Algebraic structure underlying spherical, parabolic and prolate spheroidal bases of the nine-dimensional MICZ-Kepler problem

Octonion algebra $\mathbb{O}$ has recently been used to study the fundamental physics of the Standard Model, such as its three-generation structure and its possibility of unifying gravity and quantum mechanics. Interestingly, this octonion algebra $\mathbb{O}$ has also been related to the $SO(8)$ monopole and, consequently, links to the nine-dimensional MICZ-Kepler problem. This problem has been solved exactly by the variables separation method in three different coordinate systems, spherical, parabolic, and prolate spheroidal. In the present study, we establish a relationship between the variable-separation and the algebraic structure of $SO(10)$ symmetry. Each of the spherical, parabolic, or prolate spheroidal bases is proved to be a set of eigenfunctions of a corresponding nonuplet of algebraically-independent integrals of motion. This finding also helps us to establish connections between the bases by the algebraic method. This connection, in turn, allows calculating a complicated integral of confluent Heun, generalized Laguerre, and generalized Jacobi polynomials, which may be engaging in analytics.Comment: 21 pages, no figures. Submitted to Physica Script

Electronic transport in two-dimensional strained Dirac materials under multi-step Fermi velocity barrier: transfer matrix method for supersymmetric systems

In recent years, graphene and other two-dimensional Dirac materials like silicene, germanene, etc. have been studied from different points of view: from mathematical physics, condensed matter physics to high energy physics. In this study, we utilize both supersymmetric quantum mechanics (SUSY-QM) and transfer matrix method (TTM) to examine electronic transport in two-dimensional Dirac materials under the influences of multi-step deformation as well as multi-step Fermi velocity barrier. The effects of multi-step effective mass and multi-step applied fields are also taken into account in our investigation. Results show the possibility of modulating the Klein tunneling of Dirac electron by using strain or electric field.Comment: 22 pages, 7 figures, published on European Physical Journal

Thermal effect on magnetoexciton energy spectra in monolayer transition metal dichalcogenides

It is widely comprehended that temperature may cause phonon-exciton scattering, enhancing the energy level's linewidth and leading to some spectrum shifts. However, in the present paper, we suggest a different mechanism that allows the thermal motion of the exciton's center of mass (c.m.) to affect the magnetoexciton energies in monolayer dichalcogenides (TMDCs). By the nontrivial but precise separation of the c.m. motion from an exciton in a monolayer TMDC with a magnetic field, we obtain an equation for the relative motion containing a motional Stark term proportional to the c.m. pseudomomentum, related to the temperature of the exciton gas but neglected in the previous studies. Solving the Schr\"odinger equation without omitting the motional Stark potential at room temperature shows approximately a few meV thermal-magnetic shifts in the exciton energies, significant enough for experimental detection. Moreover, this thermal effect causes a change in exciton radius and diamagnetic coefficient and enhances the exciton lifetime as a consequence. Surprisingly, the thermoinduced motional Stark potential breaks the system's SO(2) symmetry, conducting new peaks in the exciton absorption spectra at room temperature besides those of the $s$ states. This mechanism could be extended for other magnetoquasiparticles such as trions and biexcitons.Comment: 8 pages, 4 figures, 3 tables for main manuscript; 20 pages, 6 figures, 6 tables for supplementary. Published on Physical Review

Radiation Dose Estimation of Cement Samples Used in Lao PDR

The natural radioactivity due to presence of 226Ra, 232Th and 40K radionuclides in Lao PDR cements was measured for first time using a gamma-spectrometry with HPGe detector. Two different types of cement produced by 4 local cement companies in Lao PDR have been investigated.  The specific radioactivity of 226Ra, 232Th and 40K in the investigated samples ranged from 24.83 ± 1.18  to 54.39 ± 5.90  Bq kg-1 with a mean of 37.76 ± 10.71 Bq kg-1, 6.63 ± 1.59 to 21.17 ± 0.48 Bq kg-1 with a mean of 13.77 ± 5.85 Bq kg-1 and 43.28 ± 7.68 to 168.70 ± 3.34 Bq kg-1 with a mean of 116.07 ± 47.50 Bq kg-1, respectively. The radium equivalent activity (Raeq), the gamma-index, the external and internal hazard indices, Absorb Dose Rate in Air (D) and Annual Effective Dose Equivalent (AEDE) were estimated for the radiation hazard of the natural radioactivity in all cement samples. The obtained results were compared with the corresponding values for cement of different countries. The calculated Raeq values of Lao PDR samples are lower than the limit of 370 Bq kg-1 set fo building materials. The mean indoor absorbed dose rate is slightly lower than the population-weighted average of 84 nGy h-1 while the corresponding effective dose was 79% less than the dose ft of 1 mSv y-1. The results obtained in this study show no significant radiological hazards arising from using Lao PDR cement for construction of houses

Twisted bilayered graphenes at magic angles and Casimir interactions: correlation-driven effects

