Anomalous Dependence Research Articles

Anomalous Nernst effect dependence on composition in Fe100−X Rh X alloys

We studied the anomalous Nernst effect (ANE) in CsCl-type Fe100−X Rh X (X = 45, 48, 50, 52, 54, 60) with a thickness of 50 nm deposited on a thermally oxidized Si substrate. Samples with X < 48 certainly have a ferromagnetic phase, exhibiting the ANE. The composition dependence of the anomalous Nernst coefficient agreed with the transverse thermoelectric conductivity and were maximized at X = 48, which has a ferromagnetic state close to the phase transition state. The maximization of at X = 48 can be explained using band structure-based calculations, where rapidly increases near the phase transition.

Surface morphology and dispersion interaction induced anomalous dynamics of solvation water of a hydrophobic fullerene molecule

Knowledge of accurate structural and dynamical features of the surrounding water of a C60 molecule is essential for the proposed uses of C60 in a wide variety of applications viz., in inhibiting HIV protease, DNA cleaving, macromolecular binding and drug delivery. Using molecular dynamics simulations, the present study demonstrates that the solute-water dispersion interaction induces anomalous bulk density dependence of dynamics of solvation water of the C60. In order to elucidate the origin of such behaviour, the analyses of the simulation trajectories are performed and it reveals the presence of two dynamically different types of water molecules: one (designated as Type 1 here), which has no radially outward movements (with respect to C60) throughout the simulation time and performs “bouncing ball” movements on the C60 surface by hopping from one face to another and the other one (Type 2) is fast and goes in and out of the solvation shell frequently. The anomalous dynamics is a consequence of the variable presence of such dynamically heterogeneous water molecules as a function of bulk density, and it, in turn, arises due to the interplay between two opposing effects emanating from the free volume (which depends on bulk density) and the inhomogeneous energy surface of the C60 arising due to icosahedral arrangement of carbon atoms on the surface and attractive solute-water dispersion interaction. It is to emphasize that model C60 with no attractive dispersion interaction does not show any anomalous dynamics.

Atypical dependence of excited exciton energy levels and electron-hole correlation on emission energy in pyramidal InP-based quantum dots

We calculate the spectrum of excited exciton states in application-relevant self-assembled pyramidal quantum dots grown in InAs/InP and InAs/AlGaInAs material systems. These types of dots have been recently shown to combine the emission in the third optical fiber window with low surface density and a reasonable level of in-plane symmetry of emitters, which predestines them for studies on single- and entangled-photon emission and for corresponding applications. The spectrum of optically active excited states is crucial for successful resonant and quasi-resonant excitation of emitters, allowing for conservation of angular momentum and addressing individual selected quantum states. Here, we show that in both types of studied dots, due to their specific morphology of truncated pyramid, the density of excited-state ladder, especially the s–p shell splitting may follow an unconventional dependence on emission energy, opposite to the one typically met in regular quantum dots. We obtain this result via modeling based on available morphological data and calculation within the multi-band {{varvec{k}} {cdot } {varvec{p}}} envelope-function theory combined with the configuration-interaction method used to calculate exciton states. Then, we explain this observation in purely geometric terms, as a result of an increasing effective quantum confinement width in a pyramid that is progressively cut from the top. Additionally, we show that the inverted trend is also manifested in the amount of electron-hole correlation in the exciton ground state, which also shows an anomalous dependence on emission energy and quantum dot volume.

Correlation between Structure and Dynamics of Co2 Confined in Mg-Mof-74 and the Role of Inter-Crystalline Space: A Molecular Dynamics Simulation Study

Mg-MOF-74 is a metal-organic framework (MOF) that exhibits a high capacity for CO$_2$ adsorption. Given the importance of CO$_2$ confinement in Mg-MOF-74 for capture and storage applications, it is important to understand the structural and dynamical behavior of CO$_2$ in Mg-MOF-74 pores. While most molecular simulation studies use ideal single crystal models of nano-porous substrates, the existence of inter-crystalline space has been shown to have profound effects on the sorption, structure and dynamics of the adsorbed fluid. To address these issues, we report a molecular dynamics simulation study at 300 K, of CO$_2$ confined in several models of Mg-MOF-74 with systematically inserted inter-crystalline spacing of different widths. Both structural and dynamical behavior of CO$_2$ is studied in 5 models of Mg-MOF-74, each at 4 different loadings. Six strong sites of CO$_2$ adsorption are found at the periphery of the pores of Mg-MOF-74 in addition to a relatively weak adsorption at the center of the pore. On insertion of inter-crystalline spacing, additional six sites of strong adsorption are seen in the inter-crystalline space close to the pore opening. These additional sites delocalize as the inter-crystalline space is widened and the population of guest molecules adsorbed at the pore center grows at the expense of peripheral population. This redistribution of guest molecules has important implications for their dynamics. While in the model without inter-crystalline space, translation motion is found to be slower at higher loadings, as wider inter-crystalline space is introduced, anomalous loading dependence of translational diffusivity is observed. In general, inserting inter-crystalline spacing is found to enhance both translational as well as rotational motion of the guest molecules. The results reported here provide valuable insight to carbon capture and storage.

