Crystalline Electric Field and Kondo Effect in SmOs4Sb12

Our ultrasound results obtained in pulsed magnetic fields show that the filled-skutterudite compound SmOs$_4$Sb$_{12}$ has the $\Gamma_{67}$ quartet crystalline-electric-field ground state. This fact suggests that the multipolar degrees of freedom of the $\Gamma_{67}$ quartet play an important role in the unusual physical properties of this material. On the other hand, the elastic response below $\approx$ 20 T cannot be explained using the localized 4$f$-electron model, which does not take into account the Kondo effect or ferromagnetic ordering. The analysis result suggests the presence of a Kondo-like screened state at low magnetic fields and its suppression at high magnetic fields above 20 T even at low temperatures.Comment: 4 pages, 4 figure

Magnetoelectric effect and phase transitions in CuO in external magnetic fields

Apart from being so far the only known binary multiferroic compound, CuO has a much higher transition temperature into the multiferroic state, 230 K, than any other known material in which the electric polarization is induced by spontaneous magnetic order, typically lower than 100 K. Although the magnetically induced ferroelectricity of CuO is firmly established, no magnetoelectric effect has been observed so far as direct crosstalk between bulk magnetization and electric polarization counterparts. Here we demonstrate that high magnetic fields of about 50 T are able to suppress the helical modulation of the spins in the multiferroic phase and dramatically affect the electric polarization. Furthermore, just below the spontaneous transition from commensurate (paraelectric) to incommensurate (ferroelectric) structures at 213 K, even modest magnetic fields induce a transition into the incommensurate structure and then suppress it at higher field. Thus, remarkable hidden magnetoelectric features are uncovered, establishing CuO as prototype multiferroic with abundance of competitive magnetic interactions.Comment: 26 pages, 5 figure

Magnetoelectric effect and phase transitions in CuO in external magnetic fields

Apart from being so far the only known binary multiferroic compound, CuO has a much higher transition temperature into the multiferroic state, 230 K, than any other known material in which the electric polarization is induced by spontaneous magnetic order, typically lower than 100 K. Although the magnetically induced ferroelectricity of CuO is firmly established, no magnetoelectric effect has been observed so far as direct crosstalk between bulk magnetization and electric polarization counterparts. Here we demonstrate that high magnetic fields of E50 T are able to suppress the helical modulation of the spins in the multiferroic phase and dramatically affect the electric polarization. Furthermore, just below the spontaneous transition from commensurate (paraelectric) to incommensurate (ferroelectric) structures at 213 K, even modest magnetic fields induce a transition into the incommensurate structure and then suppress it at higher field. Thus, remarkable hidden magnetoelectric features are uncovered, establishing CuO as prototype multiferroic with abundance of competitive magnetic interactions

An adiabatic silica taper based on two sequential tapering routines

Microfiber-based devices have a great potential in many applications due to their extraordinary optical and mechanical properties. An adiabatic silica-based taper is required for most of the applications and thus, adiabaticity criterion has to be estimated and satisfied to avoid high optical loss emerging when taper’s profile is not controlled properly. This requires obtaining propagation constants via solving boundary condition problem at each position along the taper. Yet, this procedure involves intensive computational and time-consuming solving of complex Maxwell vector equations. This paper proposed an efficient method to model the taper profile, evaluate the adiabaticity and simulate it using Finite Element Analysis software. The model facilitates design phase and optimize fabrication process for any fiber-based device. A slow gradual radius reduction rates can guarantee adiabatic profiles with the expense of longer transition sections. In miniature devices, such as sensors and micro-resonators, transition regions are preferable to be as short as possible while the narrow waist is preferred to be long and uniform. To balance between short transition preference and low loss condition, we proposed a design based on two tapering sequential routines. The simulation results confirmed our design adiabaticity. From the optical spectrum of the fabricated taper, it is found that the loss is less than 1dBm and the spectrum is not distorted

Relative humidity sensing using a PMMA doped Agarose gel microfiber

Humidity sensors rely on humidity-induced refractive index change in the sensing material despite the sensor configuration. Polymer-based microwires can absorb water vapor molecules and detect humidity changes without the need of further coating. However, the sensitivity-simplicity trade-off is still a challenge. Sophisticated coating methods, complex resonating structures and nano-structured films are reported as methods to enhance the device sensitivity. A simple technique, to build a high sensitivity RH sensor based on an agarose-doped Poly Methyl Methacrylate (PMMA) sensor head, is demonstrated. The waist diameter and uniform length of the PMMA doped agarose gel microfiber were measured to be 6 μm and 10 mm, respectively. The sensor can achieve power variation of up to 2.9μW in a wide relative humidity range (50-80%), and display linear response with a correlation coefficient of 98.29 %, sensitivity of 0.421 dB/%RH and resolution of 0.431%RH. This agarose-based optical sensor provides a beneficial complement to the existing electrical ones, and will promote the employment of agarose in chemical sensing techniques

