Possible origin of the 0.5 plateau in the ballistic conductance of quantum point contacts
Possible origin of the 0.5 plateau in the ballistic conductance of quantum point contacts
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DOI：
10.1103/physrevb.80.155440
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发表时间：
2009-10-01
影响因子：
3.7
通讯作者：
Newrock, R.
中科院分区：
文献类型：
--
作者：
Wan, J.;Cahay, M.;Newrock, R.
采用非平衡格林函数的形式，研究了侧向自旋-轨道耦合（LSOC）存在时侧门控量子点接触（QPC）的电导。两个侧栅极（SGs）之间的偏置电压差很小，导致LSOC在通道相对边缘之间的反转不对称。在输运的单电子模型中，这触发了QPC中自发但不显著的自旋极化。然而，考虑电子-电子相互作用的影响时，QPC的自旋极化明显增强。在没有任何外磁场的情况下，自旋极化足以导致在0.5G(0) (G（0)= 2e(2)/h）时出现电导平台。在我们对模型QPC器件的模拟中，发现0.5平台非常稳健，并且可以在40 K的温度下存活。自发自旋极化和由此产生的QPC的磁化可以通过翻转源的极性来漏极偏置或两个SGs之间的电位差来逆转。这些数值模拟结果与最近由低带隙半导体InAs制成的侧门控qpc的实验结果吻合得很好。
A nonequilibrium Green's function formalism is used to study the conductance of a side-gated quantum point contact (QPC) in the presence of the lateral spin-orbit coupling (LSOC). A small difference of bias voltage between the two side gates (SGs) leads to an inversion asymmetry in the LSOC between the opposite edges of the channel. In the single-electron modeling of transport, this triggers a spontaneous but insignificant spin polarization in the QPC. However, the spin polarization of the QPC is enhanced substantially when the effect of electron-electron interaction is included. The spin polarization is strong enough to result in the occurrence of a conductance plateau at 0.5G(0) (G(0)= 2e(2)/h) in the absence of any external magnetic field. In our simulations of a model QPC device, the 0.5 plateau is found to be quite robust and survives up to a temperature of 40 K. The spontaneous spin polarization and the resulting magnetization of the QPC can be reversed by flipping the polarity of the source to drain bias or the potential difference between the two SGs. These numerical simulations are in good agreement with recent experimental results for side-gated QPCs made from the low band-gap semiconductor InAs.