Spin-current Rectification Research Articles

Spin current rectification in a helical magnetic system with vanishing net magnetization

We report the phenomenon of spin current rectification in an antiferromagnetic helix, subjected to a transverse electric field, within a tight-binding framework based on Green’s function formalism. The electric field makes the site energies of the helix aperiodic in the Aunry–André–Harper (AAH) form, which breaks the symmetry among up and down spin sub-Hamiltonians. Under this condition, a finite bias drop along the helix yields different spin specific junction currents in two bias polarities, resulting in a spin current rectification. In the absence of either helicity or electric field, no such behavior is observed. Our analysis may provide a new route for getting spin current rectification through similar kinds of helical magnetic systems with vanishing net magnetization.

Charge and Spin Current Rectification through Functionalized Boron Nitride Bilayers

Charge and Spin Current Rectification through Functionalized Boron Nitride Bilayers

Molecular rectification assisted by spin-polarized hybrid interfacial states

Based on first-principles method, we construct molecular rectifiers by designing asymmetric hybrid interfacial states. The devices contain a ferromagnetic interface with sp3-d hybrid interfacial states and a nonmagnetic interface without hybrid interfacial states. The transport calculation demonstrates that obvious charge-current rectification and spin-current rectification are realized. The analysis of spin-resolved transmission reveals that the asymmetric shift of hybrid interfacial states plays an important role in determining the rectification ratio as well as the spin polarization orientation of the spin current, and hence the form of spin-current rectification. The effect of molecular length is further discussed. A length-induced increase of rectification ratio is observed for the charge-current rectification, while the largest spin-current rectification ratio appears at a specific length. This work demonstrates the potential of hybrid interfacial states in designing excellent molecular spinterface devices.

Multifunctional spintronic device based on zigzag SiC nanoribbon heterojunction via edge asymmetric dual-hydrogenation

The authors propose a method to obtain the multifunctional spintronic device by investigating the spin-resolved transport characteristics of zigzag SiC nanoribbon (zSiCNR) heterojunction via edge asymmetric dual-hydrogenation. The spin-resolved band structures show that the dual-hydrogenation on edge C or Si atoms all can change the initial metallicity of the pristine zSiCNR with the edge mono-hydrogenation to semiconductor in the presence of ferromagnetic field. The spin-resolved current-voltage characteristics of the zSiCNR heterojunction can show spin current rectification in the same rectify direction under the parallel magnetic field. The up-spin rectification ratio of our junction can be close to 10 13 at −0.5 V, which is much larger than rectification ratios of the previous junctions induced by the anti-parallel magnetic field. The zSiCNR heterojunction also exhibits a perfect spin filtering behavior with 100% spin filtering efficiency in both positive and negative bias regions under the anti-parallel magnetic field. More interestingly, the magnetoresistance is achieved by manipulating the external magnetic field in our zSiCNR heterojunction with the giant magnetoresistance ratio 5000% at 0.5 V. Therefore, the zSiCNR heterojunction via edge asymmetric dual-hydrogenation can be designed into the multifunctional spintronic devices, which has broad application prospects in the field of future spintronics. • Zigzag silicon carbon nanoribbon has potential in spin devices. • Giant spin current rectification is obtained in the presence of a ferromagnetic field. • Maximum spin current rectification ratios is closing to 10 13 . • Perfect spin filtering and magnetoresistance behaviors are also obtained.

Giant rectification of ferromagnetic zigzag SiC nanoribbons connecting anthradithiophene molecules

Using non-equilibrium Green's function combined with density functional theory, we investigate the spin-resolved transport properties of the zigzag SiC nanoribbon (zSiCNR) connecting anthradithiophene (ADT) molecules and obtain the giant spin current rectification in the presence of a ferromagnetic field. The dual-hydrogenation on edge C atoms or Si atoms can change the initial metallicity of the pristine zSiCNR with the edge mono-hydrogenation into semiconductivity in the presence of a ferromagnetic field. The up-spin current-voltage characteristic of the cis-ADT device and the trans-ADT device can present the significant rectification, and the corresponding giant spin current rectification ratios are close to 10<sup>11</sup> and 10<sup>10</sup> respectively. In addition, the current-voltage characteristics of two devices both perform a perfect spin filtering behavior in the positive bias region due to the huge difference between the up-spin current value and the down-spin current value. These findings are of great significance in the functional applications of spin-resolved molecular devices in the future.

Giant rectification in segmented, strongly interacting spin chains despite the presence of perturbations.

