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Origin of doping-induced suppression and reemergence of magnetism in LaFeAsO1−xHx
Moon, Chang-Youn,Park, Hyowon,Haule, Kristjan,Shim, Ji Hoon American Physical Society 2016 Physical Review B Vol.94 No.22
<P>We investigate the evolution of magnetic properties as a function of hydrogen doping in the iron-based superconductor LaFeAsO1-xHx using dynamical mean-field theory combined with density-functional theory. We find that two independent consequences of doping, namely the increase of the electron occupation and the structural modification, have the opposite effects on the strength of electron correlation and magnetism, resulting in the minimum of the calculated magnetic moment around the intermediate doping level as a function of x. Our result provides a natural explanation for the recent, puzzling experimental discovery of two separated antiferromagnetic phases at low and high doping limits. Furthermore, the increase of the orbital occupation and correlation strength with doping results in reduced orbital polarization of d(xz/yz) orbitals and an enhanced role of the d(xy) orbital in the magnetism at high doping levels, and their possible implications on the superconductivity are discussed in line with the essential role of the magnetism.</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>