Use of frit-disc crucibles for routine and exploratory solution growth of single crystalline samples

Solution growth of single crystals from high temperature solutions often involves the separation of residual solution from the grown crystals. For many growths of intermetallic compounds, this separation has historically been achieved with the use of plugs of silica wool. Whereas this is generally efficient in a mechanical sense, it leads to a significant contamination of the decanted liquid with silica fibers. In this paper we present a simple design for frit-disc alumina crucible sets that has made their use in the growth single crystals from high temperature solutions both simple and affordable. An alumina frit-disc allows for the clean separation of the residual liquid from the solid phase. This allows for the reuse of the decanted liquid, either for further growth of the same phase, or for subsequent growth of other, related phases. In this paper we provide examples of the growth of isotopically substituted TbCd$_{6}$ and icosahedral i-$R$Cd quasicrystals, as well as the separation of (i) the closely related Bi$_{2}$Rh$_{3}$S$_{2}$ and Bi$_{2}$Rh$_{3.5}$S$_{2}$ phases and (ii) PrZn$_{11}$ and Pr$_{2}$Zn$_{17}$.Comment: submitted to Philosophical Magazin

Three-dimensionality of the bulk electronic structure in WTe2

We use temperature- and field-dependent resistivity measurements [Shubnikov--de Haas (SdH) quantum oscillations] and ultrahigh resolution, tunable, vacuum ultraviolet (VUV) laser-based angle-resolved photoemission spectroscopy (ARPES) to study the three-dimensionality (3D) of the bulk electronic structure in WTe2, a type-II Weyl semimetal. The bulk Fermi surface (FS) consists of two pairs of electron pockets and two pairs of hole pockets along the X-Gamma-X direction as detected by using an incident photon energy of 6.7 eV, which is consistent with the previously reported data. However, if using an incident photon energy of 6.36 eV, another pair of tiny electron pockets is detected on both sides of the Gamma point, which is in agreement with the small quantum oscillation frequency peak observed in the magnetoresistance. Therefore, the bulk, 3D FS consists of three pairs of electron pockets and two pairs of hole pockets in total. With the ability of fine tuning the incident photon energy, we demonstrate the strong three-dimensionality of the bulk electronic structure in WTe2. The combination of resistivity and ARPES measurements reveal the complete, and consistent, picture of the bulk electronic structure of this material.Comment: 6 pages, 3 figure

Photometric defocus observations of transiting extrasolar planets

We have carried out photometric follow-up observations of bright transiting extrasolar planets using the CbNUOJ 0.6m telescope. We have tested the possibility of obtaining high photometric precision by applying the telescope defocus technique allowing the use of several hundred seconds in exposure time for a single measurement. We demonstrate that this technique is capable of obtaining a root-mean-square scatter of order sub-millimagnitude over several hours for a V $\sim$ 10 host star typical for transiting planets detected from ground-based survey facilities. We compare our results with transit observations with the telescope operated in in-focus mode. High photometric precision is obtained due to the collection of a larger amount of photons resulting in a higher signal compared to other random and systematic noise sources. Accurate telescope tracking is likely to further contribute to lowering systematic noise by probing the same pixels on the CCD. Furthermore, a longer exposure time helps reducing the effect of scintillation noise which otherwise has a significant effect for small-aperture telescopes operated in in-focus mode. Finally we present the results of modelling four light-curves for which a root-mean-square scatter of 0.70 to 2.3 milli-magnitudes have been achieved.Comment: 12 pages, 11 figures, 5 tables. Submitted to Journal of Astronomy and Space Sciences (JASS

