Effect Of Coulomb Interaction Research Articles

Turbulent hydrodynamics in strongly correlated Kagome metals

A current challenge in condensed matter physics is the realization of strongly correlated, viscous electron fluids. These fluids can be described by holography, that is, by mapping them onto a weakly curved gravitational theory via gauge/gravity duality. The canonical system considered for realizations has been graphene. In this work, we show that Kagome systems with electron fillings adjusted to the Dirac nodes provide a much more compelling platform for realizations of viscous electron fluids, including non-linear effects such as turbulence. In particular, we find that in Scandium Herbertsmithite, the fine-structure constant, which measures the effective Coulomb interaction, is enhanced by a factor of about 3.2 as compared to graphene. We employ holography to estimate the ratio of the shear viscosity over the entropy density in Sc-Herbertsmithite, and find it about three times smaller than in graphene. These findings put the turbulent flow regime described by holography within the reach of experiments.

Effects of ionicity and chain structure on the physicochemical properties of protic ionic liquids

AbstractThe physicochemical properties of protic ionic liquids (PILs) determine their industrial applications. In this study, six PILs based on 1‐vinylimidazole were synthesized, and their ionicities were determined by 1H NMR method. The thermodynamic properties, viscosities, densities, and conductivities of these PILs were correlated with the ionicities and the chain lengths of the anions. The ionicity was found to depend on the acidity of the alkyl carboxylic acid. Since HAc has the strongest acidity among these acid precursors, Vim·HAc has the highest ionicity and thus the strongest Coulombic interactions among the six PILs. The other five PILs have similar ionicities but different chain lengths in their anions. So, we can separately identify the effects of Coulombic interactions and van der Waals forces on the physicochemical properties of PILs. From these trends, the viscosity and conductivity of PILs may be tuned by varying the acidity and alkyl chain length of the precursors.

Extending the Gutzwiller approximation to intersite interactions

We develop an extension of the Gutzwiller approximation (GA) formalism that includes the effects of Coulomb interactions of arbitrary range (including density density, exchange, pair hopping, and Coulomb-assisted hopping terms). This formalism reduces to the ordinary GA formalism for the multiband Hubbard models in the presence of only local interactions. This is accomplished by combining the $1/z$ expansion---where $z$ is the coordination number, and only the leading-order terms contribute in the limit of infinite dimensions---with a ${P}_{R}^{\ifmmode\dagger\else\textdagger\fi{}}{P}_{R}\ensuremath{-}I$ expansion, where ${P}_{R}$ is the Gutzwiller projector on the site $R$. The method is conveniently formulated in terms of a Gutzwiller Lagrange function. We apply our theory to the extended single-band Hubbard model. Similarly to the usual Brinkman-Rice mechanism, we find a Mott transition. A valence skipping transition is observed, where the occupation of the empty and doubly occupied states for the Gutzwiller wave function is enhanced with respect to the uncorrelated Slater determinant wave function.

Constrained random phase approximation of the effective Coulomb interaction in lattice models of twisted bilayer graphene

Recent experiments on twisted bilayer graphene show the urgent need for establishing a low-energy lattice model for the system. We use the constrained random phase approximation to study the interaction parameters of such models, taking into account screening from the moir\'e bands left outside the model space. Based on an atomic-scale tight-binding model, we numerically compute the polarization function and study its behavior for different twist angles. We discuss an approximation scheme which allows us to compute the screened interaction, in spite of the very large number of atoms in the unit cell. We find that the polarization has three different momentum regimes. For small momenta, the polarization is quadratic, leading to a linear dielectric function expected for a two-dimensional dielectric material. For large momenta, the polarization becomes independent of the twist angle and approaches that of uncoupled graphene layers. In the intermediate-momentum regime, the dependence on the twist angle is strong. Close to the largest magic angle the dielectric function peaks at a momentum of $1/(4\phantom{\rule{4.pt}{0ex}}\text{nm})$, attaining values of 18--25, depending on the exact model, meaning very strong screening at intermediate distances. We also calculate the effective screened Coulomb interaction in real space and give estimates for the on-site and extended interaction terms for the recently developed hexagonal-lattice model. For freestanding twisted bilayer graphene, the effective interaction decays slower than $1/r$ at intermediate distances $r$, while it remains essentially unscreened at large enough $r$.

