Gapped ground state in the zigzag pseudospin-1/2 quantum antiferromagnetic chain compound PrTiNbO6

We report a single-crystal study on the magnetism of the rare-earth compound PrTiNbO$_6$ that experimentally realizes the zigzag pseudospin-$\frac{1}{2}$ quantum antiferromagnetic chain model. Random crystal electric field caused by the site mixing between non-magnetic Ti$^{4+}$ and Nb$^{5+}$, results in the non-Kramers ground state quasi-doublet of Pr$^{3+}$ with the effective pseudospin-$\frac{1}{2}$ Ising moment. Despite the antiferromagnetic intersite coupling of about 4 K, no magnetic freezing is detected down to 0.1 K, whilst the system approaches its ground state with almost zero residual spin entropy. At low temperatures, a sizable gap of about 1 K is observed in zero field. We ascribe this gap to off-diagonal anisotropy terms in the pseudospin Hamiltonian, and argue that rare-earth oxides open an interesting venue for studying magnetism of quantum spin chains.Comment: 11 pages, 10 figures, 1D correlated magnetism of non-Kramers Ising quasi-doublets in PrTiNbO

Magnetic and structural quantum phase transitions in CeCu6-xAux are independent

The heavy-fermion compound CeCu$_{6-x}$Au$_x$ has become a model system for unconventional magnetic quantum criticality. For small Au concentrations $0 \leq x < 0.16$, the compound undergoes a structural transition from orthorhombic to monoclinic crystal symmetry at a temperature $T_{s}$ with $T_{s} \rightarrow 0$ for $x \approx 0.15$. Antiferromagnetic order sets in close to $x \approx 0.1$. To shed light on the interplay between quantum critical magnetic and structural fluctuations we performed neutron-scattering and thermodynamic measurements on samples with $0 \leq x\leq 0.3$. The resulting phase diagram shows that the antiferromagnetic and monoclinic phase coexist in a tiny Au concentration range between $x\approx 0.1$ and $0.15$. The application of hydrostatic and chemical pressure allows to clearly separate the transitions from each other and to explore a possible effect of the structural transition on the magnetic quantum critical behavior. Our measurements demonstrate that at low temperatures the unconventional quantum criticality exclusively arises from magnetic fluctuations and is not affected by the monoclinic distortion.Comment: 5 pages, 3 figure

Gapless spin-liquid state in the structurally disorder-free triangular antiferromagnet NaYbO2_2

We present the structural characterization and low-temperature magnetism of the triangular-lattice delafossite NaYbO$_2$. Synchrotron x-ray diffraction and neutron scattering exclude both structural disorder and crystal-electric-field randomness, whereas heat-capacity measurements and muon spectroscopy reveal the absence of magnetic order and persistent spin dynamics down to at least 70\,mK. Continuous magnetic excitations with the low-energy spectral weight accumulating at the $K$-point of the Brillouin zone indicate the formation of a novel spin-liquid phase in a triangular antiferromagnet. This phase is gapless and shows a non-trivial evolution of the low-temperature specific heat. Our work demonstrates that NaYbO$_2$ practically gives the most direct experimental access to the spin-liquid physics of triangular antiferromagnets.Comment: 6 pages, 4figure

A microstructured fiber with defined borosilicate regions to produce a radial micronozzle array for nanoelectrospray ionization

This work highlights the possibility of using microstructured fibres with predefined doped regions to produce functional microstructures at a fibre facet with differential chemical etching. A specially designed silica microstructured fibre (MSF) that possesses specific boron-doped silica regions was fabricated for the purpose of generating a radial micronozzle array. The MSF was drawn from a preform comprising pure silica capillaries surrounded by boron-doped silica rods. Different etching rates of the boron-doped and silica regions at the fiber facet produces raised nozzles where the silica capillaries were placed. Fabrication parameters were explored in relation to the fidelity and protrusion length of the nozzle. Using etching alone, the nozzle protrusion length was limited, and the inner diameter of the channels in the array is expanded. However with the addition of a protective water counter flow, nozzle protrusion is increased to 60 μm with a limited increase in hole diameter. The radial micronozzle array generated nine individual electrosprays which were characterized using spray current measurements and related to theoretical prediction. Signal enhancement for the higher charge state ions for two peptides showed a substantial signal enhancement compared to conventional emitter technology.Y. Fu, S. Morency, K. Bachus, D. Simon, T. Hutama, G. T. T. Gibson, Y. Messaddeq and R. D. Oleschu

