Giant Modulation of Refractive Index from Picoscale Atomic Displacements

Boyang Zhao; Guodong Ren; Hongyan Mei; Vincent C Wu; Shantanu Singh; Gwan Yeong Jung; Huandong Chen; Raynald Giovine; Shanyuan Niu; Arashdeep S Thind; Jad Salman; Nick S Settineri; Bryan C Chakoumakos; Michael E Manley; Raphael P Hermann; Andrew R Lupini; Miaofang Chi; Jordan A Hachtel; Arkadiy Simonov; Simon J Teat; Raphaële J Clément; Mikhail A Kats; Jayakanth Ravichandran; Rohan Mishra

doi:10.1002/adma.202311559

Giant Modulation of Refractive Index from Picoscale Atomic Displacements

Adv Mater. 2024 Jun;36(24):e2311559. doi: 10.1002/adma.202311559. Epub 2024 Apr 10.

Authors

Boyang Zhao¹, Guodong Ren², Hongyan Mei³, Vincent C Wu⁴, Shantanu Singh¹, Gwan Yeong Jung⁵, Huandong Chen¹, Raynald Giovine⁴, Shanyuan Niu^{1

6}, Arashdeep S Thind², Jad Salman³, Nick S Settineri⁷, Bryan C Chakoumakos⁸, Michael E Manley⁹, Raphael P Hermann⁹, Andrew R Lupini¹⁰, Miaofang Chi¹⁰, Jordan A Hachtel¹⁰, Arkadiy Simonov¹¹, Simon J Teat⁷, Raphaële J Clément⁴, Mikhail A Kats³, Jayakanth Ravichandran^{1

12

13}, Rohan Mishra^{2

5}

Affiliations

¹ Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, CA, 90089, USA.
² Institute of Materials Science and Engineering, Washington University in St. Louis, St. Louis, MO, 63130, USA.
³ Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, WI, 53706, USA.
⁴ Materials Department and Materials Research Laboratory, University of California, Santa Barbara, CA, 93106, USA.
⁵ Department of Mechanical Engineering and Materials Science, Washington University in St. Louis, St. Louis, MO, 63130, USA.
⁶ College of Engineering and Applied Sciences, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing, 210093, China.
⁷ Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
⁸ Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
⁹ Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
¹⁰ Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
¹¹ Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 1-5/10, Zürich, 8093, Switzerland.
¹² Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, CA, 90089, USA.
¹³ Core Center of Excellence in Nano Imaging, University of Southern California, Los Angeles, CA, 90089, USA.

PMID: 38520395
DOI: 10.1002/adma.202311559

Abstract

It is shown that structural disorder-in the form of anisotropic, picoscale atomic displacements-modulates the refractive index tensor and results in the giant optical anisotropy observed in BaTiS₃, a quasi-1D hexagonal chalcogenide. Single-crystal X-ray diffraction studies reveal the presence of antipolar displacements of Ti atoms within adjacent TiS₆ chains along the c-axis, and threefold degenerate Ti displacements in the a-b plane. ^47/49Ti solid-state NMR provides additional evidence for those Ti displacements in the form of a three-horned NMR lineshape resulting from a low symmetry local environment around Ti atoms. Scanning transmission electron microscopy is used to directly observe the globally disordered Ti a-b plane displacements and find them to be ordered locally over a few unit cells. First-principles calculations show that the Ti a-b plane displacements selectively reduce the refractive index along the ab-plane, while having minimal impact on the refractive index along the chain direction, thus resulting in a giant enhancement in the optical anisotropy. By showing a strong connection between structural disorder with picoscale displacements and the optical response in BaTiS₃, this study opens a pathway for designing optical materials with high refractive index and functionalities such as large optical anisotropy and nonlinearity.

Keywords: DFT; NMR; STEM; anisotropy; refractive index; structural disorder; synchrotron diffraction.

Abstract

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