Weak Electron Localization Research Articles

Pseudosymmetry in Tetragonal Perovskite SrIrO3 Synthesized under High Pressure.

In this study, we report a tetragonal perovskite structure of SrIrO3 (P4/mmm, a = 3.9362(9) Å, c = 7.880(3) Å) synthesized at 6 GPa and 1400 °C, employing the ambient pressure monoclinic SrIrO3 with distorted 6H structure as a precursor. The crystal structure of tetragonal SrIrO3 was evaluated on the basis of single-crystal and powder X-ray diffraction. A cubic indexing was observed, which was attributed to overlooked superlattice reflections. Weak fractional peaks in the H and K dimensions suggest possible structure modulation by oxygen defects. Magnetization study reveals weak paramagnetic behavior down to 2 K, indicative of the interplay between spin-orbit coupling, electron correlations, and the crystal electric field. Additionally, measurements of electrical resistivity display metallic behavior with an upturn at about 54 K, which is ascribed to weak electron localization and possible structural defects.

The enhanced antiferromagnetic interaction and tunable temperature coefficient of resistivity in antiperovskite compounds Mn3−xCoxAgN (0≤x≤0.2)

The magnetic and electric evolution with the substitution level of Co element has been investigated in Mn[Formula: see text]CoxAgN. The DC magnetic measurements demonstrate that the substitution of Co for Mn enhances the antiferromagnetic (AFM) interaction and weakens the magnetic irreversibility at low temperature. The strengthening of AFM order in Mn[Formula: see text]CoxAgN has been attributed to the enhanced Co–Mn AFM interaction and weakened Co–N–Mn ferromagnetic (FM) interaction. Additionally, with the gradual increase of Co content, the temperature coefficient of resistivity (TCR) in paramagnetic (PM) region changes from a positive one to a negative one gradually. When [Formula: see text], the TCR value is only [Formula: see text]5[Formula: see text]ppm/K, which is one magnitude smaller than that of conventional standard resistor materials. The negative TCR phenomenon is closely associated with the Co-element-induced lattice disorder, which leads to the weak localization of conduction electrons.

Time-domain interferometry of electron weak localization through terahertz nonlinear response

We study theoretically the nonlinear optical response of disordered electrons in the regime of weak (anti)localization. Our analytical and numerical calculations reveal that in orthogonal/symplectic class systems, two consecutive, phase-coherent optical pulses generate an electric current echo that appears after the second pulse, and at a time equal to the pulse delay time. The current echo reflects the quantum interference between a self-intersecting electron path and its time-reversal partner, and, therefore, provides a time-domain interferometry of weak (anti)localization. Our results can be potentially tested on disordered metal films by using terahertz two-dimensional coherent spectroscopy or ultrafast transport measurements. Published by the American Physical Society 2024

High-order cavity coupled plasmon polaritons in resonant cavity-monolayer MoS<sub>2</sub> system

Compared with graphene, two-dimensional (2D) transition metal sulfides, represented by mono-/few-layer MoS<sub>2</sub>, have tunable non-zero bandgap, and thus their applications in optoelectronic devices are more advantageous. By using classical electromagnetic theory and finite element method (FEM), we investigate the cavity coupled plasmon polaritons (CCPPs) formed through the coupling between cavity modes in a resonator and plasmons in monolayer MoS<sub>2</sub>, particularly calculate and verify the properties of the high-order CCPPs. In previous work, it was demonstrated that the substrates, defects, and polycrystalline grains of the CVD grown monolayer MoS<sub>2</sub> usually induce weak electron localization, which leads to the deviation from the Drude model based on the approximation of free electron gas. Therefore, here we use the Drude-Smith model with characteristic parameters obtained experimentally to describe the optical conductivity of monolayer MoS<sub>2</sub> in our theoretical calculation and simulation. Then, we not only derive and solve the dispersion equations of the high-order CCPPs, but also verify the existence and analyze the properties of these high-order modes. Specifically, there are three types of CCPPs in the asymmetric cavity-monolayer MoS<sub>2</sub> system, i.e. the FP-like-modes (FPLMs), the surface-plasmon-like modes (SPLMs), and the quasi-localized modes (QLMs). Among them, the FPLMs and QLMs can support high-order modes whereas the SPLMs only support the fundamental modes. According to our model, we calculate the wave localization properties for the 7th-order and 8th-order FPLM, the 3rd-order and 6th-order QLM, and the SPLM. These theoretical results are in good agreement with the simulation results. Moreover, the effects of weak electron localization are also shown by comparing the field distributions of the CCPPs based on the Drude model with those based on the Drude-Smith model. It is found that weak electron localization can reduce the coupling between the cavity modes and the plasmons in monolayer MoS<sub>2</sub>. These results can deepen our understanding of the excitation of plasmons in 2D materials as well as the modulation of their properties. Furthermore, the theoretical model can also be extended to other plasmonic systems related to low-dimensional and topological quantum materials.

