All-Electric Quantum Point Contact Spin Valve

Spin filter and spin valve in ferromagnetic graphene

We propose and demonstrate that a EuO-induced and top-gated graphene ferromagnetic junction can be simultaneously operated as a spin filter as well as a spin valve. We attribute such a remarkable result to a coexistence of a half-metal band and a common energy gap for opposite spins in ferromagnetic graphene. We show that, both the spin filter and the spin valve can be effectively controlled by a back gate voltage, and they survive for practical metal contacts and finite temperature. Specifically, larger single spin currents and on-state currents can be reached with contacts with work function…

Current-field diagram of magnetic states of a surface spin valve in a point contact with a single ferromagnetic film

We present a study of the influence of an external magnetic field H and an electric current I on the spin-valve (SV) effect between a ferromagnetic thin film (F) and a sharp tip of a nonmagnetic metal (N). To explain our observations, we propose a model of a local surface SV which is formed in such a N/F contact. In this model, a ferromagnetic cluster at the N/F interface plays the role of the free layer in this SV. This cluster exhibits a larger coercive field than the bulk of the ferromagnetic film, presumably due to its nanoscale nature. Finally, we construct a magnetic state diagram of the…

Contact Induced Spin Relaxation in Graphene Spin Valves with Al2O3 and MgO Tunnel Barriers

We investigate spin relaxation in graphene by systematically comparing the roles of spin absorption, other contact-induced effects (e.g. fringe fields, etc.), and bulk spin relaxation for graphene spin valves with MgO barriers, Al2O3 barriers, and transparent contacts. We obtain effective spin lifetimes by fitting the Hanle spin precession data with two models that include or exclude the effect of spin absorption. Results indicate that additional contact-induced spin relaxation other than spin absorption dominates the contact effect. For tunneling contacts, we find reasonable agreement between…

Role of MgO barriers for spin and charge transport in Co/MgO/graphene non-local spin-valve devices

We investigate spin and charge transport in both single and bilayer graphene non-local spin-valve devices. Similar to previous studies on bilayer graphene, we observe an inverse dependence of the spin lifetime on the carrier mobility in our single layer devices. This general trend is only observed in devices with large contact resistances. Furthermore, we observe a second Dirac peak in devices with long spin lifetimes. This results from charge transport underneath the contacts. In contrast, all devices with low ohmic contact resistances only exhibit a single Dirac peak. Additionally, the spin …

Strong Spin-Filtering and Spin-Valve Effects in a Molecular V-C60-V Contact

Motivated by the recent achievements in manipulation of C60 molecules in STM experiments, we study theoretically the structure and electronic properties of a C60 molecule in an STM-tunneljunction with a magnetic tip and magnetic adatom on a Cu(111) surface from first-principle calculations. For the case of V tip/adatom, we demonstrate how spin-coupling between the magnetic V atoms mediated by the C60 can be observed in the electronic transport, which display a strong spin-filtering effect, allowing mainly majority-spin electrons to pass(>95%). Moreover, we find a significant change in the cond…

Competition between Thickness and Electrical Conditioning Influence in Enhancing Giant Magnetoresistance Ratio for NiCoFe/Alq3/NiCoFe Spin Valve

Spacer thickness and electrical conditioning have their own influence in enhancing giant magnetoresistance (GMR) ratio. At some condition one factor can override the other as reported by experiment results. An empiric model about competition about these two factors is discussed in this work. Comparison from experiment results to validate the model are also shown and explained. A formulation is proposed to extend the existing one that now accommodates both spacer thickness and electrical conditioning in one form.

Electrically Controllable van der Waals Antiferromagnetic Spin Valve

We propose a spin valve that is based on van der Waals antiferromagnetism and fully electrically controlled. The device is composed of two antiferromagnetic terminals that allow for vertical bias control and a linked central scattering potential region. The magnetoresistance varies significantly when the bias orientations in two terminals are switched from parallel to antiparallel because this switch induces a mismatch of the bands for the same spin projection in different parts of the system. It is shown from density functional calculations that bilayer graphene encapsulated by two atomic lay…

Effect of ferromagnetic contacts on spin accumulation in an all-metallic lateral spin-valve system: Semiclassical spin drift-diffusion equations

