Nonlinear Electrical Response Research Articles

Wideband coherent microwave conversion via magnon nonlinearity in a hybrid quantum system

Frequency conversion is a widely realized physical process in nonlinear systems of optics and electronics. As an emerging nonlinear platform, spintronic devices have the potential to achieve stronger frequency conversion. Here, we demonstrated a microwave frequency conversion method in a hybrid quantum system, integrating nitrogen-vacancy centers in diamond with magnetic thin film CoFeB. We achieve a conversion bandwidth ranging from 0.1 to 12 GHz, presenting an up to 25th order frequency conversion and further display the application of this method for frequency detection and qubits coherent control. Distinct from traditional frequency conversion techniques based on nonlinear electric response, our approach employs nonlinear magnetic response in spintronic devices. The nonlinearity, originating from the symmetry breaking such as domain walls in magnetic films, presents that our method can be adapted to hybrid systems of other spintronic devices and spin qubits, expanding the application scope of spintronic devices and providing a promising on-chip platform for coupling quantum systems.

Elastic Janus Microarray Film Strain Sensors with Heterogeneous Modulus and Conductivity for Healthcare and Braille Identification

AbstractMost stretchable film strain sensors generally present nonlinear electrical responses to applied strain, leading to an inaccurate acquisition of sophisticated signals, difficult signal processing, and zero‐calibration, which hampers practical applications severely. Here, a Janus hetero‐structured microarray film sensor is developed by in‐situ growth of silver nanoparticles on the surface of micro‐patterned elastomer films fabricated via low‐temperature imprinting followed by scraping‐induced particle trapping. Heterogeneous property designs in both modulus and electrical conductivity via introducing polymer microarrays enable modulating the electron transport manner in the conductive layer of elastic Janus films upon stretching, allowing to tune signal linearity effectively. Therefore, such a hetero‐structured film sensor shows good signal linearity (fluctuation of gauge factor [GF] below ±0.02) and relatively high sensitivity (GF > 10) within 55% strain, a detection limit of 0.2% strain, and a response/recovery time of 16.3/46.9 ms, respectively. Correspondingly, it enables monitoring human respiration and body motion with higher resolution compared with the nonlinear one, meanwhile, it is capable of detecting tiny pressure to discriminate braille alphabets via touch identification. Overall, it unveils a simple strategy to fabricate film strain sensors for high‐resolution healthcare and body motion monitoring, as well as electronic skins toward tactile sensing and touch identification.

Large and nonlinear electric field response in a two-dimensional ferroelectric Rashba material

The achievement of electrical spin control is highly desirable. One promising strategy involves electrically modulating the Rashba spin orbital coupling effect in materials. A semiconductor with high sensitivity in its Rashba constant to external electric fields holds great potential for short channel lengths in spin field-effect transistors, which is crucial for preserving spin coherence and enhancing integration density. Hence, two-dimensional (2D) Rashba semiconductors with large Rashba constants and significant electric field responses are highly desirable. Herein, by employing first-principles calculations, we design a thermodynamically stable 2D Rashba semiconductor, YSbTe<sub>3</sub>, which possesses an indirect band gap of 1.04 eV, a large Rashba constant of 1.54 eV·Å and a strong electric field response of up to 4.80 e·Å<sup>2</sup>. In particular, the Rashba constant dependence on the electric field shows an unusual nonlinear relationship. At the same time, YSbTe<sub>3</sub> has been identified as a 2D ferroelectric material with a moderate polarization switching energy barrier (~ 0.33 eV per formula). By changing the electric polarization direction, the Rashba spin texture of YSbTe<sub>3</sub> can be reversed. These outstanding properties make the ferroelectric Rashba semiconductor YSbTe<sub>3</sub> quite promising for spintronic applications.

