ordinary Klein tunneling at normal incidence. In the presence of a vector potential, $\theta_K$ exists only if $ a/u $ is a real constant in the range $-1<a/u<1$. Then the analogy of Klein tunneling arises for particles incident at a nonzero angle $\theta_K$. It is interesting to note that this condition can be satisfied even if $a(x)$ and $u(x)$ are arbitrary functions of $x$, including random functions, as long as their ratio is constant.

![Transmittance $T$ plotted versus incident angle $\theta$, when massless Dirac particles are incident on an inhomogeneous strip of thickness $L$ with the normalized scalar potential, $u=2-2x/L$, and the normalized vector potential, $a=a_m(1-x/L)$ ($a_m=1.732$, 1, 0, $-1$, $-1.732$), in the region $0\le x\le L$. In the transmitted region ($x<0$), the potentials are $u=2$ and $a=a_m$. The strip thickness is given by (a) $kL=100$ and (b) $kL=1000$.[]{data-label="fig:a"}](fig1.eps){width="\linewidth"}

In Fig. \[fig:a\], we illustrate the total transmission phenomenon at oblique angles of incidence, when $u$ and $a$ are given by the linear functions $u=u_m(1-x/L)$ and $a=a_m(1-x/L)$ in the region $0\le x\le L$. In the incident region ($x>L$), $u$ and $a$ are both zero, and in the transmitted region ($x<0$), we set $u=u_m$ and $a=a_m$ to make the potentials continuous. The 