Nature of anomalous electrical resistance in Co73-xFe4CrxSi12B11 amorphous microwires

Influence of structural relaxation and composition of microwires of metallic amorphous alloys Co73-xFe4CrxSi12B11 (x = 0, 2, 4, 6, 8) on the character and mechanisms of temperature dependence of electrical resistance r(T) has been studied in a wide temperature range (from 4.2 K to crystallization temperature). It is shown that alloys with more than 2 at.% Cr have a number of specific properties, which are significantly differentiate them from Fe- and Ni-rich alloys, as well as many Co-rich amorphous alloys. The features of Cr-doped Co-rich alloys are explained by two reasons: firstly, very strong quantum interference effects of the electron-electron interaction and weak localization of electrons caused by scattering of electrons by the potential created by randomly distributed chromium atoms, and secondly, partially reversible compositional structural relaxation leading to clustering of the amorphous phase at T > 300 °C. It is assumed that the resulting Cr-rich clusters, in which chromium atoms are bonded to metalloid atoms, can enhance these interference effects. The contributions from various mechanisms of interaction and scattering of electrons to the change in electrical resistance with temperature and composition of the alloy are analyzed. The fitting parameters for them are determined and compared with the known data.

Structural deterioration of calcium aluminosilicate hydrate by sulfate attack: Atomic processes of Al-Si chain breaking

Calcium-aluminosilicate-hydrates (C-A-S-H) is the major hydration product of sustainable concrete that incorporates industrial waste as a partial substitute for cement. Although C-A-S-H is considered a durable material, it’s susceptible to sulfate attack. To better understand this phenomenon, the atomic process of sulfate attack on C-A-S-H was studied using semi-empirical quantum chemical methods. The results showed that sulfate attacks can be broken down into several subprocesses: adsorption, vibration, and breaking. The underlying causes of these processes were revealed through electronic structures, in which the weak AlO bond and strong electronegativity are the main factors leading to Al-Si breaking. The Atom in Molecular theory revealed that the weak electron localization of the [AlO4] tetrahedron leads to a lower water-assisted bond dissociated energy for breaking the AlO bond (18.3KJ/mol) than the SiO bond (109.4KJ/mol). This study provides valuable insights into the sulfate attack on C-A-S-H and its implications for improving the durability of sustainable concrete.

Weak Localization of Light in a Magneto-Active Medium

The interference contribution to the optical conductance (total transmittance) of a sample of a disordered Faraday medium is calculated. The suppression of wave interference in a magnetic field is shown to be due to helicity-flip scattering events. The magnetic field does not destroy the interference of waves with a given helicity, but suppresses it if the helicity changes along different parts of the wave trajectory. This leads to a decrease in the interference contribution to the conductance with increasing the magnetic field. A similar phenomenon, negative magnetoresistance, is known as a consequence of weak localization of electrons in metals with impurities. It is found that, as the magnetic field increases, the change in the interference correction to the optical conductance tends to a certain limiting value, which depends on the ratio of the transport mean free path to the helicity-flip scattering mean free path. We also discuss the possibility of controlling the transition to the regime of strong “Anderson” localization in the quasi-one-dimensional case by means of the field.

Tunable rapid electron transport in titanium oxide thin films

Rapid electron transport triggers many novel physical phenomena and becomes a critical point for high-speed electronics. Two-dimensional electron gas (2DEG) has drawn great attention due to its high electron mobility, and this has been observed in different materials, such as semiconductor, oxide interfaces, and 2D materials. In this paper, we report, for the first time, the existence and electrical manipulation of 2DEG in the Schottky quantum well, which was formed in the titanium oxide thin films. We take the asymmetry interface electron scattering effect into consideration when studying the electrical transport properties of our multilayer thin films. We found electrons would be transferred from the low-mobility semiconducting and metallic conductive channels to the high-mobility 2DEG conductive channel with an in-plane applied electric field. Therefore, electron concentration and mobility of the 2DEG formed in the Schottky quantum well could be tuned, and the nano-devices exhibited non-linear voltage–current curves. The differential resistivity of the nano-devices could decrease by two orders with increasing electric field at room temperature. Weak electron localization of electrons was experimentally observed in our nano-devices at low temperature, which further demonstrated the existence of 2DEG in the Schottky quantum well. Our work will provide us new physics about the rapid electron transport in the multilayer thin films and bring novel functional devices for the modern microelectronic industry.