Pairing transition in a double layer with interlayer Coulomb repulsion

We study the effect of interlayer Coulomb interaction in an electronic double layer. Assuming that each of the layers consists of a bipartite lattice, a sufficiently strong interlayer interaction leads to an interlayer pairing of electrons with a staggered order parameter. We show that the correlated pairing state is dual to the excitonic pairing state with uniform order parameter in an electron-hole double layer. The interlayer pairing of electrons leads to strong current-current correlations between the layers. We also analyze the interlayer conductivity and the fluctuations of the order parameter, which consists of a gapped and a gapless mode.

Effect of Coulomb interactions on optoelectronic properties of Eu doped lanthanide stannates pyrochlore: DFT ​+ ​U investigations

In optoelectronics, the perovskite structures in layered form, also called pyrochlore have been demonstrated to be very largely favorable to the insertion of lanthanides ions, which led them to create new phosphor emitting in a broad spectral range going from visible to near infrared. The pyrochlore oxides such as La2Sn2O7 have attained much interest due to their electronic and optical properties. In the present work, we used first-principle calculations to compute the electronic band structure and related optical properties for pure La2Sn2O7 and La2Sn2O7 doped with europium. Spin orbit coupling (SOC) and electron-electron interaction, both within the generalized gradient approximation plus Hubbard parameter U (SOC ​+ ​GGA ​+ ​U) approximations have been used within the framework of density functional theory (DFT). It was found that La2Sn2O7 compound exhibits a direct band gap semiconductor with 2.7 ​eV. Doping of europium further decreases the band gap of pyrochlore of material up to 1.8 ​eV. Optical properties revealed that both compounds are potential materials for optoelectronic device fabrication.

Two-electron selective coupling in an edge-state based conditional phase shifter

We investigate the effect of long-range Coulomb interaction on the two-electron scattering in the integer quantum Hall regime at bulk filling factor 2. A parallel version of the Split-Step Fourier method evolves the exact two-particle wave function in a 2D potential background reproducing the effect of depleting gates in a realistic heterostructure, with the charge carrier represented by a localized wavepacket of edge states. We compare the spatial shift induced by Coulomb repulsion in the final two-electron wave function for two indistinguishable electrons initialized in different configurations according to their Landau index, and analyze their bunching probability and the effect of screening. We finally prove the feasibility of the present operating regime as a two-qubit conditional phase shifter to generate entanglement from product states.

Band structure and insulating states driven by Coulomb interaction in twisted bilayer graphene

We analyze the phase diagram of twisted graphene bilayers near a magic angle. We consider the effect of the long range Coulomb interaction, treated within the self consistent Hartree-Fock approximation, and we study arbitrary band fillings. We find a rich phase diagram, with different broken symmetry phases, although tehy do not show necessarily a gap at the Fermi energy. There are non trivial effects of the electrostatic potential on the shape and the gaps of the bands in the broken symmetry phases. The results suggest that the non superconducting broken symmetry phases observed experimentally are induced by the long range exchange interaction.

Effect of Coulomb interactions on the Seebeck coefficient of the organic Dirac electron system α−(BEDT-TTF)2I3

Motivated by the results of recent thermoelectric effect studies, we show the effects of Coulomb interactions on the Seebeck coefficient based on an extended Hubbard model that describes the electronic states of a slightly doped organic Dirac electron system, $\alpha$-(BEDT-TTF)$_2$I$_3$. Our results indicate that the Hartree terms of the Coulomb interactions enhance the electron-hole asymmetry of the energy band structure and change the energy dependence of the relaxation time from impurity scattering, which reflects the shape of the density of states. Thus, the Seebeck coefficient exhibits a non-monotonic $T$ dependence which qualitatively agrees with the experimental results. Furthermore, we also show that the signs of the Seebeck coefficient and the Hall coefficient calculated by linear response theory do not necessarily correspond to the sign of the chemical potential using a modified Weyl model with electron-hole asymmetry. These results point out that changing the electron-hole asymmetry by strong Coulomb interaction has the potential to controllable the sign and value of the Seebeck coefficient in the Dirac electron systems.

