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Y. Zhou

Publications and source records attributed to Y. Zhou.

At least 109 records · Page 6Linked to original sources
arXiv2017

Creation,transport and detection of imprinted magnetic solitons stabilized by spin-polarized current

With the recent proposition of skyrmion utilization in racetrack memories at room temperature, skyrmionics has become a very attractive field. However, for the stability of skyrmions, it is essential to incorporate the Dzyaloshinskii-Moriya interaction (DMI) and the out-of-plane magnetic field into the system. In this work, we explore a system without these interactions. First, we propose a controlled way for the creation of magnetic skyrmions and skyrmioniums imprinted on a ferromagnetic nanotrack via a nanopatterned nanodisk with the magnetic vortex state. Then we investigate the detachment of the imprinted spin textures from the underneath of the nanodisk, as well as its transport by the spin-transfer torque imposed by spin-polarized current pulses applied in the nanotrack. A prominent feature of the moving imprinted spin texture is that its topological number Q is oscillating around the averaged value of Q=0 as if it is a resonant state between the skyrmions with Q= +/- 1 and the bubble with Q=0. We may call it a resonant magnetic soliton (RMS). A RMS moves along a straight line since it is free from the skyrmion Hall effect. In our studied device, the same electrodes are employed to realize the imprinted spin texture detachment and its transport. In addition, we have investigated the interaction between the RMS and a magnetic tunnel junction sensor, where the passing of the RMS in the nanotrack can be well detected. Our results would be useful for the development of novel spintronic devices based on moveable spin textures.

cond-mat.mes-hall↗
arXiv2016

Detection of HIV-1 antigen based on magnetic tunnel junction sensor and magnetic nanoparticles

In recent years, it is evidenced that the individuals newly infected HIV are transmitting the virus prior to knowing their HIV status. Identifying individuals that are early in infection with HIV antibody negative (window period) remains problematic. In the newly infected individuals, HIV antigen p24 is usually present in their serum or plasma 7-10 days before the HIV antibody. After antibody production initiates, the p24 antigen is bound into immune complexes. That means the detectable p24 antigens in serum/plasma are short-lived, and their amount is in the pg/ml range. Thus, a rapid quantitative bio-detection system with high-sensitivity is required to achieve early disease diagnosis. Magnetoresistive (MR) biosensor with ultra-high sensitivity possesses great potential in this area. In this study, a p24 detection assay using MgO-based magnetic tunnel junction (MTJ) sensor and 20-nm magnetic nanoparticles is reported.

cond-mat.mes-hall↗
arXiv2016

In-situ Instrumental Setup for Influence Study of Hard-axis Bias Magnetic Field on MR transfer curves of sing MTJ sensor and MTJs array sensor

Establishment of home-made measurement setups for the characterization of MR sensor is proposed and described here. The MR loops of MR sensors can be obtained with the instrument using two-point probe measurement and four-point probe measurement. Two pairs of Helmholtz coils can supply a hard-axis magnetic field and a soft-axis magnetic field for the sensor. The single MTJ sensor and MTJs array sensor in Wheatstone bridge were characterized and compared here. The influence of hard-bias magnetic field on MR transfer curves of sing MTJ sensor and MTJs array sensor are investigated. The corresponding optimal hard-axis magnetic fields were obtained through Helmholtz coils to eliminate the hysteresis for linear response of single MTJ sensor and MTJs array sensor.

cond-mat.mes-hall↗
arXiv2016

Near-infrared luminescent phosphors enabled by topotactic reduction of bismuth-activated red-emitting crystals

Bismuth-doped luminescent materials have gained significant attention in the past years owing to their huge potential for the applications in telecommunications, biomedicine, and displays. However, the controlled synthesis of these materials, in particular for those luminescing in the near-infrared (NIR), remains a challenging subject of continuous research effort. Herein, we show that the low-temperature topotactic reduction by using Al metal powders as oxygen getters can be adopted as a powerful technique for the conversion of bismuth-doped red-emitting systems into NIR-emitting cousins as a result of the creation of unique crystalline networks. Thorough experimental characterization indicates that the framework oxygen of hosts can be topotactically extracted, thus producing unique metal-oxygen-metal networks in the reduced phases while preserving the crystalline structure of the precursor. We anticipate that this low-temperature topotactic reduction strategy can be applied to the development of more novel Bi-doped luminescent materials in various forms that can find a broad range of functional applications.

cond-mat.mtrl-sci↗
arXiv2016

Merging droplets in double nano-contact spin torque oscillators

We demonstrate how magnetic droplet soliton pairs, nucleated by two separated nano-contact (NC) spin torque oscillators, can merge into a single droplet soliton. A detailed description of the magnetization dynamics of this merger process is obtained by micromagnetic simulations: A droplet pair with a steady-state in-phase spin precession is generated through the spin-transfer torque effect underneath two separate NCs, followed by a gradual expansion of the droplets volume and the out phase of magnetization on the inner side of the two droplets, resulting in the droplets merging into a larger droplet. This merger occurs only when the NC separation is smaller than a critical value. A transient breathing mode is observed before the merged droplet stabilizes into a steady precession state. The precession frequency of the merged droplet is lower than that of the droplet pair, consistent with its larger size. Merged droplets can again break up into droplet pairs at high enough magnetic field with a strong hysteretic response.

