Perfect separation of intraband and interband excitations in PdCoO2_2

The temperature dependence of the optical properties of the delafossite PdCoO$_2$ has been measured in the a-b planes over a wide frequency range. The optical conductivity due to the free-carrier (intraband) response falls well below the interband transitions, allowing the plasma frequency to be determined from the $f$-sum rule. Drude-Lorentz fits to the complex optical conductivity yield estimates for the free-carrier plasma frequency and scattering rate. The in-plane plasma frequency has also been calculated using density functional theory. The experimentally-determined and calculated values for the plasma frequencies are all in good agreement; however, at low temperature the optically-determined scattering rate is much larger than the estimate for the transport scattering rate, indicating a strong frequency-dependent renormalization of the optical scattering rate. In addition to the expected in-plane infrared-active modes, two very strong features are observed that are attributed to the coupling of the in-plane carriers to the out-of-plane longitudinal optic modes.Comment: 7 pages with five figures and three tables; 4 pages of supplementary materia

Cervial cancer screening among HIV-positive women in rural Cambodia: a pilot programme

Mexico AIDS Conference 200

Information and Particle Physics

Information measures for relativistic quantum spinors are constructed to satisfy various postulated properties such as normalisation invariance and positivity. Those measures are then used to motivate generalised Lagrangians meant to probe shorter distance physics within the maximum uncertainty framework. The modified evolution equations that follow are necessarily nonlinear and simultaneously violate Lorentz invariance, supporting previous heuristic arguments linking quantum nonlinearity with Lorentz violation. The nonlinear equations also break discrete symmetries. We discuss the implications of our results for physics in the neutrino sector and cosmology

Visualization of defects in single-crystal and thin-film PdCoO2 using aberration-corrected scanning transmission electron microscopy

Funding: This work was primarily supported by the U.S. Department of Energy, Office of Basic Sciences, Division of Materials Sciences and Engineering, under Award No. DE-SC0002334.Single-crystal delafossite PdCoO2 is known to have an extremely low intrinsic impurity concentration of ~0.001%, demonstrating extraordinarily high conductivity with a mean free path of ~20 microns at low temperatures. However, when grown as thin films, the resistivity at room temperature increases by a factor of 3 to 80 times, depending on the film thickness. Using scanning transmission electron microscopy, we identify different classes of defects for the single crystal vs epitaxial thin film. The dominant defect for single-crystal PdCoO2 is found to be ribbon-like defects. For the thin films, we identify different types of defects arising in epitaxial thin films mainly due to substrate termination that disrupt the lateral connectivity of the conducting planes. Our results are consistent with the high conductivity of single crystals and increased electrical resistivity of the thin films compared to that of single crystals, suggesting that selecting a proper substrate, improving surface quality, and reducing the step density are the keys to enhance the film quality for utilizing PdCoO2 as a platform for future applications.PostprintPeer reviewe

Interplay between carrier and impurity concentrations in annealed Ga1−x_{1-x}Mnx_{x}As intrinsic anomalous Hall Effect

Investigating the scaling behavior of annealed Ga$_{1-x}$Mn$_{x}$As anomalous Hall coefficients, we note a universal crossover regime where the scaling behavior changes from quadratic to linear, attributed to the anomalous Hall Effect intrinsic and extrinsic origins, respectively. Furthermore, measured anomalous Hall conductivities when properly scaled by carrier concentration remain constant, equal to theoretically predicated values, spanning nearly a decade in conductivity as well as over 100 K in T$_{C}$. Both the qualitative and quantitative agreement confirms the validity of new equations of motion including the Berry phase contributions as well as tunablility of the intrinsic anomalous Hall Effect.Comment: 4 pages, 5 figure