Identification of a new source of magnon relaxation in interface between epitaxial iron garnet ferrite films and GGG substrate

We have investigated the intermediate layer between the gallium-gadolinium garnet substrate and the yttrium-iron garnet epitaxial film. This interlayer is characterized by a large magnetic moment at low temperatures, which leads to an anomalous dependence of the susceptibility and a shift in the magnetic resonance frequency upon cooling. This shift is much larger than might be expected due to magnetization anisotropy, substrate paramagnetic ions, and magnetostriction. We found that this interlayer plays a major role in magnetic relaxation processes in the temperature range below 50 K.

Double-humped temperature dependence of plastic behaviour of K403 superalloy and its constitutive model

ABSTRACT In this study, uniaxial compression experiments of K403 superalloy were conducted over temperature range of 298–1073 K and strain rate range of 0.1–5200/s. Temperature and strain rate effects on the flow stress were analysed. Double anomalous stress humps were noticed in the flow stress vs. temperature curves. The flow stress of the superalloy showed independence on strain rate over low strain rate range and an enormous increase with increasing strain rate over high strain rate range. Then, the effects of temperature and strain rate on the microstructure were observed and analysed. Due to the double-humped temperature dependence, the existing constitutive models were unable to accurately predict the plastic behaviour of K403 superalloy. Thus, a constitutive model was developed to describe the plastic behaviour of K403 superalloy. The model was able to capture the double-humped temperature dependence and anomalous strain rate dependence of plastic behaviour. It was shown that the plastic behaviour of the superalloy can be accurately predicted over a wide range of temperatures and strain rates.

Anomalous dependence of ionization probability and electron angular distributions on orientation of molecular axis in photoionization of : effect of two-center interference

A theoretical and computational study of photoionization of the one-electron molecular ion initially in the 1σ u state is performed. The laser pulse is linearly polarized with the carrier wavelength in the extreme ultraviolet and soft x-ray regions. The electron wave function is obtained by solving the time-dependent Schrödinger equation with the help of the generalized pseudospectral method. The dependence of the total ionization probability and photoelectron spectra on the orientation of the molecular axis is analyzed. Within the wavelength interval 6 to 23 nm, anomalous behavior of the ionization probability is found, where it increases with the angle between the polarization vector of the external field and the molecular axis and reaches a maximum at the perpendicular orientation of the molecule. The phenomenon is explained as resulting from the two-center interference in the wave function of the emitted electron.

Molecular Structure and Surface Accumulation Dynamics of Hyaluronan at the Water-Air Interface.

Hyaluronan is a biopolymer that is essential for many biological processes in the human body, like the regulation of tissue lubrication and inflammatory responses. Here, we study the behavior of hyaluronan at aqueous surfaces using heterodyne-detected vibrational sum-frequency generation spectroscopy (HD-VSFG). Low-molecular-weight hyaluronan (∼150 kDa) gradually covers the water–air interface within hours, leading to a negatively charged surface and a reorientation of interfacial water molecules. The rate of surface accumulation strongly increases when the bulk concentration of low-molecular-weight hyaluronan is increased. In contrast, high-molecular-weight hyaluronan (>1 MDa) cannot be detected at the surface, even hours after the addition of the polymer to the aqueous solution. The strong dependence on the polymer molecular weight can be explained by entanglements of the hyaluronan polymers. We also find that for low-molecular-weight hyaluronan the migration kinetics of hyaluronan in aqueous media shows an anomalous dependence on the pH of the solution, which can be explained from the interplay of hydrogen bonding and electrostatic interactions of hyaluronan polymers.

