The quantum mechanical current of the Pauli equation

We argue that the process of constructing the quantum mechanical current of the Pauli equation by copying the line of argument used in the spin-0 case , i.e., the Schrodinger equation, is ambiguous. We show that a nonrelativis tic reduction of the relativistic Dirac four-vector current is, however, ca pable of fully resolving the problem. This analysis reveals that the nonrel ativistic current of the Pauli equation should include an extra term of the form del X(psi(dagger)sigma psi). We present an initial exploration of the potential consequences of this new "spin term'' by solving the Pauli equat ion for crossed magnetic and electric fields and calculating the correspond ing current. (C) 1999 American Association of Physics Teachers.