Range Coulomb Interaction Research Articles

Spin and charge fluctuation induced pairing in ABCB tetralayer graphene

Motivated by the recent experimental realization of ABCB stacked tetralayer graphene [Wirth , ], we study correlated phenomena in moiré-less graphene tetralayers for realistic interaction profiles using an orbital resolved random phase approximation approach. We demonstrate that magnetic fluctuations originating from local interactions are crucial close to the van Hove singularities on the electron- and hole-doped side promoting layer selective ferrimagnetic states. Spin fluctuations around these magnetic states enhance unconventional spin-triplet, valley-singlet superconductivity with f-wave symmetry due to intervalley scattering. Charge fluctuations arising from long range Coulomb interactions promote doubly degenerate p-wave superconductivity close to the van Hove singularities. At the conduction band edge of ABCB graphene, we find that both spin and charge fluctuations drive f-wave superconductivity. Our analysis suggests a strong competition between superconducting states emerging from long- and short-ranged Coulomb interactions and thus stresses the importance of microscopically derived interaction profiles to make reliable predictions for the origin of superconductivity in graphene-based heterostructures. Published by the American Physical Society 2024

Joint probability calculation of the lateral velocity distribution in strong field ionization process

We describe an approach to the description of the time-development of the process of strong field ionization of atoms based on the calculation of the joint probability of occurrence of two events, event B being finding atom in the ionized state after the end of the laser pulse, event A being finding a particular value of a given physical observable at a moment of time inside the laser pulse duration. As an example of such an physical observable we consider lateral velocity component of the electron’s velocity. Our approach allows us to study time-evolution of the lateral velocity distribution for the ionized electron during the interval of the laser pulse duration. We present results of such a study for the cases of target atomic systems with short range Yukawa and Coulomb interactions.

Binding of human serum albumin with uranyl ion at various pH: an all atom molecular dynamics study

Uranium is routinely handled in various stages of nuclear fuel cycle and its association with human serum albumin (HSA) has been reported in literature, however, their binding characteristics still remains obscure. The present study aims to understand interaction of uranium with HSA by employing all atom molecular dynamics simulation of the HSA-metal ion complex. His67, His247 and Asp249 residues constitute the major binding site of HSA, which capture the uranyl ion (UO2 2+). A total of six sets of initial coordinates are used for Zn2+-HSA and UO2 2+-HSA system at pH = 4, 7.4 and 9, respectively. Enhance sampling method, namely, well-tempered meta-dynamics (WT-MtD) is employed to study the binding and un-binding processes of UO2 2+ and Zn2+ ions. Potential of mean force (PMF) profiles are generated for all the six sets of complexes from the converged WT-MtD run. Various basins and barriers are observed along the (un)binding pathways. Hydrogen bond dynamics and short-range Coulomb interactions are evaluated from the equilibrium run at each basins and barriers for both the ions at all pH values. The binding of UO2 2+ ion with HSA is the result of the dynamical balance between UO2 2+-HSA and UO2 2+-water short range Coulomb interactions. Zn2+ ion interact more strongly than UO2 2+ at all pH through short range Coulomb interactions. PMF values further concludes that UO2 2+ cannot associate to the Zn2+ bound HSA protein but can be captured by free HSA at all pH values i.e. endosomal, alkaline and physiological pH. Communicated by Ramaswamy H. Sarma

Correlated second-order Dirac semimetals with Coulomb interactions

We investigate the effects of long range Coulomb interactions on the low-temperature properties of a second-order Dirac semimetal in terms of the renormalization group. In contrast to the first-order Dirac semimetal, the full rotation symmetry is broken even in the continuum limit, and thus the low-energy physics is controlled by two dimensionless parameters: the dimensionless coupling constant and the ratio of the anisotropy parameters. We show that the former flows to zero and the latter flows to a fixed value at low energies. Thus, one may calculate physical quantities in terms of the renormalized perturbation theory. As an application, we determine the temperature dependence of the specific heat by solving the renormalization-group equations. Following from the breaking of the full rotation symmetry, there exists a crossover temperature scale $T_c$ (and a length scale $L_c$). Physical quantities approach the values for the first-order Dirac semimetal only when the temperature is much smaller than $T_c$. Similarly, the screened Coulomb potential will become anisotropic when the distance is smaller than $L_c$, while the unscreened form is recovered at its tail.

