Lee Teik-Hui, Chen Chii-Dong
Department of Physics, National Taiwan University, Taipei 106, Taiwan.
Nano Science and Technology Program, Taiwan International Graduate Program, Academia Sinica, Taipei 115, Taiwan.
Sci Rep. 2015 Sep 8;5:13704. doi: 10.1038/srep13704.
The interplay between spin and charge in solids is currently among the most discussed topics in condensed matter physics. Such interplay gives rise to magneto-electric coupling, which in the case of solids was named magneto-electric effect, as predicted by Curie on the basis of symmetry considerations. This effect enables the manipulation of magnetization using electrical field or, conversely, the manipulation of electrical polarization by magnetic field. The latter is known as the magnetocapacitance effect. Here, we show that non-equilibrium spin accumulation can induce tunnel magnetocapacitance through the formation of a tiny charge dipole. This dipole can effectively give rise to an additional serial capacitance, which represents an extra charging energy that the tunneling electrons would encounter. In the sequential tunneling regime, this extra energy can be understood as the energy required for a single spin to flip. A ferromagnetic single-electron-transistor with tunable magnetic configuration is utilized to demonstrate the proposed mechanism. It is found that the extra threshold energy is experienced only by electrons entering the islands, bringing about asymmetry in the measured Coulomb diamond. This asymmetry is an unambiguous evidence of spin accumulation induced tunnel magnetocapacitance, and the measured magnetocapacitance value is as high as 40%.
固体中自旋与电荷之间的相互作用目前是凝聚态物理中讨论最多的话题之一。这种相互作用产生了磁电耦合，在固体情况下，根据居里基于对称性考虑的预测，这种耦合被称为磁电效应。这种效应使得能够利用电场来操纵磁化强度，或者相反，利用磁场来操纵电极化强度。后者被称为磁电容效应。在此，我们表明非平衡自旋积累能够通过形成一个微小的电荷偶极来诱导隧道磁电容。这个偶极能够有效地产生一个额外的串联电容，它代表了隧穿电子将会遇到的额外充电能量。在顺序隧穿 regime 中，这个额外的能量可以被理解为单个自旋翻转所需的能量。利用具有可调磁结构的铁磁单电子晶体管来证明所提出的机制。发现只有进入岛中的电子才会经历额外的阈值能量，这导致在测量的库仑菱形中出现不对称性。这种不对称性是自旋积累诱导隧道磁电容的明确证据，并且测量到的磁电容值高达 40%。
