We studied the drift of electron spins under an applied dc electric field in single layer graphene spin valves in a field-effect transport geometry at room temperature. In the metallic conduction regime (n approximately 3.5 x 10(16) m(-2)), for dc fields of about +/- 70 kV/m applied between the spin injector and spin detector, the spin valve signals are increased or decreased, depending on the direction of the dc field and the carrier type, by as much as +/- 50%. Sign reversal of the drift effect is observed when switching from hole to electron conduction. In the vicinity of the Dirac neutrality point the drift effect is strongly suppressed. The experiments are in quantitative agreement with a drift-diffusion model of spin transport. 相似文献
Graphene is a new promising candidate for application in radio-frequency(RF) electronics due to its excellent electronic properties such as ultrahigh carrier mobility, large threshold current density, and high saturation velocity. Recently,much progress has been made in the graphene-based RF field-effect transistors(RF-FETs). Here we present for the first time the high-performance top-gated RF transistors using millimeter-scale single graphene domain on a SiO2/Si substrate through a conventional microfabrication process. A maximum cut-off frequency of 178 GHz and a peak maximum oscillation frequency of 35 GHz are achieved in the graphene-domain-based FET with a gate length of 50 nm and 150 nm,respectively. This work shows that the millimeter-scale single graphene domain has great potential applications in RF devices and circuits. 相似文献
We investigate the Andreev tunneling and Josephson current in graphene irradiated with high-frequency linearly polarized light. The corresponding stroboscopic dynamics can be solved using Floquet mechanism which results in an effective stationary theory to the problem exhibiting an anisotropic Dirac spectrum and modified pseudospin-momentum locking. When applied to an irradiated normal graphene - superconductor (NS) interface, such analysis reveal Andreev reflection (AR) to become an oscillatory function of the optical strength. Specifically we find that, by varying the polarization direction we can both suppress AR considerably or cause the Andreev transport to remain maximum at sub-gap excitation energies even in the presence of Fermi level mismatch. Furthermore, we study the optical effect on the Andreev bound states (ABS) within a short normal-graphene sheet, sandwiched between two s-wave superconductors. It shows redistribution of the low energy regime in the ABS spectrum, which in turn, has major effect in shaping the Josephson super-current. Subjected to efficient tuning, such current can be sufficiently altered even at the charge neutrality point. Our observations provide useful feedback in regulating the quantum transport in Dirac-like systems, achieved via controlled off-resonant optical irradiation on them. 相似文献
The lattice dynamics in the CuIr2S4 system have been
investigated through Raman spectroscopy and the induced-pressure
effect. Four Raman active modes are observed experimentally. Upon
cooling, these Raman spectra undergo changes due to the
Peierls-like phase transition. In addition, the substitution of Ag
for Cu affects the amplitude of the Raman spectra while keeping
their wave number unchanged. Furthermore, the positive and
negative pressure effects are induced by shrinking and expanding
the lattice. It is suggested that the pressure effect is an
effective proof of the orbital-induced Peierls state mechanism. 相似文献
Phase locking in a basic two-dimensional Josephson junction array consisting of two coupled SQUIDs is studied exploiting a new method combining the ideas of harmonic balance with the phase-slip procedure. This permits not only including the effect of non-vanishing junction capacitance, but extending our earlier investigations of the same circuit to arbitrary ring inductances, including inductances l ≈ 1 as well. As a result, our earlier finding that only antiphase oscillations can be stable in such a circuit are modified by observing a transition to the in-phase regime for larger values of the junction capacitance. The transition between both regimes is found to be determined by the resonance condition between ring inductance and junction capacitance. 相似文献
Summary The switching dynamics of a Josephson junction is discussed in connection with the problem of a Brownian particle in a one-dimensional
washboard potential. The particle is supposed to escape from a potential well and results concerning the probability of retrapping
in another well before the transition into the running state are obtained for the first time. The analysis is restricted to
the very-low-damping case and the ?first-passage time? technique is used.
Riassunto Si discute la dinamica del decadimento dello stato a tensione nulla di una giunzione Josephson nell'ambito del problema del
moto browniano. Il potenziale è unidimensionale periodico ed inclinato e sono permessi molti stati metastabili. Si considera
la probabilità d'intrappolamento in una buca di potenziale di una particella proveniente da uno stato metastabile a potenziale
piú alto.
Резюме В связи с проблемой броуновской частицы в одномерном потенциале обсуждается динамика переключения перехода Джозефсона. Предполагается,
что частица освобождается из потенциальной ямы, и впервые определяется вероятность повторного захвата в другую яму перед переходом
в движущееся состояние. Анализ ограничивается случаем очень малого затухания и используется техника ?двремени первого хода?.
