arXiv subjects

F. Zhai

Publications and source records attributed to F. Zhai.

5 recordsLinked to original sources

arXiv2015

Electronic and magneto-optical properties of monolayer phosphorene quantum dots

We theoretically investigate the electronic and magneto-optical properties of rectangular, hexangular, and triangular monolayer phosphorene quantum dots (MPQDs) utilizing the tight-binding method. The electronic states, density of states, electronic density distribution, and Laudau levels as well as the optical absorption spectrum are calculated numerically. Our calculations show that: (1) edge states appear in the band gap in all kinds of MPQDs regardless of their shapes and edge configurations due to the anisotropic electron hopping in monolayer phosphorene (MLP). Electrons in any edge state appear only in the armchair direction of the dot boundary, which is distinct from that in graphene quantum dots; (2) the magnetic levels of MPQDs exhibit a Hofstadter-butterfly spectrum and approach the Landau levels of MLP as the magnetic field increases . A "flat band" appears in the magneto-energy spectrum which is totally different from that of MLP; (3) the electronic and optical properties can be tuned by the dot size, the types of boundary edges and the external magnetic field.

cond-mat.mes-hall↗

arXiv2015

Landau levels and magneto-transport property of monolayer phosphorene

We investigate theoretically the Landau levels (LLs) and magneto-transport properties of phosphorene under a perpendicular magnetic field within the framework of the effective \textbf{\emph{k$\cdot$p}} Hamiltonian and tight-binding (TB) model. At low field regime, we find that the LLs linearly depend both on the LL index $n$ and magnetic field $B$, which is similar with that of conventional semiconductor two-dimensional electron gas. The Landau splittings of conduction and valence band are different and the wavefunctions corresponding to the LLs are strongly anisotropic due to the different anisotropic effective masses. An analytical expression for the LLs in low energy regime is obtained via solving the decoupled Hamiltonian, which agrees well with the numerical calculations. At high magnetic regime, a self-similar Hofstadter butterfly (HB) spectrum is obtained by using the TB model. The HB spectrum is consistent with the Landau level fan calculated from the effective \textbf{\emph{k$\cdot$p}} theory in a wide regime of magnetic fields. We find the LLs of phosphorene nanoribbon depend strongly on the ribbon orientation due to the anisotropic hopping parameters. The Hall and the longitudinal conductances (resistances) clearly reveal the structure of LLs.

cond-mat.mes-hall↗

arXiv2011

Valley-dependent Brewster angles and Goos-Hanchen effect in strained graphene

We demonstrate theoretically how local strains in graphene can be tailored to generate a valley polarized current. By suitable engineering of local strain profiles, we find that electrons in opposite valleys (K or K') show different Brewster-like angles and Goos-Hänchen shifts, exhibiting a close analogy with light propagating behavior. In a strain-induced waveguide, electrons in K and K' valleys have different group velocities, which can be used to construct a valley filter in graphene without the need for any external fields.

cond-mat.mes-hall↗

arXiv2008

Spin current diode based on an electron waveguide with spin-orbit interaction

We propose a spin current diode which can work even in a small applied bias condition (the linear-response regime). The prototypal device consists of a hornlike electron waveguide with Rashba spin-orbit interaction, which is connected to two leads with different widths. It is demonstrated that when electrons are incident from the narrow lead, the generated spin conductance fluctuates around a constant value in a wide range of incident energy. When the transport direction is reversed, the spin conductance is suppressed strongly. Such a remarkable difference arises from spin-flipped transitions caused by the spin-orbit interaction.

cond-mat.mes-hall↗

arXiv2008

Theory of huge tunneling magnetoresistance in graphene

We investigate theoretically the spin-independent tunneling magnetoresistance effect in a graphene monolayer modulated by two parallel ferromagnets deposited on a dielectric layer. For the parallel magnetization configuration, Klein tunneling can be observed in the transmission spectrum, but at specific oblique incident angles. For the antiparallel magnetization configuration, the transmission can be blocked by the magnetic-electric barrier provided by the ferromagnets. Such a transmission discrepancy results in a tremendous magnetoresistance ratio and can be tuned by the inclusion of an electric barrier.

cond-mat.mes-hall↗