Scaling and diffusion of Dirac composite fermions

The authors use effective low-energy theories involving Dirac composite fermions to investigate the effects of a dissipative Coulomb interaction on certain superconductor-insulator and integer quantum Hall transitions in the presence of quenched randomness in two spatial dimensions. The paper shows how composite fermions provide a unifying framework for various diffusive quantum critical points.

High thermoelectric performance in excitonic bilayer graphene

We consider the excitonic effects on the thermal properties in the AB-stacked bilayer graphene. The calculations are based on the bilayer generalization of the usual Hubbard model at the half-filling. The full interaction bandwidth is used without any low-energy assumption. We obtain the unusually high values for the electronic figure of merit even at the room-temperatures which is very promising for the thermoelectric applications of the AB-bilayer structure. We discuss the effects of the interlayer Coulomb interaction and temperature on different thermal parameters in the bilayer graphene and we emphasize the role of the charge neutrality point in the thermal properties and within the excitonic insulator transition scenario. The calculated values of the rate of thermoelectric conversion efficiency suggest the possibility of high-performance device applications of AB-bilayer graphene.

Instability threshold in a large balanced magneto-optical trap

Large clouds of cold atoms prepared in a magneto-optical trap can develop spatiotemporal instabilities when the frequency of the trapping lasers is brought close to the atomic resonance. This system bears close similarities with trapped plasmas, whereby effective Coulomb interactions are induced by the exchange of scattered photons and lead to collective nonlinear dynamics of the trapped atoms. We report in this paper a detailed experimental study of the instability threshold, and comparisons with three-dimensional simulations of the interacting, laser-driven cloud.

Probing of incomplete fusion dynamics in $${}^{{14}}\text {N} + {}^{{124}}\text {Sn}$$ system and its correlation with various entrance channel effects

Measurements of excitation functions were done for the evaporation residues populated in $${}^{{14}}\text {N}+{}^{{124}}\text {Sn}$$ system at low energy. The present analysis shows the appearance of incomplete fusion by the breakup of non- $$\upalpha $$ cluster structured projectile $$^{{14}}\text {N}$$ into $$\upalpha + {}^{{10}}\text {B}$$ . A correlation between the combined effects of total asymmetry and $$\text {Z}_{\mathrm {P}}\text {Z}_{\mathrm {T}}$$ has been studied through three new parameters total asymmetry ( $$S_{{ TAS}}$$ ), Coulomb asymmetry parameters; $$Z_{P} Z_{T} /S_{{ TAS}} $$ and $$Z_{P} Z_{T} .S_{{ TAS}} $$ . These new parameters were found more sensitive and effective to encounter the combined effects of coulomb interactions and entire asymmetry effect of the system on incomplete fusion dynamics. The complete fusion and total fusion cross-sections of two systems $${}^{{14}}\text {N}+{}^{{124}}\text {Sn}$$ and $${}^{{16}}\text {O}+{}^{124}\text {Sn}$$ have been reduced using two different standard reduction procedures, which shows that the incomplete fusion probability for reactions induced by projectile $${}^{{16}}\text {O}$$ is generally larger than $${}^{{14}}\text {N}$$ induced reactions. The experimental fusion functions are found to be suppressed as compared to universal fusion function for systems $${}^{{14}}\text {N}+{}^{{124}}\text {Sn}$$ and $${}^{{16}}\text {O}+{}^{{124}}\text {Sn}$$ . The different values of suppression factor for projectiles $${}^{{14}}\text {N}$$ and $${}^{{16}}\text {O}$$ indicate that the probability of $$\upalpha $$ -breakup is different for these projectiles. Further, the total fusion functions for systems $${}^{{14}}\text {N}+{}^{{124}}\text {Sn}$$ and $${}^{{16}}\text {O}+{}^{{124}}\text {Sn}$$ agree well with the universal fusion function. However, the present results clearly show that the shell closure of nuclei also affect the low energy incomplete fusion dynamics along with the structure of projectile.

Exciton optical absorption in asymmetric ZnO/ZnMgO double quantum wells with mixed phases**Project supported by the National Natural Science Foundation of China (Grant No. 61764012).

