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Dive into the research topics where Zilong Jiang is active.

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Featured researches published by Zilong Jiang.


Nature Communications | 2016

Enhanced spin Seebeck effect signal due to spin-momentum locked topological surface states

Zilong Jiang; Cui-Zu Chang; Massoud Ramezani Masir; Chi Tang; Yadong Xu; Jagadeesh S. Moodera; A. H. MacDonald; Jing Shi

Spin-momentum locking in protected surface states enables efficient electrical detection of magnon decay at a magnetic-insulator/topological-insulator heterojunction. Here we demonstrate this property using the spin Seebeck effect (SSE), that is, measuring the transverse thermoelectric response to a temperature gradient across a thin film of yttrium iron garnet, an insulating ferrimagnet, and forming a heterojunction with (BixSb1−x)2Te3, a topological insulator. The non-equilibrium magnon population established at the interface can decay in part by interactions of magnons with electrons near the Fermi energy of the topological insulator. When this decay channel is made active by tuning (BixSb1−x)2Te3 into a bulk insulator, a large electromotive force emerges in the direction perpendicular to the in-plane magnetization of yttrium iron garnet. The enhanced, tunable SSE which occurs when the Fermi level lies in the bulk gap offers unique advantages over the usual SSE in metals and therefore opens up exciting possibilities in spintronics.


Nano Letters | 2015

Independent Tuning of Electronic Properties and Induced Ferromagnetism in Topological Insulators with Heterostructure Approach

Zilong Jiang; Cui-Zu Chang; Chi Tang; Peng Wei; Jagadeesh S. Moodera; Jing Shi

The quantum anomalous Hall effect (QAHE) has been recently demonstrated in Cr- and V-doped three-dimensional topological insulators (TIs) at temperatures below 100 mK. In those materials, the spins of unfilled d-electrons in the transition metal dopants are exchange coupled to develop a long-range ferromagnetic order, which is essential for realizing QAHE. However, the addition of random dopants does not only introduce excess charge carriers that require readjusting the Bi/Sb ratio, but also unavoidably introduces paramagnetic spins that can adversely affect the chiral edge transport in QAHE. In this work, we show a heterostructure approach to independently tune the electronic and magnetic properties of the topological surface states in (BixSb1-x)2Te3 without resorting to random doping of transition metal elements. In heterostructures consisting of a thin (BixSb1-x)2Te3 TI film and yttrium iron garnet (YIG), a high Curie temperature (∼550 K) magnetic insulator, we find that the TI surface in contact with YIG becomes ferromagnetic via proximity coupling which is revealed by the anomalous Hall effect (AHE). The Curie temperature of the magnetized TI surface ranges from 20 to 150 K but is uncorrelated with the Bi fraction x in (BixSb1-x)2Te3. In contrast, as x is varied, the AHE resistivity scales with the longitudinal resistivity. In this approach, we decouple the electronic properties from the induced ferromagnetism in TI. The independent optimization provides a pathway for realizing QAHE at higher temperatures, which is important for novel spintronic device applications.


Applied Physics Letters | 2016

Exquisite growth control and magnetic properties of yttrium iron garnet thin films

Chi Tang; Mohammed Aldosary; Zilong Jiang; Houchen Chang; Benjamin Madon; Kyle Chan; Mingzhong Wu; Javier E. Garay; Jing Shi

A layer-by-layer epitaxial growth up to 227 atomic layers of ferrimagnetic insulator yttrium iron garnet (YIG) thin films is achieved on (110)-oriented gadolinium gallium garnet substrates using pulsed laser deposition. Atomically smooth terraces are observed on YIG films up to 100 nm in thickness. The root-mean-square roughness is as low as 0.067 nm. The easy-axis lies in the film plane, indicating the dominance of shape anisotropy. For (110)-YIG films, there is well-defined two-fold in-plane anisotropy, with the easiest axis directed along [001]. The Gilbert damping constant is determined to be 1.0 × 10−4 for 100 nm thick films.


Science Advances | 2017

Above 400-K robust perpendicular ferromagnetic phase in a topological insulator

Chi Tang; Cui-Zu Chang; Gejian Zhao; Yawen Liu; Zilong Jiang; Chao-Xing Liu; Martha R. McCartney; David J. Smith; T. Y. Chen; Jagadeesh S. Moodera; Jing Shi

Topological surface states reveal proximity-induced ferromagnetism with perpendicular anisotropy persisting above 400 K. The quantum anomalous Hall effect (QAHE) that emerges under broken time-reversal symmetry in topological insulators (TIs) exhibits many fascinating physical properties for potential applications in nanoelectronics and spintronics. However, in transition metal–doped TIs, the only experimentally demonstrated QAHE system to date, the QAHE is lost at practically relevant temperatures. This constraint is imposed by the relatively low Curie temperature (Tc) and inherent spin disorder associated with the random magnetic dopants. We demonstrate drastically enhanced Tc by exchange coupling TIs to Tm3Fe5O12, a high-Tc magnetic insulator with perpendicular magnetic anisotropy. Signatures showing that the TI surface states acquire robust ferromagnetism are revealed by distinct squared anomalous Hall hysteresis loops at 400 K. Point-contact Andreev reflection spectroscopy confirms that the TI surface is spin-polarized. The greatly enhanced Tc, absence of spin disorder, and perpendicular anisotropy are all essential to the occurrence of the QAHE at high temperatures.


