Brazilian Journal of Physics最新文献

Double perovskite halides exhibit remarkable properties that make them highly promising for applications in green energy technologies, such as solar energy harvesting and thermoelectric systems. This study comprehensively investigates the structural, mechanical, optoelectronic, and thermoelectric (TE) properties of K₂TlAlX₆ (where X = Cl, Br, I). The tolerance and octahedral factors have been evaluated to assess the stability of the cubic phase. At the same time, the formation energy has been computed to determine the thermodynamic stability of these perovskite materials. The elastic constants and modulus values have been calculated to evaluate the mechanical stability and hardness of the materials. The halides under study display ductile and anisotropic characteristics, indicating their potential for use in the fabrication of foldable technologies. Band structures and density of states show band gaps of 1.58 eV, 1.30 eV, and 0.87 eV for Cl, Br, and I ions-based double perovskites. The tuning of band gaps makes them applicable for diverse optical applications from solar cells to infrared sensors. The main electron transitions and recombination exist among the p states of halide ions and Al-p states. These materials demonstrate significant absorbance with minimal energy loss in the visible spectrum. The thermoelectric aspects show their large figure of merit (0.80, 0.77, 0.71) at room temperature. Therefore, the findings of this study present various advantages of these perovskites in harvesting light energy and TE applications.

We fabricated Cu₂CoSnS₄ (CCTS) thin films using spray-coating with a dimethylformamide-based molecular ink, deposited at 100 °C and 140 °C, and annealed at 360 °C in air. X-ray diffraction and Raman spectroscopy confirmed the stannite structure, with improved crystallinity and fewer impurities at 140 °C. The films show promise as non-toxic, sulfurization-free absorber layers for solar cells, with tunable optical and electrical properties. X-ray photoelectron spectroscopy (XPS) revealed temperature-dependent shifts in chemical composition and oxidation states. These shifts indicate altered stoichiometry at higher temperatures. Morphological analyses through SEM and AFM showed increased grain size, improved uniformity, and enhanced surface roughness with higher deposition temperatures. Energy-dispersive X-ray (EDX) mapping confirmed uniform elemental distribution, with deviations from ideal stoichiometry observed at 140 °C. Optical studies indicated a reduction in the band gap from 2.06 eV at 100 °C to 1.64 eV at 140 °C. The electrical measurements via Hall Effect show that all films exhibit a transition from p-type conductivity at 100 °C (carrier concentration of 1.057 × 10¹⁰ cm⁻³, mobility of 32.85 cm²/V.s, and resistivity of 8.994 × 10² Ω.cm) to n-type conductivity at 140 °C (carrier concentration of -2.486 × 10⁶ cm⁻³, mobility of 80.26 cm²/V.s, and resistivity of 3.098 × 10⁴ Ω.cm).These findings highlight the promise of CCTS films as environmentally friendly, sulfurization-free absorber layers for thin-film solar cells and optoelectronic applications, emphasizing the crucial role of deposition optimization in achieving enhanced material properties.

In this study, we investigate the strong gravitational lensing and shadow properties of a Kalb-Ramond black hole characterized by the Lorentz parameter l, in the presence of both homogeneous and inhomogeneous plasma distributions. Starting from the equation of motion of the plasma, we derive an analytical expression for the strong deflection angle. Our results show that the radius of the photon sphere, strong field parameters, and strong deflection angle are significantly affected by the presence of the plasma. Numerical calculations were performed to compute the lensing observables, angular image position, angular image separation, and flux ratio between the outermost and remaining images for the supermassive black hole SgrA(^*), which is believed to be the supermassive black hole at the center of our galaxy, in the presence of plasma. Furthermore, we studied the impact of plasma on the shadow radius of the Kalb-Ramond black hole. The study concludes that both the Lorentz parameter and the plasma medium substantially affect the strong gravitational lensing and shadow properties, with the effects being more pronounced in the case of homogeneous plasma.

Gas breakdown induced by focused terahertz beams exhibits novel characteristics and bright application prospects, making research in this field of great significance. In this paper, numerical simulations of argon gas breakdown induced by a focused terahertz beam are carried out using a plasma fluid model. In this model, rate coefficients such as ionization rate are determined via the Boltzmann equation solver BOLSIG+. An effective electron diffusion coefficient is employed to describe the transition process from free diffusion to ambipolar diffusion. The fluid model under axisymmetric conditions is solved using the finite difference method. Simulation results show that the ionization rate derived from BOLSIG+ is in good agreement with the results of the particle-in-cell-Monte Carlo collision model. At the same mean electron energy, the ratio of ionization rate to gas density varies with pressure. When the peak electric field of the focused beam reaches the breakdown threshold of long pulses, radial electron diffusion still exerts an influence on the breakdown process, even under conditions of high gas pressure and uniform distribution of seed electrons. This is because the 1/e spot radius of the focused beam is small (on the order of millimeters), and the plasma density generated by ionization has a large gradient. As the pressure decreases, the influence of radial electron diffusion on the breakdown process becomes more significant. The accuracy of the fluid model is verified by comparing the simulated values of the breakdown threshold of the focused beam with the experimental results.

