Anomalous Dip Research Articles

Effect of COVID-19 global lockdown on our Moon

Abstract Systematic investigation of lunar night-time temperatures can possibly be thought as a stable platform to study Earth's radiation budget and climate change as advocated earlier by several researchers. In this study, we report an interesting observation possibly of changing Earth's climate as experienced by the Moon, utilising a rare and novel context of COVID-19 global lockdown. Lunar night-time surface temperatures of six different sites on the Moon's nearside were analysed during the period 2017–2023. Results showed an anomalous dip in the lunar night time surface temperatures for all the sites during April-May 2020, the strict COVID-19 global lockdown period, when compared to the values of the same period during the previous and subsequent years. Since the terrestrial radiation has also showed a significant reduction during that time, the anomalous decrease observed in lunar surface temperatures is attributed to the COVID 19 global lockdown effect. Therefore, our study shows that the Moon has possibly experienced the effect of COVID 19 lockdown, visualised as an anomalous decrease in lunar night-time surface temperatures during that period. These results can be substantiated further from Moon-based observatories in future, thereby making them potential tools for observing Earth's environmental and climate changes.

Structural evolution of versatile Bi2O3-B2O3-Cr2O3: ZrO2 glass ceramics monitored by Raman and EPR spectroscopy

A series of BBCZr glass ceramics were synthesized by the usual melt-quenching technique and subsequent two-step heat treatment with the composition (in mol.%): 30Bi2O3-70B2O3 (pure sample) and (29-x)Bi2O3-70B2O3-1Cr2O3:xZrO2 (0 ≤ x ≤ 2). Morphological, physical, thermal, structural, and magnetic characteristics of BBCZr glass ceramics have been investigated with the various concentrations of zirconium oxide nanoparticles (≈45 nm) in the composition. XRD and SEM studies have confirmed the existence of induced heterogeneous crystal phases in the glass ceramics. The Raman spectra have revealed the Boson peak at low frequencies (≈62–72 cm−1), various functional groups of primary glass forming units like [BO4], [BiO3], [CrO4]2− and [ZrO4] units, and other glass modifying units/crystallite units viz., [BO3], [BiO6], [CrO6], BOB chains, etc. The Boson peak maximum has exhibited an anomalous dip at x = 1 mol.%, at which the glass ceramic sample exhibits more heterogeneous crystal phases. The paramagnetic isolated Cr3+ ions plus Cr3+-Cr3+ ion pairs were detected by EPR studies. The BBCZr glass ceramics may be useful for potential applications such as optical elements, paramagnetic sensing elements, etc.

The geometry of the Western Boundary Fault (WBF) of Amer oil field and its influence on hydrocarbon trapping, western central Gulf of Suez, Egypt

Amer ridge holds one of the most prolific oil fields in the western central Gulf of Suez rift basin and was discovered in 1965. The brownfield produces oil from the Miocene-Eocene carbonates and Late Cretaceous sandstone reservoirs with oil water contact 1150 m. The present work provides a structural model expressing the role of inherited structures and the tectonic evolution of the western fault bounding the field. This model resulted from the multi-scale integration of subsurface data from 90 wells, various borehole images, and 3-D seismic volumes attributes. The interpretation demonstrated the vertical profile of the western boundary fault of Amer field (WBF) to be a ramp-flat-ramp geometry pattern cutting through lithological units of different rheology. The developed fault surface of the WBF divided the penetrated sedimentary succession into two distinct strain intervals. The inherited structural fabrics of the lower interval of pre-rift units are documented with 1) an anomalous southwest-stratal dip, and 2) severe deformation of the WBF footwall with extensional faults of gulf parallel and gulf-orthogonal trends. Simultaneously, the roll-over anticline-syncline structure that developed within the upper, less-strained Miocene interval, coincided with the flat of the WBF geometry.By applying this model, it was possible to i) distinguish the three-footwall structurally controlled plays of Amer area into lower ramp-1, flat, and upper ramp-2 and ii) enlarge the size of the brownfield. Recent development activity in Amer area verified the new structural model and expanded the drilling activity to target the Paleozoic clastic reservoir of Nubia C as a new exploration objective. The Amer structural model can serve as a useful analogue for oil field development and production enhancement in other complex rift basin settings.

