We report on the first systematic study of spin transport in bilayer graphene (BLG) as a function of mobility, minimum conductivity, charge density and temperature. The spin relaxation time τ s scales inversely with the mobility µ of BLG samples both at room temperature (RT) and at low temperature (LT). This indicates the importance of D'yakonov -Perel' spin scattering in BLG. Spin relaxation times of up to 2 ns at RT are observed in samples with the lowest mobility. These times are an order of magnitude longer than any values previously reported for single layer graphene (SLG). We discuss the role of intrinsic and extrinsic factors that could lead to the dominance of D'yakonov-Perel' spin scattering in BLG. In comparison to SLG, significant changes in the carrier density dependence of τ s are observed as a function of temperature.

In this letter, we demonstrate a non-volatile memory device in a graphene FET structure using ferroelectric gating. The binary information, i.e. "1" and "0", is represented by the high and low resistance states of the graphene working channels and is switched by controlling the polarization of the ferroelectric thin film using gate voltage sweep. A non-volatile resistance change exceeding 200% is achieved in our graphene-ferroelectric hybrid devices. The experimental observations are explained by the electrostatic doping of graphene by electric dipoles at the ferroelectric/graphene interface. PACS numbers: Valid PACS appear hereThe discovery of graphene in 2004 [1, 2, 3] has triggered enormous experimental and theoretical efforts [4,5]. As a gapless semiconductor, charge carriers in graphene can be tuned continuously from electrons to holes crossing the charge neutral Dirac point using an external electric field. Unlike conventional semiconductors, the doping process does not influence the mobility of charge carriers in graphene, which can exceed 10 5 cm 2 V −1 s −1 at low temperature [6,7]. Such doping-independent mobility leads to the field-dependent conductance in graphene. Based on these two properties, many novel graphene-based device applications have been predicted or demonstrated [8,9,10,11,12,13,14,15,16], including the heavilyexplored graphene-based field-effect transistor (GFET) [17,18,19,20,21,22]. However, a paradigm shift in the microelectronics industry from Si to graphene also requires graphene-based memory applications. Despite graphene intrinsically having a high resistance state at the Dirac point and a low resistance state when heavily doped, reports on graphene for non-volatile information storage is rarely seen. This is due to the difficulty in maintaining the resistance states in graphene without an external electric field. One chemical modification approach to achieve non-volatile switching in graphene has been recently proposed by Echtermeyer et al [19]. Although this method can achieve very high on-off ratio, it alters the unique crystalline structure of graphene upon which many of the extraordinary electronic properties and hence most novel device concepts are based [4,5].In this letter, we show non-volatile switching in graphene by using ferroelectric gating without having to break the lattice symmetry. We demonstrate basic writing and reading processes of this novel grapheneferroelectric memory device structure combining the field-dependent conductance of graphene with the remnant electric field of ferroelectric thin films. A bistable * Electronic address: phyob@nus.edu.sg FIG. 1: (a) Sample geometry of a finished grapheneferroelectric memory device. (b) Optical image of a graphene sample showing the Hall-bar geometry of the bottom electrodes. (c) R vs VBG of the graphene sample before P(VDF-TrFE) coating, measured in two-terminal configuration. (d) AFM image of another graphene sample after P(VDF-TrFE) spin-coating. The contrast comes from the slightly different crystallization of P(...

We use first principles calculations to study the electronic properties of rock salt rare earth monopnictides LaX (X =N, P, As, Sb, Bi). A new type of topological band crossing termed 'linked nodal rings' is found in LaN when the small spin-orbital coupling (SOC) on nitrogen orbitals is neglected. Turning on SOC gaps the nodal rings at all but two points, which remain gapless due to C4-symmetry and leads to a 3D Dirac semimetal. Interestingly, unlike LaN, compounds with other elements in the pnictogen group are found to be topological insulators (TIs), as a result of band reordering due to the increased lattice constant as well as the enhanced SOC on the pnictogen atom. These TI compounds exhibit multi-valley surface Dirac cones at three M -points on the (111)-surface.

Long, stable, and free-standing linear atomic carbon wires (carbon chains) have been carved out from graphene recently [Meyer et al. Nature (London) 2008, 454, 319; Jin et al. Phys. Rev. Lett. 2009, 102, 205501]. They can be considered as extremely narrow graphene nanoribbons or extremely thin carbon nanotubes. It might even be possible to make use of high-strength and identical (without chirality) carbon wires as a transport channel or on-chip interconnects for field-effect transistors. Here we investigate electron transport properties of linear atomic carbon wire-graphene junctions by combining nonequilibrium Green's function with density functional theory. For short wires, linear ballistic transport is observed in wires consisting of odd numbers of carbon atoms but not in those consisting of even numbers of carbon atoms. For wires longer than 2.1 nm as fabricated above, however, the ballistic conductance of carbon wire-graphene junctions is independent of the structural distortion, structural imperfections, and hydrogen impurity adsorbed on the linear carbon wires, except for oxygen impurity adsorption under a low bias. As such, the epoxy groups might be the origin of experimentally observed low conductance in the carbon chain. Moreover, double-atomic carbon chains exhibit a negative differential resistance effect.

