Kagome metals AV3Sb5 display a rich phase diagram of correlated electron
states, including superconductivity and novel density waves. Within this
landscape, recent experiments reveal signs of a new transition below T ~ 35 K
attributed to the highly sought-after electronic nematic phase that
spontaneously breaks rotational symmetry of the lattice. We use
spectroscopic-imaging scanning tunneling microscopy to study atomic-scale
signatures of electronic symmetry breaking as a function of temperature across
several materials in this family: CsV3Sb5, KV3Sb5 and Sn-doped CsV3Sb5. We find
that rotational symmetry breaking onsets universally at a high temperature in
these materials, toward the 2 x 2 charge density wave (CDW) transition
temperature T*. At a significantly lower temperature of about 30 K, we discover
a striking emergence of the quantum interference of coherent quasiparticles, a
key signature for the formation of a coherent electronic state. These
quasiparticles display a pronounced unidirectional reciprocal-space
fingerprint, which strengthens on approaching the superconducting state. Our
experiments reveal that the high-temperature charge ordering states are
separated from the superconducting ground state by an intermediate-temperature
regime with coherent unidirectional quasiparticles. Their emergence that occurs
significantly below the onset of rotational symmetry breaking is
phenomenologically different compared to high-temperature superconductors,
shedding light on the complex nature of electronic nematicity in AV3Sb5 kagome
superconductors