We study the effect of the ferromagnetic (FM) contacts on the spin accumulation in the lateral spin valve system for the collinear magnetization configurations. When an additional FM electrode is introduced in the all-metallic lateral spin-valve system, we find that the transresistance can be fractionally suppressed or very weakly influenced depending on the position of the additional FM electrode, and relative magnitudes of contact resistance and the bulk resistance defined over the spin diffusion length. Nonlocal spin signals such as nonlocal voltage drop and leakage spin currents are indepe…

Surface Spin-valve Effect

We report an observation of spin-valve like hysteresis within a few atomic layers at a ferromagnetic interface. We use phonon spectroscopy of nanometer sized point contacts as an in-situ probe to study the mechanism of the effect. Distinct in energy phonon peaks for contacts with dissimilar nonmagnetic outer electrodes allow to localize the observed spin switching to the top or bottom interfaces for nanometer thin ferromagnetic layers. The mechanism consistent with our data is energetically distinct atomically thin surface spin layers that can form current or field driven surface spin-valves w…

Spin-valve effects in point contacts to exchange biased Co40Fe40B20 films

Nonlinear current-voltage characteristics and magnetoresistance of point contacts between a normal metal (N) and films of amorphous ferromagnet (F) Co40Fe40B20 of different thickness, exchange-biased by antiferromagnetic Mn80Ir20 are studied. A surface spin valve effect in the conductance of such F-N contacts is observed. The effect of exchange bias is found to be inversely proportional to the Co40Fe40B20 film thickness. This behavior as well as other magneto-transport effects we observe on single exchange-pinned ferromagnetic films are similar in nature to those found in conventional three-la…

Modeling the Oblique Spin Precession in Lateral Spin Valves for Accurate Determination of Spin Lifetime Anisotropy: Effect of Finite Contact Resistance and Channel Length

The spin lifetime anisotropy is an important quantity for investigating the spin relaxation mechanisms in graphene and in heterostructures of two-dimensional materials. We generalize the diffusive spin transport equations of oblique spin precession in a lateral spin valve with finite contact resistance. This yields a method to determine the spin lifetime anisotropy ratio ξ=τ$_{\perp}$/τ$_{\parallel}$, which is the ratio between lifetimes of spin polarized perpendicular and parallel to the graphene surface. By solving the steady-state Bloch equations, we show that the line-shape of the oblique …

Effect of anisotropic spin absorption on the Hanle effect in lateral spin valves

We have succeeded in fully describing dynamic properties of spin current including the different spin absorption mechanism for longitudinal and transverse spins in lateral spin valves, which enables to elucidate intrinsic spin transport and relaxation mechanism in the nonmagnet. The deduced spin lifetimes are found independent of the contact type. From the transit-time distribution of spin current extracted from the Fourier transform in Hanle measurement data, the velocity of the spin current in Ag with Py/Ag Ohmic contact turns out much faster than that expected from the widely used model.

An observation of spin-valve effects in a semiconductor field effect transistor: a novel spintronic device

We present the first spintronic semiconductor field effect transistor. The injector and collector contacts of this device were made from magnetic permalloy thin films with different coercive fields so that they could be magnetized either parallel or antiparallel to each other in different applied magnetic fields. The conducting medium was a two dimensional electron gas (2DEG) formed in an AlSb/InAs quantum well. Data from this device suggest that its resistance is controlled by two different types of spin-valve effect: the first occurring at the ferromagnet-2DEG interfaces; and the second occu…

Valley filter and valley valve in graphene

It is known that the lowest propagating mode in a narrow ballistic ribbon of graphene may lack the twofold valley degeneracy of higher modes. Depending on the crystallographic orientation of the ribbon axis, the lowest mode mixes both valleys or lies predominantly in a single valley (chosen by the direction of propagation). We show, using a tight-binding model calculation, that a nonequilibrium valley polarization can be realized in a sheet of graphene, upon injection of current through a ballistic point contact with zigzag edges. The polarity can be inverted by local application of a gate vol…

Electrical detection of spin accumulation and spin precession at room temperature in metallic spin valves

We have fabricated a multi terminal lateral mesoscopic metallic spin valve demonstrating spin precession at room temperature, using tunnel barriers in combination with metallic ferromagnetic electrodes as spin injector and detector. The observed modulation of the output signal due to the spin precession is discussed and explained in terms of a time of flight experiment of electrons in a diffusive conductor. The obtained spin relaxation length lambda_{sf}=500 nm in an Al strip will make possible detailed studies of spin dependent transport phenomena and allow to explore the possibilities of the…

