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Wang, Zhen

Publications and source records attributed to Wang, Zhen.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Digital quantum simulation of Floquet symmetry-protected topological phases

Quantum many-body systems away from equilibrium host a rich variety of exotic phenomena that are forbidden by equilibrium thermodynamics. A prominent example is that of discrete time crystals, in which time-translational symmetry is spontaneously broken in periodically driven systems. Pioneering experiments have observed signatures of time crystalline phases with trapped ions, solid-state spin systems, ultracold atoms and superconducting qubits. Here we report the observation of a distinct type of non-equilibrium state of matter, Floquet symmetry-protected topological phases, which are implemented through digital quantum simulation with an array of programmable superconducting qubits. We observe robust long-lived temporal correlations and subharmonic temporal response for the edge spins over up to 40 driving cycles using a circuit of depth exceeding 240 and acting on 26 qubits. We demonstrate that the subharmonic response is independent of the initial state, and experimentally map out a phase boundary between the Floquet symmetry-protected topological and thermal phases. Our results establish a versatile digital simulation approach to exploring exotic non-equilibrium phases of matter with current noisy intermediate-scale quantum processors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Revealing aggregation of non-fullerene acceptors in intermixed phase by ultraviolet-visible absorption spectroscopy

Non-fullerene acceptor (NFA) aggregation is crucial in determining bulk-heterojunction (BHJ) organic photovoltaic (OPV) performance. However, it is still a big challenge to characterize the nanostructure of NFAs in the disordered donor-acceptor intermixed phase. Here, we demonstrate a method to characterize NFA aggregation and composition in the intermixed phase by measuring NFA concentration-dependent ultraviolet-visible (UV-vis) absorption spectroscopy of BHJ films. In various polymer:NFA films, an absorption shift as a function of increasing molecular concentration (ASIMC) phenomenon is observed, and different NFA aggregation behaviors can be distinguished. The ASIMC method was then applied to study the influence of processing conditions on the NFA concentration in the intermixed phase of devices to establish a correlation with device efficiency. The current work provides a feasible tool to study the nanostructure of NFAs in the complex polymer matrix and to understand the variations in the NFA concentration in the intermixed phase under non-equilibrium conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Eu 5 Al 3 Sb 6 : Al 4 Tetrahedra Embedded in a Rock-Salt-Like Structure

The new Eu 5 Al 3 Sb 6 phase has been successfully synthesized as a pure phase through Sn flux methods yielding large, high-quality crystals. This structure type features disordered Al clusters that appear in the form of dual tetrahedra. It crystallizes in the monoclinic C2/m space group exhibiting a rock-salt-like Eu–Sb framework with [Al 4 ] tetrahedra replacing some of the cationic Eu atoms (space group: C2/m, a = 8.151(1) Å, b = 14.181(2) Å, c = 8.145(1) Å, β = 109.577(2)°). The structure models the [Al 4 ] as dual tetrahedra with the Al atom sites 37.5% occupied along with Eu present on the central site at 8% occupancy and the remainder of the site being vacant. The presence of the [Al 4 ] cluster is further supported by HRTEM. Electronic structure calculations show that this material is a semimetal with observed band crossings close to the Fermi level. Strong Al–Sb antibonding interactions were found from COHP calculations close to the Fermi level and provide the rationale for the deficiency of the Al cluster. Mössbauer spectroscopy on Eu-151 and Sb-121 provides oxidation states of 2+ and 3– along with the local environment. Magnetic susceptibility measurements can be described well with a Curie–Weiss law where an effective moment of 7.80 μB/mol Eu is obtained, consistent with Eu 2+ , and show canted antiferromagnetic behavior below 10 K. Temperature dependent resistivity shows a Kondo-like low-temperature upturn caused by enhanced scattering of the itinerant electrons with the 4f orbitals of Eu.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Origin of insulating and nonferromagnetic SrRuO 3 monolayers

The electro-magnetic properties of ultrathin epitaxial ruthenate films have long been the subject of debate. Here we combine experimental with theoretical investigations of (SrTiO 3 ) 5 -(SrRuO 3 ) n -(SrTiO 3 ) 5 (STO 5 -SRO n -STO 5 ) heterostructures with n = 1 and 2 unit cells, including extensive atomic-resolution scanning-transmission-electron-microscopy imaging, electron-energy-loss-spectroscopy chemical mapping, as well as transport and magneto-transport measurements. The experimental data demonstrate that the STO 5 -SRO 2 -STO 5 heterostructure is nearly stoichiometric, metallic, and ferromagnetic with T C ~ 128 K, even though it lacks the characteristic bulk-SRO octahedral tilts and matches the cubic STO structure. In contrast, the STO 5 -SRO 1 -STO 5 heterostructure features Ru-Ti intermixing in the RuO 2 layer, also without octahedral tilts, but is accompanied by a loss of metallicity and ferromagnetism. Density-functional-theory calculations show that stoichiometric n = 1 and n = 2 heterostructures are metallic and ferromagnetic with no octahedral tilts, while non-stoichiometry in the Ru sublattice in the n = 1 case opens an energy gap and induces antiferromagnetic ordering. Furthermore, the results indicate that the observed non-stoichiometry is the cause of the observed loss of metallicity and ferromagnetism in the n = 1 case.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Abrupt orthorhombic relaxation in compressively strained ultrathin SrRuO 3 films