Strain tuning in microstructured quantum materials F

The application of strain to quantum materials is a powerful technique for tuning electronic correla-tions and the balance between interaction parameters by favoring specific electronic phases over al-most degenerate competing orders via breaking underlying crystal symmetries. For example, it can promote a long-range charge-ordered state over high-temperature superconductivity in cuprates [1,2] or induce a chiral state in Kagome metals [3]. To maximize surface strains, we exploit the enhanced yield strain of micron-scale materials, well-stud-ied in materials science [4]. State-of-the-art microfabrication using focused ion beam techniques allow precise design of crystalline samples, achieving desired strain fields such as uniaxial stress or more complex strain gradients [5]. We microcarve the entire sample into a flexible cantilever without a sub-strate and then bend it, enabling arbitrary and especially out-of-plane tensile strain even in layered quantum materials [6]. Raman scattering directly probes long-wavelength phonon modes, which are highly sensitive to lattice strain. With submicrometer spatial resolution, it provides a direct measure of strain variations. It also detects local symmetry breaking and gives access to electronic, magnetic, and orbital excitations, prob-ing the electronic ground state. Even without a change in lattice symmetry under stress, the phonon mode frequency serves as an extremely sensitive probe, determined with high energy resolution. The layered crystal structure of delafossite PdCoO2, with weak interlayer coupling, makes it an ideal candidate for studying out-of-plane tensile strain. Its exceptional purity [7] minimizes extrinsic disorder effects. Among the various Raman modes allowed by group theory, the fully symmetric A1g phonon, consisting of oxygen ion vibrations along the c-direction [8], is particularly interesting. Finite element simulations guide the design of a cantilever manufactured from high-quality single crystals of PdCoO2. Together with DFT-calculations our Micro-Raman measurements confirm quantitively the spatial strain distribution on the cantilever. Furthermore, we investigate the role of the amorphous layer thickness for Raman spectra. [1] Kim, H. H. et al. Uniaxial pressure control of competing orders in a high-temperature superconductor. Science 362, 1040-1044, doi:10.1126/science.aat4708 (2018). [2] Kim, H. H. et al. Charge Density Waves in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.67}$ Probed by Resonant X-Ray Scattering under Uniaxial Compression. Physical Review Letters 126, 037002, doi:10.1103/PhysRevLett.126.037002 (2021). [3] Guo, C. et al. Switchable chiral transport in charge-ordered kagome metal CsV3Sb5. Nature 611, 461-466, doi:10.1038/s41586-022-05127-9 (2022)

Evidence of metallic clustering in annealed Ga1-xMnxAs from atypical scaling behavior of the anomalous Hall coefficient

We report on the anomalous Hall coefficient and longitudinal resistivity scaling relationships on a series of annealed Ga1-xMnxAs epilayers (x~0.055). As-grown samples exhibit scaling parameter n of ~ 1. Near the optimal annealing temperature, we find n ~ 2 to be consistent with recent theories on the intrinsic origins of anomalous Hall Effect in Ga1-xMnxAs. For annealing temperatures far above the optimum, we note n > 3, similar behavior to certain inhomogeneous systems. This observation of atypical behavior agrees well with characteristic features attributable to spherical resonance from metallic inclusions from optical spectroscopy measurements.Comment: 3 pages, 3 figure

Quasi two-dimensional Fermi surface topography of the delafossite PdRhO2

The authors acknowledge the financial support from the European Research Council (through the QUESTDO project), the Engineering and Physical Sciences Research Council UK (Grants No. EP/I031014/1 and No. EP/L015110/1), the Royal Society, and the Max-Planck Society.We report on a combined study of the de Haas-van Alphen effect and angle resolved photoemission spectroscopy on single crystals of the metallic delafossite PdRhO2 rounded off by ab initio band structure calculations. A high sensitivity torque magnetometry setup with SQUID readout and synchrotron-based photoemission with a light spot size of ~50μm enabled high resolution data to be obtained from samples as small as 150 × 100 × 20(μm)3. The Fermi surface shape is nearly cylindrical with a rounded hexagonal cross section enclosing a Luttinger volume of 1.00(1) electrons per formula unit.PostprintPeer reviewe

Crossing the ballistic-ohmic transition via high energy electron irradiation

P.H.M. and M.D.B. received PhD studentship support from the UK Engineering and Physical Science Research Council via Grant No. EP/L015110/1. C.P. and P.J.W.M. are supported by the European Research Council under the European Union's Horizon 2020 research and innovation programme (Microstructured Topological Materials Grant No. 715730). E. Z. acknowledges support from the International Max Planck Research School for Chemistry and Physics of Quantum Materials (IMPRS-CPQM). Irradiation experiments performed on the SIRIUS platform were supported by the French National Network of Accelerators for Irradiation and Analysis of Molecules and Materials (EMIR&A) under Project No. EMIR 2019 18-7099.The delafossite metal PtCoO2 is among the highest-purity materials known, with low-temperature mean free path up to 5 μm in the best as-grown single crystals. It exhibits a strongly faceted, nearly hexagonal Fermi surface. This property has profound consequences for nonlocal transport within this material, such as in the classic ballistic-regime measurement of bend resistance in mesoscopic squares. Here, we report the results of experiments in which high-energy electron irradiation was used to introduce pointlike disorder into such squares, reducing the mean free path and therefore the strength of the ballistic-regime transport phenomena. We demonstrate that high-energy electron irradiation is a well-controlled technique to cross from nonlocal to local transport behavior and therefore determine the nature and extent of unconventional transport regimes. Using this technique, we confirm the origins of the directional ballistic effects observed in delafossite metals and demonstrate how the strongly faceted Fermi surface both leads to unconventional transport behavior and enhances the length scale over which such effects are important. © 2023 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.Publisher PDFPeer reviewe