Accurate Electron Drift Mobility Measurements in Moderately Dense Helium Gas at Several Temperatures

We report new accurate measurements of the drift mobility μ of quasifree electrons in moderately dense helium gas in the temperature range 26K≤T≤300K for densities lower than those at which states of electrons localized in bubbles appear. By heuristically including multiple-scattering effects into classical kinetic formulas, as previously done for neon and argon, an excellent description of the field E, density N, and temperature T dependence of μ is obtained. Moreover, the experimental evidence suggests that the strong decrease of the zero-field density-normalized mobility μ0N with increasing N from the low up to intermediate density regime is mainly due to weak localization of electrons caused by the intrinsic disorder of the system, whereas the further decrease of μ0N for even larger N is due to electron self-trapping in cavities. We suggest that a distinction between weakly localized and electron bubble states can be done by inspecting the behavior of μ0N as a function of N at intermediate densities.

Permutation Symmetry in Coherent Electrons Scattering by Disordered Media

A non-Anderson weak localization of an electron beam scattered from disordered matter is considered with respect to the principle of electron indistinguishability. A weak localization of electrons of a new type is essentially associated with inelastic processing. The origin of inelasticity is not essential. We take into account the identity principle for electron beam and electrons of the atom of the scatterer with an open shell. In spite of isotropic scattering by each individual scatterer, the electron exchange contribution has a hidden parameters effect on the resulting angular dependence of the scattering cross-section. In this case, the electrons of the open shell of an atomic scatterer can be in the s-state, that is, the atomic shell remains spherically symmetric. The methods of an invariant time-dependent exchange perturbation theory and a Green functions with exchange were applied. An additional angular dependence of the scattering cross-section appears during the coherent scattering process. It is shown exactly for the helium scatterer that the role of exchange effects in the case of a singlet is negligible, while for the triplet state, it is decisive, especially for those values of the energy of incident electrons when de Broglie’s waves are commensurate with the atomic.

Enhanced photocatalytic degradation of organic contaminants over CaFe2O4 under visible LED light irradiation mediated by peroxymonosulfate

A simple sol-gel approach is proposed herein to fabricate CaFe2O4 for the degradation of various organic pollutants (rhodamine B (RhB), tetracycline hydrochloride, humic acid, and methylene orange) under LED light irradiation mediated by peroxymonosulfate (PMS). The results indicate that the calcination temperature can significantly influence the performance of CaFe2O4 for PMS activation, and the CaFe2O4 sample obtained at 800 °C (CaFe2O4-800) exhibits the best efficiency in degrading RhB, which is much higher than that of Fe2O3-800. This can be attributed to the efficient separation of photogenerated electrons (e−) and holes (h+) by PMS, which is validated by transient photocurrent response and photoluminescence measurements. Results from density functional theory calculations indicate that the valence band of CaFe2O4-800 exhibits a high concentration of carriers and weak localization of electrons, which are favorable for PMS activation. Radical scavenging results confirm that h+ and O2•− are the dominant reactive species. Moreover, CaFe2O4-800 not only demonstrated a stable performance during eight cycling runs with negligible iron leaching but also exhibited excellent degradation efficiency under natural water and sunlight. Finally, the mechanism and pathway of RhB degradation by the CaFe2O4-800/PMS/LED system are also proposed. This work presents the enormous prospect of CaFe2O4 as an environmentally benign photocatalyst for PMS activation.

Weak localization competes with the quantum oscillations in a natural electronic superlattice: The case of Na1.5(PO2)4(WO3)20

We report an investigation of the combined structural and electronic properties of the bronze Na$_{1.5}$(PO$_{2}$)$_{4}$(WO$_{3}$)$_{20}$. Its low dimensional structure and possible large reconstruction of the Fermi surface due to charge density wave instability makes this bulk material a natural superlattice with a reduced number of carriers and Fermi energy. Signatures of multilayered 2D electron weak localization are consequently reported, with an enhanced influence of quantum oscillations. A crossover between these two antagonistic entities previously observed only in genuine low dimensional materials and devices, is shown to occur in a bulk crystal due to its hidden 2D nature.