Electrochemical Seebeck coefficient of Fe2+/Fe3+ in acetone–methanol mixed solution

The electrochemical Seebeck coefficient (α) of Fe2+/Fe3+ in acetone–methanol (MeOH) mixed solution was systematically investigated against the acetone molar ratio (n) and molar ratio of Fe3+ to Fe (n Fe3+). At n Fe3+ = 0.75, α monotonously increases with increase in n from 0.3 mV K−1 at n = 0.00 to 3.4 mV K−1 at n = 1.00. At n Fe3+ = 0.50 and 0.25, we found anomalous dip structures in the n−α plot at n ≈ 0.9 and 0.4, respectively. Based on a spectroscopic investigation, we interpreted the observed dip structures in terms of the transition state between the FeCl4-active and FeL 6-active regions.

Fully resolved currents from quantum transport calculations

We extract local current distributions from interatomic currents calculated using a fully relativistic quantum mechanical scattering formalism by interpolation onto a three-dimensional grid. The method is illustrated with calculations for Pt$|$Ir and Pt$|$Au multilayers as well as for thin films of Pt and Au that include temperature-dependent lattice disorder. The current flow is studied in the "classical" and "Knudsen" limits determined by the sample thickness relative to the mean free path $\lambda$, introducing current streamlines to visualize the results. For periodic multilayers, our results in the classical limit reveal that transport inside a metal can be described using a single value of resistivity $\rho$ combined with a linear variation of $\rho$ at the interface while the Knudsen limit indicates a strong spatial dependence of $\rho$ inside a metal and an anomalous dip of the current density at the interface which is accentuated in a region where transient shunting persists.

Pressure tuning of superconductivity in Mo8Ga41 single crystals

We report on pressure tuning of superconductivity in a strongly coupled superconductor ${\mathrm{Mo}}_{8}{\mathrm{Ga}}_{41}$ with a critical temperature ${T}_{c}\ensuremath{\sim}9.8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Resistance measurements show that ${T}_{c}$ is suppressed to 3.6 K at 19 GPa followed by a nonmonotonic variation at higher pressures. Synchrotron x-ray diffraction experiments reveal an amorphization taking place at the critical pressure ${P}_{c}\ensuremath{\sim}19\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. As comparing with $\mathrm{Mg}{\mathrm{B}}_{2}$, the ${\mathrm{Mo}}_{8}{\mathrm{Ga}}_{41}$ shows a relative low decreasing rate of ${T}_{c}$, which might be attributed to its unique vertex-sharing type of cluster architecture. Survival of superconductivity across the crystalline to amorphous transition indicates that, although long-range structural order of endohedral Ga clusters is destroyed, short-range-ordered intracluster structure still exists and allows for local Cooper pairing. Due to presence of disorders in the amorphous phase, establishment of Cooper pair coherence is shifted to lower temperatures, which causes unusual transport behaviors near ${T}_{c}$, e.g., the anomalous resistance peak and dip. The amorphous superconducting phase is able to be retained to ambient pressure and therefore provides an ideal platform to study disorder effects on superconductivity.

