Strength Of Electronic Correlations Research Articles

Strain-induced modulation of electronic structure in correlated Dirac semimetal Pv-CaIrO3 epitaxial thin films

Perovskite CaIrO3 is theoretically predicted to be a Dirac node semimetal near the Mott transition, which possesses a considerable interplay between electron correlations and spin–orbit coupling. Electron correlations can significantly tune the behavior of relativistic Dirac fermions. Here, we have grown high-quality perovskite CaIrO3 thin films on different substrates using oxide molecular beam epitaxy to modulate both electron correlations and Dirac electron states. Through in situ angle-resolved photoemission spectroscopy, we demonstrate a systematic evolution of the bandwidth and effective mass of Jeff=1/2 band in perovskite CaIrO3 induced by strain. The bandwidth of the Jeff=1/2 band undergoes an evident increase under in-plane compressive strain, which could be attributed to the weakening of electron correlations. The compressive strain can potentially shift the position of the Dirac node relative to the Fermi level and play a vital role in the transition from hole-type to electron-type transport characteristics. Our work provides a feasible approach for manipulating the topological Dirac electron states by engineering the strength of electron correlations.

Evolution of the Magnetic Excitations in Electron-Doped La_{2-x}Ce_{x}CuO_{4}.

We investigated the high energy spin excitations in electron-doped La_{2-x}Ce_{x}CuO_{4}, a cuprate superconductor, by resonant inelastic x-ray scattering (RIXS) measurements. Efforts were paid to disentangle the paramagnon signal from non-spin-flip spectral weight mixing in the RIXS spectrum at Q_{∥}=(0.6π,0) and (0.9π,0) along the (1 0) direction. Our results show that, for doping level x from 0.07 to 0.185, the variation of the paramagnon excitation energy is marginal. We discuss the implication of our results in connection with the evolution of the electron correlation strength in this system.

Stability of the interorbital-hopping mechanism for ferromagnetism in multi-orbital Hubbard models

The emergence of insulating ferromagnetic phase in iron oxychalcogenide chain system has been recently argued to be originated by interorbital hopping mechanism. However, the practical conditions for the stability of such mechanism still prevents the observation of ferromagnetic in many materials. Here, we study the stability range of such ferromagnetic phase under modifications in the crystal fields and electronic correlation strength, constructing a theoretical phase diagram. We find a rich emergence of phases, including a ferromagnetic Mott insulator, a ferromagnetic orbital-selective Mott phase, together with antiferromagnetic and ferromagnetic metallic states. We characterize the stability of the ferromagnetic regime in both the Mott insulator and the ferromagnetic orbital-selective Mott phase forms. We identify a large stability range in the phase diagram at both intermediate and strong electronic correlations, demonstrating the capability of the interorbital hopping mechanism in stabilizing ferromagnetic insulators. Our results may enable additional design strategies to expand the relatively small family of known ferromagnetic insulators.

Bandwidth Control and Symmetry Breaking in a Mott‐Hubbard Correlated Metal

AbstractIn Mott materials strong electron correlation yields a spectrum of complex electronic structures. Recent synthesis advancements open realistic opportunities for harnessing Mott physics to design transformative devices. However, a major bottleneck in realizing such devices remains the lack of control over the electron correlation strength. This stems from the complexity of the electronic structure, which often veils the basic mechanisms underlying the correlation strength. This study presents control of the correlation strength by tuning the degree of orbital overlap using picometer‐scale lattice engineering. This study illustrates how bandwidth control and concurrent symmetry breaking can govern the electronic structure of a correlated SrVO3 model system. This study shows how tensile and compressive biaxial strain oppositely affect the SrVO3 in‐plane and out‐of‐plane orbital occupancy, resulting in the partial alleviation of the orbital degeneracy. The spectral weight redistribution under strain is derived and explained, which illustrates how high tensile strain drives the system toward a Mott insulating state. Implementation of such concepts can push correlated electron phenomena closer toward new solid‐state devices and circuits. These findings therefore pave the way for understanding and controlling electron correlation in a broad range of functional materials, driving this powerful resource for novel electronics closer toward practical realization.