Thermodynamic measurements on frustrated triangular and honeycomb lattices in the Millikelvin range

Frustrated magnets potentially host new phase of matters such as Quantum Spin Liquids (QSL). In contrast to conventional magnets, QSL do not show magnetic ordering even at 0K, and they have been suggested to be relevant for high-temperature superconductivity or fault-tolerant quantum computing. Therefore, it is one of the central tasks in solid state physics to synthesize a material exhibiting this peculiar phase. In general, the characterization of potential QSL candidate materials is extremely challenging because it requires temperatures as close as possible to 0K. In this thesis, several promising frustrated magnets on honeycomb and triangular lattices have been investigated in a He3/He4-dilution refrigerator. Thermodynamic measurements such as specific heat, magnetic Grüneisen parameter and magnetization have been performed over a broad temperature and magnetic field range down to 40mK and up to 15T. First, this thesis focuses on four different Yb{3+} based triangular lattice materials (YbMgGaO4, KYbS2, NaYbO2, KBaYb(BO3)2). None of these materials undergoes a magnetic phase transition down to the lowest accessible temperature, and potentially emerging QSL phases are discussed. The field-evolution turns out to be non-trivial in several materials and is investigated in detail for comparison with theoretical predictions on triangular lattices. Furthermore, a potential application of KBaYBb(BO3)2 for adiabatic demagnetization down to the 20mK has been shown. The second central part focuses on the Kitaev magnet alpha-RuCl3 on a honeycomb lattice, which shows zigzag magnetic order in zero field. However, a potential field-induced QSL has been vividly debated in the last years. In this thesis, measurements of the field-dependent magnetic Grüneisen parameter in combination with the specific heat has been applied to identify the phase transitions in this Kitaev material. The phase boundaries and the putative existence of a QSL in the phase diagram of alpha-RuCl3 is carefully discussed.In frustrierten Magneten können neuartige und exotische Phasen auftreten wie Quantenspinflüssigkeiten (Quantum Spin Liquids: QSL). Im Gegensatz zu konventionellen Magneten weisen QSL keine magnetische Ordnung auf, nicht einmal am absoluten Nullpunkt von 0K. Die Realisierung solch einer QSL in Festkörpern ist seit Jahrzehnten ein zentrales Unterfangen in der Festkörperphysik, unter anderem wegen ihrer möglichen Verbindung zu Hochtemperatursupraleitern oder fehlertoleranten Quantencomputern. Die Charakterisierung möglicher QSL Kandidaten ist extrem herausfordernd, da in der Regel Temperaturen möglichst nahe am absoluten Nullpunkt erforderlich sind. In der vorliegenden Arbeit wurden mehrere vielversprechende frustrierte Magnete, bei denen die magnetischen Momente auf einem Dreiecks- bzw einem Honigwabengitter angeordnet sind, in einem He3/He4-Entmischungskryostaten untersucht. Es wurden thermodynamische Messungen wie die spezifische Wärme, magnetischer Grüneisen Parameter und Magnetisierung in einem Temperaturbereich bis hinab zu 40mK in magnetischen Feldern bis zu 15T durchgeführt. Der Fokus liegt zunächst auf vier verschiedenen Yb{3+}-basierten Materialien auf einem Dreiecksgitter (YbMgGaO4, KYbS2, NaYbO2, KBaYb(BO3)2). Keines dieser Materialien weist einen Phasenübergang bis zu den tiefsten erreichbaren Temperaturen auf. In diesem Kontext werden potentielle QSL Phasen diskutiert. Einige der Materialien zeigen eine nicht-triviale Feldabhängigkeit, die im Detail untersucht und mit theoretischen Vorhersagen für zweidimensionale Dreiecksgitter verglichen wird. Zudem wird die mögliche Anwendung von KBaYb(BO3)2 im Bereich der adiabatischen Demagnetisierung bis hinab zu 20mK gezeigt. Der zweite Teil der Arbeit handelt vom Kitaev Magneten alpha-RuCl3 mit einem Honigwabengitter, der im Nullfeld einen magnetischen Phasenübergang zu einer geordneten Phase aufweist und somit keine QSL ist. Dennoch wurde in den letzten Jahren lebhafte Diskussionen über eine mögliche feldinduzierte QSL Phase in alpha-RuCl3 geführt. In der vorliegenden Arbeit werden Messungen des magnetischen Grüneisen Parameters an alpha-RuCl3 in Kombination mit der spezifischen Wärme präsentiert, um mögliche feldinduzierte Phasenübergänge zu identifizieren. Die Phasengrenzen sowie die vermeintliche Existenz einer QSL Phase im Phasendiagramm werden sorgfältig diskutiert

