ϕI(x)=A0eik0x+B0e−ik0x,ϕII(x)=A1eik1x. We define a transmission (T) and reflection (R...\boldsymbol{\begin{align} ϕ_I (x) &= A 0 e^{ i k_0 x} + B_0 e^{ − i k_0 x} , \label{6.7} \\[5pt] ϕ_{II} (x) &= A_1 e^{ i k_1 x} . \label{6.8} \end{align}} We define a transmission (T) and reflection (R) coefficient as the ratio of currents between reflected or transmitted wave and the incoming wave, where we have canceled a common factor A1=2k0k0+k1A0B0=k0−k1k0+k1A0,
