量子點鏈之閘控同調量子態

Gate-controlled Coherent Quantum States in a Quantum Dot Chain

魏文耀(Wei, Wen Yao)

指導教授 ： 陳正中

國立清華大學/理學院/物理學系/博士(2015年)

摘要

This thesis presents experimental studies of the transport properties of a one-dimensional quantum dot array (QDA), consisting of six quantum dots defined by the surface gating technique in the two-dimensional electron gas formed at the interface of the GaAs/AlGaAs heterostructure. The gate geometry allows for control of both the inter-dot coupling and the potential of the array and enables us to explore the conductance (G) of the QDA from a confined electron system (G<2e2/h) to an open systems (G≥2e2/h). The G in the high magnetic field exhibits a series of Coulomb blockade peaks before the channel is pinched off, and a series of dip and peak structures on the last quantized plateau by biasing the gate voltage to a less negative value. The thesis describes two sets of experiments that focus on the regimes in G<2e2/h and G≈2e2/h, respectively. In the first set of experiments with G<2e2/h, we found that the Hubbard model is needed to explain the experimental results and present evidence of the Mott transition in the QDA. Through a combined operation of two gate voltages, the inter-dot coupling can be fine-tuned continuously to enable the QDA conductance spectrum to undergo a localization to delocalization transition process. The transformation of a single conductance peak to multiple overlapping peaks, indicating the elimination of charge quantization in the individual dots, is qualitatively consistent with descriptions of the Mott insulator to metal transition. In the second set of experiment with G≈2e2/h, we report the edge-state mediated transport property of the QDA. The conductance dips and peaks, superimposed on the last quantized plateau, evolve with the magnetic field and reveal a pronounced charging effect, which is gradually smeared with increasing temperature. The Coulomb blockade diamonds in the differential conductance spectrum show nested features distinctly different from those observed in conventional quantum dot systems. Novel collective quantum transport in the QDA network mediated by the edge states is responsible for the observed phenomena.

關鍵字

Quantum dot array ； Mott transition

參考文獻

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