Spin injection and detection up to room temperature in Heusler~alloy/$n$-GaAs spin valves

We have measured the spin injection efficiency and spin lifetime in Co$_2$FeSi/$n$-GaAs lateral nonlocal spin valves from 20 to 300 K. We observe large ($\sim$40 $μ$V) spin valve signals at room temperature and injector currents of $10^3~$A/cm$^2$, facilitated by fabricating spin valve separations smaller than the 1 $μ$m spin diffusion length and applying a forward bias to the detector contact. The spin transport parameters are measured by comparing the injector-detector contact separation dependence of the spin valve signal with a numerical model accounting for spin drift and diffusion. The a…

Coherent spin valve phenomena and electrical spin injection in ferromagnetic/semiconductor/ferromagnetic junctions

Coherent quantum transport in ferromagnetic/ semiconductor/ ferromagnetic junctions is studied theoretically within the Landauer framework of ballistic transport. We show that quantum coherence can have unexpected implications for spin injection and that some intuitive spintronic concepts which are founded in semi-classical physics no longer apply: A quantum spin-valve (QSV) effect occurs even in the absence of a net spin polarized current flowing through the device, unlike in the classical regime. The converse effect also arises, i.e. a zero spin-valve signal for a non-vanishing spin-current.…

Electrical Detection of Spin Precession in Single Layer Graphene Spin Valves with Transparent Contacts

Spin accumulation and spin precession in single-layer graphene are studied by non-local spin valve measurements at room temperature. The dependence of the non-local magnetoresistance on electrode spacing is investigated and the results indicate a spin diffusion length of ~1.6 microns and a spin injection/detection efficiency of 0.013. Electrical detection of the spin precession confirms that the non-local signal originates from spin injection and transport. Fitting of the Hanle spin precession data yields a spin relaxation time of ~84 ps and a spin diffusion length of ~1.5 microns, which is co…

Confined dissipative droplet solitons in spin-valve nanowires with perpendicular magnetic anisotropy

Magnetic dissipative droplets are localized, strongly nonlinear dynamical modes excited in nano-contact spin valves with perpendicular magnetic anisotropy. These modes find potential application in nanoscale structures for magnetic storage and computation, but dissipative droplet studies have so far been limited to extended thin films. Here, numerical and asymptotic analyses are used to demonstrate the existence and properties of novel solitons in confined structures. As a nanowire's width is decreased with a nano-contact of fixed size at its center, the observed modes undergo transitions from…

Gate-dependent spin-torque in a nanoconductor-based spin-valve

This article discusses the spin-torque effect in a spin-valve made out of two ferromagnetic leads connected through a coherent nanoconductor (NC), in the limit where a single channel of the NC lies near the Fermi energy of the leads. Due to quantum interferences inside the NC, the spin-torque presents clear qualitative differences with respect to the case of a multichannel disordered spin-valve. In particular, it can be modulated with the NC gate voltage. In principle, this modulation can be observed experimentally, assuming that the spin-torque affects a ferromagnetic nano-domain in direct co…

Closed-loop electric currents and non-local resistance measurements with wide F/I/N tunnel contacts

Lateral spin valves are used to generate and characterize pure spin currents. Non-local voltage measured in such structures provides information about spin polarization and spin decay rates. For wide high-transparency F/N contacts it was shown that the Johnson-Silsbee non-local effect is substantially enriched by closed-loop electric currents driven by local spin injection in the electrically dangling part of the valve. For valves with low-transparency F/I/N tunnel contacts such circular currents are strongly suppressed, yet we show that the voltage modifications persist, may be significant, a…

Unambiguous Electrical Detection of Spin-Charge Conversion in Lateral Spin-Valves

Efficient detection of spin-charge conversion is crucial for advancing our understanding of emergent phenomena in spin-orbit-coupled nanostructures. Here, we provide proof of principle of an electrical detection scheme of spin-charge conversion that enables full disentanglement of competing spin-orbit coupling transport phenomena in diffusive lateral channels i.e. the inverse spin Hall effect (ISHE) and the spin galvanic effect (SGE). A suitable detection geometry in an applied oblique magnetic field is shown to provide direct access to spin-charge transport coefficients through a simple symme…

Accumulation of spin-polarized states of charge carriers and a spintronic battery

