Vortex entropy and superconducting fluctuations in ultrathin underdoped Bi2Sr2CaCu2O8+x superconductor.

Vortices in superconductors can help identify emergent phenomena but certain fundamental aspects of vortices, such as their entropy, remain poorly understood. Here, we study the vortex entropy in underdoped Bi2Sr2CaCu2O8+x by measuring both magneto-resistivity and Nernst effect on ultrathin flakes (≤2 unit-cell). We extract the London penetration depth from the magneto-transport measurements on samples with different doping levels. It reveals that the superfluid phase stiffness ρs scales linearly with the superconducting transition temperature Tc, down to the extremely underdoped case. On the same batch of ultrathin flakes, we measure the Nernst effect via on-chip thermometry. Together, we obtain the vortex entropy and find that it decays exponentially with Tc or ρs. We further analyze the Nernst signal above Tc in the framework of Gaussian superconducting fluctuations. The combination of electrical and thermoelectric measurements in the two-dimensional limit provides fresh insight into high temperature superconductivity.

Prominent Josephson tunneling between twisted single copper oxide planes of Bi2Sr2-xLaxCuO6+y.

Josephson tunneling in twisted cuprate junctions provides a litmus test for the pairing symmetry, which is fundamental for understanding the microscopic mechanism of high temperature superconductivity. This issue is rekindled by experimental advances in van der Waals stacking and the proposal of an emergent d+id-wave. So far, all experiments have been carried out on Bi2Sr2CaCu2O8+x (Bi-2212) with double CuO2 planes but show controversial results. Here, we investigate junctions made of Bi2Sr2-xLaxCuO6+y (Bi-2201) with single CuO2 planes. Our on-site cold stacking technique ensures uncompromised crystalline quality and stoichiometry at the interface. Junctions with carefully calibrated twist angles around 45° show strong Josephson tunneling and conventional temperature dependence. Furthermore, we observe standard Fraunhofer diffraction patterns and integer Fiske steps in a junction with a twist angle of 45.0±0.2°. Together, these results pose strong constraints on the d or d+id-wave pairing and suggest an indispensable isotropic pairing component.

Direct α-C-H Alkylation of Structurally Diverse Alcohols via Combined Tavaborole and Photoredox Catalysis.

Herein, we report a method that uses antifungal tavaborole as a co-catalyst for direct α-C-H alkylation of structurally diverse alcohols through photoredox catalysis. The protocol features mild conditions, remarkable scope, and wide functional group tolerance, which allows for the construction of a wide array of highly functionalized alcohols, including homoserine derivatives and C-glycosyl amino acids. We also demonstrate the synthetic applications of this methodology to the late-stage functionalization of pharmaceuticals and natural products.

Little-Parks like oscillations in lightly doped cuprate superconductors.

Understanding the rich and competing electronic orders in cuprate superconductors may provide important insight into the mechanism of high-temperature superconductivity. Here, by measuring Bi2Sr2CaCu2O8+x in the extremely underdoped regime, we obtain evidence for a distinct type of ordering, which manifests itself as resistance oscillations at low magnetic fields (≤10 T) and at temperatures around the superconducting transition. By tuning the doping level p continuously, we reveal that these low-field oscillations occur only when p < 0.1. The oscillation amplitude increases with decreasing p but the oscillation period stays almost constant. We show that these low-field oscillations can be well described by assuming a periodic superconducting structure with a mesh size of about 50 nm. Such a charge order, which is distinctly different from the well-established charge density wave and pair density wave, seems to be an unexpected piece of the puzzle on the correlated physics in cuprates.

Chronic type II diabetes mellitus leads to changes in neuropeptide Y receptor expression and distribution in human myocardial tissue.

Neuropeptide Y is one of the most abundant neurotransmitters in the myocardium, and is known to influence cardiovascular remodeling. We hypothesized that diabetic neuropathy could possibly be associated with altered neuropeptide Y and its receptor expression levels in myocardium and plasma. Plasma neuropeptide Y levels in diabetic (n=24, HgbA1c 7.9 ± 1.1%) and non-diabetic (n=27, HgbA1c 5.8 ± 0.5%) patients undergoing cardiac surgery utilizing cardiopulmonary bypass were analyzed. Right atrial tissue of these patients was used to determine the expression of neuropeptide Y, the receptors 1-5, and leptin by immunoblotting, real-time PCR and immunofluorescence. Apoptosis signaling and endostatin and angiostatin were measured to determine the effects of leptin. Plasma neuropeptide Y levels were significantly increased in patients with Type II diabetes mellitus as compared to non-diabetic patients (P=0.026). Atrial tissue neuropeptide Y mRNA levels were lower in diabetic patients (P=0.036). There was a significant up-regulation of myocardial Y(2) and Y(5) receptors (P=0.009, P=0.01 respectively) in the diabetic patients. Leptin, involved with apoptosis and angiogenesis, was down regulated in diabetic patients (P=0.05). The levels of caspase-3, endostatin and angiostatin were significantly elevated in diabetic patients (P=0.003, P=0.008, P=0.01 respectively). Y(1) receptors were more likely to be localized within the nuclei of cardiomyocytes and vascular smooth muscle cells. Neuropeptide expression is altered differentially in the serum and myocardium by diabetes. Altered regulation of this system in diabetics may be in part responsible for the decreased angiogenesis, increased apoptosis, and increased vascular smooth muscle proliferation leading to coronary artery disease and heart failure in this patient population.