Priority Research Program Research Articles

A high performance fast-Fourier-transform spectrum analyzer for measuring spin noise spectrums**Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDC0702200), the National Key R&D Program of China (Grant Nos. 2018YFA0306600 and 2016YFB0501603), the National Natural Science Foundation of China (Grant No. 11927811), the Chinese Academy of Sciences (Grants Nos. GJJSTD20170001 and QYZDY-SSW-SLH004), Anhui

A high performance fast-Fourier-transform (FFT) spectrum analyzer, which is developed for measure spin noise spectrums, is presented in this paper. The analyzer is implemented with a field-programmable-gate-arrays (FPGA) chip for data and command management. An analog-to-digital-convertor chip is integrated for analog signal acquisition. In order to meet the various requirements of measuring different types of spin noise spectrums, multiple operating modes are designed and realized using the reprogrammable FPGA logic resources. The FFT function is fully managed by the programmable resource inside the FPGA chip. A 1 GSa/s sampling rate and a 100 percent data coverage ratio with non-dead-time are obtained. 30534 FFT spectrums can be acquired per second, and the spectrums can be on-board accumulated and averaged. Digital filters, multi-stage reconfigurable data reconstruction modules, and frequency down conversion modules are also implemented in the FPGA to provide flexible real-time data processing capacity, thus the noise floor and signals aliasing can be suppressed effectively. An efficiency comparison between the FPGA-based FFT spectrum analyzer and the software-based FFT is demonstrated, and the high performance FFT spectrum analyzer has a significant advantage in obtaining high resolution spin noise spectrums with enhanced efficiency.

Weakly nonlinear multi-mode Bell–Plesset growth in cylindrical geometry**Project supported by the Fundamental Research Funds for the Central Universities, China (Grant No. 2019QS04), the National Natural Science Foundation of China (Grant No. 11574390), and the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDA 25051000).

Bell–Plesset (BP) effect caused perturbation growth plays an important role in better understanding of characteristics of the convergence effect. Governing equations for multi-mode perturbation growth on a cylindrically convergent interface are derived. The second-order weakly nonlinear (WN) solutions for two-mode perturbations at the interface which is subject to uniformly radical motion are obtained. Our WN theory is consistent with the numerical result in terms of mode-coupling effect in converging Richtmyer–Meshkov instability. Nonlinear mode-coupling effects will cause irregular deformation of the convergent interface. The mode-coupling behavior in convergent geometry depends on the mode number, Atwood number A and convergence ratio Cr. The A = –1.0 at the interface results in larger perturbation growth than A = 1.0. The growth of generated perturbation modes from two similar modes at the initial stage are smaller than that from two dissimilar modes.

Dynamics of the Entanglement Spectrum of the Haldane Model under a Sudden Quench**Supported by the National Natural Science Foundation of China (Grant No. 11674282) and the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB28000000).

One of the appealing features of topological systems is the presence of robust edge modes. Under a sudden quantum quench, the edge modes survive for a characteristic time that scales with the system size, during which the nontrivial topology continues to manifest in entanglement properties, even though the post-quench Hamiltonian belongs to a trivial phase. We exemplify this in the quench dynamics of a two-dimensional Haldane model with the help of one-particle entanglement spectrum and the probability density of its mid-states. We find that, beyond our knowledge in one-dimensional models, the momentum dependence of the transverse velocity plays a crucial role in the out-of-equilibrium evolution of the entanglement properties.

EarthDataMiner: A Cloud-Based Big Earth Data Intelligence Analysis Platform

Big Earth data mining analysis involves complex data processing, pattern extraction and knowledge discovery processes, and requires easy to use integrated software tools to deal with large-scale data. With the support of Big Earth Data Science Engineering Project (CASEarth) of the Chinese Academy of Sciences Strategic Priority Research Program, our team are ongoing developing EarthDataMiner, a cloud-based Big Earth data intelligence analysis platform for scientists in the field of Earth sciences, which brings together cross-domain common models, introduces advanced artificial intelligence algorithms, supports online satellite imagery visually interactive analysis,and achieves efficient task processing through a series of distributed execution systems.

