arXiv subjects

Jia-Ying Zhang

Publications and source records attributed to Jia-Ying Zhang.

4 recordsLinked to original sources

arXiv2026

Observational Signatures of Thin Accretion Disks around Rotating Black Holes Embedded in Dark Matter Halos

Black holes embedded in a dark matter background represent an important candidate model that extends the standard vacuum case, characterizing the strong gravitational environments at galactic centers and the gravitational influence of dark matter. This study focuses on dark matter halo-modified Kerr black holes and systematically investigates the observational characteristics of their surrounding thin accretion disks. The dark matter halo is modeled by a general double power-law density profile, whose integrated mass $M_D(r)$ modifies the radial mass function of Kerr metric to $m(r) = M + M_D(r)$. Based on this spacetime, we analyze the observational properties of their thin accretion disk, including the radiative flux, temperature, differential luminosity, and spectral luminosity as a function of radius, with respect to the black hole spin and dark matter halo parameters. Furthermore, by combining ray-tracing methods, we simulate the bolometric image of the thin accretion disk under different black hole spins, dark matter halo parameters, and viewing inclinations. The dark matter halo enhances the gravitational potential, shifting the innermost stable circular orbit (ISCO) of the accretion disk outward, suppressing the peak radiative flux, and producing a fainter image, thereby generating signatures that are possibly observational distinguishable from standard vacuum Kerr black holes.

gr-qc↗

arXiv2026

Controlled Manipulation of Intermediate State in a Type-I Superconductor

The intermediate state of type-I superconductors presents a classic paradigm of modulated pattern formation, arising from the competition between short-range attractive and long-range repulsive vortex-vortex interactions. However, direct visualization and, more importantly, active control over the topology and dynamics of these flux structures have remained significant challenges, limiting our ability to manipulate them for fundamental studies and potential applications. Here, using low-temperature magnetic force microscopy, we achieve direct imaging and controllable manipulation of the flux structures in a high-purity tantalum single crystal. We systematically track the evolution of flux morphology - from tubes to stripes - during flux penetration and expulsion, revealing a pronounced topological hysteresis originating from the geometric barrier. Furthermore, we demonstrate precise local control by using the magnetic tip to drag and merge individual flux tubes and to reconfigure entire stripe domains. Under global alternating current (AC) excitation, we discover a reversible stripe-grid-stripe transition, a dynamic reorganization driven by current-induced flux penetration and pinning effects. The corresponding phase diagram shows that the threshold current decreases with magnetic field but increases with AC frequency. Our work establishes a pathway for active flux manipulation in type-I superconductors, revealing rich dynamics and paving the way for flux-based superconducting devices.

cond-mat.supr-con↗

arXiv2026

Competing Constraints on Superconductivity in Thick FeSe films

Superconducting films emerge from the complex interplay of multiple growth parameters, making their optimization challenging. In iron-based superconductors, compressive strain is known to enhance the transition temperature (Tc) of FeSe films, yet reported Tc values vary widely even on identical substrates, indicating factors beyond strain are critical. Here, we develop a high-throughput off-center pulsed laser deposition strategy that transforms plume inhomogeneity into combinatorial FeSe film libraries with continuous gradients in lattice parameter, composition, and disorder. We discover that the maximum Tc does not coincide with the plume center but can shift off-center, revealing a competition between favorable c-axis expansion, stoichiometry, and defect scattering. Systematic characterization of 80 thick films (>50 nm), combined with interpretable machine learning, shows that besides the strong correlate of c-axis lattice parameter to Tc, the stoichiometry and disorder scattering impose critical constraints on the achievable transition temperature, defining a narrow optimization window rather than a simple monotonic relationship. This framework yields Tconset=17.1 K in thick FeSe films and establishes a general framework combining combinatorial synthesis with machine learning to uncover constrained optimization landscapes in complex functional materials.

cond-mat.supr-con↗

arXiv2025

Coexistence of topological surface states and superconductivity in Dirac semimetal NiTe$_2$

The coexistence of topological bands around the Fermi level ($E_F$) and superconductivity provides a fundamental platform for exploring their interplay. However, few materials inherently display both properties. In this study, we demonstrate the coexistence of topological surface states at the $E_F$ and superconductivity in NiTe$_2$ single crystals, a material hitherto not recognized as superconducting. Quasiparticle interference measurements performed via scanning tunneling microscopy suggest the presence of topological surface states at the $E_F$, which is further corroborated by density functional theory simulations. Experimental evidence for superconductivity is provided via electronic transport measurements and specific heat capacity analyses. Our results suggest that NiTe$_2$ represents a promising platform for investigating the rich interplay between topological states and superconductivity.

cond-mat.supr-con↗