Browsing by Author "Lin, Jiunn-Yuan"

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Anisotropic superconductivity induced by periodic multiferroic domain patterns
(2019-12-06)
Huang, Yen-Lin
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Huang, Bo-Chao
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Wang, Yan-Ting
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Xue, Fei
;
Lin, Jheng-Cyuan
The competition between order parameters, such as ferroelectricity, ferromagnetism, and superconductivity, is one of the most fascinating topics in condensed matter physics. Here, we report intriguing anisotropic superconductivity in YBa2Cu3O7-x films induced by a multiferroic, BiFeO3, with periodic domain patterns. The anisotropic superconductivity was investigated by transport measurements and supported by phase-field simulations, and then the detailed local electronic structures were revealed by cross-sectional scanning tunneling microscopy. We found that the oxygen redistribution in YBa2Cu3O7-x modulated by the ferroelectric polarization in BiFeO3 was the key mechanism driving this anisotropic superconductivity. The presented heteroarchitecture of a high-temperature superconductor and a domain-engineered multiferroic provides a new approach to tune superconductivity and offers potential advantages for the design of future multifunctional devices.
Control of the Metal-Insulator Transition at Complex Oxide Heterointerfaces through Visible Light
(2016-01-27)
Lin, Jheng-Cyuan
;
Vu Thanh Tra
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Tsai, Dung-Sheng
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Lin, Tai-Te
;
Huang, Po-Cheng
The coupling of the localized surface plasmon resonance of Au nanoparticles is utilized to deliver a visible-light stimulus to control conduction at the LaAlO3/SrTiO3 interface. A giant photoresponse and the controllable metal-insulator transition are characterized at this heterointerface. This study paves a new route to optical control of the functionality at the heterointerfaces.
Controllable electrical conduction at complex oxide interfaces
(2014-06-01)
Vu Thanh Tra
;
Yang, Jan-Chi
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Hsieh, Ying-Hui
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Lin, Jiunn-Yuan
;
Chen, Yi-Chun
Oxide interfaces have sparked considerable interest due to their fascinating physical properties and promising possibilities for next-generation nanoelectronics. Three intriguing oxide interfaces, hetero-, homo-, and tubular interfaces, will be discussed in detail in this review. First, the development and fundamental properties of classical heterointerfaces will be elaborated. Using LaAlO3/SrTiO3 as a case study, we present the most generic approach to control the two-dimensional electron conduction at the heterointerface. Secondly, several key issues based on interesting observations on ferroic homointerfaces will be addressed. Multiple controls of fascinating functionalities based on multiferroic BiFeO3 domain walls will be presented as a model system. Finally, as the most challenging task, we review a new type of complex oxide interfaces, the tubular interface. Further insights of recently emerged tubular interfaces in BiFeO3/CoFe2O4 system will be explored, which serve as one of the focal roles in developing new functional interfaces and potentially new type of nanostructures. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Crossover between superconductivity and magnetism in SrRuO3 mesocrystal embedded YBa2Cu3O7-x heterostructures
(2016)
Suresh, Vandrangi
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Lin, Jheng-Cyuan
;
Liu, Heng-Jui
;
Zhang, Zaoli
;
Chiang, Ping-Chih
The competition between superconductivity and ferromagnetism poses great challenges and has attracted renewed interest for applications in novel spintronic devices. In order to emphasize their interactions, we fabricated a heterostructure composed of superconducting YBa2Cu3O7-delta (YBCO) film embedded with itinerant ferromagnetic SrRuO3 (SRO) mesocrystals. Starting from a doping concentration of 10 vol% of SRO mesocrystal in a YBCO matrix, corresponding to the density of SRO nanocrystals similar to 5 x 10(9) cm(-2), which exhibits the typical characteristic of a metal-superconductor transition, and then increasing the magnetic interactions as a function of SRO embedment, the electronic correlation and the interplay between superconductivity and magnetism throughout the temperature regime were investigated. A metal-insulator transition in the normal state of YBCO and a crossover between superconductivity and magnetism at low temperatures were found upon increasing the density of nano-size SRO crystallites in the YBCO matrix as a consequence of competing interactions between these two ordered phases.
