In this study, via angular Shubnikov–de Haas (SdH) quantum oscillations measurements, we determine the Fermi surface topology of NbAs, a Weyl semimetal candidate. The SdH oscillations consist of two ...frequencies corresponding to two Fermi surface extrema: 20.8 T (α pocket) and 15.6 T (β pocket). The analysis, including a Landau fan plot, shows that the β pocket has a Berry phase of π and a small effective mass of ~ 0.033 m0, indicative of a nontrivial topology in momentum space, whereas the α pocket has a trivial Berry phase of 0 and a heavier effective mass of ~ 0.066 m0. From the effective mass and the β -pocket frequency, we determine that the Weyl node is 110.5 meV from the chemical potential. An electron-hole compensation effect is discussed in this system, and its impact on magnetotransport properties is addressed. Finally, the difference between NbAs and other monopnictide Weyl semimetals is also discussed.
Plutonium metal undergoes an anomalously large 25% collapse in volume from its largest volume δ phase (δ-Pu) to its low temperature α phase, yet the underlying thermodynamic mechanism has largely ...remained a mystery. Here we use magnetostriction measurements to isolate a previously hidden yet substantial electronic contribution to the entropy of δ-Pu, which we show to be crucial for the stabilization of this phase. The entropy originates from two competing instabilities of the 5f-electron shell, which we show to drive the volume of Pu in opposing directions, depending on the temperature and volume. Using calorimetry measurements, we establish a robust thermodynamic connection between the two excitation energies, the atomic volume, and the previously reported excess entropy of δ-Pu at elevated temperatures.
We present a detailed study of the low-temperature and high-magnetic-field phases in the chemical substitution series URu2Si2−xPx using electrical transport and magnetization in pulsed magnetic ...fields up to 65 T. Within the hidden-order x regime (0<x≲0.035) the field-induced ordering that was earlier seen for x = 0 is robust, even as the hidden-order temperature is suppressed. Earlier work shows that for 0.035≲x≲0.26 there is a Kondo lattice with a no-ordered state that is replaced by antiferromagnetism for 0.26≲x≲0.5. We observe a simplified continuation of the field-induced order in the no-order x regime and an enhancement of the field-induced order upon the destruction of the antiferromagnetism with magnetic field. These results closely resemble what is seen for URu2−xRhxSi2,1 from which we infer that charge tuning dominantly controls the ground state of URu2Si2, regardless of whether s/p or d electrons are replaced. Contraction of the unit-cell volume may also play a role at large x. This provides guidance for determining the specific factors that lead to hidden order versus magnetism in this family of materials and constrains possible models for hidden order.
The application of de-icing salts for winter road maintenance is recognized as a major contributor to the decline of urban trees. We conducted a long-term monitoring program across several locations ...in the City of Edmonton (Alberta, Canada) to evaluate the impact of roadway salt application on tree species widely planted in boulevards and right-of-ways: Ulmus americana, Fraxinus pennsylvanica, Pinus contorta, and Picea glauca. Soil and leaf samples were collected from a total of 16 sites over six years. There were four sites selected for each tree species: three mid- to high- traffic roadside sites that received regular winter maintenance and one non-serviced site (control). Sampling was performed three times per year from late spring to late summer. Airborne salinity was assessed in four locations at different distances from the road. In 50% of the roadside sites, soil electrical conductivity (EC) values exceeded 2dSm−1. Soil pH in all of the roadside sites was also significantly higher than in the control sites, with values ranging from 7.6 to 8.5. In all four species, trees growing in sites with high soil EC had increased leaf Na concentrations and reduced leaf chlorophyll concentrations. Among the airborne monitoring sites, Na deposition in high traffic locations was over four-fold higher than those measured in the control location. Furthermore, Na levels remained relatively high at 20–50m from the main road. Our data suggest that while soil salinity is among the main stressors affecting roadside trees in Edmonton, salt spray deposition may also have a significant impact on trees located close to high vehicle traffic areas and dense road networks. Our study highlights the importance of collecting data over several years and from multiple locations to account for the spatial and temporal heterogeneity of the urban environments in order to better evaluate the impact of road salt application on urban trees.