Influence of Output Optical Losses on the Dynamic Characteristics of 1.55-μm Wafer-Fused Vertical-Cavity Surface-Emitting Lasers

The results of studying the dynamic characteristics of 1.55-μm single-mode vertical-cavity surface-emitting lasers (VCSELs) formed by the fusion of wafers of high-quality Bragg reflectors and an active region based on thin highly strained InGaAs/InAlGaAs quantum wells are presented. It is found that the proposed design of the active region and optical microcavity of the laser make it possible in principle to attain a high level of differential laser gain in the temperature range of 20°C–85°C, but weak electron localization leads to an increase in gain compression at elevated temperatures. Due to this fact, the VCSEL modulation bandwidth at 20°C can be increased from 9.2 to 11.5 GHz due to an increase in output optical losses, while the modulation bandwidth at 85°C does not exceed 8.5 GHz, depends weakly on the output optical losses, and is mainly limited by the optical-gain saturation.

Polyhydride CeH9 with an atomic-like hydrogen clathrate structure

Compression of hydrogen-rich hydrides has been proposed as an alternative way to attain the atomic metallic hydrogen state or high-temperature superconductors. However, it remains a challenge to get access to these states by synthesizing novel polyhydrides with unusually high hydrogen-to-metal ratios. Here we synthesize a series of cerium (Ce) polyhydrides by a direct reaction of Ce and H2 at high pressures. We discover that cerium polyhydride CeH9, formed above 100 GPa, presents a three-dimensional hydrogen network composed of clathrate H29 cages. The electron localization function together with band structure calculations elucidate the weak electron localization between H-H atoms and confirm its metallic character. By means of Ce atom doping, metallic hydrogen structure can be realized via the existence of CeH9. Particularly, Ce atoms play a positive role to stabilize the sublattice of hydrogen cages similar to the recently discovered near-room-temperature lanthanum hydride superconductors.

Влияние потерь на вывод излучения на динамические характеристики вертикально-излучающих лазеров спектрального диапазона 1.55 мкм, изготовленных методом спекания эпитаксиальных пластин

AbstractThe results of studying the dynamic characteristics of 1.55-μm single-mode vertical-cavity surface-emitting lasers (VCSELs) formed by the fusion of wafers of high-quality Bragg reflectors and an active region based on thin highly strained InGaAs/InAlGaAs quantum wells are presented. It is found that the proposed design of the active region and optical microcavity of the laser make it possible in principle to attain a high level of differential laser gain in the temperature range of 20°C–85°C, but weak electron localization leads to an increase in gain compression at elevated temperatures. Due to this fact, the VCSEL modulation bandwidth at 20°C can be increased from 9.2 to 11.5 GHz due to an increase in output optical losses, while the modulation bandwidth at 85°C does not exceed 8.5 GHz, depends weakly on the output optical losses, and is mainly limited by the optical-gain saturation.

Magnetic properties of disordered interacting electron system FeAl2-xGax (0 ≤ x ≤ 0.5): Origin of local moment behaviour and the stabilization of an antiferromagnetic phase by weak interplanar magnetic interaction

In this report, we have investigated the magnetic properties of the disordered interacting electron system FeAl2-xGax (0 ≤ x ≤ 0.5) through the measurements of dc magnetization, ac susceptibility and heat capacity, and constructed the magnetic phase diagram. This system shows an intriguing phenomenon in which an antiferromagnetic transition occurs concomitantly with a disorder-induced weak localization of electrons implying a cooperative nature of the disorder-induced effects and electron-electron interactions which is in contradiction to their established competitive nature. Our investigation reveals that, in addition to the antiferromagnetic transition at TN, a spin glass transition occurs at a lower temperature at Tg (Tg < TN). As the Ga concentration increases, TN increases while Tg decreases. The investigation reveals that the Fe-Fe antiferromagnetic interactions predominantly lie in a plane and the antiferromagnetic phase is stabilized by a weak interplanar Fe-Fe interaction. With increasing Ga concentration, this interplanar Fe-Fe distance decreases and results in the increase of the Néel temperature TN. Fe moments in this system are found to be partially localized due to the interplay between disorder and electron-electron interactions. Competing interactions between the finite spin clusters give rise to a cluster spin glass state at low temperatures.

