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Journal of Physics: Condensed Matter - latest papers

Latest articles for Journal of Physics: Condensed Matter

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  • The Meissner effect in superconductors: emergence versus reductionism
    The Meissner effect, the expulsion of magnetic field from the interior of a metal entering the superconducting state, is arguably the most fundamental property of superconductors, discovered in 1933. The conventional theory of superconductivity developed in 1957 is generally believed to fully explain the Meissner effect. We will review the arguments that support this consensus, rooted in the concept of emergence. However, recent work has shown that there are questions related to momentum conservation in the process of magnetic field expulsion that have not been addressed within the conventional theory. Within a reductionist approach, it has been proposed that those questions can only be resolved by introducing physics that is not part of the conventional theory, namely that there is radial motion of electric charge in the transition process. This is consistent with the behavior of classical plasmas, where motion of magnetic field lines is always associated with motion of charges. We review how this approach explains puzzles associated with momentum transfer between electrons and ions in the Meissner effect. Whether or not radial charge motion is associated with the Meissner effect has fundamental implications regarding superconductivity mechanisms in materials and regarding strategies to search for new materials with higher superconducting transition temperatures. Therefore, adjudication of this question is urgent and important.

  • Interfacial evolution and bonding mechanisms in γ-TiAl/Al explosive welding: a molecular dynamics study
    The explosive welding (EXW) of γ-TiAl to Al offers a promising route to fabricate lightweight, high-strength hybrid structures, yet the atomic-scale bonding mechanisms remain unclear. In this work, large-scale molecular dynamics simulations were performed to investigate the effects of flyer velocity (1.5–2.9 km s−1) and collision angle (10°–40°) on the thermal response, diffusion behavior, phase evolution, and mechanical performance of γ-TiAl/Al EXW. Increasing flyer velocity drives a transition from solid–solid contact to solid–liquid and ultimately liquid–liquid mixing, accompanied by elevated interfacial temperature, thicker diffusion layers, and extensive amorphization. During cooling, the Al base exhibits strong face-centered cubic recrystallization but retains vacancy defects, whereas the γ-TiAl flyer preserves stable HCP bands and quenched disorder. Mechanical tests reveal that a flyer velocity of 2.5 km s−1 achieves the best strength-ductility balance (∼5.1 GPa peak stress, ∼0.08 fracture strain) through the formation of a well-mixed interface. At this velocity, increasing the collision angle from 10°–30° gradually improves joint strength and ductility by promoting more uniform defect evolution and plastic deformation, whereas an excessive angle (40°) induces shear-driven separation that weakens bonding. These findings elucidate the fundamental atomic processes governing γ-TiAl/Al EXW and provide quantitative guidance for optimizing processing parameters in advanced lightweight structural applications.

  • Impact of small-molecule adsorbates on the morphology of PuO2 nanoparticles from first-principles modelling
    The safe management of legacy civil plutonium stockpiles is among the most difficult challenges facing the nuclear industry. While geological disposal facilities (GDFs) are seen as the optimal solution, anticipating the evolution of waste forms over the lifetime of the GDF forms a critical part of the safety case. In the typical storage form of PuO2 powders, the chemical reactivity of Pu is determined by the exposed crystal facets and surface speciation, which are a complex function of temperature and the partial pressures of oxygen and small-molecule adsorbates. In this work, we use a first-principles modelling approach to develop a predictive thermodynamic model for the impact of the ubiquitous environmental compounds H2O, CO2 and H2O2 on the equilibrium particle morphology and surface speciation of stoichiometric and oxygen-deficient PuO2. We find that the presence of multiple adsorbates can lead to both synergistic and antagonistic interactions, with significant impacts on the energetically-accessible nanoparticle morphologies and the exposure of the major , and facets. Our model provides important reference data for the impact of environmental conditions on the surface chemistry of PuO2, and can be systematically enhanced to account for other variables including additional adsorbates, solvation, and surface coverage.

  • Néel vector controlled charge and spin transport in altermagnetic junctions
    Altermagnets (AMs) - magnetic materials that have spin-split bandstructure with zero net spin polarization can be classified as weak or strong depending upon the strength of altermagnetic term in the Hamiltonian. We theoretically investigate electron transport in junctions between the two AMs in strong and weak altermagnetic phases. The charge and spin conductivities are analyzed as functions of angle θ between the Néel vectors of the two AMs. In the strong AM regime, the charge conductivity vanishes as , while in the weak AM regime it remains finite. Introducing a normal metal (NM) between two AMs leads to Fabry–Pérot-type oscillations in charge conductivity which can be controlled by an applied gate voltage. In the strong regime, transport in AM-NM-AM junctions is dominated by up-spin electrons, whereas both spin channels contribute in the weak regime. These results highlight the potential of AM-based heterostructures for spintronic applications, such as spin filters, and quantum interference-based spintronic devices, where tunable spin-dependent transport and interference effects can be utilized in electronic devices without a need for externally applied magnetic field.

  • A comparative ab initio study of collective dynamics in Al90Si10 and Al90Mg10 liquid alloys
    Dispersion of acoustic and optic collective excitations are comparatively studied in two Al-based liquid metallic alloys, which contain ten atomic percent of Si with four valence electrons or Mg with two ones. Partial density–density and current–current time correlation functions are analyzed by a combination of ab initio molecular dynamics simulations and theoretical generalized collective modes approach. We obtain and analyze the dispersion of acoustic and optic collective excitations and wave number dependence of the slowest relaxation process as eigenmodes of the generalized Langevin equation in matrix form. These findings allow understanding of different factors responsible for features in collective dynamics of the two liquid metallic alloys.