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1. Tuning metal/superconductor to insulator/superconductor coupling via control of proximity enhancement between NbSe 2 monolayers

   https://doi.org/10.1088/1361-648X/acbf92  

   Chiatti, Olivio ; Mihov, Klara ; Griffin, Theodor U. ; Grosse, Corinna ; Alemayehu, Matti B. ; Hite, Kyle ; Hamann, Danielle ; Mogilatenko, Anna ; Johnson, David C. ; Fischer, Saskia F. ( March 2023 , Journal of Physics: Condensed Matter)

   The interplay between charge transfer and electronic disorder in transition-metal dichalcogenide multilayers gives rise to superconductive coupling driven by proximity enhancement, tunneling and superconducting fluctuations, of a yet unwieldy variety. Artificial spacer layers introduced with atomic precision change the density of states by charge transfer. Here, we tune the superconductive coupling between$\text{NbS}{\text{e}}_{\text{2}}$monolayers from proximity-enhanced to tunneling-dominated. We correlate normal and superconducting properties in${\left[{\left(\text{SnSe}\right)}_{1+\delta }\right]}_m{\left[\text{NbS}{\text{e}}_{\text{2}}\right]}_1$tailored multilayers with varying SnSe layer thickness ($m=1-15$). From high-field magnetotransport the critical fields yield Ginzburg–Landau coherence lengths with an increase of$140\mathrm{\%}$cross-plane ($m=1-9$), trending towards two-dimensional superconductivity for$m>9$. We show cross-overs between three regimes: metallic with proximity-enhanced coupling ($m=1-4$), disordered-metallic with intermediate coupling ($m=5-9$) and insulating with Josephson tunneling ($m>9$). Our results demonstrate that stacking metal mono- and dichalcogenides allows to convert a metal/superconductor into an insulator/superconductor system, prospecting the control of two-dimensional superconductivity in embedded layers.

    

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2. Artificial Pinning Centers in (Y,RE)-Ba-Cu-O Superconductors: Recent Progress and Future Perspective

   https://doi.org/1088/1361-6668/ab4ccd  

   Timothy J. Haugan, Teresa Puig ( October 2019 , Superconductor science technology)

   A microscopic understanding of vortex pinning in type II superconductors began with the theoretical discovery of magnetic vortices by Abrikosov, which received the 2003 Nobel Prize in Physics [1, 2]. When type II superconductors are exposed to magnetic fields (H), the magnetic field enters as quantized vortices, each with a fundamental flux j0 = 2.07 × 10−11 T cm−2 , or 2.07 × 10−15 Wb. The vortex core size on the order of the superconducting coherence length can be very small, e.g. ∼1–2 nm for the cuprate family of high-temperature superconductors (HTSs). The vortices electrically interact with each other by repelling, and act collectively together as a flux lattice that is affected by the intrinsic crystal lattice properties and microstructure defects. For superconducting power applications where applied magnetic fields are in the range of 0.1 T to >30 T, the areal number density of the vortices can reach incredibly high values. For example, for an applied magnetic field of 5 T, the vortex areal density is around 2.5 × 1011 cm−2 , which translates to inter-vortex spacing of about 20 nm (assuming a square lattice for vortices). Somewhat surprisingly, if the crystal lattice for type II superconductors, such as HTS cuprates [3] is nearly perfect without any defects to pin vortices, the vortices can move collectively and almost freely in an applied magnetic field due to Lorentz forces, which results in electrical resistance at a fairly low critical current density Jc(H, T) at an applied magnetic field (H) and temperature (T). In order to realize useful critical current densities in type II superconductors, imperfections and defects must be added to the crystal lattice to effectively pin vortices. The simplest example of this was achieved in the (Y, RE)Ba2Cu3O7 (where RE is rare earth elements) family by depositing thin films, in which high densities of dislocations and other growth defects are added into the film microstructure and dramatically increase the critical current density Jc(77 K, H//c-axis) > 106 A cm−2 compared to Jc (77 K) < 103 A cm−2 for single crystals [4–6] 

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3. Anomalous behavior in high-pressure carbonaceous sulfur hydride

   https://doi.org/https://doi.org/10.1016/j.physc.2021.1353851  

   Dogan, M. ; Cohen, M. L. ( January 2021 , Physical chemistry chemical physics)

   null (Ed.)

