Nanoscale Femtosecond Dynamics of Mott Insulator (Ca0.99Sr0.01)2RuO4

Rocco A Vitalone; Aaron J Sternbach; Benjamin A Foutty; Alexander S McLeod; Chanchal Sow; Denis Golez; Fumihiko Nakamura; Yoshiteru Maeno; Abhay N Pasupathy; Antoine Georges; Andrew J Millis; D N Basov

doi:10.1021/acs.nanolett.2c00581

Nanoscale Femtosecond Dynamics of Mott Insulator (Ca_0.99Sr_0.01)₂RuO₄

Nano Lett. 2022 Jul 27;22(14):5689-5697. doi: 10.1021/acs.nanolett.2c00581. Epub 2022 Jul 15.

Authors

Rocco A Vitalone¹, Aaron J Sternbach¹, Benjamin A Foutty^{1

2}, Alexander S McLeod^{1

3}, Chanchal Sow^{4

5}, Denis Golez^{6

7

8}, Fumihiko Nakamura⁹, Yoshiteru Maeno⁴, Abhay N Pasupathy¹, Antoine Georges^{6

10

11

12}, Andrew J Millis^{1

6}, D N Basov¹

Affiliations

¹ Department of Physics, Columbia University, 1150 Amsterdam Avenue, New York, New York 10027, United States.
² Department of Physics, Stanford University, 450 Serra Mall, Stanford, California 94305m United States.
³ School of Physics and Astronomy, University of Minnesota Twin Cities, 115 Union Street SE, Minneapolis, Minnesota 55455, United States.
⁴ Deparment of Physics, Kyoto University, Yoshidahonmachi, Sakyo Ward, Kyoto 606-8501, Japan.
⁵ Department of Physics, IIT Kanpur, Kalyanpur Kanpur, Uttar Pradesh, India 209016.
⁶ Center for Computational Physics, Flatiron Institute, 162 Fifth Avenue, New York, New York 10010, United States.
⁷ Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia.
⁸ Faculty of Mathematics and Physics, University of Ljubljana, Jandranska 19, 1000 Ljubljana, Slovenia.
⁹ Department of Education and Creation Engineering, Kurume Institute of Technology, Kurume, Fukuoka 830-0052, Japan.
¹⁰ Department of Physics, College of France, 11Pl. Marcelin, Berthelot, Paris, France FR 75231.
¹¹ CPHT, CNRS, Polytechnic Institute of Paris, Ecole Polytechnique Palaiseau, Paris, France FR 91128.
¹² DQMP, Universite de Geneve, 24 Quai Ernest Ansermet, Geneve CH-1211, Switzerland.

PMID: 35839312
DOI: 10.1021/acs.nanolett.2c00581

Abstract

Ca₂RuO₄ is a transition-metal oxide that exhibits a Mott insulator-metal transition (IMT) concurrent with a symmetry-preserving Jahn-Teller distortion (JT) at 350 K. The coincidence of these two transitions demonstrates a high level of coupling between the electronic and structural degrees of freedom in Ca₂RuO₄. Using spectroscopic measurements with nanoscale spatial resolution, we interrogate the interplay of the JT and IMT through the temperature-driven transition. Then, we introduce photoexcitation with subpicosecond temporal resolution to explore the coupling of the JT and IMT via electron-hole injection under ambient conditions. Through the temperature-driven IMT, we observe phase coexistence in the form of a stripe phase existing at the domain wall between macroscopic insulating and metallic domains. Through ultrafast carrier injection, we observe the formation of midgap states via enhanced optical absorption. We propose that these midgap states become trapped by lattice polarons originating from the local perturbation of the JT.

Keywords: Ca2RuO4, correlated Mott insulator; insulator−metal transition; midgap states; transient scanning near-field optical microscopy (Tr-SNOM); ultrafast pump−probe.