Temperature-dependent Measurements Research Articles

Possible Superconductivity Transition in Nitrogen-Doped Lutetium Hydride Observed at Megabar Pressure.

The pursuit of room-temperature superconductivity at an accessible synthetic pressure has been a long-held dream for both theoretical and experimental physicists. Recently, a controversial report by Dasenbrock-Gammon et al. claims that the nitrogen-doped lutetium trihydride exhibits room-temperature superconductivity at near-ambient pressure. However, many researchers have failed to independently reproduce these results, which has sparked intense skepticism on this report. In this work, a LuH2±xNy sample is fabricated using high-pressure and high-temperature methods. The composition and structural characterization are the same as the aforementioned near-ambient superconductor. In situ X-ray diffraction investigations indicate that a high-pressure phase transition toward Fm m-LuH3±xNy occurred in the sample at 59GPa. The temperature-dependent resistance measurements reveal that two possible superconductivity transition are observed at 95GPa, with Tc1 ≈6.5 K for high-Tc phase and Tc2 ≈2.1 K for low-Tc phase, arising from the disparate phases in the sample. Resistivity measurements in the Fm m-LuH3±xNy phase under varying magnetic fields exhibited characteristics consistent with superconductivity, with an upper critical field μ0Hc2(0) of 3.3 T measured at 163GPa. This work is expected to shed some light on the controversy surrounding superconductivity in the nitrogen-doped lutetium hydride system.

Correlating Ionic Conductivity to Structure and Dynamics of Li-Ion Battery Electrolyte Systems: Raman Spectroscopy, Dielectric Relaxation Measurements, and Streak Camera Solvation Data Analysis.

A correlation between ionic conductivity and electrolyte solution structure and dynamics was explored by performing electrolyte concentration- and temperature-dependent measurements of conductivity, viscosity, and dielectric relaxation (DR) in solutions of lithium bis(trifluoromethane)sulfonimide (LiTFSI) in triethylene glycol dimethyl ether (also known as triglyme, G3). In addition, an electrolyte concentration-dependent Raman spectroscopic study and ultrafast dynamic fluorescence Stokes shift measurements of solvation of a dissolved solute by employing a streak camera detection technique were carried out. Measured conductivities (σ) and the average DR times (⟨τDR⟩) were found to be partially decoupled from the solution viscosities (η) and obeyed the relation, σ or ⟨τDR⟩-1 ∝(η/T)-p, with p = 0.6-0.75 for σ and p = 0.2-0.45 for ⟨τDR⟩-1. Raman data indicated the formation of ion pairs and ionic aggregates in these solutions, while the measured glass transition temperature increased with LiTFSI concentration. Conductivities (σ) showed a nonlinear concentration dependence but increased linearly with the solution static dielectric constants (εs). The latter may be explained by considering the temperature effects on complex electrolyte species and the subsequent solution dielectric behavior. Interestingly, an inverse power-law dependence of σ on the measured DR or solvation time scales, σ ∝ (τx)-m, with m = 1.2-1.9, was observed. This dependence may be explained by considering that the same environmental friction regulates both the ion diffusion and the medium polarization relaxation. The control of a slow process (ion translation) by relatively faster medium dynamics (dipolar rotation), although quite fascinating for the present system, warrants further experimental scrutiny for other electrolyte systems relevant to battery applications.

Diagnosing the Charge Dynamic Behaviors in Quantum-Dot Light-Emitting Diodes by Temperature-Dependent Measurements.

Distinguishing and understanding the nonradiative recombination of charges are crucial for optimizing quantum-dot light-emitting diodes (QLEDs). Auger recombination (AR), a well-known nonradiative process, is widely recognized to occur in QLEDs. However, it has not yet been directly observed in a real working QLED. Here, the AR effect is verified in the QLED at temperatures of <150 K. At low temperatures, the QLED exhibits a unique S-shaped external quantum efficiency (EQE) evolution as the driving current density increases. Experimental and modeling results indicate that this S-shaped EQE results from the asynchronous changes in the behavior of injection of electrons and holes into the quantum-dot emission layer. At low driving voltages, both electron and hole currents are limited by the Fowler-Nordheim (F-N) tunneling behavior. The relatively low barrier for electrons leads to overwhelming electron injection and seriously imbalanced charges in the quantum dots, triggering the AR process. As the voltage increases, the electron current within the emission layer is no longer governed by F-N tunneling but limited by space charges. Then, charge injection becomes balanced, and the EQE increases. These results offer valuable insights into the charge injection and recombination processes within QLEDs, as well as implications for device design.