Fermionic Analogue of High Temperature Hawking Radiation in Black Phosphorus**Supported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0300902 and 2016YFA0202300), the National Basic Research Program of China (Grant No. 2015CB921001), the National Natural Science Foundation of China (Grant Nos. 11774396, 91850120 and 11974045), and the Strategic Priority Research Program (B) of CAS (Grant Nos. XDB30000000

Time-periodic laser driving can create nonequilibrium states not accessible in equilibrium, opening new regimes in materials engineering and topological phase transitions. We report that black phosphorus (BP) exhibits spatially nonuniform topological Floquet–Dirac states under laser illumination, mimicking the “gravity” felt by fermionic quasiparticles in the same way as that for a Schwarzschild black hole (SBH). Quantum tunneling of electrons from a type-II Dirac cone (inside BH) to a type-I Dirac cone (outside BH) emits an SBH-like Planck radiation spectrum. The Hawking temperature TH obtained for a fermionic analog of BH in the bilayer BP is approximately 3 K, which is several orders of magnitude higher than that in previous works. Our work sheds light on increasing TH from the perspective of engineering 2D materials by time-periodic light illumination. The predicted SBH-like Hawking radiation, accessible in BP thin films, provides clues to probe analogous astrophysical phenomena in solids.

Experimental Synthesis of Strained Monolayer Silver Arsenide on Ag(111) Substrates**Supported by the National Key Research & Development Program of China (Grant Nos. 2016YFA0202300 and 2018YFA0305800), the National Natural Science Foundation of China (Grant Nos. 61888102, 11604373, 61622116, and 51872284), the Strategic Priority Research Program of Chinese Academy of Sciences (Grant Nos. XDB30000000 and XDB28000000), and the University of Chinese Academy

Two-dimensional (2D) materials are playing more and more important roles in both basic sciences and industrial applications. For 2D materials, strain could tune the properties and enlarge applications. Since the growth of 2D materials on substrates is often accompanied by strain, the interaction between 2D materials and substrates is worthy of careful attention. Here we demonstrate the fabrication of strained monolayer silver arsenide (AgAs) on Ag(111) by molecular beam epitaxy, which shows one-dimensional stripe structures arising from uniaxial strain. The atomic geometric structure and electronic band structure are investigated by low energy electron diffraction, scanning tunneling microscopy, x-ray photoelectron spectroscopy, angle-resolved photoemission spectroscopy and first-principle calculations. Monolayer AgAs synthesized on Ag(111) provides a platform to study the physical properties of strained 2D materials.

Symmetry Breaking and Reversible Hydrogenation of Two-Dimensional Semiconductor Sn2Bi**Supported by the National Key Research and Development Program of China (Grant Nos. 2018YFE0202700, 2016YFA0202301, and 2016YFA0300904), the National Natural Science Foundation of China (Grant Nos. 11761141013, 11674366, 11825405, and 11674368), the Beijing Municipal Natural Science Foundation (Grant No. Z180007), and the Strategic Priority Research Program of the Chinese Academy of Sciences

The hydrogenation of two-dimensional (2D) systems can efficiently modify the physical and chemical properties of materials. Here we report a systematic study on the hydrogenation of 2D semiconductor Sn2Bi on Si(111) by scanning tunneling microscopy experiments and first principle calculations. The unique butterfly-like and trench-like features were observed for single H adsorption sites and hydrogen-saturated surfaces respectively, from which the bridge-site adsorption geometry can be unambiguously determined. The structural model was further confirmed by the theoretical calculations, which is in good agreement with the experimental observation. In addition, the hydrogenation is found to vanish the flat band of Sn2Bi and increase the band gap obviously.

Suppression of Coriolis error in weak equivalence principle test using 85Rb–87Rb dual-species atom interferometer**Project supported by the National Key Research and Development Program of China (Grant No. 2016YFA0302002), the National Natural Science Foundation of China (Grant Nos. 91736311 and 11574354), Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB21010100), and the Youth Innovation Promotion Association of

Coriolis effect is an important error source in the weak equivalence principle (WEP) test using atom interferometer. In this paper, the problem of Coriolis error in WEP test is studied theoretically and experimentally. In theoretical simulation, the Coriolis effect is analyzed by establishing an error model. The measurement errors of Eötvös coefficient (η) in WEP test related to experimental parameters, such as horizontal-velocity difference and horizontal-position difference of atomic clouds, horizontal-position difference of detectors, and rotation compensation of Raman laser’s mirror are calculated. In experimental investigation, the position difference between 85Rb and 87Rb atomic clouds is reduced to 0.1 mm by optimizing the experimental parameters, an alternating detection method is used to suppress the error caused by detection position difference, thus the Coriolis error related to the atomic clouds and detectors is reduced to 1.1× 10−9. This Coriolis error is further corrected by compensating the rotation of Raman laser’s mirror, and the total uncertainty of η measurement related to the Coriolis effect is reduced as δη = 4.4 × 10−11.