Бимодальность в массивах гибридных квантово-размерных гетероструктур In-=SUB=-0.4-=/SUB=-Ga-=SUB=-0.6-=/SUB=-As, выращенных на подложках GaAs

AbstractHybrid quantum-confined heterostructures grown by metal-organic vapor-phase epitaxy (MOVPE) via the deposition of In_0.4Ga_0.6As layers with various nominal thicknesses onto vicinal GaAs substrates are studied by photoluminescence spectroscopy and transmission electron microscopy. The photoluminescence spectra of these structures show the superposition of two spectral lines, which is indicative of the bimodal distribution of the size and/or shape of light-emitting objects in an array. The dominant spectral line is attributed to the luminescence of hybrid “quantum well–dot” nanostructures in the form of a dense array of relatively small quantum dots (QDs) with weak electron and hole localization. The second, lower intensity line is attributed to luminescence from a less dense array of comparatively larger QDs. Analysis of the behavior of the spectral line intensities at various temperatures showed that the density of larger QDs grows with increasing thickness of the InGaAs layer.

Bimodality in Arrays of In0.4Ga0.6As Hybrid Quantum-Confined Heterostructures Grown on GaAs Substrates

Hybrid quantum-confined heterostructures grown by metal-organic vapor-phase epitaxy (MOVPE) via the deposition of In0.4Ga0.6As layers with various nominal thicknesses onto vicinal GaAs substrates are studied by photoluminescence spectroscopy and transmission electron microscopy. The photoluminescence spectra of these structures show the superposition of two spectral lines, which is indicative of the bimodal distribution of the size and/or shape of light-emitting objects in an array. The dominant spectral line is attributed to the luminescence of hybrid “quantum well–dot” nanostructures in the form of a dense array of relatively small quantum dots (QDs) with weak electron and hole localization. The second, lower intensity line is attributed to luminescence from a less dense array of comparatively larger QDs. Analysis of the behavior of the spectral line intensities at various temperatures showed that the density of larger QDs grows with increasing thickness of the InGaAs layer.

Pressure-Induced Metallization in Iron-Based Ladder Compounds Ba1−xCsxFe2Se3

Electrical resistivity measurements have been performed on the iron-based ladder compounds Ba$_{1-x}$Cs$_x$Fe$_2$Se$_3$ ($x$ = 0, 0.25, 0.65, and 1) under high pressure. A cubic anvil press was used up to 8.0 GPa, whereas further higher pressure was applied using a diamond anvil cell up to 30.0 GPa. Metallic behavior of the electrical conductivity was confirmed in the $x$ = 0.25 and 0.65 samples for pressures greater than 11.3 and 14.4 GPa, respectively, with the low-temperature $\log T$ upturn being consistent with weak localization of 2D electrons due to random potential. At pressures higher than 23.8 GPa, three-dimensional Fermi-liquid-like behavior was observed in the latter sample. No metallic conductivity was observed in the parent compounds BaFe$_2$Se$_3$ ($x $ = 0) up to 30.0 GPa and CsFe$_2$Se$_3$ ($x$ = 1) up to 17.0 GPa. The present results indicate that the origins of the insulating ground states in the parent and intermediate compounds are intrinsically different; the former is a Mott insulator, whereas the latter is an Anderson insulator owing to the random substitution of Cs for Ba.

Magneto-ballistic transport in GaN nanowires

The ballistic filtering property of nanoscale crosses was used to investigate the effect of perpendicular magnetic fields on the ballistic transport of electrons on wide band-gap GaN heterostructures. The straight scattering-less trajectory of electrons was modified by a perpendicular magnetic field which produced a strong non-linear behavior in the measured output voltage of the ballistic filters and allowed the observation of semi-classical and quantum effects, such as quenching of the Hall resistance and manifestation of the last plateau, in excellent agreement with the theoretical predictions. A large measured phase coherence length of 190 nm allowed the observation of universal quantum fluctuations and weak localization of electrons due to quantum interference up to ∼25 K. This work also reveals the prospect of wide band-gap GaN semiconductors as a platform for basic transport and quantum studies, whose properties allow the investigation of ballistic transport and quantum phenomena at much larger voltages and temperatures than in other semiconductors.