  Kagome metals AV3Sb5 (where the A can stand for K, Cs, or Rb) display a rich
phase diagram of correlated electron states, including superconductivity and
density waves. Within this landscape, recent experiments revealed signs of a
transition below approximately 35 K attributed to an electronic nematic phase
that spontaneously breaks rotational symmetry of the lattice. Here, we show
that rotational symmetry breaking initiates universally at a high temperature
in these materials, toward the 2 x 2 charge density wave transition
temperature. We do this via spectroscopic-imaging scanning tunneling microscopy
and study atomic-scale signatures of electronic symmetry breaking across
several materials in the AV3Sb5 family: CsV3Sb5, KV3Sb5 and Sn-doped CsV3Sb5.
Below a significantly lower temperature of about 30 K, we measure quantum
interference of quasiparticles, a key signature for the formation of a coherent
electronic state. These quasiparticles display a pronounced unidirectional
feature in reciprocal space that strengthens as the superconducting state is
approached. Our experiments reveal that high-temperature rotation symmetry
breaking and the charge ordering states are separated from the superconducting
ground state by an intermediate-temperature regime with coherent unidirectional
quasiparticles. This picture is phenomenologically different compared to that
in high-temperature superconductors, shedding light on the complex nature of
rotation symmetry breaking in AV3Sb5 kagome superconductors.

Strongly Correlated Electrons;Superconductivity