Redox-based ion-gating reservoir consisting of (104) oriented LiCoO2 film, assisted by physical masking

Reservoir computing (RC) is a machine learning framework suitable for processing time series data, and is a computationally inexpensive and fast learning model. A physical reservoir is a hardware implementation of RC using a physical system, which is expected to become the social infrastructure of a data society that needs to process vast amounts of information. Ion-gating reservoirs (IGR) are compact and suitable for integration with various physical reservoirs, but the prediction accuracy and operating speed of redox-IGRs using WO3 as the channel are not sufficient due to irreversible Li+ trapping in the WO3 matrix during operation. Here, in order to enhance the computation performance of redox-IGRs, we developed a redox-based IGR using a (104) oriented LiCoO2 thin film with high electronic and ionic conductivity as a trap-free channel material. The subject IGR utilizes resistance change that is due to a redox reaction (LiCoO2 ⟺ Li1−xCoO2 + xLi+ + xe−) with the insertion and desertion of Li+. The prediction error in the subject IGR was reduced by 72% and the operation speed was increased by 4 times compared to the previously reported WO3, which changes are due to the nonlinear and reversible electrical response of LiCoO2 and the high dimensionality enhanced by a newly developed physical masking technique. This study has demonstrated the possibility of developing high-performance IGRs by utilizing materials with stronger nonlinearity and by increasing output dimensionality.

Tunable Chirality-Dependent Nonlinear Electrical Responses in 2D Tellurium.

Tellurium (Te) is an elemental semiconductor with a simple chiral crystal structure. Te in a two-dimensional (2D) form synthesized by a solution-based method shows excellent electrical, optical, and thermal properties. In this work, the chirality of hydrothermally grown 2D Te is identified and analyzed by hot sulfuric acid etching and high-angle tilted high-resolution scanning transmission electron microscopy. The gate-tunable nonlinear electrical responses, including the nonreciprocal electrical transport in the longitudinal direction and the nonlinear planar Hall effect in the transverse direction, are observed in 2D Te under a magnetic field. Moreover, the nonlinear electrical responses have opposite signs in left- and right-handed 2D Te due to the opposite spin polarizations ensured by the chiral symmetry. The fundamental relationship between the spin-orbit coupling and the crystal symmetry in two enantiomers provides a viable platform for realizing chirality-based electronic devices by introducing the degree of freedom of chirality into electron transport.

Topological enhancement of nonlinear transport in unconventional point-node semimetals

The topological singularity of the Bloch states close to the Fermi level significantly enhances nonlinear electric responses in topological semimetals. Here, we systematically characterize this enhancement for a large class of topological nodal-point fermions, including those with linear, linear-quadratic, and quadratic dispersions. Specifically, we determine the leading power-law dependence of the nonlinear response functions on the chemical potential $\ensuremath{\mu}$ defined relative to the nodal point. We identify two characteristics that qualitatively improve nonlinear transports compared to those of conventional Dirac and Weyl fermions. First, the type-II (overtilted) spectrum leads to the $log\ensuremath{\mu}$ enhancement of nonlinear response functions having zero scaling dimension with respect to $\ensuremath{\mu}$, which is not seen in a type-I (moderately or not tilted) spectrum. Second, the anisotropic linear-quadratic dispersion increases the power of small-$\ensuremath{\mu}$ divergence for the nonlinear response tensors along the linearly dispersing direction. Our work reveals new experimental signatures of unconventional nodal points in topological semimetals as well as provides a guiding principle for giant nonlinear electric responses.

Unifying semiclassics and quantum perturbation theory at nonlinear order

Nonlinear electrical response permits a unique window into effects of band structure geometry. It can be calculated either starting from a Boltzmann approach for small frequencies, or using Kubo’s formula for resonances at finite frequency. However, a precise connection between both approaches has not been established. Focusing on the second order nonlinear response, here we show how the semiclassical limit can be recovered from perturbation theory in the velocity gauge, provided that finite quasiparticle lifetimes are taken into account. We find that matrix elements related to the band geometry combine in this limit to produce the semiclassical nonlinear conductivity. We demonstrate the power of the new formalism by deriving a quantum contribution to the nonlinear conductivity which is of order \tau^{-1}τ−1 in the relaxation time \tauτ, which is principally inaccessible within the Boltzmann approach. We outline which steps can be generalized to higher orders in the applied perturbation, and comment about potential experimental signatures of our results.