Anomalous electron-electron interactions in epitaxial graphene on SiC

Electron-electron interactions (EEI) play a pivotal role in the transport behavior of carriers confined in a two-dimensional system. The strength of the interaction can be tuned by changing carrier concentration in a conventional two-dimensional system, while it expectedly cannot be controlled in monolayer graphene with a linear dispersion relation since the interaction parameter is not related to carrier concentration. Here, an anomalous carrier-concentration dependence of the EEI is observed in epitaxial graphene on SiC. From quantum transport measurement, a logarithmic temperature dependence of the Hall coefficient is obtained, which is a manifestation of the EEI. From the logarithmic temperature dependence, the EEI-related factor Kee is extracted. Unexpectedly, the extracted Kee shows an increase on increasing carrier concentration, which is further confirmed by analyzing logarithmic correction to the Drude conductivity. This can be attributed to the carrier-concentration dependence of Fermi-liquid constant F0σ due to gas absorption, which offers a route to control the EEI in graphene.

Carbon bearing aluminosilicate melt at high pressure

It is well known that volatiles such as water has significant influence on the properties of silicate melts. Carbon dioxide (CO2) is also an abundant volatile in deep Earth, however the effect of CO2 on the properties of polymerized melts, particularly the transport properties, are poorly understood. This is crucial for better understanding of the generation and migration of carbon bearing silicate magma in deep crustal and mantle settings. In this study, we explore the structure and properties of carbon bearing aluminosilicate melt up to a pressure of ~25 GPa and temperature range of 2500–4000 K using first principles molecular dynamics (FPMD) simulation. Our results show that CO2 in the aluminosilicate melts dissolves as molecular CO2 and carbonate (CO32-) at lower pressures (~0–3 GPa). However, at higher pressures (>3 GPa) relevant to most of the upper mantle, CO32- is predominant carbon species along with carbon in 4-fold coordination (CO4). Fraction of CO32- increases with decreasing temperature and increasing pressure. We find that at the reference isotherm (2500 K), the density of the aluminosilicate melt is reduced by addition of CO2 (in wt.%) with dρdXCO2 = −0.0214. Effect of water on the density of melt is more pronounced with dρdXH2O = −0.0422. Thus, the gravity-driven buoyancy of volatile rich magma will be greater than that of the magma without volatile components. The compressibility of the aluminosilicate melt is also affected by volatiles. For instance, both bulk modulus (KT0) and its pressure derivative (KT0') for volatile bearing melts are respectively lower and higher than that of dry melt. Aluminosilicate melts are highly polymerized and show an anomalous pressure dependence of melt viscosity. Pressure dependence of viscosity at low pressure regime (P < 5 GPa) is significant with dlog(η)dP=-2.06. Melt viscosity is further reduced by the addition of volatiles. Effect of volatiles on viscosity is more pronounced at low pressures and it minimizes at pressures where the melt viscosity exhibits minima. Due to the lower viscosity and larger buoyancy for both the H2O and CO2 bearing aluminosilicate melts at crustal and upper mantle depths, magma mobility (Δρη) is greater for volatile bearing melts. Thus, the residence time of such melts are expected to be shorter than volatile free melts in those settings. Like the mobility, electrical conductivity of aluminosilicate melts also increases when volatile is present in the silicate melt. We find that that as low as <1 vol.% volatile bearing aluminosilicate melt mixed with mantle matrix could be sufficient to explain the observed electrical conductivity anomalies in the upper mantle.

Effects of Confinement and Ion Adsorption in Ionic Liquid Supercapacitors with Nanoporous Electrodes.

We investigate the effects of pore size and ion adsorption on the room-temperature ionic liquid capacitor with nanoporous electrodes, with a focus on optimizing the capacitance and energy storage. Using a recently developed modified BSK model accounting for both ion correlations and nonelectrostatic interactions, we find that ion crowding proximate to the electrode surface induced by the spontaneous charge separation due to strong ion correlations is responsible for the anomalous increase in the capacitance with decreasing pore sizes observed in experiments. Reducing the strength of ion correlations increases the capacitance and suppresses the anomalous size dependence. For a given pore size, the capacitance peak diverges when the ion correlation strength α reaches a critical value, αsc,L. The capacitance peak shifts to smaller pore size as α decreases because of rapid decrease of αsc,L with decreasing pore size. Asymmetric preferential ion adsorption is shown to lead to significantly enhanced energy storage close to the transition point for any pore sizes. For a given correlation strength, the energy storage is optimal at a pore size where α = αsc,L.

