arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1903.09083cond-mat.supr-concond-mat.softcond-mat.stat-mech
收藏

II型超导体热涡旋蠕变的强钉扎理论

Strong pinning theory of thermal vortex creep in type II superconductors

Martin Buchacek, Vadim B. Geshkenbein, Roland Willa, Gianni Blatter

摘要:

我们研究了第二类超导体中的热效应对钉扎和蠕变的影响,其中涡旋与低密度$n_p$的强点状缺陷相互作用,钉扎能量为$e_p$,扩展为$ξ$,即涡旋核的大小。如果单个钉和单个涡之间的相互作用导致出现描述钉扎和自由涡配置的非线性解,则将缺陷归类为强缺陷。扩展强钉扎理论,占热波动,我们提供了一个定量分析的涡旋脱钉和蠕变。利用Kramer速率理论,我们确定了涡旋态之间的热激活跃迁,并发现了涡旋态的非平衡稳态占据。后者取决于温度$T$和涡旋速度$v$,并决定了超导体在有限温度下的电流-电压(或力-速度)特性。我们发现,$T=0$线性过电流特性$v \propto (j-j_c) \, Θ(j-j_c)$在临界电流密度$j_c$处具有急剧转变,保持其整体形状,但由于热蠕变而以三种方式修改:$j_c$到热脱钉电流密度$j_\mathrm{dp}(T) < j_c$的向下重整,$j_\mathrm{dp}(T)$周围的特性的平滑舍入,以及在小驱动器$j \ll j_c$处出现热辅助磁通流(TAFF)${v \propto j \exp(-U_0/k_{\rm \scriptscriptstyle B} T)}$,其中激活势垒$U_0$通过自由分支和钉扎分支的交叉处的能量景观来定义。这一特性强调了在超过临界电流密度时蠕变的钉扎的持久性。

英文摘要:

We study thermal effects on pinning and creep in type-II superconductors where vortices interact with a low density $n_p$ of strong point-like defects with pinning energy $e_p$ and extension $ξ$, the vortex core size. Defects are classified as strong if the interaction between a single pin and an individual vortex leads to the appearance of bistable solutions describing pinned and free vortex configurations. Extending the strong pinning theory to account for thermal fluctuations, we provide a quantitative analysis of vortex depinning and creep. We determine the thermally activated transitions between bistable states using Kramer's rate theory and find the non-equilibrium steady-state occupation of vortex states. The latter depends on the temperature $T$ and vortex velocity $v$ and determines the current--voltage (or force--velocity) characteristic of the superconductor at finite temperatures. We find that the $T=0$ linear excess-current characteristic $v \propto (j-j_c) \, Θ(j-j_c)$ with its sharp transition at the critical current density $j_c$, keeps its overall shape but is modified in three ways due to thermal creep: a downward renormalization of $j_c$ to the thermal depinning current density $j_\mathrm{dp}(T) < j_c$, a smooth rounding of the characteristic around $j_\mathrm{dp}(T)$, and the appearance of thermally assisted flux flow (TAFF) ${v \propto j \exp(-U_0/k_{\rm \scriptscriptstyle B} T)}$ at small drive $j \ll j_c$, with the activation barrier $U_0$ defined through the energy landscape at the intersection of free and pinned branches. This characteristic emphasizes the persistence of pinning of creep at current densities beyond critical.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