Interfacial Strain Gradients Control Nanoscale Domain Morphology in Epitaxial BiFeO3 Multiferroic Films

AbstractDomain switching pathways fundamentally control performance in ferroelectric thin film devices. In epitaxial bismuth ferrite (BiFeO3) films, the domain morphology is known to influence the multiferroic orders. While both striped and mosaic domains have been observed, the origins of the latter have remained unclear. Here, it is shown that domain morphology is defined by the strain profile across the film–substrate interface. In samples with mosaic domains, X‐ray diffraction analysis reveals strong strain gradients, while geometric phase analysis using scanning transmission electron microscopy finds that within 5 nm of the film–substrate interface, the out‐of‐plane strain shows an anomalous dip while the in‐plane strain is constant. Conversely, if uniform strain is maintained across the interface with zero strain gradient, striped domains are formed. Critically, an ex situ thermal treatment, which eliminates the interfacial strain gradient, converts the domains from mosaic to striped. The antiferromagnetic state of the BiFeO3 is also influenced by the domain structure, whereby the mosaic domains disrupt the long‐range spin cycloid. This work demonstrates that atomic scale tuning of interfacial strain gradients is a powerful route to manipulate the global multiferroic orders in epitaxial films.

Temperature-dependent transport properties of a FeTe compound

Temperature-dependent transport properties of a FeTe parent compound have been investigated by measurements of electrical resistivity \(\rho (T)\), thermal conductivity \(\kappa (T)\) and Seebeck coefficient S(T). The sample was synthesized using a standard solid state reaction route via vacuum encapsulation and characterized by X-ray diffraction spectroscopy, which indicated a tetragonal phase with the space group \(P4/{ nmm}\). The resistivity measurement data of the parent FeTe compound do not exhibit superconductivity however, it shows an anomaly in the temperature-dependent resistivity at around 67 K, which corresponds to structural phase transition in the vicinity of a magnetic phase transition. In the low temperature regime, Seebeck coefficient, S(T), exhibited an anomalous dip feature and negative throughout the temperature range, indicating an electron-like, single band charge carrier mechanism. We have also estimated the power factor and thermoelectric figure of merit ZT, which is found to be significantly smaller than other compositions of iron chalcogenides.

Influence of sulfur doping on the electrical and thermal transport properties of FeTe1-xSx superconductors

In this study, we determined the structural, electrical, and thermal transport properties of the FeTe1−xSx system, where x = 0.0, 0.1, 0.2, and 0.3. The samples were synthesized using a standard solid-state reaction route via vacuum encapsulation and characterized by X-ray diffraction, which indicated a tetragonal phase with the P4/nmm space group. The parent compound FeTe exhibited an anomaly according to the resistivity measurements at around 67 K due to structural change. The S-substituted samples exhibited negative dependence on the temperature at an electrical resistivity above 10 K, and quantitative analysis indicated that the variable range hopping mechanism governs electrical conduction in the FeTe1−xSx system. In the low-temperature regime, the Seebeck coefficient, S(T), had an anomalous dip feature with crossover of the sign, which can be understood based on the phonon drag contributions and the multiband picture, respectively. The lattice phonons made major contributions to the measured thermal conductivity, κ(T). In addition, we observed a reduction in the height of the low-temperature phonon peak with κ due to the substitution of S for Te, thereby indicating strong enhancement of the disorder-induced phonon scattering. Moreover, a positive dκ/dT was observed in the normal state, which might be related to local anharmonic lattice distortions. Overall, based on our analyses, we conclude that phonons play important roles in the transport properties of FeTe1-xSx superconductors.

Crustal structure of the southeastern Tibetan Plateau from gravity data: New evidence for clockwise movement of the Chuan–Dian rhombic block

The crustal deformation beneath the Chuan–Dian rhombic block (CDB) and surrounding regions has been studied in geological and geodetic methods, and provide important insights into the kinematics and dynamics about the clockwise movement of this tectonic block. In this work, we present images of the normalized full gradient (NFG) of the Bouguer gravity anomalies from five gravity profiles across the boundary faults of the CDB measured in recent years, and investigate the distribution characteristics of the crustal anomalous bodies along the profiles. Firstly, an anomalous body with eastward dipping exist beneath the Xianshuihe fault, suggesting that crustal mass move to east. Secondly, near the Xiaojiang fault, two anomalous bodies dip westward with depth increasing. The inferred movement direction of the north one is from west to east, and the south one is from east to west. Thirdly, anomalous bodies on the northeast and southwest sides of the Red River fault suggest the directions of crustal movement is from northeast to southwest. These results are also consistent with GPS solutions, and provide gravity evidence for crustal deformation of the CDB with clockwise rotation.