Large-scale analysis of whole genome sequencing data from formalin-fixed paraffin-embedded cancer specimens demonstrates preservation of clinical utility

Whole genome sequencing (WGS) provides comprehensive, individualised cancer genomic information. However, routine tumour biopsies are formalin-fixed and paraffin-embedded (FFPE), damaging DNA, historically limiting their use in WGS. Here we analyse FFPE cancer WGS datasets from England’s 100,000 Genomes Project, comparing 578 FFPE samples with 11,014 fresh frozen (FF) samples across multiple tumour types. We use an approach that characterises rather than discards artefacts. We identify three artefactual signatures, including one known (SBS57) and two previously uncharacterised (SBS FFPE, ID FFPE), and develop an “FFPEImpact” score that quantifies sample artefacts. Despite inferior sequencing quality, FFPE-derived data identifies clinically-actionable variants, mutational signatures and permits algorithmic stratification. Matched FF/FFPE validation cohorts shows good concordance while acknowledging SBS, ID and copy-number artefacts. While FF-derived WGS data remains the gold standard, FFPE-samples can be used for WGS if required, using analytical advancements developed here, potentially democratising whole cancer genomics to many

Elektronenspinresonanz an niedrigdimensionalen Spinketten und Metallen

In this work, detailed multi-frequency X-band (9.5 GHz), Q-band (34 GHz) and W-band (95 GHz) electron spin resonance (ESR) investigations of the quasi one-dimensional organic spin chain (TMTTF)2X (X = ReO4, AsF6 and SbF6) are performed in order to explore the spin and charge ordered state and to specify the nature of the relaxation processes. Furthermore, transport, SQUID and X-band ESR measurements of the alloyed series kappa-(BEDT-TTF)2Cu[N(CN)2]BrxCl1-x are carried out to study the phase diagram in the vicinity of the Mott-Hubbard transition as a function of the Bromine content (x). The temperature dependence of the spin susceptibility at constant volume for T > 160 K of (TMTTF)2ReO4 can be modeled using the theoretical models of Bonner and Fisher, and Eggert, Affleck and Takahashi (EAT-model) S = 1/2 antiferromagnetic spin chain. Using these models, the AFM exchange constant |J| is found to be 425 K. In the paramagnetic state, a nearly linear decrease of the linewidth with decreasing temperatures down to the anion ordering transition temperature (TAO = 157 K) is observed. At TAO a step-like decrease in the linewidth is observed, followed by an increase of the linewidth with decreasing temperature. Additionally, the spin susceptibility decreases exponentially by lowering the temperature down to 120 K where the ESR spectra vanished. This decrease in the susceptibility corresponds to spin-singlet ground state. The spin susceptibility in this region is described by an activated law. The calculated singlet-triplet spin gap in the anion ordered state is delta = 1100 K. This huge gap is attributed to a strong charge disproportionation in the AO state. The temperature dependence of the linewidth and the g-value of (TMTTF)2AsF6 and (TMTTF)2SbF6 along the three principle magnetic axes were frequency independent. The angular dependence ESR linewidth in a-b plane in the charge ordered state for both compounds showed a doubling in the periodicity with a maximum along the 45 degree and 135 degree directions. The enhanced linewidth along 45 degree in a-b plane at different temperatures below TCO shows a quadratic frequency dependence which is characteristic for anisotropic Zeeman interaction, this indicates that the charge ordering transition in both compounds results in two inequivalent magnetic sites. The dc resistivity of kappa-(BEDT-TTF)2Cu[N(CN)2]BrxCl1-x shows semi-conductor like behaviour in the temperature range 300 K - 100 K. Below 100 K the resistivity strongly depends on the Br/C ratio. For x 0.7, a broad maximum in the resistivity occurs at around 80 - 100 K, and at lower temperatures the samples become metallic down to the superconducting transition temperature (Tc = 12 K). In the metallic regime (12K>T>30K) the resistivity in the superconducting samples shows a quadratic temperature dependence in agreement with Fermi liquid theory. The temperature dependence of the ESR linewidth for all Br dopings is approximately identical. The linewidth increases from room temperature with decreasing temperature, reaches a broad maximum around 60 - 80 K, then decreases sharply down to low temperature. The broadening mechanism of the linewidth is attributed to the scattering of the conduction electrons caused by vibrations of the terminal ethylene groups of the BEDT-TTF molecules. The g-value along both directions in all compounds is temperature independent in the whole temperature range with weak anomalies at low temperatures due to the change of the internal magnetic field associated with the antiferromagnetic or superconducting phase transitions. For all x, the temperature dependence of the spin susceptibility is nearly temperature independent at high temperatures (T > 100 K) as expected for the Pauli susceptibility of metals. In the superconducting samples, the spin susceptibility below 100 K decreases with decreasing temperature with a sharp drop at 50 K down