Lattice structure can dictate electronic and magnetic properties of a material. Especially, reconstruction at a surface or heterointerface can create properties that are fundamentally different from those of the corresponding bulk material. In this work, we have investigated the lattice structure on the surface and in the thin films of epitaxial SrRuO 3 with the film thickness up to 22 pseudo-cubic unit cells (u.c.), using the combination of surface sensitive low energy electron diffraction and bulk sensitive scanning transmission electron microscopy. Our analysis indicates that, in contrast to many perovskite oxides, the RuO6 tilt and rotational distortions appear even in single unit cell SrRuO 3 thin films on cubic SrTiO 3 , while the full relaxation to the bulk-like orthorhombic structures takes 3-4 u.c. from the interface for thicker films. Yet the TiO 6 octahedra of the substrate near the interface with SrRuO 3 films show no sign of distortion, unlike those near the interface with CaRuO 3 films. Two orthogonal in-plane rotated structural domains are identified. These octahedral distortions are essential for the understanding of the thickness dependent transport and magnetism in ultrathin films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

High Miscibility Compatible with Ordered Molecular Packing Enables an Excellent Efficiency of 16.2% in All-Small-Molecule Organic Solar Cells

In all-small-molecule organic solar cells (ASM-OSCs), a high short-circuit current (Jsc) usually needs a small phase separation, while a high fill factor (FF) is generally realized in a highly ordered packing system. However, small domain and ordered packing always conflicted each other in ASM-OSCs, leading to a mutually restricted J sc and FF. Here, in this study, alleviation of the previous dilemma by the strategy of obtaining simultaneous good miscibility and ordered packing through modulating homo- and heteromolecular interactions is proposed. By moving the alkyl-thiolation side chains from the para- to the meta-position in the small-molecule donor, the surface tension and molecular planarity are synchronously enhanced, resulting in compatible properties of good miscibility with acceptor BTP-eC9 and strong self-assembly ability. As a result, an optimized morphology with multi-length-scale domains and highly ordered packing is realized. The device exhibits a long carrier lifetime (39.8 μs) and fast charge collection (15.5 ns). A record efficiency of 16.2% with a high FF of 75.6% and a J sc of 25.4 mA cm –2 in the ASM-OSCs is obtained. These results demonstrate that the strategy of simultaneously obtaining good miscibility with high crystallinity could be an efficient photovoltaic material design principle for high-performance ASM-OSCs.

14 SOLAR ENERGY↗
DOE OSTI2021

Sepsis induces muscle atrophy by inhibiting proliferation and promoting apoptosis via PLK1‐AKT signalling

Abstract Sepsis and sepsis‐induced skeletal muscle atrophy are common in patients in intensive care units with high mortality, while the mechanisms are controversial and complicated. In the present study, the atrophy of skeletal muscle was evaluated in sepsis mouse model as well as the apoptosis of muscle fibres. Sepsis induced atrophy of skeletal muscle and apoptosis of myofibres in vivo and in vitro. In cell‐based in vitro experiments, lipopolysaccharide (LPS) stimulation also inhibited the proliferation of myoblasts. At the molecular level, the expression of polo‐like kinase 1 (PLK1) and phosphorylated protein kinase B (p‐AKT) was decreased. Overexpression of PLK1 partly rescued LPS‐induced apoptosis, proliferation suppression and atrophy in C2C12 cells. Furthermore, inhibiting the AKT pathway deteriorated LPS‐induced atrophy in PLK1‐overexpressing C2C12 myotubes. PLK1 was found to participate in regulating apoptosis and E3 ubiquitin ligase activity in C2C12 cells. Taken together, these results indicate that sepsis induces skeletal muscle atrophy by promoting apoptosis of muscle fibres and inhibiting proliferation of myoblasts via regulation of the PLK1‐AKT pathway. These findings enhance understanding of the mechanism of sepsis‐induced skeletal muscle atrophy.

