Interactions In Low-dimensional Systems Research Articles

Brueckner G -matrix approach to two-dimensional Fermi gases with finite-range attractive interactions

Two-dimensional spin-1/2 fermions with finite-range interactions are theoretically studied. Characterizing the attractive interaction in terms of the scattering length and the effective range, we discuss the finite-range effects on the ground-state properties in this system. The Brueckner $G$-matrix approach is employed to analyze the finite-range effects on an attractive Fermi-polaron energy and the equation of state throughout the BEC-BCS crossover in two dimensions, which can be realized in the population-imbalanced and -balanced cases between two components, respectively. The analytical formulas for these ground states obtained in this study would be useful for understanding many-body phenomena with finite-range interactions in low-dimensional systems.

Role of the Magnetic Anisotropy in Atomic-Spin Sensing of 1D Molecular Chains.

One-dimensional metal-organic chains often possess a complex magnetic structure susceptible to modification by alteration of their chemical composition. The possibility to tune their magnetic properties provides an interesting playground to explore quasi-particle interactions in low-dimensional systems. Despite the great effort invested so far, a detailed understanding of the interactions governing the electronic and magnetic properties of the low-dimensional systems is still incomplete. One of the reasons is the limited ability to characterize their magnetic properties at the atomic scale. Here, we provide a comprehensive study of the magnetic properties of metal-organic one-dimensional (1D) coordination polymers consisting of 2,5-diamino-1,4-benzoquinonediimine ligands coordinated with Co or Cr atoms synthesized under ultrahigh-vacuum conditions on a Au(111) surface. A combination of integral X-ray spectroscopy with local-probe inelastic electron tunneling spectroscopy corroborated by multiplet analysis, density functional theory, and inelastic electron tunneling simulations enables us to obtain essential information about their magnetic structures, including the spin magnitude and orientation at the magnetic atoms, as well as the magnetic anisotropy.

Study of Influence of The Electron-Phonon Interaction on Quantum Dot Coupled to Microcavity

In this present paper, we presented about the study of the electron-phonon interaction on quantum dot coupled to microcavity has the same energy scale as the other relevant interactions in low-dimensional systems and it is therefore important to study the polaronic effects in these systems [1-5]. First, we consider a one-dimensional (1D) electron system incorporating the electron-electron and electron-phonon interactions using the Luttinger model. We explicitly consider both the electron-optical-phonon interaction and the electron-acoustic-phonon interaction together with the electron-electron interaction. This system can be referred to as the Frhlich-Toyozawa-Luttinger (FTL) liquid [6-13]. We calculate the momentum distribution function of an FTL liquid exactly and examine how the momentum distribution function is affected by the electron-phonon interactions. Our results will be significant in the context of nanotubes and other systems where researchers have observed the Luttinger liquid behaviour experimentally [14-15].

Plasmon coupling in topological insulator multilayers

Topological insulators (TIs) house two-dimensional Dirac plasmons on their surfaces. In TI thin films, plasmons on the top and bottom surfaces couple electrostatically, giving rise to an acoustic and an optical plasmon mode. By extension, a superlattice comprising TI layers and trivially insulating layers could house multiple complex plasmon modes which could be used to create a new type of Dirac metamaterial. In this paper, we synthesize TI superlattices, fabricate them into stripe arrays, characterize their optical and plasmonic properties, and model the samples using transfer matrices. We excite plasmon modes that couple to the phonons in the superlattice, resulting in hybrid plasmon-phonon polaritons. These modes are modeled using an analytical Fano resonance model and the extracted resonant positions are reproduced by transfer matrix modeling. We also excite an epsilon near-zero mode in the top dielectric material ${({\mathrm{Bi}}_{0.5}{\mathrm{In}}_{0.5})}_{2}{\mathrm{Se}}_{3}$. Understanding the behavior of the polariton modes in this complex system will lend insight into the many-body interaction in low-dimensional systems.