We report the integration of inorganic nanotubes into metal-oxide-solution field effect transistors (FETs) which exhibit rapid field effect modulation of ionic conductance. Surface functionalization, analogous to doping in semiconductors, can switch the nanofluidic transistors from p-type to ambipolar and n-type field effect transistors. Transient study reveals the kinetics of field effect modulation is controlled by ion-exchange step. Nanofluidic FETs have potential implications in subfemtoliter analytical technology and large-scale nanofluidic integration. 相似文献
We report on the fabrication and transport characteristics of van der Waals (vdW)-contacted planar Josephson junctions. In a device, two pieces of cleaved 2H-NbSe2 superconducting flakes and a monolayer graphene sheet serve as the superconducting electrodes and the normal-conducting spacer, respectively. A stack of NbSe2?graphene?hexagonal-boron-nitride (hBN) heterostructure with clean and flat interfaces was prepared by a dry transfer technique. The outermost hBN layer protected the NbSe2?graphene?NbSe2 Josephson junction from chemical contamination during the fabrication processes. The Josephson coupling was confirmed by a periodic modulation of the junction critical current in a perpendicular magnetic field. The temperature dependence of showed long and diffusive Josephson coupling characteristics. The temperature dependence of the superconducting gap, obtained from the multiple Andreev reflection features, followed the Bardeen?Cooper?Schrieffer (BCS) prediction. 相似文献
Sub-10 nm wide graphene nanoribbon field-effect transistors (GNRFETs) are studied systematically. All sub-10 nm GNRs afforded semiconducting FETs without exception, with Ion/Ioff ratio up to 10(6) and on-state current density as high as approximately 2000 microA/microm. We estimated carrier mobility approximately 200 cm2/V s and scattering mean free path approximately 10 nm in sub-10 nm GNRs. Scattering mechanisms by edges, acoustic phonon, and defects are discussed. The sub-10 nm GNRFETs are comparable to small diameter (d< or = approximately 1.2 nm) carbon nanotube FETs with Pd contacts in on-state current density and Ion/Ioff ratio, but have the advantage of producing all-semiconducting devices. 相似文献
A concept is presented that uses epitaxial graphene on silicon carbide (SiC) for digital circuits. It uses graphene as a metal and the underlying substrate SiC as semiconductor. On the base of transistors with excellent switching behavior, Inverter and NAND operation is demonstrated.
We investigate the switching between two surface plasmon polariton modes in a non-Hermitian system composed of a pair of graphene sheets using topological operations. The topological operation is implemented by suitably designing the waveguide geometry and the chemical potential of graphene, which is equivalent to changing the system parameters along a closed loop in the parameter space. Efficient and robust mode switching takes place as the loop encloses an exceptional point and the wave experiences a sufficiently large propagation length. Moreover, we show this mode switching is chiral, in the sense that the output modes are different for choosing different loop directions. The study provides a promising approach to robust mode switching on a deep-subwavelength scale. 相似文献
We study the stochastic nature of switching current in hysteretic current-voltage characteristics of superconductor-graphene-superconductor junctions. We find that the dispersion of the switching current distribution scales with temperature as σ(I) proportional to T(α(G)) with α(G) as low as 1/3. This observation is in sharp contrast to the known Josephson junction behavior where σ(I) proportional to T(α(J)) with α(J)=2/3. We propose an explanation using a generalized version of Kurkij?rvi's theory for the flux stability in rf-SQUID and attribute this anomalous effect to the temperature dependence of the critical current which persists down to low temperatures. 相似文献
We study spin-dependent valley currents and magnetoresistance (TMR) in double magnetic layer graphene-based N/F1/St/F2/N junction where N, F1,2 and St are normal, ferromagnetic and strain-engineered graphene, respectively. Local strain in the St region causes a pseudo-vector potential with the same magnitude for the K- and K′-valleys but different sign, leading to valley polarization when applying real vector potential into the junction. The F layers cause the Zeeman field for controlling spin current and can be orientated either parallel (P) or anti parallel (AP). As an effect of the interplay of the Zeeman field and the strain field, the current in the junction is split into four current groups, Ik↑, Ik↓, Ik′↑ and Ik′↓, called spin-valley currents. We find that, the interplay of the Zeeman and strain field causes a perfect spin-valley filtering in the angular space only for the P configuration. Large TMR and switching of TMR triggered by a very small strain are also predicted. Our work reveals the potential of the interplay of the Zeeman and the strain field for application of spin-valley-based nanoelectronics and the switching effect induced by a very small strain should be applicable for strain sensor device. 相似文献
The transport properties of graphene field effect transistors are typically characterized using a conventional test structure consisting of graphene on silicon dioxide with deposited metal contacts. Two of the primary parameters affecting the total resistance of this structure are the channel mobility and contact resistance. A simple model is used to describe the impact of these parameters on total device resistance and experimentally extract them. Important issues related to characterizing the transport properties of graphene field effect transistors are presented and discussed. 相似文献
Carbon nanomaterials,including the one-dimensional(1-D) carbon nanotube(CNT) and two-dimensional(2-D) graphene,are heralded as ideal candidates for next generation nanoelectronics.An essential component for the development of advanced nanoelectronics devices is processing-compatible oxide.Here,in analogy to the widespread use of silicon dioxide(SiO2) in silicon microelectronic industry,we report the proof-of-principle use of graphite oxide(GO) as a gate dielectrics for CNT field-effect transistor(FET) via a... 相似文献