Optical tuning and ultrafast dynamics of high-temperature superconducting terahertz metamaterials
Optical tuning and ultrafast dynamics of high-temperature superconducting terahertz metamaterials
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DOI：
10.1515/nanoph-2012-0007
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发表时间：
2012-01-01
期刊：
影响因子：
7.5
通讯作者：
Chen, Hou-Tong
中科院分区：
文献类型：
--
作者：
Singh, Ranjan;Xiong, Jie;Chen, Hou-Tong
通过将半导体或复合氧化物集成到金属谐振器中，已经通过使用外部刺激改变环境来实现可调谐超材料。金属提供高导电性以实现超材料中的强共振响应;然而，它们对可调谐性的贡献非常小。高温超导薄膜的复杂电导率对外部扰动高度敏感，这为直接从谐振元件获得可调谐超材料提供了新的机会。此外，超导超材料有望实现强非线性响应和量子效应，特别是当约瑟夫森结集成到超材料谐振元件中时。在这里，我们展示了在太赫兹（THz）频率范围内的超快动态调谐的谐振在YBa 2Cu 3 O 7 -8（YBCO）的开口环谐振器（SRR）阵列由近红外飞秒激光脉冲激发。光激发使超导库珀对断裂，产生准粒子。这极大地改变了复电导率的虚部，并因此改变了超快时间尺度上的超材料共振，尽管真实的电导率没有显著改变。我们观察到共振开关伴随着大量的频率调谐作为光激发通量的函数，这也强烈依赖于纳米尺度的超导薄膜的厚度。我们所有的实验结果同意使用的分析模型，其中考虑到的YBCO薄膜的复杂的导电性的贡献，SRR电阻和动力学电感的计算。理论计算表明，随着光激发能量密度的增加，SRR电阻的增加导致了共振强度的降低，而电阻和动力学电感的变化导致了共振频率的移动。
Through the integration of semiconductors or complex oxides into metal resonators, tunable metamaterials have been achieved by a change of environment using an external stimulus. Metals provide high conductivity to realize a strong resonant response in metamaterials; however, they contribute very little to the tunability. The complex conductivity in high-temperature superconducting films is highly sensitive to external perturbations, which provides new opportunities in achieving tunable metamaterials resulting directly from the resonant elements. Additionally, superconducting metamaterials are expected to enable strong nonlinear response and quantum effects, particularly when Josephson junctions are integrated into the metamaterial resonant elements. Here we demonstrate ultrafast dynamical tuning of resonance in the terahertz (THz) frequency range in YBa2Cu3O7-8 (YBCO) split-ring resonator (SRR) arrays excited by near infrared femtosecond laser pulses. The photoexcitation breaks the superconducting Cooper pairs to create quasiparticles. This dramatically modifies the imaginary part of the complex conductivity and consequently the metamaterial resonance on an ultrafast timescale, although the real conductivity does not change significantly. We observed resonance switching accompanied by substantial frequency tuning as a function of photoexcitation fluence, which also strongly depends on the nanoscale thickness of the superconducting films. All of our experimental results agree with calculations using an analytical model, which takes into account the contributions of the complex conductivity of the YBCO films to SRR resistance and kinetic inductance. The theoretical calculations reveal that the increasing SRR resistance upon increasing photoexcitation fluence is responsible for the reduction of resonance strength, and changes in both the resistance and kinetic inductance cause the resonance frequency shifts.