Switchable chiral transport in charge-ordered kagome metal CsV3Sb5

When electric conductors differ from their mirror image, unusual chiral transport coefficients appear that are forbidden in achiral metals, such as a non-linear electric response known as electronic magnetochiral anisotropy (eMChA)1–6. Although chiral transport signatures are allowed by symmetry in many conductors without a centre of inversion, they reach appreciable levels only in rare cases in which an exceptionally strong chiral coupling to the itinerant electrons is present. So far, observations of chiral transport have been limited to materials in which the atomic positions strongly break mirror symmetries. Here, we report chiral transport in the centrosymmetric layered kagome metal CsV3Sb5 observed via second-harmonic generation under an in-plane magnetic field. The eMChA signal becomes significant only at temperatures below {T}^{{prime} }approx 35 K, deep within the charge-ordered state of CsV3Sb5 (TCDW ≈ 94 K). This temperature dependence reveals a direct correspondence between electronic chirality, unidirectional charge order7 and spontaneous time-reversal symmetry breaking due to putative orbital loop currents8–10. We show that the chirality is set by the out-of-plane field component and that a transition from left- to right-handed transport can be induced by changing the field sign. CsV3Sb5 is the first material in which strong chiral transport can be controlled and switched by small magnetic field changes, in stark contrast to structurally chiral materials, which is a prerequisite for applications in chiral electronics.

Dielectric properties with high dielectric permittivity and low loss tangent and nonlinear electrical response of sol-gel synthesized Na1/2Sm1/2Cu3Ti4O12 perovskite ceramic

Giant dielectric ceramic, Na1/2Sm1/2Cu3Ti4O12, was successfully prepared by a modified sol-gel method. X-ray diffraction experiments indicated that a body-centered cubic structure with a space group of Im3 was obtained. Our density functional theory calculations revealed that codoping Na and Sm in the CaCu3Ti4O12 structure resulted in charge compensation between Na and Sm ions in this structure, whereas the oxidation states of Cu and Ti were unaltered. Giant dielectric permittivity ∼7.21 × 103 - 8.04 × 103 and low dielectric loss tangent ∼0.045–0.049 were accomplished at a sintering temperature of 1050 °C for 12–18 h. Nonlinear J - E property with breakdown electric field ∼5.13 – 5.78 × 103 V/cm and nonlinear coefficient ∼6.08–6.82 were also achieved. The n-type semiconducting grain originated from short-range migrations of mixed Cu+/Cu2+ and Ti3+/Ti4+ charges. Finally, our charge analysis showed that the occurrence of Cu+ and Ti3+ was related to the existence of oxygen vacancy in these ceramics.

Investigation of microstructural evolution and suitable potential barrier model for non-linear electrical response of Sr and Nb co-doped CaCu3Ti4O12 ceramics

This work reported about impact of co-doping on structural and non-linear electrical property of CaCu 3 Ti 4 O 12 (CCTO) ceramics with composition Ca 0·95 Sr 0·05 Cu 3 Ti 3·94 Nb 0·06 O 12 prepared by solid state reaction technique. Rietveld refinement of X-ray diffraction data was performed to analyse various parameters for its structure exploration. Microstructure and compositional information of prepared ceramic was determined by SEM, EDX and elemental mapping. The grain size was found 2.32 μm with the use of ImageJ software on SEM images. The identical Raman mode were observed in present doped CCTO ceramics comparative to that reported for pure CCTO in Raman spectroscopy. The resistivity of prepared sample reveals NTC behaviour of the ceramic. The parameters; non-linear coefficient (α = 1.86), breakdown electric field (E b = 191.56V/cm) and leakage current (I = 0.44 mA) were obtained by current voltage measurement at room temperature (RT∼303K). The detail comparative study of various barrier models was carried out and found Schottky barriers as most suited model for potential barrier at grain boundaries in the present system. • Ca0·95Sr0·05Cu3Ti3·94Nb0·06O12 ceramic was synthesized using Solid State Reaction method. • Structural Properties were investigated by XRD, SEM, Raman and FT-IR spectroscopy. • Schottky emission model was found most suitable for non-linear electrical response of prepared ceramics. • The value of nonlinear coefficient and Breakdown field suggest it was suitable for low voltage application. • The present sample exhibits good NTC behaviour at low DC voltage and found useful for varistor and thermistor application.

