Quantitative Determination of the Critical Points of Mott Metal-Insulator Transition in Strongly Correlated Systems

The Mottness is at the heart of the essential physics in a strongly correlated system as many novel quantum phenomena occur at the metallic phase near the Mott metal-insulator transition. We investigate the Mott metal-insulator transition in a strongly-correlated electron system based on the Hubbard model. The on-site moment evaluated by the dynamical mean-field theory is employed to depict the Mott metal-insulator transition. Conveniently, the on-site moment is a more proper order parameter to quantitatively determine the Mott critical point, in comparison with the corresponding quasiparticle coherent weight. Moreover, this order parameter also gives a consistent description of two distinct forms of the critical points of the Mott metal-insulator transition.Comment: 6 pages, 4 figure

InAlN/GaN MOSHEMTs with high drain current of 2.3 A/mm high on/off ratio of 1012 and low SS of 64 mV/dec enabled by atomic-layer-epitaxial MgCaO as gate dielectric

Summary form only given. Recently, GaN-based high-electron-mobility-transistor (HEMT) has demonstrated its promise in high frequency, high power and low noise electronic devices. The lattice matched InAlN/GaN HEMT structure provides a higher 2D electron density than AlGaN/GaN due to a larger bandgap offset and minimized short-channel-effects due to its thinner barrier. However, because of its several-nm thin barrier, those devices usually suffer from high gate leakage and interface trap issues, the device off-state performance is degraded and thereby the off-state breakdown voltage is decreased. Therefore, finding a good method to reduce the gate leakage and interface trap density is of great importance to improve the device off-state performance. In this study, we use atomic layer epitaxial MgCaO as gate dielectric to fabricate sub-100nm InAlN/GaN MOSHEMTs with significantly improved maximum drain current, current on/off ratio and low subthreshold swing.Chemistry and Chemical Biolog

A cryogen-free dilution refrigerator based Josephson qubit measurement system

This is the published version, also available here: http://dx.doi.org/10.1063/1.3698001.We develop a small-signal measurement system on cryogen-free dilution refrigerator which is suitable for superconductingqubit studies. Cryogen-free refrigerators have several advantages such as less manpower for system operation and large sample space for experiment, but concern remains about whether the noise introduced by the coldhead can be made sufficiently low. In this work, we demonstrate some effective approaches of acoustic isolation to reduce the noise impact. The electronic circuit that includes the current, voltage, and microwave lines for qubit coherent state measurement is described. For the current and voltage lines designed to have a low pass of dc-100 kHz, we show that the measurements of Josephson junction's switching current distribution with a width down to 1 nA, and quantum coherent Rabi oscillation and Ramsey interference of the superconductingqubit can be successfully performed

Quantum and classical resonant escapes of a strongly driven Josephson junction

This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevB.81.144518.The properties of phase escape in a dc superconducting quantum interference device (SQUID) at 25 mK, which is well below quantum-to-classical crossover temperature Tcr, in the presence of strong resonant ac driving have been investigated. The SQUID contains two Nb/Al-AlOx/Nb tunnel junctions with Josephson inductance much larger than the loop inductance so it can be viewed as a single junction having adjustable critical current. We find that with increasing microwave power W and at certain frequencies ν and ν/2, the single primary peak in the switching current distribution, which is the result of macroscopic quantum tunneling of the phase across the junction, first shifts toward lower bias current I and then a resonant peak develops. These results are explained by quantum resonant phase escape involving single and two photons with microwave-suppressed potential barrier. As W further increases, the primary peak gradually disappears and the resonant peak grows into a single one while shifting further to lower I. At certain W, a second resonant peak appears, which can locate at very low I depending on the value of ν. Analysis based on the classical equation of motion shows that such resonant peak can arise from the resonant escape of the phase particle with extremely large oscillation amplitude resulting from bifurcation of the nonlinear system. Our experimental result and theoretical analysis demonstrate that at T⪡Tcr, escape of the phase particle could be dominated by classical process, such as dynamical bifurcation of nonlinear systems under strong ac driving

Influence of tree spacing on soil nitrogen mineralization and availability in hybrid poplar plantations

