Interplay of bound states in the continuum and Fano--Andreev interference in a hybrid triple quantum dot

TL;DR

This paper explores how bound states in the continuum and Fano--Andreev interference phenomena emerge and interact in a hybrid triple quantum dot system, revealing new transport behaviors and internal diagnostics.

Contribution

It introduces the concept of Fano--Andreev BICs and quasi-BICs in a hybrid quantum dot system, demonstrating their formation and crossover through interference effects.

Findings

Sharp antiresonances in electron tunneling signal BIC formation.

Transport zeros indicate the presence of (quasi-)BICs.

Occupation changes in the side dot correlate with bound state signatures.

Abstract

We investigate bound states in the continuum (BICs) in a hybrid normal--superconducting triple quantum dot system, where the central dot is coupled to two normal leads and the lateral dots are proximity-coupled to superconducting electrodes. Local electron--electron interactions are treated within the Hubbard approximation. Finite bias, together with lateral-dot detuning and superconducting proximity, induces interference between elastic electron tunneling (ET) and Andreev reflection (AR) channels, mediated by BIC-related modes and proximity-induced Andreev bound states. As the bias is swept through the subgap resonances, ET exhibits sharp antiresonances that evolve into exact transport zeros, signaling the emergence of (quasi-)BICs. We further find a continuous crossover from a Fano--Andreev BIC-supported regime to a Fano--Andreev quasi-BIC regime as the detuning asymmetry increases. The formation of BICs and quasi-BICs is accompanied by a pronounced change in the occupation of the side quantum dot, providing an internal diagnostic directly correlated with the transport signatures of the bound states.