Calorons, monopoles and stable, charged solitons

We discuss the similarity of the constituent monopoles of calorons and stable topological solitons with long range Coulombic interaction, classical solutions of the model of topological particles. In the interpretation as electric charges they can be compared to electrons and positrons with spin up and down, with quantised charge and finite mass.

Coulomb interactions and effective quantum inertia of charge carriers in a macroscopic conductor

We study the low frequency admittance of a quantum Hall bar of size much larger than the electronic coherence length. We find that this macroscopic conductor behaves as an ideal quantum conductor with vanishing longitudinal resistance and purely inductive behavior up to f<1MHz. Using several measurement configurations, we study the dependence of this inductance on the length of the edge channel and on the integer quantum Hall filling fraction. The experimental data are well described by a scattering model for edge magnetoplasmons taking into account effective long range Coulomb interactions within the sample. This demonstrates that the inductance's dependence on the filling fraction arises from the effective quantum inertia of charge carriers induced by Coulomb interactions within an ungated macroscopic quantum Hall bar.

Narrow bands, electrostatic interactions and band topology in graphene stacks

The occurrence of superconducting and insulating phases is well-established in twisted graphene bilayers, and they have also been reported in other arrangements of graphene layers. We investigate three such arrangements: untwisted AB bilayer graphene on an hBN substrate, two graphene bilayers twisted with respect to each other, and a single ABC stacked graphene trilayer on an hBN substrate. Narrow bands with different topology occur in all cases, producing a high density of states which enhances the role of interactions. We investigate the effect of the long range Coulomb interaction, treated within the self consistent Hartree–Fock approximation. We find that the on-site part of the Fock potential strongly modifies the band structure at charge neutrality. The Hartree part does not significantly modify the shape and width of the bands in the three cases considered here, in contrast to the effect that such a potential has in twisted bilayer graphene.

Theory of Inhomogeneous Rod-like Coulomb Fluids

A field theoretic representation of the classical partition function is derived for a system composed of a mixture of anisotropic and isotropic mobile charges that interact via long range Coulomb and short range nematic interactions. The field theory is then solved on a saddle-point approximation level, leading to a coupled system of Poisson–Boltzmann and Maier–Saupe equations. Explicit solutions are finally obtained for a rod-like counterion-only system in proximity to a charged planar wall. The nematic order parameter profile, the counterion density profile and the electrostatic potential profile are interpreted within the framework of a nematic–isotropic wetting phase with a Donnan potential difference.

Analysis of structural phase stability and thermo-elastic properties of alloy of rare earth sulfides (LaxPr1-xS) under high pressure at room temperature

The high pressure structural behavior and associated properties of mixed rare earth sulfides (LaxPr1-xS) have been investigated by applying a Realistic Interaction Potential (RIP) model, including temperature effects. This model explains the inter-atomic interactions as it incorporates long range coulomb interaction; three body interaction (TBI), vdW (van der Waals) interaction, short range overlap repulsive interaction up to second neighbors and zero point energy effects including the temperature effects. We have predicted the high pressure structural phase transition from NaCl (B1 -type) to CsCl-type (B2-type) phase and associated volume drops for these compounds. The pressure induced phase transition is found to be a first order. Estimation of the elastic, thermal properties and Every’s parameters of these compounds has been performed during study. The results obtained are found to be in reasonable agreement with experimental and other theoretical data.

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.

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.

Enhanced entanglement induced by Coulomb interaction in coupled optomechanical systems

We consider a coupled optomechanical system, in which two charged mechanical resonators are coupled through long range Coulomb interaction. It is shown that remote entanglement between the two charged mechanical resonators can be achieved by long range Coulomb interaction. Such a coupled optomechanical system exhibits the classical to quantum transition behavior. The outcome of our numerical simulation shows that in the absence of optomechanical coupling, quantum entanglement between the two mechanical resonators can be achieved for large Coulomb coupling strengths and small effective temperature. In addition, the entanglement between the two mechanical resonators can be enhanced through input laser power. We also investigate the entanglement transfer through Coulomb interaction and optomechanical couplings.