to 8 K. This is attributed to the reduction of the density of states at Fermi surface induced by the vibrations of the terminal ethylene groups. The temperature dependence of the spin susceptibility in the superconducting samples is fitted using the double gap model. Our dc, SQUID and ESR results enabled as to map the critical temperatures of the metal-to-insulator, antiferromagnetic and superconducting transitions into the phase diagram for different Br dopings. The temperature/Br concentration phase diagram shows that kappa-(BEDT-TTF)2Cu[N(CN)2]BrxCl1-x serves as a model system for a bandwidth controlled Mott-Hubbard transition.Im Rahmen der vorliegenden Arbeit wurden ausführliche Multifrequenz X-Band (9.5 GHz), Q-Band (34 GHz) and W-Band (95 GHz) Elektronenspinresonanz (ESR) Untersuchungen an den quasi eindimensionalen organischen Spinketten (TMTTF)2X (X = ReO4, AsF6 and SbF6) durchgeführt, um den spin- und ladungsgeordneten Zustand zu untersuchen und die Natur der Relexationsprozesse bestimmen zu können. Des Weiteren wurden während dieser Doktorarbeit Transport-, SQUID und X-Band ESR-Messungen an der Verbindungsserie kappa-(BEDT-TTF)2Cu[N(CN)2]BrxCl1-x ausgeführt, um das Phasendiagramm in der Nähe des Mott-Hubbard-Überganges in Abhängigkeit des Bromgehaltes (x) zu untersuchen. Die Temperaturabhängigkeit der Spin-Suszeptibilität bei konstanten Volumen von (TMTTF)2ReO4 kann bei Temperaturen T>160K durch die theoretischen Modelle von Bonner und Fisher bzw. Eggert, Affleck und Takahashi für antiferromagnetische (AFM) S =1/2 Spinketten beschrieben werden. Unter Verwendung dieser Modelle ergibt sich für die AFM Austauschwechselwirkung |J| ein Wert von 425K. Im paramagnetischen Zustand, wird ein nahezu linearer Abfall der Linienbreite für sinkende Temperaturen bis hin zum Anionen-Ordungs-Übergang bei TAO=157K beobachtet. Bei TAO wird ein stufenartiger Abfall der Linienbreite beobachtet, auf welchen ein Anstieg der Linienbreite für fallende Temperaturen folgt. Des Weiteren, sinkt die Spin-Suszeptibilität exponentiell für fallende Temperaturen bis 120K, wo das ESR-Spektrum schließlich vollständig verschwindet. Dieser Abfall der Spin-Suszeptibilität entspricht dem Entstehen eines Spin-Singulett Grundzustand und lässt sich in diesem Temperaturbereich durch thermisch aktiviertes Verhalten beschreiben. Für die Anregungsenergie des Spin-Triplett-Zustands im anionen- geordneten Zustand ergibt sich mit obiger Anpassung delta=1100K. Diese sehr große Anregungsenergie ist auf eine deutliche Ladungsungleichverteilung in dem AO Zustand zurückzuführen. Die temperaturabhängige Linienbreite und der g-Wert von (TMTTF)2AsF6 und (TMTTF)2SbF6 entlang der drei magnetischen Hauptachsen sind frequenzunabhängig. Unterhalb der Ladungsordnungstemperatur TCO und in der ab’-Ebene zeigen sowohl die Q- und W-Band als auch die X-Band Linienbreite für beide Verbindungen eine vergleichbare Winkelabhängigkeit, das Maximum befindet sich nicht entlang einer der Kristallrichtungen, sondern entlang der Diagonalen zwischen a und b' Richtung. Für Temperaturen unterhalb von TCO zeigt die Linienbreite entlang dieser Diagonalen eine quadratische Frequenzabhängigkeit. Dieses Ergebnis deutet auf die anisotrope Zeeman-Wechselwirkung als Relaxationsprozess hin. Unterhalb des Ladungsordnungs-Überganges liegen somit zwei magnetisch nicht äquivalente Gitterplätze vor. DC-Widerstandsmessungen an Einkristallen der Verbindungsserie kappa-(BEDT-TTF)2Cu[N(CN)2]BrxCl1-x zeigen im Temperaturbereich zwischen 300K und 100 K zeigen die typische Temperaturabhängigkeit eines Halbleiters. Eine deutliche Abhängigkeit des spezifischen Widerstandes vom Br/Cl-Verhältnis tritt beim Abkühlen der Proben unter 100K auf. Die Kristalle mit x 0.7 tritt im Bereich 80-100K ein breites Maximum auf. Für niedrigere Temperaturen ist der Widerstandsverlauf, bis hin zum starken Abfall beim Eintritt in die Supraleitung bei Tc = 12K, der eines Metalls. Die supraleitenden Proben zeigen hier zwischen 12 K und 30 K eine quadratische Temperaturabhängigkeit in Einklang mit Fermi-Flüssigkeit Theorie. Die Temperaturabhängigkeit der ESR-Linienbreite für alle Bromkonzentrationen ist nahezu identisch. Ausgehend von 300K steigt die Linienbreite für abnehmende Temperaturen an, erreicht ein breites Maximum bei 60 - 80K und fällt anschließend für tiefe Temperaturen stark ab. Die Linienverbreiterung wird durch die Streuung der Leitungselektronen an den Vibrationen der Ethylen-Endgruppen der BEDT-TTF Molekülen verursacht. Für alle Bromkonzentrationen x, ist die Spinsuszeptibilität im Temperaturbereich 300K - 100K nahezu temperaturunabhängig, passend zur Pauli Spinsuszeptibilität eines Metalls. Für x = oder > 0.7 nimmt die Suszeptibilität unterhalb von 100K mit der Temperatur ab und fällt von 50 K bis hin zu 8K stark ab. Im Allgemeinen wird die Reduktion der Suszeptibilität bei niedrigen Temperaturen der geringeren Zustandsdichte an der Fermikante zugeschrieben, welche durch die Vibrationen der Ethylene-Endgruppen verursacht wird. Die Ergebnisse der vorliegenden Arbeit ermöglichen die Darstellung der kritischen Temperaturen des Metall-Isolator-Überganges und der Phasenübergänge in den antiferromagnetischen bzw. supraleitenden Zustand für die verschiedenen Bromkonzentrationen in einem Phasendiagramm

