Real and reciprocal space topology in rare earth intermetallics

Event start: 2026-07-03T15:00:00Z Event end: 2026-07-03T16:00:00Z Location: Brockman Hall for Physics   Speaker: Kevin Allen Doctoral Candidate Thesis Defense Department: Physics & Astronomy Location: Brockman Hall for Physics 200 Topology in magnetic materials manifests across both real and reciprocal space, encompassing exotic band crossings in momentum space and nontrivial spin textures in real space. In strongly correlated and rare earth systems, these two aspects of topology are intertwined through the interplay of magnetic order, spin-orbit coupling, and electronic structure, giving rise to emergent phenomena including large anomalous Hall responses, extremely large magnetoresistance, and field-tunable soliton excitations. This dissertation presents four projects unified by this theme, spanning magnetic topological semimetals, atomically-sharp spin textures, strongly correlated heavy fermions, and spin-polarized surface catalysis. The first project identifies EuGa4 as a magnetic Weyl nodal ring semimetal, in which mirror symmetry protection stabilizes closed nodal line rings near the Fermi level in the spin-polarized state. Using angle-resolved photoemission spectroscopy (ARPES), quantum oscillation (QO) measurements, and density functional theory (DFT), we characterize the Weyl nodal ring states and their Landau quantization. The associated high carrier mobility gives rise to a transverse magnetoresistance ex- ceeding 200, 000% at 2 K and 14 T, more than two orders of magnitude large than any previously known magnetic topological semimetal, with non-saturating behavior up to 40 T explained by a theoretical model rooted in the nodal ring electronic structure. The second project demonstrates that the square-net rare earth compound EuRhAl4Si2 hosts atomically-sharp, field-tunable one-dimensional magnetic solitons stabilized by the competition between frustrated Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange and uniaxial magnetic anisotropy. Magnetization measurements reveal a robust 1/3 magnetization plateau with fine steps corresponding to discrete soliton insertions, confirmed by anisotropic magnetotransport on a Focus ion beam (FIB)-fabricated microstructure. Neutron diffraction establishes the collinear ferrimagnetic ↑↑↓ ground state, while magnetic force microscopy (MFM) directly images the real space soliton lattice. First-principles exchange parameters and an effective J1–J2–K Heisenberg model, supplemented by Monte Carlo simulations, reproduce the observed field evolution and identify the soliton defects as the fundamental excitation. We further explore related square-net compounds by studying the series RTM4M'2 (R = Eu, Gd; T = Rh, Ir; M = Al, Ga; M' = Si, Ge), to identify additional candidates for hosting magnetic solitons and examine how structural and chemical tuning controls their stability. The third project reports a large anomalous Hall conductivity of approximately 1.6×104 Ω−1cm−1 in the centrosymmetric Kondo lattice compound Ce3Al11, a moderate heavy fermion with Kondo temperature TK