Crucial Role of Site Disorder and Frustration in Unusual Magnetic Properties of Quasi-2D Triangular Lattice Antimonate Na4FeSbO6
(2015-10-01)
Zvereva, Elena A.
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Presniakov, Igor A.
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Whangbo, Myung-Hwan
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Koo, Hyun-Joo
;
Frantsuzenko, Tatyana V.
The effect of antisite disorder in the layered sodium iron antimonate Na4FeSbO6 was examined both experimentally and theoretically. The magnetic susceptibility and specific heat measurements show that Na4FeSbO6 does not undergo a long-range antiferromagnetic order, unlike its structural analog Li4FeSbO6. The electron spin resonance yields the complicated picture of coexistence of two magnetic subsystems corresponding to two different Fe cation positions in the lattice (regular and antisite) and driving the magnetic properties of the Na4FeSbO6. This conclusion found perfect confirmation from both the Mossbauer and X-ray absorption data which show the presence of two kinds of Fe3+ ions being in high-spin Fe3+ (S = 5/2) and low-spin Fe3+ (S = 1/2) states. These findings arise from the antisite disorder between the Fe3+ and Sb5+ ions in the (NaFeSbO6)(3-) layers of Na4FeSbO6. Our density functional calculations show that the Fe3+ ions located at the Sb5+ sites exist as low-spin Fe3+ ions, and that the spins of each Fe3+ (S = 5/2)-Fe3+ (S = 1/2)-Fe3+ (S = 5/2) trimer generated by the antisite disorder has a ferrimagnetic arrangement Fe(3+)a dagger aEuro"Fe(3+)a dagger"aEuro"Fe(3+)a dagger, which enhances the magnetization of Na4FeSbO6 and leads to an apparently positive Curie-Weiss temperature.
Effects of Strain and Ordering of Rare-Earth Element Moments on Magnetic-Reordering in Orthorhombic Multiferroic Manganites
(2013-10-01)
Hsiao, Yen-Fu
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Lai, Jun-Yo
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Lin, Jun-Yu
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Fang, Hau-Wei
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Hung, Yi-Tse
Orthorhombic multiferroic manganite thin films with various orientations and strain states were prepared to show the effects of anisotropic strain and antiferromagnetic (AFM) ordering of rare-earth f-electrons on the orientation of the incommensurate-to-commensurate AFM reordering. Systematic analyses suggest that the low-temperature AFM ordering of the rare-earth f-electrons may have played a decisive role in causing the orientation changes in AFM reordering, although the b-axis strain does have a significant influence on the zero-field magnetization behaviors. (C) 2013 The Japan Society of Applied Physics
Effects of strain on the electronic structure and magnetic properties in SrMn0.5Fe0.5O3
(2016-09-01)
Mi, Chun-Wei
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Chin, Yi-Ying
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Hsiao, Yen-Fu
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Fang, Hau-Wei
;
Luo, Chih-Wei
The electronic structure and magnetic properties of SrMn0.5Fe0.5O3 powder and films grown on (100)-SrTiO3 (STO) and (100)-LaAlO3 (LAO) substrates by pulsed laser deposition (PLD) were investigated by temperature dependent magnetization and soft x-ray absorption. The results exhibit characteristics of 3d(5) Fe3+, 3d(5) (L) under bar Fe4+, and 3d(3) + 3d(4) (L) under bar Mn4+ at room temperature in all samples. However, the features of 3d(5) Fe3+ and 3d(3) Mn4+ increased significantly for SMFO/LAO at 35 K, which also displayed substantial competition between antiferromagnetic and ferromagnetic order well-above the Neel temperature of SrFeO3 (T-N similar to 134 K). We attributed this to being caused by charge disproportionation resulting from ligand-hole localization, which is more favorable to take place when the sample is under compressive strain.