cond-mat.mes-hall↗
arXiv2015

Design and construction of a multi-layer CsI(Tl) telescope for high-energy reaction studies

A prototype of a new CsI(Tl) telescope, which will be used in the reaction studies of light isotopes with energy of several hundred AMeV, has been constructed and tested at the Institute of Modern Physics, Chinese Academy of Sciences. The telescope has a multi-layer structure and the range information will be obtained to improve the particle identification performance. This prototype has seven layers of different thickness. A 5.0% (FWHM) energy resolution has been extracted for one of the layers in a beam test experiment. Obvious improvement for the identification of $^{14}$O and $^{15}$O isotopes was achieved by using the range information.

physics.ins-det↗
arXiv2015

Cosmic Ray Test of Mini-drift Thick Gas Electron Multiplier Chamber for Transition Radiation Detector

A thick gas electron multiplier (THGEM) chamber with an effective readout area of 10$\times$10 cm$^{2}$ and a 11.3 mm ionization gap has been tested along with two regular gas electron multiplier (GEM) chambers in a cosmic ray test system. The thick ionization gap makes the THGEM chamber a mini-drift chamber. This kind mini-drift THGEM chamber is proposed as part of a transition radiation detector (TRD) for identifying electrons at an Electron Ion Collider (EIC) experiment. Through this cosmic ray test, an efficiency larger than 94$\%$ and a spatial resolution $\sim$220 $μ$m are achieved for the THGEM chamber at -3.65 kV. Thanks to its outstanding spatial resolution and thick ionization gap, the THGEM chamber shows excellent track reconstruction capability. The gain uniformity and stability of the THGEM chamber are also presented.

physics.ins-det↗
arXiv2014

Dynamical magnetic skyrmions

Spin transfer torque (STT) affords magnetic nanodevices the potential to act as memory, computing, and microwave elements operating at ultra-low currents and at a low energy cost. Spin transfer torque is not only effective in manipulating well-known magnetic structures, such as domain walls and vortices, but can also nucleate previously unattainable nano-magnetic objects, such as magnetic droplets and skyrmions. While the droplet and the skyrmion are both solitons, the former is inherently dynamic and non-topological, whereas the latter is static but topologically protected. Here we show that it is possible to combine these properties into a novel topologically protected dynamical skyrmion, which adds additional degrees of freedom, and functionality, to both droplet and skyrmion based applications. Unlike static skyrmions, the dynamical skyrmion can be nucleated and sustained without Dzyaloshinskii-Moriya interaction (DMI) or dipole-dipole interaction (DDI), and is a generic soliton solution independent of STT and damping once nucleated. In the presence of large DMI, the dynamical skyrmion experiences strong breathing with particular promise for skyrmion-based memory and microwave applications.

cond-mat.mes-hall↗
arXiv2013

Majorana fermions in $T$-shaped semiconductor nanostructures

We investigate the Majorana fermions in a $T$-shaped semiconductor nanostructure with the Rashba spin-orbit coupling and a magnetic field in the proximity of an s-wave superconductor. It is found that the properties of the low-energy modes (including the Majorana and near-zero-energy modes) at the ends of this system are similar to those in the Majorana nanowire. However, very distinct from the nanowire, one Majorana mode emerges at the intersection of the $T$-shaped structure when the number of the low-energy modes at each end $N$ is odd, whereas neither Majorana nor near-zero-energy mode appears at the intersection for even $N$. We also discover that the intersection Majorana mode plays an important role in the transport through the above $T$-shaped nanostructure with each end connected with a normal lead. Due to the presence of the intersection mode, the deviation of the zero-bias conductance from the ideal value in the long-arm limit $Ne^2/h$ is more pronounced in the regime of odd $N$ compared to the one of even $N$. Furthermore, when the magnetic field increases from the regime of odd $N$ to the one of even $N+1$, the deviation from the ideal value tends to decrease. This behavior is also very distinct from that in a nanowire, where the deviation always tends to increase with the increase of magnetic field.

cond-mat.mes-hall↗
arXiv2013

Comment on "Magnetotransport through graphene spin valves" and its following works

We show that the key formula in the works [Ding, Zhu, and Berakdar, Phys. Rev. B {\bf 79}, 045405 (2009); {\bf 84}, 115433 (2011); Ding, Zhu, Zhang, and Berakdar, Phys. Rev. B {\bf 82}, 155143 (2010)] is invalid in the extended graphene system they investigated. The correct formalism in the extended infinite system is also presented in this comment.

cond-mat.mes-hall↗
arXiv2013

Anomalous D'yakonov-Perel' spin relaxation in semiconductor quantum wells under strong magnetic field in Voigt configuration

