Bias induced spin state transition mediated by electron excitations.
Bias induced spin state transition mediated by electron excitations.
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DOI：
10.1063/1.5126968
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发表时间：
2019-09
期刊：
影响因子：
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通讯作者：
H. Hao;T. Jia;Xiaohong Zheng;Peng Liu;Z. Zeng
中科院分区：
文献类型：
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作者：
H. Hao;T. Jia;Xiaohong Zheng;Peng Liu;Z. Zeng
最近的实验报道了自旋态跃迁是通过施加偏置电压实现的。然而，这些偏倚引起的转变尚未完全了解，特别是其机制。实验已经证实，光辐射激活的金属-配体电荷转移（MLCT）激发可以导致从低自旋（LS）到高自旋（HS）的转变，并且由于金属中心（MC）的激发，光可以实现从HS到LS的转变。此外，在偏置电压下，通过分子结中的非弹性共隧道可以获得电子激发。基于这两个事实，我们提出MLCT激励是由LS到HS的偏置诱导转变的原因，而从HS到LS的偏置诱导转变归因于MC激励。通过比较第一性原理结果和实验观察结果，证明了我们提出的机制的合理性。理论上预测的MLCT和MC激发的阈值电压与达到从LS到HS的偏置电压以及实验中从HS到LS的偏置电压一致[Miyamachi et al., Nat. comm . 3,938(2012)]。MLCT或MC激发的激活取决于偏置极性，这可以解释实验中过渡的偏置极性依赖性。本研究对进一步设计基于偏控跃迁的分子自旋电子器件具有重要意义。
Recent experiments reported that spin state transitions were realized by applying bias voltages. However, these bias-induced transitions are not fully understood, especially the mechanism. It is well established in experiments that the metal-to-ligand charge transfer (MLCT) excitation activated by light radiation can lead to the transition from low spin (LS) to high spin (HS), and the transition from HS to LS can be achieved by light due to the metal-centered (MC) excitation. Moreover, electronic excitations are accessible by inelastic cotunneling in molecular junctions under bias voltages. Based on these two facts, we propose that the MLCT excitation is responsible for the bias-induced transition from LS to HS, and the bias-induced transition from HS to LS is attributed to the MC excitation. The rationality of our proposed mechanism is demonstrated by comparing first-principles results and experimental observations. Threshold voltages of MLCT and MC excitations predicted in theory are consistent with bias voltages used to reach the transition from LS to HS and that from HS to LS in the experiment [Miyamachi et al., Nat. Commun. 3, 938 (2012)]. Activation of MLCT or MC excitation depends on the bias polarity, which can explain the bias-polarity dependence of the transition in the experiment. Our study is important for further design of molecular spintronic devices working on the bias-controlled transition.