Terahertz superconducting metamaterials for magnetic tunability (original) (raw)

Tuning the Resonance in High-Temperature Superconducting Terahertz Metamaterials

Physical Review Letters, 2010

In this Letter we present resonance properties in terahertz metamaterials consisting of a split-ring resonator array made from high temperature superconducting films. By varying the temperature, we observed efficient metamaterial resonance switching and frequency tuning with some features not revealed before. The results were well reproduced by numerical simulations of metamaterial resonance using the experimentally measured complex conductivity of the superconducting film. We developed a theoretical model that explains the tuning features, which takes into account the resistive resonance damping and additional split-ring inductance contributed from both the real and imaginary parts of the temperature-dependent complex conductivity. The theoretical model further predicted more efficient resonance switching and frequency shifting in metamaterials consisting of a thinner superconducting split-ring resonator array, which were also verified in experiments. PACS numbers: 78.67.Pt, 74.25.N-Metamaterials consisting of metallic elements have enabled a structurally scalable electrical and/or magnetic resonant response, from which exotic electromagnetic phenomena absent in natural materials have been observed . Metals provide high conductivity that is necessary to realize strong electrical/magnetic metamaterial response . Metals, however, play a negligible role in active/dynamical metamaterial resonance switching and/or frequency tuning, which has been typically accomplished through the integration of metamaterials with other natural materials (e.g. semiconductors) or devices, and by the application of external stimuli . It is essentially the modification of the metamaterial embedded environment that contributes to such previously observed functionalities.

Tuning of superconducting niobium nitride terahertz metamaterials

Optics express, 2011

Superconducting planar terahertz (THz) metamaterials (MMs), with unit cells of different sizes, are fabricated on 200 nm-thick niobium nitride (NbN) films deposited on MgO substrates. They are characterized using THz time domain spectroscopy over a temperature range from 8.1 K to 300 K, crossing the critical temperature of NbN films. As the gap frequency (f(g) = 2Δ0/h, where Δ0 is the energy gap at 0 K and h is the Plank constant) of NbN is 1.18 THz, the experimentally observed THz spectra span a frequency range from below f(g) to above it. We have found that, as the resonance frequency approaches f(g), the relative tuning range of MMs is quite wide (30%). We attribute this observation to the large change of kinetic inductance of superconducting film.

Sensing, Switching and Modulating applications of a Superconducting THz Metamaterial

IEEE Sensors Journal

The emergence of planar metamaterials (PrMMs) has opened a gateway to unprecedented electromagnetic (EM) properties and functionality unattainable from naturally occurring materials, thus enabling a family of PrMM based devices. In this paper, a novel class of superconducting (SC) PrMM is presented and a series of THz reflectance spectral responses simulations reveals that these SC PrMM structures portend applications in a variety of temperature sensors, thermooptical modulators, and magnetic switch devices.

Low-loss terahertz metamaterial from superconducting niobium nitride films

Optics Express, 2012

This paper reports a type of low Ohmic loss terahertz (THz) metamaterials made from low-temperature superconducting niobium nitride (NbN) films. Its resonance properties are studied by THz time domain spectroscopy. Our experiments show that its unloaded quality factor reaches as high as 178 at 8 K with the resonance frequency at around 0.58 THz, which is about 24 times that of gold metamaterial at the same temperature. The unloaded quality factor keeps at a high level, above 90, even when the resonance frequency increases to 1.02 THz, which is close to the gap frequency of NbN film. All these experimental observations fit well into the framework of Bardeen-Copper-Schrieffer theory and equivalent circuit model. These new metamaterials offer an efficient way to the design and implementation of high performance THz electronic devices.

