International Journal of Physics | Vol. 4, No. 12, December 2013 | pp. 89–96
DOI: 10.46882/2013/IJP/000044
Research Article
Title: Superconducting Gap Structure and Spin Fluctuations in Electron-Doped Pnictide Ba(Fe0.92Co0.08)2As2 Single Crystals
Names of Authors: I. R. Sokolov¹, E. C. Sterling²
Authors’ Affiliations: ¹Kapitza Institute for Physical Problems, Russian Academy of Sciences, Moscow 119334, Russia; ²Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge CB3 0HE, United Kingdom
Abstract: Uncovering the exact pairing symmetry of iron-based superconductors remains a critical challenge in modern condensed matter physics. We synthesized high-quality single crystals of electron-doped Ba(Fe0.92Co0.08)2As2 utilizing a self-flux method. The superconducting gap structure and spin fluctuations were evaluated through high-resolution angle-resolved photoemission spectroscopy and low-temperature London penetration depth measurements. The single crystals exhibited a sharp superconducting transition at Tc = 25.4 K with a magnetic susceptibility transition width of ΔT = 0.3 K. The temperature dependence of the London penetration depth shows an exponential behavior at low temperatures (T less than 0.3 Tc), which rules out the presence of line nodes in the order parameter. The photoemission spectra revealed two distinct, fully gapped isotropic superconducting superconducting bands. The larger gap value was measured at Δ1 = 6.8 meV on the inner hole-like Fermi surface sheet, while the smaller gap was found at Δ2 = 3.4 meV on the electron-like sheets. This gap configuration yields a strong-coupling ratio of 2Δ1/kBTc = 6.2, indicating strong-coupling superconductivity. These experimental results align with the s± pairing symmetry model driven by interband spin fluctuations.
Keywords: Iron-based superconductors; gap structure; angle-resolved photoemission spectroscopy; London penetration depth; pairing symmetry; spin fluctuations
Manuscript Timeline: Received: August 18, 2013; Revised: October 10, 2013; Accepted: November 02, 2013; Published: December 16, 2013
Citation: Sokolov, I. R., & Sterling, E. C. (2013). Superconducting Gap Structure and Spin Fluctuations in Electron-Doped Pnictide Ba(Fe0.92Co0.08)2As2 Single Crystals. International Journal of Physics, 4(12), 89–96.
International Journal of Physics | Vol. 4, No. 11, November 2013 | pp. 81–88
DOI: 10.46882/2013/IJP/000043
Research Article
Title: Thermal Conductivity Anomalies and Phonon Scattering Mechanisms in Silicon-Germanium Superlattices
Names of Authors: D. W. Meyer¹, Z. L. Wang²
Authors’ Affiliations: ¹Institute of Physics, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany; ²State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, CAS, Beijing 100083, China
Abstract: Controlling thermal transport across semiconductor heterostructures is essential for designing efficient thermoelectric energy harvesters and preventing hotspot formation in nanoelectronics. This study examines cross-plane thermal conductivity anomalies and maps phonon scattering mechanisms in silicon-germanium (Si/Ge) superlattices. We performed molecular dynamics simulations based on the Stillinger-Weber potential, evaluating superlattice periods ranging from 2.0 nm to 20.0 nm at temperatures between 100.0 K and 500.0 K. The calculated data show a non-monotonic dependence of thermal conductivity on the superlattice period. The cross-plane thermal conductivity drops to a minimum value of 4.2 W/m-K at a period of 4.5 nm under room temperature conditions. This minimum point represents a shift from coherent wave-like phonon transport to incoherent particle-like phonon scattering. For periods smaller than 4.5 nm, wave-like transport dominates, and the thermal conductivity scales upward due to the formation of acoustic minibands. For periods larger than 4.5 nm, diffuse interface scattering and Umklapp processes restrict heat carrier lifetimes, yielding an average phonon mean free path of 24.5 nm. These results clarify the wave-particle duality of heat-carrying phonons, assisting in the development of targeted thermal barriers for microprocessors.
Keywords: Superlattices; thermal conductivity; molecular dynamics; phonon scattering; thermoelectricity; wave-particle duality
Manuscript Timeline: Received: July 12, 2013; Revised: September 04, 2013; Accepted: September 22, 2013; Published: November 12, 2013
Citation: Meyer, D. W., & Wang, Z. L. (2013). Thermal Conductivity Anomalies and Phonon Scattering Mechanisms in Silicon-Germanium Superlattices. International Journal of Physics, 4(11), 81–88.