Efficiency boost of CZTS solar cells based on double-absorber architecture: Device modeling and analysis

In this study, we present a new alternative approach that utilizes Si as a second absorber along with the primary CZTS absorber to improve all photovoltaics performance parameters for CZTS based thin-film solar cell devices. The proposed ZnO:Al/CdS/CZTS/Si/Mo with a double-absorber hybrid structure has been extensively investigated and analyzed by employing the SCAPS-1D simulation package. Initial direct integration of a thin Si layer with thickness as low as 200 nm between the Mo back-contact and the primary CZTS active layer has resulted in a significant efficiency boost of 16.32%. Further optimization of several material parameters such as thickness, bandgap energy, and doping concentration for both absorbers have resulted in additional enhancement of many photovoltaic performance parameters such as the FF, Jsc, Voc, and PCE. The correlation study between the two absorbers suggests that maximum efficiency of 19.40%, FF of 88.54%, Voc of 0.84 V and JSC of 27.55 mA/cm2 can be attained at absorbers thicknesses of about 2 µm and high doping level up to 1018 cm−3. This can be attributed to the generation of more charge carriers with the increase of absorbers thicknesses. Additionally, the proposed model shows a stable performance with the rise of the operating temperature up to 350 K. Adding Si layer to the cell structure has resulted in pronounced quantum efficiency (QE) improvement due to the increase of solar spectrum absorption at longer wavelengths. A significant improvement in I-V characteristics was also detected with the decrease of the double-absorber structure\u27s series resistance compared to the conventional single-absorber CZTS structure. The outcomes of this study represent a promising solution toward the fabrication of high-performance and cost-effective thin CZTS solar cell devices

Γ3-type Lattice Instability and the Hidden Order of URu2Si2

We have performed ultrasonic measurements on single-crystalline URu2Si2 with pulsed magnetic fields, in order to check for possible lattice instabilities due to the hybridized state and the hidden-order state of this compound. The elastic constant (C11-C12)/2, which is associated with a response to the Γ3-type symmetry-breaking (orthorhombic) strain field, shows a three-step increase at H 35 T for H k c at low temperatures, where successive meta-magnetic transitions are observed in the magnetization. We discovered a new fact that the absolute change of the softening of (C11-C12)/2 in the temperature dependence is quantitatively recovered at the suppression of hybridized-electronic state and the hidden order in high-magnetic field for H k c associated with the successive transitions. The present results suggest that the Γ3-type lattice instability, is related to both the emergence of the hybridized electronic state and the hidden-order parameter of URu2Si2. On the other hand, magnetic fields H k [100] and [110] enhance the softening of (C11-C12)/2 in the hidden order phase, while no step-like anomaly is observed up to 68.7 T.We discuss the limitation of the localized-electron picture for describing these features of URu2Si2 by examination of a crystalline electric field model in terms of mean-field theory