Suppressed Andreev Reflection at the Normal-Metal / Heavy-Fermion Superconductor CeCoIn5_5 Interface

Dynamic conductance spectra are taken from Au/CeCoIn$_5$ point contacts in the Sharvin limit along the (001) and (110) directions. Our conductance spectra, reproducibly obtained over wide ranges of temperature, constitute the cleanest data sets ever reported for HFSs. A signature for the emerging heavy-fermion liquid is evidenced by the development of the asymmetry in the background in the normal state. Below $T_c$, an enhancement of the sub-gap conductance arising from Andreev reflection is observed, with the magnitude of $\sim$ 13.3 % and $\sim$ 11.8 % for the (001) and the (110) point contacts, respectively, an order of magnitude smaller than those observed in conventional superconductors but consistent with those in other HFSs. Our zero-bias conductance data for the (001) point contacts are best fit with the extended BTK model using the d-wave order parameter. The fit to the full conductance curve of the (001) point contact indicates the strong coupling nature ($2\Delta/k_{B}T_c = 4.64$). However, our observed suppression of both the Andreev reflection signal and the energy gap indicates the failure of existing models. We provide possible directions for theoretical formulations of the electronic transport across an N/HFS interface. Several qualitative features observed in the (110) point contacts provide the first clear spectroscopic evidence for the $d_{x^2-y^2}$ symmetry.Comment: 13 pages, 7 figures, LaTeX, paper invited and submitted to SPIE Conference on Strongly Correlated Electron Materials: Physics and Nanoengineering, in San Diego, California, July 31 - August 4, 200

Andreev reflection spectroscopy of the heavy-fermion superconductor CeCoIn5_5 along three different crystallographic orientations

Andreev reflection spectroscopy has been performed on the heavy-fermion superconductor (HFS) CeCoIn$_5$ single crystals along three different crystallographic orientations, (001), (110), and (100), using Au tips as counter-electrodes. Dynamic conductance spectra are reproducible over wide temperature ranges and consistent with each other, ensuring the spectroscopic nature. Features common to all directions are: i) asymmetric behaviors of the background conductance, which we attribute to the emerging coherent heavy-fermion liquid; ii) energy scales (~1 meV) for conductance enhancement due to Andreev reflection; iii) magnitudes of enhanced zero-bias conductance (10 - 13 %). These values are an order of magnitude smaller than the predicted value by the Blonder-Tinkham-Klapwijk (BTK) theory, but comparable to those for other HFSs. Using the d-wave BTK model, we obtain an energy gap of ~ 460 ueV. However, it is found that extended BTK models considering the mismatch in Fermi surface parameters do not account for our data completely, which we attribute to the shift of spectral weight to low energy as well as to the suppressed Andreev reflection. A qualitative comparison of the conductance spectra with calculated curves shows a consistency with d$_{x^2-y^2}$-symmetry, providing the first spectroscopic evidence for the order parameter symmetry and resolving the controversy over the location of the line nodes.Comment: invited talk submitted to the 8th M2S conference to be held in Dresden Germany, July 9-14, 2006, 4 pages, 3 figure

Elevated cellular cholesterol in Familial Alzheimer’s presenilin 1 mutation is associated with lipid raft localization of β-amyloid precursor protein

Familial Alzheimer’s disease (FAD)-associated presenilin 1 (PS1) serves as a catalytic subunit of γ-secretase complex, which mediates the proteolytic liberation of β-amyloid (Aβ) from β-amyloid precursor protein (APP). In addition to its proteolytic role, PS1 is involved in non-proteolytic functions such as protein trafficking and ion channel regulation. Furthermore, postmortem AD brains as well as AD patients showed dysregulation of cholesterol metabolism. Since cholesterol has been implicated in regulating Aβ production, we investigated whether the FAD PS1-associated cholesterol elevation could influence APP processing. We found that in CHO cells stably expressing FAD-associated PS1 ΔE9, total cholesterol levels are elevated compared to cells expressing wild-type PS1. We also found that localization of APP in cholesterol-enriched lipid rafts is substantially increased in the mutant cells. Reducing the cholesterol levels by either methyl-β-cyclodextrin or an inhibitor of CYP51, an enzyme mediating the elevated cholesterol in PS1 ΔE9-expressing cells, significantly reduced lipid raft-associated APP. In contrast, exogenous cholesterol increased lipid raft-associated APP. These data suggest that in the FAD PS1 ΔE9 cells, the elevated cellular cholesterol level contributes to the altered APP processing by increasing APP localized in lipid rafts

