Teruo Izumi | Searcharxiv

arXiv2026

Higher critical currents yet faster vortex creep in EuBa$_2$Cu$_3$O$_y$ films containing coherent artificial pinning centers

The electromagnetic properties of type-II superconductors depend on vortices -- magnetic flux lines whose motion introduces dissipation that can be mitigated by pinning from material defects. The material disorder landscape is tuned by the choice of materials growth technique and incorporation of impurities that serve as vortex pinning centers. For example, metal organic deposition (MOD) and pulsed laser deposition (PLD) produce high-quality superconducting films with uncorrelated versus correlated disorder, respectively. Here, we study vortex dynamics in PLD-grown EuBa$_2$Cu$_3$O$_y$ films containing varying concentrations of BaHfO$_3$ inclusions and compare our results with those of MOD-grown (Y,Gd)Ba$_2$Cu$_3$O$_y$ films. Despite both systems exhibiting behavior consistent with strong pinning theory, which predicts the critical current density $J_c$ based on vortex trapping by randomly distributed spherical inclusions, we find striking differences in the vortex dynamics owing to the correlated versus uncorrelated disorder. Specifically, we find that the EuBa$_2$Cu$_3$O$_y$ films grown without inclusions exhibit surprisingly slow vortex creep, comparable to the slowest creep rates achieved in (Y,Gd)Ba$_2$Cu$_3$O$_y$ films containing high concentrations of BaHfO$_3$. Whereas adding inclusions to (Y,Gd)Ba$_2$Cu$_3$O$_y$ is effective in slowing creep, BaHfO$_3$ increases creep in EuBa$_2$Cu$_3$O$_y$ even while concomitantly improving $J_c$. Lastly, we find evidence of variable range hopping and that $J_c$ is maximized at the BaHfO$_3$ concentration that hosts creep of large vortex bundles or a Bose glass state.

cond-mat.supr-con↗

arXiv2022

Thermodynamic approach for enhancing superconducting critical current performance

The addition of artificial pinning centers has led to an impressive increase in critical current density ($J_{\rm c}$) in a superconductor, enabling record-breaking all-superconducting magnets and other applications. $J_{\rm c}$ has reached $\sim 0.2$-$0.3$ $J_{\rm d}$, where $J_{\rm d}$ is the depairing current density, and the numerical factor depends on the pinning optimization. By modifying $λ$ and/or $ξ$, the penetration depth and coherence length, respectively, we can increase $J_{\rm d}$. For (Y$_{0.77}$Gd$_{0.23}$)Ba$_2$Cu$_3$O$_y$ ((Y,Gd)123) we achieve this by controlling the carrier density, which is related to $λ$ and $ξ$. We also tune $λ$ and $ξ$ by controlling the chemical pressure in the Fe-based superconductors, BaFe$_2$(As$_{1-x}$P$_x$)$_2$ films. The variation of $λ$ and $ξ$ leads to an intrinsic improvement of $J_{\rm c}$, via $J_{\rm d}$, obtaining extremely high values of $J_{\rm c}$ of $130$ MA/cm$^2$ and $8.0$ MA/cm$^2$ at $4.2$ K, consistent with an enhancement of $J_{\rm d}$ of a factor of $2$ for both incoherent nanoparticle-doped (Y,Gd)123 coated conductors (CCs) and BaFe$_2$(As$_{1-x}$P$_x$)$_2$ films, showing that this new material design is useful to achieving high critical current densities for a wide array of superconductors. The remarkably high vortex-pinning force in combination with this thermodynamic and pinning optimization route for the (Y,Gd)123 CCs reached $\sim 3.17$ TN/m$^3$ at $4.2$ K and 18 T (${\bf H}\parallel c$), the highest values ever reported in any superconductor.

cond-mat.supr-con↗