Europium spin dilution in the ferromagnetic solid solution Eu4–x Ca x PdMg

Abstract The intermetallic compounds Eu4PdMg and Ca4PdMg form a complete solid solution Eu4–x Ca x PdMg. Further phase analytical studies showed that Eu4PdMg does not allow substitution with strontium. The polycrystalline Eu4–x Ca x PdMg samples were characterized by powder X-ray diffraction. The structure of Eu2.233(6)Ca1.767PdMg was refined from single crystal X-ray diffractometer data: Gd4RhIn type, F 4 ‾ 3m, a = 1,475.42(10) pm, wR2 = 0.0476, 674 F 2 values, 23 variables. Temperature dependent magnetic susceptibility measurements show a drastic decrease of the Curie temperature with increasing calcium substitution. 151Eu Mössbauer spectra of Eu4PdMg and Eu2Ca2PdMg confirm the divalent ground state of europium.

PTHF/LATP Composite Polymer Electrolyte for Solid State Batteries.

The novel crosslinked composite polymer electrolyte (CPE) was developed and investigated using polytetrahydrofuran (PTHF) and polyethyleneglycol diacrylate (PEGDA), incorporating lithium aluminum titanium phosphate (LATP) particles and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. Composite polymer electrolytes (CPEs) for solid-state lithium-ion batteries (LIBs) were synthesized by harnessing the synergistic effects of PTHF crosslinking and the addition of LATP ceramics, while systematically varying the film composition and LATP content. CPEs containing 15 wt% LATP (PPL15) demonstrated improved mechanical strength and electrochemical stability, achieving a high conductivity of 1.16 × 10-5 S·cm-1 at 80 °C, outperforming conventional PEO-based polymer electrolytes. The CPE system effectively addresses safety concerns and mitigates the rapid degradation typically associated with polyether electrolytes. The incorporation of PEGDA not only enhances mechanical stability but also facilitates lithium salt dissociation and ion transport, leading to a uniform microstructure free from agglomerated particles. The temperature-dependent ionic conductivity measurements indicated optimal performance at lower LATP concentrations, highlighting the impact of ceramic particle agglomeration onion transport pathways. These findings contribute to advancing solid-state battery systems toward practical application.

Increased Formation of Trions and Charged Biexcitons by Above-Gap Excitation in Single-layer WSe2.

Two-dimensional semiconductors exhibit pronounced many-body effects and intense optical responses due to strong Coulombic interactions. Consequently, subtle differences in photoexcitation conditions can strongly influence how the material dissipates energy during thermalization. Here, using multiple excitation spectroscopies, we show that a distinct thermalization pathway emerges at elevated excitation energies, enhancing the formation of trions and charged biexcitons in single-layer WSe2 by up to 2× and 5× , respectively. Power- and temperature-dependent measurements lend insights into the origin of the enhancement. These observations underscore the complexity of excited state relaxation in monolayer semiconductors, provide insights for the continued development of carrier thermalization models, and highlight the potential to precisely control excitonic yields and probe nonequilibrium dynamics in 2D semiconductors.

Colossal Strain Tuning of Ferroelectric Transitions in KNbO3 Thin Films.

Strong coupling between polarization (P) and strain (ɛ) in ferroelectric complex oxides offers unique opportunities to dramatically tune their properties. Here colossal strain tuning of ferroelectricity in epitaxial KNbO3 thin films grown by sub-oxide molecular beam epitaxy is demonstrated. While bulk KNbO3 exhibits three ferroelectric transitions and a Curie temperature (Tc) of ≈676K, phase-field modeling predicts that a biaxial strain of as little as -0.6% pushes its Tc >975K, its decomposition temperature in air, and for -1.4% strain, to Tc >1325K, its melting point. Furthermore, a strain of -1.5% can stabilize a single phase throughout the entire temperature range of its stability. A combination of temperature-dependent second harmonic generation measurements, synchrotron-based X-ray reciprocal space mapping, ferroelectric measurements, and transmission electron microscopy reveal a single tetragonal phase from 10 K to 975K, an enhancement of ≈46% in the tetragonal phase remanent polarization (Pr),and a ≈200% enhancementin its optical second harmonic generation coefficients over bulk values. These properties in a lead-free system, but with properties comparable or superior to lead-based systems, make it an attractive candidate for applications ranging from high-temperature ferroelectric memory to cryogenic temperature quantum computing.