(Pu) has an unusually rich phase diagram that includes seven distinct solid state phases and an unusually large 25% collapse in volume from its delta phase to its low temperature alpha phase via a ...series of structural transitions. Despite considerable advances in our understanding of strong electronic correlations within various structural phases of Pu and other actinides, the thermodynamic mechanism responsible for driving the volume collapse has continued to remain a mystery. Here we utilize the unique sensitivity of magnetostriction measurements to unstable f electron shells to uncover the crucial role played by electronic entropy in stabilizing delta-Pu against volume collapse. We find that in contrast to valence fluctuating rare earths, which typically have a single f electron shell instability whose excitations drive the volume in a single direction in temperature and magnetic field, delta-Pu exhibits two such instabilities whose excitations drive the volume in opposite directions while producing an abundance of entropy at elevated temperatures. The two instabilities imply a near degeneracy between several different configurations of the 5f atomic shell, giving rise to a considerably richer behavior than found in rare earth metals. We use heat capacity measurements to establish a robust thermodynamic connection between the two excitation energies, the atomic volume, and the previously reported excess entropy of delta-Pu at elevated temperatures.
We present a detailed study of the low temperature and high magnetic field phases in the chemical substitution series URu\(_2\)Si\(_{2-x}\)P\(_x\) using electrical transport and magnetization in ...pulsed magnetic fields up to 65T. Within the hidden order region (0 $\ x$$\ \( 0.035) the high field ordering is robust even as the hidden order temperature is suppressed. Earlier work shows that for 0.035 \)\ x\( \)\ \( 0.26 there is a Kondo lattice with a no-ordered state that is replaced by antiferromagnetism for 0.26 \)\ x\( 0.5. We observe a simplified continuation of the high field ordering in the no-order \)x\(-region and an enhancement of the high field state upon the destruction of the antiferromagnetism with magnetic field. These results closely resemble what is seen for URu\)_{2-x}\(Rh\)_x\(Si\)_2\(\footnote{The concentration in this paper is defined as URu\)_{2-x}\(Rh\)_x\(Si\)_2\( while the chemical formula in the literature is given as U(Ru\)_{1-x}\(Rh\)_x\()\)_2\(Si\)_2\( 24-26}, from which we infer that charge tuning uniformly controls the ground state of URu\)_2\(Si\)_2$, regardless of whether s/p or d-electrons are replaced. This provides guidance for determining the specific factors that lead to hidden order versus magnetism in this family of materials.
Pseudogap in elemental plutonium Wartenbe, M; Tobash, P H; Singleton, J ...
arXiv (Cornell University),
01/2022
Paper, Journal Article
Odprti dostop
Electronic correlations associated with incipient magnetism have long been recognized as an important factor in stabilizing the largest atomic volume \(\delta\) phase of plutonium, yet their strength ...compared to those in the rare earths and neighboring actinides in the Periodic Table has largely remained a mystery. We show here using calorimetry measurements, together with prior detailed measurements of the phonon dispersion, that the \(5f\) electrons of the \(\delta\) phase reside in a pseudogapped state, accompanied by reductions in various physical properties below a characteristic temperature \(T^\ast\approx\)~100~K. The small characteristic energy scale of the pseudogapped state implies that the \(5f\) electrons in plutonium are much closer to the threshold for localization and magnetic order than has been suggested by state-of-the-art electronic structure theory, revealing plutonium to be arguably the most strongly correlated of the elements.
Via angular Shubnikov-de Hass (SdH) quantum oscillations measurements, we determine the Fermi surface topology of NbAs, a Weyl semimetal candidate. The SdH oscillations consist of two frequencies, ...corresponding to two Fermi surface extrema: 20.8 T (\(\alpha\)-pocket) and 15.6 T (\(\beta\)-pocket). The analysis, including a Landau fan plot, shows that the \(\beta\)-pocket has a Berry phase of \(\pi\) and a small effective mass \(\sim\)0.033 \(m_0\), indicative of a nontrivial topology in momentum space; whereas the \(\alpha\)-pocket has a trivial Berry phase of 0 and a heavier effective mass \(\sim\)0.066 \(m_0\). From the effective mass and the \(\beta\)-pocket frequency we determine that the Weyl node is 110.5 meV from the chemical potential. A novel electron-hole compensation effect is discussed in this system, and its impact on magneto-transport properties is addressed. The difference between NbAs and other monopnictide Weyl semimetals is also discussed.
For materials that harbour a continuous phase transition, the susceptibility of the material to various fields can be used to understand the nature of the fluctuating order and hence the nature of ...the ordered state. Here we use anisotropic biaxial strain to probe the nematic susceptibility of URu2Si2, a heavy fermion material for which the nature of the low temperature 'hidden order' state has defied comprehensive understanding for over 30 years. Our measurements reveal that the fluctuating order has a nematic component, confirming reports of twofold anisotropy in the broken symmetry state and strongly constraining theoretical models of the hidden-order phase.
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