Twisted bilayered graphenes at magic angles are systems housing long ranged periodicity of Moir\'e pattern together with short ranged periodicity associated with the individual graphenes. Such materials are a fertile ground for novel states largely driven by electronic correlations. Here we find that the ubiquitous Casimir force can serve as a platform for macroscopic manifestations of the quantum effects stemming from the magic angle bilayered graphenes properties and their phases determined by electronic correlations. By utilizing comprehensive calculations for the electronic and optical response, we find that Casimir torque can probe anisotropy from the Drude conductivities in nematic states, while repulsion in the Casimir force can help identify topologically nontrivial phases in magic angle twisted bilayered graphenes.Comment: 9 pages, 6 figures (main), 7 pages, 7 figures (supplementary); provisionally accepted for publication in 2D Material

Giant anisotropy and Casimir phenomena: the case of carbon nanotube metasurfaces

The Casimir interaction and torque are related phenomena originating from the exchange of electromagnetic excitations between objects. While the Casimir force exists between any types of objects, the materials or geometrical anisotropy drives the emergence of the Casimir torque. Here both phenomena are studied theoretically between dielectric films with immersed parallel single wall carbon nanotubes in the dilute limit with their chirality and collective electronic and optical response properties taken into account. It is found that the Casimir interaction is dominated by thermal fluctuations at sub-micron separations, while the torque is primarily determined by quantum mechanical effects. This peculiar quantum vs. thermal separation is attributed to the strong influence of reduced dimensionality and inherent anisotropy of the materials. Our study suggests that nanostructured anisotropic materials can serve as novel platforms to uncover new functionalities in ubiquitous Casimir phenomena.Comment: 9 pages, 4 figures, submitted to Phys. Rev.

Retrieval of material properties of monolayer transition-metal dichalcogenides from magnetoexciton energy spectra

Reduced exciton mass, polarizability, and dielectric constant of the surrounding medium are essential properties for semiconduction materials, and they can be extracted recently from the magnetoexciton energies. However, the acceptable accuracy of the previously suggested method requires very high magnetic intensity. Therefore, in the present paper, we propose an alternative method of extracting these material properties from recently available experimental magnetoexciton s-state energies in monolayer transition-metal dichalcogenides (TMDCs). The method is based on the high sensitivity of exciton energies to the material parameters in the Rytova-Keldysh model. It allows us to vary the considered material parameters to get the best fit of the theoretical calculation to the experimental exciton energies for the $1s$, $2s$, and $3s$ states. This procedure gives values of the exciton reduced mass and 2D polarizability. Then, the experimental magnetoexciton spectra compared to the theoretical calculation gives also the average dielectric constant. Concrete applications are presented only for monolayers WSe$_2$ and WS$_2$ from the recently available experimental data. However, the presented approach is universal and can be applied to other monolayer TMDCs. The mentioned fitting procedure requires a fast and effective method of solving the Schr\"{o}dinger of an exciton in monolayer TMDCs with a magnetic field. Therefore, we also develop such a method in this study for highly accurate magnetoexciton energies.Comment: 8 pages, 4 figures, 4 table

Insight into the effect of zinc oxide nanoparticles coated multi-walled carbon nanotubes (ZnO/MWCNTs) on the thermal conductivity of epoxy nanocomposite as an electrical-insulating coating

The effect of zinc oxide (ZnO) nanoparticles on the thermal conductivity of zinc oxide/multi-walled carbon nanotubes (ZnO/MWCNTs) nanocomposite electrical-insulating coating was investigated. ZnO/MWCNTs was prepared by sol–gel method and incorporated into the epoxy matrix by ultrasonic-mechanical mixing to form the nanocomposite (ZnO/MWCNTs/epoxy). The SEM, XRD, and TGA analysis results showed that ZnO nanoparticles with 3–4 nm size formed layers on MWCNTs wires with a 10-nm diameter. The formed ZnO/CNT nanofillers had a diameter about 20–40 nm and had a highly homogeneous dispersion in the epoxy matrix. The thermal property of the nanocomposites was examined by the thermal imaging method. It was found that both MWCNTs and ZnO/MWCNTs nanofillers have significantly enhanced the thermal conduction of composites even at a low content load of 0.25 wt%. The thermal conductivity of ZnO/MWCNTs/epoxy and MWCNTs/epoxy composites was 0.62 and 1.09 Wm−1 K−1 respectively. The formation of ZnO nanoparticles on MWCNTs was thus led to a decreasing of about 43% in thermal conductivity of the composite. However, the thermal conduction of the ZnO/MWCNTs/epoxy composite is significantly improved about 210% compared to that of neat epoxy. These results proposed a useful method to modify the surface of MWCNTs for the fabrication of epoxy nanocomposite where electrical-insulating and thermal conducting are both required. The composite was applied as an insulating edge coating for capacitive deionization electrodes