Hubbard Subbands and Superconductivity in the Infinite-Layer Nickelate

An effective two-dimensional two-band model for infinite-layer nickelates consists of bands obtained from $d_{x^2-y^2}$ and $s$--like orbitals. We investigate whether it could be mapped onto a single-band Hubbard model and the filling of Hubbard bands. We find that both one-band physics and a Kondo-lattice regime emerge from the same two-orbital model, depending on the strength of electronic correlations and the filling of the itinerant $s$-band. Next we investigate one-particle excitations by changing the screening. First, for weak screening the strong correlations push electrons out of the $s$-band so that the undoped nickelate is similar to a cuprate. Second, for strong screening the $s$ and $d_{x^2-y^2}$ bands are both partly filled and weakly couple. Particularly in this latter regime mapping to a one-band model gives significant spectral weight transfer between the Hubbard subbands. Finally we point out that the superconducting phases may have either $d$-wave or $s$-wave symmetry.

Evidence of electron correlation and weak bulk plasmon in SrMoO3

We investigate the electronic structure of highly conducting perovskite SrMoO3 using valence band photoemission spectroscopy and electronic structure calculations. Large intensity corresponding to coherent feature close to Fermi level is captured by density functional theory (DFT) calculation. An additional satellite at ∼3 eV binding energy remains absent in DFT, hybrid functional (DFT-hybrid) and dynamical mean field theory (DFT + DMFT) calculations. Mo 4d spectra obtained with different surface sensitive photoemission spectroscopy suggest different surface and bulk electronic structures. DFT + DMFT spectral function is in excellent agreement with the coherent feature in the bulk Mo 4d spectra, revealing moderate electron correlation strength. A large plasmon satellite and signature of strong electron correlation are observed in the surface spectra, while the bulk spectra exhibits a weak plasmon satellite.

Correlated electronic structure of the kagome metal Mn3Sn

${\mathrm{Mn}}_{3}\mathrm{Sn}$ is a fascinating kagome metal exhibiting anomalous Hall effect, spin Hall effect, and anomalous Nernst effect. Using density functional theory plus dynamical mean-field theory ($\mathrm{DFT}+\mathrm{DMFT}$), we investigate the electronic structures of ${\mathrm{Mn}}_{3}\mathrm{Sn}$ in the paramagnetic and noncollinear antiferromagnetic (NAFM) states. In the paramagnetic state, ${\mathrm{Mn}}_{3}\mathrm{Sn}$ has intermediate electronic correlation strength and exhibits typical features of kagome metals including flat bands, Dirac points, and saddle points. In the NAFM state, $\mathrm{DFT}+\mathrm{DMFT}$ calculations reproduce well the experimental Mn magnetic moment and angle-resolved photoemission spectroscopy measurements. Electronic correlation shifts the bands around ${E}_{F}$ and moves the Weyl point between $K$ and $M$ points from $\ensuremath{\sim}40\phantom{\rule{0.28em}{0ex}}\mathrm{meV}$ above ${E}_{F}$ in DFT calculations to $\ensuremath{\sim}5\phantom{\rule{0.28em}{0ex}}\mathrm{meV}$ below ${E}_{F}$, which can strongly enhance the anomalous Hall effect and chiral anomaly observed in ${\mathrm{Mn}}_{3}\mathrm{Sn}$. More importantly, we find that the existence of the Weyl point along the $K\text{\ensuremath{-}}M$ path depends strongly on the ordering pattern of the Mn moments in the NAFM state, which implies that the exotic properties arising from the Weyl points in ${\mathrm{Mn}}_{3}\mathrm{Sn}$ can be manipulated by tuning the ordering pattern of the Mn moments in the NAFM state.

Screening in a two-band model for superconducting infinite-layer nickelate

Starting from an effective two-dimensional two-band model for infinite layered nickelates, consisting of bands obtained from $d$ and $s$--like orbitals, we investigate to which extend it can be mapped onto a single-band Hubbard model. We identify screening of the more itinerant $s$-like band as an important driver. In absence of screening one strongly-correlated band gives an antiferromagnetic ground state. For weak screening, the strong correlations push electrons out of the $s$-band so that the undoped nickelate remains a Mott insulator with half filled $d$ orbitals. This regime markedly differs from the observations in high-$T_c$ cuprates and pairing with $s$-wave symmetry would rather be expected in the superconducting state. In contrast, for strong screening, the $s$ and $d_{x^2-y^2}$ bands are both partly filled and couple only weakly, so that one approximately finds a self-doped $d$ band as well as tendencies towards $d$-wave pairing. Particularly in the regime of strong screening mapping to a one-band model gives interesting spectral weight transfers when a second $s$ band is also partly filled. We thus find that both one-band physics and a Kondo-lattice--like regime emerge from the same two-orbital model, depending on the strength of electronic correlations and the size of the $s$-band pocket.