Selective linear etching of monolayer black phosphorus using electron beams**Project supported by the National Natural Science Foundation of China (Grant Nos. 11622437, 61674171, 11804247, and 11974422), the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB30000000), Key Research Program of Frontier Sciences, Chinese Academy of Sciences (B.L, W.Z.), the Fundamental Research Funds for the Central Universities, China,

Point and line defects are of vital importance to the physical and chemical properties of certain two-dimensional (2D) materials. Although electron beams have been demonstrated to be capable of creating single- and multi-atom defects in 2D materials, the products are often random and difficult to predict without theoretical inputs. In this study, the thermal motion of atoms and electron incident angle were additionally considered to study the vacancy evolution in a black phosphorus (BP) monolayer by using an improved first-principles molecular dynamics method. The P atoms in monolayer BP tend to be struck away one by one under an electron beam within the displacement threshold energy range of 8.55–8.79 eV, which ultimately induces the formation of a zigzag-like chain vacancy. The chain vacancy is a thermodynamically metastable state and is difficult to obtain by conventional synthesis methods because the vacancy formation energy of 0.79 eV/edge atom is higher than the typical energy in monolayer BP. Covalent-like quasi-bonds and a charge density wave are formed along the chain vacancy, exhibiting rich electronic properties. This work proposes a theoretical protocol for simulating a complete elastic collision process of electron beams with 2D layers and will facilitate the establishment of detailed theoretical guidelines for experiments on 2D material etching using focused high-energy electron beams.

A transportable optical lattice clock at the National Time Service Center**Project supported by the National Natural Science Foundation of China (Grant Nos. 61775220 and 11803042), the Key Research Project of Frontier Science of the Chinese Academy of Sciences (Grant No. QYZDB-SSW-JSC004), and the strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB21030100).

We report a transportable one-dimensional optical lattice clock based on 87Sr at the National Time Service Center. The transportable apparatus consists of a compact vacuum system and compact optical subsystems. The vacuum system with a size of 90 cm× 20 cm× 42 cm and the beam distributors are assembled on a double-layer optical breadboard. The modularized optical subsystems are integrated on independent optical breadboards. By using a 230 ms clock laser pulse, spin-polarized spectroscopy with a linewidth of 4.8 Hz is obtained which is close to the 3.9 Hz Fourier-limit linewidth. The time interleaved self-comparison frequency instability is determined to be 6.3 × 10–17 at an averaging time of 2000 s.

Solution-Phase DNA-Compatible Pictet-Spengler Reaction Aided by Machine Learning Building Block Filtering.

SummaryThe application of machine learning toward DNA encoded library (DEL) technology is lacking despite obvious synergy between these two advancing technologies. Herein, a machine learning algorithm has been developed that predicts the conversion rate for the DNA-compatible reaction of a building block with a model DNA-conjugate. We exemplify the value of this technique with a challenging reaction, the Pictet-Spengler, where acidic conditions are normally required to achieve the desired cyclization between tryptophan and aldehydes to provide tryptolines. This is the first demonstration of using a machine learning algorithm to cull potential building blocks prior to their purchase and testing for DNA-encoded library synthesis. Importantly, this allows for a challenging reaction, with an otherwise very low building block pass rate in the test reaction, to still be used in DEL synthesis. Furthermore, because our protocol is solution phase it is directly applicable to standard plate-based DEL synthesis.

Monolithic 0–f Scheme-Based Frequency Comb Directly Driven by a High-Power Ti:Sapphire Oscillator**Supported by the National Key R&D Program of China (Grant No. 2017YFC0110301), the National Natural Science Foundation of China (Grant Nos. 91950113, 61575219, 61210017, 11774234, 11674386, 11434016, and 91850209), the Strategic Priority Research Program of the CAS (Grant No. XDB23030203), and the Youth Innovation Promotion Association of the CAS

A monolithic 0–f scheme-based femtosecond optical frequency comb directly driven by a high-power Ti:sapphire laser oscillator is demonstrated. The spectrum covering from 650 nm to 950 nm is generated from the Ti:sapphire oscillator with a repetition rate of 170 MHz. The average output power up to 630 mW is delivered under the pump power of 4.5 W. A 44-dB signal-to-noise ratio (SNR) of the carrier-envelope phase offset (CEO) beat note is achieved under the resolution of 100 kHz and is long-term stabilized to a reference source at 20 MHz. The integrated phase noise (IPN) in the range from 1 Hz to 1 MHz is calculated to be 138 mrad, corresponding to the timing jitter of 63 as at the central wavelength of 790 nm.

