Higher-dimensional topological phases play a key role in understanding the lower-dimensional
topological phases and the related topological responses through a dimensional reduction procedure.
In this work, we present a Dirac-type model of four-dimensional (4D) Z2 topological insulator (TI)
protected by CP-symmetry, whose 3D boundary supports an odd number of Dirac cones. A specific
perturbation splits each bulk massive Dirac cone into two valleys separated in energy-momentum
space with opposite second Chern numbers, in which the 3D boundary modes become a nodal
sphere or a Weyl semimetallic phase. By introducing the electromagnetic (EM) and pseudo-EM
fields, exotic topological responses of our 4D system are revealed, which are found to be described
by the (4+1)D mixed Chern-Simons theories in the low-energy regime. Notably, several topological
phase transitions occur from a CP-broken Z2 TI to a Z TI when the bulk gap closes by giving
rise to exotic double-nodal-line/nodal-hyper-torus gapless phases. Finally, we propose to probe
experimentally these topological effects in cold atoms.
|Presenter name||Giandomenico Palumbo|
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