Thermally induced spin transport in magnetized zigzag graphene nanoribbons (M-ZGNRs) is explored using first-principles calculations. By applying temperature difference between the source and the drain of a M-ZGNR device, spin-up and spin-down currents flowing in opposite directions can be induced. This spin Seebeck effect in M-ZGNRs can be attributed to the asymmetric electron-hole transmission spectra of spin-up and spin-down electrons. Furthermore, these spin currents can be modulated and completely polarized by tuning the back gate voltage. Finally, thermal magnetoresistance of ZGNRs between ground states and magnetized states can reach 10(4)% without an external bias. Our results indicate the possibility of developing graphene-based spin caloritronic devices.

Spintronics holds the promise for future information technologies. Devices based on manipulation of spin are most likely to replace the current silicon complementary metal‐oxide semiconductor devices that are based on manipulation of charge. The challenge is to identify or design materials that can be used to generate, detect, and manipulate spin. Since the successful isolation of graphene and other two‐dimensional (2D) materials, there has been a strong focus on spintronics based on 2D materials due to their attractive properties, and much progress has been made, both theoretically and experimentally. Here, we summarize recent developments in spintronics based on 2D materials. We focus mainly on materials of truly 2D nature, that is, atomic crystal layers such as graphene, phosphorene, monolayer transition metal dichalcogenides, and others, but also highlight current research foci in heterostructures or interfaces. In particular, we emphasize roles played by computation based on first‐principles methods which has contributed significantly in the designs of spintronic materials and devices. We also highlight challenges and suggest possible directions for further studies. WIREs Comput Mol Sci 2017, 7:e1313. doi: 10.1002/wcms.1313 This article is categorized under: Structure and Mechanism > Computational Materials Science Electronic Structure Theory > Ab Initio Electronic Structure Methods Electronic Structure Theory > Density Functional Theory

We report ab initio calculations of spin-dependent transport in single atomic carbon chains bridging two zigzag graphene nanoribbon electrodes. Our calculations show that carbon atomic chains coupled to graphene electrodes are perfect spin-filters with almost 100 % spin polarization. Moreover, carbon atomic chains can also show a very large bias-dependent magnetoresistance up to 10 6 % as perfect spin-valves. These two spin-related properties are independent on the length of carbon chains. Our report, the spin-filter and spin-valve are conserved in a single device simultaneously, opens a new way to the application of all-carbon composite spintronics.Due to the ballistic quantum transport and remarkable long spin-coherence times and distances in carbon-based nanostructures, all-carbon nanodevices have attracted considerable attention for their possible application in electronics or spintronics.1,2 Recently, all-carbon graphene nanoribbon (GNR) based field-effect transistors (FETs) are experimentally fabricated by Ponomarenko et al., which make all-carbon electronics devices becoming realization.3 In order to get semiconducting GNRFETs, sub-10-nm GNRs is necessary but difficult to get due to the limitation of the current lithography technique.4 Very recently, linear carbon atomic chains have been carved out from graphene with a high energy electron beam in two groups.5,6 Such ground-breaking experiments pave a wave for novel allcarbon FETs with many merits compared with GNR-or carbon nanotube-(CNT) based one. The reason is that carbon atomic chains are identical and can be considered as extremely narrow GNRs or thin CNTs. Therefore, they eliminate the need for sorting through a pile of different chiral GNRs and CNTs. Motivated by experiments, Shen et al:and Chen et al: theoretically studied the electron transport properties of carbon chain-graphene junctions and discussed their potential applications in electronics.7,8Spintronics is an emerging technology that exploits the intrinsic spin degree of freedom of the electron. Several carbon-based materials are proposed for spintronics applications, such as graphene and carbon nanotubes. Graphene can be used as a spin valleytronics device by adjusting of its band valley9 and Zigzag edged GNRs are predicted to be half-metallic under electrical field, which can be used as a spintronics device.10 Tombros et al: experimentally studied spin-diffusion in graphene device and observed long spin flip time/length.11 Kim et al: theoretically predicted a very large values of magnetoresistance in a GNR-based all-carbon FET as a spin valve.12-14 Karpan et al: predicted graphene as a perfect spin filter when bridging ferromagnetic leads.15 The narrowest GNRs, carbon atomic chains, also have been theoretically studied as perfect spin filters between nonmagnetic Au electrodes or spin-valves bridging Al electrodes under magnetic fields.16,17 Moreover, modified carbon chains have been predicted as spin-filters or spin-valves. For example, Yang et al: proposed half-metallic properties of c...

Searching for new plasmonic building blocks which offer tunability and design flexibility beyond noble metals is crucial for advancing the field of plasmonics. Herein, we report that solution-synthesized hexagonal Bi2Te3 nanoplates, in the absence of grating configurations, can exhibit multiple plasmon modes covering the entire visible range, as observed by transmission electron microscopy (TEM)-based electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) spectroscopy. Moreover, different plasmon modes are observed in the center and edge of the single Bi2Te3 nanoplate and a breathing mode is discovered for the first time in a non-noble metal. Theoretical calculations show that the plasmons observed in the visible range are mainly due to strong spin-orbit coupling induced metallic surface states of Bi2Te3. The versatility of shape- and size-engineered Bi2Te3 nanocrystals suggests exciting possibilities in plasmonics-enabled technology.