Nonlinear electric response of the diffuse double layer to an abrupt charge displacement inside a biological membrane

In order to elucidate the old, still unsolved problem of how the diffuse electric double layer responds to an abrupt, intramolecular charge displacement inside a biological membrane, we investigated the fastest components of the light-induced electric signals of bacteriorhodopsin and its mutants, in numerous ionic and buffer solutions. The obtained data for temperature and solute concentration dependence were interpreted as a consequence of changes in the capacity of the diffuse double layer surrounding the purple membrane. The possible physiological consequences of this so far not demonstrated phenomenon are discussed.

Heavy water influences memcapacitive behavior of droplet interface bilayers

Memory resistors (memristors) and capacitors (memcapacitors) are circuit elements whose behavior depends on their prior history and are the result of different combinations of nonlinear electric responses. Currently, only a few systems have been shown to exhibit memcapacitive behavior. One of them is the droplet interface bilayer (DIB), developed to study membrane and membrane protein properties in a planar lipid bilayer system. DIBs are formed by suspending two aqueous lipid droplets attached to Ag/AgCl electrodes in an alkane oil reservoir with a lipid monolayer forming at the water-oil interface, where the lipid headgroups interact with water and the acyl chains with the oil phase.

Nonlinear Ballistic Response of Quantum Spin Hall Edge States.

Topological edge states (TES) exhibit dissipationless transport, yet their dispersion has never been probed. Here we show that the nonlinear electrical response of ballistic TES ascertains the presence of symmetry breaking terms, such as deviations from nonlinearity and tilted spin quantization axes. The nonlinear response stems from discontinuities in the band occupation on either side of a Zeeman gap, and its direction is set by the spin orientation with respect to the Zeeman field. We determine the edge dispersion for several classes of TES and discuss experimental measurement.

Strain-gated nonlinear Hall effect in two-dimensional MoSe2/WSe2 van der Waals heterostructure

It is recently found that the Hall effect can survive in the presence of time-reversal symmetry but with inversion-symmetry breaking, which is known as the nonlinear Hall effect. So far, the studies concerning the nonlinear Hall effect are mainly focused on the homogeneous systems, while less attention has been paid to the van der Waals (vdW) heterostructure, which in fact naturally breaks the spatial inversion symmetry. In this study, we systematically study the nonlinear electric response in $1{\text{T}}^{\ensuremath{'}}$-phase ${\mathrm{MoSe}}_{2}/{\mathrm{WSe}}_{2}$ vdW heterostructure. Our results demonstrate that ${\mathrm{MoSe}}_{2}/{\mathrm{WSe}}_{2}$ vdW heterostructure owns a large Berry curvature dipole, which is comparable with those of homogeneous multilayers and much larger than that predicted for monolayers under the in-plane uniaxial strain. In addition, the nonlinear Hall response in vdW heterostructure is sensitive to the relative position between the Fermi energy and tilted Dirac cones, and can be effectively manipulated from positive to negative values by applying an out-of-plane strain. Further study indicates that this can be ascribed to the charge transfer within the vdW interlayer. Based on these findings, our work provides a fundamental understanding of the nature of strain-gated nonlinear Hall effect in vdW heterostructures, which may facilitate the design of novel high-frequency nanodevices.

Spin-boson model of quantum dissipation in graphene: Nonlinear electrical response

Dissipation in the quantum solid of graphene is couched in the methodology of nonequilibrium statistical mechanics of an open quantum system. Of specific interest is the absorption accompanied by relaxation of energy because of an external frequency-dependent oscillatory electric field. At optical frequencies and for sizable amplitude of the electric field, the response is nonlinear, the treatment of which is simplified by means of a ``rotating wave approximation'' in which rapidly changing, off-resonance terms are omitted. The characteristic resonant frequency is what quantifies the tunneling between the valence and the conduction bands across the so-called Dirac point in graphene. The valence and the conduction states are mapped into the eigenstates of pseudo Pauli spin operators and the corresponding Hamiltonian, when embedded in a dissipative heat bath comprising the surrounding phonons and other electrons, makes possible a comprehensive analysis in terms of the much-studied spin-boson model of dissipative quantum statistical mechanics. A master equation for the density operator associated with this Hamiltonian yields rate equations for the mean population of the valence and the conduction states as well as the transition (matrix elements) between them. Further approximation of these rate equations allows contact with phenomenological treatments of the nonlinear optical conductivity. The present paper then provides a microscopic framework for investigating the response characteristics of a material of great topical interest using contemporary methods of quantum dissipation.