The optical absorption of exciton interstate transition in Zn1 − xlMgxlO/ZnO/Zn1 − xcMgxcO/ZnO/Zn1 − xrMgxrO asymmetric double quantum wells (ADQWs) with mixed phases of zinc-blende and wurtzite in Zn1 − xMgxO for 0.37 < x < 0.62 is discussed. The mixed phases are taken into account by our weight model of fitting. The states of excitons are obtained by a finite difference method and a variational procedure in consideration of built-in electric fields (BEFs) and the Hartree potential. The optical absorption coefficients (OACs) of exciton interstate transition are obtained by the density matrix method. The results show that Hartree potential bends the conduction and valence bands, whereas a BEF tilts the bands and the combined effect enforces electrons and holes to approach the opposite interfaces to decrease the Coulomb interaction effects between electrons and holes. Furthermore, the OACs indicate a transformation between direct and indirect excitons in zinc-blende ADQWs due to the quantum confinement effects. There are two kinds of peaks corresponding to wurtzite and zinc-blende structures respectively, and the OACs merge together under some special conditions. The computed result of exciton interband emission energy agrees well with a previous experiment. Our conclusions are helpful for further relative theoretical studies, experiments, and design of devices consisting of these quantum well structures.

Electron correlation effects and magneto-optical properties of yttrium iron garnet

The electronic structure, magnetic, optical and magneto-optical properties of yttrium iron garnet (YIG) were investigated by using first-principles calculations with Hubbard energy correction for the treatment of the strong electron correlation. The effective on-site Coulomb interaction parameters Ueff for YIG were determined from the constrained density functional theory within a linear response theory. Our results find a hybridization between the O-2p and Fe-3d orbitals. We also observe the crucial role of the electron correlation of the Fe-3d orbitals according to the magneto-optical properties of YIG.

Role of spin-orbit interactions on the entropy and heat capacity of a quantum dot helium placed in an external magnetic field

The effects of Rashba, Dresselhaus and Coulomb interactions on the entropy and heat capacity of a two-electron quantum dot placed in an external magnetic field are studied at finite temperature. The effect of electron-electron interaction is studied by using the Johnson-Payne harmonic model which is exactly soluble, while the Rashba and Dresselhus spin-orbit coupling effects are dealt with using unitary transformations. It is observed that as a function of the magnetic field, the heat capacity has a double peak structure with the minima between the peaks occurring at the singlet-triplet transition point and the e-e interaction shifts the peaks to lower magnetic fields. It is also observed that the coulomb correlation reduces the heat capacity in the low temperature regime while in the high temperature regime it enhances it. Interestingly, however, in the high field regime, the heat capacity does not seem to be influenced by the electron-electron interaction. The entropy is found to show a single peak as a function of magnetic field at the singlet-triplet transition point. The Rashba spin-orbit interaction reduces the heat capacity and the Dresselhaus interaction enhances it whereas the opposite effect is exhibited by the entropy. The temperature behaviour of both the entropy and heat capacity clearly demonstrates the effect of zero field spin-splitting. • A quantum dot with two electrons is considered in a magnetic field at finite temperature. • Role of Rashba and Dresselhauss interactions (RI & DI) are studied on heat capacity ( C v ) and entropy (S). • Coulomb interaction between electrons is treated by the exactly soluble Johnson-Payne model. • RI reduces C v and DI enhances it while S shows just an opposite behaviour. • Temperature behaviour of C v and S exhibits zero-field splitting.

XFe4Ge2(X=Y,Lu) and Mn3Pt : Filling-enforced magnetic topological metals

Magnetism, coupled with nontrivial band topology, can bring about many interesting and exotic phenomena, so that magnetic topological materials have attracted persistent research interest. However, compared with non-magnetic topological materials (TMs), the magnetic TMs are less studied, since their magnetic structures and topological phase transitions are usually complex and the first-principles predictions are usually sensitive on the effect of Coulomb interaction. In this work, we present a comprehensive investigation of XFe4Ge2 (X = Y, Lu) and Mn3Pt, and find these materials to be filling-enforced magnetic topological metals. Our first-principles calculations show that XFe4Ge2 (X = Y, Lu) host Dirac points near the Fermi level at high symmetry point S. These Dirac points are protected by PT symmetry (P and T are inversion and time-reversal transformations, respectively) and a 2-fold screw rotation symmetry. Moreover, through breaking PT symmetry, the Dirac points would split into Weyl nodes. Mn3Pt is found to host 4-fold degenerate band crossings in the whole high symmetry path of A-Z. We also utilize the GGA+U scheme to take into account the effect of Coulomb repulsion and find that the filling-enforced topological properties are naturally insensitive on U.