Probing Franck–Condon-like Excitations in Anchoring of Phthalocyanine Molecules on Au(111)

The nuclear motions coupled with electronic excitations of reactants play an essential role in electron-induced chemical reactions. Here, we study the vibrational–electronic (vibronic) coupling effects in the anchoring of Ni-phthalocyanine molecules (NiPCs) on Au(111) using scanning tunneling microscopy. The anchoring occurs through the dehydrogenation of a C–H bond in NiPC by tunneling electrons. By counting the number of anchored molecules, we measure the reaction rate as a function of the bias voltage. We find an unexpected dip feature in the reaction rate near the bias voltage of 4.8 V. To understand this, we employ density functional theory calculations to study atomic force exerted on a NiPC by Franck–Condon-like excitations. We find the molecule anchoring is enhanced when the C–H bonds are stretched by the induced force, which is lacking for the bias voltage near 4.8 V and thus responsible for the anomalous dip in the reaction rate.

Emergence of a resistance anomaly by Cu-doping in TaSe3

We have synthesized single crystals doped with Cu atoms in TaSe3 which exhibits no Charge Density Wave (CDW) transition, and measured precisely the temperature dependence of the resistance. We discover an anomalous sharp dip in the temperature derivative of the resistance at about 91 K in Cu-doped TaSe3, which is never observed in pure TaSe3. The dip suggests that there is a phase transition with a relative increase in resistance. In addition, the dip is “γ” shaped. We reveal that the same “γ”-shaped dip in dR/dT is commonly observed at the CDW transition temperature in many CDW conductors, which is a universal consequence resulting from the opening and growth of a CDW gap on a Fermi surface. Furthermore, the result of the single-crystal X-ray diffraction (XRD) analysis implies that Cu-doping increases the lattice parameter of the a-axis and c-axis and decreases that of the b-axis, leading to an improvement in the nesting condition. Based on the “γ”-shaped dip and the result of the single-crystal XRD analysis, we conclude that a CDW emerges by Cu-doping in TaSe3.

Anomalous variation of Boson peak and fragility and their correlations with intermediate-range structure in PbO-B2O3 glasses

Understanding the microscopic origin of physical properties is fundamental to the study of glasses. In the present study, unique trends were observed in structural and dynamical properties in lead-borate [xPbO:(1-x)B2O3] glasses upon increasing the modifier. Properties driven by short-range structural changes like, glass transition temperature (Tg) and elastic modulii exhibit a broad maxima around x = 0.3, in congruence with the average coordination number <r>. Using Raman spectroscopy, this behaviour is attributed to the gradual conversion of three-coordinate (B3) to four-coordinate (B4) boron species. However, dynamic properties like the Boson peak and fragility behave similar to the above structural properties except an anomalous dip at x = 0.3. The corresponding dynamic correlation length, therefore, exhibits a decrease except a peak at x = 0.3 with increasing x. The static correlation lengths estimated from the first sharp diffraction peak (FSDP), did not follow a linear trend with the dynamic correlation lengths, indicating a different spatial origin. The analysis of the Boson peak and FSDP suggests that while the Boson peak arises from intermediate-range ordering within the network units, the FSDP arises due to ordering of voids between such units. Moreover, the Boson peak maximum showed a linear decrease with increasing <r>, while the Boson peak position and fragility were found to vary linearly. These correlations emerge from the evolution of the network packing and connectivity with the addition of modifier and changing role of lead oxide as a glass former at higher concentrations. The anomalous variation in dynamical properties reflects the critical role of Pb2+ in tuning the intermediate-range structure of the vitreous network.

