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Dive into the research topics where Junying Shen is active.

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Featured researches published by Junying Shen.


Nano Letters | 2016

Achieving Ultrahigh Carrier Mobility in Two-Dimensional Hole Gas of Black Phosphorus

Gen Long; Denis Maryenko; Junying Shen; Shuigang Xu; Jianqiang Hou; Zefei Wu; Wing Ki Wong; Tianyi Han; Jiangxiazi Lin; Yuan Cai; Rolf Walter Lortz; Ning Wang

We demonstrate that a field effect transistor (FET) made of few layer black phosphorus (BP) encapsulated in hexagonal boron nitride (h-BN) in vacuum, exhibts the room temperature hole mobility of 5200 cm 2 /Vs being limited just by the phonon scattering. At cryogenic tempeature the FET mobility increases up to 45,000 cm 2 /Vs, which is eight times higher compared with the mobility obtained in earlier reports. The unprecedentedly clean h-BN/BP/h-BN heterostructure exhibits Shubnikov-de Haas oscillations and quantum Hall effect with Landau level (LL) filling factors down to v=2 in conventional laboratory magnetic fields. Moreover, carrier density independent effective mass m=0.26 m0 is


arXiv: Materials Science | 2016

Universal low-temperature Ohmic contacts for quantum transport in transition metal dichalcogenides

Shiuigang Xu; Zefei Wu; Huanhuan Lu; Yu Han; Gen Long; Xiaolong Chen; Tianyi Han; Weiguang Ye; Yingying Wu; Jiangxiazi Lin; Junying Shen; Yuan Cai; Yuheng He; Fan Zhang; Rolf Walter Lortz; Chun Cheng; Ning Wang

Low carrier mobility and high electrical contact resistance are two major obstacles prohibiting explorations of quantum transport in TMDCs. Here, we demonstrate an effective method to establish low-temperature Ohmic contacts in boron nitride encapsulated TMDC devices based on selective etching and conventional electron-beam evaporation of metal electrodes. This method works for most extensively studied TMDCs in recent years, including MoS2, MoSe2, WSe2, WS2, and 2H-MoTe2. Low electrical contact resistance is achieved at 2 K. All of the few-layer TMDC devices studied show excellent performance with remarkably improved field-effect mobilities ranging from 2300 cm2/V s to 16000 cm2/V s, as verified by the high carrier mobilities extracted from Hall effect measurements. Moreover, both high-mobility n-type and p-type TMDC channels can be realized by simply using appropriate contact metals. Prominent Shubnikov-de Haas oscillations have been observed and investigated in these high-quality TMDC devices.


Physical Review B | 2015

Detection of interlayer interaction in few-layer graphene

Zefei Wu; Yu Han; Jiangxiazi Lin; Wei Zhu; Mingquan He; Shuigang Xu; Xiaolong Chen; Huanhuan Lu; Weiguang Ye; Tianyi Han; Yingying Wu; Gen Long; Junying Shen; Rui Huang; Lin Wang; Yuheng He; Yuan Cai; Rolf Walter Lortz; Dang Sheng Su; Ning Wang

Research Grants Council of Hong Kong [604112, N_HKUST613/12, 16302215, HKUST9/CRF/08, CRF_HKU9/CRF/13G]; Raith-HKUST Nanotechnology Laboratory electron-beam lithography facility [SEG HKUST08]


RSC Advances | 2015

Role of multivalent Cu, oxygen vacancies and CuO nanophase in the ferromagnetic properties of ZnO: Cu thin films

Muhammad Younas; Junying Shen; Mingquan He; Rolf Walter Lortz; Fahad Azad; Muhammad Javed Akhtar; Asghari Maqsood; Francis Chi-Chung Ling

Comprehensive microstructural, electronic and magnetic analyses have been carried out on ZnO:Cu thin films grown by pulsed laser deposition on c-plane sapphire under different oxygen partial pressures. Detailed X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM) analyses reveal that increase in oxygen growth pressure degrades the epitaxy of ZnO:Cu thin films due to inclusion of nanosize CuO in the ZnO host lattice. HRTEM and magnetization studies suggest that thin film quality plays a less effective role in governing the magnetic properties of these samples. Instead, room temperature ferromagnetism (FM) of these ZnO:Cu thin film samples are highly tunable by the simultaneous presence of CuO nanophases and multivalent Cu and concentrations, which are in strong contest with each other. For low oxygen partial pressure grown sample, the effective network is the main contributor to the observed FM and is in competition with CuO nanophases only when there is a relatively low concentration with a dominant Cu2+ oxidation state. For vacuum grown samples containing high concentration and Cu1+ as dominant oxidation state, the network becomes less effective and a CuO nanophase (4–5 nm) is the dominent FM supplier. The extrinsic FM in the vacuum grown sample, which is the best epitaxial quality sample, is further confirmed by the zero field cooled (ZFC) and field cooled (FC) magnetization protocols.