Nitrogen (N) availability and mineralization are key parameters and transformation processes that impact plant growth and forest productivity. We hypothesized that suitable plantation spacing can lead to enhanced soil N mineralization and nitrification, which in turn promote tree growth. Studies were conducted to evaluate seasonal patterns of soil inorganic N pools as well as rates of nitrification and N mineralization of three soil layers under four tree spacing treatments. Results showed tree spacing significantly affected annual net N mineralization, whereas inorganic N content in surface soils was significantly affected by tree spacing only during the growing season. The total annual cumulative net N mineralization ranged from 80.3–136.0 mg·kg−1 in the surface soils (0–20 cm), whereas the cumulative net N mineralization of 6 × 6 m and 4.5 × 8 m spacings was 65% and 24% higher than that of the 5 × 5 m, respectively. In general, tree spacing would affect N availability in soil by altering N mineralization rates, while high annual N mineralization was found in soils of low density plantations, with higher rates in square spacing than rectangular spacing. The obtained results suggest that suitable spacing could lead to enhanced N mineralization, but seasonal variation of soil N mineralization may not only be directly related to plantation productivity but also to understory vegetation productivity.Peer reviewedPlant and Soil Science

Coherent population transfer between uncoupled or weakly coupled states in ladder-type superconducting qutrits

Stimulated Raman adiabatic passage offers significant advantages for coherent population transfer between uncoupled or weakly coupled states and has the potential of realizing efficient quantum gate, qubit entanglement and quantum information transfer. Here we report on the realization of the process in the superconducting Xmon and phase qutrits—two ladder-type three-level systems in which the ground state population is coherently transferred to the second excited state via the dark state subspace. We demonstrate that the population transfer efficiency is no less than 96% and 67% for the two devices, which agree well with the numerical simulation of the master equation. Population transfer via stimulated Raman adiabatic passage is significantly more robust against variations of the experimental parameters compared with that via the conventional resonant π pulse method. Our work opens up a new venue for exploring the process for quantum information processing using the superconducting artificial atoms.This work was supported by the Ministry of Science and Technology of China (Grant Nos. 2011CBA00106, 2014CB921202, and 2015CB921104) and the National Natural Science Foundation of China (Grant Nos. 91321208, 11222437, and 11161130519). S. Han acknowledges support by the US NSF (PHY-1314861)

Omnidirectional whispering-gallery-mode lasing in GaN microdisk obtained by selective area growth on sapphire substrate

The optical properties of hexagonal GaN microdisk arrays grown on sapphire substrates by selective area growth (SAG) technique were investigated both experimentally and theoretically. Whispering-gallery-mode (WGM) lasing is observed from various directions of the GaN pyramids collected at room temperature, with the dominant lasing mode being Transverse-Electric (TE) polarized. A relaxation of compressive strain in the lateral overgrown region of the GaN microdisk is illustrated by photoluminescence (PL) mapping and Raman spectroscopy. A strong correlation between the crystalline quality and lasing behavior of the GaN microdisks was also demonstrated

Deconvolution of single-cell multi-omics layers reveals regulatory heterogeneity

Heterogeneity in gene expression and epigenetic states exists across individual cells. Here, the authors develop scCAT-seq, a technique for simultaneously performing ATAC-seq and RNA-seq within the same single cell

Spatiotemporal transcriptomic atlas of mouse organogenesis using DNA nanoball-patterned arrays.

Spatially resolved transcriptomic technologies are promising tools to study complex biological processes such as mammalian embryogenesis. However, the imbalance between resolution, gene capture, and field of view of current methodologies precludes their systematic application to analyze relatively large and three-dimensional mid- and late-gestation embryos. Here, we combined DNA nanoball (DNB)-patterned arrays and in situ RNA capture to create spatial enhanced resolution omics-sequencing (Stereo-seq). We applied Stereo-seq to generate the mouse organogenesis spatiotemporal transcriptomic atlas (MOSTA), which maps with single-cell resolution and high sensitivity the kinetics and directionality of transcriptional variation during mouse organogenesis. We used this information to gain insight into the molecular basis of spatial cell heterogeneity and cell fate specification in developing tissues such as the dorsal midbrain. Our panoramic atlas will facilitate in-depth investigation of longstanding questions concerning normal and abnormal mammalian development.This work is part of the ‘‘SpatioTemporal Omics Consortium’’ (STOC) paper package. A list of STOC members is available at: http://sto-consortium.org. We would like to thank the MOTIC China Group, Rongqin Ke (Huaqiao University, Xiamen, China), Jiazuan Ni (Shenzhen University, Shenzhen, China), Wei Huang (Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai, China), and Jonathan S. Weissman (Whitehead Institute, Boston, USA) for their help. This work was supported by the grant of Top Ten Foundamental Research Institutes of Shenzhen, the Shenzhen Key Laboratory of Single-Cell Omics (ZDSYS20190902093613831), and the Guangdong Provincial Key Laboratory of Genome Read and Write (2017B030301011); Longqi Liu was supported by the National Natural Science Foundation of China (31900466) and Miguel A. Esteban’s laboratory at the Guangzhou Institutes of Biomedicine and Health by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA16030502), National Natural Science Foundation of China (92068106), and the Guangdong Basic and Applied Basic Research Foundation (2021B1515120075).S