Interaction of in-plane Drude carrier with c -axis phonon in PdCoO2

Funding: E.C. was supported by the NRF-2021R1A2C1009073 of Korea funded by the Ministry of Education. D.S. was partially supported by MOLIT as an Innovative Talent Education Program for Smart City. The work at Rutgers University is supported by the National Science Foundation’s DMR2004125 and the Army Research Office’s W911NF2010108. S.B.C. was supported by the National Research Foundation of Korea (NRF) grants funded by the Korean government (MSIT)(NRF-2023R1A2C1006144, NRF-2020R1A2C1007554, and NRF-2018R1A6A1A06024977). Research in Dresden benefits from the environment provided by the DFG Cluster of Excellence ct.qmat (EXC 2147, project ID 390858490). The work at HYU was supported by the NRF grant funded by the Korean government (MSIT) (2022R1F1A1072865), the BrainLink program funded by MSIT (2022H1D3A3A01077468), and the Quantum Simulator Development Project for Materials Innovation through the NRF funded by MSIT (2023M3K5A1094813).We performed polarized reflection and transmission measurements on the layered conducting oxide PdCoO2 thin films. For the ab-plane, an optical peak near Ω ≈ 750 cm−1 drives the scattering rate 1/τ(ω) and effective mass m*(ω) of the Drude carrier to increase and decrease respectively for ω ≧ Ω. For the c-axis, a longitudinal optical phonon (LO) is present at Ω as evidenced by a peak in the loss function Im[−1/εc(ω)]. Further polarized measurements in different light propagation (q) and electric field (E) configurations indicate that the Peak at Ω results from an electron-phonon coupling of the ab-plane carrier with the c-LO phonon, which leads to the frequency-dependent 1/τ(ω) and m*(ω). This unusual interaction was previously reported in high-temperature superconductors (HTSC) between a non-Drude, mid-infrared (IR) band and a c-LO. On the contrary, it is the Drude carrier that couples in PdCoO2. The coupling between the ab-plane Drude carrier and c-LO suggests that the c-LO phonon may play a significant role in the characteristic ab-plane electronic properties of PdCoO2, including the ultra-high dc-conductivity, phonon-drag, and hydrodynamic electron transport.Publisher PDFPeer reviewe

Interaction of in-plane Drude carrier with c-axis phonon in PdCoO2\rm PdCoO_2

We performed polarized reflection and transmission measurements on the layered conducting oxide $\rm PdCoO_2$ thin films. For the ab-plane, an optical peak near $\Omega$ $\approx$ 750 cm$^{-1}$ drives the scattering rate $\gamma^{*}(\omega)$ and effective mass $m^{*}(\omega)$ of the Drude carrier to increase and decrease respectively for $\omega$ $\geqq$ $\Omega$. For the c-axis, a longitudinal optical phonon (LO) is present at $\Omega$ as evidenced by a peak in the loss function Im[$-1/\varepsilon_{c}(\omega)$]. Further polarized measurements in different light propagation (q) and electric field (E) configurations indicate that the Peak at $\Omega$ results from an electron-phonon coupling of the ab-plane carrier with the c-LO phonon, which leads to the frequency-dependent $\gamma^{*}(\omega)$ and $m^{*}(\omega)$. This unusual interaction was previously reported in high-temperature superconductors (HTSC) between a non-Drude, mid-infrared band and a c-LO. On the contrary, it is the Drude carrier that couples in $\rm PdCoO_2$. The coupling between the ab-plane Drude carrier and c-LO suggests that the c-LO phonon may play a significant role in the characteristic ab-plane electronic properties of $\rm PdCoO_2$ including the ultra-high dc-conductivity, phonon-drag, and hydrodynamic electron transport.Comment: 4 figure

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Extraordinarily High Conductivity of Stretchable Fibers of Polyurethane and Silver Nanoflowers

Stretchable conductive composites have received considerable attention recently, and they should have high conductivity and mechanical strength. Here we report highly conductive stretchable fibers synthesized by the scalable wet spinning process using flower-shaped silver nanoparticles with nanodisc-shaped petals (Ag nanoflowers) and polyurethane. An extraordinarily high conductivity (41245 S cm-1) was obtained by Ag nanoflowers, which is 2 orders of magnitude greater than that of fibers synthesized using spherical Ag nanoparticles. This was due to the enhanced surface area and vigorous coalescence of nanodisc-shaped petals during the curing process. There was a trade-off relationship between conductivity and stretchability, and the maximum rupture strain was 776%. An analytical model revealed that the enhanced adhesion between Ag nanoflowers and polyurethane provided a high Young's modulus (731.5 MPa) and ultimate strength (39.6 MPa) of the fibers. The fibers exhibited an elastic property after prestretching, and the resistance change of weft-knitted fabric was negligible up to 200% strain. The fibers with extraordinarily high conductivity, stretchability, and mechanical strength may be useful for wearable electronics applications. © 2015 American Chemical Society253