Interfacial States and Fano–Feshbach Resonance in Graphene–Silicon Vertical Junction

Interfacial quantum states are drawing tremendous attention recently because of their importance in design of low-dimensional quantum heterostructures with desired charge, spin, or topological properties. Although most studies of the interfacial exchange interactions were mainly performed across the interface vertically, the lateral transport nowadays is still a major experimental method to probe these interactions indirectly. In this Letter, we fabricated a graphene and hydrogen passivated silicon interface to study the interfacial exchange processes. For the first time we found and confirmed a novel interfacial quantum state, which is specific to the 2D-3D interface. The vertically propagating electrons from silicon to graphene result in electron oscillation states at the 2D-3D interface. A harmonic oscillator model is used to explain this interfacial state. In addition, the interaction between this interfacial state (discrete energy spectrum) and the lateral band structure of graphene (continuous energy spectrum) results in Fano-Feshbach resonance. Our results show that the conventional description of the interfacial interaction in low-dimensional systems is valid only in considering the lateral band structure and its density-of-states and is incomplete for the ease of vertical transport. Our experimental observation and theoretical explanation provide more insightful understanding of various interfacial effects in low-dimensional materials, such as proximity effect, quantum tunneling, etc. More important, the Fano-Feshbach resonance may be used to realize all solid-state and scalable quantum interferometers.

Asymmetric hot-carrier thermalization and broadband photoresponse in graphene-2D semiconductor lateral heterojunctions.

The massless Dirac electron transport in graphene has led to a variety of unique light-matter interaction phenomena, which promise many novel optoelectronic applications. Most of the effects are only accessible by breaking the spatial symmetry, through introducing edges, p-n junctions, or heterogeneous interfaces. The recent development of direct synthesis of lateral heterostructures offers new opportunities to achieve the desired asymmetry. As a proof of concept, we study the photothermoelectric effect in an asymmetric lateral heterojunction between the Dirac semimetallic monolayer graphene and the parabolic semiconducting monolayer MoS2. Very different hot-carrier cooling mechanisms on the graphene and the MoS2 sides allow us to resolve the asymmetric thermalization pathways of photoinduced hot carriers spatially with electrostatic gate tunability. We also demonstrate the potential of graphene-2D semiconductor lateral heterojunctions as broadband infrared photodetectors. The proposed structure shows an extreme in-plane asymmetry and provides a new platform to study light-matter interactions in low-dimensional systems.

(Invited) Novel Nanophotonic Devices By Engineering Light-Matter Interactions in Low-Dimensional Systems

Strongly confined electrical, optical and thermal excitations drastically modify material’s properties and break local symmetries that can enable precisely tunable novel responses and new functionalities. With an emphasis on low-dimensional materials such as nanowires and monolayer MoS2, we will discuss how extreme confinement of fields interacting with materials produces new and unexpected materials response. For example, we will discuss how the strong plasmonic fields can lead to a new paradigm of nanoscale Si photonics such as optical emission in the visible region and nonlinear optical devices. Furthermore, by utilizing the fundamental symmetry breaking properties of fields, new quantum phenomena such as chirality-dependent optical and electronic properties will be discussed in non-chiral materials and utilized to enable new functionalities that are only possible in strong spin-orbit coupled materials. The role of geometry in low-dimensional systems to produce new properties in the presence of symmetry breaking fields will be discussed. Finally, effect of plasmons on light matter interactions in 2D excitonic crystals will be discussed, which can be engineered to produce novel responses such as enhanced and tunable emission, Fano resonances and strong exciton-plasmon polaritons, which can be precisely controlled by geometry and applied fields to produce novel device concepts.

Hypersound in simple one-dimensional device structures

Brillouin spectroscopy, an inelastic laser light scattering technique capable of probing long wavelength acoustic phonons in a variety of material systems, was used to study hypersound in simple one-dimensional mesoporous silicon-based device structures formed using electrochemical etching methods. Brillouin spectra of porous silicon superlattices with binary periodicity on the order of the hypersound wavelength reveal zone folding, band gaps, and localized modes, indicating that these structures behave as hypersonic phononic crystals. Superlattices with smaller modulation wavelengths act as effective elastic media. New results on the behavior of hypersound in stacked superlattices and those with deliberately introduced defects will also be presented. Collectively, these studies have led to an improved fundamental understanding of classical wave behavior and interaction in low-dimensional systems and open up exciting opportunities for phonon engineering in a silicon-based platform.

Coulomb drag between in-plane graphene double ribbons and the impact of the dielectric constant

With recent developments in the search for novel device ideas, understanding electron-electron interaction in low dimensional systems is of particular interest. Coulomb drag measurements can provide critical insights in this context. In this article, we present a novel planar graphene double ribbon structure that shows for the first time that Coulomb drag is observable in two adjacent monolayer ribbons in the same plane at room temperature. Moreover, our planar devices enable experimentally study of the impact of the dielectric constant on Coulomb drag which is difficult to explore in the typically used double layer graphene structures. Our experimental findings indicate in particular that the drag resistance is proportional to the dielectric constant (e) and does not, as recently reported, show an increasing trend of interaction strength for small e-values. In fact, we find that the drag resistance follows approximately an e 1.2-dependence. The exponent of “1.2” is consistent with the theory considering the carrier concentration in our samples, and positions our results in between the weak and strong coupling limits.