A Historical Analysis of the Socio-Economic Forces Which Shaped a Small Industrial Town in Arkansas

In 1887, bauxite, the ore of aluminum was discovered in Arkansas . State Geologist, John C. Branner, announced l the discovery in 1891. Reports soon reached the Pittsburgh Reduction Company in Pennsylvania. This young company investigated the report, purchased land in Saline County, and started mining operations. In 1903 the Pittsburgh Reduction Company built an ore - drying plant in Saline County, Arkansas. The establishment of this plant marked the beginning of the town of Bauxite. Laid out on company- owned land shortly after mining operations began, the town soon became a self- sufficient community with schools, churches, stores, roads, medical facilities, and utilities. All houses and buildings in Bauxite were company- owned and company-maintained, with the exception of the various church buildings and later the school facilities. Local ministers and company employees were the only occupants of the houses. Through sixty-four years of existence the town experienced many social and economic changes. These changes were the result of the expansion and development of the aluminum industry and subsequent company policy. By the nature of their situation, the residents of the company-owned town of Bauxite were unusually vulnerable to change. The purpose of this study was to determine the forces behind these changes and to discover the effects of such changes upon the community in general and upon individual family life in particular. Since all the inhabitants of the town were in the employ of the company, the market of aluminum and alumina products determined the prosperity and stability of the community. Specific periods of the growth and decline of the industry were considered in this study. These periods were defined generally as World War I, the depression years of the 1920\u27s and early 1930\u27s, World War II, and the years of industrial expansion after 1945

OVERCOMING SELF-OBJECTIFICATION THROUGH A MIND BODY AWARENESS PROGRAM

As previous communication scholars have noted, “In light of epidemic levels of self-objectification leading to a host of negative consequences for girls and women, intervention is crucial” (Kite, 2013, pg. III). The purpose of this MA project is to design and conduct a workshop to assist women in resisting self-objectification. The following literature review outlines the theoretical foundations for the project, as well as the most constructive interventions suggested by previous research. I will first review the literature on objectification and self-objectification, then examine the impacts of self-objectification on women. Next, I will discuss what the literature suggests as the most efficacious interventions to self-objectification and conclude with a detailed overview of my proposed workshop

Risk Assessment And Geographic Impact Of Virtual Power Purchase Agreements And Unbundled Renewable Energy Certificates On Greenhouse Gas Abatement

Fossil fuel-generated energy consumption via electricity purchased by organizations makes up much of worldwide greenhouse gas (GHG) emissions. Commercial and industrial users consume more than two-thirds of electricity. Companies with warehouses, offices, data centers, and other facilities that engage in industrial processes consume significant amounts of purchased energy to power their operations. Most organizations do not generate electricity or have operational control of their energy generation; instead, they purchase it from public utilities and other providers. Many organizations are making climate commitments to support the Paris Agreement’s Net-Zero pledge by reducing or offsetting their indirect “Scope 2” greenhouse emissions and promoting the development of more renewable energy and less dependency on fossil-fuel-generated electricity. Renewable energy infrastructure may or may not be available depending on the locations of organizations’ facilities. Understanding the risks and benefits of options such as virtual power purchase agreements and unbundled renewable energy certificates in pursuit of renewable energy is vital to corporations and renewable energy developers. Companies may also need to understand the impact of the location of a renewable energy project and whether it is a significant factor in abating greenhouse gas emissions. The research study assessed the risk of virtual power purchase agreements and unbundled renewable energy certificates. It also involved a case study that explored the impact and significance of the geographical locations of renewable energy on abating greenhouse gas emissions

