Haochi Yu
Fudan University
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Publication
Featured researches published by Haochi Yu.
Npg Asia Materials | 2016
Xiang Yuan; Cheng Zhang; Yanwen Liu; Awadhesh Narayan; Chaoyu Song; Shoudong Shen; Xing Sui; Jie Xu; Haochi Yu; Zhenghua An; Jun Zhao; Stefano Sanvito; Hugen Yan; Faxian Xiu
Since the discovery of graphene, layered materials have attracted extensive interests owing to their unique electronic and optical characteristics. Among them, Dirac semimetal, one of the most appealing categories, has been a long-sought objective in layered systems beyond graphene. Recently, layered pentatelluride ZrTe5 was found to host signatures of Dirac semimetal. However, the low Fermi level in ZrTe5 strongly hinders a comprehensive understanding of the whole picture of electronic states through photoemission measurements, especially in the conduction band. Here, we report the observation of Dirac fermions in ZrTe5 through magneto-optics and magneto-transport. By applying magnetic field, we observe a square-root-B dependence of inter-Landau-level resonance and Shubnikov-de Haas (SdH) oscillations with non-trivial Berry phase, both of which are hallmarks of Dirac fermions. The angular-dependent SdH oscillations show a clear quasi-two-dimensional feature with highly anisotropic Fermi surface and band topology, in stark contrast to the 3D Dirac semimetal such as Cd3As2. This is further confirmed by the angle-dependent Berry phase measurements and the observation of bulk quantum Hall plateaus. The unique band dispersion is theoretically understood: the system is at the critical point between a 3D Dirac semimetal and a topological insulator phase. With the confined interlayer dispersion and reducible dimensionality, our work establishes ZrTe5 as an ideal platform for exploring exotic physical phenomena of Dirac fermions.
Optics Express | 2016
Jie Xu; Ziyi Zhao; Haochi Yu; Le Yang; Peng Gou; Jun Cao; Yuexin Zou; Jie Qian; Tianjun Shi; Qijun Ren; Zhenghua An
A triple-band perfect plasmonic metamaterial absorber based on a metal/insulator/metal (MIM) structure is designed. A new freedom through tuning the thicknesses of each ring structures is introduced to realize a quasi-three-dimensional perfect absorber at three extinction wavelengths by using the finite difference time domain method. The physical machine is explained by the time domain field analyses and the coupled mode theory. The characteristics of the absorber make our proposed strategy applicable for the design of more general multiband and broadband perfect absorbers. In addition, these perfect absorbing metamaterials are found to exhibit excellent performance in refractive index sensing.
Nano Letters | 2017
Zhiqiang Mu; Haochi Yu; Miao Zhang; Aimin Wu; Gongmin Qi; Paul K. Chu; Zhenghua An; Zengfeng Di; Xi Wang
Besides the well-known quantum confinement effect, hot luminescence from indirect bandgap Si provides a new and promising approach to realize monolithically integrated silicon optoelectronics due to phonon-assisted light emission. In this work, multiband hot photoluminescence is generated from Si nanowire arrays by introducing trapezoid-shaped nanocavities that support hybrid photonic-plasmonic modes. By continuously adjusting the geometric parameters of the Si nanowires with trapezoidal nanocavities, the multiband hot photoluminescence can be tuned in the range from visible to near-infrared independent of the excitation laser wavelength. The highly tunable wavelength bands and concomitant compatibility with Si-integrated electronics enable tailoring of silicon-based light sources suitable for next-generation optoelectronics devices.
Applied Physics Letters | 2009
A. Q. Jiang; Haochi Yu; T. A. Tang
Fast imprint measurements of coercive voltages from domain switching current after various dc biasing voltages at low temperatures evidence multilevel interfacial charge injections in Pt/IrO2/Pb(Zr0.4Ti0.6)O3/IrO2/Pt thin-film capacitors with suppressed thermal noises. Initially, a quick charge injection occurs during domain switching with injection current equal to domain switching current. After completion of polarization reversal, a slow charge injection continues with ultimate injected charge density nearly independent of biasing voltages at 77.6 K. This is very different from normal observations of a semilogarithmic time dependence of the coercive voltage at room temperature above 1 μs.
Integrated Ferroelectrics | 2012
A. Q. Jiang; M. C. Chen; Haochi Yu; T. A. Tang
Nonvolatile memories on the basis of tunneling junctions of ferroelectric ultrathin-film barriers make use of resistance switching between high and low conductance states upon polarization reversal, which facilitates the nondestructive readout of the binary information within a tiny memory cell. The apparent electroresistance effect for the generation of a large on/off current ratio depends on the modulation of the tunneling barrier height in two opposite polarization orientations due to asymmetric finite screening lengths of top and bottom electrodes, where the direct tunneling current attenuates quickly with enhanced film thickness. To break through the atomistic thickness requirement of the tunneling junction, we separately observed the same electroresistance effect in a semiconducting BiFeO3 film with the thickness of 120 nm. Its working mechanism depends on the formation of a ferroelectric diode for the film in contacts with top and bottom electrodes, where the polarity of diode junction can be switched by polarization reversal.
