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The ultrafast modulation of terahertz (THz) waves is essential for numerous applications, such as high-rate wireless communication, nonreciprocal transmission, and linear frequency conversion. However, high-speed THz devices are rare due to the lack of materials that rapidly respond to external stimuli. Here, we demonstrate a dynamic THz metasurface by introducing an ultrathin superconducting microbridge into metallic resonators to form a superconductor-metal hybrid structure. Exploiting the susceptibility of superconducting films to external optical and THz pumps, we realized resonance mode switching within a few picoseconds. The maximum on/off ratio achieved is 11 dB. The observed periodic oscillation of transmission spectra both in the time and frequency domain under intense THz pump pulse excitation reveals the excitation of Higgs amplitude mode, which is used to realize picosecond scale THz modulation. This study opens the door to ultrafast manipulation of THz waves using collective modes of condensates, and highlights an avenue for developing agile THz modulation devices.

Controlling spin behavior via external stimuli is a key route to develop molecular spintronics devices. Photons, temperature, pressure, chemicals, and electric field are the possible stimuli. Herei...

Reconfigurable intelligent surfaces (RISs) play an essential role in various applications, such as next-generation communication, uncrewed vehicles, and vital sign recognizers. However, in the terahertz (THz) region, the development of RISs is limited because of lacking tunable phase shifters and low-cost sensors. Here, we developed an integrated self-adaptive metasurface (SAM) with THz wave detection and modulation capabilities based on the phase change material. By applying various coding sequences, the metasurface could deflect THz beams over an angle range of 42.8°. We established a software-defined sensing reaction system for intelligent THz wave manipulation. In the system, the SAM self-adaptively adjusted the THz beam deflection angle and stabilized the reflected power in response to the detected signal without human intervention, showing vast potential in eliminating coverage dead zones and other applications in THz communication. Our programmable controlled SAM creates a platform for intelligent electromagnetic information processing in the THz regime.

The system detection efficiency of superconducting nanowire single-photon detectors ( SNSPD ) has rapidly improved in recent years. In this study, we fabricated NbN, WSi and MoSi ultra-thin films, which are widely used for SNSPD fabrication, employing magnetron sputtering. We characterized the films in the presence of a magnetic field to study the upper critical magnetic field Hc2 and the anisotropy. According to the results obtained in our experiments, we calculated the coherence length and diffusion coefficient of these films. The knowledge of these parameters will guide the modelling and the interpretation of the different features observed in SNSPD made out of NbN, WSi and MoSi.

The inverse spin Hall effect (ISHE) is one of the accessible and reliable methods to detect spin current. The magnetization-dependent inverse spin Hall effect has been observed in magnets, expanding the dimension for spin-to-charge conversion. However, antiferromagnetic Néel-vector-dependent ISHE, which has been long time highly pursued, is still elusive. Here, ISHE in Mn

We show the diffuse and specular reflection images of defective foams placed on iron plates, which are obtained by a bifocal active imaging system at 0.22 THz. Foam materials studied are extruded polystyrene boards and acetate copolymer boards with artificially embedded defects. In the field of view of approximately 50 × 90 cm2, the incident angle of the emitting and receiving cochannel system affects the reflected signal intensity and the imaging method. We build a light reflection model, which corrects the angle-dependent intensity behavior, to make the imaging results more intuitive. Experimental results show that large-angle imaging, which collects mainly diffuse reflection light, can be used to detect defects and is actually more suitable for detecting small defects than small-angle imaging, which mainly collects specular reflection light.