Optical tuning and ultrafast dynamics of high-temperature superconducting terahertz metamaterials

Nanophotonics, 2012

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 fi lms 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 YBa 2 Cu 3 O 7-δ (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 modifi es the imaginary part of the complex conductivity and consequently the metamaterial resonance on an ultrafast timescale, although the real conductivity does not change signifi cantly. We observed resonance switching accompanied by substantial frequency tuning as a function of photoexcitation fl uence, which also strongly depends on the nanoscale thickness of the superconducting fi lms. 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 fi lms to SRR resistance and kinetic inductance. The theoretical calculations reveal that the increasing SRR resistance upon increasing photoexcitation fl uence is responsible for the reduction of resonance strength, and changes in both the resistance and kinetic inductance cause the resonance frequency shifts.

Terahertz superconductor metamaterial

Applied Physics Letters, 2010

We characterize the behaviour of split ring resonators made up of high-transition temperature YBCO superconductor using terahertz timedomain spectroscopy. The superconductor metamaterial shows sharp change in the transmission spectrum at the fundamental inductive-capacitive resonance and the dipole resonance as the temperature dips below the transition temperature. Our results reveal that the high performance of such a metamaterial is limited by material imperfections and defects such as cracks, voids and secondary phases which play dominant role in partially impeding the flow of current causing dissipation of energy and electrical resistance to appear in the superconductor film.

Thermally tunable magnetic metamaterials at THz frequencies

Journal of Optics, 2013

We investigate theoretically and numerically the tunability of the magnetic property of metamaterial in the THz region via thermal control. One component of the meta-atom is InSb, playing an important role as an alterable metal. When the temperature of the InSb stack increases from 300 to 350 K, the resonance peak of the transmission spectra shows a shift from 0.6 to 0.85 THz accompanied by a stronger magnetic behavior. The S-parameter retrieval method realizes the tunability of the negative permeability achieved in the above heating range.

Response of High-Tc Superconductor Metamaterials to High Intensity THz Radiation

2012

We report the observation of a nonlinear terahertz response of splitring resonator arrays made of high-temperature superconducting films. Intensitydependent transmission measurements indicate that the resonance strength decreases dramatically (i.e. transient bleaching) and the resonance frequency shifts as the intensity is increased. Pump-probe measurements confirm this behaviour and reveal dynamics on the few-picosecond timescale.

A terahertz Brewster switch based on superconductor hyperbolic metamaterial

Journal of Applied Physics, 2020

Active polarization switching devices are important to control the polarization state of light including terahertz (THz) waves that are technologically challenging to manipulate. Here, we propose and numerically demonstrate a hyperbolic metamaterial-based (HMM-based) active Brewster polarization switch for the intensity and phase modulation of THz light. The proposed multilayered HMM consists of alternating thin layers of high temperature superconductors such as yttrium barium copper oxide and dielectric materials such as lanthanum aluminate. The HMM shows elliptical dispersion above the superconducting phase transition temperature and type II hyperbolic dispersion in the superconducting state. By varying the temperature from the dielectric to the superconducting phase of the HMM, we demonstrate above 98% THz intensity modulation and 100% phase tunability (180°) at Brewster's angle. The proposed HMM can work as an efficient reflective THz modulator by properly selecting the angle of incidence.

Terahertz Resonators Based on YBa2Cu3O7 High-Tc Superconductor

Applied Sciences

Superconducting split-ring resonator arrays allow to overcome two main limitations affecting metallic metamaterial resonating in the terahertz (THz) range: ohmic losses and tunability of their optical response. In this work, we design and experimentally realize direct and complementary square arrays of superconducting YBa2Cu3O7 (YBCO) split-ring resonators working in the THz spectral range. The main purpose of this paper is to show how the metamaterial resonances can be tuned by temperature (T) when crossing the superconducting transition temperature Tc of YBCO. The tuning property can be quantified by describing the THz transmittance of the patterned YBCO films vs. T through a model of coupled resonators. This model allows us to estimate the THz resonances of split-ring arrays and their interaction, showing how the kinetic inductance Lk in the superconducting state is the main parameter affecting the metamaterial properties.