Vanadate Inclusion Leading to Red-Ox-Rich Zircon PrCrO4: Synthesis, Magnetic, and Catalytic Properties.

Rare-earth-based ternary compounds with the formula REBO4 (B = V, Cr, P, As) exhibit rich structural chemistry and associated technologically significant properties. Among the rare-earth chromates, realizing PrCrO4 in a single polymorphic modification has been challenging. Herein, we report the successful stabilization of the zircon polymorph of PrCrO4 by introducing 10 mol % of VO43- instead of CrO43- following a solution combustion method. Compositions with progressively higher amounts of vanadate have been synthesized and characterized extensively. XPS analysis of 10 and 50 mol % VO43- substituted PrCrO4 samples ascertained the existence of Pr3+/4+, Cr4+,5+, and V5+ in them, making it a red-ox-rich system. The tetragonal symmetry of PrCr0.50V0.50O4 was confirmed from the HRTEM images and SAED patterns. FTIR and Raman spectral analyses indicated distorted tetrahedral (Cr/VO4) units with a local site symmetry below D2d. Both d-d and f-f transitions of Cr4+ and Pr3+, respectively, were observed in the absorption spectra. Field and temperature-dependent magnetic measurements of PrCr0.50V0.50O4 confirmed its predominant paramagnetic behavior. The samples possessed porous morphology with a reasonable surface area. PrCr1-xVxO4 (x = 0.00-0.50) samples catalyzed the oxidation of phenol. This study demonstrated B-site tuning in ABO4 systems to select a desired polymorph preferentially.

Peierls Distortion Induced Giant Linear Dichroism, Second-Harmonic Generation, and In-Plane Ferroelectricity in NbOBr2.

The Peierls distortion plays an essential role in governing the in-plane ferroelectricity and nonlinear optical characteristics of anisotropic niobium oxide dihalides, such as NbOCl2 and NbOI2. Despite its significance, experimental investigation into the structural, optical, and ferroelectric properties of NbOBr2 has been lacking. Here, the successful fabrication of centimeter-sized, high-quality NbOBr2 single crystals, enabling direct observation of Peierls distortion using aberration-corrected scanning transmission electron microscopy, is reported. Notably, the magnitude of Peierls distortion in NbOBr2 falls between that observed in NbOCl2 and NbOI2. Furthermore, the existence of giant linear dichroism absorption and second-harmonic generation (SHG) phenomena associated with Peierls distortion is confirmed. Exfoliated NbOBr2 flakes exhibit single-domain ferroelectricity, with the polarization switchable by an electric field. Temperature-dependent SHG measurements reveal a Curie temperature of ≈502K for ferroelectric NbOBr2. This work demonstrates that NbOBr2 holds promise for polarized nonlinear optical devices, as well as for nonvolatile information processing and storage devices.

Enhancement of superconducting properties of grown FeTe0.65Se0.35 single crystals through air annealing

Abstract This work investigates the annealing effects on the superconducting properties of FeTe0.65Se0.35 single crystals. We examine the impact of varying annealing times on the magnetotransport, magnetic, and vortex pinning properties of the single crystals. The structural analysis shows the single crystalline growth of crystals along the c-axis. X-ray photoelectron spectroscopy results confirm the presence of iron oxides in the annealed samples. Temperature-dependent resistivity and magnetization measurements confirm the superconductivity in the as-grown and annealed samples. However, the as-grown sample shows a broad superconducting transition and low superconducting volume fraction, but after annealing, significant improvement in both is observed. Moreover, the self-field critical current density at 2 K is enhanced by a factor of ~4.5 for the optimally annealed sample compared to the as-grown sample. Experimental observations have been analyzed with the theoretical models to understand the effects of annealing on the vortex pinning mechanisms. Further, the specific heat study confirms the bulk superconductivity in the annealed sample compared to the as-grown single crystal. Overall, our study indicates that the superconducting properties vary with the annealing time, and the best results are obtained at an optimum annealing time.

