Yanzhou Chen

© The Author 2016.Topological quantum materials represent a new class of matter with both exotic physical phenomena and novel application potentials. Many Heusler compounds, which exhibit rich emergent properties such as unusual magnetism, superconductivity and heavy fermion behaviour, have been predicted to host non-trivial topological electronic structures. The coexistence of topological order and other unusual properties makes Heusler materials ideal platform to search for new topological quantum phases. By carrying out angle-resolved photoemission spectroscopy and ab initio calculations on rare-earth half-Heusler compounds LnPtBi, we directly observe the unusual topological surface states on these materials, establishing them as first members with non-trivial topological electronic structure in this class of materials. Moreover, as LnPtBi compounds are non-centrosymmetric superconductors, our discovery further highlights them as promising candidates of topological superconductors.

© 2015 American Physical Society.The level of electronic correlation has been one of the key questions in understanding the nature of superconductivity. Among the iron-based superconductors, the iron chalcogenide family exhibits the strongest electron correlations. To gauge the correlation strength, we performed a systematic angle-resolved photoemission spectroscopy study on the iron chalcogenide series Fe1+ySexTe1-x, a model system with the simplest structure. Our measurement reveals an incoherent-to-coherent crossover in the electronic structure as the selenium ratio increases and the system evolves from a weakly localized to a more itinerant state. Furthermore, we found that the effective mass of bands dominated by the dxy orbital character significantly decreases with increasing selenium ratio, as compared to the dxz/dyz orbital-dominated bands. The orbital-dependent change in the correlation level agrees with theoretical calculations on the band structure renormalization, and may help to understand the onset of superconductivity in Fe1+ySexTe1-x.

This report describes the analytical models Lawrence Berkeley National Laboratory developed to estimate impacts of the U.S. Environmental Protection Agency’s WaterSense® labeling program. The models assess national impacts for WaterSense labeled toilets, faucets, faucet aerators, showerheads, flushing urinals, commercial pre-rinse spray valves, and weather or soil moisture sensor-based irrigation controllers by analyzing national inputs for water use in residential and commercial/institutional markets. For irrigation controllers, LBNL’s methodology also incorporates a scenario that evaluates impacts in three key large states that are considered to be the principal market for “smart” irrigation controllers: California, Florida, and Texas. The models estimate impacts for the water savings attributable to the program and the net present value of the lifetime water savings from more efficient products.

© The Author 2017.Topological Weyl semimetal, a new state of quantum matter, has sparked enormous research interest recently. Possessing unique Weyl fermions in the bulk and Fermi arcs on the surface, TWSs offer a rare platform for realizing many exotic physical phenomena. TWSs can be classified into type-I that respect Lorentz symmetry and type-II that do not. Here, we directly visualize the electronic structure of MoTe 2, a recently proposed type-II TWS. Using angle-resolved photoemission spectroscopy, we unravel the unique surface Fermi arcs, in good agreement with our ab initio calculations that have nontrivial topological nature. Our work not only leads to new understandings of the unusual properties discovered in this family of compounds, but also allows for the further exploration of exotic properties and practical applications of type-II TWSs, as well as the interplay between superconductivity and their topological order.

© 2016 American Chemical Society.Layered transition metal chalcogenides with large spin orbit coupling have recently sparked much interest due to their potential applications for electronic, optoelectronic, spintronics, and valleytronics. However, most current understanding of the electronic structure near band valleys in momentum space is based on either theoretical investigations or optical measurements, leaving the detailed band structure elusive. For example, the exact position of the conduction band valley of bulk MoS2 remains controversial. Here, using angle-resolved photoemission spectroscopy with submicron spatial resolution, we systematically imaged the conduction/valence band structure evolution across representative chalcogenides MoS2, WS2, and WSe2, as well as the thickness dependent electronic structure from bulk to the monolayer limit. These results establish a solid basis to understand the underlying valley physics of these materials, and also provide a link between chalcogenide electronic band structure and their physical properties for potential valleytronics applications.

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimSuperconductivity in monolayer niobium diselenide on bilayer graphene is studied by electrical transport. Monolayer NbSe2 is grown on bilayer graphene by molecular beam epitaxy and capped with a selenium film to avoid degradation in air. The selenium capped samples have TC = 1.9 K. In situ measurements down to 4 K in ultrahigh vacuum show that the effect of the selenium layer on the transport is negligible. The superconducting transition and upper critical fields in air exposed and selenium capped samples are compared. Schematic of monolayer NbSe2/bilayer graphene with selenium capping layer and electrical contacts.