Ferromagnetism in quantum dot plaquettes

Following the recent claimed obsevation of Nagaoka ferromagnetism in finite size quantum dot plaquettes, a general theoretical analysis is warranted in order to ascertain in rather generic terms which arrangements of a small number of quantum dots can produce saturated ferromagnetic ground states and under which constraints on interaction and inter-dot tunneling in the plaquette. This is particularly necessary since Nagaoka ferromagnetism is fragile and arises only under rather special conditions. We test the robustness of ground state ferromagnetism in the presence of a long-range Coulomb interaction and long-range as well as short-range interdot hopping by modeling a wide range of different plaquette geometries accessible by arranging a few (~4) quantum dots in a controlled manner. We find that ferromagnetism is robust to the presence of long range Coulomb interactions, and we develop conditions constraining the tunneling strength such that the ground state is ferromagnetic. Additionally, we predict the presence of a partially spin-polarized ferromagnetic state for 4 electrons in a Y-shaped 4-quantum dot plaquette. Finally, we consider 4 electrons in a ring of 5 dots. This does not satisfy the Nagaoka condition, however, we show that the ground state is spin one for strong, but not infinite, onsite interaction. Thus, even though Nagaoka's theorem does not apply, the ground state for the finite system with one hole in a ring of 5 dots is partially ferromagnetic. We provide detailed fully analytical results for the existence or not of ferromagnetic ground states in several quantum dot geometries which can be studied in currently available coupled quantum dot systems.

Finite Speed of Quantum Scrambling with Long Range Interactions.

In a locally interacting many-body system, two isolated qubits, separated by a large distance r, become correlated and entangled with each other at a time t≥r/v. This finite speed v of quantum information scrambling limits quantum information processing, thermalization, and even equilibrium correlations. Yet most experimental systems contain long range power-law interactions-qubits separated by r have potential energy V(r)∝r^{-α}. Examples include the long range Coulomb interactions in plasma (α=1) and dipolar interactions between spins (α=3). In one spatial dimension, we prove that the speed of quantum scrambling remains finite for sufficiently large α. This result parametrically improves previous bounds, compares favorably with recent numerical simulations, and can be realized in quantum simulators with dipolar interactions. Our new mathematical methods lead to improved algorithms for classically simulating quantum systems, and improve bounds on environmental decoherence in experimental quantum information processors.

Collective spin density excitation of fractional quantum Hall states in dilute ultra-cold Bose atoms

We have studied collective spin density excitation of fractional quantum Hall effect (FQHE) in rotating Bose–Einstein condensation for the three filling fractions of first series of Jain’s composite fermion sequences. We have considered short-ranged contact interactions between the Bose atoms as well as long range Coulomb interactions to compare the nature of the spectra with FQHE of electrons. Using Monte-Carlo method for finite but large number of particles, the lowest order collective modes of spin-reversed sectors is calculated here, by computing the energy differences of the respective excitons from the fully polarized ground states.

Interaction-induced charge transfer in a mesoscopic electron spectrometer

A novel mesoscopic electron spectrometer allows for the probing of relaxation processes in quantum Hall edge channels. The device is composed of an emitter quantum dot that injects energy-resolved electrons into the channel closest to the sample edge, to be subsequently probed downstream by a detector quantum dot of the same type. In addition to inelastic processes in the sample that stem from interactions inside the region between the quantum dot energy filters (inner region), anomalous signals are measured when the detector energy exceeds the emitter energy. Considering finite range Coulomb interactions in the sample, we find that energy exchange between electrons in the current inducing source channel and the inner region, similar to Auger recombination processes, is responsible for such anomalous currents. In addition, our perturbative treatment of interactions shows that electrons emitted from the source, which dissipate energy to the inner region before entering the detector, contribute to the current most strongly when emitter-detector energies are comparable. Charge transfer in which the emitted electron is exchanged for a charge carrier from the Fermi sea, on the other hand, preferentially occurs close to the Fermi level.

