Abstract
We use finite element simulations in both the frequency and the time-domain to study the terahertz resonance characteristics of a metamaterial (MM) comprising a spiral connected to a straight arm. The MM acts as a RLC circuit whose resonance frequency can be precisely tuned by varying the characteristic geometrical parameters of the spiral: inner and outer radius, width and number of turns. We provide a simple analytical model that uses these geometrical parameters as input to give accurate estimates of the resonance frequency. Finite element simulations show that linearly polarized terahertz radiation efficiently couples to the MM thanks to the straight arm, inducing a current in the spiral, which in turn induces a resonant magnetic field enhancement at the center of the spiral. We observe a large (approximately 40 times) and uniform (over an area of ∼10 μm2) enhancement of the magnetic field for narrowband terahertz radiation with frequency matching the resonance frequency of the MM. When a broadband, single-cycle terahertz pulse propagates towards the MM, the peak magnetic field of the resulting band-passed waveform still maintains a six-fold enhancement compared to the peak impinging field. Using existing laser-based terahertz sources, our MM design allows to generate magnetic fields of the order of 2 T over a time scale of several picoseconds, enabling the investigation of nonlinear ultrafast spin dynamics in table-top experiments. Furthermore, our MM can be implemented to generate intense near-field narrowband, multi-cycle electromagnetic fields to study generic ultrafast resonant terahertz dynamics in condensed matter.
Highlights
With the advances in the development of laser-based, tabletop sources [1,2,3,4], strong terahertz radiation has become a novel tool to investigate low-energy excitations in condensed matter physics [5,6,7,8,9,10,11]
We use finite element simulations in both the frequency and the time-domain to study the terahertz resonance characteristics of a metamaterial (MM) comprising a spiral connected to a straight arm
We provide a simple analytical model that uses these geometrical parameters as input to give accurate estimates of the resonance frequency
Summary
With the advances in the development of laser-based, tabletop sources [1,2,3,4], strong terahertz radiation has become a novel tool to investigate low-energy excitations in condensed matter physics [5,6,7,8,9,10,11]. We have recently shown that, by introducing an asymmetric arm in a circular split-ring resonator, a relatively fabricated structure, the terahertz magnetic field can be enhanced tenfold in the central gap of the MM, while the corresponding electric field enhancement remained small [29]. We go beyond our previous study [29] by thoroughly investigating the design of an asymmetric spiral split-ring resonator that greatly enhances the magnetic component of the terahertz radiation, while only slightly enhancing the electric field component. We use finite element simulations in both the frequency- and the time-domain to investigate the three-dimensional distribution of electric and magnetic fields in such a structure. We find that finite element simulations in the time domain are necessary to reveal the complex evolution of the electromagnetic field in the MM, and to correctly estimate the peakfield enhancement with respect to an incoming broadband, single-cycle terahertz source
Published Version
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