Terahertz (THz) filters with high transmission coefficient (T) in the passband and frequency selectivity are critical in numerous applications such as astronomical detection and next-generation wireless communication. Freestanding bandpass filters eliminate the Fabry–Pérot effect of substrate, thus providing a promising choice for cascaded THz metasurfaces. However, the freestanding bandpass filters (BPFs) using the traditional fabrication process are costly and fragile. Here, we demonstrate a methodology to fabricate THz BPFs using aluminum (Al) foils. We designed a series of filters with center frequencies below 2 THz and manufacture them on 2-inch Al foils with various thicknesses. By optimizing the geometry, T of the filter at the center frequency is over 92%, and the relative full-width half maxima (FWHM) is as narrow as 9%. The responses of BPFs show that “cross-shaped” structures are insensitive to the polarization direction. The simple and low-cost fabrication process of the freestanding BPFs promise their widespread applications in THz systems.

Subwavelength-sized metallic structures exhibit extraordinary responses to electromagnetic waves due to their geometry, generating surface plasmon polaritons (SPPs) at the metal–dielectric interface. The development and application of terahertz (THz) science, which is an emerging science, can be advanced by studying SPPs in the THz band. Because the field strength of SPPs gradually weakens in the propagation direction, a coherent phase-matched THz SPP enhancement structure was designed. Here, we demonstrated an asymmetrical circular groove structure. And using this structure, THz SPPs can be excited and can be focused and enhanced under the illumination of linearly polarized THz pulses, generating a subwavelength-sized focal spot. These functions are achieved via phase matching. Furthermore, the original structure was modified by controlling the propagation phase of the THz SPPs and a periodic enhancement structure was designed. Compared to the original structure, the periodic enhancement structure has a stronger focusing effect on THz SPPs. Moreover, we imaged the THz SPPs by using a THz real-time near-field spectral imaging system and verified the feasibility of the designed structure by comparing with the simulation results. The study results are of great significance to the application of THz SPPs and the fabrication of related devices.

Herein, the structure and dielectric properties of Sm(Nb1−xVx)O4 (SNV-x) (0.0 ≤ x ≤ 0.9) ceramics were studied by crystal structure refinement, Raman, transmission electron microscope (TEM), far-infrared/THz reflectivity spectroscopy and microwave dielectric tests. Three kinds of ultra-low dielectric loss and temperature-stable Sm(Nb1−xVx)O4 (0.2 ≤ x ≤ 0.4) ceramics with permittivities of 18.01–16.89, Q × f values of 97 800–75 200 GHz (@∼8.6 GHz), and TCF of −5.6 (x = 0.2), to +2.3 ppm °C−1 (x = 0.3), then −6.3 (x = 0.4) ppm °C−1 were synthesized in this system. It was found that V5+ substitution can reliably induce the phase transition of monoclinic fergusonite (M-fergusonite, I2/a) to tetragonal zircon phase (T-zircon, I41/amd) (x ≈ 0.3), while effectively reducing the phase transition temperature. TEM shows that there were two different orientation domain structures in the M-fergusonite phase, and the widths of the two domain structures get closer with an increase in B-site substitution. Moreover, the variations in permittivity (er), quality factor (Q × f), and the temperature coefficient of resonance frequency (TCF) were strongly related to the crystal distortion and phase transition. Notably, a rectangular dielectric resonator antenna (RDRA) was fabricated with an Sm(Nb0.8V0.2)O4 (SNV-0.2) specimen. The antenna resonated at 27.04 GHz and had a bandwidth of ∼820 MHz (S11 < −10 dB). This system is a good candidate for 5G and future millimeter-wave applications.

The oxygen octahedral rotation around out-of-plane axis is explored to study its effect on metastable status, magnetic cluster glass in manganite. The antiphase rotation around the out-of-plane axis (TiO6 a0a0c-) of SrTiO3 enhances the Mn-O bond anisotropy along in-plane and out-of-plane directions, and weakens the ferromagnetic interactions in 12 nm Pr0.67Sr0.33MnO3 film on (001) SrTiO3 substrate, which together promote the formation of magnetic cluster-glassiness and enlarges the irreversible magnetoresistance effect with enhanced relaxation time of charge carrier. The effect of TiO6 a0a0c- in SrTiO3 substrate on materials properties is obvious with large irreversible magnetoresistance effect for thin film, which fades away with the increase of film thickness. At 10 K, the irreversible magnetoresistance is 0.91 for 12 nm film, and 0.22 for 30 nm film. This work extends current understanding on interfacial coupling to metastable status, and could help to explore other systems in perovskite structure with octahedral rotation.