Applied Physics Letters | 2014

A comparative transport study of Bi2Se3 and Bi2Se3/yttrium iron garnet

Zilong Jiang; Ferhat Katmis; Chi Tang; Peng Wei; Jagadeesh S. Moodera; Jing Shi

Bilayers of 20 quintuple layer Bi2Se3 on 30 nm thick yttrium iron garnet (YIG) have been grown with molecular beam epitaxy in conjunction with pulsed laser deposition. The presence of the ferri-magnetic insulator YIG causes additional scattering to the surface states of the Bi2Se3 topological insulator layer, as indicated by the temperature dependence of the resistivity. From the two-channel analysis of the Hall data, we find that the surface contribution in the bilayer samples is greatly reduced. Furthermore, the weak antilocalization effect from the surface states is clearly suppressed due to the presence of the YIG layer.


AIP Advances | 2016

Structural and proximity-induced ferromagnetic properties of topological insulator-magnetic insulator heterostructures

Zilong Jiang; Cui-Zu Chang; Chi Tang; Jian-Guo Zheng; Jagadeesh S. Moodera; Jing Shi

The spontaneously broken time reversal symmetry can lead to the formation of an energy gap in the Dirac spectrum of the surface states of a topological insulator (TI) which can consequently give rise to a variety of interesting phenomena potentially useful for spintronics. In this work, we couple a non-magnetic TI to a high Curie temperature TC magnetic insulator to induce strong exchange interaction via the proximity effect. We have successfully grown 5 quintuple layer thick ternary TI (BixSb1-x)2Te3 films on atomically flat yttrium iron garnet (YIG) film with the combination of molecular beam epitaxy and pulsed laser deposition, in which the Fermi level position relative to the Dirac point is varied by controlling the Bi:Sb ratio. The anomalous Hall effect (AHE) and suppressed weak antilocalization (WAL) measured under out of plane magnetic fields reveal that the TI surface in contact with YIG is magnetized. Our high-quality (BixSb1-x)2Te3/Y IG heterostructure provides a tunable system for exploring the quantum anomalous Hall effect (QAHE) at higher temperatures in TI-based spintronic devices.


Applied Physics Letters | 2014

Heat-driven spin transport in a ferromagnetic metal

Yadong Xu; Bowen Yang; Chi Tang; Zilong Jiang; Michael Schneider; Renu Whig; Jing Shi

As a non-magnetic heavy metal is attached to a ferromagnet, a vertically flowing heat-driven spin current is converted to a transverse electric voltage, which is known as the longitudinal spin Seebeck effect (SSE). If the ferromagnet is a metal, this voltage is also accompanied by voltages from two other sources, i.e., the anomalous Nernst effect in both the ferromagnet and the proximity-induced ferromagnetic boundary layer. By properly identifying and carefully separating those different effects, we find that in this pure spin current circuit the additional spin current drawn by the heavy metal generates another significant voltage by the ferromagnetic metal itself which should be present in all relevant experiments.


APL Materials | 2018

Approaching quantum anomalous Hall effect in proximity-coupled YIG/graphene/h-BN sandwich structure

Chi Tang; Bin Cheng; Mohammed Aldosary; Zhiyong Wang; Zilong Jiang; Kenji Watanabe; T. Taniguchi; Marc Bockrath; Jing Shi

Quantum anomalous Hall state is expected to emerge in Dirac electron systems such as graphene under both sufficiently strong exchange and spin-orbit interactions. In pristine graphene, neither interaction exists; however, both interactions can be acquired by coupling graphene to a magnetic insulator as revealed by the anomalous Hall effect. Here, we show enhanced magnetic proximity coupling by sandwiching graphene between a ferrimagnetic insulator yttrium iron garnet (YIG) and hexagonal-boron nitride (h-BN) which also serves as a top gate dielectric. By sweeping the top-gate voltage, we observe Fermi level-dependent anomalous Hall conductance. As the Dirac point is approached from both electron and hole sides, the anomalous Hall conductance reaches ¼ of the quantum anomalous Hall conductance 2e2/h. The exchange coupling strength is determined to be as high as 27 meV from the transition temperature of the induced magnetic phase. YIG/graphene/h-BN is an excellent heterostructure for demonstrating proximity-...


Bulletin of the American Physical Society | 2015

Spin current draining effect on heat-driven spin transport

Yadong Xu; Bowen Yang; Chi Tang; Zilong Jiang; Jing Shi; Michael Schneider; Renu Whig


Bulletin of the American Physical Society | 2015

Nonlinear Hall effect in h-BN/graphene on ferri-magnetic substrates

Chi Tang; Bin Cheng; Zhiyong Wang; Zilong Jiang; Mohammed Aldosary; Yafis Barlas; Marc Bockrath; Jing Shi; T. Taniguchi; Kenji Watanabe

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Jing Shi

University of California

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Chi Tang

University of California

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Jagadeesh S. Moodera

Massachusetts Institute of Technology

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Cui-Zu Chang

Massachusetts Institute of Technology

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Peng Wei

Massachusetts Institute of Technology

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Yadong Xu

University of California

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Zhiyong Wang

University of California

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Bin Cheng

University of California

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Bowen Yang

University of California

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