One-dimensional Hopping Model Research Articles

Full analysis on coupling strengths between split ring resonators for double negative microwave tight-binding models.

Previous studies have shown that split-ring resonators (SRRs) can be utilized to achieve finely tuned nearest-neighbor coupling strengths in various one-dimensional hopping models. In our study, we present a systematic investigation of resonator coupling, providing a comprehensive quantitative description of the interaction between SRRs and complementary split-ring resonators (CSRRs) for any orientation combination. Our method includes an estimation of the coupling strength through a linear combination of periodic functions based on two orientation angles, with a sinusoidal expansion of up to the 3rd order, allowing for efficient and streamlined microwave structure design. Through our approach, we offer a satisfactory explanation of the band structure of SRR chains using a microwave-hopping model, which facilitates the exploration of exotic photonic band structures based on tight-binding theory.

Fractons from polarons

Fractons are a type of emergent quasiparticle which cannot move freely in isolation, but can easily move in bound pairs. Similar phenomenology is found in boson-affected hopping models, encountered in the study of polaron systems and hole-doped Ising antiferromagnets, in which motion of a particle requires the creation or absorption of bosonic excitations. We show that boson-affected hopping models can provide a natural realization of fractons, either approximately or exactly, depending on the details of the system. We first consider a generic one-dimensional boson-affected hopping model, in which we show that single particles move only at sixth order in perturbation theory, while motion of bound states occurs at second order, allowing for a broad parameter regime exhibiting approximate fracton phenomenology. We explicitly map the model onto a fracton Hamiltonian featuring conservation of dipole moment via integrating out the mediating bosons. We then consider a special type of boson-affected hopping models with mutual hard-core repulsion between particles and bosons, accessible in hole-doped mixed-dimensional Ising antiferromagnets, in which the hole motion is one dimensional in an otherwise two-dimensional antiferromagnetic background. We show that this system, which is within the current reach of ultracold-atom experiments, exhibits perfect fracton behavior to all orders in perturbation theory, thereby enabling the experimental study of dipole-conserving field theories. We further discuss diagnostic signatures of fractonic behavior in these systems. In studying these models, we also identify simple effective one-dimensional microscopic Hamiltonians featuring perfect fractonic behavior, paving the way to future studies on fracton physics in lower dimensions.

Many-body dynamics in long-range hopping models in the presence of correlated and uncorrelated disorder

Much have been learned about universal properties of entanglement entropy (EE) and participation ration (PR) for Anderson localization. We find a new sub-extensive scaling with system size of the above measures for algebraic localization as noticed in one-dimensional long-range hopping models in the presence of uncorrelated disorder. While the scaling exponent of EE seems to vary universally with the long distance localization exponent of single particle states (SPSs), PR does not show such university as it also depends on the short range correlations of SPSs. On the other hand, in presence of correlated disorder, an admixture of two species of SPSs (ergodic delocalized and non-ergodic multifractal or localized) are observed, which leads to extensive (sub-extensive) scaling of EE (PR). Considering typical many-body eigenstates, we obtain above results that are further corroborated with the asymptotic dynamics. Additionally, a finite time secondary slow growth in EE is witnessed only for correlated case while for uncorrelated case there exists only primary growth followed by the saturation. We believe that our findings from typical many-body eigenstate would remain unaltered even in the weakly interacting limit.

Low-temperature electrical and magnetic properties of La0.6Sr0.4Co0.2Fe0.8O3-δ nanofibers prepared by electrospinning

The microstructural, magnetic, and electrical properties of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCFO) nanofibers prepared by electrospinning and calcination were systematically investigated. It was found that the as-prepared nanofibers manifested ferromagnetism at low temperatures. Moreover, the resistance and magnetoresistance (MR) data conformed to the one-dimensional variable range hopping (1D VRH) model and revealed that LSCFO nanofibers had different electronic conduction behavior at different temperatures and magnetic fields. LSCFO nanofibers had small negative MR at low temperatures and large positive MR at high temperatures, and the transition temperature ranged between 240 and 260 K. The negative MR and the positive MR of LSCFO nanofibers manifested a fit to the 1D weak localization model and the 1D VRH model, respectively. Therefore, the proposed work can provide an important reference to the design of solid oxide fuel cells (SOFCs) based on the LSCFO cathode.