Uncovering upconversion photoluminescence in layered PbI2 above room temperature.

As a van der Waals (vdW) layered semiconductor material, lead iodide (PbI2) possessing a direct bandgap with strong photoluminescence emission in visible range has gained wide attention in applications of photonic and optoelectronic devices. Here, upconversion photoluminescence (UPL) in exfoliated PbI2 flakes is demonstrated at room temperature and elevated temperatures. The linear power dependence of UPL emission with 532nm excitation suggests the one-photon involved multiphonon-assisted UPL emission process, which is revealed by the temperature-dependent UPL emission measurement. Meanwhile, the nonlinear power dependence of UPL emission with 561nm excitation indicates the transition of UPL emission mechanism from linear to nonlinear regime, and the temperature-dependent UPL emission study further shows that the upconversion is contributed by both the multiphonon-assisted UPL process and the two-photon absorption induced PL process. This study will provide an insight to the understanding of photon upconversion in vdW layered semiconductors and advancing applications in temperature-controlled photon upconversion, tunable photonics, photodetection and imaging.

Top-down approach for the preparation of Au/ZnO nanostructures by glancing-angle ion irradiation: Morphological, structural and optical studies

We report the 100 keV glancing-angle Xe+ ions irradiation based top down approach for the preparation of ZnO and Au/ZnO hybrid nanostructures and its morphological, structural and optical properties. FESEM micrographs reveal Xe+ ion irradiation favours the nucleation and formation of highly aligned, dense nanostrips like structures. Crystalline structure of ZnO, Xe+ ions irradiated ZnO and Au/ZnO hybrid nanostructures were analysed by grazing incident X-ray diffraction and Raman scattering measurements. The elemental compositions and thickness of the grown nanostructures were estimated using Rutherford backscattering spectrometry analysis. The influence of Xe+ ion irradiation on the photoluminescence (PL) behaviour of ZnO and Au/ZnO hybrid nanostructures were studied in detail using temperature dependent PL measurements in the range of 80–298 K. Strong PL emission associated with free excitons (FX) and its longitudinal optical phonon replicas observed in ion irradiated Au/ZnO hybrid nanostructures clearly reveal the strong coupling of the localized surface plasmons in the Au nanoparticles to the FX in ZnO. Our experimental results reveal ion beam irradiation is one of the effective approaches to tailor the optical properties of ZnO and Au/ZnO hybrid nanostructures.

Detection of antiferromagnetic order in a RuO2/Pt bilayer by spin Hall magnetoresistance

Altermagnets have spin-split band structures that correspond to the rotational symmetry of the two sublattices in real space. Theoretically, their unique band structures are expected to exhibit intriguing transport phenomena, depending on their magnetic structures. Anomalous Hall effect (AHE) measurement is a method by which to electrically detect magnetic structure and has been reported for typical altermagnets, such as RuO2 and MnTe. However, AHE measurements are limited to specific cases. Thus, it is important to apply other methods by which to determine functionality based on magnetic structure. In this study, we report the spin Hall magnetoresistance (SMR) in a RuO2 (1 nm)/Pt (10 nm) system. A negative SMR signal is clearly observed, indicating the spin-flop antiferromagnetic structure of RuO2. Interestingly, a negative SMR was observed, even at 1 T, which is much smaller than the estimated spin-flop field reported in a previous study. This reflects the thinner film of RuO2 in our study, suggesting that thickness control is effective in adjusting the magnetic anisotropy of RuO2. In addition, the temperature-dependent SMR measurement revealed the Néel temperature of 1 nm thick RuO2 to be 70 ± 9 K. Our results show that SMR measurement can serve as an efficient tool to explore the magnetic features in an altermagnet.

Dynamics of Photoinduced Charge Carriers in Metal-Halide Perovskites.

The measurement and description of the charge-carrier lifetime (τc) is crucial for the wide-ranging applications of lead-halide perovskites. We present time-resolved microwave-detected photoconductivity decay (TRMCD) measurements and a detailed analysis of the possible recombination mechanisms including trap-assisted, radiative, and Auger recombination. We prove that performing injection-dependent measurement is crucial in identifying the recombination mechanism. We present temperature and injection level dependent measurements in CsPbBr3, which is the most common inorganic lead-halide perovskite. In this material, we observe the dominance of charge-carrier trapping, which results in ultra-long charge-carrier lifetimes. Although charge trapping can limit the effectiveness of materials in photovoltaic applications, it also offers significant advantages for various alternative uses, including delayed and persistent photodetection, charge-trap memory, afterglow light-emitting diodes, quantum information storage, and photocatalytic activity.

