This paper reports the first experimental realization of a 3D topological insulator in the quantum spin Hall phase. The authors, D. Hsieh and colleagues from Princeton University, used incident-photon-energy-modulated angle-resolved photoemission spectroscopy (IPEM-ARPES) to study the electronic properties of Bi$_{1-x}$Sb$_x$ single crystals. They found that Bi$_{0.9}$Sb$_{0.1}$ exhibits a 3D Dirac point, characterized by a linear dispersion near the Fermi level, and topological Dirac particles in the bulk. The surface states of this material are gapless and form a "topological metal," with an odd number of crossings between the bulk and surface states, indicating a non-trivial topological phase. This material is predicted to have potential applications in next-generation quantum computing devices due to its unique electronic properties and the possibility of realizing "light-like" bulk carriers and topologically protected spin-textured edge-surface currents. The study provides a new methodology for investigating novel topological orders in exotic quantum materials.This paper reports the first experimental realization of a 3D topological insulator in the quantum spin Hall phase. The authors, D. Hsieh and colleagues from Princeton University, used incident-photon-energy-modulated angle-resolved photoemission spectroscopy (IPEM-ARPES) to study the electronic properties of Bi$_{1-x}$Sb$_x$ single crystals. They found that Bi$_{0.9}$Sb$_{0.1}$ exhibits a 3D Dirac point, characterized by a linear dispersion near the Fermi level, and topological Dirac particles in the bulk. The surface states of this material are gapless and form a "topological metal," with an odd number of crossings between the bulk and surface states, indicating a non-trivial topological phase. This material is predicted to have potential applications in next-generation quantum computing devices due to its unique electronic properties and the possibility of realizing "light-like" bulk carriers and topologically protected spin-textured edge-surface currents. The study provides a new methodology for investigating novel topological orders in exotic quantum materials.