Balachandran et al. [Phys. Rev. Lett. 120, 200603 (2018)PRLTAO0031-900710.1103/PhysRevLett.120.200603] presented a segmented XXZ spin chain with zero anisotropy in one half and a large anisotropy on the other half that gave rise to a spin current rectification which is perfect in the thermodynamic limit. Here we extend the previous study to segmented chains with interacting integrable as well as nonintegrable halves, considering even cases in which no ballistic transport can emerge in either half. We demonstrate that, also in this more general case, it is possible to obtain giant rectification when the two interacting half chains are sufficiently different. We also show that the mechanism causing this effect is the emergence of an energy gap in the excitation spectrum of the out-of-equilibrium insulating steady state in one of the two biases. Finally, we demonstrate that in the thermodynamic limit there is no perfect rectification when each of the two half chains is interacting.

Rectification induced by geometry in two-dimensional quantum spin lattices.

We address the role of geometrical asymmetry in the occurrence of spin rectification in two-dimensional quantum spin chains subject to two reservoirs at the boundaries, modeled by quantum master equations. We discuss the differences in the rectification for some one-dimensional cases, and present numerical results of the rectification coefficient R for different values of the anisotropy parameter of the XXZ model, and different configurations of boundary drives, including both local and nonlocal dissipators. Our results also show that geometrical asymmetry, along with inhomogeneous magnetic fields, can induce spin current rectification even in the XX model, indicating that the phenomenon of rectification due to geometry may be of general occurrence in quantum spin systems.

Giant Spin Current Rectification Due to the Interplay of Negative Differential Conductance and a Non-Uniform Magnetic Field.

In XXZ chains with large enough interactions, spin transport can be significantly suppressed when the bias of the dissipative driving becomes large enough. This phenomenon of negative differential conductance is caused by the formation of two oppositely polarized ferromagnetic domains at the edges of the chain. Here, we show that this many-body effect, combined with a non-uniform magnetic field, can allow for a high degree of control of the spin current. In particular, by studying all of the possible shapes of local magnetic fields potentials, we find that a configuration in which the magnetic field points up for half of the chain and down for the other half, can result in giant spin-current rectification, for example, up to for a system with only 8 spins. Our results show clear indications that the rectification can increase with the system size.

Modeling and implementation of spin diode based on two dimensional materials using Monte Carlo sampling method

PurposeA “spin-diode” is the spintronics equivalent of an electrical diode: applying an external magnetic field greater than the limit of spin-diode BT flips the spin-diode between an isolating state and a conducting state [1]. While conventional electrical diodes are two-terminal devices with electrical current between the two terminals modulated by an electrical field, these two-terminal magneto resistive devices can generally be referred to as “spin-diodes” in which a magnetic field modulates the electrical current between the two terminals.Design/methodology/approachCurrent modulation and rectification are an important subject of electronics as well as spintronics spin diode is two-terminal magnetoresistive devices in which change in resistance in response to an applied magnetic field; this magnetoresistance occurs due to a variety of phenomena and with varying magnitudes and directions.FindingsIn this paper, an efficient rectifying spin diode is introduced. The resulting spin diode is formed from graphene gallium and indium quantum dots and antimony-doped molybdenum disulfide. Converting an alternating bias voltage to direct current is the main achievement of this model device with an additional profit of rectified spin-current. The non-equilibrium density functional theory with a Monte Carlo sampling method is used to evaluate the flow of electrons and rectification ratio of the system.Originality/valueThe results indicate that spin diode displaying both spin-current and charge-current rectification should be possible and may find practical application in nanoscale devices that combine logic and memory functions.

Controlled charge and spin current rectifications in a spin polarized device

Quasicrystals have been the subject of intense research in the discipline of condensed matter physics due to their non-trivial characteristic features. In the present work we put forward a new prescription to realize both charge and spin current rectifications considering a one-dimensional quasicrystal whose site energies and/or nearest-neighbor hopping (NNH) integrals are modulated in the form of well known Aubry-Andr\'{e} or Harper (AAH) model, a classic example of an aperiodic system. Each site of the chain contains a finite magnetic moment which is responsible for spin separation, and, in presence of finite bias an electric field is generated along the chain which essentially makes the asymmetric band structures under forward and reverse biased conditions, yielding finite rectification. Rectification is observed in two forms: (i) positive and (ii) negative, depending on the sign of currents in two bias polarities. These two forms can only be observed in the case of spin current rectification, while charge current shows conventional rectification operation. Moreover, we discuss how rectification ratio and especially its direction can be controlled by AAH phase which is always beneficial for efficient designing of a device. Finally, we critically examine the role of dephasing on rectification operations. Our study gives a new platform to analyze current rectification at nano-scale level, and can be verified in different quasi-crystals along with quantum Hall systems.