Quantum Transport Through a ``Charge" Kondo Circuit: Effects of Weak Repulsive Interaction in Luttinger Liquid

We investigate theoretically quantum transport through the ``charge" Kondo circuit consisting of the quantum dot (QD) coupled weakly to an electrode at temperature \(T+\Delta T\) and connected strongly to another electrode at the reference temperature \(T\) by a single-mode quantum point contact (QPC). To account for the effects of Coulomb interaction in the QD-QPC setup operating in the integer quantum Hall regime we describe the edge current in the quantum circuit by Luttinger model characterized by the Luttinger parameter \(g\). It is shown that the temperature dependence of both electric conductance \(G\propto T^{2/g}\) and thermoelectric coefficient \(G_T\propto T^{1+2/g}\) detours from the Fermi-liquid (FL) theory predictions. The behaviour of the thermoelectric power \(S=G_T/G\propto T\) in a regime of a single-channel Kondo effect is, by contrast, consistent with the FL paradigm. We demonstrate that the interplay between the mesoscopic Coulomb blockade in QD and weak repulsive interaction in the Luttinger Liquid \(g=1-\alpha\) \((\alpha \ll 1)\) results in the enhancement of the thermopower. This enhancement is attributed to suppression of the Kondo correlations in the ``charge" circuit by the destructive quantum interference effects.

First-principles electronic structure, phonon properties, lattice thermal conductivity and prediction of figure of merit of FeVSb half-Heusler

In this work, we have studied the electronic structure of a promising thermoelectric half-Heusler FeVSb using FP-LAPW method and SCAN meta-GGA including spin–orbit coupling. Using the obtained electronic structure and transport calculations we try to address the experimental Seebeck coefficient S of FeVSb samples. The good agreement between the experimental and calculated S suggests the band gap could be ∼0.7 eV. This is supported by the obtained mBJ band gap of ∼0.7 eV. Further, we study and report the phonon dispersion, density of states and thermodynamic properties. The effect of long range Coulomb interactions on phonon frequencies are also included by nonanalytical term correction. Under quasi-harmonic approximation, the thermal expansion behaviour up to 1200 K is calculated. Using the first-principles anharmonic phonon calculations, the lattice thermal conductivity κ ph of FeVSb is obtained under single-mode relaxation time approximation considering the phonon-phonon interaction. At 300 K, the calculated κ ph is ∼18.6 W m−1 K−1 which is higher compared to experimental value. But, above 500 K the calculated κ ph is in good agreement with experiment. A prediction of figure of merit ZT and efficiency for p-type and n-type FeVSb is made by finding out optimal carrier concentration. At 1200 K, a maximum ZT of ∼0.66 and ∼0.44 is expected for p-type and n-type FeVSb, respectively. For p-type and n-type materials, maximum efficiency of ∼12.2% and ∼6.0% are estimated for hot and cold temperature of 1200 K and 300 K, respectively. A possibility of achieving n-type and p-type FeVSb by elemental doping/vacancy is also discussed. Our study is expected to help in further exploring the thermoelectric material FeVSb.

Thickness-induced metal to insulator transition in Ru nanosheets probed by photoemission spectroscopy: Effects of disorder and Coulomb interaction

We investigated the electronic structures of mono- and few-layered Ru nanosheets (N layers (L) with N = 1, ~6, and ~9) on Si substrate by ultra-violet and x-ray photoemission spectroscopies. The spectral density of states (DOS) near EF of ~6 L and 1 L is suppressed as it approaches EF in contrast to that of ~9 L, which is consistent with the Ru 3 d core-level shift indicating the reduction of the metallic conductivity. A power law g(ε) ∝ |ε − εF|α well reproduces the observed spectral DOS of ~6 L and 1 L. The evolution of the power factor α suggests that the transition from the metallic state of ~9 L to the 2-dimensional insulating state with the soft Coulomb gap of 1 L through the disordered 3-dimensional metallic state of ~6 L.