Asian Journal of Mathematics

Volume 23 (2019)

Number 1

Equivariant minimal surfaces in $\mathbb{CH}^2$ and their Higgs bundles

Pages: 71 – 106



John Loftin (Department of Mathematics and Computer Science, Rutgers University, Newark, New Jersey, U.S.A.)

Ian McIntosh (Department of Mathematics, University of York, United Kingdom)


This paper gives a construction for all minimal immersions $f$ of the Poincaré disc into the complex hyperbolic plane $\mathbb{CH}^2$ which are equivariant with respect to an irreducible representation $\rho$ of a hyperbolic surface group into $PU(2, 1)$. We exploit the fact that each such immersion is a twisted conformal harmonic map and therefore has a corresponding Higgs bundle. We identify the structure of these Higgs bundles and show how each is determined by properties of the map, including the induced metric and a holomorphic cubic differential on the surface. We show that the moduli space of pairs $(\rho, f)$ is a disjoint union of finitely many complex manifolds, whose structure we fully describe. The holomorphic (or anti-holomorphic) maps provide multiple components of this union, as do the non-holomorphic maps. Each of the latter components has the same dimension as the representation variety for $PU(2, 1)$, and is indexed by the number of complex and anti-complex points of the immersion. These numbers determine the Toledo invariant and the Euler number of the normal bundle of the immersion. We show that there is an open set of quasi-Fuchsian representations of Toledo invariant zero for which the minimal surface is unique and Lagrangian.


minimal surface, Higgs bundle, complex hyperbolic plane

2010 Mathematics Subject Classification

20H10, 53C43, 58E20

Received 8 May 2017

Accepted 27 July 2017

Published 3 May 2019