Enhanced giant dielectric properties and improved nonlinear electrical response in acceptor-donor (Al3+, Ta5+)-substituted CaCu3Ti4O12 ceramics

The giant dielectric behavior of CaCu3Ti4O12 (CCTO) has been widely investigated owing to its potential applications in electronics; however, the loss tangent (tanδ) of this material is too large for many applications. A partial substitution of CCTO ceramics with either Al3+ or Ta5+ ions generally results in poorer nonlinear properties and an associated increase in tanδ (to ~0.29–1.15). However, first-principles calculations showed that self-charge compensation occurs between these two dopant ions when co-doped into Ti4+ sites, which can improve the electrical properties of the grain boundary (GB). Surprisingly, in this study, a greatly enhanced breakdown electric field (~200–6588 V/cm) and nonlinear coefficient (~4.8–15.2) with a significantly reduced tanδ (~0.010–0.036) were obtained by simultaneous partial substitution of CCTO with acceptor-donor (Al3+, Ta5+) dopants to produce (Al3+, Ta5+)-CCTO ceramics. The reduced tanδ and improved nonlinear properties were attributed to the synergistic effects of the co-dopants in the doped CCTO structure. The significant reduction in the mean grain size of the (Al3+, Ta5+)-CCTO ceramics compared to pure CCTO was mainly because of the Ta5+ ions. Accordingly, the increased GB density due to the reduced grain size and the larger Schottky barrier height (Φb) at the GBs of the co-doped CCTO ceramics were the main reasons for the greatly increased GB resistance, improved nonlinear properties, and reduced tanδ values compared to pure and single-doped CCTO. In addition, high dielectric constant values (ε′ ≈ (0.52–2.7) × 104) were obtained. A fine-grained microstructure with highly insulating GBs was obtained by Ta5+ doping, while co-doping with Ta5+ and Al3+ resulted in a high Φb. The obtained results are expected to provide useful guidelines for developing new giant dielectric ceramics with excellent dielectric properties.

Charge transport through molecular ensembles: Recent progress in molecular electronics

This review focuses on molecular ensemble junctions in which the individual molecules of a monolayer each span two electrodes. This geometry favors quantum mechanical tunneling as the dominant mechanism of charge transport, which translates perturbances on the scale of bond lengths into nonlinear electrical responses. The ability to affect these responses at low voltages and with a variety of inputs, such as de/protonation, photon absorption, isomerization, oxidation/reduction, etc., creates the possibility to fabricate molecule-scale electronic devices that augment; extend; and, in some cases, outperform conventional semiconductor-based electronics. Moreover, these molecular devices, in part, fabricate themselves by defining single-nanometer features with atomic precision via self-assembly. Although these junctions share many properties with single-molecule junctions, they also possess unique properties that present a different set of problems and exhibit unique properties. The primary trade-off of ensemble junctions is complexity for functionality; disordered molecular ensembles are significantly more difficult to model, particularly atomistically, but they are static and can be incorporated into integrated circuits. Progress toward useful functionality has accelerated in recent years, concomitant with deeper scientific insight into the mediation of charge transport by ensembles of molecules and experimental platforms that enable empirical studies to control for defects and artifacts. This review separates junctions by the trade-offs, complexity, and sensitivity of their constituents; the bottom electrode to which the ensembles are anchored and the nature of the anchoring chemistry both chemically and with respect to electronic coupling; the molecular layer and the relationship among electronic structure, mechanism of charge transport, and electrical output; and the top electrode that realizes an individual junction by defining its geometry and a second molecule–electrode interface. Due to growing interest in and accessibility of this interdisciplinary field, there is now sufficient variety in each of these parts to be able to treat them separately. When viewed this way, clear structure–function relationships emerge that can serve as design rules for extracting useful functionality.