High temperature thermoelectric properties of BaxSr2−xFeCoO6 double perovskites

Abstract In this study, environmentally benign BaxSr2-xFeCoO6 (BSFC) double perovskites are synthesized via solid-state reaction route for high-temperature thermoelectric applications. The crystal structure and morphology of the ceramic samples are analyzed using XRD and SEM, respectively. Rietveld refinement of XRD data confirms a cubic structure with Pm3̅m space-group. High-temperature thermoelectric measurements exhibits that substituting Ba for Sr in Sr2FeCoO6 increases the Seebeck coefficient (S) but at the expense of the electrical conductivity (σ). The highest Seebeck coefficient of 117 μV/K has been observed in Ba0.5Sr1.5FeCoO6 at 910 K. Temperature-dependent electrical conductivity measurements indicates a semiconductor-to-metal like transition in all samples, with BSFC (x = 0.1) achieving the highest conductivity of 4 × 104 S m−1 at ∼623 K. The thermoelectric power factor has been enhanced by over 50% with Ba substitution in Sr2FeCoO6. Electron transport in these double perovskites is found to follow the small polaron hopping conduction mechanism.

Is Native Mass Spectrometry in Ammonium Acetate Really Native? Protein Stability Differences in Biochemically Relevant Salt Solutions.

Ammonium acetate is widely used in native mass spectrometry to provide adequate ionic strength without adducting to protein ions, but different ions can preferentially stabilize or destabilize the native form of proteins in solution. The stability of bovine serum albumin (BSA) was investigated in 50 mM solutions of a variety of salts using electrospray emitters with submicron tips to desalt protein ions. The charge-state distribution of BSA is narrow (+14 to +18) in ammonium acetate (AmmAc), whereas it is much broader (+13 to +42) in solutions containing sodium acetate (NaAc), ammonium chloride (AmmCl), potassium chloride (KCl), and sodium chloride (NaCl). The average charge state and percent of unfolded protein increase in these respective solutions, indicating greater extents of protein destabilization and conformational changes. In contrast, no high charge states of either bovine carbonic anhydrase II or IgG1 were formed in AmmAc or NaCl despite their similar melting temperatures to BSA, indicating that the presence of unfolded BSA in some of these solutions is not an artifact of the electrospray ionization process. The charge states formed from the nonvolatile salt solutions do not change significantly for up to 7 min of electrospray, but higher charging occurs after 10 min, consistent with solution acidification. Formation of unfolded BSA in NaAc but not in AmmAc indicates that the cation identity, not acidification, is responsible for structural differences in these two solutions. Temperature-dependent measurements show both increased charging and aggregation at lower temperatures in NaCl:Tris than in AmmAc, consistent with lower protein stability in the former solution. These results are consistent with the order of these ions in the Hofmeister series and indicate that data on protein stability in AmmAc may not be representative of solutions containing nonvolatile salts that are directly relevant to biology.

Crystalline electric field excitations and their nonlinear splitting under magnetic fields in YbOCl

Recently reported van der Waals layered honeycomb rare-earth chalcohalides REChX (RE = rare earth, Ch = chalcogen, and X = halogen) are considered to be promising Kitaev spin liquid (KSL) candidates. The high-quality single crystals of YbOCl, a representative member of the family with an effective spin of 1/2, are available now. The crystalline electric field (CEF) excitations in a rare-earth spin system are fundamentally important for understanding both finite-temperature and ground-state magnetism but remain unexplored in YbOCl so far. In this paper, we conduct a comprehensive Raman scattering study to unambiguously identify the CEF excitations in YbOCl and determine the CEF parameters and wave functions. Our Raman experiments further reveal the anomalous nonlinear CEF splitting under magnetic fields. We have grown single crystals of YbOCl, the nonmagnetic LuOCl, and the diluted magnetic Lu0.86Yb0.14OCl to make a completely comparative investigation. Polarized Raman spectra on the samples at 1.8 K allow us to clearly assign all the Raman-active phonon modes and explicitly identify the CEF excitations in YbOCl. The CEF excitations are further examined using temperature-dependent Raman measurements and careful symmetry analysis based on Raman tensors related to CEF excitations. By applying the CEF Hamiltonian to the experimentally determined CEF excitations, we extract the CEF parameters and eventually determine the CEF wave functions. The study experimentally pins down the CEF excitations in the Kitaev compound YbOCl and sets a foundation for understanding its finite-temperature magnetism and exploring the possible nontrivial spin ground state. Published by the American Physical Society 2024

