光驱动高$T_c$超导体中的瞬态增强层间隧穿
Transiently enhanced interlayer tunneling in optically driven high $T_c$ superconductors
摘要：
最近的泵浦-探测实验报道了由调谐到特定晶格振动的中红外光泵浦脉冲引起的欠掺杂YBa $_2$ Cu $_3$ O $_{6+δ}$（YBCO）沿$c$轴的超导输运的增强。为了理解这种瞬态非平衡态，我们发展了一种约瑟夫森结堆的泵浦-探测形式，并考虑了超短光脉冲调制下的隧穿强度。我们表明，瞬态增强的约瑟夫森耦合可以获得脉冲激发，这可以是甚至大于在一个连续驱动的稳态。特别有趣的是，当材料以高于等离子体频率的频率参数驱动时，效果最大，这与实验发现的一致。对于双层约瑟夫森结，类似的增强实验预测低于临界温度$T_c$。该模型再现了在$T_c$下测量的增强的基本特征。为了重现上述$T_c$的实验结果，我们将在其他地方探索该模型的扩展，例如面内波动和振幅波动。
英文摘要：
Recent pump-probe experiments reported an enhancement of superconducting transport along the $c$-axis of underdoped YBa$_2$Cu$_3$O$_{6+δ}$ (YBCO), induced by a mid-infrared optical pump pulse tuned to a specific lattice vibration. To understand this transient non-equilibrium state, we develop a pump-probe formalism for a stack of Josephson junctions, and we consider the tunneling strengths in presence of modulation with an ultrashort optical pulse. We demonstrate that a transient enhancement of the Josephson coupling can be obtained for pulsed excitation and that this can be even larger than in a continuously driven steady-state. Especially interesting is the conclusion that the effect is largest when the material is parametrically driven at a frequency immediately above the plasma frequency, in agreement with what is found experimentally. For bilayer Josephson junctions, an enhancement similar to that experimentally is predicted below the critical temperature $T_c$. This model reproduces the essential features of the enhancement measured below $T_c$. To reproduce the experimental results above $T_c$, we will explore extensions of this model, such as in-plane and amplitude fluctuations, elsewhere.
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