Discovery of magnetic topological crystals

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 Co${}_2$MnGa [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 Co${}_2$MnGa arises from the Weyl lines. I hope that my discovery of Co${}_2$MnGa establishes topological magnetism as a new frontier in condensed matter physics.

arXiv commentPh.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

References in corpus (34)

• Observation of a topological 3D Dirac semimetal phase in high-mobility Cd3As2
• Discovery of a Weyl Fermion semimetal state in NbAs
• Signatures of the Adler-Bell-Jackiw chiral anomaly in a Weyl Fermion semimetal
• A topological crystalline insulator (TCI) phase via topological phase transition and crystalline mirror symmetry
• Experimental discovery of a topological Weyl semimetal state in TaP
• Observation of Topological Nodal Fermion Semimetal Phase in ZrSiS
• A new type of Weyl semimetal with quadratic double Weyl fermions in SrSi2
• Discovery of topological chiral crystals with helicoid arc states
• Surface electronic structure of the topological Kondo insulator candidate correlated electron system SmB6
• Drumhead Surface States and Topological Nodal-Line Fermions in TlTaSe2
• Arc-tunable Weyl Fermion metallic state in Mo${}_x$W${}_{1-x}$Te${}_2$
• Discovery of a new type of topological Weyl fermion semimetal state in Mo${}_x$W${}_{1-x}$Te${}_2$
• Criteria for directly detecting topological Fermi arcs in Weyl semimetals
• Fermi arc topology and interconnectivity in Weyl fermion semimetals TaAs, TaP, NbAs, and NbP
• Tunability of the topological nodal-line semimetal phase in ZrSiX-type materials
• Momentum space imaging of Cooper pairing in a half-Dirac-gas topological superconductor (a helical 2D topological superconductor)
• Observation of monolayer valence band spin-orbit effect and induced quantum well states (QWS) in MoX2
• Observation of Quantum-Tunneling Modulated Spin Texture in Ultrathin Topological Insulator Bi2Se3 Films
• New fermions on the line in topological symmorphic metals
• Atomic Scale Visualization of Quantum Interference on a Weyl Semimetal Surface by Scanning Tunneling Microscopy/Spectroscopy
• Spin polarization and texture of the Fermi arcs in the Weyl Fermion semimetal TaAs
• Gigantic surface life-time of an intrinsic topological insulator revealed via time-resolved (pump-probe) ARPES
• Quasi-particle interferences of the Weyl semimetals TaAs and NbP
• Observation of the spin-polarized surface state in a noncentrosymmetric superconductor BiPd
• Non-Kondo-like Electronic Structure in the Correlated Rare-Earth Hexaboride YbB${}_6$
• Fermi Surface Topology and Hotspots Distribution in Kondo Lattice System CeB6
• Oscillatory surface dichroism of an insulating topological insulator Bi2Te2Se
• Unconventional transformation of spin Dirac phase across a topological quantum phase transition
• Topological phase diagram and saddle point singularity in a tunable topological crystalline insulator
• Lifshitz transition and van Hove singularity in a Topological Dirac Semimetal
• Experimental Observation of Two Massless Dirac-Fermion Gases in Graphene-Topological Insulator Heterostructure
• Surface Versus Bulk Dirac States Tuning in a Three-Dimensional Topological Dirac Semimetal
• Spin correlated electronic state on the surface of a spin-orbit Mott system (Layered Iridates)
• A minimal, "hydrogen atom" version of an inversion-breaking Weyl semimetal