Optical signatures of multifold fermions in the chiral topological semimetal CoSi

Abstract

We report the optical conductivity in high-quality crystals of the chiral topological semimetal CoSi, which hosts exotic quasiparticles known as multifold fermions. We find that the optical response is separated into several distinct regions as a function of frequency, each dominated by different types of quasiparticles. The low-frequency intraband response is captured by a narrow Drude peak from a high-mobility electron pocket of double Weyl quasi-particles, and the temperature dependence of the spectral weight is consistent with its Fermi velocity. By subtracting the low-frequency sharp Drude and phonon peaks at low temperatures, we reveal two intermediate quasi-linear inter-band contributions separated by a kink at 0.2 eV. Using Wannier tight-binding models based on first-principle calculations, we link the optical conductivity above and below 0.2 eV to interband transitions near the double Weyl fermion and a threefold fermion, respectively. We analyze and determine the chemical potential relative to the energy of the threefold fermion, revealing the importance of transitions between a linearly dispersing band and a flat band. More strikingly, below 0.1 eV our data are best explained if spin-orbit coupling is included, suggesting that at these energies the optical response is governed by transitions between a previously unobserved four-fold spin-3/2 node and a Weyl node. Our comprehensive combined experimental and theoretical study provides a way to resolve different types of multifold fermions in CoSi at different energy. More broadly our results provide the necessary basis to interpret the burgeoning set of optical and transport experiments in chiral topological semimetals.

References in corpus (17)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Universal Dynamic Conductivity and Quantized Visible Opacity of Suspended Graphene
• Phase transition between the quantum spin Hall and insulator phases in 3D: emergence of a topological gapless phase
• Universal dynamical conductance in graphite
• Discovery of topological Weyl fermion lines and drumhead surface states in a room temperature magnet
• Multiple types of topological fermions in transition metal silicides
• Large Fermi Arcs in Unconventional Weyl Semimetal RhSi
• Discovery of topological chiral crystals with helicoid arc states
• New classes of chiral topological nodes with non-contractible surface Fermi arcs in CoSi
• Chiral anomaly and optical absorption in Weyl semimetals
• Giant topological longitudinal circular photo-galvanic effect in the chiral multifold semimetal CoSi
• Linear and nonlinear optical responses in the chiral multifold semimetal RhSi
• Low frequency optical conductivity in graphene and in other scale-invariant two-band systems
• Crystal growth and quantum oscillations in the topological chiral semimetal CoSi
• Linear optical conductivity of chiral multifold fermions
• Optical signature of Weyl electronic structures in tantalum pnictides Ta$Pn$ ($Pn=$ P, As)
• Unconventional free charge in the correlated semimetal Nd2Ir2O7

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