Phonon anomalies and lattice dynamics in the superconducting oxychlorides Ca2−xCuO2Cl2

We present a comprehensive study of the phonon dispersion in an underdoped, superconducting Ca${}_{2\ensuremath{-}x}$CuO${}_{2}$Cl${}_{2}$ crystal. We interpret the results using lattice dynamical calculations based on a shell model, and we compare the results to other hole-doped cuprates, in particular, to the ones isomorphic to La${}_{2\ensuremath{-}x}$Sr${}_{x}$CuO${}_{4}$ (LSCO). We found that an anomalous dip in the Cu-O bond stretching dispersion develops in oxychlorides with a simultaneous marked broadening of the mode. The broadening is maximum at $\ensuremath{\approx}$$[\ensuremath{\pi}/(2a)\phantom{\rule{0.28em}{0ex}}0\phantom{\rule{0.28em}{0ex}}\phantom{\rule{4pt}{0ex}}0]$, which corresponds to the charge-modulation propagation vector. Our analysis also suggests that screening effects in calculations may cause an apparent cosine-shaped bending of the Cu-O bond-stretching dispersion along both the ($q$ 0 0) and ($q$ $q$ 0) directions, which is not observed on the data close to optimal doping. This observation suggests that the discrepancy between experimental data and ab initio calculations on this mode originates from an overestimation of the doping effects on the mode.

Magnetic tunnel junctions of perpendicularly magnetized L10-MnGa/Fe/MgO/CoFe structures: Fe-layer-thickness dependences of magnetoresistance effect and tunnelling conductance spectra

The tunnel magnetoresistance (TMR) effect and the bias voltage dependence of tunnelling conductance spectra were measured in L10 Mn-Ga/Fe/MgO/CoFe magnetic tunnel junctions (MTJs). The TMR ratio and bias-voltage dependences on annealing conditions and Fe-layer thickness were investigated. The TMR ratio showed an increase subsequent to Fe-layer deposition under the optimum annealing condition, and a maximum value of 24% was achieved in an MTJ with a perpendicularly magnetized Fe layer of thickness of 1.1 nm at room temperature; this corresponded to a 57% TMR ratio in the case of completely antiparallel magnetization configuration. In the tunnelling conductance spectra, an anomalous dip, the so-called zero-bias anomaly, was observed for all the samples. The zero-bias anomaly is speculated to have appeared because of an increase in magnon excitation at the magnetic layer/barrier interfaces according to the model by Zhang et al (1997 Phys. Rev. Lett. 79 3744). In our experiments magnitude of the zero-bias anomaly depended on both the annealing condition and the Fe-layer thickness. We discuss our observation of the variation in the Curie temperature of the magnetic layer at the barrier layer interface depending on the the preparation conditions of the Fe insertion layer, which caused the change in the magnitude of the zero-bias anomaly.

Anomalous dip observed in intensity autocorrelation function as an inherent nature of single-photon emitters

We report the observation of an anomalous antibunching dip in intensity autocorrelation function with photon correlation measurements on a single-photon emitter (SPE). We show that the anomalous dip observed is a manifestation of quantum nature of SPEs. Taking population dynamics in a quantum two-level system into account correctly, we redefine intensity autocorrelation function. This is of primary importance for precisely evaluating the lowest-level probability of multiphoton generation in SPEs toward realizing versatile pure SPEs for quantum information and communication.

Crustal deformation of the Andean foreland at 31° 30′S (Argentina) constrained by magnetotelluric survey