Enhancement of optical and electrical properties of PVC/PMMA blend films doped with Li4Ti5O12 nanoparticles

Nanocomposite films of polyvinyl chloride/polymethyl methacrylate (PVC/PMMA)/ lithium titanium oxide (Li4Ti5O12) were prepared through a casting method. The structural features of the prepared films were investigated using XRD, TEM, FTIR, SEM, and UV/Vis. spectroscopy techniques. XRD pattern reveals the formation of the crystalline phase of lithium titanium oxide of average crystallite size 40nm embedded in the amorphous polymeric matrix. The average crystallite size observed from TEM images is in good agreement with the XRD results. The physical interaction between the PVC/PMMA blend and Li4Ti5O12 NPs was confirmed by FTIR through the formation of a hydrogen bond. SEM micrographs showed partial compatibility between the polymer blend and the Li4Ti5O12 NPs. UV/Vis. analysis displayed that the values of the optical energy gap are decreased with increasing the concentration of Li4Ti5O12 NPs, this means that charge transfer complexes are arising between the polymer blend and Li-ions. The DC conductivity results are explained in the light of an intrachain one-dimensional interpolaron hopping model. The obtained results recommend the choice of Li4Ti5O12 NPs as dopants to enhance the electrical properties of virgin PVC/PMMA blend. Also, nanocomposite films can be employed in different electrochemical and industrial fields such as Li-ion batteries.

Preparation and low-temperature electrical and magnetic properties of La0.33Pr0.34Ca0.33MnO3 nanofibers via electrospinning

We systematically studied the structure, magnetism, resistance, magnetoresistance (MR) and nonlinear current-voltage (I-V) curves of La0.33Pr0.34Ca0.33MnO3 (LPCMO) nanofibers via electrospinning and followed calcination. Magnetic study shows that this nanosystem can form long-range order and generate spin-glass states at low temperatures. The resistance and MR studies indicate the presence of metal insulator transitions and colossal MR effects in the system, respectively. One-dimensional variable range hopping (1D VRH) model is used to explain the high-temperature segment behavior of resistance and MR. The behavior of the nonlinear I-V curves indicates the exist of threshold voltage and zero bias conductance at low temperatures in the LPCMO nanowires, which represents the existence of Coulomb gap.

Structural, Optical, Morphological and Electrical Properties of CoCl2-filled Poly(vinyl chloride-co-vinyl acetate-co-2- hydroxypropyl acrylate) Terpolymer

Films of the poly(vinyl chloride-co-vinyl acetate-co-2-hydroxypropyl acrylate) copolymer (PVVH) filled with different concentrations of CoCl2 (1, 2, 5, 10 and 20 wt. %) were prepared through a casting method. X-ray diffraction analysis (XRD) revealed the amorphous nature of the PVVH copolymer and its composite samples and the degree of crystallinity decreased with increasing CoCl2 content. Fourier transform infrared (FTIR) spectroscopy was performed to depict the structural variations due to the filling process. The absorption spectra of the ultraviolet/visible (UV/Vis) technique confirmed that the CoCl2 filler affects the optical properties (such as optical energy gap Eg, refractive index n and Urbach energy Eu) of PVVH composites. The scanning electron microscope (SEM) micrographs showed that the morphological properties of composite samples were influenced by and depended on the filling level (FL) of CoCl2. The results of DC measurement are discussed on the basis of an intrachain one-dimensional interpolaron hopping model and the obtained hopping distance was largely dependent on FL.

