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European Journal of Physics

A Laplace transform approach to the reflection and transmission of electrons at semi-infinite potential barriers

Hassan Mohamed Abdelalim Abdalla

Published Jul 13, 2016• 0 citations
Publisher

Abstract

Abstract The logic of the Schrödinger equation may be understood most readily by a consideration of a very important class of problems, i.e. those of the transmission and reflection of electrons through semi-infinite potential barriers. In this paper I revisit this problem by applying an alternative approach via Laplace transforms, demonstrating how effective they are in the determination of the solution.

DOI
10.1088/0143-0807/37/5/055408

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Abstract The logic of the Schrödinger equation may be understood most readily by a consideration of a very important class of problems, i.e. those of the transmission and reflection of electrons through semi-infinite potential barriers. In this paper I revisit this problem by applying an alternative approach via Laplace transforms, demonstrating how effective they are in the determination of the solution.
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Synopsis: At this point we are equipped to solve some simple but fundamental one-dimensional problems with the Schrödinger equation. After setting the stage with an introduction, four quantum mechanical problems are specified and solved. Along the way, we encounter important concepts such as parity in the case of the infinite well and harmonic oscillator problems, transmission and reflection coefficients in the case of the finite barrier, and energy bands and gaps in a model of conduction in solids. Raising and lowering ladder operators are introduced in the harmonic oscillator and square well cases. I conclude with some qualitative comments regarding expected types of solutions in one-dimensional problems.
Synopsis: At this point we are equipped to solve some simple but fundamental one-dimensional problems with the Schrödinger equation. After setting the stage with an introduction, four quantum mechanical problems are specified and solved. Along the way, we encounter important concepts such as parity in the case of the infinite well and harmonic oscillator problems, transmission and reflection coefficients in the case of the finite barrier, and energy bands and gaps in a model of conduction in solids. Raising and lowering ladder operators are introduced in the harmonic oscillator and square well cases. I conclude with some qualitative comments regarding expected types of solutions in one-dimensional problems.
In a recent paper diffused in the literature, the quantum problem of a particle in a infinite square well potential was claimed to be solved via Laplace transform. Surprisingly, the correct solutions were found for an eigenvalue problem with variable defined on a finite range. As a matter of fact, the authors have misused the Laplace transform of the time-independent Schrödinger equation, and they have also used incorrectly the inversion process. In the present paper it is pointed out carefully and clearly those mistakes that might occur with the use of inappropriate methods for a given eigenvalue problem.
The probability of a particle being reflected by a semi-infinite energy barrier was solved using Schrödinger's equations that describe the quantum mechanical behavior of the particle. The continuity of the functions at the origin allowed the wave functions and their respective derivatives to be equated. Solution of the resulting system yielded values A1 and B1 which were used to calculate the reflection coefficient, (B1/A1)2. The conclusions obtained from these results stated that the particle would be reflected by the barrier when E