Identification of normal modes responsible for ferroelectric properties in organic ferroelectric CBDC

Structure and dynamics of hydrogen bonded organic ferroelectric CBDC (1-cyclobutene-1,2-dicarboxylic acid, C6H8O4) have been investigated using inelastic neutron scattering (INS) spectroscopy and first principles lattice dynamics. Vibrational modes of O–H–O bending, related with two different types of hydrogen bonds, inter and intra-molecular, are manifested as two sets of doublets in the range of 900–1400 cm−1 in the INS spectrum. First principles density functional theory (DFT) is used to assign these doublets to out-of-the-plane and in-plane vibrations of these two types of O–H—O bending modes. Correlating structure and dynamics we find that although the local structures of the hydrogen bonded protons are similar, their medium range order may influence their vibrational frequencies. Vibrational modes of non-hydrogen bonded protons also are assigned separately in the spectrum. Comparing the calculated and the experimental INS spectra it is predicted that hydrogen bonded O–H bonds are more anharmonic than non-hydrogen bonded C–H bonds. From the calculated Born effective charge tensor it is predicted that inter-molecular hydrogen bonds contribute more to the ferroelectric polarisation of CBDC than intra-molecular ones. A large LO-TO splitting of the O–H stretching mode at 2471 cm−1 is identified with the mode that has significant contribution to the ferroelectric polarisation. As this mode is sensitive to long range Coulomb interactions and is responsible for ferroelectric properties of the material, vibrational spectroscopy combined with DFT calculations is proposed as a characterisation tool to investigate ferroelectric properties in the CBDC molecular crystal.

Two-qubit entangling gates within arbitrarily long chains of trapped ions

Ion trap systems are a leading platform for large scale quantum computers. Trapped ion qubit crystals are fully-connected and reconfigurable, owing to their long range Coulomb interaction that can be modulated with external optical forces. However, the spectral crowding of collective motional modes could pose a challenge to the control of such interactions for large numbers of qubits. Here, we show that high-fidelity quantum gate operations are still possible with very large trapped ion crystals, simplifying the scaling of ion trap quantum computers. To this end, we present analytical work that determines how parallel entangling gates produce a crosstalk error that falls off as the inverse cube of the distance between the pairs. We also show experimental work demonstrating entangling gates on a fully-connected chain of seventeen $^{171}{\rm{Yb}}^{+}$ ions with fidelities as high as $97(1)\%$.

Molecularly Imprinted Polyacrylamide with Fluorescent Nanodiamond for Creatinine Detection.

Creatinine measurement in blood and urine is an important diagnostic test for assessing kidney health. In this study, a molecularly imprinted polymer was obtained by incorporating fluorescent nanodiamond into a creatinine-imprinted polyacrylamide hydrogel. The quenching of peak nanodiamond fluorescence was significantly higher in the creatinine-imprinted polymer compared to the non-imprinted polymer, indicative of higher creatinine affinity in the imprinted polymer. Fourier transform infrared spectroscopy and microscopic imaging was used to investigate the nature of chemical bonding and distribution of nanodiamonds inside the hydrogel network. Nanodiamonds bind strongly to the hydrogel network, but as aggregates with average particle diameter of 3.4 ± 1.8 µm and 3.1 ± 1.9 µm for the non-imprinted and molecularly imprinted polymer, respectively. Nanodiamond fluorescence from nitrogen-vacancy color centers (NV− and NV0) was also used to detect creatinine based on nanodiamond-creatinine surface charge interaction. Results show a 15% decrease of NV−/NV0 emission ratio for the creatinine-imprinted polymer compared to the non-imprinted polymer, and are explained in terms of changes in the near-surface band structure of diamond with addition of creatinine. With further improvement of sensor design to better disperse nanodiamond within the hydrogel, fluorescent sensing from nitrogen-vacancy centers is expected to yield higher sensitivity with a longer range (Coulombic) interaction to imprinted sites than that for a sensor based on acceptor/donor resonance energy transfer.

Spin–Lattice Relaxation Rate in Organic Dirac Electron System α-(BEDT-TTF)2I3 under Strong Magnetic Field

Spin–lattice relaxation rate divided by temperature, 1/T1T, under strong magnetic field is calculated in the tilted Weyl Hamiltonian with the long range Coulomb interaction, which describes the low...