Spontaneous growth of the reconnection electric field during magnetic reconnection with a guide field: A theoretical model and particle-in-cell simulations**Project supported by the National Natural Science of China (Grant Nos. 41527804 and 41774169), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB 41000000), and the Key Research Program of Frontier Sciences of the Chinese Academy

Reconnection electric field is a key element of magnetic reconnection. It quantifies the change of magnetic topology and the dissipation of magnetic energy. In this work, two-dimensional (2D) particle-in-cell (PIC) simulations are performed to study the growth of the reconnection electric field in the electron diffusion region (EDR) during magnetic reconnection with a guide field. At first, a seed electric field is produced due to the excitation of the tearing-mode instability. Then, the reconnection electric field in the EDR, which is dominated by the electron pressure tensor term, suffers a spontaneous growth stage and grows exponentially until it saturates. A theoretical model is also proposed to explain such a kind of growth. The reconnection electric field in the EDR is found to be directly proportional to the electron outflow speed. The time derivative of electron outflow speed is proportional to the reconnection electric field in the EDR because the outflow is formed after the inflow electrons are accelerated by the reconnection electric field in the EDR and then directed away along the outflow direction. This kind of reinforcing process at last leads to the exponential growth of the reconnection electric field in the EDR.

Anomalous Hall effect in ferromagneticWeyl semimetal candidate Zr1−xVxCo1.6Sn**Project supported by the National Natural Science Foundation of China (Grant Nos. 11774007 and U1832214), the National Key R&D Program of China (Grant No. 2018YFA0305601), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB28000000).

We grew single crystals of vanadium-substituted, ferromagnetic Weyl semimetal candidate Zr1−xVxCo1.6Sn from molten tin flux. These solid solutions all crystallize in a full Heusler structure (L21) while their Curie temperatures and magnetic moments are enhanced by V-substitution. Their resistivity gradually changes from bad-metal-like to semiconductor-like with increasing x while the anomalous Hall effect (AHE), which can be well fitted by Tian–Ye–Jin (TYJ) scaling,[] is also enhanced. Moreover, we find an apparent electron–electron interaction (EEI) induced quantum correction in resistivity at low temperature. The anomalous Hall conductivity (AHC) dominated by the intrinsic term is not corrected.

Epitaxial fabrication of monolayer copper arsenide on Cu(111)**Project supported by the National Key Research & Development Program of China (Grant Nos. 2016YFA0202300 and 2018YFA0305800), the National Natural Science Foundation of China (Grant Nos. 61888102, 11604373, 61622116, and 51872284), the Strategic Priority Research Program of Chinese Academy of Sciences (Grant Nos. XDB30000000 and XDB28000000), and the University of Chinese Academy of

We report the epitaxial growth of monolayer copper arsenide (CuAs) with a honeycomb lattice on Cu(111) by molecular beam epitaxy (MBE). Scanning tunneling microscopy (STM), low energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) verify the superlattice of monolayer CuAs on Cu(111) substrate. Angle-resolved photoemission spectroscopy (ARPES) measurements together with DFT calculations demonstrate the electronic band structures of monolayer CuAs and reveal its metallic nature. Further calculations show that charge transfer from Cu(111) substrate to monolayer CuAs lifts the Fermi level and tunes the band structure of the monolayer CuAs. This high-quality epitaxial monolayer CuAs with potential tunable band gap holds promise on the applications in nano-electronic devices.

Thickness-dependent magnetic order and phase transition in V5S8**Project supported by the National Natural Science Foundation of China (Grant Nos. 51922011 and 61888102), the National Key Research & Development Project of China (Grant Nos. 2016YFA0202300 and 2019YFA0308500), and the Strategic Priority Research Program of Chinese Academy of Sciences (Grant Nos. XDB30000000 and XDB28000000). A portion of the research was performed in

V5S8 is an ideal candidate to explore the magnetism at the two-dimensional (2D) limit. A recent experiment has shown that the V5S8 thin films exhibit an antiferromagnetic (AFM) to ferromagnetic (FM) phase transition with reducing thickness. Here, for the first time, using density functional theory calculations, we report the antiferromagnetic order of bulk V5S8, which is consistent with the previous experiments. The specific antiferromagnetic order is reproduced when Ueff = 2 eV is applied on the intercalated vanadium atoms within LDA. We find that the origin of the magnetic ordering is from superexchange interaction. We also investigate the thickness-dependent magnetic order in V5S8 thin films. It is found that there is an antiferromagnetic to ferromagnetic phase transition when V5S8 is thinned down to 2.2 nm. The main magnetic moments of the antiferromagnetic and ferromagnetic states of the thin films are located on the interlayered vanadium atoms, which is the same as that in the bulk. Meanwhile, the strain in the thin films also influences the AFM–FM phase transition. Our results not only reveal the magnetic order and origin in bulk V5S8 and thin films, but also provide a set of parameters which can be used in future calculations.