Excitonics of semiconductor quantum dots and wires for lighting and displays

In the past two decades, semiconductor quantum dots and wires have developed into new, promising classes of materials for next-generation lighting and display systems due to their superior optical properties. In particular, exciton–exciton interactions through nonradiative energy transfer in hybrid systems of these quantum-confined structures have enabled exciting possibilities in light generation. This review focuses on the excitonics of such quantum dot and wire emitters, particularly transfer of the excitons in the complex media of the quantum dots and wires. Mastering excitonic interactions in low-dimensional systems is essential for the development of better light sources, e.g., high-efficiency, high-quality white-light generation; wide-range color tuning; and high-purity color generation. In addition, introducing plasmon coupling provides the ability to amplify emission in specially designed exciton–plasmon nanostructures and also to exceed the Förster limit in excitonic interactions. In this respect, new routes to control excitonic pathways are reviewed in this paper. The review further discusses research opportunities and challenges in the quantum dot and wire excitonics with a future outlook.

SPIN-POLARONS IN AN EXCHANGE MODEL

Spin-polarons are obtained using an Ising-like exchange model consisting of double and super-exchange interactions in low-dimensional systems. At zero temperature, a new phase separation between small magnetic polarons, one conduction electron self-trapped in a magnetic domain of two or three sites, and the antiferromagnetic phase was previously reported. On the other hand the important effect of temperature was missed. Temperature diminishes Boltzmann probability allowing excited states in the system. Static magnetic susceptibility and short-range spin–spin correlations at zero magnetic field were calculated to explore the spin-polaron formation. At high temperature Curie–Weiss behavior is obtained and compared with the Curie-like behavior observed in the nickelate one-dimensional compound Y 2-n Ca n BaNiO 5.

Confined State and Electronic Transport in an Artificial Graphene-Based Tunnel Junction

Artificial graphene structures embedded in semiconductors could open novel routes for studies of electron interactions in low-dimensional systems. We propose a way to manipulate the transport properties of massless Dirac fermions in an artificial graphene-based tunnel junction. Velocity-modulation control of electron wave propagation in the different regions can be regarded as velocity barriers. Transmission probability of electron is affected profoundly by this velocity barrier. We find that there is no confinement for Dirac electron as the velocity ratio ξ is less than 1, but when the velocity ratio is larger than 1 the confined state appears in the continuum band. These localized Dirac electrons may lead to the decreasing of transmission probability.

Vortex-to-Polarization Phase Transformation Path in FerroelectricPb(ZrTi)O3Nanoparticles

Phase transformation in finite-size ferroelectrics is of fundamental relevance for understanding collective behaviors and balance of competing interactions in low-dimensional systems. We report a first-principles effective Hamiltonian study of vortex-to-polarization transformation in Pb(Zr0.5Ti0.5)O3 nanoparticles, caused by homogeneous electric fields normal to the vortex plane. The transformation is shown to (1) follow an unusual macroscopic path that is symmetry nonconforming and characterized by the occurrence of a previously unknown structure as the bridging phase, and (2) lead to the discovery of a striking collective phenomenon, revealing how ferroelectric vortex is annihilated microscopically. Interactions underlying these behaviors are discussed.

New Method to Calculate the Sign and Relative Strength of Magnetic Interactions in Low-Dimensional Systems on the Basis of Structural Data

The connection of strength of magnetic interactions and type ordering the magnetic moments with crystal chemical characteristics in low-dimensional magnets is investigated. The new method to calculate the sign and relative strength of magnetic interactions in low-dimensional systems on the basis of the structural data is proposed. This method allows to estimate magnetic interactions not only inside low-dimensional fragments but also between them, and also to predict the possibility of the occurrence of magnetic phase transitions and anomalies of the magnetic interactions. Moreover, it can be used for search of low-dimensional magnets among the compounds whose crystal structures are known. The possibilities of the method are illustrated in an example of research of magnetic interactions in familiar low-dimensional magnets SrCu2(BO3)2, CaCuGe2O6, CaV4O9, Cu2Te2O5Cl2, Cu2Te2O5Br2, BaCu2Si2O7, BaCu2Ge2O7, BaCuSi2O6, LiCu2O2, and NaCu2O2.

New method to calculate the sign and relative strength of magnetic interactions in low-dimensional systems on the basis of structural data

New method to calculate the sign and relative strength of magnetic interactions in low-dimensional systems on the basis of structural data