Abstract
The rise of two-dimensional (2D) crystalline superconductors has opened a new frontier of investigating unconventional quantum phenomena in low dimensions. However, despite the enormous ...advances achieved towards understanding the underlying physics, practical device applications like sensors and detectors using 2D superconductors are still lacking. Here, we demonstrate nonreciprocal antenna devices based on atomically thin NbSe
2
. Reversible nonreciprocal charge transport is unveiled in 2D NbSe
2
through multi-reversal antisymmetric second harmonic magnetoresistance isotherms. Based on this nonreciprocity, our NbSe
2
antenna devices exhibit a reversible nonreciprocal sensitivity to externally alternating current (AC) electromagnetic waves, which is attributed to the vortex flow in asymmetric pinning potentials driven by the AC driving force. More importantly, a successful control of the nonreciprocal sensitivity of the antenna devices has been achieved by applying electromagnetic waves with different frequencies and amplitudes. The device’s response increases with increasing electromagnetic wave amplitude and exhibits prominent broadband sensing from 5 to 900 MHz.
Superconductor-ferromagnet interfaces in two-dimensional heterostructures present a unique opportunity to study the interplay between superconductivity and ferromagnetism. The realization of such ...nanoscale heterostructures in van der Waals (vdW) crystals remains largely unexplored due to the challenge of making atomically-sharp interfaces from their layered structures. Here, we build a vdW ferromagnetic Josephson junction (JJ) by inserting a few-layer ferromagnetic insulator Cr
Ge
Te
into two layers of superconductor NbSe
. The critical current and corresponding junction resistance exhibit a hysteretic and oscillatory behavior against in-plane magnetic fields, manifesting itself as a strong Josephson coupling state. Also, we observe a central minimum of critical current in some JJ devices as well as a nontrivial phase shift in SQUID structures, evidencing the coexistence of 0 and π phase in the junction region. Our study paves the way to exploring sensitive probes of weak magnetism and multifunctional building-blocks for phase-related superconducting circuits using vdW heterostructures.
Abstract
The thermoelectric effects of topological semimetals have attracted tremendous research interest because many topological semimetals are excellent thermoelectric materials and ...thermoelectricity serves as one of their most important potential applications. In this work, we reveal the transient photothermoelectric response of Dirac semimetallic Cd
3
As
2
, namely the photo-Seebeck effect and photo-Nernst effect, by studying the terahertz (THz) emission from the transient photocurrent induced by these effects. Our excitation polarization and power dependence confirm that the observed THz emission is due to photothermoelectric effect instead of other nonlinear optical effect. Furthermore, when a weak magnetic field (~0.4 T) is applied, the response clearly indicates an order of magnitude enhancement on transient photothermoelectric current generation compared to the photo-Seebeck effect. Such enhancement supports an ambipolar transport nature of the photo-Nernst current generation in Cd
3
As
2
. These results highlight the enhancement of thermoelectric performance can be achieved in topological Dirac semimetals based on the Nernst effect, and our transient studies pave the way for thermoelectric devices applicable for high field circumstance when nonequilibrium state matters. The large THz emission due to highly efficient photothermoelectric conversion is comparable to conventional semiconductors through optical rectification and photo-Dember effect.
The Dirac semimetal cadmium arsenide (Cd3As2), a 3D electronic analog of graphene, has sparked renewed research interests for its novel topological phases and excellent optoelectronic properties. The ...gapless nature of its 3D electronic band facilitates strong optical nonlinearity and supports Dirac plasmons that are of particular interest to realize high‐performance electronic and photonic devices at terahertz (1 THz = 4.1 meV) frequencies, where the performance of most dynamic materials are limited by the tradeoff between power‐efficiency and switching speed. Here, all‐optical, low‐power, ultrafast broadband modulation of terahertz waves using an ultrathin film (100 nm, λ/3000) of Cd3As2 are experimentally demonstrated through active tailoring of the photoconductivity. The measurements reveal the photosensitive metallic behavior of Cd3As2 with high terahertz electron mobility of 7200 cm2 (Vs)−1. In addition, optical fluence dependent ultrafast charge carrier relaxation (15.5 ps), terahertz mobility, and long momentum scattering time (157 fs) comparable to superconductors that invoke kinetic inductance at terahertz frequencies are demonstrated. These remarkable properties of 3D Dirac topological semimetal envision a new class of power‐efficient, high speed, compact, tunable electronic, and photonic devices.