Nanoscale spintronics switch based on a three-terminal dsDNA molecule junction

Fundamental research associated with the chirality has exhibited the promising perspective for further technological applications. By means of the nonequilibrium Green’s function method, we study the spin and charge transport through a chiral double-stranded DNA molecule connected to three nonmagnetic electrodes. The spin and charge currents of the zero-bias terminal as an invasive probe manifests the conspicuous rectification feature, even the pure spin current with the zero charge current can be achieved. Interestingly, the three terminal DNA-based device can be used as a spin-charge switch that relies on the system parameters, such as the spin–orbit coupling strength, the helix angle, the molecular length, and the position of the invasive probe. Furthermore, the chiral-induced negative differential spin conductance can be observed. These results open up the possibility of utilizing chiral organic molecules as spintronics devices without magnetic materials. By introducing ferromagnetic leads, the strength and direction of the spin current rectification can be effectively regulated.

Towards Rectifying Performance at the Molecular Scale.

Molecular diode, proposed by Mark Ratner and Arieh Aviram in 1974, is the first single-molecule device investigated in molecular electronics. As a fundamental device in an electric circuit, molecular diode has attracted an enduring and extensive focus during the past decades. In this review, the theoretical and experimental progresses of both charge-based and spin-based molecular diodes are summarized. For the charge-based molecular diodes, the rectifying properties originated from asymmetric molecules including D-σ-A, D-π-A, D-A, and σ-π type compounds, asymmetric electrodes, asymmetric nanoribbons, and their combination are analyzed. Correspondingly, the rectification mechanisms are discussed in detail. Furthermore, a series of strategies for modulating rectification performance is figured out. Discussion on concept of molecular spin diode is also involved based on a magnetic co-oligomer. At the same time, the intrinsic mechanism as well as the modulation of the spin-current rectification performance is introduced. Finally, several crucial issues that need to be addressed in the future are given.

Spin-dependent transport and functional design in organic ferromagnetic devices.

Organic ferromagnets are intriguing materials in that they combine ferromagnetic and organic properties. Although challenges in their synthesis still remain, the development of organic spintronics has triggered strong interest in high-performance organic ferromagnetic devices. This review first introduces our theory for spin-dependent electron transport through organic ferromagnetic devices, which combines an extended Su–Schrieffer–Heeger model with the Green’s function method. The effects of the intrinsic interactions in the organic ferromagnets, including strong electron–lattice interaction and spin–spin correlation between π-electrons and radicals, are highlighted. Several interesting functional designs of organic ferromagnetic devices are discussed, specifically the concepts of a spin filter, multi-state magnetoresistance, and spin-current rectification. The mechanism of each phenomenon is explained by transmission and orbital analysis. These works show that organic ferromagnets are promising components for spintronic devices that deserve to be designed and examined in future experiments.

Inversion of spin-current rectification in magnetic co-oligomer diodes

The authors propose an inversion of spin-current rectification in magnetic co-oligomer diodes by investigating the rectification mechanism and rectifying direction theoretically. The results reveal two potential rectification mechanisms with opposite rectifying directions in magnetic co-oligomers, where the determined rectifying direction of each mechanism further varies relying on the involved frontier molecular orbital. The theoretical analysis indicates that an inversion of spin-current rectification, either in the form of inverted preferred amplitude or inverted spin polarization of the current, may be achieved by exchanging the dominant rectification mechanism or adjusting the involved conducting orbital. The inversion of rectification is demonstrated numerically in the subsequent current-voltage calculation by means of changing the molecular length or applying a gate voltage. This work indicates an intriguing prospect of magnetic co-oligomers as molecular spin diodes with controllable rectifying direction.

Length dependence of rectification in organic co-oligomer spin rectifiers**Project supported by the National Natural Science Foundation of China (Grant No. 11374195), the Natural Science Foundation of Shandong Province, China (Grant No. ZR2014AM017), the Taishan Scholar Project of Shandong Province, China, and the Excellent Young Scholars Research Fund of Shandong Normal University, China.

The rectification ratio of organic magnetic co-oligomer diodes is investigated theoretically by changing the molecular length. The results reveal two distinct length dependences of the rectification ratio: for a short molecular diode, the charge-current rectification changes little with the increase of molecular length, while the spin-current rectification is weakened sharply by the length; for a long molecular diode, both the charge-current and spin-current rectification ratios increase quickly with the length. The two kinds of dependence switch at a specific length accompanied with an inversion of the rectifying direction. The molecular ortibals and spin-resolved transmission analysis indicate that the dominant mechanism of rectification suffers a change at this specific length, that is, from asymmetric shift of molecular eigenlevels to asymmetric spatial localization of wave functions upon the reversal of bias. This work demonstrates a feasible way to control the rectification in organic co-oligomer spin diodes by adjusting the molecular length.

