Many-Body Physics
Selected Publications
A universal feature of multi-band superconductivity
We show that the superconductivity-induced spectral weight transfer, previously thought to be a strong correlation effect, is actually a universal property of multiband superconductors within BCS theory. We identify this as geometric superfluidity, highlighting the role of quantum geometry in unconventional phenomena in multiband superconductors.
Junyeong Ahn and N. Nagaosa, “Superconductivity-induced spectral weight transfer due to quantum geometry”, Physical Review B 104, L100501 (2021).
Ferromagnetic topological superconductivity
We propose centrosymmetric ferromagnetic semimetals as promising platforms for higher-order topological superconductivity in any dimensions. This work is based on a generalization of the Fu-Kane-Sato parity formula for conventional topological superconductors to parity formulas for inversion-symmetric higher-order topological superconductors.
Junyeong Ahn and B.-J. Yang, “Higher-order topological superconductivity of spin-polarized fermions”, Physical Review Research 2, 012060(R) (2020).
Unconventional optical responses in superconductors
The optical transition across the superconducting gap is known to be forbidden in clean conventional superconductors. Here, we propose three conditions that intrinsic optical excitations can occur in clean multi-band superconductors by satisfying one of the three.
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Junyeong Ahn and N. Nagaosa, “Theory of optical responses in clean multiband superconductors”, Nature Communications 12, 1617 (2021).
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Junyeong Ahn and N. Nagaosa, “Many-body selection rule for quasiparticle pair creations in centrosymmetric superconductors”, arxiv:2108.04846.
Unconventional Majorana fermions on the surface
This work introduces new types of Majorana fermions that appear on the surface of topological superconductors. They include higher-spin Majorana fermions, Majorana Fermi lines, and a group of four interconnected fermions, whose band structures are unique to superconductors and distinct from those of the surface states of topological insulators.
Junyeong Ahn and B.-J. Yang, "Unconventional Majorana fermions on the surface of topological superconductors protected by rotational symmetry", Physical Review B 103, 184502 (2021).