Cadmium arsenide (Cd3As2), a 3D Dirac semimetal, exhibits remarkable properties suitable for developing efficient opto‐electronics and photonic devices. Here, using transient THz spectroscopy, long scattering times, high mobility, and phototunable plasmonic properties in Cd3As2 are shown. An ultrasensitive and ultrafast THz modulator using ultrathin Cd3As2 is further demonstrated that can enable a novel material platform for compact high‐frequency RF electronics and ultrafast photonics.
In this work, high-performance ultraviolet to long-wave infrared (UV–LIR) devices based on an N-type three-dimensional (3D) Dirac semimetal Cd3As2 and P-type organic (small molecules and polymers) ...heterojunction are prepared. Primarily, the photodetector shows a broadband photoresponse from 365 to 10600 nm. The optimized device responsivity is 729 mA/W, along with a fast response time of 282 μs and a high on–off ratio of 6268, which are 2 orders of magnitude higher than those previously reported for a 3D Dirac semimetal-based device. In the LIR region (10600 nm), the responsivity and on–off ratio can reach 81.3 mA/W and 100, respectively. In addition, the time-resolved femtosecond pump detection technology is used to reveal the relaxation time of Cd3As2/organic thin films (4.30 ps), indicating that Cd3As2/organic thin films have great potential for the manufacture of fast IR devices. These results demonstrate that the 3D Dirac semimetal/organic thin film heterojunction photodetectors will be a feasible solution for high-speed and broadband photodetectors in large-array imaging.
In practical exploration, the complex and diverse topographic effects are important for the processing and interpretation of EM exploration data. The interpretation of the electromagnetic data ...results in large errors when the influence of topographical factors is simply ignored. At present, the study of TEM is mainly based on the ideal situation of flat terrain, and the study of topographic effect is less. However, topographic relief is inevitable in practical exploration. In this article, the correctness of the time-domain 3-D forward evolution based on the finite-element method (FEM) is verified by comparing the numerical results with those of the homogeneous full-space and half-space analytical solutions and the lumped high conductor model. In this article, 3-D numerical simulations of time-domain transient electromagnetic methods are calculated based on the FEM. Several exploration scenarios for complex terrain were constructed under the transmitting loop source, and the effect of terrain size and filling medium changes on the electromagnetic response was analyzed. The parameters of the topographic effect, earth resistivity, surface resistivity, and target conductivity are analyzed from the z -component of the magnetic field, apparent resistivity, and time-domain numerical solution, and the relative error distribution results in the whole observation period are shown. The results show that the influence of topographic effects on the electromagnetic response is concentrated in the early part of the time domain, with puddles of the same size having a higher influence on the electromagnetic response than raised soils and hollows. In practical exploration, puddles should be avoided where possible, whereas small-sized topographic reliefs and hollows have a negligible effect on the electromagnetic response.
The anomalous Hall effect (AHE) is a key transport signature revealing the topological properties of magnetic compounds. In quantum materials, the classical linear dependence of the AHE on ...magnetization often breaks down, which is typically ascribed to the presence of topological magnetic or electronic textures. However, the complex electronic structure of these compounds may offer alternative, unexplored mechanisms. Here, we show that a giant nonlinear AHE can originate from a series of magnetic-field-induced Lifshitz transitions in the spin-dependent band structure. In our experiments on EuCd_{2}As_{2} the AHE contributes to 97% of the total Hall response, corresponding to a record anomalous Hall angle of 21%. Our scaling analysis and first-principles calculations demonstrate that the electronic structure is extremely sensitive to spin canting, with the magnetic field causing band crossing and band inversion and introducing a band gap when oriented along specific directions. Our results not only provide an ideal platform for Berry curvature engineering but reveal a general effect that may be applied to other material systems.
