Controlling Electronic Phase Separation on the Nanoscale

I will discuss recent work from the M. Liu group to elucidate the nature of electronic phase transitions in strongly-correlated and heavy fermion systems VO2, Ca2RuO4, and Sm1-xYxS [1-3]. These studies rely on a combination of nano-FTIR and s-SNOM imaging to acquire the knowledge necessary to both answer open questions in long-studied materials and to explore potential device applications. In VO2/TiO2 (110)R thin films, substrate patterning causes the local strain environment and intrinsic phase separation lengths compete, enabling selective control of the anisotropy, metallic phase fraction, and transition temperature without sacrificing VO2 film quality [1]. This understanding of the VO2/TiO2 interface could pave the way for improved opto-electronic devices. In marked contrast to the filamentary metallization typical of oxides, the Ca2RuO4 phase boundary exhibits spontaneous orientation-dependent metal-insulator microstripes when the transition is electrically induced [2]. The comparably low currents required to electrically switch Ca2RuO4 make this an appealing material for energy-efficient devices. In Sm1-xYxS single crystals, manipulation of the nanoscale strain environment and phase diagram allows independent control of two plasmonic resonances (visible and IR) in a particular sample; enabling creation of a novel dual-band metamaterial [3]. I will relate the critical importance of nano-FTIR and s-SNOM imaging for understanding electronic phase separation, and also discuss the benefits of a multimodal approach to materials characterization.

[1] S. N. Gilbert Corder, et. al. PRB 96, 161110(R) (2017).
[2] J. Zhang, et. al. PRX 9, 011032 (2019).
[3] S. N. Gilbert Corder, et. al. Nat. Comm. 8, 2262 (2017).

Acknowledgements: The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract No. DE-AC02-05CH11231.