The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
Claus Ropers - One of the best experts on this subject based on the ideXlab platform.
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ultrafast nanoimaging of the order parameter in a Structural Phase Transition
Science, 2021Co-Authors: Thomas Danz, Claus Ropers, Till DomroseAbstract:Understanding microscopic processes in materials and devices that can be switched by light requires experimental access to dynamics on nanometer length and femtosecond time scales. Here, we introduce ultrafast dark-field electron microscopy to map the order parameter across a Structural Phase Transition. We use ultrashort laser pulses to locally excite a 1T-TaS2 (1T-polytype of tantalum disulfide) thin film and image the transient state of the specimen by ultrashort electron pulses. A tailored dark-field aperture array allows us to track the evolution of charge-density wave domains in the material with simultaneous femtosecond temporal and 5-nanometer spatial resolution, elucidating relaxation pathways and domain wall dynamics. The distinctive benefits of selective contrast enhancement will inspire future beam-shaping technology in ultrafast transmission electron microscopy.
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coherent control of a surface Structural Phase Transition
Nature, 2020Co-Authors: Jan Gerrit Horstmann, Hannes Bockmann, Bareld Wit, Felix Kurtz, Gero Storeck, Claus RopersAbstract:Active optical control over matter is desirable in many scientific disciplines, with prominent examples in all-optical magnetic switching1,2, light-induced metastable or exotic Phases of solids3–8 and the coherent control of chemical reactions9,10. Typically, these approaches dynamically steer a system towards states or reaction products far from equilibrium. In solids, metal-to-insulator Transitions are an important target for optical manipulation, offering ultrafast changes of the electronic4 and lattice11–16 properties. The impact of coherences on the efficiencies and thresholds of such Transitions, however, remains a largely open subject. Here, we demonstrate coherent control over a metal–insulator Structural Phase Transition in a quasi-one-dimensional solid-state surface system. A femtosecond double-pulse excitation scheme17–20 is used to switch the system from the insulating to a metastable metallic state, and the corresponding Structural changes are monitored by ultrafast low-energy electron diffraction21,22. To govern the Transition, we harness vibrational coherence in key Structural modes connecting both Phases, and observe delay-dependent oscillations in the double-pulse switching efficiency. Mode-selective coherent control of solids and surfaces could open new routes to switching chemical and physical functionalities, enabled by metastable and non-equilibrium states. A Structural Phase Transition from metal to insulator on a solid surface is controlled by an ultrafast sequence of optical pulses.
Junfa Zhu - One of the best experts on this subject based on the ideXlab platform.
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doping induced Structural Phase Transition in cobalt diselenide enables enhanced hydrogen evolution catalysis
Nature Communications, 2018Co-Authors: Yarong Zheng, Minrui Gao, Xiaolong Zhang, Feiyue Gao, Qiang Gao, Rui You, Weixin Huang, Shoujie Liu, Junfa ZhuAbstract:Transition metal dichalcogenide materials have been explored extensively as catalysts to negotiate the hydrogen evolution reaction, but they often run at a large excess thermodynamic cost. Although activating strategies, such as defects and composition engineering, have led to remarkable activity gains, there remains the requirement for better performance that aims for real device applications. We report here a phosphorus-doping-induced Phase Transition from cubic to orthorhombic Phases in CoSe2. It has been found that the achieved orthorhombic CoSe2 with appropriate phosphorus dopant (8 wt%) needs the lowest overpotential of 104 mV at 10 mA cm−2 in 1 M KOH, with onset potential as small as −31 mV. This catalyst demonstrates negligible activity decay after 20 h of operation. The striking catalysis performance can be attributed to the favorable electronic structure and local coordination environment created by this doping-induced Structural Phase Transition strategy. Transition metal dichalcogenides represent an exciting class of earth-abundant hydrogen-from-water electrocatalysts, although low efficiencies limit commercialization. Here, authors present a doping strategy to induce a Phase Transition in cobalt selenide and boost H2-evolution performance.
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suppression of Structural Phase Transition in vo2 by epitaxial strain in vicinity of metal insulator Transition
Scientific Reports, 2016Co-Authors: Mengmeng Yang, Yuanjun Yang, Bin Hong, Lei Wang, Yongqi Dong, Haoliang Huang, Jiangtao Zhao, Haiping Chen, Li Song, Junfa ZhuAbstract:Mechanism of metal-insulator Transition (MIT) in strained VO2 thin films is very complicated and incompletely understood despite three scenarios with potential explanations including electronic correlation (Mott mechanism), Structural transformation (Peierls theory) and collaborative Mott-Peierls Transition. Herein, we have decoupled coactions of Structural and electronic Phase Transitions across the MIT by implementing epitaxial strain on 13-nm-thick (001)-VO2 films in comparison to thicker films. The Structural evolution during MIT characterized by temperature-dependent synchrotron radiation high-resolution X-ray diffraction reciprocal space mapping and Raman spectroscopy suggested that the Structural Phase Transition in the temperature range of vicinity of the MIT is suppressed by epitaxial strain. Furthermore, temperature-dependent Ultraviolet Photoelectron Spectroscopy (UPS) revealed the changes in electron occupancy near the Fermi energy EF of V 3d orbital, implying that the electronic Transition triggers the MIT in the strained films. Thus the MIT in the bi-axially strained VO2 thin films should be only driven by electronic Transition without assistance of Structural Phase Transition. Density functional theoretical calculations further confirmed that the tetragonal Phase across the MIT can be both in insulating and metallic states in the strained (001)-VO2/TiO2 thin films. This work offers a better understanding of the mechanism of MIT in the strained VO2 films.