   A new experimental study by Snider et al. [Nature 586, 373-377 (2020)] reported behavior in a high-pressure carbon-sulfur-hydrogen system that has been interpreted by the authors as superconductivity at room temperature. The sudden drop of electrical resistance at a critical temperature and the change of the R vs. T behavior with an applied magnetic field point to superconductivity. This is a very exciting study in one of the most important areas of science, hence, it is crucial for the community to investigate these findings and hopefully reproduce these results. In this comment, we present calculations that expand upon the arguments put forth by Hirsch and Marsiglio [arXiv:2010.10307], and offer some speculations about physical mechanisms that might explain the observed data. In agreement with Hirsch and Marsiglio, we show that there are errors in the analysis presented in the experimental paper, and with the correct analysis, the reported R vs. T data significantly deviate from the expected behavior. In particular, the extremely sharp change in resistance at the superconducting transition is not consistent with a strongly type II superconductor. 

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4. The effects of electroporation buffer composition on cell viability and electro-transfection efficiency

   https://doi.org/10.1038/s41598-020-59790-x  

   Sherba, Joseph J. ; Hogquist, Stephen ; Lin, Hao ; Shan, Jerry W. ; Shreiber, David I. ; Zahn, Jeffrey D. ( February 2020 , Scientific Reports)

   Electroporation is an electro-physical, non-viral approach to perform DNA, RNA, and protein transfections of cells. Upon application of an electric field, the cell membrane is compromised, allowing the delivery of exogenous materials into cells. Cell viability and electro-transfection efficiency (eTE) are dependent on various experimental factors, including pulse waveform, vector concentration, cell type/density, and electroporation buffer properties. In this work, the effects of buffer composition on cell viability and eTE were systematically explored for plasmid DNA encoding green fluorescent protein following electroporation of 3T3 fibroblasts. A HEPES-based buffer was used in conjunction with various salts and sugars to modulate conductivity and osmolality, respectively. Pulse applications were chosen to maintain constant applied electrical energy (J) or total charge flux (C/m²). The energy of the pulse application primarily dictated cell viability, with Mg²⁺-based buffers expanding the reversible electroporation range. The enhancement of viability with Mg²⁺-based buffers led to the hypothesis that this enhancement is due to ATPase activation via re-establishing ionic homeostasis. We show preliminary evidence for this mechanism by demonstrating that the enhanced viability is eliminated by introducing lidocaine, an ATPase inhibitor. However, Mg²⁺also hinders eTE compared to K⁺-based buffers. Collectively, the results demonstrate that the rational selection of pulsing conditions and buffer compositions are critical for the design of electroporation protocols to maximize viability and eTE.

    

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5. Superconducting phase transition in inhomogeneous chains of superconducting islands

   https://doi.org/doi.org/10.1103/PhysRevB.102.134502  

   Eduard Ilin, Irina Burkova ( October 2020 , Physical review and Physical review letters index)

   We study one-dimensional chains of superconducting islands with a particular emphasis on the regime in which every second island is switched into its normal state, thus forming a superconductor-insulator-normal metal (S-I-N) repetition pattern. As is known since Giaever tunneling experiments, tunneling charge transport between a superconductor and a normal metal becomes exponentially suppressed, and zero-bias resistance diverges, as the temperature is reduced and the energy gap of the superconductor grows larger than the thermal energy. Here we demonstrate that this physical phenomenon strongly impacts transport properties of inhomogeneous superconductors made of weakly coupled islands with fluctuating values of the critical temperature. We observe a nonmonotonous dependence of the chain resistance on both temperature and magnetic field, with a pronounced resistance peak at temperatures at which some but not all islands are superconducting. We explain this phenomenon by the inhomogeneity of the chains, in which neighboring superconducting islands have slightly different critical temperatures. We argue that the Giaever’s resistance divergence can also occur in the zero-temperature limit. Such quantum transition can occur if the magnetic field is tuned such that it suppresses superconductivity in the islands with the weaker critical field, while the islands with stronger energy gap remain superconducting. In such a field, the system acts as a chain of S-I-N junctions. 

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