International Journal of Physics | Vol. 4, No. 10, October 2013 | pp. 73–80
DOI: 10.46882/2013/IJP/000042
Research Article
Title: Soliton Stability and Modulational Instability in Non-Local Nonlinear Optical Media with Exponential Response Functions
Names of Authors: G. S. Campbell¹, F. Z. Al-Rawi²
Authors’ Affiliations: ¹Research School of Physics and Engineering, Australian National University, Canberra, ACT 2601, Australia; ²Department of Physics, Faculty of Science, University of Baghdad, Baghdad 10071, Iraq
Abstract: Non-local nonlinear optical media provide unique opportunities for steering and controlling light beams due to their non-local spatial interactions. This study analyzes the structural stability of spatial optical solitons and characterizes modulational instability parameters within a non-local medium governed by an exponential response function. We developed an analytical model using the non-local nonlinear Schrödinger equation. This model was solved via a variational approach combined with split-step Fourier numerical simulations. The analytical framework derives the exact power thresholds required to initiate stable spatial soliton propagation across varying degrees of non-locality. The results show that a highly non-local response completely suppresses collapse modes, stabilizing two-dimensional localized structures that are unstable in local Kerr media. The modulation instability growth rate was calculated as a function of perturbation frequency. This analysis revealed a maximum gain value of g = 2.45 cm^-1 under an input beam intensity of 1.5 kW/cm². Increasing the non-locality parameter from 0.5 mm to 3.0 mm reduces the maximum instability gain by 62.0% and shifts the peak gain toward longer perturbation wavelengths. These findings provide strategies for controlling filamentation in laser beams and optimizing data transport in soft-matter waveguide networks.
Keywords: Nonlinear optics; spatial solitons; nonlinear Schrödinger equation; modulational instability; non-local media; split-step Fourier method
Manuscript Timeline: Received: June 04, 2013; Revised: July 28, 2013; Accepted: August 18, 2013; Published: October 14, 2013
Citation: Campbell, G. S., & Al-Rawi, F. Z. (2013). Soliton Stability and Modulational Instability in Non-Local Nonlinear Optical Media with Exponential Response Functions. International Journal of Physics, 4(10), 73–80.
International Journal of Physics | Vol. 4, No. 9, September 2013 | pp. 65–72
DOI: 10.46882/2013/IJP/000041
Research Article
Title: Kinetic Alfvén Wave Dissipation and Electron Acceleration Profiles in Magnetic Reconnection Sheets
Names of Authors: C. H. Jenkins¹, A. L. Mendoza²
Authors’ Affiliations: ¹Space Sciences Laboratory, University of California, Berkeley, California 94720, USA; ²Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Mexico City 04510, Mexico
Abstract: Magnetic reconnection is the fundamental plasma process responsible for explosive energy release events in solar flares and planetary magnetospheres. This paper examines the dissipation mechanisms of kinetic Alfvén waves (KAWs) and models the resulting electron acceleration profiles within a scaling magnetic reconnection layer. We carried out high-resolution two-and-a-half-dimensional particle-in-cell (PIC) simulations under a guide-field configuration. The initial plasma beta parameter was set to 0.05, and the ion-to-electron mass ratio was configured at 1836.0 to accurately track kinetic scale limits. Our numerical simulations show that as the reconnection jet collides with the ambient magnetic field, it excites intense KAWs at the exhaust boundaries. These waves display short perpendicular wavelengths that match the local electron skin depth scale. The wave dissipation process generates a parallel electric field amplitude of E = 12.5 mV/m. This field efficiently trapping and accelerates thermal electrons into a non-thermal power-law distribution. The calculated energy spectrum exhibits a power-law index of p = -3.2, which matches solar flare X-ray observations. These findings show that kinetic wave dissipation at the margins of reconnection sheets is a primary mechanism driving high-energy particle acceleration in space plasmas.
Keywords: Magnetic reconnection; particle-in-cell simulation; kinetic Alfvén waves; electron acceleration; space plasma; solar flares
Manuscript Timeline: Received: May 12, 2013; Revised: July 03, 2013; Accepted: July 25, 2013; Published: September 10, 2013
Citation: Jenkins, C. H., & Mendoza, A. L. (2013). Kinetic Alfvén Wave Dissipation and Electron Acceleration Profiles in Magnetic Reconnection Sheets. International Journal of Physics, 4(9), 65–72.