The Extraction of the Density of States of Atomic-Layer-Deposited ZnO Transistors by Analyzing Gate-Dependent Field-Effect Mobility

In this study, we investigated the density of states extraction method for atomic-deposited ZnO thin-film transistors (TFTs) by analyzing gate-dependent field-effect mobility. The atomic layer deposition (ALD) method offers ultra-thin and smooth ZnO films, but these films suffer from interface and semiconductor defects, which lead to disordered localized electronic structures. Hence, to investigate the unstable localized structure of ZnO TFTs, we tried to derive the electronic state relationship by assuming field-effect mobility can be expressed as a gate-dependent Arrhenius relation, and the activation energy in the relation is the required energy for hopping. Following this derived relationship, the DOS of the atomic-deposited ZnO transistor was extracted and found to be consistent with those using temperature-dependent measurements. Moreover, to ensure the proposed method is reliable, we applied methods for the extraction of DOSs of doped ZnO transistors, which show enhanced mobilities with shifted threshold voltages, and the results show that the extraction method is reliable. Thus, we can state that the mobility-based DOS extraction method offers practical benefits for estimating the density of states of disordered transistors using a single transfer characteristic of these devices.

Structure and Magnetic Properties of the n = 3 Ruddlesden-Popper Oxyfluoride La0.5Sr3.5Fe3O7.5F2.6.

Ruddlesden-Popper (RP) compounds of the general formula (AX)(ABX3)n with their unique sequence of perovskite-like (ABX3) and rock-salt-like units (AX) promise applications in diverse fields such as catalysis and superconductivity. Fluorination of RP oxides often leads to dramatic changes in the material properties, caused by differences in the atomic and electronic structure. While current research focuses on fluorination of n = 1 type RP oxides (A2BO4), n = 3 RP oxyfluorides have remained elusive. We present the synthesis of the first iron-based n = 3 RP oxyfluoride, La0.5Sr3.5Fe3O7.5F2.6, which was obtained from an oxide precursor by topochemical fluorination with poly(vinylidene fluoride). Joint Rietveld refinements of neutron and powder X-ray diffraction data were used to determine the crystal structure. Best results were obtained in the space group Pbca (No. 61) with a = 5.5374(1) Å, b = 5.5441(1) Å, and c = 29.2541(2) Å. The effect of the aliovalent incorporation of fluoride ions is particularly evident with respect to changes in structure and magnetic properties. The magnetic behavior was studied using field- and temperature-dependent magnetization measurements, Mößbauer spectroscopy, and neutron diffraction. Additional magnetic Bragg reflections observed in the room-temperature neutron data were successfully refined in the space group Pbca (61.1.497 in Opechowski-Guccione notation), indicating a G-type antiferromagnetic ordering with a surprisingly high Néel temperature above 300 K. This strong increase of TN by several hundred Kelvin compared to the parent oxide is particularly remarkable.

Electrical properties of completely compensated single-crystal Ge-on-GaAs films with two-dimension Coulomb disorder

We present electrical properties of heavily doped and completely compensated Ge films grown on semiinsulating GaAs(100) substrates by vacuum evaporation. The thin (∼100 nm) Ge films are single-crystal and characterized using temperature-dependent transport measurements, with anomalously large activation energy up to half the Ge bandgap, anisotropy of the transverse magnetoresistance, high resistivity (up to 140 Ω cm), low free charge carrier mobility (∼50 cm2/V·s), and concentration (∼1014–1015 cm−3). This behaviour is attributed to a completely compensated semiconductors arising from Ga and As impurity incorporation and large-scale potential fluctuations. Analysis suggests a two-dimensional percolative transport mechanism in Ge-on-GaAs heterostructures.