This paper presents a low-profile 400 GHz Airy beam generator using a reflective anisotropic metasurface based on a phase-only modified Fourier-transform-type method. To efficiently launch 2-D terahertz (THz) Airy waves of compact size, the proposed Airy-beam system adopts a folded topology consisting of a single-layered reflective metasurface and a polarizing grid. Different from the conventional dielectric lens or single-layered transmitting metasurface, the proposed folded reflective structure achieves the required cubic phase using a quartz-based reflective metasurface with reduced volume and increased efficiency. A quasi-I-shaped unit cell is proposed for the metasurface to manipulate the incident THz wave by efficiently converting the initial illumination to its cross polarization and simultaneously adjusting its phase with a range of $2\pi $ . A reflective metasurface and a THz polarizing grid are designed and integrated to show both the unique transverse acceleration behavior and the self-reconstruction property at the 400 GHz band. The simulated and measured results demonstrate that the proposed folded topology can produce the expected THz Airy beam with compact size and polarization conversion efficiency over 90%.

Active metasurfaces have attracted increased attention due to their capabilities in function switching and wavefront shaping. Here we develop a new paradigm for active control of metasurfaces via integrating a tunable and programmable spintronic terahertz emitter (STE). While compatible with almost all conventional materials for metasurfaces, the STE can empower the passive metasurfaces to be active with increased flexibility. For the sake of illustration, a STE integrated metasurface quarter-wave plate is demonstrated, which enables broadband full polarization control over the entire Poincaré sphere. We also share a future perspective that the STE integrated metasurface can be readily programmed by using a commercial spatial light modulator. This work bridges the studies of metasurfaces and spintronic THz emitters, and may inspire more fruitful active metasurface designs and applications.

Pancharatnam-Berry (PB) metasurfaces have demonstrated mighty capability to manipulate electromagnetic (EM) waves, and exhibited potential applications for devices with broadband and efficient functionality. However, it remains a challenge to simultaneously achieve broadband and efficient wavefront manipulation for terahertz (THz) components with simple profiles. Herein, we introduce a simple ultra-thin PB metasurface with superior properties in the THz region. The structure is composed of a simple metallic C-Shaped Split Ring Resonator (CSRR) patterned on a flexible polyimide support layer. It is verified that the circular transmission efficiency is close to the theoretical limit of the single-layer metasurface in the range of 0.6 - 1.2 THz. Furthermore, we design metasurfaces based on the PB meta-atoms with spatially rotated orientation to achieve beam steering and superposition of vortex waves. The results are basically in line with expectations, validating the good performances of our proposal. This simple and easily deployable metasurface will give rise to more possibilities for the design of THz functional devices.

Asymmetric manipulation of electromagnetic waves exhibits tremendous capabilities in the applications of encryption, ultrafast information processing, and communication. However, compact and broadband terahertz (THz) components for asymmetric applications are still scarce. Here, we demonstrate broadband, ultrathin, and efficient metasurface-based asymmetric transmission and wavefront manipulation in the THz region. The metasurface consists of tri-layer metallic structures separated by two flexible polyimide dielectrics. This ultrathin structure exhibits superior asymmetric response which can act as an efficient device with a high linear polarization conversion ratio over 0.9 ranging from 0.5 to 1.1 THz. We also develop THz asymmetric applications based on the flexible metasurface for beam deflector and orbital angular momentum generation. The THz time-domain spectroscopy system and spectral imaging system are used to characterize the broadband asymmetric properties. The experimental results confirm that the beam deflection and vortex waves can be realized over broadband under one linearly polarized incidence while blocked under its orthogonal incidence. This work may provide a promising route to achieve broadband asymmetric applications in information encryption, THz wireless communication, and spectroscopy applications.

