We study the electronic transport through an all-carbon quantum ring side-coupled to a quantum wire. We employ both first-principles calculations and a tight-binding approach; the latter allows for the derivation of analytical expressions for the conductance and density of states, which facilitates the interpretation of the transport characteristics. Two bond models are employed: either all the hoppings are equal (cumulenic ring) or they have alternating bonds (polyynic ring). Assuming cumulenic bonds, if the number of atoms in the carbon ring is a multiple of four, it produces an antiresonant peak in the conductance at the Fermi level. This effect disappears for the polyynic configuration, i.e., when the hoppings in the carbon rings are alternating. Additionally, a gap opens at the Fermi energy in the polyynic rings, yielding distinct transport signatures for the two bond configurations. Comparison to first-principles calculations shows an excellent agreement on the changes of the conductance due to the carbon ring. We propose such transport measurements as a way to elucidate the character of the bonds in these novel carbon nanostructures.

中文翻译：

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少原子碳环的传输特征

我们通过侧面耦合到量子线的全碳量子环研究电子传输。我们采用第一性原理计算和紧束缚方法；后者允许推导状态的电导和密度的分析表达式，这有助于解释传输特性。使用了两种键模型：所有跳跃都相等（积聚环）或它们具有交替键（多环）。假设 cumulenic 键，如果碳环中的原子数是四的倍数，它会在费米能级的电导中产生一个反共振峰。这种效应在多态配置中消失了，即，当碳环中的跳跃是交替的。此外，在多环中的费米能量处打开了一个间隙，为两种键配置产生了不同的传输特征。与第一性原理计算的比较表明，碳环引起的电导变化非常一致。我们提出这样的传输测量作为阐明这些新型碳纳米结构中键的特征的一种方式。