Spin valves based on materials in which the spin-flip is suppressed by the spatial separation of charge carriers, while maintaining electric neutrality in the valve volume, are considered. The possibility of using these valves as electric batteries is discussed. It is shown that if the potential difference across the valve is controlled, incommensurability effects such as the "devil's staircase" may be expected, which are associated with the Coulomb interaction and redistribution of electrons occurring while the battery is charged and discharged. The effects of the emergence and vanishing of s…

Simulations on the influence of spatially-varying spin transport parameters on the measured spin lifetime in graphene non-local spin valves

Spin transport properties of graphene non-local spin valve devices are typically determined from Hanle spin precession measurements by using a simplified solution of the one-dimensional Bloch-Torrey equation which assumes infinitely long transport channels and uniform spin transport parameter. We investigate the effects of a finite graphene size and explore the influence of spatially-varying transport parameters on the measured Hanle curves by finite element simulations. We assume enhanced spin dephasing in the contact-covered graphene areas with additional Fermi level pinning and explore the …

Topological insulator based spin valve devices: evidence for spin polarized transport of spin-momentum-locked topological surface states

Spin-momentum helical locking is one of the most important properties of the nontrivial topological surface states (TSS) in 3D topological insulators (TI). It underlies the iconic topological protection (suppressing elastic backscattering) of TSS and is foundational to many exotic physics (eg., majorana fermions) and device applications (eg., spintronics) predicted for TIs. Based on this spin-momentum locking, a current flowing on the surface of a TI would be spin-polarized in a characteristic in-plane direction perpendicular to the current, and the spin-polarization would reverse when the cur…

Charge and spin transport in spin valves with anisotropic spin relaxation

We investigate effects of spin-orbit splitting on electronic transport in a spin valve consisting of a large quantum dot defined on a two-dimensional electron gas with two ferromagnetic contacts. In the presence of both structure inversion asymmetry (SIA) and bulk inversion asymmetry (BIA) a giant anisotropy in the spin-relaxation times has been predicted. We show how such an anisotropy affects the electronic transport properties such as the angular magnetoresistance and the spin-transfer torque. Counterintuitively, anisotropic spin-relaxation processes sometimes enhance the spin accumulation.

Electric-field control of tunneling magnetoresistance effect in a Ni/InAs/Ni quantum-dot spin valve

We demonstrate an electric-field control of tunneling magnetoresistance (TMR) effect in a semiconductor quantum-dot (QD) spin-valve device. By using ferromagnetic Ni nano-gap electrodes, we observe the Coulomb blockade oscillations at a small bias voltage. In the vicinity of the Coulomb blockade peak, the TMR effect is significantly modulated and even its sign is switched by changing the gate voltage, where the sign of the TMR value changes at the resonant condition.

Resistance noise in spin valves

Fluctuations of the magnetization in spin valves are shown to cause resistance noise that strongly depends on the magnetic configuration. Due to the applied external field and the dynamic exchange interaction through the normal metal spacer, the electrical noise level of the antiparallel configuration can exceed that of the parallel one by an order of magnitude, in agreement with recent experimental results.

Shot noise in a diffusive F-N-F spin valve

Fluctuations of electric current in a spin valve consisting of a diffusive conductor connected to ferromagnetic leads and operated in the giant magnetoresistance regime are studied. It is shown that a new source of fluctuations due to spin-flip scattering enhances strongly shot noise up to a point where the Fano factor approaches the full Poissonian value.

Thermal spin injection and interface insensitivity in permalloy/aluminum metallic non-local spin valves

We present measurements of thermal and electrical spin injection in nanoscale metallic non-local spin valve (NLSV) structures. Informed by measurements of the Seebeck coefficient and thermal conductivity of representative films made using a micromachined Si-N thermal isolation platform, we use simple analytical and finite element thermal models to determine limits on the thermal gradient driving thermal spin injection and calculate the spin dependent Seebeck coefficient to be $-0.5\ μ\mathrm{V}/\mathrm{K}< S_{s}<-1.3\ μ\mathrm{V}/\mathrm{K}$. This is comparable in terms of the fraction of the …

Non-monotonic angular magnetoresistance in asymmetric spin valves

The electric resistance of ferromagnet/normal-metal/ferromagnet perpendicular spin valves depends on the relative angle between the magnetization directions. In contrast to common wisdom, this angular magnetoresistance is found to be not necessarily a monotone function of the angle. The parameter dependence of the global resistance minimum at finite angles is studied and the conditions for experimental observation are specified.