In this work, we applied terahertz near-field microscope based electro-optic sampling to animal tissue imaging. As a label-free diagnostic technique, fast THz near-field imaging system with a micrometer-scale spatial resolution can be constructed as an intraoperative diagnostic device for cancer clinical detection.

We designed and fabricated a kind of NbN-gold hybrid metamaterial-based modulator. They had tunable spectra response under thermal stimuli. This terahertz (THz) wave active modulator possesses good prospect for the application of THz imaging and communication.

Molecular geometries and electronic structure calculations and spectroscopic assignments for metallonaphthalocyanines NiNc, CuNc and ZnNc are performed on the optimized geometries at B3LYP/6–31G* level. The order of the bond lengths of the N M bonds is computed to be NiNc CuNc > ZnNc, which is in reverse sequence of the N–M bond length. The strongest Raman lines predicted at 1570 (NiNc), 1546 (CuNc) and 1525 (ZnNc) cm−1 are highly sensitive to the metal ion. Comparison of the calculated properties of MNcs and MPcs (metallphthalocyanines) compounds reveals some interesting and meaningful results due to extension of the conjugated systems.

Photon-number-resolving (PNR) is an important functionality in many applications. The traditional single photon detectors (SNSPDs) operated with the conventional readout scheme does not have the PNR functionality. In this paper, we demonstrate a superconducting photon-number-resolving detector operating at the visible wavelength regime, based on the serial connection of six superconducting nanowires. The results of our 6-element PNR device show clear evidence of n -photons differentiation with n ranging from 1 to 6. The system detection efficiency reaches 54% with the dark counts rate below 10 Hz at 660 nm. The demonstrated 6-element PNR device does not require a complex readout circuit compared with the SNSPD array device, and is expected to have wider applications in addition to imaging and communication.

Compact high-gain antennas are highly desired in the high-speed terahertz (THz) wireless system, especially for the space limited application, such as the high-speed inter link inside the high density wireless communication base station. To this end, a 400-GHz folded reflectarray (FRA) antenna with high gain, high aperture efficiency, and compact profile is proposed in this paper. It is composed of a feed source, a single-layered reflectarray using a lithography process on quartz, and a wire-grid polarizer implemented by the printed-circuit-board technology. A 3-D printed fixture is used to assemble all parts together. In order to design accurately the proposed antenna, the THz electromagnetic properties of the supporting dielectric materials are extracted by using a THz time-domain spectrometer system. Then, a single-layered phasing element, made up of a pair of orthogonally I-shaped structures with an open square ring, is proposed and designed based on the extracted material characteristics. Both phase compensation and polarization conversion can be realized by the proposed unit cell. A reflectarray is designed by using the proposed phasing element with the conventional array synthesizing theory, and a THz grid polarizer is designed with strips on a 0.127 mm Taconic TLY-5 substrate. The THz grid is placed in front of the THz feed and the reflectarray, which is fully reflective to the feed and transparent to the reflectarray. All components of the FRA antenna have been fabricated and assembled. Experiments show that the FRA prototype has a peak gain of 33.66 dBi at 400 GHz with an aperture efficiency of 33.65%, and a 3-dB gain bandwidth of 16% (357–421 GHz).

Various kinds of metasurfaces have been proposed because they can be tailored to achieve the desired modulations on electromagnetic wave that do not occur in nature. Compared to conventional metamaterials, coding metasurfaces integrated with information science theory possess numerous distinctive advantages - simple design, time-saving and compatibility with digital devices. Here we propose terahertz multifunctional anisotropic reflective metasurfaces with a metal-insulator-metal cavity structure whose top constructional layer consists of a pair of gold arc-rings and a gold cut-wire located between them. Two different functions of narrow-band absorption and broadband polarization conversion are realized based on different coding matrices using the binary codes ‘0’ and ‘1’. Furthermore, we integrate a specific coding metasurface with vanadium dioxide (VO2) to realize a temperature-controlled active metasurface. Through the temperature change, dynamic functionalities switching between a narrow-band polarization converter with a polarization conversion ratio over 94% and an efficient low-pass filter are achieved under the phase transition of VO2, and the active metasurface is polarization independent. The proposed coding metasurfaces are verified numerically and experimentally, and have promising applications in terahertz modulation and functional devices.