Magnetism in single-layer of Zrse[formula omitted] by substituting 3[formula omitted] transition metals for Zr: Structural symmetry versus exchange splitting

To understand the magnetic properties of the novel two-dimensional materials and other phenomena which depend on electron correlation, finding the states located around Fermi energy (EF) and contributing to the correlated states of the system is basically important. In this paper, using the density functional theory, we investigate the electronic properties of substitution of 3d transition metal (TM) atoms for Zr in trigonal prismatic 2H and octahedral 1T structure of monolayer TM-doped ZrSe2 materials. The band structure, orbital projected density of states (DOS), and the number of electrons in the d-shell show that the correlated subspace depends strongly on the structural phase of the systems. The case of Mn substitution has the highest magnetic moment, 2.91 μB and 3.30 μB in 2H and 1T phases, respectively. In the 1T structure of Mn-doped ZrSe2, almost partially filled t2g impurity bands is well separated from eg states in the non-magnetic calculation, having a small bandwidth of about Wb= 0.4 eV. As a consequence, the strength of electron correlation U/Wb increases (U is effective on-site Coulomb interaction) and puts this compound in the moderately or strongly correlated regime, and causes a stronger electron spin separation than the 2H phase. In the 2H phase, the correlated states include two impurity bands with dominantly dxy and dx2−y2 characters and induce a smaller magnetic moment. Due to the large DOS of Mn and Cr atoms at the EF in both 1T and 2H structures, the Stoner criterion I.D(EF)>1 is satisfied, which is reasonably consistent with our results of ferromagnetic total energy calculations and the sizable magnetic moments.

Quantum electron liquid and its possible phase transition.

Purely quantum electron systems exhibit intriguing correlated electronic phases by virtue of quantum fluctuations in addition to electron-electron interactions. To realize such quantum electron systems, a key ingredient is dense electrons decoupled from other degrees of freedom. Here, we report the discovery of a pure quantum electron liquid that spreads up to ~3 Å in a vacuum on the surface of an electride crystal. Its extremely high electron density and weak hybridization with buried atomic orbitals show the quantum and pure nature of the electrons, which exhibit a polarized liquid phase, as demonstrated by our spin-dependent measurement. Furthermore, upon enhancing the electron correlation strength, the dynamics of the quantum electrons change to that of a non-Fermi liquid along with an anomalous band deformation, suggestive of a transition to a hexatic liquid crystal phase. Our findings develop the frontier of quantum electron systems and serve as a platform for exploring correlated electronic phases in a pure fashion.

Electron correlations in the of Fe y SeS x (0.10 0.24, 0.9)

We report on the evolution of the electronic correlation strength across the nematic critical point in Fe y SeS x (), inferred from the measurements of the slope of the upper critical field . Superconducting transition T c and quasiparticle mass exhibit similar reduction with sulfur content x. Our results indicate that electronic correlations from all Fermi surface pockets show strong interconnection with pairing strength and are not governed by the change of nematic fluctuations. The upper critical field anisotropy γ H = / exhibits a minimum in the critical region and stronger temperature dependence away from it.

Many-body electronic structure of d9−δ layered nickelates

The recent observation of superconductivity in an infinite-layer and quintuple-layer nickelate within the same $R_{n+1}$Ni$_{n}$O$_{2n+2}$ series ($R$ = rare-earth, $n=2-\infty$, with $n$ indicating the number of NiO$_{2}$ layers along the $c$-axis), unlocks their potential to embody a whole family of unconventional superconductors. Here, we systematically investigate the many-body electronic structure of the layered nickelates (with $n=2-6,\infty$) within a density-functional theory plus dynamical mean-field theory framework and contrast it with that of the known superconducting members of the series and with the cuprates. We find that many features of the electronic structure are common to the entire nickelate series, namely, strongly correlated Ni-$d_{x^{2}-y^{2}}$ orbitals that dominate the low-energy physics, mixed Mott-Hubbard/charge-transfer characteristics, and $R$($5d$) orbitals acting as charge reservoirs. Interestingly, we uncover that the electronic structure of the layered nickelates is highly tunable as the dimensionality changes from quasi-two-dimensional to three-dimensional as $n \rightarrow \infty$. Specifically, we identify the tunable electronic features to be: the charge-transfer energy, presence of $R(5d)$ states around the Fermi level, and the strength of electronic correlations.

