Vortex fluctuations in superconducting La-Sr-Cu-O

Vortex fluctuations in the $La_{2-x}Sr_{x}CuO_{4+\delta}$ system have been studied as a function of magnetic field, temperature and carrier concentration in order to determine the dimensionality of the fluctuations. For a $x=0.10$ sample, there is a unique crossing-temperature on the magnetization vs. temperature plots for all magnetic fields up to 7 T, and the data scale very well with 2D fluctuation theory. At lower x-values where $H_{c2}$ is much smaller, there are two well defined crossing points, one at low fields (typically less than 1 T) and another at high fields (typically 3-7 T). A fit of the data to fluctuation theory shows that the low field crossing data scale as 2D fluctuations and the high field crossing data scale as 3D fluctuations. It would appear that as the magnetic field approaches $H_{c2}$, there is a 2D to 3D cross-over where the low field 2D pancake vortex structure transforms into a 3D vortex structure

Electronic density of states derived from thermodynamic critical field curves for underdoped La-Sr-Cu-O

Thermodynamic critical field curves have been measured for $La_{2-x}Sr_{x}CuO_{4+\delta}$ over the full range of carrier concentrations where superconductivity occurs in order to determine changes in the normal state density of states with carrier concentration. There is a substantial window in the $H-T$ plane where the measurements are possible because the samples are both thermodynamically reversible and the temperature is low enough that vortex fluctuations are not important. In this window, the data fit Hao-Clem rather well, so this model is used to determine $H_c$ and $\kappa_c$ for each temperature and carrier concentration. Using N(0) and the ratio of the energy gap to transition temperature, $\Delta (0)/k_BT_c$, as fitting parameters, the $H_c vs T$ curves give $\Delta (0)/k_BT_c \sim 2.0$ over the whole range of $x$. Values of N(0) remain rather constant in the optimum-doped and overdoped regime, but drops quickly toward zero in the underdoped regime.

Emergence of the erythroid lineage from multipotent hematopoiesis [preprint]

Red cell formation begins with the hematopoietic stem cell, but the manner by which it gives rise to erythroid progenitors, and their subsequent developmental path, remain unclear. Here we combined single-cell transcriptomics of murine hematopoietic tissues with fate potential assays to infer a continuous yet hierarchical structure for the hematopoietic network. We define the erythroid differentiation trajectory as it emerges from multipotency and diverges from 6 other blood lineages. With the aid of a new flow-cytometric sorting strategy, we validated predicted cell fate potentials at the single cell level, revealing a coupling between erythroid and basophil/mast cell fates. We uncovered novel growth factor receptor regulators of the erythroid trajectory, including the proinflammatory IL- 17RA, found to be a strong erythroid stimulator; and identified a global hematopoietic response to stress erythropoiesis. We further identified transcriptional and high-purity FACS gates for the complete isolation of all classically-defined erythroid burst-forming (BFU-e) and colony-forming progenitors (CFU-e), finding that they express a dedicated transcriptional program, distinct from that of terminally-differentiating erythroblasts. Intriguingly, profound remodeling of the cell cycle is intimately entwined with CFU-e developmental progression and with a sharp transcriptional switch that extinguishes the CFU-e stage and activates terminal differentiation. Underlying these results, our work showcases the utility of theoretic approaches linking transcriptomic data to predictive fate models, providing key insights into lineage development in vivo

Near-room-temperature magnetocaloric properties of La1−xSrxMnO3 (x = 0.11, 0.17, and 0.19) nanoparticles

The growth of chemically stable magnetic materials showing a magnetic transition near room temperature with a strong magnetocaloric effect is important for the development of roomtemperature magnetic refrigeration technology. Single-phase nanoparticles of La1−xSrxMnO3 (x = 0.11, 0.17, and 0.19) (LSMO) materials in the rhombohedral crystal structure with particle sizes between 20 nm and 30 nm were prepared using the sol-gel method. The crystal structure, morphology, magnetic properties and magnetocaloric effect (MCE)were investigated. The ferromagnetic to paramagnetic phase transitions of these nanoparticles are of second order in nature and the transition temperatures(Tc)lie between 284 K and 327 K. The magnetic entropy change (ΔSM) and relative cooling power(RCP) exhibit a linear dependence on the applied magnetic field. All samples show relatively large cooling efficiency with ΔSM,max of 3.26 Jkg−1 K−1 for La0.89Sr0.11MnO3 at 297 K and RCP of 201 Jkg−1 for La0.81Sr0.19MnO3 both measured at H = 30 kOe. These results suggest that the LSMO nanoparticles have potential for room-temperature magnetic refrigeration