Discovery of magnetic topological crystals

2020/10/30 by Ilya Belopolski
Physics and Astronomy · #cond-mat.str-el #cond-mat.mes-hall #cond-mat.mtrl-sci

paper · pdf

published as Ph.D. Thesis, Princeton University (2019) · Ph.D. Thesis. Based on arXiv:1502.03807, arXiv:1501.00755, arXiv:1703.04537, arXiv:1601.04327, arXiv:1509.07465, arXiv:1604.07079, arXiv:1512.09099, arXiv:1612.05990, arXiv:1610.02013, arXiv:1812.04466, arXiv:1712.09992 and arXiv:2004.00004. Available at http://arks.princeton.edu/ark:/88435/dsp01zs25xc34m

arxiv created 2020/10/30 · arxiv updated 2020/11/03

Abstract

Topological phases of matter have established a new paradigm in physics, bringing quantum phenomena to the macroscopic scale and hosting exotic emergent quasiparticles. In this thesis, I theoretically and experimentally demonstrate with my collaborators the first Weyl semimetal, TaAs, using angle-resolved photoemission spectroscopy (ARPES), directly observing its emergent Weyl fermions and topological Fermi arc surface states [Science 349, 6248 (2015); Nat. Commun. 6, 7373 (2015); PRL 116, 066802 (2016)]. Next, I discover high-degeneracy topological chiral fermions in the chiral crystals RhSi and CoSi, with wide topological energy window, maximal separation in momentum space and giant Fermi arcs [Nature 567, 500 (2019); Nat. Mat. 17, 978 (2018)]. I establish a natural relationship between the structural and topological chirality, associated with a robust topological state which we predict supports a four-unit quantized photogalvanic effect [PRL 119, 206401 (2017)]. I also discuss the first quantum topological superlattice, in multilayer heterostructures consisting of alternating topological and trivial insulators [Sci. Adv. 3, e1501692 (2017)]. The Dirac cones at each interface tunnel across layers, forming an emergent atomic chain where the Dirac cones serve as atomic orbitals. I achieve unprecedented control of hopping amplitudes within the superlattice, realizing a topological phase transition. Lastly, I discover a room-temperature topological magnet in Co₂MnGa [Science 365, 1278 (2019); PRL 119, 156401 (2017)]. I observe topological Weyl lines and drumhead surface states by ARPES, demonstrating a topological invariant supported by the material's intrinsic magnetic order. I also find that the large anomalous Hall effect in Co₂MnGa arises from the Weyl lines. I hope that my discovery of Co₂MnGa establishes topological magnetism as a new frontier in condensed matter physics.

Citations

• Discovery of a Weyl fermion semimetal and topological Fermi arcs
• Theoretical Discovery/Prediction: Weyl Semimetal states in the TaAs material (TaAs, NbAs, NbP, TaP) class
• A novel artificial condensed matter lattice and a new platform for one-dimensional topological phases
• Criteria for directly detecting topological Fermi arcs in Weyl semimetals
• Observation of surface states derived from topological Fermi arcs in the Weyl semimetal NbP
• Measuring Chern numbers above the Fermi level in the Type II Weyl semimetal Mo_xW_1-xTe₂
• Unoccupied electronic structure and signatures of topological Fermi arcs in the Weyl semimetal candidate Mo_xW_1-xTe₂
• Discovery of a new type of topological Weyl fermion semimetal state in Mo_xW_1-xTe₂
• A minimal, "hydrogen atom" version of an inversion-breaking Weyl semimetal
• Discovery of topological chiral crystals with helicoid arc states
• A three-dimensional magnetic topological phase
• Discovery of topological Weyl fermion lines and drumhead surface states in a room temperature magnet