The European Physical Journal B最新文献

Raman scattering measurements are performed on the pure benzene (B), 2,2’-bipyridine (BD), and the saturated BD-B solution at 295 and 80 K to investigate the solute–solvent interaction on the vibrational properties. The spectrum of the BD-B shows almost a simply addition of the individual spectra of BD and B, suggesting no strong interaction among BD and B molecules. At low temperature, the solution crystallizes and its spectrum shows obvious changes including the inter- and intramolecular modes, especially the modes associated with the lattice vibrations, C–H in-plane bending, C–C interring stretching, and high-frequency C–H stretching. Our work contributes to understand the interaction between organic solute and solvent.

Following the unexpected experimental discovery of “sideband” peaks in the fluctuation spectrum of thin Co films driven by a slowly oscillating magnetic field with a constant bias (Riego et al. in Phys Rev Lett 118:117202, 2017), numerical studies of two-state Ising and three-state Blume–Capel (BC) ferromagnets in this dynamically supercritical regime have flourished and been successful in explaining this phenomenon. Here, we give a comparative review of this new literature and its connections to earlier work. Following an introduction and a presentation of the two models and the computational method used in many of these studies, we present numerical results for both models. Particular attention is paid to the fact that zero spins in the BC model tend to collect at the interfaces between regions of the two nonzero spin values, ± 1. We present strong arguments that this phenomenon leads to a reduction of the effective interface tension in the BC model, compared to the Ising model.

Using the geodesic nudged elastic band method and the harmonic approximation of transition state theory the magnetic properties of finite-length Mn atomic chains on the Pt(332) surface have been investigated. Our study accounted for exchange interaction, magnetic anisotropy energy, Dzyaloshinskii–Moriya interaction (DMI), and long-range dipole–dipole interactions. We found that finite-length Mn chains can exhibit both quasicollinear and helical structures, with the DMI at the chain ends playing a crucial role in stabilizing these configurations. The competition between magnetic anisotropy energy and DMI determines the plane in which the helical structures are oriented. Additionally, dipole–dipole interactions contribute to narrowing the domain wall width and reducing the deviation of magnetic moments at the chain ends from the easy magnetization axis. Our results show that the lifetimes of magnetic states are highly sensitive to temperature and chain length. For certain chain lengths, the lifetimes of four or even six different magnetic states are nearly identical or very close. This result may be interesting for future technical applications.

The dynamic region of out-of-time-ordered correlators (OTOCs) serves as a powerful indicator of chaos in classical and semiclassical systems, capturing the characteristic exponential growth. However, in spin systems, the dynamic region of OTOCs does not reliably quantify chaos as both integrable and chaotic systems display similar behavior. Instead, we utilize the saturation behavior of OTOCs to differentiate between chaotic and integrable regimes. In integrable systems, the saturation region of OTOCs exhibits oscillatory behavior, while in chaotic systems, it shows a stable saturation. To evaluate this distinction, we investigate a time-dependent Ising spin system subjected to a linearly ramping transverse field, analyzing both integrable (without longitudinal field) and non-integrable (with longitudinal field) scenarios. This setup accelerates system ergodicity due to the introduction of an additional time scale within the system, enhancing chaotic dynamics in the non-integrable regime, and provides a compelling model for studying the interplay between integrability and chaos in quantum systems. To further support our findings, we investigate the level spacing distribution of time-dependent unitary operators, which effectively distinguishes chaotic from regular regions in our system and corroborates the results obtained from the saturation behavior of the OTOC. Additionally, we calculate a metric for the normalized Fourier spectrum of the OTOC which is dependent on the number of frequency components present to gain insights into the observed oscillations and its dependence on the ramping field.

A comparative study of the thermodynamic and transport properties of the ultra-relativistic quark–gluon plasma produced in heavy ion collisions with the “quasi-relativistic” massless electron–hole plasma in graphene sample have been performed. We observe that the enthalpy per net charge carrier emerges as a useful physical quantity determining the transport variables in hydrodynamic domain. Lorenz ratio is defined as thermal to electrical conductivity ratio, normalized by temperature and Lorenz number (L_{0}=frac{pi ^{2}}{3}left( frac{k_{B}}{e}right) ^{2}). The validity of the Wiedemann–Franz law can be checked by evaluating the Lorenz ratio, which is expected to be unity. We investigate the validity of the Wiedemann–Franz law by examining whether the Lorenz ratio equals unity or deviates from it. Our findings indicate that, within the fluid-based framework, the Lorenz ratio consistently leads to a violation of the Wiedemann–Franz law. This is attributed to the proportional relation between Lorenz ratio and enthalpy per net charge carrier in the fluid. Based on the experimental observation, graphene and quark–gluon plasma, both systems at a low net carrier density, violate the Wiedemann–Franz law due to their fluidic nature. However, graphene at a relatively high net carrier density obeys the Wiedemann–Franz law, followed by metals with high Fermi energy or electron density. It indicates a fluid to the non-fluid transition of the graphene system from low to high carrier density. In this regard, the fluid or non-fluid aspect of quark–gluon plasma at high density is yet to be explored by future facilities such as Compressed Baryonic Matter and Nuclotron-based Ion Collider fAcility experiments.