Non-classical correlations, quantified by uncertainty measures such as Local Quantum Uncertainty (LQU) and Quantum Interferometric Power (QIP), are vital resources in quantum information, existing even in non-entangled mixed states. This study investigates the quantum correlations of Bell cat states under amplitude damping, employing LQU and QIP as quantifiers. This work investigates the dynamics of these correlations in two-mode Bell cat states under the influence of amplitude damping noise. We derive analytic expressions for both LQU and QIP for these states, which are constructed from Glauber coherent states. Furthermore, the study explores the potential of these correlations for enhancing phase estimation precision in quantum metrology. We also analyze the resilience of non-classical correlations, quantified by LQU, in Bell cat states subject to phase damping, depolarizing, and phase reversal channels. Our results provide crucial insights into the robustness and utility of these correlations, highlighting their significance for quantum information processing and communication.

Advances in quantum computing over the last two decades have required sophisticated mathematical frameworks to deepen the understanding of quantum algorithms. In this review, we introduce the theory of Lie groups and their algebras to analyze two fundamental problems in quantum computing as done in some recent works, e.g., Nielsen (Quantum Inf. Comput. 6(3), 213–262 2006) and Cerezo et al. (Nat. Rev. Phys. 3(9), 625–644 2021). Firstly, we describe the geometric formulation of quantum computational complexity, given by the length of the shortest path on the (SU(2^n)) manifold with respect to a right-invariant Finsler metric. Secondly, we deal with the barren plateau phenomenon in variational quantum algorithms (VQAs), where we use the dynamical Lie algebra (DLA) to identify algebraic sources of untrainability.

A many-body Fourier transformation with logarithmic scaling in the number of necessary two-site gates is implemented. The protocol is applied to study the Bethe chain as a prototype of a translationally invariant system. The resulting energy diagram features flat bands and a homogeneous gap that closely matches the interaction constant. The introduced protocol can be applied to a wide spectrum of scenarios and provides a tool to obtain many-body band diagrams of interacting systems.

This article presents a biosensor based on a two-dimensional rod-in-air photonic crystal slab with a hexagonal lattice, specifically designed for glucose detection in both urine and blood samples. The photonic band structure is studied using the plane-wave expansion (PWE) method, while sensing parameters are analyzed using the finite-difference time-domain (FDTD) method. To enhance device performance, the nanocavity width and radii of silicon rods above the w1 waveguide are optimized. The design provides a wide bandgap and strong optical confinement within the cavity, ensuring high sensitivity to refractive-index variations. The 2D and 3D configurations of the structure are investigated. The sensor demonstrates a noticeable frequency shift and significant variation in transmitted output power in response to minute refractive-index variations. Simulation results confirm high performance, achieving a maximum sensitivity of 850 nm/ RIU, a high quality factor of 1.8956(times )10(^textrm{4}), a low detection limit of 1.115(times )10(^{-5}) RIU, and a high figure of merit of (approx 8968) (textrm{RIU}^{-1}). Moreover, the device operates reliably over a wide temperature range (0–80 °C), and the effect of fabrication tolerances on performance is thoroughly analyzed. With its compact footprint of (approx 100) (mu m^2) and excellent sensing characteristics, the proposed sensor is a strong candidate for integration into on-chip photonic circuits.

In this study, the impact of relativistic temperature on the catastrophic loss of the double Beltrami equilibrium state in a relativistic hot electron-ion plasma is explored. In the accretion disks of black holes, this particular type of plasma can be found. A set of algebraic equations relating the amplitudes and eigenvalues of the DB equilibrium to the relativistic temperature, magnetofluid energy, magnetic helicity, and generalized helicity are used to analyze and predict catastrophic transformations. The study demonstrates that the values of critical energy and macroscale structure are significantly impacted by relativistic temperature. It is also shown that due to the catastrophic loss of equilibrium, magnetic energy transforms to kinetic energy. The current study also highlights the potential ramifications for the accreting disks of black holes.