Effects of Structural Strain and Rare-Earth Moments on Spin Cycloidal-Plane in Multiferroic Rare-Earth Manganites
(2016-05)
Hsiao, Yen-Fu
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Kuo, Wei-Cheng
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Mi, Chun-Wei
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Chang, Kai-Ting
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Luo, Chih-Wei
A series of orthorhombic multiferroic manganites (o-ReMnO3) thin films with deliberately designed strain states and different rare-earth elements were prepared to unveil the roles played by the strain and 4f-electron moments in determining the magnetic ordering and associated polarizations. The results obtained from temperature-dependent magnetization, dielectric and ferroelectric measurements revealed that the orientations of magnetic reordering and polarization varied with the specific rare-earth element involved. Namely, with the increase of total angular momentum J of the 4f-electrons of rare-earth element the orientation of magnetic reordering was changed from the b-axis (sinusoidal state) for Yb3+ to the a-axis (ab-cycloidal) for Tm3+ and, eventually to the c-axis (bc-cycloidal) for Er3+ and Ho3+. These results indicate that the Re-Mn magnetic exchange interaction plays a more important role than the external strain does in determining the magnetic and hence polarization states in multiferroic o-ReMnO3 manganites. Our results also confirmed the coexistence of different magnetic spin states in o-ReMnO3 thin films.
Enhanced critical current density in the pressure-induced magnetic state of the high-temperature superconductor FeSe
(2015-11-09)
Jung, Soon-Gil
;
Kang, Ji-Hoon
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Park, Eunsung
;
Lee, Sangyun
;
Lin, Jiunn-Yuan
We investigate the relation of the critical current density (J(c)) and the remarkably increased superconducting transition temperature (T-c) for the FeSe single crystals under pressures up to 2.43 GPa, where the T-c is increased by similar to 8 K/GPa. The critical current density corresponding to the free flux flow is monotonically enhanced by pressure which is due to the increase in T-c, whereas the depinning critical current density at which the vortex starts to move is more influenced by the pressure-induced magnetic state compared to the increase of T-c. Unlike other high-T-c superconductors, FeSe is not magnetic, but superconducting at ambient pressure. Above a critical pressure where magnetic state is induced and coexists with superconductivity, the depinning Jc abruptly increases even though the increase of the zero-resistivity T-c is negligible, directly indicating that the flux pinning property compared to the T-c enhancement is a more crucial factor for an achievement of a large J(c). In addition, the sharp increase in J(c) in the coexisting superconducting phase of FeSe demonstrates that vortices can be effectively trapped by the competing antiferromagnetic order, even though its antagonistic nature against superconductivity is well documented. These results provide new guidance toward technological applications of high-temperature superconductors.
Ferroelectric Control of the Conduction at the LaAlO3/SrTiO3 Heterointerface
(2013-06-25)
Vu Thanh Tra
;
Chen, Jhih-Wei
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Huang, Po-Cheng
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Huang, Bo-Chao
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Cao, Ye
Helicity-dependent terahertz emission spectroscopy of topological insulator Sb2Te3 thin films
(2017-11-06)
Tu, Chien-Ming
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Chen, Yi-Cheng
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Huang, Ping
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Chuang, Pei-Yu
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Lin, Ming-Yu
We report on helicity-dependent terahertz emissions that originate from the helicity-dependent photocurrents in topological insulator Sb2Te3 thin films due to ultrafast optical excitation. The polarity of the emitted terahertz radiation is controlled by both the incident angle and the helicity of optical pulses. Using an unprecedented decomposition-recombination procedure in the time domain, the signals of the Dirac fermions are fully separated from bulk contributions. These results provide insights into the optical coupling of topological surface states and open up opportunities for applying helicity-dependent terahertz emission spectroscopy in spintronics.
Helicity-Dependent Terahertz Radiation from Topological Insulator Sb2Te3 Thin Film by Femtosecond Optical Excitation
(2016)
Tu, Chien-Ming
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Chen, Yi-Cheng
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Huang, Ping
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Chuang, Pei-Yu
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Lin, Ming-Yu
We report on terahertz radiation from topological insulator (TI)Sb2Te3 thin film under ultrafast optical excitation with different helicity. Polarity-reversals of the emitted THz radiation were observed as the helicity of optical pulses reversed. The observed phenomena are coincident with the characteristics of the helicity-dependent photocurrent on TIs. Our work demonstrates the potential applications of surface photocurrents on TIs for opto-spintronics devices.
