A specific potential in Dirac equation is considered on a finite
interval, and the resulting, notoriously known Poeschl-Teller
energy spectrum is discussed.



MR2303496 Castro, Luis B.; de Castro, Antonio S. Relativistic
confinement of neutral fermions with a trigonometric tangent
potential. J. Phys. A 40 (2007), no. 2, 263--270. 81Q05