量子点接触中边界电流隧穿随偏压和温度变化的研究

Fractional quantum Hall states are entirely new states of matter that cannot be expected from broken symmetry described by Landau theory. Instead, there exists a more subtle order, which is named topological order. At fractional quantum Hall states, currents are edge excitations travel in only one direction and protected by the topology of the system. Tunneling current between counter-propagating edges has been calculated as a function of bias voltage, assuming tunneling across a constriction of a fractional quantum Hall state or between the edges of different fractional states. Edges excitations, also called chiral Luttinger liquids, show a power law behavior as a function of voltage, which has been experimental observed between edge channels and metal in cleaved edge overgrowth samples. The observation follows the power law behavior but not fully described by the predictions of the chiral Luttinger liquid theory. Experiment results of tunneling between the same fractional states only found good agreement with the theory at certain states. In recent years there has been great interest in non-abelian statistics where degenerate ground states are insensitive to environmental noise and thus provide a basis for a new kind of quantum computer. The 5/2 fractional quantum Hall state is believed to be a good candidate of such a non-abelian state. However, there is no conclusive answer to the wave function of the 5/2 state. Tunneling between 5/2 edge channels in a quantum point contact is used as a powerful law to study the ground state at 5/2, which requires a systematic study to test the tunneling theory at simple fractional quantum Hall states, like 1/3, in a quantum point contact.

分数量子霍尔效应是一个无法用常规的对称性破缺朗道理论解释的新体系，这个体系中粒子的行为需要用一个拓扑序来描述。由于系统的拓扑保护，通常分数量子霍尔效应中的电流只出现在边界，单向流动；反向电流无法与之有相互作用。假设相同量子态内边界电流被限制而互相靠近，或者两个量子霍尔态非常靠近，这时反向移动的边界电流之间可能发生隧穿。在特殊生长的异质结样品中，不同量子态之间的隧穿与偏压的关系满足理论预测的指数关系，但是具体数值与理论预测不符。相同量子态内的隧穿实验结果与理论关系也比较复杂，只在少数量子态中观察到。最近5/2态因为可能有可用于量子计算的非阿贝尔统计而受到广泛研究，5/2边界电流在量子点接触处的隧穿是其中一个有效的研究手段。基于此，系统地分析简单量子态中，如1/3态中，在量子点接触里面的隧穿实验与理论符合程度非常必要。

分数量子霍尔效应是一个无法用常规的对称性破缺朗道理论解释的新体系，这个体系中粒子的行为需要用一个拓扑序来描述。由于系统的拓扑保护，通常分数量子霍尔效应中的电流只出现在边界，单向流动；反向电流无法与之有相互作用。假设相同量子态内边界电流被限制而互相靠近，或者两个量子霍尔态非常靠近，这时反向移动的边界电流之间可能发生隧穿。在特殊生长的异质结样品中，不同量子态之间的隧穿与偏压的关系满足理论预测的指数关系，但是具体数值与理论预测不符。相同量子态内的隧穿实验结果与理论关系也比较复杂，只在少数量子态中观察到。最近5/2态因为可能有可用于量子计算的非阿贝尔统计而受到广泛研究，5/2边界电流在量子点接触处的隧穿是其中一个有效的研究手段。基于此，系统地分析简单量子态中，如1/3态中，在量子点接触里面的隧穿实验与理论符合程度非常必要。我们在分数量子霍尔态中开展了边界电流隧穿的实验测量，在以3为分母的简单分数态上验证了弱隧穿理论，还在5/2态中发现了非阿贝尔统计存在的证据。近些年通过局域条件开展的边界电流隧穿实验中，早期结果支持非阿贝尔统计存在，然而更新的实验却支持阿贝尔统计存在，对此，我们还发现5/2态的波函数可能可以被局域条件所调制。该工作的意义不仅在于澄清了前期相关实验中的矛盾，还为拓扑量子计算器件的设计提供信息。