Large Magnetoresistance in Magnetically Coupled SrRuO3-CoFe2O4 Self-Assembled Nanostructures
(2013-09-14)
Liu, Heng-Jui
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Vu-Thanh Tra
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Chen, Ying-Jiun
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Huang, Rong
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Duan, Chun-Gang
Manifestation of a Second Dirac Surface State and Bulk Bands in THz Radiation from Topological Insulators
(2015-09-15)
Tu, Chien-Ming
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Yeh, Tien-Tien
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Tzeng, Wen-Yen
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Chen, Yi-Ru
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Chen, Hsueh-Ju
Topological insulators (TIs) are interesting quantum matters that have a narrow bandgap for bulk and a Dirac-cone-like conducting surface state (SS). The recent discovered second Dirac surface state (SS) and bulk bands (BBs) located similar to 1.5 eV above the first SS are important for optical coupling in TIs. Here, we report on the time-domain measurements of THz radiation generated from TIs n-type Cu0.02Bi2Se3 and p-type Bi2Te3 single crystals by ultrafast optical pulse excitation. The observed polarity-reversal of the THz pulse originated from transient current is unusual, and cannot be reconciled with the photo-Dember effect. The second SS and BBs are found to be indispensable for the explanation of the unusual phenomenon. Thanks to the existence of the second SS and BBs, TIs manifest an effective wide band gap in THz generation. The present study demonstrates that time-domain THz spectroscopy provide rich information of the optical coupling and the electronic structure of TIs.
Mapping Band Alignment across Complex Oxide Heterointerfaces
(2012-12-12)
Huang, Bo-Chao
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Chiu, Ya-Ping
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Huang, Po-Cheng
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Wang, Wen-Ching
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Vu Thanh Tra
In this study, direct observation of the evolution of electronic structures across complex oxide interfaces has been revealed in the LaAlO3/SrTiO3 model system using cross-sectional scanning tunneling microscopy and spectroscopy. The conduction and valence band structures across the LaAlO3/SrTiO3 interface are spatially resolved at the atomic level by measuring the local density of states. This study directly maps out the electronic reconstructions and a built-in electric field in the polar LaAlO3 layer. Results also clearly reveal the band bending and the notched band structure in the SrTiO3 adjacent to the interface. DOI: 10.1103/PhysRevLett.109.246807
Nanomechanical, structural, and transport properties of Bi3Se2Te thin films
(2016-09-15)
Phuoc Huu Le
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Chiu, Shao-Pin
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Jian, Sheng-Rui
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Luo, Chih Wei
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Lin, Jiunn-Yuan
New ternary phase of Bi3Se2Te thin films were successfully grown through pulsed laser deposition with a single Bi2Se2Te crystal as the target. Bi-rich and Se-and Te-deficient compositions deposited at a substrate temperature (T-s) of 250 degrees C and helium gas pressures (P-He) ranging from 2.0 x 10(-5) to 6.5 x 10(-1) Torr aided the formation of the dominant Bi-rich phase: Bi3Se2Te. The films were grown epitaxially on Al2O3 (001) substrates with Bi3Se2Te [001]//Al2O3 [001] and Bi3Se2Te [110]//Al2O3 [210]. An increase in P-He remarkably enhanced the hardness and Young\'s modulus of the films, primarily because of the decrease in nanograin size, following the HallePetch relationship. Moreover, the Bi3Se2Te films present linear magnetoresistance under a high perpendicular magnetic field (B >= 4 T) and twodimensional weak antilocalization effect under a low B (+/- 1 T) which may be attributed to topological insulator surface state (TSS). Clearly, further theoretical calculations and experiments are needed to confirm the suggested interpretation. (C) 2016 Elsevier B.V. All rights reserved.
