How would one display just the Author and Year of the citation in the margin, while keeping the full citation in the references page?
I've tried to modify a previous suggestion that would display abbreviated citations only after they had be cited once. This unfortunately didn't work -- the reference number appears instead of any citation at all:

This is what they usually look like:

As you can see it gets very busy very quickly. Some pages the margin is all citations!
I've searched everywhere for this and tried editing solutions to similar requests -- alas! No luck. Any help or advice would be greatly appreciated.
Thanks!
Edit: Here's a minimal working example:
\documentclass[a4paper,nofonts,oneside]{tufte-book}
\usepackage{amsfonts, amsmath, amssymb}
\begin{document}
%------------------------------------------------
\subsection{Non-equilibrium Spin Mixing}
Spontaneous Magnetization!! \cite{lamport94}
Under the constraint of number and magnetization conservation, there are just two dynamical variables\cite{lamport94}: $\rho_0$, the fractional population of the $m=0$ component, and relative phase difference $\theta (t)\equiv\theta_+ + \theta_- - 2\theta_0$. $\theta$ can be thought of as a control for the degree of magnetization.
Under the SMA, the spin-dependent energy functional is given by\cite{lamport94}:
\begin{thebibliography}{9}
\bibitem{lamport94}
Leslie Lamport,
\emph{\LaTeX: A Document Preparation System}.
Addison Wesley, Massachusetts,
2nd Edition,
1994.
\end{thebibliography}
\end{document}