Temperature dependence of spin polarization in ferromagnetic metals using lateral spin valves

A high reproducibility in the performance of cobalt/copper and permalloy/copper lateral spin valves with transparent contacts is obtained by optimizing the interface quality and the purity of copper. This allows us to study comprehensively the spin injection properties of both ferromagnetic materials, as well as the spin transport properties of copper, which are not affected by the used ferromagnetic material, leading to long spin diffusion lengths. Spin polarizations of permalloy and cobalt are obtained as a function of temperature. Analysis of the temperature dependence of both the spin pola…

Non-collinear single-electron spin-valve transistors

We study interaction effects on transport through a small metallic cluster connected to two ferromagnetic leads (a single-electron spin-valve transistor) in the "orthodox model" for the Coulomb blockade. The non-local exchange between the spin accumulation on the island and the ferromagnetic leads is shown to affect the transport properties such as the electric current and spin-transfer torque as a function of the magnetic configuration, gate voltage, and applied magnetic field.

Decay of spin polarized hot carrier current in a quasi one-dimensional spin valve structure

We study the spatial decay of spin polarized hot carrier current in a spin-valve structure consisting of a semiconductor quantum wire flanked by half-metallic ferromagnetic contacts. The current decays because of D'yakonov-Perel' spin relaxation in the semiconductor caused by Rashba spin orbit interaction. The associated relaxation length is found to decrease with increasing lattice temperature (in the range 30-77 K) and exhibit a non-monotonic dependence on the electric field driving the current. The relaxation lengths are several tens of microns which are at least an order of magnitude large…

Spin lifetimes exceeding 12 nanoseconds in graphene non-local spin valve devices

We show spin lifetimes of 12.6 ns and spin diffusion lengths as long as 30.5 μm in single layer graphene non-local spin transport devices at room temperature. This is accomplished by the fabrication of Co/MgO-electrodes on a Si/SiO$_2$ substrate and the subsequent dry transfer of a graphene-hBN-stack on top of this electrode structure where a large hBN flake is needed in order to diminish the ingress of solvents along the hBN-to-substrate interface. Interestingly, long spin lifetimes are observed despite the fact that both conductive scanning force microscopy and contact resistance measurement…

A Double Quantum Dot Spin Valve

A most fundamental and longstanding goal in spintronics is to electrically tune highly efficient spin injectors and detectors, preferably compatible with nanoscale electronics. Here, we demonstrate all these points using semiconductor quantum dots (QDs), individually spin-polarized by ferromagnetic split-gates (FSGs). As a proof of principle, we fabricated a double QD spin valve consisting of two weakly coupled semiconducting QDs in an InAs nanowire (NW), each with independent FSGs that can be magnetized in parallel or anti-parallel. In tunneling magnetoresistance (TMR) experiments at zero ext…

Anomalous-Nernst and anisotropic magnetoresistive heating in a lateral spin valve

We measured the anomalous-Nernst effect and anisotropic magnetoresistive heating in a lateral multiterminal Permalloy/Copper spin valve using all-electrical lock-in measurements. To interpret the results, a three-dimensional thermoelectric finite-element-model is developed. Using this model, we extract the heat profile which we use to determine the anomalous Nernst coefficient of Permalloy Rn=0.13 and also determine the maximum angle of theta=8 degrees of the magnetization prior to the switching process when an opposing non-collinear 10$^{\circ}$ magnetic field is applied.

Nanoconstriction Microscopy of the Giant Magnetoresistance in Cobalt/Copper Spin Valves

We use nanometer-sized point contacts to a Co/Cu spin valve to study the giant magnetoresistance (GMR) of only a few Co domains. The measured data show strong device-to-device differences of the GMR curve, which we attribute to the absence of averaging over many domains. The GMR ratio decreases with increasing bias current. For one particular device, this is accompanied by the development of two distinct GMR plateaus, the plateau level depending on bias polarity and sweep direction of the magnetic field. We attribute the observed behavior to current-induced changes of the magnetization, involv…

Current-induced Pinwheel Oscillations in Perpendicular Magnetic Anisotropy Spin Valve Nanopillars

Nanopillar spin valve devices are typically comprised of two ferromagnetic layers: a reference layer and a free layer whose magnetic orientation can be changed by both an external magnetic field and through the introduction of spin-polarized electric current. Here we report the continuous repeated switching behavior of both the reference and free layers of a perpendicular spin valve made of Co/Pd and Co/Ni multilayers that arises for sufficiently large DC currents. This periodic switching of the two layers produces an oscillating signal in the MHz regime but is only observed for one sign of th…

