and two-photon photoemission experiments for a monolayer AgTe on Ag(111). Using quantitative low-energy electron diffraction analysis, we determine the structural parameters and the stacking of the honeycomb overlayer with picometer precision. Based on an orbital-symmetry analysis in ARPES and supported by first-principles calculations, we unequivocally relate the presence and absence of Rashba-type spin splittings in different bands of AgTe to the existence of OAM. [ABSTRACT FROM AUTHOR]

Gold nanostructures have important applications in nanoelectronics, nano-optics, and in precision metrology due to their intriguing optoelectronic properties. These properties are governed by the bulk band structure but to some extent are tunable via geometrical resonances. Here we show that the band structure of gold itself exhibits significant size-dependent changes already for mesoscopic critical dimensions below 30 nm. To suppress the effects of geometrical resonances and grain boundaries, we prepared atomically flat ultrathin films of various thicknesses by utilizing large chemically grown single-crystalline gold platelets. We experimentally probe thickness-dependent changes of the band structure by means of two-photon photoluminescence and observe a surprising 100-fold increase of the nonlinear signal when the gold film thickness is reduced below 30 nm allowing us to optically resolve single-unit-cell steps. The effect is well explained by density functional calculations of the thickness-dependent 2D band structure of gold. [ABSTRACT FROM AUTHOR]

The monopnictides TaAs and TaP are well-established Weyl semimetals. Yet, a precise assignment of Fermi arcs, accommodating the predicted chiral charge of the bulk Weyl points, has been difficult in these systems, and the topological character of different surface features in the Fermi surface is not fully understood. Here, employing a joint analysis from linear dichroism in angle-resolved photoemission and first-principles calculations, we unveil the orbital texture on the full Fermi surface of TaP(001). We observe pronounced switches in the orbital texture at the projected Weyl nodes, and show how they facilitate a topological classification of the surface band structure. Our findings establish a critical role of the orbital degrees of freedom in mediating the surface-bulk connectivity in Weyl semimetals. [ABSTRACT FROM AUTHOR]

Double Dirac fermions have recently been identified as possible quasiparticles hosted by three-dimensional crystals with particular nonsymmorphic point-group symmetries. Applying a combined approach of ab initio methods and dynamical mean-field theory, we investigate how interactions and double Dirac band topology conspire to form the electronic quantum state of Bi2CuO4. We derive a downfolded eight-band model of the pristine material at low energies around the Fermi level. By tuning the model parameters from the free band structure to the realistic strongly correlated regime, we find a persistence of the double Dirac dispersion until its constituting time-reversal symmetry is broken due to the onset of magnetic ordering at the Mott transition. Our calculations suggest that the double Dirac fermions in Bi2CuO4 can be restored by experimentally accessible hydrostatic pressures. In light of the growing attention to the topological quantum chemistry approach, our results on Bi2CuO4 show how many-body effects must be included beyond the static mean-field level for reliable predictions on new materials. [ABSTRACT FROM AUTHOR]

We use a real-space slave-rotor theory of the physics of topological Mott insulators, using the Kane-Mele-Hubbard model as an example, and show that a topological gap in the Green function zeros corresponds to a gap in the bulk spinon spectrum and implies a gapless band of edge zeros and a spinon edge mode. We then consider an interface between a topological Mott insulator and a conventional topological insulator showing how the spinon edge mode of the topological Mott insulator combines with the spin part of the conventional electron topological edge state, leaving a non-Fermi liquid edge mode described by a gapless propagating holon and gapped spinon state. Our work demonstrates the physical meaning of Green function zeros and shows that interfaces between conventional and Mott topological insulators are a rich source of new physics.

The demonstration of a topological band inversion constitutes the most elementary proof of a quantum spin Hall insulator (QSHI). On a fundamental level, such an inverted band gap is intrinsically related to the bulk Berry curvature, a gauge-invariant fingerprint of the wave function's quantum geometric properties in Hilbert space. Intimately tied to orbital angular momentum (OAM), the Berry curvature can be, in principle, extracted from circular dichroism in angle-resolved photoemission spectroscopy (CD-ARPES), were it not for interfering final state photoelectron emission channels that obscure the initial state OAM signature. Here, we outline a full-experimental strategy to avoid such interference artifacts and isolate the clean OAM from the CD-ARPES response. Bench-marking this strategy for the recently discovered atomic monolayer system indenene, we demonstrate its distinct QSHI character and establish CD-ARPES as a scalable bulk probe to experimentally classify the topology of two-dimensional quantum materials with time reversal symmetry.