Applied Physics Letters | 2016
Jie Xu; Le Yang; Haochi Yu; Qianchun Weng; Pingping Chen; Bo Zhang; Ting-Ting Kang; Susumu Komiyama; Wei Lu; Zhenghua An
Charge-sensitive infrared phototransistors (CSIPs) with a built-in field-effect-induced amplification mechanism have much higher infrared photoresponsivity ( ≥103 A/W) than conventional detectors, which is often restricted by background black-body radiation induced saturation. Here, we report that dynamically controlling the electrostatic potential of the photosensitive floating gate of a CSIP can counterbalance this background-induced saturation effect. As a result, the CSIP photoresponsivity can be improved by about one order of magnitude, reaching as high as ∼1.2×104 A/W to external blinking light. Our work suggests that time-domain manipulation could be an agile degree of freedom in optimizing the CSIP performance and provide insight into operating more general phototransistors for a wide variety of optoelectronic applications.
Scientific Reports | 2017
Peng Gou; Jie Qian; Fuchun Xi; Yuexin Zou; Jun Cao; Haochi Yu; Ziyi Zhao; Le Yang; Jie Xu; Hengliang Wang; Lijian Zhang; Zhenghua An
The applications of spin dynamos, which could potentially power complex nanoscopic devices, have so far been limited owing to their extremely low energy conversion efficiencies. Here, we present a unique plasmonic diabolo cavity (PDC) that dramatically improves the spin rectification signal (enhancement of more than three orders of magnitude) under microwave excitation; further, it enables an energy conversion efficiency of up to ~0.69 mV/mW, compared with ~0.27 μV/mW without a PDC. This remarkable improvement arises from the simultaneous enhancement of the microwave electric field (~13-fold) and the magnetic field (~195-fold), which cooperate in the spin precession process generates photovoltage (PV) efficiently under ferromagnetic resonance (FMR) conditions. The interplay of the microwave electromagnetic resonance and the ferromagnetic resonance originates from a hybridized mode based on the plasmonic resonance of the diabolo structure and Fabry-Perot-like modes in the PDC. Our work sheds light on how more efficient spin dynamo devices for practical applications could be realized and paves the way for future studies utilizing both artificial and natural magnetism for applications in many disciplines, such as for the design of future efficient wireless energy conversion devices, high frequent resonant spintronic devices, and magnonic metamaterials.
Applied Physics Letters | 2017
Chuanling Men; Ri Qu; Jun Cao; Haochi Yu; Peng Gou; Yuexin Zou; Le Yang; Jie Qian; Ziyi Zhao; Jie Xu; Zhenghua An
We study the optical properties of a corrugated plasmonic cavity consisting of a perforated metal film and a flat metal sheet separated by a semiconductor spacer. Corrugation enhances dramatically the coupling between the propagating surface plasmon and the Fabry-Perot mode and induces Rabi-like splitting forming bright bonding and dark anti-bonding modes. The anti-bonding mode exhibits considerably higher volume-averaged field enhancement factors (∼16.5 for E-field and ∼14.1 for Ez-component) than its bonding counterpart as well as a very high polarization conversion ratio (∼85.5%) from transverse electric to transverse magnetic waves. These characteristics make the corrugation induced anti-bonding mode particularly suitable for semiconductor quantum well intersubband photodetectors. Our work may provide a general guideline to the design of metamaterial-coupled intersubband hybrid devices for practical applications.
Selected Proceedings of the Photoelectronic Technology Committee Conferences held June-July 2015 | 2015
Qianchun Weng; Le Yang; Jie Xu; Qingbai Qian; Haochi Yu; Bo Zhang; Zhenghua An; Ziqiang Zhu; Wei Lu
We present a novel scattering-type scanning near-field optical microscope (s-SNOM) operating in the terahertz (THz) wavelength. A home-made ultra-high sensitive detector named charge sensitive infrared phototransistor (CSIP, detection wavelength ~15 μm) is equipped for spontaneous thermal radiation detection (external illumination should be avoided). Thermal emission from room-temperature objects is collected by a cassegrain objective lens placed above the sample, and focused to a pinhole (d=250 μm) which is kept in liquid-helium (LHe) temperature(4.2 K). With the background radiation from environment efficiently blocked by the low-temperature pinhole, the detector is only sensitive to the THz radiation from a small spot (~λ) on sample surface (the confocal point). As a result, thermal radiation spontaneously emitted by object itself is measured with an excellent spatial resolution of ~14 μm (diffraction-limit). For overcoming the diffraction limit by detecting the near-field evanescent waves, this THz microscope is combined with a home-built atomic-force microscope (AFM). With sharp AFM tip (<100 nm) scattering the evanescent waves with an improved tip-modulation method, we successfully obtained thermal near-field images with a spatial resolution of ~100 nm, which is already less than 1% of the detection wavelength (15 μm). This THz s-SNOM should be a powerful tool for various material research down to the nanometer scale.
Integrated Ferroelectrics | 2011
A. Q. Jiang; Haochi Yu; T. A. Tang
We developed a ferroelectric assisted current-voltage characterization technique for continuous/semicontinuous high-k ultrathin films under the field as high as 17 MV/cm without invoking of dielectric breakdown. The leakage current of the ultrathin films equals domain switching current with breakdown paths blocked efficiently by underneath ferroelectric thick layer. The extracted field dependences of current density for a 1– 6 nm thick Al2O3 layer deposited on top of a 300 nm thick Pb(Zr,Ti)O3 layer obey the equation of Schottky mission. This technique is helpful for investigations of high-field charge emission and quantum physics for ultrathin films in loss of the atomic-layer flatness.