Nonmonotonic bias dependence of local spin accumulation signals in ferromagnet/semiconductor lateral spin-valve devices

We find extraordinary behavior of the local two-terminal spin accumulation signals in ferromagnet (FM)/semiconductor (SC) lateral spin-valve devices. With respect to the bias voltage applied between two FM/SC Schottky tunnel contacts, the local spin-accumulation signal can show nonmonotonic variations, including a sign inversion. A part of the nonmonotonic features can be understood qualitatively by considering the rapid reduction in the spin polarization of the FM/SC interfaces with increasing bias voltage. In addition to the sign inversion of the FM/SC interface spin polarization, the influe…

Switching of a Quantum Dot Spin Valve by Single Molecule Magnets

We explore theoretically the spin transport in nanostructures consisting of a gold quantum dot bridging nonmagnetic electrodes and two Mn12-Ph single molecule magnets (SMMs) that are thiol-bonded to the dot but are not in direct contact with the electrodes. We find that reversal of the magnetic moment of either SMM by the application of a magnetic field leads to a large change in the resistance of the dot, i.e., a strong spin valve effect. We show that this phenomenon arises from a novel physical principle: The spin-dependent molecular orbitals that extend over the dot and both SMMs change dra…

Proximity effects in bilayer graphene on monolayer WSe$_2$: Field-effect spin-valley locking, spin-orbit valve, and spin transistor

Proximity orbital and spin-orbit effects of bilayer graphene on monolayer WSe$_2$ are investigated from first-principles. We find that the built-in electric field induces an orbital band gap of about 10 meV in bilayer graphene. Remarkably, the proximity spin-orbit splitting for holes is two orders of magnitude---the spin-orbit splitting of the valence band at K is about 2 meV---more than for electrons. Effectively, holes experience spin-valley locking due to the strong proximity of the lower graphene layer to WSe$_2$. However, applying an external transverse electric field of some 1 V/nm, coun…

Electrically switchable valley polarization, spin/valley filter, and valve effects in transition-metal dichalcogenide monolayers interfaced with two-dimensional ferromagnetic semiconductors

Electron valleys in transition-metal dichalcogenide monolayers drive novel physics and allow designing multifunctional architectures for applications. We propose to manipulate the electron valleys in these systems for spin/valley filter and valve devices through band engineering. Instead of the magnetic proximity effect that has been extensively used in previous studies, in our strategy, the electron valleys are directly coupled to the spin-polarized states of the two-dimensional ferromagnets. We find that this coupling results in a valley-selective gap opening due to the spin-momentum locking…

Spin injection and spin accumulation in all-metal mesoscopic spin valves

We study the electrical injection and detection of spin accumulation in lateral ferromagnetic metal-nonmagnetic metal-ferromagnetic metal (F/N/F) spin valve devices with transparent interfaces. Different ferromagnetic metals, permalloy (Py), cobalt (Co) and nickel (Ni), are used as electrical spin injectors and detectors. For the nonmagnetic metal both aluminium (Al) and copper (Cu) are used. Our multi-terminal geometry allows us to experimentally separate the spin valve effect from other magneto resistance signals such as the anomalous magneto resistance (AMR) and Hall effects. We find that t…

太赫兹驱动的弗洛凯自旋阀调制器

THz-Driven Floquet Spin Valve-Modulator

研究一维量子环中自旋相关量子输运，基于散射矩阵框架，利用太赫兹场实现高精度自旋通道切换，借助电子游标效应产生选择性自旋相位旋转器等，提供热免疫、高速替代传统半导体静态自旋晶体管的方案。

通过自旋阀实现硅自旋量子比特的超快可切换自旋轨道耦合

Ultrafast switchable spin-orbit coupling for silicon spin qubits via spin valves

本文提出基于自旋阀的硅自旋量子比特架构，通过亚纳秒电控磁化取向实现超快可切换自旋轨道耦合，使SWAP和远距离量子态转移保真度超过99%，为硅基量子芯片构建铺路。

Conductance of Ferro- and Antiferro-magnetic single-atom contacts: A first-principles study

