Abstract
Broadband tunability is a central theme in contemporary nanophotonics and metamaterials research. Combining metamaterials with phase change media offers a promising approach to achieve such tunability, which requires a comprehensive investigation of the electromagnetic responses of novel materials at subwavelength scales. In this work, we demonstrate an innovative way to tailor band-selective electromagnetic responses at the surface of a heavy fermion compound, samarium sulfide (SmS). By utilizing the intrinsic, pressure sensitive, and multi-band electron responses of SmS, we create a proof-of-principle heavy fermion metamaterial, which is fabricated and characterized using scanning near-field microscopes with <50 nm spatial resolution. The optical responses at the infrared and visible frequency ranges can be selectively and separately tuned via modifying the occupation of the 4f and 5d band electrons. The unique pressure, doping, and temperature tunability demonstrated represents a paradigm shift for nanoscale metamaterial and metasurface design.
Highlights
Broadband tunability is a central theme in contemporary nanophotonics and metamaterials research
The Sm 4f6 states are highly localized such that the overlap between these electron wavefunctions vanishes and no plasma resonance exists in spite of the high 4f electron concentration[16]
With increasing pressure, samarium sulfide (SmS) undergoes an isostructural phase transition to a golden intermediate valence (IV) state: from Sm2+ to a fractional valence of Sm2.6−2.8+. This intermediate valence is a result of the 5d t2g conduction band shifting lower in energy and hybridizing with the 4f6 band on the neighboring atomic site
Summary
Broadband tunability is a central theme in contemporary nanophotonics and metamaterials research. Recent developments have embraced a reverse trend in which the intrinsic optical properties of natural materials are employed to aid in the design of new generations of MM devices[4] This is especially relevant in the construction of switchable or tunable MM with dynamic control. Tunable MM design has mainly focused on altering/tuning the response of noble-metal resonators in composite devices by relying heavily on the single band electron properties of the SCES as functional substrates[5,6,8,9,10]. We control and monitor the plasmonic response of d-band electrons, as in noble metals or transition metal oxides, and of f-band electrons This is achieved by utilizing the local phase transition in samarium sulfide (SmS), a canonical correlated heavy fermion system with 5d and 4f electrons. A combination of near-field and far-field optical techniques enables us to characterize the nanoscale phase separation and probe the electromagnetic response of the resulting devices from submicroscopic to macroscopic scales
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