  The recently discovered kagome superconductors AV3Sb5 exhibit tantalizing
high-pressure phase diagrams, in which a new dome-like superconducting phase
emerges under moderate pressure. However, its origin is as yet unknown. Here,
we carried out the high-pressure electrical measurements up to 150 GPa,
together with the high-pressure X-ray diffraction measurements and
first-principles calculations on CsV3Sb5. We find the new superconducting phase
to be rather robust and inherently linked to the interlayer Sb2-Sb2
interactions. The formation of Sb2-Sb2 bonds at high pressure tunes the system
from two-dimensional to three-dimensional and pushes the Pz orbital of Sb2
upward across the Fermi level, resulting in enhanced density of states and
increase of TC. Our work demonstrates that the dimensional crossover at high
pressure can induce a topological phase transition and is related to the
abnormal high-pressure TC evolution. Our findings should apply for other
layered materials.
