Elijah A. Abbey | Searcharxiv

arXiv2026

Tachyonic AdS/QCD, Determining the Strong Running Coupling and β-function in both UV and IR Regions of AdS Space

In this paper, we investigate the Quantum Chromodynamics (QCD)-like running coupling, $α_s^{AdS}(Q^{2})$, and its associated $β$-function within a tachyonic Anti-de Sitter (AdS)/QCD framework. The $\text{AdS}_5$ bulk geometry is deformed through the introduction of a color dielectric function $G(ϕ(z))$, associated with a tachyon field $ϕ(z)$. This function governs the behavior of $α_s^{AdS}(Q^{2})$ across all momentum scales by modifying the AdS background at both small and large values of the holographic coordinate $z$.In the ultraviolet (UV) regime (small $z$), the deformation is driven by free tachyons and reproduces features consistent with perturbative QCD. In contrast, in the infrared (IR) regime (large $z$), tachyon condensation dominates, yielding behavior characteristic of nonperturbative QCD. This construction enables a unified description of the running coupling and its $β$-function over the full range of momentum transfer $Q^2$, where $Q^2$ denotes the space-like momentum scale.

hep-ph↗

arXiv2026

Probing Electromigration of Oxygen Vacancies in YBa$_2$Cu$_3$O$_{7-δ}$ Devices by Multimodal X-ray Techniques

Control of oxygen vacancies by electrical currents in complex oxides such as YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO) has attracted considerable interest due to the relative simplicity of its implementation and its potential for both fundamental studies and the tuning of superconducting device properties. However, the structural evolution and depth-dependent effects associated with current-based techniques remain largely unexplored, particularly with respect to the connection between optical signatures and the spatial distribution of oxygen vacancies. Here, we combine nanoprobe X-ray Diffraction (NanoXRD), Cu K-edge X-ray Absorption Near-Edge Structure (XANES), X-ray Photoelectron Spectroscopy (XPS), electrical transport, and optical measurements to reveal modifications induced in YBCO microbridges by pulsed electromigration. We observe a c-axis expansion correlated with spectroscopic features of oxygen depletion in the Cu-O chains, and we confirm that oxygen redistribution, crystallographic changes, and copper coordination evolve consistently across techniques. Notably, the spatial profile of unit-cell expansion closely follows the optical contrast observed after electromigration, demonstrating that the different signatures capture the same underlying oxygen reordering. We further show that optical microscopy cannot reliably capture bipolar electromigration involving strong resistance modifications, as surface deoxygenation appears largely irreversible. Taken together, our findings provide a significant step toward a microscopic understanding of current-assisted oxygen migration in YBCO and establish a framework for effectively exploiting vacancy control in high-temperature superconducting devices.

cond-mat.supr-con↗