Michelson laser interferometer-based vibration noise contribution measurement method for cold atom interferometry gravimeter**Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB 21030200) and the National Natural Science Foundation of China (Grant No. 11904408).

The measurement performance of the atom interferometry absolute gravimeter is strongly affected by the ground vibration noise. We propose a vibration noise evaluation scheme using a Michelson laser interferometer constructed by the intrinsic Raman laser of the atomic gravimeter. Theoretical analysis shows that the vibration phase measurement accuracy is better than 4 mrad, which corresponds to about 10−10 g accuracy for a single shot gravity measurement. Compared with the commercial seismometer or accelerometer, this method is a simple, low cost, direct, and fully synchronized measurement of the vibration phase which should benefit the development of the atomic gravimeter. On the other side, limited by equivalence principle, the result of the laser interferometer is not absolute but relative vibration measurement. Triangular cap method could be used to evaluation the noise contribution of vibration, which is a different method from others and should benefit the development of the atomic gravimeter.

Extinction mechanisms of hyperbolic h-BN nanodisk**Project supported by the National Key Research and Development Program of China (Grant No. 2016YFA0203500), the National Natural Science Foundation of China (Grant No. 11874407), and Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB 30000000).

We applied the finite element method to calculate the extinction spectrum of single hyperbolic hexagonal boron nitride (h-BN) nanodisk. We show that the hyperbolic h-BN nanodisk exhibits two extinction mechanisms in the mid-infrared region. The volume confined phonon polaritons resonances of the nanodisk give rise to a series of weak extinction peaks. The localized surface phonon polaritons lead to a robust dipolar extinction, and the extinction peak position is tunable by varying the size of the h-BN nanodisk. These findings reveal the mechanisms of the interaction between light and resonant h-BN nanodisk, which are essential for h-BN related opto-electromagnetic applications.

High-Pressure Ultrafast Dynamics in Sr2IrO4: Pressure-Induced Phonon Bottleneck Effect**Supported by the National Key Research and Development Program of China (Grant Nos. 2017YFA0303603, 2016YFA0300303, 2018YFA0305703), the National Natural Science Foundation of China (Grant Nos. 11774408, 11574383, 11874075, U1530402), the Strategic Priority Research Program of CAS (Grant No. XDB30000000), the International Partnership Program of Chinese Academy of Sciences (Grant Nos. GJHZ1826, GJHZ1403),

By integrating pump-probe ultrafast spectroscopy with diamond anvil cell (DAC) technique, we demonstrate a time-resolved ultrafast dynamics study on non-equilibrium quasiparticle (QP) states in Sr2IrO4 under high pressure. On-site in situ condition is realized, where both the sample and DAC have fixed position during the experiment. The QP dynamics exhibits a salient pressure-induced phonon bottleneck feature at 20 GPa, which corresponds to a gap shrinkage in the electronic structure. A structural transition is also observed at 32 GPa. In addition, the slowest relaxation component reveals possible heat diffusion or pressure-controlled local spin fluctuation associated with the gap shrinkage. Our work enables precise pressure dependence investigations of ultrafast dynamics, paving the way for reliable studies of high-pressure excited state physics.

Nonadiabatic and Multielectron Effects in the Attoclock Experimental Scheme* *Supported by the National Key Research and Development Program of China (Nos. 2019YFA0307700 and 2016YFA0401100), the National Natural Science Foundation of China (Nos. 11527807, 11774387, 11834015, 11847243, 11804374, 11874392, and 11974383), the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB21010400), and the Science and Technology Department of

The problem of how long it takes for an electron to tunnel from one side of a barrier to the other has been debated for decades and the attoclock is a promising experimental procedure to address this problem. In the attoclock experiment, many physical effects will contribute to the experimental results and it is difficult to extract the tunneling time accurately. We numerically investigate a method of measuring the residual equivalent temporal offset (RETO) induced by the physical effects except for tunneling delay. The Coulomb potential effect, the nonadiabatic effect, the multielectron effect, and the Stark effect are considered in the theoretical model. It is shown that the ratio of the RETO of the target atoms to that of H is insensitive to the wavelength and is linearly proportional to . This work can help to improve the accuracy of the attoclock technique.