Supersymmetric Quantum Mechanics and Painlev\'e IV Equation

As it has been proven, the determination of general one-dimensional Schr"odinger Hamiltonians having third-order differential ladder operators requires to solve the Painlev'e IV equation. In this work, it will be shown that some specific subsets of the higher-order supersymmetric partners of the harmonic oscillator possess third-order differential ladder operators. This allows us to introduce a simple technique for generating solutions of the Painlev'e IV equation. Finally, we classify these solutions into three relevant hierarchies.