Ching-song Shern - One of the best experts on this subject based on the ideXlab platform.
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Depression of Curie temperature by surface Structural Phase Transition
Applied Physics Letters, 2007Co-Authors: Y. J. Chen, E. J. Hwang, Ching-song ShernAbstract:The comparative study in Structural properties for the mirror systems, 1 ML Ni/1 ML Co∕Pt(111) and 1 ML Co/1 ML Ni∕Pt(111) surface ordered alloys, reveals a Structural Phase Transition from NixCo1−xPt to NixCo1−xPt3 ordered surface alloy when the annealing temperature is between 750 and 800K. The Curie temperature speeds up to decrease when the surface structure changes from NixCo1−xPt to NixCo1−xPt3. The value of critical exponent β near the Curie point crosses from a two-dimensional-like magnetic Phase to a three-dimensional-like one after the Phase Transition. From the composition dependence of the Curie temperature, one can adjust the Curie temperatures of the surface alloy by controlling the annealing temperature.
Ryan Manso - One of the best experts on this subject based on the ideXlab platform.
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probing the pathway of an ultrafast Structural Phase Transition to illuminate the Transition mechanism in cu2s
Applied Physics Letters, 2018Co-Authors: Kai Sun, Qingping Meng, Weiguo Yin, Marcus Babzien, Mikhail Fedurin, Christina Swinson, R Malone, Mark Palmer, Leanne Mathurin, Ryan MansoAbstract:Disentangling the primary order parameter from secondary order parameters in Phase Transitions is critical to the interpretation of Transition mechanisms in strongly correlated systems and quantum materials. Here, we present a study of Structural Phase Transition pathways in superionic Cu2S nanocrystals that exhibit intriguing properties. Utilizing ultrafast electron diffraction techniques sensitive to both the momentum-space and the time-domain, we distinguish the dynamics of crystal symmetry breaking and lattice expansion in this system. We are able to follow the transient states along the Transition pathway, and so observe the dynamics of both the primary and secondary order parameters. Based on these observations, we argue that the mechanism of Structural Phase Transition in Cu2S is dominated by the electron-phonon coupling. This mechanism advances the understanding from previous results, where the focus was solely on dynamic observations of the lattice expansion.Disentangling the primary order parameter from secondary order parameters in Phase Transitions is critical to the interpretation of Transition mechanisms in strongly correlated systems and quantum materials. Here, we present a study of Structural Phase Transition pathways in superionic Cu2S nanocrystals that exhibit intriguing properties. Utilizing ultrafast electron diffraction techniques sensitive to both the momentum-space and the time-domain, we distinguish the dynamics of crystal symmetry breaking and lattice expansion in this system. We are able to follow the transient states along the Transition pathway, and so observe the dynamics of both the primary and secondary order parameters. Based on these observations, we argue that the mechanism of Structural Phase Transition in Cu2S is dominated by the electron-phonon coupling. This mechanism advances the understanding from previous results, where the focus was solely on dynamic observations of the lattice expansion.
Yoshitami Saito - One of the best experts on this subject based on the ideXlab platform.
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Superconductivity and low-temperature Structural Phase Transition in La1.98-xCe0.02BaxCuO4
Solid State Communications, 1991Co-Authors: Yoji Koike, T. Kawaguchi, Naoki Watanabe, Takashi Noji, Yoshitami SaitoAbstract:Abstract Effects of the partial substitution of Ce for La on the superconductivity and the low-temperature Structural Phase Transition have been investigated in La2-xBaxCuO4. The local minimum of Tc as a function of Ba concentration x, appearing near x = 0.125 for La2-xBaxCuO4, clearly shifts to x = 0.145 for La1.98-xCe0.02BaxCuO4. The range of x, where a resistance minimum relating to the low-temperature Structural Phase Transition appears, shifts to that of larger x values, too. These suggest that the low-temperature Structural Phase Transition around x = 0.125 in La2-xBaxCuO4 is due to the optimum hole concentration of 0.125 per Cu atom rather than plausible atomic ordering of La and Ba.