Effect of charge carrier transport on sulfur dioxide monitoring performance of highly porous polyaniline nanofibres

Polyaniline nanofibres (NFs) with controlled diameters were synthesized using a template-free method, with ammonium peroxidisulfate (APS) or ferric chloride (FeCl3) as oxidants. Porosity studies reveal that NFs prepared with FeCl3 possess higher effective surface area and larger pore volume compared to NFs prepared with APS. The FeCl3-assisted NFs show around twofold enhanced sensing response (ca 4.5%) towards 5 ppm of SO2 at room temperature compared to APS-assisted NFs (ca 2%). The enhancement can be attributed to the lower diameter, higher effective surface area and larger porosity of FeCl3-assisted NFs. To further explain this enhanced sensing response, the conduction mechanism was studied. NFs possessing a smaller diameter (ca 10 nm) are found to follow the one-dimensional variable range hopping (VRH) model, whereas NFs with larger diameter (ca 100 nm) follow the conventional three-dimensional VRH model. This can be due to the restriction of charge carrier transport into only one direction due to quantum size effects. Furthermore, the calculated Mott parameters suggest that the NFs prepared using FeCl3 provide a better pathway for charge transport of charge carriers as compared to NFs prepared using APS in terms of shorter hopping distance, lower activation energy and lower hopping energy, and weaker localization of charge carriers.

Structural and electrical characterizations of nanocrystalline Zn1−xCdxS (0≤x≤0.9) prepared by low cost dip coating

Thin films of nanocrystalline Zn1−xCdxS (0≤x≤0.9) were deposited by a dip coating method on glass substrates from aqueous solution containing cadmium acetate, zinc acetate and thiourea at 200°C. The morphological, structural and electrical properties of the deposited Zn1−xCdxS thin films were studied by atomic force microscopy (AFM), X-ray diffractometer (XRD), selected area electron diffraction (SAED) and photoluminescence (PL). To understand the predominant conduction mechanism of the nanocrystalline Zn1−xCdxS (0≤x≤0.9) thin films, DC electrical conductivity was measured in the temperature range of 300–420K. These measurements revealed that the DC behavior of the films can be described by a one-dimensional variable range hopping (VRH) model in the entire temperature range instead of a three-dimensional variable range hopping (VRH) model. The current density–voltage (J–V) characteristics of Zn1−xCdxS (0≤x≤0.9) thin films shows that the current conduction is ohmic type at the low-voltage region while the charge transport phenomenon appears to be space charge limited current (SCLC) at the higher-voltage regions. The latter conduction is attributed to the presence of a discrete trapping level. Various electrical parameters were determined and studied as a function of Cd-content such as electron mobility (μ0), density of states in conduction band (Nc), Fermi energy (EF), trap energy (Et) and trap electron density (Nt).

PAni-SnO<sub>2 </sub>Nanocomposite: Irradiation Induced Charge Transport Processes

The films of polyaniline–tin oxide (PAni–SnO2) nanocomposites were synthesized by chemical oxidative polymerization technique. These films were irradiated with 90 MeV O7+ ions at the fluences of 5×1010, 1×1011, 5×1011, and 1×1012 ions/cm2. X-ray diffraction studies show that microstrain and domain crystallite size of SnO2 nanoparticles in PAni matrix increase with the increase of ion fluence, resulting in highly ordered PAni–SnO2 nanocomposites. DC electrical conductivity is found to increase with the increase of fluence and conduction mechanism follows a quasi one-dimensional variable-range hopping model. AC electrical conductivity also increases with the increase of ion fluence and obeys correlated barrier-hopping model.

Nonlocal asymmetric exclusion process on a ring and conformal invariance

We present a one-dimensional nonlocal hopping model with exclusion on a ring. The model is related to the Raise and Peel growth model. A nonnegative parameter u controls the ratio of the local backwards and nonlocal forwards hopping rates. The phase diagram, and consequently the values of the current, depend on u and the density of particles. In the special case of half-filling and u = 1 the system is conformal invariant and an exact value of the current for any size L of the system is conjectured and checked for large lattice sizes in Monte Carlo simulations. For u > 1 the current has a non-analytic dependence on the density when the latter approaches the half-filling value.