A portable diagnostic tool for the absolute determination of photon fluxes in low pressure plasmas down to the VUV region

Plasmas allow a wide range of material modifications in order to optimize material properties for a specific purpose including etching processes in the semiconductor industry, generating functional layers via plasma enhanced chemical vapour deposition or sterilizing medical instruments and human skin, respectively. These examples illustrate the great number of plasma treatment processes which all use the different plasma species. Heavy particles (i.e. atoms, molecules, ions or radicals), electrons as well as photons produce a collective flux onto the material. The resulting effect depends both on the particular absolute fluxes and the energy of the impinging particle species. Photons cover a wide energy range from the infrared with energies below 1.8 eV to the vacuum ultraviolet region with a photon energy above 6.2 eV. Due to the high photon energy, VUV/UV photons might have a significant influence on the material. While the supply gas roughly sets the photons’ spectral distribution, the discharge’s operating parameters (e.g. pressure, input power) have an influence on the absolute fluxes as well as on the photon-to-ion flux ratios. Depending on the specific application, the photon-to-ion flux ratio might affect the process performance beneficially or adversely and can serve as tuning knob to optimize or to tailor a specific plasma setup. For this purpose, an energy resolved quantification of VUV/UV photon fluxes with respect to external operating parameters is essential. However, this claim implies great challenges regarding absolute in-situ wavelength resolved measurements down to the vacuum ultraviolet range for which large and expensive VUV spectrometers are commonly used. Due to their size, these instruments cannot be easily transported or applied at different setups. For the required absolute intensity calibration, radiation produced by electron storage rings serves as typical primary standard source below 116 nm which is associated with high efforts. To overcome these difficulties regarding VUV spectrometers, the recent years have shown a growing interest in transferrable VUV detectors. Wavelength resolution can be achieved by inserting spectral filters between the plasma and the detector. In this work, a portable diagnostic tool based on a VUV silicon diode and a set of bandpass and edge filters is developed. Its unique feature is the direct absolute calibration against an absolutely intensity calibrated VUV spectrometer. This calibration is performed both individually for each filter and specifically for a variety of supply gases. It directly includes the wavelength dependency of the filter transmission and the diode’s sensitivity as well as the viewing volume of the device. The absolute intensity calibration of the VUV spectrometer is performed in-house. It extends the standard method based on a deuterium arc lamp and branching ratios in nitrogen by applying a high current hollow cathode. Absolute scaling against an absolutely intensity calibrated optical spectrometer using a helium discharge leads to an absolute intensity calibration in the wavelength range between 46 nm and 300 nm. In order to compile appropriate filter sets for the VUV diode system, emission ranges of gases that are typically applied for process plasmas are investigated in pressure and power scans at the experimental setup PlanICE. These gases include the pure gases argon, hydrogen, nitrogen and oxygen as well as mixtures thereof in a pressure range between 0.3 Pa and 10 Pa. Emission ranges with relevant photon fluxes are identified with respect to the ion flux. The latter is determined using Langmuir probe measurements and an energy resolved mass spectrometer. Having selected appropriate filter sets, the diode system is absolutely calibrated in each gas and for each corresponding filter individually against the VUV spectrometer. Furthermore, a detailed characterization of the diode system is carried out regarding, inter alia, different performance aspects (e.g. reproducibility, linearity) and aging effects due to high energetic VUV radiation. It is complemented by extensive benchmark measurements at PlanICE using the VUV spectrometer and the optical spectrometer as reference. The diode system’s applicability as a portable, flexible and reliable VUV diagnostic tool is demonstrated at three different plasma experiments—the in-house laboratory setup ACCesS, the low pressure sterilization reactor PlasmaDecon at the Ruhr-Universität Bochum and the ion source of the Batman Upgrade test stand at the Max-Planck-Institut für Plasmaphysik (IPP, Garching)