Cao, Ying‐Ya↗
DOE OSTI2021

Characterization of reactive MgO-modified calcium sulfoaluminate cements upon carbonation

This study characterizes reactive MgO-modified calcium sulfoaluminate (CSA) cement upon carbonation. Paste samples were fabricated by replacing CSA cement with reactive MgO at levels of 0, 5, 10, and 20 wt%. The samples were cured for 56 days and further cured at a CO{sub 2} concentration of 3% for 28 days. MgO incorporation into the CSA cement favored the formation of monosulfate over ettringite. Externally supplied MgO in the CSA cement reduced Al uptake in C-A-S-H and formed hydrotalcite as a secondary phase, which is associated with a reduction in the carbonation degree. In addition, the incorporated MgO inhibited the carbonation of ettringite and monosulfate, while more C-A-S-H and aluminum hydroxide were formed in neat CSA cement upon carbonation, showing the nearly full decomposition of ettringite and monosulfate. The tetrahedral Al network of the MgO-modified sample was not altered upon carbonation, indicating that MgO modified the route of carbonation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Down-regulation of A3AR signaling by IL-6-induced GRK2 activation contributes to Th17 cell differentiation

Highlights: • Cyclic AMP-PKA signaling is involved in Th17 cell differentiation. • IL-6 stimulation triggers the internalization of A{sub 3}AR and promotes cAMP production in T cells. • IL-6 induces A{sub 3}AR internalization in a GRK2 dependent manner. • GRK2 is a potential therapeutic target for treating Th17 driving immune diseases. IL-6-triggered Th17 cell expansion is responsible for the pathogenesis of many immune diseases including rheumatoid arthritis (RA). Traditionally, IL-6 induces Th17 cell differentiation through JAK-STAT3 signaling. In the present work, PKA inhibition reduces in vitro induction of Th17 cells, while IL-6 stimulation of T cells facilitates the internalization of A{sub 3}AR and increased cAMP production in a GRK2 dependent manner. Inhibition of GRK2 by paroxetine (PAR) or genetic depletion of GRK2 restored A{sub 3}AR distribution and prevented Th17 cell differentiation. Furthermore, in vivo PAR treatment effectively reduced the splenic Th17 cell proportion in a rat model of collagen-induced arthritis (CIA) which was accompanied by a significant improvement in clinical manifestations. These results indicate that IL-6-induced Th17 cell differentiation not only occurs through JAK-STAT3-RORγt but is also mediated through GRK2-A{sub 3}AR-cAMP-PKA-CREB/ICER-RORγt. This elucidates the significance of GRK2-controlled cAMP signaling in the differentiation of Th17 cells and its potential application in treating Th17-driven immune diseases such as RA.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Thermodynamic Properties and Molecular Packing Explain Performance and Processing Procedures of Three D18:NFA Organic Solar Cells

Abstract Organic solar cells (OSCs) based on D18:Y6 have recently exhibited a record power conversion efficiency of over 18%. The initial work is extended and the device performance of D18‐based OSCs is compared with three non‐fullerene acceptors, Y6, IT‐4F, and IEICO‐4Cl, and their molecular packing characteristics and miscibility are studied. The D18 polymer shows unusually strong chain extension and excellent backbone ordering in all films, which likely contributes to the excellent hole‐transporting properties. Thermodynamic characterization indicates a room‐temperature miscibility for D18:Y6 and D18:IT‐4F near the percolation threshold. This corresponds to an ideal quench depth and explains the use of solvent vapor annealing rather than thermal annealing. In contrast, D18:IEICO‐4Cl is a low‐miscibility system with a deep quench depth during casting and poor morphology control and low performance. A failure of ternary blends with PC 71 BM is likely due to the near‐ideal miscibility of Y6 to begin with and indicates that strategies for developing successful ternary or quaternary solar cells are likely very different for D18 than for other high‐performing donors. This work reveals several unique property–performance relations of D18‐based photovoltaic devices and helps guide design or fabrication of yet higher efficiency OSCs.

Wang, Zhen↗
DOE OSTI2020

Modulating Energy Level on an A‐D‐A′‐D‐A‐Type Unfused Acceptor by a Benzothiadiazole Core Enables Organic Solar Cells with Simple Procedure and High Performance

Unfused‐ring acceptors (UFAs) have gained considerable research attention as they offer simple chemical structures through simplified synthesis methods, which would boost the commercialization of organic solar cells (OSCs). Recently, a new small molecule acceptor (SMA) named Y6 was reported, yielding high‐performance OSCs. Herein, the Y6‐like A‐DA′D‐A framework is developed to A‐D‐A′‐D‐A‐type backbone adopted in constructing UFAs. Two new Y6‐like UFAs are synthesized within four steps and the effect of noncovalent atoms at the central electron‐deficient core on material properties and device performances is studied. It is found that the introduction of fluorine atoms can bring larger red‐shift in the absorption spectra and better aggregation of the resulting UFA film states compared with those of oxygen atoms. Interestingly, the variations in the noncovalent interaction atoms induce different intermolecular charge transfer between donors and UFAs. When blended with another economical donor, PTQ10, F substitution at the benzothiadiazole ring is more effective than O substitution, leading to the increased short‐circuit current density ( J SC ) and higher efficiency of over 12%, among the best performances of UFA‐based OSCs. This contribution demonstrates the appropriate introduction of noncovalent interaction is a promising method for tuning energy levels, absorption, and aggregation of UFAs for high‐performance OSCs.

Yu, Han↗