We report an anomalous scaling of the D'yakonov-Perel' spin relaxation with the momentum relaxation in semiconductor quantum wells under a strong magnetic field in the Voigt configuration. We focus on the case that the external magnetic field is perpendicular to the spin-orbit-coupling--induced effective magnetic field and its magnitude is much larger than the later one. It is found that the longitudinal spin relaxation time is proportional to the momentum relaxation time even in the strong scattering limit, indicating that the D'yakonov-Perel' spin relaxation shows the Elliott-Yafet-like behaviour. Moreover, the transverse spin relaxation time is inversely proportional (proportional) to the momentum relaxation time in the weak (strong) scattering limit, both in the opposite trends against the well-established conventional D'yakonov-Perel' spin relaxation behaviours. We further demonstrate that all the above anomalous scaling relations come from the unique form of the effective inhomogeneous broadening.

cond-mat.mes-hall↗
arXiv2013

Superconducting Resonance and paring symmetry in electron-doped cuprates

The magnetic excitations in the superconducting electron-doped cuprates are studied in the framework of spin-density-wave description. The superconducting resonance is a natural product of the superconductivity due to the opening of d-wave gap. Its resonance energy exhibits well linear scaling with superconducting gap as $E_{res}/2Δ\sim 0.6$, quantitatively consisting with the experimental discovery. This ratio is insensitive to the selected parameters, manifesting its universality. Another lower-energy peak below resonance energy is predicted when the hole pocket emerges due to suppression of spin-density wave. We further verify that the ratio of linear scales is intimately related to the pairing symmetry. Distinct ratio can be found with respective pairing symmetry. In comparison with the inelastic neutron scattering data, the monotonic d-wave superconductivity is the most likely candidate in the electron-doped cuprates. Furthermore, we proposed a new method to check the pairing symmetry by the inelastic neutron scattering measurements.

cond-mat.supr-con↗
arXiv2013

Origin of the pseudogap and its influence on superconducting state

When holes move in the background of strong antiferromagnetic correlation, two effects with different spatial scale emerge, leading to a much reduced hopping integral with an additional phase factor. An effective Hamiltonian is then proposed to investigate the underdoped cuprates. We argue that the pseudogap is the consequence of dressed hole moving in the antiferromagnetic background and has nothing to do with the superconductivity. The momentum distributions of the gap are qualitatively consistent with the recent ARPES measurements both in the pseudogap and superconducting state. Two thermal qualities are further calculated to justify our model. A two-gap scenario is concluded to describe the relation between the two gaps.

cond-mat.str-el↗
arXiv2012

The commensurate magnetic excitations induced by band-splitting and Fermi surface topology in n-type Cuprates

The antiferromagnetic correlation plays an important role in high-T$_{c}$ superconductors. Considering this effect, the magnetic excitations in n-type cuprates near the optimal doping are studied within the spin density wave description. The magnetic excitations are commensurate in the low energy regime and further develop into spin wave-like dispersion at higher energy, well consistent with the inelastic neutron scattering measurements. We clearly demonstrate that the commensurability originates from the band splitting and Fermi surface topology. The commensurability is a normal state property, and has nothing to do with d-wave superconductivity. The distinct behaviors of magnetic excitation between the n-type and p-type cuprates are further discussed. Our results strongly suggest the essential role of antiferromagnetic correlations in the cuprates.

cond-mat.str-el↗
arXiv2012

Phase Diagram of Ferroelastic Systems in the Presence of Disorder: Analytical Model and Experimental Verification

There is little consensus on the nature of the glass state and its relationship to other strain states in ferroelastic materials which show the shape memory effect and superelasticity. We provide a thermodynamic interpretation of the known strain states, including precursory tweed and strain glass, by mapping the problem onto a spin model and analytically obtaining the phase diagram using real-space renormalization group methods. We further predict a spontaneous transition from the glass state to the ordered martensite phase. We verify this prediction by mapping out the experimental phase diagram for the ternary ferroelastic alloy Ti$_{50}$(Pd$_{50-x}$Cr$_x$) and demonstrate the emergence of the spontaneous transition. Our work thus provides a consistent framework to understand the various experimental and theoretical studies on the glassy behavior associated with ferroelastic materials.

cond-mat.mtrl-sci↗
arXiv2012

Some comments on the note "Comment on 'Single-parameter quantum charge and spin pumping in armchair graphene nanoribbons' by Zhu and Berakdar (arXiv:1207.3457)"

In response to the comment by Zhu and Berakdar (arXiv:1207.3457) that the physical system considered by them in their previous work [Ding et al., PRB 84, 115433 (2011)] is conceptually different from ours in the appendix of our latest paper [Zhou and Wu, arXiv:1206.3435], we show why they are relevant and further point out conceptually the problems in their work. We also point out that the main supporting arguments in their comment are incorrect.

cond-mat.mes-hall↗