International Journal of Physics | Vol. 4, No. 8, August 2013 | pp. 57–64
DOI: 10.46882/2013/IJP/000040
Research Article
Title: Spin-Orbit Coupling and Electronic Band Inversion in Bismuth-Based Half-Heusler Topological Compounds
Names of Authors: T. M. Nguyen¹, K. K. Suzuki²
Authors’ Affiliations: ¹Department of Physics, Vietnam National University, Hanoi 100000, Vietnam; ²Department of Physics, Graduate School of Science, Tohoku University, Sendai 180-8578, Japan
Abstract: Half-Heusler alloys have emerged as a versatile platform for exploring the intersection of topological states, superconductivity, and heavy-fermion physics. This study evaluates the electronic band structure and quantifies the spin-orbit coupling effects in bismuth-based Heusler compounds (LuPtBi and YPtBi). We performed fully relativistic density functional theory calculations including core-level corrections and customized electron correlation parameters. The calculated electronic structures demonstrate a distinct band inversion at the Gamma high-symmetry point of the Brillouin zone. In LuPtBi, the bismuth 6p states are shifted above the platinum 5d states, creating a negative band gap value of -0.42 eV. This configuration confirms the non-trivial topological character of the material. We verified the existence of topological surface states by computing the surface state density using the Green's function methodology on a semi-infinite crystal slab. The surface calculations show a well-defined Dirac cone intersecting the Fermi level with a high Fermi velocity of vF = 5.2 x 10^7 cm/s. The calculation of the Z2 topological invariant yields (1;000), classifying these intermetallic systems as strong topological insulators. These solid-state properties make these compounds promising materials for developing robust quantum computing components and low-power spintronic devices.
Keywords: Topological insulators; half-Heusler alloys; density functional theory; spin-orbit coupling; band inversion; Dirac cone
Manuscript Timeline: Received: April 15, 2013; Revised: June 02, 2013; Accepted: June 22, 2013; Published: August 19, 2013
Citation: Nguyen, T. M., & Suzuki, K. K. (2013). Spin-Orbit Coupling and Electronic Band Inversion in Bismuth-Based Half-Heusler Topological Compounds. International Journal of Physics, 4(8), 57–64.
International Journal of Physics | Vol. 4, No. 7, July 2013 | pp. 49–56
DOI: 10.46882/2013/IJP/000039
Research Article
Title: Hydrodynamic Evolution and Quark-Gluon Plasma Instabilities in High-Energy Heavy-Ion Collisions
Names of Authors: S. C. O’Brien¹, D. M. Richter²
Authors’ Affiliations: ¹School of Physics, University College Dublin, Dublin 4, Ireland; ²Max-Planck-Institut für Kernphysik, 69117 Heidelberg, Germany
Abstract: High-energy heavy-ion collisions recreate the extreme conditions of the early universe, allowing for the study of the quark-gluon plasma (QGP). This paper presents a detailed numerical model of the hydrodynamic evolution and filamentation instabilities within an anisotropic QGP expansion. We solved the relativistic Boltzmann transport equations coupled with self-consistent color fields using a three-dimensional parton-cascade simulation framework. The initial conditions were calibrated to simulate lead-lead (Pb-Pb) collisions at a center-of-mass energy of 2.76 TeV per nucleon pair. Our simulation tracks the rapid development of color-magnetic fields triggered by the Chromo-Weibel instability during the early non-equilibrium phase (t less than 1.0 fm/c). The calculations indicate that these generated fields reach a peak value of eB = 0.45 GeV² within a local volume. This acceleration drives isotropic momentum distributions faster than standard viscous hydrodynamics models predict. The inclusion of this turbulent field evolution reduces the calculated thermalization time scale by approximately 30.0%, reaching equilibrium at t = 0.6 fm/c. The resulting elliptic flow coefficient (v2) matches experimental data collected by the Large Hadron Collider across a wide range of impact parameters. This agreement clarifies the role of non-Abelian plasma instabilities in establishing early-stage hydrodynamic collective behavior.
Keywords: Quark-gluon plasma; relativistic hydrodynamics; Chromo-Weibel instability; heavy-ion collisions; parton cascade; thermalization
Manuscript Timeline: Received: March 20, 2013; Revised: May 05, 2013; Accepted: May 28, 2013; Published: July 15, 2013
Citation: O’Brien, S. C., & Richter, D. M. (2013). Hydrodynamic Evolution and Quark-Gluon Plasma Instabilities in High-Energy Heavy-Ion Collisions. International Journal of Physics, 4(7), 49–56.