Tuning the magnetic anisotropy and topological phase with electronic correlation in single-layer H−FeBr2

Electronic correlation can strongly influence the electronic properties of two-dimensional (2D) materials with open d- or f-orbitals. Herein, by taking single-layer (SL) H-FeBr$_2$ as a representative of the SL H-FeX$_2$ (X=Cl, Br, I) family, we investigated the electronic correlation effects in the magnetic anisotropy and electronic topology of such a system based on first-principles calculations with DFT+\textit{U} approach. Our result is that the magnetic anisotropy energy (MAE) of SL H-FeBr$_2$ shows a non-monotonic evolution behaviour with increasing electronic correlation strength, which is mainly due to the competition between different element-resolved MAEs of Fe and Br. Further investigations show that the evolution of element-resolved MAE arises from the variation of the spin-orbital coupling (SOC) interaction between different orbitals in each atom. Moreover, tuning the strength of the electronic correlation can drive the occurrence of band inversions, causing the system to undergoes multiple topological phase transitions, resulting in a quantum anomalous valley Hall (QAVH) effect. These exotic properties are universal for the SL H-FeX$_2$ (X = Cl, Br, I) family. Our work sheds light on the role of electronic correlation effects in tuning magnetic and electronic structures in the SL H-FeX$_2$ (X = Cl, Br, I) family, which could guide advances in the development of new spintronics and valleytronics devices based on these materials.

Tuning moiré excitons and correlated electronic states through layer degree of freedom

Moiré coupling in transition metal dichalcogenides (TMDCs) superlattices introduces flat minibands that enable strong electronic correlation and fascinating correlated states, and it also modifies the strong Coulomb-interaction-driven excitons and gives rise to moiré excitons. Here, we introduce the layer degree of freedom to the WSe2/WS2 moiré superlattice by changing WSe2 from monolayer to bilayer and trilayer. We observe systematic changes of optical spectra of the moiré excitons, which directly confirm the highly interfacial nature of moiré coupling at the WSe2/WS2 interface. In addition, the energy resonances of moiré excitons are strongly modified, with their separation significantly increased in multilayer WSe2/monolayer WS2 moiré superlattice. The additional WSe2 layers also modulate the strong electronic correlation strength, evidenced by the reduced Mott transition temperature with added WSe2 layer(s). The layer dependence of both moiré excitons and correlated electronic states can be well described by our theoretical model. Our study presents a new method to tune the strong electronic correlation and moiré exciton bands in the TMDCs moiré superlattices, ushering in an exciting platform to engineer quantum phenomena stemming from strong correlation and Coulomb interaction.

Nonadiabatic Exchange-Correlation Potential for Strongly Correlated Materials in the Weak and Strong Interaction Limits

In this work, nonadiabatic exchange-correlation (XC) potentials for time-dependent density-functional theory (TDDFT) for strongly correlated materials are derived in the limits of strong and weak correlations. After summarizing some essentials of the available dynamical mean-field theory (DMFT) XC potentials valid for these systems, we present details of the Sham–Schluter equation approach that we use to obtain, in principle, an exact XC potential from a many-body theory solution for the nonequilibrium electron self-energy. We derive the XC potentials for the one-band Hubbard model in the limits of weak and strong on-site Coulomb repulsion. To test the accuracy of the obtained potentials, we compare the TDDFT results obtained with these potentials with the corresponding nonequilibrium DMFT solution for the one-band Hubbard model and find that the agreement between the solutions is rather good. We also discuss possible directions to obtain a universal XC potential that would be appropriate for the case of intermediate interaction strengths, i.e., a nonadiabatic potential that can be used to perform TDDFT analysis of nonequilibrium phenomena, such as transport and other ultrafast properties of materials with any strength of electron correlation at any value in the applied perturbing field.

Investigation of double perovskites Sr2SmNbO6 and X2CoNbO6 (X=Sr,Ba) with SCAN functional and plus U correction

The double perovskites Sr 2 SmNbO 6 , Sr 2 CoNbO 6 and Ba 2 CoNbO 6 were investigated with first principles computations based on the density functional theory and plus U treatment. Firstly, different calculation methods were examined in order to quantitatively approach the exact band gap. It was found that neither the strongly constrained and appropriately normed (SCAN) semilocal density functional nor the hybrid HSE06 functional can well address the semiconducting nature of the investigated double perovskites, while PBE ​+ ​U or SCAN ​+ ​U with appropriately determining the U value can have good performance, which paves the way for future studies of double perovskites. With self-consistently calculated electron correlation strength, the magnetic states and the band gaps of the Sr 2 CoNbO 6 and Ba 2 CoNbO 6 were ​more precisely determined. The electronic, optical and thermoelectric properties were then investigated and discussed for possible applications. To create your abstract, type over the instructions in the template box below.