Chemically driven carbon-nanotube-guided thermopower waves

Theoretical calculations predict that by coupling an exothermic chemical reaction with a nanotube or nanowire possessing a high axial thermal conductivity, a self-propagating reactive wave can be driven along its length. Herein, such waves are realized using a 7-nm cyclotrimethylene trinitramine annular shell around a multiwalled carbon nanotube and are amplified by more than 10[superscript 4] times the bulk value, propagating faster than 2 m s[superscript −1], with an effective thermal conductivity of 1.28±0.2 kW m[superscript −1] K[superscript −1] at 2,860 K. This wave produces a concomitant electrical pulse of disproportionately high specific power, as large as 7 kW kg[superscript −1], which we identify as a thermopower wave. Thermally excited carriers flow in the direction of the propagating reaction with a specific power that scales inversely with system size. The reaction also evolves an anisotropic pressure wave of high total impulse per mass (300 N s kg[superscript −1]). Such waves of high power density may find uses as unique energy sources.United States. Air Force Office of Scientific ResearchNational Science Foundation (U.S.) (Career Award)National Science Foundation (U.S.)ILJU Academy and Culture FoundationKorea (South). Ministry of Education & Human Resources Development (MOEHRD) (KRF-2006-214-D00117

Enhanced thermoelectric performance of Bi0.5Sb1.5Te3-expanded graphene composites by simultaneous modulation of electronic and thermal carrier transport

Solution-based synthesis of thermoelectric nanoplates, which provides a low thermal conductivity due to the grain boundary scattering, has received considerable attention as a scalable method. However, the scattering also decreased electrical conductivity leading to a low thermoelectric figure of merit (ZT). Here we employed expanded graphene to enhance thermoelectric performance of p-type Bi0.5Sb1.5Te3 composites by simultaneous improvement in electrical conduction and phonon scattering. The addition of expanded graphene (0.1vol%) improved both carrier concentration and electrical conductivity of composites due to the high intrinsic p-type carrier concentration of graphene. Besides, it significantly decreased lattice thermal conductivity due to the phase boundary phonon scattering in spite of the high intrinsic thermal conductivity of graphene. The increased carrier concentration also suppressed the bipolar conduction resulting in a moderate increase in power factor and a slow increase in bipolar thermal conductivity at elevated temperatures. Overall, the maximum ZT increased by 45% (1.13 at 360K) by the addition of expanded graphene. A similar trend with a greater maximum ZT (1.24 at 360K) was observed when ball-milled Bi0.5Sb1.5Te3 ingot powders were employed providing reliability of the suggested mechanism. © 2015 Elsevier Ltd126251sciescopu

Exome sequencing reveals DNMT3A and ASXL1 variants associate with progression of chronic myeloid leukemia after tyrosine kinase inhibitor therapy

Objective The development of tyrosine kinase inhibitors (TKIs) has significantly improved the treatment of chronic myeloid leukemia (CML). However, approximately one third of patients are resistant to TKI and/or progress to advanced disease stages. TKI therapy failure has a well-known association with ABL1 kinase domain (KD) mutations, but only around half of TKI non-responders have detectable ABL1 KD mutations. Method We attempt to identify genetic markers associated with TKI therapy failure in 13 patients (5 resistant, 8 progressed) without ABL1 KD mutations using whole-exome sequencing. Results In 6 patients, we detected mutations in 6 genes commonly mutated in other myeloid neoplasms: ABL1, ASXL1, DNMT3A, IDH1, SETBP1, and TP63. We then used targeted deep sequencing to validate our finding in an independent cohort consisting of 100 CML patients with varying drug responses (74 responsive, 18 resistant, and 8 progressed patients). Mutations in genes associated with epigenetic regulations such as DNMT3A and ASXL1 seem to play an important role in the pathogenesis of CML progression and TKI-resistance independent of ABL1 KD mutations. Conclusion This study suggests the involvement of other somatic mutations in the development of TKI resistant progression to advanced disease stages in CML, particularly in patients lacking ABL1 KD mutations