Short description: By placing a nanoresonator (NR) near mesoscopic conductors one assembles the so-called nano-electromechanical systems (NEMS) whose applicative potential in sensoristics and metrology is expected to overcome the successful micro-electromechanical systems (MEMS). Moreover, the observation of quantized vibrational modes (“vibrons”) of various NRs provided a long awaited insight into the quantum limits of mechanical motion. The next natural step is to upgrade NEMS from “friendly hosts” of electron-vibron coupling to devices of forthcoming nano-electronics. To this end our proposal aims at new theoretical investigations of transport and nanomechanical sensing properties of quantum dot (QD) NEMS submitted to external driving. By developing/improving theoretical tools for studying the transient regime of driven NEMS we shall be able to study unexplored vibron-assisted effects in QD-NEMS. The 1st objective of the project is focused on nanomechanical detection by a quantum dot turnstile. These systems are known to display stand-alone non-trivial transport properties but were not yet studied as components of NEMS devices (e.g QD nanoshuttles). The 2nd objective is motivated by recent experimental results still lacking a theoretical description and investigates the excited states filling of a 3D quantum dot (QD) electostatically coupled to driven nanoresonators. Finally we propose a new exciton-based motion detector and explore the transducer efficiency of an optically active QD placed near a driven nanoresonator. The project demands substantial extensions of currently used theoretical approaches by: a) studying the many-body correlation effects, b) deriving a realistic position-dependent electron-vibron coupling and c) adapting transport formalisms for the transient regime of driven QD-NEMS. The needed formal tools include: the envelope-function kp theory, generalized Master equation method, non-equilibrium Green's function machinery, and homemade numerical codes.

Objecives: This project will provide a fresh theoretical insight into dynamical effects in quantum dot nanoelectromechanical systems (NEMS). By tackling the largely unexplored transient transport of NEMS in the quantum regime we shall adapt and improve state-of-the-art formal methods in non-equilibrium transport and set a theoretical backup for cutting edge applications in nanoelectronics and quantum metrology. The project objectives point towards: 1) Transient regime and correlation effects in nanomechanical quantum dots, 2) Probing the excited states of a quantum dot coupled to a nanoresonator, and 3) Optical detection of nanomechanical motion.

We shall develop a quantum transport formalism which allows us: a) to capture the correlation effects within the electronic component of NEMS and b) to calculate the NR displacement and the transient currents. Also we shall implement a Generalized Master Equation approach to the time-dependent charging processes of self-assembled QDs in the presence of a nanoresonator. Finally we present a theoretical description of the optical response of a self-assembled QD in the presence of a nanoresonator.

Valeriu Moldoveanu Experienced Researcher

Ion Viorel Dinu Experienced Researcher

Radu Dragomir Postdoc Researcher

Bogdan Ostahie PhD Student

Stefan Stanciu Master's Student

A. Interaction and size effects in open nanoelectromechanical systems

We investigated the intertwined dynamics of a 2D quantum wire (QW) electrostatically coupled to a nearby nanoresonator in the quantum regime. The vibron dynamics and the transport properties of this nano-electromechanical system (NEMS) are described within a generalized master equation approach which is exact with respect to the electron-vibron coupling. We introduce a detailed description of the electron-vibron coupling by taking into account its dependence on the wavefunctions of the quantum nanowire. It is shown that the tunneling processes in the QW trigger changes in the average vibron number even in the absence of a bias. The time-dependent filling of the vibronic states changes as the nanoresonator moves along the quantum wire. We calculated the populations associated to different vibron numbers and investigated their dynamics for various locations of the NR on the $x$-axis. The coupling of the nanoresonator to a thermal bath limits the number of vibronic states excited by the current passing through the wire and drives the system to a steady state. If the states participating to the transport are well within the bias window the nanowire cannot detect the vibron dynamics. The role of the open quantum wire remains however crucial as it sets the NR into motion and changes its equilibrium position.

Preliminary reports of drafts are available below:

vibrons

cmp-keldysh

pssb-journal-S-18-00550

List of Publications:
1. V. Moldoveanu, Claude-Alain Pillet, Horia D. Cornean, A Mathematical Account of the NEGF Formalism, ANNALES HENRI POINCARE 19, 411-442 (2018).

2. B. Ostahie, M. Nita, and A. Aldea, Edge-state mechanism for the anomalous quantum Hall effect in a diatomic square lattice, Phys. Rev. B 98, 125403 (2018).

Conferences:

- B. Tanatar, V. Moldoveanu, R. Dragomir, S. Stanciu, "Interaction and size effects in open nanoelectromechanical systems" Poster session at ICPS 2018 International Conference on the Physics of Semiconductors (Montpellier) http://www.icps2018.org/en/.

- R. Dragomir "Transient transport properties of nanoelectrochemical system ", invited talk at International Workshop on Advances in Nanomaterials, September 17-21, 2018, Bucharest-Magurele (http://www.infim.ro/iwan_2018/index.php/progamme).