Interacting fermions in two dimension in simultaneous presence of disorder and magnetic field

We study the revival of Hofstadter butterfly due to the competition between disorder and electronic interaction using mean field approximation of unrestricted Hartree Fock method at zero temperature for two dimensional square and honeycomb lattices. Interplay of disorder and electronic correlation to nullify each other is corroborated by the fact that honeycomb lattice needs more strength of electronic correlation owing to its less co-ordination number which enhances the effect of disorder. The extent of revival of the butterfly is better in square lattice than honeycomb lattice due to higher coordination number. The effect of disorder and interaction is also investigated to study entanglement entropy and entanglement spectrum. We find that for honeycomb lattice area law of entanglement entropy is obeyed in all cases but for square lattice there is some departure from area law for larger subsystems. The entanglement spectrum have the reflection symmetry of the original butterfly of the Hofstadter spectrum. The interaction induces a gap in the entanglement spectrum as well conforming the correspondence between physical spectrum and entanglement spectrum. The effect of disorder closes the interaction induced gap in the entanglement spectrum establishing the nullification of interaction due to disorder and vice versa.

Correlation-driven electron-hole asymmetry in graphene field effect devices

Electron-hole asymmetry is a fundamental property in solids that can determine the nature of quantum phase transitions and the regime of operation for devices. The observation of electron-hole asymmetry in graphene and recently in twisted graphene and moiré heterostructures has spurred interest into whether it stems from single-particle effects or from correlations, which are core to the emergence of intriguing phases in moiré systems. Here, we report an effective way to access electron-hole asymmetry in 2D materials by directly measuring the quasiparticle self-energy in graphene/Boron Nitride field-effect devices. As the chemical potential moves from the hole to the electron-doped side, we see an increased strength of electronic correlations manifested by an increase in the band velocity and inverse quasiparticle lifetime. These results suggest that electronic correlations intrinsically drive the electron-hole asymmetry in graphene and by leveraging this asymmetry can provide alternative avenues to generate exotic phases in twisted moiré heterostructures.

Electronic Correlation Strength of Inorganic Electrides from First Principles.

Strongly correlated electron systems, generally recognized as d- and f-electron systems, have attracted attention as a platform for the emergence of exotic properties such as high-Tc superconductivity. However, correlated electron behaviors have been recently observed in a group of novel materials, electrides, in which s-electrons are confined in subnanometer-sized spaces. Here, we present a trend of electronic correlation of electrides by evaluating the electronic correlation strength obtained from model parameters characterizing effective Hamiltonians of 19 electrides from first principles. The calculated strengths vary in the order 0D ≫ 1D > 2D ∼ 3D electrides, which corresponds to experimental trends, and exceed 10 (a measure for the emergence of exotic properties) in all of the 0D and some of the 1D electrides. We also found the electronic correlation depends on the cation species surrounding the s-electrons. The results indicate that low-dimensional electrides will be new research targets for studies of strongly correlated electron systems.

Moving Dirac nodes by chemical substitution

Dirac fermions play a central role in the study of topological phases, for they can generate a variety of exotic states, such as Weyl semimetals and topological insulators. The control and manipulation of Dirac fermions constitute a fundamental step toward the realization of novel concepts of electronic devices and quantum computation. By means of Angle-Resolved Photo-Emission Spectroscopy (ARPES) experiments and ab initio simulations, here, we show that Dirac states can be effectively tuned by doping a transition metal sulfide, [Formula: see text], through Co/Ni substitution. The symmetry and chemical characteristics of this material, combined with the modification of the charge-transfer gap of [Formula: see text] across its phase diagram, lead to the formation of Dirac lines, whose position in k-space can be displaced along the [Formula: see text] symmetry direction and their form reshaped. Not only does the doping x tailor the location and shape of the Dirac bands, but it also controls the metal-insulator transition in the same compound, making [Formula: see text] a model system to functionalize Dirac materials by varying the strength of electron correlations.