Inverse magnetic hysteresis of the Josephson supercurrent: Study of the magnetic properties of thin niobium/permalloy (Fe20Ni80 ) interfaces

We propose a picture for the magnetic properties of superconductor/ferromagnet (S/F) heterostructures based on Nb and permalloy $(\mathrm{Py}:{\mathrm{Fe}}_{20}{\mathrm{Ni}}_{80})$. By measuring the magnetic moment as a function of the temperature in S/F/S trilayers for different thicknesses of the middle F layer, we give evidence of the presence of a magnetic stray field of the F layer. For values of F-layer thickness below a threshold, we establish a correlation between the magnetic measurements of the S/F/S trilayers and the anomalous magnetic dependence of the critical current in S/Insulator/thin superconducting film/F/S (SIsFS) Josephson junctions (JJs). These complementary investigations provide a self-consistent method to fully characterize S/F heterostructures and possibly demonstrate effects arising from the mutual interactions between ferromagnetism and superconductivity. A shift in the Fraunhofer critical current oscillations has been observed in the opposite direction to the one commonly observed in JJs with F barriers, as it has been recently predicted by inverse and electromagnetic proximity theories. This inverse memory effect is relevant for the design of these heterostructures as memory cells and spintronic devices.

Gauge theories on compact toric manifolds

We compute the mathcal{N}=2 supersymmetric partition function of a gauge theory on a four-dimensional compact toric manifold via equivariant localization. The result is given by a piecewise constant function of the Kähler form with jumps along the walls where the gauge symmetry gets enhanced. The partition function on such manifolds is written as a sum over the residues of a product of partition functions on mathbb {C}^2. The evaluation of these residues is greatly simplified by using an “abstruse duality” that relates the residues at the poles of the one-loop and instanton parts of the mathbb {C}^2 partition function. As particular cases, our formulae compute the SU(2) and SU(3) equivariant Donaldson invariants of mathbb {P}^2 and mathbb {F}_n and in the non-equivariant limit reproduce the results obtained via wall-crossing and blow up methods in the SU(2) case. Finally, we show that the U(1) self-dual connections induce an anomalous dependence on the gauge coupling, which turns out to satisfy a mathcal {N}=2 analog of the mathcal {N}=4 holomorphic anomaly equations.

Anomalous ellipticity dependence of the generation of near-threshold harmonics in noble gases

We measured the ellipticity dependence of the harmonic yield of He, Ne, Ar, Kr, and Xe. It is found that the harmonic yield in general decreases monotonically with increasing laser ellipticity but anomalous dependence does occur for each atom for some harmonic orders. We found that the degree of anomaly is weakest in helium but is stronger for the heavier atoms. The anomaly also depends on laser intensity. To explain these features, we developed a quantum trajectory Monte Carlo (QTMC) model based on the quantum path integral theory to study high-order harmonic generation (HHG). The model includes the effect of Coulomb potential from the target ion, thus it is capable of calculating near-threshold harmonics quantitatively. This model reveals that the presence of Coulomb potential would generate orbiting trajectories which are responsible for the anomalous ellipticity dependence near the threshold.

Numerical Modeling of the Anomalous Low-Temperature Dependence of the Tunneling Conductance of a "Dirty" N-I-N Junction

A numerical study of the low-temperature tunneling conductance G(T) of the “dirty” (low concentrations of the same non-magnetic impurities in the I layer) N-I-N junction (N is a normal metal; I is an insulator) with random quantum jumpers penetrating the disordered I-layer is performed. In a wide range of low impurity concentrations, the dependence G(T) anomalously, both qualitatively and quantitatively, differs from the corresponding dependence G0(T) in the “pure” (without impurities in the I layer) N-I-N junction. The numerical analysis of the dependence G(T) shows the possibility of the experimental manifestation of these anomalies.

Anomalous diameter dependent electrical transport in individual CuO nanowire

Cupric oxide (CuO) nanostructure arrays have been extensively investigated for solar energy harvesting, electrochemical energy storage, chemical sensing, field-effect transistors, etc. Although most of these applications depend on the collective behavior of an array of such structures, analysis of electrical transport in a single nanostructure, which are the building blocks, is essential for understanding both the fundamental aspects and device performance. Here we report the electrical conduction mechanism in thermally grown single CuO nanowire (NW), which reveals that the current density has an anomalous dependence on the diameter of the NWs—decreasing with an increase in diameter. An analysis of the electrical behavior at room temperature shows that the current density in CuO NWs has different slopes in different regions of the applied bias indicating distinct types of charge transport, which are characterized as near Ohmic (lower voltage), trap controlled, and space charge limited conduction (higher applied voltage). Further, the trap density and activation energy are calculated from the temperature-dependent current density data, which shows higher values (9.38 × 1015cm−3, 79.4 meV) in thicker NWs compared to that in the thinner ones (3.96 × 1015 cm−3, 63.9 meV). Investigation of the NWs with Raman and photoluminescence spectra establishes the presence of Cu2O phase in thicker NWs, which act as hole traps to hinder the charge transport in p-type CuO and resulting in lower conductivity at higher diameters. This study helps to design and fabricate prototype nanodevices with desired conductivity based on CuO NWs.

