arXiv subjects

Henan Fang

Publications and source records attributed to Henan Fang.

3 recordsLinked to original sources

arXiv2021

Tunnel junctions with moiré superlattice as barrier

Recently, moiré superlattices have attracted considerable attentions because they are found to exhibit intriguing electronic phenomena of tunable Mott insulators and unconventional superconductivity. These phenomena are highly related to the physical mechanism of the interlayer coupling. However, up to now, there has not existed any theory that can completely interpret the experimental results of the interlayer conductance of moiré superlattice. In order to solve this problem, the superposition of periods and the corresponding coherence, which are the essential characteristics of moiré superlattice, should be considered more sufficiently. Therefore, it is quite necessary to introduce optical methods to study moiré superlattices. Here, we develop a theory for moiré superlattices which are founded on traditional optical scattering theory. The theory can interpret both the continuously decreasing background and the peak of the interlayer conductance observed in the experiments by a unified mechanism. We show that, the decreasing background of the interlayer conductance arises from the increasing strength of the interface potential, and the peak roots from the scattering resonance of the interface potential. The present work is crucial for understanding the interlayer coupling of the moiré superlattice, and provide a solid theoretical foundation for the application of moiré superlattice.

cond-mat.mes-hall↗

arXiv2017

Temperature effects of the magnetic tunnel junctions with periodic grating barrier

We have developed a tunneling theory to describe the temperature dependence of tunneling magnetoresistance (TMR) of the magnetic tunnel junctions (MTJs) with periodic grating barrier. Through the Patterson function approach, the theory can handle easily the influence of the lattice distortion of the barrier on the tunneling process of the electrons. The lattice distortion of the barrier is sensible to the temperature and can be quite easily weakened by the thermal relaxation of the strain, and thus the tunneling process of the electrons gets changed highly with the variation of the temperature of the system. That is just the physical mechanism for the temperature dependence of the TMR. From it, we find that the decrease of TMR with rising temperature is mostly carried by a change in the antiparallel resistance ($R_{AP}$), and the parallel resistance ($R_{P}$) changes so little that it seems roughly constant, if compared to the $R_{AP}$, and that, for the annealed MTJ, the $R_{AP}$ is significantly more sensitive to the strain than the $R_{P}$, and for non-annealed MTJ, both the $R_{P}$ and $R_{AP}$ are not sensitive to the strain. They are both in agreement with the experiments of the MgO-based MTJs. Other relevant properties are also discussed.

cond-mat.mes-hall↗

arXiv2016

Magnetic coherent tunnel junctions with periodic grating barrier

A new spintronic theory has been developed for the magnetic tunnel junction (MTJ) with single-crystal barrier. The barrier will be treated as a diffraction grating with intralayer periodicity, the diffracted waves of tunneling electrons thus contain strong coherence, both in charge and especially in spin. The theory can answer the two basic problems present in MgO-based MTJs: (1) Why does the tunneling magnetoresistance (TMR) oscillate with the barrier thickness? (2) Why is the TMR still far away from infinity when the two electrodes are both half-metallic? Other principal features of TMR can also be explained and reproduced by the present work. It also provides possible ways to modulate the oscillation of TMR, and to enhance TMR so that it can tend to infinity. Within the theory, the barrier, as a periodic diffraction grating, can get rid of the confinement in width, it can vary from nanoscale to microscale. Based on those results, a future-generation MTJ is proposed where the three pieces can be fabricated separately and then assembled together, it is especially appropriate for the layered materials, e.g., MoS2 and graphite, and most feasible for industries.

cond-mat.mes-hall↗