  Spontaneous symmetry breaking-the phenomenon where an infinitesimal
perturbation can cause the system to break the underlying symmetry-is a
cornerstone concept in the understanding of interacting solid-state systems. In
a typical series of temperature-driven phase transitions, higher temperature
phases are more symmetric due to the stabilizing effect of entropy that becomes
dominant as the temperature is increased. However, the opposite is rare but
possible when there are multiple degrees of freedom in the system. Here, we
present such an example of a symmetry-ascending phenomenon in a magnetic kagome
metal FeGe by utilizing neutron Larmor diffraction and Raman spectroscopy. In
the paramagnetic state at 460K, we confirm that the crystal structure is indeed
hexagonal kagome lattice. On cooling to TN, the crystal structure changes from
hexagonal to monoclinic with in-plane lattice distortions on the order of
10^(-4) and the associated splitting of the double degenerate phonon mode of
the pristine kagome lattice. Upon further cooling to TCDW, the kagome lattice
shows a small negative thermal expansion, and the crystal structure becomes
more symmetric gradually upon further cooling. Increasing the crystalline
symmetry upon cooling is unusual, it originates from an extremely weak
structural instability that coexists and competes with the CDW and magnetic
orders. These observations are against the expectations for a simple model with
a single order parameter, hence can only be explained by a Landau free energy
expansion that takes into account multiple lattice, charge, and spin degrees of
freedom. Thus, the determination of the crystalline lattice symmetry as well as
the unusual spin-lattice coupling is a first step towards understanding the
rich electronic and magnetic properties of the system and sheds new light on
intertwined orders where the lattice degree of freedom is no longer dominant.