Ambipolar carrier transport properties in a built-in donor–acceptor discogen

Carrier transport in the hexagonal columnar mesophase of a discogen with a built-in dipole moment in the core—hexaalkoxydibenzo[a,c]phenazine (HDBP-3) was investigated. The temperature and field dependences of bipolar carrier mobilities up to the order of 10−3cm2V−1s−1 in the homeotropically aligned HDBP-3 have been revealed by time-of-flight (TOF) measurement. One-dimensional hopping model was used to discuss the effect of built-in donor–acceptor molecular dipole in the core. The calculation of charge transfer integral also supported the results of mobility measurement. The donor–acceptor molecular dipole in the discogen not only stabilized the mesophase but also contributed to the nondispersive ambipolar nature and substantially enhanced the electron transport in HDBP-3.

Electrical and optical studies in polyaniline nanofibre–SnO2 nanocomposites

Polyaniline nanofibre–tin oxide (PAni-SnO2) nanocomposites are synthesized and mixed with polyvinyl alcohol (PVA) as stabilizer to cast free-standing films. Composite films are characterized by X-ray diffraction studies (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence spectroscopy (PL) and UV-visible spectroscopy. XRD confirms the formation of PAni nanofibre–SnO2 nanocomposite. From TEM images, diameter of the polyaniline nanofibre and SnO2 nanoparticles in the PAni-SnO2 nanocomposite are found to be 20–60 nm. SEM results show fibrous morphology of the PAni nanofibre and spherical morphology of polyaniline-SnO2 composites. The nanocomposites exhibit high relative photoluminescence intensity in violet as well as green–yellow region of visible spectrum. From electrical conductivity measurement, it is confirmed that PAni nanofibre–SnO2 nanocomposite follows Mott’s one-dimensional variable range hopping (VRH) model.

Integration of intrinsic muscle properties, feed-forward and feedback signals for generating and stabilizing hopping

It was hypothesized that a tight integration of feed-forward and feedback-driven muscle activation with the characteristic intrinsic muscle properties is a key feature of locomotion in challenging environments. In this simulation study it was investigated whether a combination of feed-forward and feedback signals improves hopping stability compared with those simulations with one individual type of activation. In a reduced one-dimensional hopping model with a Hill-type muscle (one contractile element, neither serial nor parallel elastic elements), the level of detail of the muscle's force-length-velocity relation and the type of activation generation (feed-forward, feedback and combination of both) were varied to test their influence on periodic hopping. The stability of the hopping patterns was evaluated by return map analysis. It was found that the combination of feed-forward and proprioceptive feedback improved hopping stability. Furthermore, the nonlinear Hill-type representation of intrinsic muscle properties led to a faster reduction of perturbations than a linear approximation, independent of the type of activation. The results emphasize the ability of organisms to exploit the stabilizing properties of intrinsic muscle characteristics.

Electrical conductivity, dielectric properties and optical absorption of organic based nanocrystalline sodium copper chlorophyllin for photodiode application

Sodium copper chlorophyllin (SCC) thin films were successfully prepared, using dip coating technique. Thermal gravimetric analysis (TGA) was performed for studying the thermal stability of SCC film. The surface morphology of thin films was studied by using scanning electron microscopy (SEM). The crystalline structural characteristics were undertaken with the aim of determining the lattice parameters together with a complete list of the Miller indices and interplanar spacing for SCC. The molecular structure and electronic transitions of SCC were investigated by Fourier-transform infrared (FTIR) and absorption spectrum, respectively. Temperature dependence of the DC electrical conductivity, ( σ DC) was investigated in the temperature range 289–373 K. Measurements revealed that the σ DC behavior of the films can be described by Mott's one-dimensional variable range hopping (VRH) model in the entire temperature range. The AC conductivity, ( σ AC( ω)) results were discussed in terms of the correlated barrier hopping (CBH) mechanism for charge carrier transport. The maximum barrier height and the hopping length were estimated. The temperature dependence of the σ AC( ω) shows Arrhenius type with one thermal activation energy for each frequency. The behavior of the real and imaginary parts of the dielectric constant as a function of both temperature and frequency were discussed. The energy band model was applied and the type of the optical transitions responsible for optical absorption was found to be direct allowed transition. Position dependent for SCC thin film photo-detector was studied by using laser diode source.