Formation and Chromatographic Detection of Organic Compound Hydrates

The formation of hydrates of inorganic compounds is well known and is widely discussed in the contemporary literature. The reasons for the insufficiently detailed characterization of numerous well-known hydrates of organic compounds are analyzed, the main of which is their instability. The CAS numbers assigned to many of these hydrates confirm interest in these hydrates. We found that the reversible formation of the hydrates of various organic compounds can be a reason for anomalous dependences of their retention parameters (tR) on the concentration of an organic eluent modifier (c) in reversed-phase high-performance liquid chromatography. The recurrent approximation of the retention parameters tR(c + Δc) = atR(c) + b (*), where Δc = const is a constant step of c, is the most effective way to detect these anomalies. Deviations of dependences like (*) from linearity are observed with compounds in which variations in c and, consequently, in the water content of the eluent (1 – c) affect the equilibrium of the reaction $${\text{X}} + n{{{\text{H}}}_{{\text{2}}}}{\text{O }} \rightleftarrows {\text{X}} \cdot n{{{\text{H}}}_{{\text{2}}}}{\text{O}}.$$

Raman and Infrared Studies of CdSe/CdS Core/Shell Nanoplatelets

The vibrational spectroscopy of semiconductor nanostructures can provide important information on their structure. In this work, experimental Raman and infrared spectra are compared with vibrational spectra of CdSe/CdS core/shell nanoplatelets calculated from first principles using the density functional theory. The calculations confirm the two-mode behavior of phonon spectra of nanostructures. An analysis of the experimental spectra reveals the absence of modes with a high amplitude of vibrations of surface atoms, which indicates their strong damping. Taking into account the difference in the damping of different modes and their calculated intensities, all bands in the spectra are unambiguously identified. It is found that the frequencies of longitudinal optical modes in heterostructures are close to the frequencies of LO phonons in bulk strained constituents, whereas the frequencies of transverse modes can differ significantly from those of the corresponding TO phonons. It is shown that an anomalous thickness dependence of CdS TO mode is due to a noticeable surface relaxation of the outer Cd layer in the nanostructure.

Quantifying the anomalous water absorption behavior of cement mortar in view of its physical sensitivity to water

The one-dimensional water absorption into cement-based materials, possibly the simplest case of unsaturated water flow playing a fundamental role in predicting mass transport and durability, is still far from being completely understood due to several puzzling anomalies. Considering the water sensitivity of C-S-H gels (swell upon wetting and contract upon drying), a modified Richards equation (MRE) is proposed to quantify the anomalous water absorption into cement-based materials of changing porosity. Consistent experimental tests on a cement mortar and calculations indicate that the MRE with time-decaying water permeability can quantitatively capture the long-term absorption with two linear stages and a nonlinear transition stage between them. The water sensitivity is validated to be responsible for the anomalous deviation of water absorption from the classical square root of time law. It also partially contributes to the anomalous dependence of sorptivity on the temperature-dependent surface tension and viscosity of water and many organic liquids.

Anomalous thickness dependence of Curie temperature in air-stable two-dimensional ferromagnetic 1T-CrTe2 grown by chemical vapor deposition

The discovery of ferromagnetic two-dimensional van der Waals materials has opened up opportunities to explore intriguing physics and to develop innovative spintronic devices. However, controllable synthesis of these 2D ferromagnets and enhancing their stability under ambient conditions remain challenging. Here, we report chemical vapor deposition growth of air-stable 2D metallic 1T-CrTe2 ultrathin crystals with controlled thickness. Their long-range ferromagnetic ordering is confirmed by a robust anomalous Hall effect, which has seldom been observed in other layered 2D materials grown by chemical vapor deposition. With reducing the thickness of 1T-CrTe2 from tens of nanometers to several nanometers, the easy axis changes from in-plane to out-of-plane. Monotonic increase of Curie temperature with the thickness decreasing from ~130.0 to ~7.6 nm is observed. Theoretical calculations indicate that the weakening of the Coulomb screening in the two-dimensional limit plays a crucial role in the change of magnetic properties.