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53 results on '"Lukáš Horák"'

51. Quasi-Two-Dimensional Anomalous Hall Mott Insulator of Topologically Engineered J_{eff}=1/2 Electrons

Author

Junyi Yang, Hidemaro Suwa, Derek Meyers, Han Zhang, Lukas Horak, Zhaosheng Wang, Gilberto Fabbris, Yongseong Choi, Jenia Karapetrova, Jong-Woo Kim, Daniel Haskel, Philip J. Ryan, M. P. M. Dean, Lin Hao, and Jian Liu

Subjects
Physics, QC1-999
Abstract

We investigate an experimental toy-model system of a pseudospin-half square-lattice Hubbard Hamiltonian in [(SrIrO_{3})_{1}/(CaTiO_{3})_{1}] to include both nontrivial complex hopping and moderate electron correlation. While the former induces electronic Berry phases as anticipated from the weak-coupling limit, the latter stabilizes an antiferromagnetic Mott insulator ground state analogous to the strong-coupling limit. Their combined results in the real system are found to be an anomalous Hall effect with a nonmonotonic temperature dependence due to the competition of the antiferromagnetic order and charge excitations in the Mott state, and an exceptionally large Ising anisotropy that is captured as a giant magnon gap beyond the superexchange approach. The unusual phenomena highlight the rich interplay of electronic topology and electron correlation in the intermediate-coupling regime that is largely unexplored and challenging in theoretical modeling.

Published
2022
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52. Correlating light-induced deep defects and phase segregation in mixed-halide perovskites

Author

Katarína Ridzoňová, Roman Grill, Amalraj Peter Amalathas, Branislav Dzurňák, Neda Neykova, Lukáš Horák, Peter Fiala, Xin Yu Chin, Christian M. Wolff, Quentin Jeangros, and Jakub Holovský

Subjects
tolerance, Renewable Energy, Sustainability and the Environment, impact, ion-transport, General Materials Science, lead iodide, General Chemistry, films, traps, photocurrent spectroscopy, migration, performance, hybrid perovskites
Abstract

Mixed-halide perovskites are highly promising materials for tandem solar cells. The phenomenon of phase segregation, however hinders their application. Here, we combine Fourier-Transform photocurrent spectroscopy with photoluminescence and current density-voltage (J-V) measurements to study the effect of light soaking on such materials and devices. At first, we observe a gradual formation of an I-rich phase, which correlates with an increase in deep defect level concentration. We attribute these deep defects to charged iodide interstitials and associate phase segregation with iodide migration through interstitial positions. Upon further light soaking, the second less I-rich phase forms, while the deep level concentration simultaneously decreases. An empirical model describing the phase segregation mechanism is proposed to rationalize these observations. Further, we point to an important role of grain size in determining the degree and terminal phase of segregation.

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