In this paper, an estimation algorithm for the position and velocity of a moving target in a multistatic radar system is investigated. Estimation accuracy is improved by using bistatic range (BR), ...time-difference-of-arrival (TDOA), and Doppler shifts. Multistatic radar system includes several independent receivers and transmitters of time synchronization. Different transmitters radiate signals of different frequencies, and receivers detect the Doppler shifts of the received signals. These estimation parameters, BR, TDOA, and Doppler shifts, are readily available. The proposed algorithm combines different estimated parameters and optimizes estimation accuracy by two-step weighted least squares minimisations (WLS). This estimation algorithm is analysed and verified by simulations, which can reach the Cramer–Rao lower bound (CRLB) performance under mild Gaussian noise when the measurement error is small. Numerical simulations also demonstrate the superior performance of this method.
Three-dimensional (3D) Dirac semimetal materials have great application prospects in broad-spectrum photodetectors (PDs) working at wavebands up to the mid/far infrared region owing to their unique ...topological energy-band architectures and excellent photoelectric properties. However, the relatively high dark current in most Dirac semimetal-based PDs limits their photodetection performance, with poor signal-to-noise ratios (SNRs). Herein, we developed an ultra-low-noise-level PD linear array based on a 3D Dirac semimetal (Cd
1−
x
Zn
x
)
3
As
2
/Sb
2
Se
3
back-to-back (BTB) heterojunction using a molecular beam epitaxy (MBE)-grown (Cd
1−
x
Zn
x
)
3
As
2
film. Benefiting from the effective double-heterojunction design strategy, the as-fabricated (Cd
1−
x
Zn
x
)
3
As
2
/Sb
2
Se
3
linear-array PD exhibited an outstanding photodetection capacity from the visible to mid-infrared region (450 nm to 4.5 µm), with the highest recorded SNR close to 10
4
, excellent peak specific detectivity of 5.2 × 10
12
Jones, and high response speed of about 87.5 µs at room temperature. Furthermore, the PD exhibited long-term stability and uniformity as only minor photocurrent fluctuations occurred among different PD linear-array units demonstrating the feasibility of the PD for advanced optoelectronic applications, such as real-time light trajectory tracking. This work provides a reference strategy for the fabrication of fast-response broadband PDs with ultrahigh SNRs using the 3D Dirac semimetal (Cd
1−
x
Zn
x
)
3
As
2
/Sb
2
Se
3
BTB heterojunction and demonstrates the great prospect of 3D Dirac semimetal materials for the manufacture of fast-response uncooled focal-plane-array devices.
Recently, heterojunction photodetectors have attracted significant interest due to the multiple degrees of freedom reorganization, integrating advantages of different typed materials. Herein, a ...high‐performance photodetector based on a 3D Dirac semimetal Cd3As2/tungsten disulfide (WS2) heterojunction is demonstrated, which is constructed by directly transferring exfoliated 2D few layer WS2 on Cd3As2 nano‐belt and following by annealing treatment. The resulting Cd3As2/WS2 heterojunction device presents superior performance with a high on/off ratio (≈5.3 × 104) and a responsivity (Ri) of about 223.5 AW−1 at 520 nm, as well as an outstanding detectivity (D*) of about 2.05 × 1014 Jones at 808 nm near‐IR waveband. However, the optimized noise equivalent power (NEP) is evaluated about 6.17 × 10−14 WHz−1/2 by the noise power density spectrum. The excellent performance can be attributed to a high‐quality heterostructure interface, strong light absorption capacity, and ultralow dark current in a Cd3As2/WS2 heterojunction system. This work provides a promising platform to develop a high‐performance optoelectronic device based on 3D Dirac semimetal and 2D TMDs families.
The high‐performance photodetector based on a 3D Dirac semimetal Cd3As2/tungsten disulfide (WS2) van der Waals heterojunction device is presented, in which the excellent performance including outstanding on/off ratio, Ri, D*, and NEP can be attributed to a high‐quality heterostructure interface, strong light absorption capacity, and ultralow dark current in a Cd3As2/WS2 heterojunction system.
PDF