We present a first-principles study on the spin denpendent conductance of five single-atom magnetic junctions consisting of a magnetic tip and an adatom adsorbed on a magnetic surface, i.e., the Co-Co/Co(001) and Ni-X/Ni(001) (X=Fe, Co, Ni, Cu) junctions. When their spin configuration changes from ferromagnetism to anti-ferromagnetism, the spin-up conductance increases while the spin-down one decreases. For the junctions with a magnetic adatom, there is nearly no spin valve effect as the decreased spin-down conductance counteracts the increased spin-up one. For the junction with a nonmagnetic …

Theory of transport through noncollinear single-electron spin-valve transistors

We study the electronic transport through a noncollinear single-electron spin-valve transistor. It consists of a small metallic island weakly coupled to two ferromagnetic leads with noncollinear magnetization directions. The electric current is influenced by Coulomb charging and by spin accumulation. Furthermore, the interplay of Coulomb interaction and tunnel coupling to spin-polarized leads yields a many-body exchange field, in which the accumulated island spin precesses. We analyze the effects of this exchange field in both the linear and nonlinear transport regime. In particular, we find t…

Nanosecond spin lifetimes in bottom-up fabricated bilayer graphene spin-valves with atomic layer deposited Al$_2$O$_3$ spin injection and detection barriers

We present spin transport studies on bi- and trilayer graphene non-local spin-valves which have been fabricated by a bottom-up fabrication method. By this technique, spin injection electrodes are first deposited onto Si$^{++}$/SiO$_2$ substrates with subsequent mechanical transfer of a graphene/hBN heterostructure. We showed previously that this technique allows for nanosecond spin lifetimes at room temperature combined with carrier mobilities which exceed 20,000 cm$^2$/(Vs). Despite strongly enhanced spin and charge transport properties, the MgO injection barriers in these devices exhibit con…

Large voltage-tunable spin valve based on a double quantum dot

We study the spin-dependent transport properties of a spin valve based on a double quantum dot. Each quantum dot is assumed to be strongly coupled to its own ferromagnetic lead, while the coupling between the dots is relatively weak. The current flowing through the system is determined within the perturbation theory in the hopping between the dots, whereas the spectrum of a quantum dot-ferromagnetic lead subsystem is determined by means of the numerical renormalization group method. The spin-dependent charge fluctuations between ferromagnets and quantum dots generate an effective exchange fiel…

Gate-voltage response of a one-dimensional ballistic spin valve without spin-orbit interaction

We show that engineering of tunnel barriers forming at the interfaces of a one-dimensional spin valve provides a viable path to a strong gate-voltage tunability of the magnetoresistance effect. In particular, we investigate theoretically a carbon nanotube (CNT) spin valve in terms of the influence of the CNT-contact interface on the performance of the device. The focus is on the strength and the spin selectivity of the tunnel barriers that are modelled as Dirac-delta potentials. The scattering matrix approach is used to derive the transmission coefficient that yields the tunneling magnetoresis…

Tunnel magnetoresistance of a supramolecular spin valve

We theoretically study the transport properties of a supramolecular spin valve, consisting of a carbon nanotube with two attached magnetic molecules, weakly coupled to metallic contacts. The emphasis is put on analyzing the change of the system's transport properties with the application of an external magnetic field, which aligns the spins of the molecules. It is shown that magnetoresistive properties of the considered molecular junction, which are associated with changing the state of the molecules from superparamagnetic to the ferromagnetic one, strongly depend on the applied bias voltage a…

Creation of Localized Skyrmion Bubbles in Co/Pt Bilayers using a Spin Valve Nanopillar

We fabricate devices in which a magnetic nanopillar spin valve makes contact to a Co/Pt bilayer thin film with perpendicular magnetic anisotropy, in order to achieve local control of domains in the Co/Pt bilayer underneath the nanopillar. The goal is to develop the ability to nucleate, detect, and annihilate magnetic skyrmions in the Co/Pt using spin-polarized currents from the nanopillar. We demonstrate the ability to distinguish the local behavior of the Co/Pt film beneath the nanopillar from the extended film and show that the two can switch independently of each other. This allows us to is…

电场通过铁磁/铁电界面应变传递增强超导自旋阀效应

Electric field enhancement of the superconducting spin-valve effect via strain-transfer across a ferromagnetic/ferroelectric interface

本研究通过压电衬底应变传递实现电场控制超导自旋阀效应，增强磁化与临界温度切换，推动无磁场超导自旋电子器件发展。