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Topological Quantum Materials
Topological Quantum Materials
: Low-energy magneto-polarimetry from sub-THz to mid-infrared
: Low-energy magneto-polarimetry from sub-THz to mid-infrared
We aim to identify how time-reversal symmetry governs the selective excitation and control of topological states in magnetic topological semimetals. We employ low-energy magneto-polarimetry, which has been demonstrated to be a powerful tool for investigating multi-topological node systems, providing extensive and selective access to the topological nodes near the Fermi level.
Topological materials are a new class of quantum materials with distinctive electronic properties characterized by their surface states resulting from the topology of the bulk band structure. Among them, Weyl semimetals have attracted special interest due to quantum anomalies caused by Weyl fermions - massless, chiral quasiparticles - that enable the quantum control of topologies through electrical and optical means. Weyl fermions give rise to a band of protected surface states known as Fermi arcs. The presence of isolated Weyl nodes requires the breaking of either time-reversal symmetry (TRS) or inversion symmetry (IS). While non-magnetic Weyl semimetals usually result from broken IS in non-centrosymmetric materials, the discovery of magnetic Weyl semimetals - enabled by the simultaneous breaking of both TRS and IS - has introduced a new dimension to topological quantum materials.
We have studied magneto-polarimetry in magnetic Weyl semimetals, demonstrating that circularly polarized light can selectively excite Weyl bands at different energy scales near the Fermi level. We have conducted energy-resolved magneto-polarimetry with temperature- and magnetic field-dependent phase diagram mapping, along with comparative studies of similar systems with different magnetization platforms.
The overarching goal of this project is to develop a unified experimental framework for understanding the origin, criticality, and universality of low-energy magneto-polarimetry in magnetic topological semimetals. From a practical perspective, it has the potential to introduce a new type of quantum sensor and establish fundamental standards that remain unaffected by challenging environments, due to the protective nature of topologies.
Topological materials are a new class of quantum materials with distinctive electronic properties characterized by their surface states resulting from the topology of the bulk band structure. Among them, Weyl semimetals have attracted special interest due to quantum anomalies caused by Weyl fermions - massless, chiral quasiparticles - that enable the quantum control of topologies through electrical and optical means. Weyl fermions give rise to a band of protected surface states known as Fermi arcs. The presence of isolated Weyl nodes requires the breaking of either time-reversal symmetry (TRS) or inversion symmetry (IS). While non-magnetic Weyl semimetals usually result from broken IS in non-centrosymmetric materials, the discovery of magnetic Weyl semimetals - enabled by the simultaneous breaking of both TRS and IS - has introduced a new dimension to topological quantum materials.
We have studied magneto-polarimetry in magnetic Weyl semimetals, demonstrating that circularly polarized light can selectively excite Weyl bands at different energy scales near the Fermi level. We have conducted energy-resolved magneto-polarimetry with temperature- and magnetic field-dependent phase diagram mapping, along with comparative studies of similar systems with different magnetization platforms.
The overarching goal of this project is to develop a unified experimental framework for understanding the origin, criticality, and universality of low-energy magneto-polarimetry in magnetic topological semimetals. From a practical perspective, it has the potential to introduce a new type of quantum sensor and establish fundamental standards that remain unaffected by challenging environments, due to the protective nature of topologies.
Topological quantum materials with broken time-reversal symmetry: three research objectives in our group.
Low-energy chiral photoresponse measurement system as symmetry-sensitive probes.
Grant/ Publication/ Presentation
[1] NSF, LEAPS-MPS: Unveiling the Interplay of Chiral Transport, Magnetism, and Topology in Weyl Magnets: A Magneto-Optical Investigation, https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2317013.
Tailoring Evanescent Light on Surface
Tailoring Evanescent Light on Surface
: Surface Phonon Polaritonic Metasurfaces
: Surface Phonon Polaritonic Metasurfaces
Gradient optical metasurfaces have been used to demonstrate a wavefront control of light in free space and in optical waveguides by imposing spatially varying optical responses to the light. However, the control of light localized and propagating on surface has been challenging because the surface waves scatter intensively to the metallic metasurfaces causing the optical loss. Can we find new metasurfaces platform to tailor the surface waves of light? Our group addresses the challenge by understanding fundamentally the near-field interaction between surface waves of light and surface charge oscillations confined in gradient metasurfaces. The research project will deal with the technologically important long-wavelength infrareds and result in producing active flat optical components, perfect infrared absorbers, narrow-band thermal emitters and detectors, optical isolators, and phase modulators in mid and far infrared.
Grant/ Publication/ Presentation
[1] Coupled surface plasmon-phonon polariton nanocavity arrays for enhanced mid-infrared absorption, S. Kachiraju, I. Nekrashevich, I. Ahmad, H. Farooq, L. Chang, S. Kim, and M.-H. Kim, Nanophotonics vol. 11 no. 20 pp. 4489-4498 (2022), https://doi.org/10.1515/nanoph-2022-0339.
[2] M.-H. Kim, Z. Brown, and S. Kachiraju, "Long-wave infrared phase modulation and polarization ellipticity standard," Patent Pending, PCT/US2024/018275.
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