Structural and dielectric properties, and nonlinear electrical response of the CaCu3-xZnxTi4O12 ceramics: Experimental and computational studies

CaCu3-xZnxTi4O12 ceramics (x = 0, 0.05, 0.10) were successfully prepared by a conventional solid-state reaction method. Their structural and dielectric properties, and nonlinear electrical response were systematically inspected. The X-ray diffraction results indicated that single-phase CaCu3Ti4O12 (JCPDS no. 75–2188) was obtained in all sintered ceramics. Changes in the lattice parameter are well-matched with the computational result, indicating an occupation of Zn2+ doping ions at Cu2+ sites. The overall tendency shows that the average grain size decreases when x increases. Due to a decrease in overall grain size, the dielectric permittivity of CaCu3-xZnxTi4O12 decreases expressively. Despite a decrease in the dielectric permittivity, it remains at a high level in the doped ceramics (~3,406–11,441). Besides retention in high dielectric permittivity, the dielectric loss tangent of x = 0.05 and 0.10 (~0.074–0.076) is lower than that of x = 0 (~0.227). A reduction in the dielectric loss tangent in the CaCu3-xZnxTi4O12 ceramics is closely associated with the enhanced grain boundary response. Increases in grain boundary resistance, breakdown electric field, and conduction activation energy of grain boundary as a result of Zn2+ substitution are shown to play a crucial role in improved grain boundary response. Furthermore, the XPS analysis shows the existence of Cu+/Cu2+ and Ti3+/Ti4+, indicating charge compensation due to the loss of oxygen lattice. Based on all results of this work, enhanced dielectric properties of the Zn-doped CCTO can be explained using the internal barrier layer capacitor model.

Nonlinear electric response of chiral topological superconductors

We investigate, in the non-equilibrium Keldysh frame, a topological resistor–capacitor (RC) circuit consisting of a quantum dot coupled to a Majorana edge mode formed around a chiral topological superconductor. We implement both the adiabatic approximation and the numerical exact calculations to find out the unique non-equilibrium features of the electric response of the dissipative Majorana channel. First, the dependence of the dissipation on the frequency Ω of the ac driving on the dot is found to be greatly different whether the time-dependent dot level crosses the Fermi level or not during the driving. In the latter case, the relaxation resistance R q, the measure of the dissipation, obeys R q ∝ Ω2 for small frequencies, and in the former case, R q ∝ Ω−1/3 diverges as Ω → 0. In the former case, a universal scaling law for the dissipative part of the ac power is observed and attributed to the δ-peak in the dot density of states due to a uncoupled dot Majorana mode at the dot resonance condition. We compare the ac power, current, and the relaxation resistance between Majorana and trivial Dirac channels and clarify the Majorana nature in the dissipation.

Numerical modelling of electro‐viscoelasticity for fibre reinforced electro‐active polymers

AbstractElectro‐active polymers (EAP) are smart materials that can deform dramatically and quasi‐instantaneously in response to an applied electric field. These properties make them suitable to be used as soft robotic actuators. As any passive rubber‐like material, those electro‐sensitive components are quasi‐incompressible and may show pronounced time‐dependent hysteresis behaviour. The direction of the electric field induced deformation can be tuned by incorporating stiff fibres in a relatively soft EAP, which renders an anisotropic mechanical response of the whole composite. The contribution at hand presents a constitutive model which is suitable for the simulation of an electro‐viscoelastic behaviour of transversely isotropic EAP. The material model is based on an additive split of the total energy function into purely mechanical, electrical and coupled electro‐mechanical contributions. The mechanical part of the energy is further decomposed into isotropic and anisotropic parts. For the electrical and the coupled contributions, formulations for both the perfectly linear dielectric and the nonlinear (deformation dependent) electrical response are presented. Regarding the numerical implementation, a mixed quasi‐incompressible and quasi‐inextensible electro‐mechanical finite element is developed. In addition to the displacement and electric potential, four additional field variables are introduced. The capabilities of the proposed theory and its numerical treatment are demonstrated through simulations of several electro‐mechanical actuator structures. The utilization of a quasi‐inextensible finite element is shown to improve the convergence behaviour of the numerical solution, allowing for the simulation of complex loading scenarios of fibre reinforced EAP in an efficient manner.