289 research outputs found
Photostrictive Effect and Structure Phase Transition via Nonlinear Photocurrent
The phenomena of crystal size changes and structural phase transitions
induced by light irradiation have garnered significant interest due to their
potential for tuning and controlling a wide range of material properties
through highly cooperative interactions. However, a microscopic theory that can
comprehensively explain these phenomena in correlation with photon frequency
and polarization has remained highly desirable. In this work, we propose that
nonlinear photocurrent may correspond to driving these effects, which arise
from a competition between light-injected energy and structural variations. By
conducting first-principles simulations and comparing them with two established
experiments, we show that shift current, a second-order photocurrent, can
induce photostriction and nonreciprocal structure phase transitions. The
quantitative comparisons across key parameters such as light frequency,
irradiation time, polarization, and intensity provide further support for the
nonlinear photocurrent mechanism. Beyond shift current, this microscopic
understanding proposes to utilize more types of nonlinear photocurrent to
enhance light-structure interactions and control material properties.Comment: 17 pages with 3 figure
Ferroelectricity and Phase Transitions in Monolayer Group-IV Monochalcogenides
Ferroelectricity usually fades away as materials are thinned down below a critical value. We reveal that the unique ionic-potential anharmonicity can induce spontaneous in-plane electrical polarization and ferroelectricity in monolayer group-IV monochalcogenides MX (M=Ge, Sn; X=S, Se). An effective Hamiltonian has been successfully extracted from the parametrized energy space, making it possible to study the ferroelectric phase transitions in a single-atom layer. The ferroelectricity in these materials is found to be robust and the corresponding Curie temperatures are higher than room temperature, making them promising for realizing ultrathin ferroelectric devices of broad interest. We further provide the phase diagram and predict other potentially two-dimensional ferroelectric materials
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