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Switchable Ferroelectric Diode and Photovoltaic Effect in BiFeO<sub>3</sub>
Choi, T.,Lee, S.,Choi, Y. J.,Kiryukhin, V.,Cheong, S.-W. American Association for the Advancement of Scienc 2009 Science Vol.324 No.5923
<P>Unidirectional electric current flow, such as that found in a diode, is essential for modern electronics. It usually occurs at asymmetric interfaces such as p-n junctions or metal/semiconductor interfaces with Schottky barriers. We report on a diode effect associated with the direction of bulk electric polarization in BiFeO3: a ferroelectric with a small optical gap edge of approximately 2.2 electron volts. We found that bulk electric conduction in ferroelectric monodomain BiFeO3 crystals is highly nonlinear and unidirectional. This diode effect switches its direction when the electric polarization is flipped by an external voltage. A substantial visible-light photovoltaic effect is observed in BiFeO3 diode structures. These results should improve understanding of charge conduction mechanisms in leaky ferroelectrics and advance the design of switchable devices combining ferroelectric, electronic, and optical functionalities.</P>
Visualizing anisotropic propagation of stripe domain walls in staircaselike transitions ofIrTe2
Mauerer, Tobias,Vogt, Matthias,Hsu, Pin-Jui,Pascut, Gheorghe Lucian,Haule, Kristjan,Kiryukhin, Valery,Yang, Junjie,Cheong, Sang-Wook,Wu, Weida,Bode, Matthias American Physical Society 2016 Physical Review B Vol.94 No.1
<P>We present a scanning tunneling microscopy (STM) study of the domain evolution across two first-order phase transitions of stripe modulations in IrTe2 that occur at T-C approximate to 275 K and T-S approximate to 180 K, respectively. Phase coexistence of the hexagonal (1 x 1) structure and the (5 x 1) stripe modulation is observed at TC, while various (p x 1) modulations (p = 3n + 2 with 2 <= n is an element of N) are observed below T-S. Using STM atomic resolution, we observe anisotropic propagation of domain boundaries along different directions, indicating significantly different kinetic energy barriers. These results are consistently explained by a theoretical analysis of the energy barrier for domain wall propagation as obtained by density functional theory. Individual switching processes observed by STM indicate that the wide temperature range of the transition from the (5 x 1) stripes to the (6 x 1)-ordered ground state is probably caused by the numerically limited subset of switching processes that are allowed between a given initial and the final state. The observations on IrTe2 are discussed in terms of a 'harmless staircase' with a finite number of first-order transitions between commensurate phases and within a 'dynamical freezing' scenario.</P>
Negative magnetostrictive magnetoelectric coupling of BiFeO3
Lee, Sanghyun,Fernandez-Diaz, M. T.,Kimura, H.,Noda, Y.,Adroja, D. T.,Lee, Seongsu,Park, Junghwan,Kiryukhin, V.,Cheong, S.-W.,Mostovoy, M.,Park, Je-Geun American Physical Society 2013 Physical review. B, Condensed matter and materials Vol.88 No.6