Effect of interfacial coupling on rectification in organic spin rectifiers**Project supported by the National Natural Science Foundation of China (Grant No. 1374195), the Natural Science Foundation of Shandong Province, China (Grant No. ZR2014AM017), and the Excellent Young Scholars Research Fund of Shandong Normal University, China.

The effect of interfacial coupling on rectification in an organic co-oligomer spin diode is investigated theoretically by considering spin-independent and spin-resolved couplings respectively. In the case of spin-independent coupling, an optimal interfacial coupling strength with a significant enhanced rectification ratio is found, whose value depends on the structural asymmetry of the molecule. In the case of spin-resolved coupling, we found that only the variation of the interfacial coupling with specific spin is effective to modulate the rectification, which is due to the spin-filtering property of the central asymmetric magnetic molecule. A transition of the spin-current rectification between parallel spin-current rectification and antiparallel spin-current rectification may be observed with the variation of the spin-resolved interfacial coupling. The interfacial effect on rectification is further analyzed from the spin-dependent transmission spectrum at different biases.

Graphitic silicon nitride: a metal-free ferromagnet with charge and spin current rectification.

As a first example, herein we show that g-Si(4)N(3) is expected to act as a metal-free ferromagnet featuring both charge and spin current rectification simultaneously. Such rectification is crucial for envisioning devices that contain both logic and memory functionality on a single chip. The spin coherent quantum-transport calculations on g-Si(4)N(3) reveal that the chosen system is a unique molecular spin filter, the current-voltage characteristics of which is asymmetric in nature, which can create a perfect background for synchronous charge and spin current rectification. To shed light on this highly unusual in-silico observation, we have meticulously inspected the bias-dependent modulation of the spin-polarized eigenstates. The results indicate that, whereas only the localized 2p orbitals of the outer-ring (OR) Si atoms participate in the transmission process in the positive bias, both OR Si and N atoms contribute in the reverse bias. Furthermore, we have evaluated the spin-polarized electron-transfer rate in the tunneling regime, and the results demonstrate that the transfer rates are unequal in the positive and negative bias range, leading to the possible realization of a simultaneous logic-memory device.

Spin-excited states and rectification in an organic spin rectifier

Spin-excited states in an asymmetric magnetic organic co-oligomer diode are investigated theoretically. The results demonstrate that the structural asymmetry of the co-oligomer is modulated by the spin-excited states, which is embodied in the wave functions of the eigenstates as well as the spin density wave. By calculating the transport property, a robust spin-current rectification concomitant with a charge-current rectification is observed in all spin-excited states. However, the current through the diode is suppressed distinctly by the spin-excited states, while the rectification ratios may be reduced or enhanced depending on the bias and the excited spins. The intrinsic mechanism is analyzed from the spin-dependent transmission combined with the change of molecular eigenstates under bias. Finally, the temperature-induced spin excitation is simulated. Significant rectification behavior is obtained even at room temperature.

Spin rectification in thermally driven XXZ spin chain via the spin-Seebeck effect

We study the phenomenon of spin-current rectification in a one-dimensional XXZ spin chain in the presence of a thermal drive. In our model a pure spin current is generated by a temperature difference between two harmonic heat baths which in turn creates a spin voltage via the spin-Seebeck effect. Along with a local spin-current operator definition and the nonequilibrium modified Redfield solution we study the spin-rectification ratio as a function of system size and external magnetic field. Intriguing effects are observed at low temperatures such as oscillations with system size and high range of tunability with external magnetic field making magnetic insulators, which are well described by the XXZ model, ideal candidates to build spin devices based on rectification.

Theory of spin blockade, charge ratchet effect, and thermoelectrical behavior in serially coupled quantum dot system

The charge transport of a serially coupled quantum dots (SCQD) connected to the metallic electrodes is theoretically investigated in the Coulomb blockade regime. A closed-form expression for the tunneling current of SCQD in the {\color{red} weak interdot hopping} limit is obtained by solving an extended two-site Hubbard model via the Green's function method. We use this expression to investigate spin current rectification, negative differential conductance, and coherent tunneling in the nonlinear response regime. The current rectification arising from the space symmetry breaking of SCQD is suppressed by increasing temperature. The calculation of SCQD is extended to the case of multiple parallel SCQDs for studying the charge ratchet effect and SCQD with multiple levels. In the linear response regime, the functionalities of spin filter and low-temperature current filter are demonstrated to coexist in this system. It is further demonstrated that two-electron spin singlet and triplet states can be readily resolved from the measurement of Seebeck coefficient rather than that of electrical conductance.