Correlation between low skeletal muscle index and 3D anthropometric data measured by 3D body scanner: screening sarcopenia

BackgroundThe screening tools for sarcopenia are measuring calf circumference, SARC-F or SPPB. However, not all of these tools have high sensitivity, specificity, and low margins of error. This research investigates potential of 3D anthropometry of the lower extremities on screening of sarcopenia.MethodsFrom October 2022 to February 2023, we retrospectively analyzed results of 3D body scanner and bio-impedance analysis for patients aged 45 to 85 at risk of sarcopenia. The 3D scanner measured the surface and volume values of both thighs and calves. When skeletal muscle index (SMI) is less than 5.7, patients were classified to Low SMI group, indicative of sarcopenia.ResultsA total six out of 62 patients were classified to Low SMI group, showing significantly lower values of right, left, mean calf volumes and mean calf surface than the other patients (right calf volume 2.62 L vs. 3.34 L, p = 0.033; left calf volume 2.62 L vs. 3.25 L, p = 0.044; mean calf volume 2.62 L vs. 3.29 L, p = 0.029; mean calf surface 0.12 m2 vs. 0.13 m2, p = 0.049). There was no statistical difference in thigh volume and surface. Through AUC-ROC analysis, mean calf volume was the most significant cut-off value (right calf volume 2.80 L, AUC = 0.768; left calf volume 2.75 L, AUC = 0.753; mean calf volume 3.06 L, AUC = 0.774; mean calf surface 0.12 m2, AUC = 0.747).ConclusionThe calf volume and surface values have significant relationship with low SMI, and the mean calf volume was the most significant cut-off screening value for Low SMI. The 3D scanner demonstrated its value as a new means for screening sarcopenia

Multilayer fabrication of unobtrusive poly(dimethylsiloxane) nanobrush for tunable cell adhesion

Precise modulation of polymer brush in its thickness and grafting density can cause unexpected cell behaviors and regulated bioactivities. Herein, a nanoscale poly(dimethylsiloxane) (PDMS) brush was employed to use as a controllable material for cell adhesion. Facile fabrication of ultrathin monolayer PDMS nanobrush on an underlying substrate facilitated regaining cell adhesion through long-range cell attractive forces such as the van der Waals forces. We showed that cell adhesion is diminished by increasing the number of nanobrush layers, causing a gradual decrease of the effectiveness of the long-range force. The result demonstrates that ultrathin PDMS nanobrush can either promote or inhibit cell adhesion, which is required for various biomedical fields such as tissue-engineering, anti-fouling coating, and implantable biomaterials and sensors

Planar Tunneling Spectroscopy of Samarium Hexaboride(SmB6)

As a well-known Kondo insulator originating from strong correlation, SmB6 has attracted much interest because of its surface states being potentially topological. In order to investigate this, we apply the technique of planar tunneling spectroscopy since it can detect the surface density of states (DOS). To acquire stable and clean tunneling spectra, we prepare SmB6 single crystal surfaces by polishing against alumina lapping film. Both (001) and (011) surfaces are studied using this method for comparison. With further ion-beam cleaning/etching under vacuum, tunnel junctions are formed by sputter deposition of Al (with approximate thickness between 2 5 nm) and subsequent plasma oxidation. Then two insulating strips are painted on the surface leaving a narrow conducting area at the center. Finally several silver counter-electrodes are deposited on the top using thermal evaporator. The junctions are defined by the intersections of the silver and the aluminum oxide barrier. Differential conductance is measured over wide ranges of temperature and magnetic field. Interesting features are detected at low temperature. For example, the overall asymmetric shape of conductance over the bias range from 300mV to 300mV, the multiple humps at negative bias voltage which do not evolve linearly with temperature, and the suppressed, linear conductance near zero bias. The asymmetric conductance is possibly a sign of Fano resonance in Kondo insulator, indicating that it might be conceivable to measure the bulk DOS using planar tunneling. The linear conductance at low bias, on the other hand, might be due to surface states. The gap feature of the spectra start to appear at around 50 K and the overall wavy background shape can sustain at around 100 K. *The work at UIUC is supported by the NSF DMR 12-06766.Ope