Browsing by Author "Tra, V. T."

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Distribution of electronic reconstruction at the n-type LaAlO(3)/SrTiO(3) interface revealed by hard x-ray photoemission spectroscopy
(2011-12-26)
Chu, Y. Y.
;
Liao, Y. F.
;
Tra, V. T.
;
Yang, J. C.
;
Liu, W. Z.
We investigated the electronic reconstruction at the n-type LaAlO(3)/SrTiO(3) interface with hard x-ray photoelectron spectroscopy (HAXPES) under grazing incidence. By exploiting the collapse of evanescent x-ray waves and the abrupt increase of x-ray absorption at the critical incidence angle, our HAXPES study reveals a 2% electronic reconstruction from Ti(4+) to Ti(3+) occurring near the interface. Such an electronic reconstruction also extends from the interface into SrTiO(3) with a depth of about 48 angstrom (similar to 12 unit cells) and an estimated total charge transfer of similar to 0.24 electrons per two-dimensional unit cell. (C) 2011 American Institute of Physics. [doi:10.1063/1.3672099]
Distribution of electronic reconstruction at the n-type LaAlO3/SrTiO3 interface revealed by hard x-ray photoemission spectroscopy
(2011-12-26)
Chu, Y. Y.
;
Liao, Y. F.
;
Tra, V. T.
;
Yang, J. C.
;
Liu, W. Z.
We investigated the electronic reconstruction at the n-type LaAlO3/SrTiO3 interface with hard x-ray photoelectron spectroscopy (HAXPES) under grazing incidence. By exploiting the collapse of evanescent x-ray waves and the abrupt increase of x-ray absorption at the critical incidence angle, our HAXPES study reveals a 2% electronic reconstruction from Ti4+ to Ti3+ occurring near the interface. Such an electronic reconstruction also extends from the interface into SrTiO3 with a depth of about 48 angstrom (similar to 12 unit cells) and an estimated total charge transfer of similar to 0.24 electrons per two-dimensional unit cell. (C) 2011 American Institute of Physics. [doi:10.1063/1.3672099]
Imaging magnetic and ferroelectric domains and interfacial spins in magnetoelectric La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 heterostructures
(2015-12-23)
Huang, C-Y
;
Zhou, J.
;
Tra, V. T.
;
White, R.
;
Trappen, R.
Strong magnetoelectric coupling can occur at the interface between ferromagnetic and ferroelectric films. Similar to work on interfacial exchange bias, photoemission electron microscopy was utilized to image both magnetic and ferroelectric domains and the resulting interfacial Ti spin in the same locations of La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 heterostructures. Multiple image analysis techniques, which could be applicable for a variety of fields needing quantitative data on image switching, confirm both improved magnetic switching and an increased population of interfacial spins with increased thickness of the ultrathin La0.7Sr0.3MnO3 layer. The perpendicular orientation of the interfacial spins is also discussed. This work suggests a magnetoelectric dead layer, with reduced interfacial magnetoelectricity when thin magnetic films are present.
Imaging magnetic and ferroelectric domains and interfacial spins in magnetoelectric La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 heterostructures
(2015-12-23)
Huang, C-Y
;
Zhou, J.
;
Tra, V. T.
;
White, R.
;
Trappen, R.
Strong magnetoelectric coupling can occur at the interface between ferromagnetic and ferroelectric films. Similar to work on interfacial exchange bias, photoemission electron microscopy was utilized to image both magnetic and ferroelectric domains and the resulting interfacial Ti spin in the same locations of La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 heterostructures. Multiple image analysis techniques, which could be applicable for a variety of fields needing quantitative data on image switching, confirm both improved magnetic switching and an increased population of interfacial spins with increased thickness of the ultrathin La0.7Sr0.3MnO3 layer. The perpendicular orientation of the interfacial spins is also discussed. This work suggests a magnetoelectric dead layer, with reduced interfacial magnetoelectricity when thin magnetic films are present.
Selective interlayer ferromagnetic coupling between the Cu spins in YBa2Cu3O7-x grown on top of La0.7Ca0.3MnO3
(2015-11-17)
Huang, S. W.
;
Wray, L. Andrew
;
Jeng, Horng-Tay
;
Tra, V. T.
;
Lee, J. M.
Studies to date on ferromagnet/d-wave superconductor heterostructures focus mainly on the effects at or near the interfaces while the response of bulk properties to heterostructuring is overlooked. Here we use resonant soft x-ray scattering spectroscopy to reveal a novel c-axis ferromagnetic coupling between the in-plane Cu spins in YBa2Cu3O7-x (YBCO) superconductor when it is grown on top of ferromagnetic La0.7Ca0.3MnO3 (LCMO) manganite layer. This coupling, present in both normal and superconducting states of YBCO, is sensitive to the interfacial termination such that it is only observed in bilayers with MnO2 but not with La0.7Ca0.3O interfacial termination. Such contrasting behaviors, we propose, are due to distinct energetic of CuO chain and CuO2 plane at the La0.7Ca0.3O and MnO2 terminated interfaces respectively, therefore influencing the transfer of spin-polarized electrons from manganite to cuprate differently. Our findings suggest that the superconducting/ferromagnetic bilayers with proper interfacial engineering can be good candidates for searching the theorized Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state in cuprates and studying the competing quantum orders in highly correlated electron systems.
The unconventional doping in YBa2Cu3O7-x/La0.7Ca0.3MnO3 heterostructures by termination control
(2017-01-16)
Tra, V. T.
;
Huang, R.
;
Gao, X.
;
Chen, Y. -J.
;
Liu, Y. T.
In strongly correlated oxides, heterostructures provide a powerful route to manipulate the charge, spin, orbital, and lattice degrees of freedom to create distinctive functionalities. In this work, we have achieved atomically precise interface control in YBa2Cu3O7-x/La0.7Ca0.3MnO3 (YBCO/LCMO) heterostructures and find a hidden effective doping. This mechanism is responsible for higher Tc in the sample with the MnO2-terminated interface than in that with the La0.7Ca0.3O-terminated interface. The MnO2-terminated sample also shows a larger magnetic moment of Mn together with a lower valence state. For more than a decade, the control of T-c in these heterostructures prior to this work has been solely via the variation of YBCO or LCMO thickness. This work hints at an alternative way of exploiting and exploring the interactions between superconductivity and magnetism in this system. Published by AIP Publishing.