© 2016 American Chemical Society.High quality WSe2 films have been grown on bilayer graphene with layer-by-layer control of thickness using molecular beam epitaxy. The combination of angle-resolved photoemission, scanning tunneling microscopy/spectroscopy, and optical absorption measurements reveal the atomic and electronic structures evolution and optical response of WSe2/BLG. We observe that a bilayer of WSe2 is a direct bandgap semiconductor, when integrated in a BLG-based heterostructure, thus shifting the direct-indirect band gap crossover to trilayer WSe2. In the monolayer limit, WSe2 shows a spin-splitting of 475 meV in the valence band at the K point, the largest value observed among all the MX2 materials. The exciton binding energy of monolayer-WSe2/BLG is found to be 0.21 eV, a value that is orders of magnitude larger than that of conventional three-dimensional semiconductors, yet small as compared to other two-dimensional transition metal dichalcogennides semiconductors. Finally, our finding regarding the overall modification of the electronic structure by an alkali metal surface electron doping opens a route to further control the electronic properties of TMDCs.

© 2016 Macmillan Publishers Limited.Layered transition metal dichalcogenides are ideal systems for exploring the effects of dimensionality on correlated electronic phases such as charge density wave order and superconductivity. In bulk NbSe 2 a CDW sets in at T CDW = 33 K and superconductivity sets in at T c = 7.2 K. Below T c these electronic states coexist but their microscopic formation mechanisms remain controversial. Here we present an electronic characterization study of a single two-dimensional layer of NbSe 2 by means of low-temperature scanning tunnelling microscopy/spectroscopy, angle-resolved photoemission spectroscopy, and electrical transport measurements. We demonstrate that 3 × 3 CDW order in NbSe 2 remains intact in two dimensions. Superconductivity also still remains in the 2D limit, but its onset temperature is depressed to 1.9 K. Our STS measurements at 5 K reveal a CDW gap of= 4 meV at the Fermi energy, which is accessible by means of STS owing to the removal of bands crossing the Fermi level for a single layer. Our observations are consistent with the simplified electronic structure of single-layer NbSe 2, thus providing insight into CDW formation and superconductivity in this model strongly correlated system.

Travelling internationally to acquire medical treatments otherwise unavailable or inaccessible in one’s home country is not a novel concept. Conventionally, such medical travel largely entailed patients from developed countries or wealthy patients from the developing world seeking care in Western facilities like the Mayo Clinic in the U.S. and myriad private clinics along Harley Street in London, England. What is different about the topical phenomenon known as “medical tourism” is the growing trend of health services export in the opposite direction. The number of patients travelling from the developed world to low- and middle-income countries for treatments has ballooned in recent years, primarily driven by difficulties with accessing affordable care at home. According to a liberal estimate by the Deloitte Center for Health Solutions, the number of Americans travelling abroad for care rose from 750,000 in 2007 to 1.6 million in 2012. On the flip side, Thailand reportedly treated a total of 1.3 million foreign nationals in 2007, which represented a 16% leap from 2001.

Venneman and colleagues argue that “do not resuscitate” (DNR) is problematic and should be replaced by “allow natural death” (AND). Their argument is flawed. First, while end-of-life discussions should be as positive as possible, they cannot and should not sidestep painful but necessary confrontations with morality. Second, while DNR can indeed be nonspecific and confusing, AND merely replaces one problematic term with another. Finally, the study’s results are not generalisable to the populations of physicians and working nurses and certainly do not support the authors’ claim that there is a movement to replace DNR with AND.

Background: Although ethics consultation has been introduced to clinical practice for many years, the results of empirical studies to evaluate the effectiveness of ethics consultation are still controversial. The design of randomised controlled trials is considered the best research design to evaluate the effect of a clinical practice on the outcomes of interests. In order to understand the effects of ethics consultation, we conducted this search for studies with the design of randomised controlled trials to evaluate ethics consultation.Objective: To provide an integrated review of studies with the design of randomised controlled trials to evaluate the effectiveness of ethics consultation.Methods: PubMed was used to search for studies using the randomised controlled trial design to evaluate the effectiveness of ethics consultation. The search term used was “ethics consultation”. The selection criterion was limited to “randomised controlled trial”.Results: Four articles that met both search criteria were retrieved. One of these articles reported a study that did not actually use the design of a randomised controlled trial and is excluded from the following discussion.Conclusions: To apply randomised controlled trials to evaluate the effectiveness of ethics consultation is extremely difficult as long as two issues are not resolved: the standardisation of ethics consultation and a placebo for ethics consultation to eliminate the placebo effect. Thus, the results generated by the design of randomised controlled trials are always problematic. Furthermore, as long as the two issues exist, the results generated by the design of quantitative research methods always pose problems