Scientific Reports | 2016

Dramatic enhancement of superconductivity in single-crystalline nanowire arrays of Sn.

Ying Zhang; Chi Ho Wong; Junying Shen; Sin Ting Sze; Bing Zhang; Haijing Zhang; Yan Dong; Hui Xu; Zifeng Yan; Yingying Li; Xijun Hu; Rolf Walter Lortz

Sn is a classical superconductor on the border between type I and type II with critical temperature of 3.7 K. We show that its critical parameters can be dramatically increased if it is brought in the form of loosely bound bundles of thin nanowires. The specific heat displays a pronounced double phase transition at 3.7 K and 5.5 K, which we attribute to the inner ‘bulk’ contribution of the nanowires and to the surface contribution, respectively. The latter is visible only because of the large volume fraction of the surface layer in relation to the bulk volume. The upper transition coincides with the onset of the resistive transition, while zero resistance is gradually approached below the lower transition. In contrast to the low critical field Hc = 0.03 T of Sn in its bulk form, a magnetic field of more than 3 T is required to fully restore the normal state.


Physical Review Letters | 2017

Odd-Integer Quantum Hall States and Giant Spin Susceptibility in p -Type Few-Layer WSe2

Shuigang Xu; Junying Shen; Gen Long; Zefei Wu; Zhiqiang Bao; Cheng-Cheng Liu; Xiao Xiao; Tianyi Han; Jiangxiazi Lin; Yingying Wu; Huanhuan Lu; Jianqiang Hou; Liheng An; Yuanwei Wang; Yuan Cai; Kin Ming Ho; Yuheng He; Rolf Walter Lortz; Fan Zhang; Ning Wang

We fabricate high-mobility p-type few-layer WSe_{2} field-effect transistors and surprisingly observe a series of quantum Hall (QH) states following an unconventional sequence predominated by odd-integer states under a moderate strength magnetic field. By tilting the magnetic field, we discover Landau level crossing effects at ultralow coincident angles, revealing that the Zeeman energy is about 3 times as large as the cyclotron energy near the valence band top at the Γ valley. This result implies the significant roles played by the exchange interactions in p-type few-layer WSe_{2}, in which itinerant or QH ferromagnetism likely occurs. Evidently, the Γ valley of few-layer WSe_{2} offers a unique platform with unusually heavy hole carriers and a substantially enhanced g factor for exploring strongly correlated phenomena.


ACS Nano | 2017

Isolation and Characterization of Few-Layer Manganese Thiophosphite

Gen Long; Ting Zhang; Xiangbin Cai; Jin Hu; Chang-woo Cho; Shuigang Xu; Junying Shen; Zefei Wu; Tianyi Han; Jiangxiazi Lin; Jingwei Wang; Yuan Cai; Rolf Walter Lortz; Zhiqiang Mao; Ning Wang

This work reports an experimental study on an antiferromagnetic honeycomb lattice of MnPS3 that couples the valley degree of freedom to a macroscopic antiferromagnetic order. The crystal structure of MnPS3 is identified by high-resolution scanning transmission electron microscopy. Layer-dependent angle-resolved polarized Raman fingerprints of the MnPS3 crystal are obtained, and the Raman peak at 383 cm-1 exhibits 100% polarity. Temperature dependences of anisotropic magnetic susceptibility of the MnPS3 crystal are measured in a superconducting quantum interference device. Anisotropic behaviors of the magnetic moment are explored on the basis of the mean field approximation model. Ambipolar electronic conducting channels in MnPS3 are realized by the liquid gating technique. The conducting channel of MnPS3 offers a platform for exploring the spin/valleytronics and magnetic orders in 2D limitation.


arXiv: Mesoscale and Nanoscale Physics | 2016

Type-controlled Nanodevices Based on Encapsulated Few-layer Black Phosphorus for Quantum Transport

