On the exactly-solvable semi-infinite quantum well of the non-rectangular step-harmonic profile

TL;DR

This paper introduces an exactly-solvable quantum model with a position-dependent mass that behaves like a semi-infinite, non-rectangular quantum well, unifying discrete and continuous spectra with known harmonic oscillator results in a specific limit.

Contribution

The paper constructs a novel exactly-solvable semi-infinite quantum well model with a position-dependent mass, connecting it to classical harmonic oscillator solutions in a limiting case.

Findings

Discrete spectrum is non-equidistant and finite, expressed via Bessel polynomials.

Wavefunctions for the continuous spectrum involve hypergeometric functions.

In the limit of large parameter, the model reduces to the standard harmonic oscillator.

Abstract

An exactly-solvable model of the non-relativistic harmonic oscillator with a position-dependent effective mass is constructed. The model behaves itself as a semi-infinite quantum well of the non-rectangular profile. Such a form of the profile looks like a step-harmonic potential as a consequence of the certain analytical dependence of the effective mass from the position and semiconfinement parameter $a$. Both states of the discrete and continuous spectrum are studied. In the case of the discrete spectrum, wavefunctions of the oscillator model are expressed through the Bessel polynomials. The discrete energy spectrum is non-equidistant and finite as a consequence of its dependence on parameter $a$, too. In the case of the continuous spectrum, wavefunctions of the oscillator model are expressed through the $_1F_1$ hypergeometric functions. At the limit, when the parameter $a$ goes to infinity, both wavefunctions, and the energy spectrum of the model under construction correctly reduce to corresponding results of the usual non-relativistic harmonic oscillator with a constant effective mass. Namely, wavefunctions of the discrete spectrum recover wavefunctions in terms of the Hermite polynomials, and wavefunctions of the continuous spectrum simply vanish. We also present a new limit relation that reduces Bessel polynomials directly to Hermite polynomials and prove its correctness using the mathematical induction technique.