טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentGoldzak Tamar
SubjectInteratomic Coulombic Decay in Quantum Wells
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisors Professor Emeritus Nimrod Moiseyev
Dr. Ido Gilary
Full Thesis textFull thesis text - English Version


Abstract

Interatomic/intermolecular Coulombic decay (ICD) is a very efficient and fast electron relaxation process relying on the correlation between electrons.

Resonances in quantum mechanics are met- stable states which have a finite life time. ICD is an autoionization process; the initiation state of the ICD is a Feshbach type resonance state.


In this research thesis work we focus on the ICD process in a system of two coupled quantum wells nano structure. We calculated the ICD life time using simple one-dimensional effective potential based on experimental parameters of the semiconductor QW layers, i.e., using the single-band effective-mass approximation. We control the ICD lifetime by changing the distance between the wells. Overall, as the distance between the wells decreases the ICD lifetime decreases. We found an unexpected result. By tuning the distance between the wells, such that the emitted electron is trapped in a one electron shape type resonance state, i.e. a meta-stable state in the continuum causes the ICD lifetime to be an order of magnitude smaller even at very long distances. This improves the efficiency of the ICD process. By using the formalism of non-Hermitian quantum mechanics one can engineer the system such that the ICD process will be enhanced, and can be the dominant decay process in the system.


To justify the use of a one dimensional model for the calculation of the ICD lifetime we analyze analytically the ICD in three dimensional quantum wells model. We showed that the one dimensional model is justified under two conditions.

Based on our results we can design an experiment that will observe the ICD phenomenon in quantum wells nanostructure. This work can lead to a design of a wavelength-sensitive detector which is efficient even at low intensities.


 Furthermore, in this research thesis we describe two approaches to study meta-stable states. The first approach is to tackle the problem through solving the time independent Schrödinger equation through the non-Hermitian formalism. The second approach is to use the Hermitian quantum mechanics formalism, and solve the time dependent Schrödinger equation to find the resonance states. In this work we show that for an initial wave packet localized in the interaction region, both approaches are equivalent. Given a quantum system, one can choose the approach that suits the problem in hand. We used these approaches to understand and study the ICD process.


 We also study the partial width and branching ratio of a quantum system in a given resonance state. This quantum system has different open channels for decay. Partial widths are the decay rates of the resonance (metastable) state into the different open channels. In this research thesis work we present a rigorous derivation of the partial widths from the solution of a time-dependent Schrödinger equation with outgoing boundary conditions. We show that the sum of the partial widths obtained from the resonance wave function is equal to the total width.