We use the topological heavy fermion (THF) model and its Kondo lattice (KL) formulation to study the possibility of a symmetric Kondo (SK) state in twisted bilayer graphene. Via a large-N approximation, we find a SK state in the KL model at fillings ν=0,±1,±2 where a KL model can be constructed. In the SK state, all symmetries are preserved and the local moments are Kondo screened by the conduction electrons. At the mean-field level of the THF model at ν=0,±1,±2,±3 we also find a similar symmetric state that is adiabatically connected to the symmetric Kondo state. We study the stability of the symmetric state by comparing its energy with the ordered (symmetry-breaking) states found in [H. Hu et al., Phys. Rev. Lett. 131, 026502 (2023).PRLTAO0031-900710.1103/PhysRevLett.131.026502, Z.-D. Song and B. A. Bernevig, Phys. Rev. Lett. 129, 047601 (2022).PRLTAO0031-900710.1103/PhysRevLett.129.047601] and find the ordered states to have lower energy at ν=0,±1,±2. However, moving away from integer fillings by doping the light bands, our mean-field calculations find the energy difference between the ordered state and the symmetric state to be reduced, which suggests the loss of ordering and a tendency toward Kondo screening. In order to include many-body effects beyond the mean-field approximation, we also performed dynamical mean-field theory calculations on the THF model in the nonordered phase. The spin susceptibility follows a Curie behavior at ν=0,±1,±2 down to ∼2  K where the onset of screening of the local moment becomes visible. This hints to very low Kondo temperatures at these fillings, in agreement with the outcome of our mean-field calculations. At noninteger filling ν=±0.5,±0.8,±1.2 dynamical mean-field theory shows deviations from a 1/T susceptibility at much higher temperatures, suggesting a more effective screening of local moments with doping. Finally, we study the effect of a C_{3z}-rotational-symmetry-breaking strain via mean-field approaches and find that a symmetric phase (that only breaks C_{3z} symmetry) can be stabilized at sufficiently large strain at ν=0,±1,±2. Our results suggest that a symmetric Kondo phase is strongly suppressed at integer fillings, but could be stabilized either at noninteger fillings or by applying strain.

We demonstrate that a finite-doping quantum critical point (QCP) naturally descends from the existence of a first-order Mott transition in the phase diagram of a strongly correlated material. In a prototypical case of a first-order Mott transition the surface associated with the equation of state for the homogeneous system is "folded" so that in a range of parameters stable metallic and insulating phases exist and are connected by an unstable metallic branch. Here we show that tuning the chemical potential, the zero-temperature equation of state gradually unfolds. Under general conditions, we find that the Mott transition evolves into a first-order transition between two metals, associated with a phase separation region ending in the finite-doping QCP. This scenario is here demonstrated solving a minimal multiorbital Hubbard model relevant for the iron-based superconductors, but its origin-the splitting of the atomic ground state multiplet by a small energy scale, here Hund's coupling-is much more general. A strong analogy with cuprate superconductors is traced.

We perform a data-driven dimensionality reduction of the scale-dependent four-point vertex function characterizing the functional renormalization group (FRG) flow for the widely studied two-dimensional t-t^{'} Hubbard model on the square lattice. We demonstrate that a deep learning architecture based on a neural ordinary differential equation solver in a low-dimensional latent space efficiently learns the FRG dynamics that delineates the various magnetic and d-wave superconducting regimes of the Hubbard model. We further present a dynamic mode decomposition analysis that confirms that a small number of modes are indeed sufficient to capture the FRG dynamics. Our Letter demonstrates the possibility of using artificial intelligence to extract compact representations of the four-point vertex functions for correlated electrons, a goal of utmost importance for the success of cutting-edge quantum field theoretical methods for tackling the many-electron problem.

The recent discovery of AV_{3}Sb_{5} (A=K,Rb,Cs) has uncovered an intriguing arena for exotic Fermi surface instabilities in a kagome metal. Among them, superconductivity is found in the vicinity of multiple van Hove singularities, exhibiting indications of unconventional pairing. We show that the sublattice interference mechanism is central to understanding the formation of superconductivity in a kagome metal. Starting from an appropriately chosen minimal tight-binding model with multiple van Hove singularities close to the Fermi level for AV_{3}Sb_{5}, we provide a random phase approximation analysis of superconducting instabilities. Nonlocal Coulomb repulsion, the sublattice profile of the van Hove bands, and the interaction strength turn out to be the crucial parameters to determine the preferred pairing symmetry. Implications for potentially topological surface states are discussed, along with a proposal for additional measurements to pin down the nature of superconductivity in AV_{3}Sb_{5}.

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. Although 5d oxides are mildly correlated, we show that the cooperative action of intraorbital repulsion and Hund's exchange becomes the dominant physical mechanism in these materials if their t_{2g} shell is half filled. Small material specific details hence result in an extremely sharp change of the electronic mobility, explaining the surprisingly different properties of the paramagnetic high-temperature phases of the two compounds.

The monopnictides TaAs and TaP are well-established Weyl semimetals. Yet, a precise assignment of Fermi arcs, accommodating the predicted chiral charge of the bulk Weyl points, has been difficult in these systems, and the topological character of different surface features in the Fermi surface is not fully understood. Here, employing a joint analysis from linear dichroism in angle-resolved photoemission and first-principles calculations, we unveil the orbital texture on the full Fermi surface of TaP(001). We observe pronounced switches in the orbital texture at the projected Weyl nodes, and show how they facilitate a topological classification of the surface band structure. Our findings establish a critical role of the orbital degrees of freedom in mediating the surface-bulk connectivity in Weyl semimetals.

We employ density functional theory plus dynamical mean field theory and identify the physical origin of why two layers of SrVO(3) on a SrTiO(3) substrate are insulating: the thin film geometry lifts the orbital degeneracy, which in turn triggers a first-order Mott-Hubbard transition. Two layers of SrVO(3) are just at the verge of a Mott-Hubbard transition and hence ideally suited for technological applications of the Mott-Hubbard transition: the heterostructure is highly sensitive to strain, electric field, and temperature. A gate voltage can also switch between metal (ON) and insulator (OFF), so that a transistor with ideal ON-OFF switching properties is realized.