Pairing symmetry and upward curvature of the upper critical field in superconducting Na0.35CoO2 center dot yH(2)O
(2007-01-01)
Kao, Jun-Ting
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Lin, Jiunn-Yuan
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Mou, Chung-Yu
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物理研究所
;
Institute of Physics
The origin for the upward curvature of the upper critical field (H-c2) observed in hydrate cobaltate Na0.35CoO2 center dot yH(2)O is investigated based on the microscopic gap equation. It is shown that the observed upward curvature results from the transition between two different pairing symmetries that occur on different energy bands. Furthermore, different pairing symmetries involved in the transition results in different upward curvatures. By considering transitions among all lowest possible pairing symmetries, it is found that the transition of the pairing symmetry from s-wave at low fields to d(x)(2)-y(2)+id(xy) at high fields is the best fit to the experimental data. Our results provide an important clue to the understanding of the superconductivity in hydrate cobaltate.
Pressure dependence of upper critical fields in FeSe single crystals
(2016-03)
Kang, Ji-Hoon
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Jung, Soon-Gil
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Lee, Sangyun
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Park, Eunsung
;
Lin, Jiunn-Yuan
We investigate the pressure dependence of the upper critical fields (mu H-0(c2)) for FeSe single crystals with pressure up to 2.57 GPa. The superconducting (SC) properties show a disparate behavior across a critical pressure where the pressure-induced antiferromagnetic phase coexists with superconductivity. The magnetoresistance for H//ab and H//c is very different: for H//c, magnetic field induces and enhances a hump in the resistivity close to the T-c for pressures higher than 1.2 GPa, while it is absent for H//ab. Since the measured mu H-0(c2) for FeSe samples is smaller than the orbital limited upper critical field (H-c2(orb)) estimated by the Werthamer, Helfand and Hohenberg model, the Maki parameter (alpha) related to Pauli spin-paramagnetic effects is additionally considered to describe the temperature dependence of mu H-0(c2)(T). Interestingly, the alpha value is hardly affected by pressure for H//ab, while it strongly increases with pressure for H//c. The pressure evolution of the mu H-0(c2)(0) for the FeSe single crystals is found to be almost similar to that of T-c(P), suggesting that the pressure-induced magnetic order adversely affects the upper critical fields as well as the SC transition temperature.
Room-temperature ferromagnetism in carbon- and nitrogen-doped rutile TiO2
(2015-02-01)
Wang, Jia-Bin
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Wu, Kuei-Ching
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Mi, Jyun-Wei
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Luo, Chih-Wei
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Wu, Kaung-Hsiung
Marked room-temperature ferromagnetism (RTFM) was obtained in carbon- and nitrogen-doped rutile powders. X-ray photoelectron spectroscopy measurements revealed the co-existence of considerable densities of states near the Fermi level () and oxygen vacancies primarily induced by C- and N-doping. Density functional theory calculations showed that the local moments responsible for the observed RTFM in N-doped were primarily attributed to the partially populated, spin-polarized Ti band. In addition to the unfilled Ti band, the spin splitting in C states near in C-doped , which may be induced by the interaction between the C impurities and neighboring oxygen ions, results in Stoner band-splitting-type ferromagnetism.
Single crystal growth and characterization of tetragonal FeSe1-x superconductors
(2013)
Chareev, Dmitriy
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Osadchii, Evgeniy
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Kuzmicheva, Tatiana
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Lin, Jiunn-Yuan
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Kuzmichev, Svetoslav
The plate-like single crystals of tetragonal (P4/nmm) FeSe1-x superconductors were grown using the KCl-AlCl3 flux technique which produced single crystalline tetragonal samples of about 4 x 4 x 0.1 mm(3) dimensions. The energy dispersive X-ray spectroscopy established a ratio of Fe : Se = 1 : 0.96 +/- 0.02. The resistivity and magnetization measurements revealed a sharp superconducting transition at T-c = 9.4 K. Multiple Andreev reflections spectroscopy pointed to the existence of two-gap superconductivity with the gap values Delta(L) = 2.4 +/- 0.2 meV and Delta(S) = 0.75 +/- 0.1 meV at 4.2 K.