Gen Long; Shuigang Xu; Junying Shen; Jianqiang Hou; Zefei Wu; Tianyi Han; Jiangxiazi Lin; Wing Ki Wong; Yuan Cai; Rolf Walter Lortz; Ning Wang

We demonstrate that encapsulation of atomically thin black phosphorus (BP) by hexagonal boron nitride (h-BN) sheets is very effective for minimizing the interface impurities induced during fabrication of BP channel material for quantum transport nanodevices. Highly stable BP nanodevices with ultrahigh mobility and controllable types are realized through depositing appropriate metal electrodes after conducting a selective etching to the BP encapsulation structure. Chromium and titanium are suitable metal electrodes for BP channels to control the transition from a p-type unipolar property to ambipolar characteristic because of different work functions. Record-high mobilities of 6000 cm2 V−1 s−1 and 8400 cm2 V−1 s−1 are respectively obtained for electrons and holes at cryogenic temperatures. High-mobility BP devices enable the investigation of quantum oscillations with an indistinguishable Zeeman effect in laboratory magnetic field.


Scientific Reports | 2016

Pseudogap and proximity effect in the Bi 2 Te 3 /Fe 1+y Te interfacial superconductor

Mingquan He; Junying Shen; Alexander Petrovic; Qinglin He; Hongchao Liu; Yuan Zheng; Chi Ho Wong; Qihong Chen; Jiannong Wang; Kam Tuen Law; Iam Keong Sou; Rolf Walter Lortz

In the interfacial superconductor Bi2Te3/Fe1+yTe, two dimensional superconductivity occurs in direct vicinity to the surface state of a topological insulator. If this state were to become involved in superconductivity, under certain conditions a topological superconducting state could be formed, which is of high interest due to the possibility of creating Majorana fermionic states. We report directional point-contact spectroscopy data on the novel Bi2Te3/Fe1+yTe interfacial superconductor for a Bi2Te3 thickness of 9 quintuple layers, bonded by van der Waals epitaxy to a Fe1+yTe film at an atomically sharp interface. Our data show highly unconventional superconductivity, which appears as complex as in the cuprate high temperature superconductors. A very large superconducting twin-gap structure is replaced by a pseudogap above ~12 K which persists up to 40 K. While the larger gap shows unconventional order parameter symmetry and is attributed to a thin FeTe layer in proximity to the interface, the smaller gap is associated with superconductivity induced via the proximity effect in the topological insulator Bi2Te3.


Journal of Physics: Condensed Matter | 2015

Anisotropic magnetic responses of a 2D-superconducting Bi2Te3/FeTe heterostructure.

Qinglin He; Mingquan He; Junying Shen; Ying Hoi Lai; Yi Liu; Hongchao Liu; Hongtao He; Gan Wang; Jiannong Wang; Rolf Walter Lortz; Iam Keong Sou

We have investigated the anisotropic magnetic responses of a 2D-superconducting Bi2Te3/FeTe heterostructure. Cross-sectional STEM imaging revealed that the excess Fe atoms in the FeTe layer occupy specific interstitial sites. They were found to show strong anisotropic magnetic responses under a magnetic field either perpendicular or parallel to the sample surface. Under perpendicular magnetic fields within 1000 Oe, conventional paramagnetic Meissner effect, superconducting diamagnetism, and anomalous enhancement of magnetization successively occur as the magnetic field increases. In contrast, under parallel magnetic fields, superconducting diamagnetism was not observed explicitly in the magnetization measurements and the anomalous enhancement of magnetization appears only for fields higher than 1000 Oe. The observed strong magnetic anisotropy provides further evidence that the induced superconductivity at the interface of the Bi2Te3/FeTe heterostucture has a 2D nature.

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Rolf Walter Lortz

Hong Kong University of Science and Technology

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Jiangxiazi Lin

Hong Kong University of Science and Technology

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Tianyi Han

Hong Kong University of Science and Technology

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Ning Wang

Chinese Academy of Sciences

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Gen Long

Hong Kong University of Science and Technology

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Zefei Wu

Hong Kong University of Science and Technology

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Shuigang Xu

Hong Kong University of Science and Technology

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Yuan Cai

Hong Kong University of Science and Technology

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Qinglin He

University of California

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Chang-woo Cho

Hong Kong University of Science and Technology

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