# [Tex/LaTex] align inside \left … \right

alignbigdelimmath-mode

I am trying to split an equation over multiple lines. To improve readability, I want to make the second line line up with the right side of the left brace of the first line as is almost achieved in the image below. Doing this, I stumbled upon the issue that alignment marks (&) do not work inside \left, \right. This question pointed me to the \biggl operators that circumvent this problem. I was however wondering: is there a way to make alignment marks inside \left and \right work as expected?

Example and code to generate it:

\documentclass[twocolumn]{article}
\usepackage{amsmath}
\begin{document}
\def\leftside{\upsilon_{N, cw}(\omega)}
\def\prefix{- \frac{1}{\Delta} \Gamma}
\def\firstline{i\omega - \xi_{cc}\bar N + \frac{\Delta\Gamma}{2}}
\def\lastline{{+}\:\left.\frac{|\kappa|^2}{2\Delta\Gamma} \exp(-i\omega\tau)}
\begin{align}
\begin{split}
\leftside =& \prefix
\begin{aligned}[t]
&\left(\firstline\right.\\
&\left.\lastline\right)
\end{aligned}
\end{split}
\end{align}
\end{document}


There's a solution with Sébastien Gouezel's \MTkillspecial command and \DeclarePairedDelimiter command from mathtools: I define a \brkparens command, which adds an implicit pair of \left … \right in its starred version. For fine tuning, the non-starred version accepts an optional argument (\big, \Big, &c.):

\documentclass[twocolumn]{article}
\usepackage{mathtools}
\newcommand\MTkillspecial[1]{% helper macro
\bgroup
\catcode\&=9
\let\\\relax%
\scantokens{#1}%
\egroup
}
\DeclarePairedDelimiter\brkparens()
\reDeclarePairedDelimiterInnerWrapper\brkparens{star}{
\mathopen{#1\vphantom{\MTkillspecial{#2}}\kern-\nulldelimiterspace\right.}
#2
\mathclose{\left.\kern-\nulldelimiterspace\vphantom{\MTkillspecial{#2}}#3}}

\begin{document}

\def\leftside{\upsilon_{N, cw}(\omega)}
\def\prefix{- \frac{1}{\Delta} \Gamma}
\def\firstline{i\omega - \xi_{cc}\bar N + \frac{\Delta\Gamma}{2}}
\def\lastline{{+}\:\frac{|\kappa|^2}{2\Delta\Gamma} \exp(-i\omega\tau)}
\begin{align}
\begin{split}
\leftside =& \prefix
\begin{aligned}[t]
&\brkparens*{\firstline\\
&\lastline}
\end{aligned}
\end{split}
\end{align}

\end{document}
`