Moore’s law is confronted with great challenges because electronic miniaturization is increasingly close to the quantum limit, and thus the industrial community turns their attentions to new technologies. Spintronics combines electron spin-dependent effects with microelectronics, which illuminates the way to develop the next generation of new functional microelectronic devices. As a result, exploring perfect spintronic functional materials, studying their spin-dependent physical properties, and then developing new spin devices become a very hot topic recently.
Zigzag graphene nanoribbons (ZGNRs) have attracted extensive interest due to the unique edge effect, i.e. the spin-polarized edge states which are shown to be very promising for applications in novel spintronics devices. Here the influences of corrugations on the spin-polarized edge states and electronic properties of ZGNR with divacancy defects are investigated by means of the first principle calculations. The results show that when the magnitude of corrugation increases the system experiences an antiferromagnetism- ferrimagnetism-nonmagnetism phase transition, while for the electronic properties the system exhibits a semiconductor-metal-semiconductor transition. If the nanoribbon is attached to a pre-stretched elastomer substrate, its corrugations can be controlled by slowly releasing and straining the substrate, thus realizing the manipulation of spin-polarized edge states and electronic properties in the nanoribbon.
ZGNRs are regarded as preponderant spintronics materials. However, there exist difficulties for using the edge magnetism directly. On the one hand, it is very difficult to make perfect ZGNRs, and on the other hand the edge states are easily destroyed by temperature, edge defects or impurities. Thus, how to effectively realize the spin polarization and spin control in graphene is worth studying. Motivated by the recent synthesis of perfect AGNRs in laboratory and their multiple electronic properties, it seems very possible for AGNRs to be applied in spintronics, if the electron spins in AGNRs can be made polarized. Using the linear response theory, the spin susceptibilities are studied in AGNRs with Rashba spin-orbit coupling (RSOC) under an oscillating magnetic field. It is shown that by tuning the field frequency, RSOC, or ribbon width to satisfy the resonance condition that can cause the electron transitions between RSOC-induced spin-split subbands, the spins in AGNRs will be effectively magnetized at room temperature due to the changes of spin-oriented distribution along the field direction. Moreover, in this process the magnitude of spin magnetization can also be flexibly manipulated by selecting different resonant frequency, or RSOC. This scheme does not exist the conductance mismatch problem, and thus can solve the low efficiency issue of spin injection.
After spin polarized carriers are injected into graphene, the issues of spin transport and control must be studied in order to realize spintronics applications. Based on the Dirac theory, Klein tunneling is investigated in the quasi ribbonlike single layer graphene with Rashba spin-orbit coupling, and the transmission coefficients are obtained analytically. Using the transmission coefficients, the spin-resolved conductance is derived, and spin polarization of transmitted electrons are studied. By tuning potential barrier or RSOC strength, the spin transport and spin states of transmitted electrons can be effectively manipulated. According to the theoretical analyses, a conceptive gate-tunable spin device is presented, which can qualify as a transistor and also can realize the functions such as spin filtration, spin switch, or electron beam collimation.
In addition, electron spins in graphene have long coherence times, and thus the spins are very promising candidates for the solid-state qubits. Based on the effective spin theory, the quantum entanglement and quantum discord are investigated in chiral graphene nanoribbons (CGNRs) thermalized with a reservoir at temperature T, and the influences of temperature, ribbon width, relative location between two spins, and Coulomb repulsion among electrons on quantum correlations are discussed. The results show that quantum entanglement between nearest-neighbor spins coupled antiferromagnetically in narrow CGNRs is approximately close to the maximum at room temperature. Further, this type of thermal entanglement is employed to realize the entanglement teleportation. For the successful entanglement teleportation, the relationship between channel and input entanglement is clarified theoretically, thus opening the possibility for quantum information processing in graphene-based solid system.