  The application of pressure has been demonstrated to induce intriguing phase
transitions in topological nodal-line semimetals. In this work we analyze how
uniaxial pressure affects the topological character of BaSn2 , a Dirac
nodal-line semimetal in the absence of spin-orbit coupling. Using calculations
based on the density functional theory and a model tight-binding Hamiltonian,
we find the emergence of a second nodal line for pressures higher than 4 GPa.
We examine the topological features of both phases demonstrating that a
nontrivial character is present in both of them. Thus, providing evidence of a
topological-to-topological phase transition in which the number of topological
nodal lines increases. The orbital overlap increase between Ba dxz and dyz
orbitals and Sn pz orbitals and the preservation of crystal symmetries are
found to be responsible for the advent of this transition. Furthermore, we pave
the way to experimentally test this kind of transition by obtaining a
topological relation between the zero-energy modes that arise in each phase
when a magnetic field is applied.
