Mesoscopic Fano Effect through a Quantum Dot in an Aharonov-Bohm Ring Kensuke Kobayashi a,1 Hisashi Aikawa a , Shingo Katsumoto a , and Yasuhiro Iye a a Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Chiba 277-8581, Japan Abstract The Fano effect illustrates how the interference and resonance cooperatively occur between a discrete state and a continuum energy state. We have realized a tunable Fano system by fabricating a quantum dot embedded in an Aharonov-Bohm ring on a 2DEG. In the Coulomb oscillation, clear asymmetric lineshapes were observed, which manifest the formation of the Fano state, namely, a mixture of the discrete state and the continuum state. The non-equilibrium transport and the temperature dependence reveal the essential role of the coherence for this effect. Through the phase controlling by the magnetic flux piercing the ring, Fano’s asymmetric parameter q is obtained as a complex number for the first time. Key words: Quantum Dot, Aharonov-Bohm Ring, Fano Effect, Coherence PACS: 73.21.La, 85.35.-p, 73.23.Hk, 72.15.Qm 1. Introduction An Aharonov-Bohm (AB) ring and a quantum dot (QD) are typical complementary mesoscopic systems: the wave nature of electron manifests itself in the for- mer while the particle nature of electron features in the latter. A combination of these two into a hybrid one, therefore, enables us to explore the problem how coher- ent is the transport of electrons through a QD, where many electrons interact with each other. In 1995, Ya- coby et al. [1] performed a pioneering work to address this issue by using such a system, namely a QD embed- ded in one arm of an AB ring. It was found [1,2] that an electron at least partially maintains its coherence in passing a QD and each level inside the QD acts as a Breit-Wigner type scatterer. In these experiments, 1 Corresponding author. E-mail: knsk@issp.u-tokyo.ac.jp however, the transport properties of a QD have been the main scope and the other arm with no QD has served as “reference”. Here, one might ask what hap- pens if the coherence of the QD-AB-ring hybrid system is fully maintained and thus the arm as well as the QD should be equally treated. In this situation, the Fano effect is expected to occur [3—9]. The Fano effect emerges in a system where a dis- crete state and the continuum energy state coexist [10]. The essence lies in the quantum interference between the two configurations in the transition process into the final states with the same energy as sketched in Fig. 1 (a); one directly through the continuum and the other through the resonance level arising around the discrete state. This “configuration interaction” yields the peculiar asymmetric lineshape in the transition probability P as a function of energy ² given by Preprint submitted to Physica E 11 June 2003