Electrically tunable dynamic nuclear spin polarization in GaAs quantum dots at zero magnetic field
Electrically tunable dynamic nuclear spin polarization in GaAs quantum dots at zero magnetic field
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DOI：
10.1063/1.5024619
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发表时间：
2018-02
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通讯作者：
M. Manca;Gang Wang;T. Kuroda;S. Shree;A. Balocchi;P. Renucci;X. Marie;M. Durnev;M. Glazov;K. Sakoda;T. Mano;T. Amand;B. Urbaszek
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文献类型：
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作者：
M. Manca;Gang Wang;T. Kuroda;S. Shree;A. Balocchi;P. Renucci;X. Marie;M. Durnev;M. Glazov;K. Sakoda;T. Mano;T. Amand;B. Urbaszek
在III-V族半导体纳米结构中，电子和核自旋动力学强烈耦合。这两种自旋系统都可以用光学方法控制。核自旋动力学已被广泛研究，但对初始化机制知之甚少。在这里，我们调查的光泵浦载流子和核自旋的电荷可调GaAs点生长在111 A衬底上。我们证明了零磁场下单量子点中带正电荷的激子X$^+$态跃迁的动态核极化（DNP）。我们通过改变所施加的偏置电压V$_g$在幅度和符号上调谐DNP。100 mV量级的$\Delta$V$_g$的变化将奥弗豪泽分裂（核自旋极化）从-30 $\mu$eV（-22%）改变到+10 $\mu$eV（+7%），尽管X$^+$光致发光极化在此电压范围内没有改变符号。这表明，结构中的吸收和向X ^+$基态的能量弛豫可能为有效的电子-核自旋触发器提供有利的方案，在X ^+$寿命的前几十ps期间产生DNP，其具有数百ps的数量级。在Hanle实验中进一步证实了DNP的电压控制。
In III-V semiconductor nano-structures the electron and nuclear spin dynamics are strongly coupled. Both spin systems can be controlled optically. The nuclear spin dynamics is widely studied, but little is known about the initialization mechanisms. Here we investigate optical pumping of carrier and nuclear spins in charge tunable GaAs dots grown on 111A substrates. We demonstrate dynamic nuclear polarization (DNP) at zero magnetic field in a single quantum dot for the positively charged exciton X$^+$ state transition. We tune the DNP in both amplitude and sign by variation of an applied bias voltage V$_g$. Variation of $\Delta$V$_g$ of the order of 100 mV changes the Overhauser splitting (nuclear spin polarization) from -30 $\mu$eV (-22 %) to +10 $\mu$eV (+7 %), although the X$^+$ photoluminescence polarization does not change sign over this voltage range. This indicates that absorption in the structure and energy relaxation towards the X$^+$ ground state might provide favourable scenarios for efficient electron-nuclear spin flip-flops, generating DNP during the first tens of ps of the X$^+$ lifetime which is of the order of hundreds of ps. Voltage control of DNP is further confirmed in Hanle experiments.