Observation of Fermi Arcs in Type-II Weyl Semimetal Candidate WTe2

We use ultrahigh resolution, tunable, vacuum ultraviolet laser angle-resolved photoemission spectroscopy (ARPES) to study the electronic properties of WTe$_2$, a material that was predicted to be a type-II Weyl semimetal. The Weyl fermion states in WTe2 were proposed to emerge at the crossing points of electron and hole pockets; and Fermi arcs connecting electron and hole pockets would be visible in the spectral function on (001) surface. Here we report the observation of such Fermi arcs in WTe2 confirming the theoretical predictions. This provides strong evidence for type-II Weyl semimetallic states in WTe2.Comment: 5 pages, 4 figure

Tuning of layered materials: Studies of CrAuTe4, PdSn4 and WTe2

Layered materials are of great and growing interest for material scientists and condensed matter physicists, not only because of their possible applications but also because of the diverse and controllable ground states. In addition, tuning of layered materials through external fields, doping, or strain can lead to the emergence of novel phenomena. In this dissertation, the importance of the study of layered materials is emphasized in Chapter 1. Before getting into experimental results, the theoretical background and experimental methods, including growth of single crystals of selected layered materials, are introduced in Chapter 2 and Chapter 3. Chapters 4, 5 and 6 are devoted to experimental results on selected layered materials. Chapter 4 presents the physical properties of CrAuTe4 at ambient pressure and the tuning of its properties using hydrostatic pressure. The physical properties of PdSn4 are shown in Chapter 5, and then the origin of extremely large magnetoresistance in this material is discussed in comparison/contrast to the physical properties of PtSn4. Chapter 6 focuses on the tuning of the physical properties of WTe2 using temperature, magnetic field and uniaxial strain. In appendix A, I list all the growth attempts regarding Te and Se containing materials. In appendix B, I explain the growth of single crystal, EuCd2As2, using salt (NaCl/KCl) as a solution. In appendix C, I summarize other publications during my Ph.D. years

An assessment of quality of care service provided to people living with HIV/AIDS by a secondary healthcare centre at Osogbo, Nigeria

Objective: The objective of this study was to assess the quality of service provided to people living with human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS) at a secondary healthcare centre at Osogbo, Nigeria.Design: Descriptive cross-sectional study design.Setting and subjects: People living with HIV/AIDS (PLWHA) at the State Hospital, Osogbo, Nigeria.Outcome measures: Quality of the services rendered to PLWHA.Results: A total of 304 PLWHA were interviewed. Their ages ranged from 16-60 years, with a mean age of 35.5 ± 8.8 years. There were 212 (69.7%) female and 92 (30.3%) male respondents, 248 (81.6%) were married and 108 (35.5%) had a tertiary education. Approximately half (148, 48.7%) rated the quality of the services rendered to them at the hospital as excellent, 132 (43.4%) rated it as good, and 24 (7.9%) as fair. None rated the services rendered as poor or very poor.Conclusion: The results of this study showed a good relationship between PLWHA and healthcare workers in general. Education, training and re-training of the health workers should be an ongoing exercise.Keywords: people living with HIV/AIDS, healthcare workers, quality of health care, quality of service, Osogbo,Nigeri

Temperature induced Lifshitz transition in WTe2

We use ultra-high resolution, tunable, VUV laser-based, angle-resolved photoemission spectroscopy (ARPES) and temperature and field dependent resistivity and thermoelectric power (TEP) measurements to study the electronic properties of WTe2, a compound that manifests exceptionally large, temperature dependent magnetoresistance. The temperature dependence of the TEP shows a change of slope at T=175 K and the Kohler rule breaks down above 70-140 K range. The Fermi surface consists of two electron pockets and two pairs of hole pockets along the X-Gamma-X direction. Upon increase of temperature from 40K, the hole pockets gradually sink below the chemical potential. Like BaFe2As2, WTe2 has clear and substantial changes in its Fermi surface driven by modest changes in temperature. In WTe2, this leads to a rare example of temperature induced Lifshitz transition, associated with the complete disappearance of the hole pockets. These dramatic changes of the electronic structure naturally explain unusual features of the transport data.Comment: 5 pages, 3 figure