Periodic one-dimensional hopping model with transitions between nonadjacent states

A one-dimensional hopping model is useful for describing the motion of microscopic particles in a thermal noise environment. Recent experiments on the new generation of light-driven rotary molecular motors found that a motor in state i can jump forward to state i+1 or i+2 or backward to state i-1 or i-2 directly. In this paper, inspired by these experiments, such a modified periodic one-dimensional hopping model with arbitrary period N is studied theoretically. The mean velocity, effective diffusion constant, and mean dwell time in one single mechanochemical cycle are obtained. The corresponding results are illustrated and verified by being applied to the synthetic rotary molecular motors.

Studies on Fourier transform infrared spectroscopy, scanning electron microscope, and direct current conductivity of polyaniline doped zinc ferrite

AbstractIn situ polymerization of aniline was carried out in the presence of zinc ferrite to synthesize polyaniline/ZnFe2O4 composites (PANI/ZnFe2O4) by chemical oxidation method. The composites have been synthesized with various compositions (10, 20, 30, 40, and 50 wt %) of zinc ferrite in PANI. From the Fourier transform infrared spectroscopy (FTIR) studies on polyaniline/ZnFe2O4 composites, the peak at 1140 cm−1 is considered to be measure of the degree of electron delocalization. The surface morphology of these composites was studied with scanning electron micrograph (SEM). The dc conductivity has been studied in the temperature range from 40–160°C and supports the one‐dimensional variable range hopping (1DVRH) model proposed by Mott. The results obtained for these composites are of scientific and technological interest. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

An effective description of a periodic one-dimensional hopping model

In this research, methods of reducing a general periodic one-dimensional hopping model to a one- or two-state model, which keeps the basic properties of the original process, are discussed. This reduction also implies that, to some extent, many processes can be well described by simple two-state or even one-state models.

Enhancements in Conductivity and Thermal Stabilities of Polypyrrole/Polyurethane Nanoblends

The current work deals with enhancements in conductivity and thermal stabilities of thermoplastic polyurethane (TPU)/dodecylbenzenesulfonic acid doped polypyrrole (PPy.DBSA) nanoblends prepared by solution intercalation (SB) and in situ (IS) methods. It is observed that the electrical conductivity (σdc) of nanoblends is influenced by interaction between PPy.DBSA and TPU as well as homogeneous nanolevel dispersion and content of PPy.DBSA in TPU matrix. The maximum value of σdc has been found at 30 wt % PPy.DBSA for the SB (0.26 S cm−1) nanoblend due to the presence of the hexagonal network. The percolation threshold is attained at 2.5 wt % of PPy.DBSA for IS and SB nanoblends. The temperature variation of conductivity for different nanoblends follows one-dimensional variable range hopping (VRH) model. A significant improvement (32 °C) in thermal stability has been observed at 50% wt loss for SB nanoblend containing 30 wt % PPy.DBSA. The PL peak of the TPU nanoblend is red-shifted with increasing wt % of PP...

Electrical Conductivity of Polyaniline/NiZnO3 Composites: A Solid State Electrolyte

In situ polymerization of aniline was carried out in the presence of nickel zinc oxide to synthesize polyaniline/NiZnO3 composites (PANI/NiZnO3) by chemical oxidation method. The composites have been synthesized with various compositions (10, 20, 30, 40 and 50 wt%) of nickel zinc oxides in PANI. From the infrared spectroscopy (FTIR) studies on polyaniline/NiZnO3 composites, the peak at 1140 cm−1 is considered to be the measure of the degree of electron delocalization. The surface morphology of these composites was studied with the scanning electron micrograph (SEM). The dc conductivity was studied in the temperature range from 40–160°C and supports the one-dimensional variable range hopping (1DVRH) model proposed by Mott. The results obtained for these composites are of scientific and technological interest.