Nearly quantized conductance plateau of vortex zero mode in an iron-based superconductor

Majorana zero-modes (MZMs) are spatially-localized zero-energy fractional quasiparticles with non-Abelian braiding statistics that hold a great promise for topological quantum computing. Due to its particle-antiparticle equivalence, an MZM exhibits robust resonant Andreev reflection and 2e2/h quantized conductance at low temperature. By utilizing variable-tunnel-coupled scanning tunneling spectroscopy, we study tunneling conductance of vortex bound states on FeTe0.55Se0.45 superconductors. We report observations of conductance plateaus as a function of tunnel coupling for zero-energy vortex bound states with values close to or even reaching the 2e2/h quantum conductance. In contrast, no such plateau behaviors were observed on either finite energy Caroli-de Genne-Matricon bound states or in the continuum of electronic states outside the superconducting gap. This unique behavior of the zero-mode conductance reaching a plateau strongly supports the existence of MZMs in this iron-based superconductor, which serves as a promising single-material platform for Majorana braiding at a relatively high temperature

Signatures of a gapless quantum spin liquid in the Kitaev material Na3_3Co2−x_{2-x}Znx_xSbO6_6

The honeycomb-lattice cobaltate Na$_3$Co$_2$SbO$_6$ has recently been proposed to be a proximate Kitaev quantum spin liquid~(QSL) candidate. However, non-Kitaev terms in the Hamiltonian lead to a zigzag-type antiferromagnetic~(AFM) order at low temperatures. Here, we partially substitute magnetic Co$^{2+}$ with nonmagnetic Zn$^{2+}$ and investigate the chemical doping effect in tuning the magnetic ground states of Na$_3$Co$_{2-x}$Zn$_x$SbO$_6$. X-ray diffraction characterizations reveal no structural transition but quite tiny changes on the lattice parameters over our substitution range $0\leq x\leq0.4$. Magnetic susceptibility and specific heat results both show that AFM transition temperature is continuously suppressed with increasing Zn content $x$ and neither long-range magnetic order nor spin freezing is observed when $x\geq0.2$. More importantly, a linear term of the specific heat representing fermionic excitations is captured below 5~K in the magnetically disordered regime, as opposed to the $C_{\rm m}\propto T^3$ behavior expected for bosonic excitations in the AFM state. Based on the data above, we establish a magnetic phase diagram of Na$_3$Co$_{2-x}$Zn$_x$SbO$_6$. Our results indicate the presence of gapless fractional excitations in the samples with no magnetic order, evidencing a potential QSL state induced by doping in a Kitaev system.Comment: 10 pages, 5 figure

Anthropogenic influence on 2019 May-June extremely low precipitation in southwestern China

Anthropogenic forcing has likely increased the likelihood of the May–June 2019 severe low precipitation event in southwestern China by approximately 6 (1.4) times based on the HADGEM3-GA6 (CMIP6) simulations

Modified nusinersen intrathecal injection method: inclusion of a septal needle-free closed infusion connector

ObjectiveNusinersen, an extremely expensive biologic drug (around 100,000 US$ per dose) that needs to be administered intrathecally, is approved for the treatment of 5q-spinal muscular atrophy (SMA). Because of the low muscle tone of the back muscles of pediatric SMA patients, especially type 1 SMA patients, the safe, effective, and fast execution of sheath injection is needed. Therefore, a modified intrathecal injection method was developed accordingly. This paper aims to describe the applicability and safety of this modified method.MethodsThe modified intrathecal injection method (MIIM) mainly includes a septal needle-free closed infusion connector between the lumbar puncture needle and the syringe, besides the procedures of routine lumbar puncture. Its applicability and safety were evaluated through clinical observation.ResultsA total of 92 children with SMA have successfully received nusinersen treatment at our hospital using the modified method since 2019 without obvious adverse events related to the modified injection method. Based on the clinical feedback of operators, the advantages of the modified method include successfully injecting the total dose of nusinersen with constant injection rate and a more stable fixation of the puncture needle, as well as making the operator more relaxed. However, compared with the routine method, the procedure of the modified method has additional steps.ConclusionThe modified intrathecal injection method is an effective and safe method to inject nusinersen when weighing the pros and cons, and it may also be used for administering intrathecal injections of other expensive medicines or for patients with other strict requirements for intrathecal injection

Fully gapped topological surface states in Bi2_2Se3_3 films induced by a d-wave high-temperature superconductor

Topological insulators are a new class of materials, that exhibit robust gapless surface states protected by time-reversal symmetry. The interplay between such symmetry-protected topological surface states and symmetry-broken states (e.g. superconductivity) provides a platform for exploring novel quantum phenomena and new functionalities, such as 1D chiral or helical gapless Majorana fermions, and Majorana zero modes which may find application in fault-tolerant quantum computation. Inducing superconductivity on topological surface states is a prerequisite for their experimental realization. Here by growing high quality topological insulator Bi$_2$Se$_3$ films on a d-wave superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ using molecular beam epitaxy, we are able to induce high temperature superconductivity on the surface states of Bi$_2$Se$_3$ films with a large pairing gap up to 15 meV. Interestingly, distinct from the d-wave pairing of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$, the proximity-induced gap on the surface states is nearly isotropic and consistent with predominant s-wave pairing as revealed by angle-resolved photoemission spectroscopy. Our work could provide a critical step toward the realization of the long sought-after Majorana zero modes.Comment: Nature Physics, DOI:10.1038/nphys274

Influences of tropical circulation and sea surface temperature anomalies on extreme heat over Northeast Asia in the midsummer of 2018

A destructive extreme heat attacked Northeast Asia (NEA) in the midsummer of 2018, characterized by the average midsummer Tmax (daily maximum air temperature at 2 m) ranking first during the study period. The current study indicates that the cyclonic anomaly over the western North Pacific (WNP) was an important cause, which presents an anomaly of two standard deviations. The cyclonic anomaly over the WNP was accompanied by anomalous convection, which favored descending and anticyclonic anomalies over NEA through a local meridional cell. The anticyclonic anomaly over NEA corresponds to the northwestward extension of the WNP subtropical high and facilitated the occurrence of extreme heat. The tropical sea surface temperature anomaly (SSTA) presents a La Niña decaying episode, but the SSTA over the tropical Pacific and North Indian Ocean was weak in the summer. In contrast, the southeastern tropical Indian Ocean (SETIO) was obviously cool, which was the coolest after detrending. The SETIO cooling triggered a low-level southeasterly anomaly, which turned into a southwesterly after crossing the equator, due to the Coriolis force. The southwesterly anomaly extended eastwards and favored the cyclonic anomaly over the WNP. Meanwhile, the circulation anomalies over the SETIO and WNP were connected via a local meridional cell, with the ascending branch over the WNP. Moreover, the above mechanism also operates for the climate statistics, verifying the robust influence of the SETIO SSTA. Considering the consistency of the SETIO SSTA, it could be a potential predictor for the climate over the WNP and NEA

Facile and Surfactant-Free Synthesis of Hierarchical ZnO Microstructures

Hierarchical ZnO crystals with flower-like microstructures were successfully synthesized via a facile hydrothermal route without using any surfactants. The morphology of these microstructures can be easily controlled by adjusting the pH of the reaction solution. The products were characterized by X-ray powder diffraction (XRD) and scanning electron microscope (SEM). Furthermore, a possible growth mechanism of ZnO hierarchical microstructures was proposed