Spatial light modulators (SLMs) exhibited the powerful capability of controlling the electromagnetic wave. They have found numerous applications at terahertz (THz) frequencies, including wireless communication, digital holography, and compressive imaging. However, the development towards large-scale, multi-level and multi-functional THz SLM encounters technical challenges. Here, we present an electrically programmable THz metamaterial consisting of an array of 8⊆8 pixels, in which the phase change material of vanadium dioxide (VO2) is embedded. After successfully suppressing the crosstalk from adjacent pixels, the THz wave could be modulated in a programmable manner. The switching speed of each pixel was on the order of 1 kHz. In particular, utilising the hysteresis effect of VO2, the memory effect is demonstrated. The THz amplitude of each pixel can be written and erased by individual current pulses. Furthermore, multi-state THz images could be generated and stored, with a retention time of more than 5 hours. This programmable metamaterial with memory effect can be extended to other frequency bands and opens a route for electromagnetic information processing.

We demonstrate a high-efficiency visualized terahertz (THz) power meter based on the THz-photothermochromism of capsulized cholesteric liquid crystals (CCLCs) embedded in three-dimensional porous graphene (3DPG). The graphene is a broadband perfect absorber for THz radiation and transfers heat efficiently, and its black background is beneficial for color measurement. Quantitative visualization of THz intensity up to 2.8 × 10 2 m W / c m 2 is presented. The minimal detectable THz power is 0.009 mW. With multi-microcapsule analysis, the relationship between THz power and the average hue value of CCLCs achieves linearity. The device can convert THz radiation to visible light and is lightweight, cheap, and easy to use.

The oxygen octahedral rotation around the out-of-plane axis is explored to study its effect on metastable status, magnetic cluster glass in manganite. The antiphase rotation around the out-of-plane axis (TiO

We fabricate vertical $\mathrm{Nb}/{\mathrm{Ti}\mathrm{O}}_{x}/\mathrm{Nb}$ Josephson junctions where the ${\mathrm{Ti}\mathrm{O}}_{x}$ layer is mostly metallic but has a high-resistance interface with the top $\mathrm{Nb}$ electrode. Thus, the junctions are in essence of the superconductor--insulator--normal-metal--superconductor type. The ${\mathrm{Ti}\mathrm{O}}_{x}$ layer extends beyond the junction area and allows one to send an in-plane current through the normal-metal layer of the junction. We investigate and analyze dc properties (critical current, current-voltage characteristics) as well as the behavior of the junctions in external microwave fields. We find a strong dependence of all properties on the voltage ${V}_{i}$ applied across the ${\mathrm{Ti}\mathrm{O}}_{x}$ lead. The dependence on ${V}_{i}$ can be mapped to the dependence of the junction parameters on the bath temperature $T$, when ${V}_{i}$ is converted to an effective electronic temperature via ${T}_{e}=[{T}^{2}+(a{V}_{i}{)}^{2}{]}^{1/2}$, with $a=3.14\phantom{\rule{0.2em}{0ex}}\mathrm{K}/\mathrm{mV}$. This relation was used before in the context of a metallic nanowire contacted by superconducting electrodes. While the geometry of our ${\mathrm{Ti}\mathrm{O}}_{x}$ layer is far from that of a nanowire, the scaling works perfectly well for all experimental data. Our data also indicate that the electronic temperature is homogeneous throughout the junction area, a result that is unexpected for the large junction sizes we use. The device allows easy and relatively fast in situ manipulation of the junction parameters.