Twenty-five new long-period magnetotelluric sites near 31.5°S were collected in a west–east profile. This profile and the previous one, aligned with and adjacent to the eastern end, have been merged to form a single profile of more than 700km long, extending from the Precordillera to the Chaco-Pampean Plain.The geotectonic scenario is characterized by a modern flat subduction zone of the Nazca plate located at a depth of around 120km and clearly defined by the distribution of earthquake hypocenters recorded by local and regional networks. A “bulge” shape at 68.5°W, with an anomalous dip to the west, is observed within this segment. The smooth slab deformation might result from the restriction on eastward motion due to the presence of an electrically resistive zone. The magnetotelluric model shows that this thick zone of increased resistivity is found from shallow crustal levels to upper mantle depths. The bulge geometry allows hot fluids and volatiles to rise from the deeper asthenospheric wedge, and reach the lower crust reducing its viscosity and letting it flow. The zones of low resistivity in the lower crust show spatial correlation with the areas of foreland deformation from Precordillera to the Sierras Pampeanas and may also suggest a ductile regime.Shear zones reactivated by Cenozoic faulting must necessarily have their roots in the levels of the ductile lower crust associated to conductive channels. The zone where the lower crust is closer to the surface coincides with the areas of greatest structural relief and erosion. The interface between the folded ductile lower crust and the brittle upper crust might act as the main level of décollement of the bordering structures between the Precordillera, Sierra de Pie de Palo and the Sierras Pampeanas. In addition, the geometry of the interface might be conditioning the vergence of those structures.

Fine features in the primordial power spectrum

A possible origin of the anomalous dip and bump in the primordial power spectrum, which are reconstructed from WMAP data corresponding to the multipole ℓ = 100 ∼ 140 by using the inversion method, is investigated as a consequence of modification of scalar field dynamics in the inflation era. Utilizing an analytic formula to handle higher order corrections to the slow-roll approximation, we evaluate the relation between a detailed shape of inflaton potential and a fine structure in the primordial power spectrum. We conclude that it is unlikely to generate the observed dip and bump in the power spectrum by adding realistic features in the inflaton potential. In order to generate the fine structure, we find that the slow-roll parameters have to become about \U0001d4aa(100) and the number of oscillations in the potential is about \U0001d4aa(102), on the scale of the structure.

As75NMR of Ba(Fe0.93Co0.07)2As2in high magnetic field

The superconducting state of an optimally doped single crystal of Ba(Fe$_{0.93}$Co$_{0.07}$)$_2$As$_2$ was investigated by $^{75}$As NMR in high magnetic fields from 6.4 T to 28 T. It was found that the Knight shift is least affected by vortex supercurrents in high magnetic fields, $H>11$ T, revealing slow, possibly higher order than linear, increase with temperature at $T \lesssim 0.5 \, T_c$, with $T_c \approx 23 \, K$. This is consistent with the extended s-wave state with $A_{1g}$ symmetry but the precise details of the gap structure are harder to resolve. Measurements of the NMR spin-spin relaxation time, $T_2$, indicate a strong indirect exchange interaction at all temperatures. Below the superconducting transition temperature vortex dynamics lead to an anomalous dip in $T_2$ at the vortex freezing transition from which we obtain the vortex phase diagram up to $H = 28$ T.

Anomalous reflection properties in high density limit fibril shaped PIC‐J aggregates in microcavity structure

AbstractWe report our recent observations on anomalous reflection properties of organic microcavity containing PIC J‐aggregates in fibril‐shaped structures as one of their highest‐density limiting case. Even in ordinary low density PIC‐Js dispersed in polymer matrices, they easily go into the exciton‐photon strong coupling regime and new quantum states, i.e. exciton‐polaritons, are formed. Vacuum Rabi‐splitting, an indicator of the coupling strength, can be controlled by the density of PIC‐Js in the microcavities in low density regime. Fibril‐shaped PIC‐J aggregates are bundle‐like, self‐assembled higher‐order structure of Js and are considered as a high‐density limiting case. Angular dependence of the local reflection spectra are observed by our improved microscopy. While in the low density cases, clear anti‐crossing behaviours of the two branches appear, which is the evidence of the polariton formations, the highest‐density limiting cases show one or two anomalous reflection dip structures with almost no angular dependence. The result is inconsistent with neither ordinary polariton reflection property nor bare exciton nor cavity photon properties. We tentatively consider that the anomaly is inherent to the fibril formation and is caused by possible breakdown of polariton coherence due to the inter‐fiber energy transfer. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)