Zhu-An Xu

Bio: Zhu-An Xu is an academic researcher from Zhejiang University. The author has contributed to research in topics: Superconductivity & Magnetoresistance. The author has an hindex of 43, co-authored 285 publications receiving 7385 citations. Previous affiliations of Zhu-An Xu include Zhejiang California International NanoSystems Institute & Nanjing University.

Majorana Zero Mode Detected with Spin Selective Andreev Reflection in the Vortex of a Topological Superconductor

Abstract: Recently, theory has predicted a Majorana zero mode (MZM) to induce spin selective Andreev reflection (SSAR), a novel magnetic property which can be used to detect the MZM. Here, spin-polarized scanning tunneling microscopy or spectroscopy has been applied to probe SSAR of MZMs in a topological superconductor of the Bi_{2}Te_{3}/NbSe_{2} heterostructure. The zero-bias peak of the tunneling differential conductance at the vortex center is observed substantially higher when the tip polarization and the external magnetic field are parallel rather than antiparallel to each other. This spin dependent tunneling effect provides direct evidence of MZM and reveals its magnetic property in addition to the zero energy modes. Our work will stimulate MZM research on these novel physical properties and, hence, is a step towards experimental study of their statistics and application in quantum computing.

Thorium-doping–induced superconductivity up to 56 K in Gd1−xThxFeAsO

Abstract: We report a new strategy to induce superconductivity in iron-based oxyarsenide. Instead of F- substitution for O2-, we employed Th4+ doping in GdFeAsO with the consideration of "lattice match" between Gd2O2 layers and Fe2As2 ones. As a result, superconductivity with Tconset as high as 56 K was realized in a Gd0.8Th0.2FeAsO polycrystalline sample. This Tc value is among the highest ever discovered in the iron-based oxypnictides.

Fermi surface nesting induced strong pairing in iron-based superconductors.

Abstract: The discovery of high-temperature superconductivity in iron pnictides raised the possibility of an unconventional superconducting mechanism in multiband materials. The observation of Fermi-surface (FS)-dependent nodeless superconducting gaps suggested that inter-FS interactions may play a crucial role in superconducting pairing. In the optimally hole-doped Ba0.6K0.4Fe2As2, the pairing strength is enhanced simultaneously (2Δ/Tc≈7) on the nearly nested FS pockets, i.e., the inner hole-like (α) FS and the 2 hybridized electron-like FSs, whereas the pairing remains weak (2Δ/Tc≈3.6) in the poorly nested outer hole-like (β) FS. Here, we report that in the electron-doped BaFe1.85Co0.15As2, the FS nesting condition switches from the α to the β FS due to the opposite size changes for hole- and electron-like FSs upon electron doping. The strong pairing strength (2Δ/Tc≈6) is also found to switch to the nested β FS, indicating an intimate connection between FS nesting and superconducting pairing, and strongly supporting the inter-FS pairing mechanism in the iron-based superconductors.

Superconductivity induced by phosphorus doping and its coexistence with ferromagnetism in EuFe2(As0.7P0.3)(2).

Abstract: We have studied ${\mathrm{EuFe}}_{2}({\mathrm{As}}_{0.7}{\mathrm{P}}_{0.3}{)}_{2}$ by the measurements of x-ray diffraction, electrical resistivity, thermopower, magnetic susceptibility, magnetoresistance, and specific heat. Partial substitution of As with P results in the shrinkage of lattice, which generates chemical pressure to the system. It is found that ${\mathrm{EuFe}}_{2}({\mathrm{As}}_{0.7}{\mathrm{P}}_{0.3}{)}_{2}$ undergoes a superconducting transition at 26 K, followed by ferromagnetic ordering of ${\mathrm{Eu}}^{2+}$ moments at 20 K. This finding is the first observation of superconductivity stabilized by internal chemical pressure, and supplies a rare example showing the coexistence of superconductivity and ferromagnetism in the ferroarsenide family.

Helicity-protected ultrahigh mobility Weyl fermions in NbP

Abstract: Noncentrosymmetric transition-metal monopnictides, including TaAs, TaP, NbAs, and NbP, are emergent topological Weyl semimetals (WSMs) hosting exotic relativistic Weyl fermions. In this Rapid Communication, we elucidate the physical origin of the unprecedented charge carrier mobility of NbP, which can reach $1\ifmmode\times\else\texttimes\fi{}{10}^{7}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{2}{\phantom{\rule{0.16em}{0ex}}\mathrm{V}}^{\ensuremath{-}1}{\phantom{\rule{0.16em}{0ex}}\mathrm{s}}^{\ensuremath{-}1}$ at 1.5 K. Angle- and temperature-dependent quantum oscillations, supported by density function theory calculations, reveal that NbP has the coexistence of $p$- and $n$-type WSM pockets in the ${k}_{z}=1.16\ensuremath{\pi}/c$ plane (W1-WSM) and in the ${k}_{z}=0$ plane near the high symmetry points $\mathrm{\ensuremath{\Sigma}}$ (W2-WSM), respectively. Uniquely, each W2-WSM pocket forms a large dumbbell-shaped Fermi surface enclosing two neighboring Weyl nodes with the opposite chirality. The magnetotransport in NbP is dominated by these highly anisotropic W2-WSM pockets, in which Weyl fermions are well protected from defect backscattering by real spin conservation associated to the chiral nodes. However, with a minimal doping of $\ensuremath{\sim}1%$ Cr, the mobility of NbP is degraded by more than two orders of magnitude, due to the invalidity of helicity protection to magnetic impurities. Helicity protected Weyl fermion transport is also manifested in chiral anomaly induced negative magnetoresistance, controlled by the W1-WSM states. In the quantum regime below 10 K, the intervalley scattering time by impurities becomes a large constant, producing the sharp and nearly identical conductivity enhancement at low magnetic field.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Weyl and Dirac semimetals in three-dimensional solids

Abstract: Weyl and Dirac semimetals are three-dimensional phases of matter with gapless electronic excitations that are protected by topology and symmetry. As three-dimensional analogs of graphene, they have generated much recent interest. Deep connections exist with particle physics models of relativistic chiral fermions, and, despite their gaplessness, to solid-state topological and Chern insulators. Their characteristic electronic properties lead to protected surface states and novel responses to applied electric and magnetic fields. The theoretical foundations of these phases, their proposed realizations in solid-state systems, and recent experiments on candidate materials as well as their relation to other states of matter are reviewed.

Solar Energy Supply and Storage for the Legacy and Nonlegacy Worlds

Abstract: 1. Setting the Scope of the Challenge 6474 1.1. The Need for Solar Energy Supply and Storage 6474 1.2. An Imperative for Discovery Research 6477 1.3. Scope of Review 6478 2. Large-Scale Centralized Energy Storage 6478 2.1. Pumped Hydroelectric Energy Storage (PHES) 6479 2.2. Compressed Air Energy Storage (CAES) 6480 3. Smaller Scale Grid and Distributed Energy Storage 6481 3.1. Flywheel Energy Storage (FES) 6481 3.2. Superconducting Magnetic Energy Storage 6482 4. Chemical Energy Storage: Electrochemical 6482 4.1. Batteries 6482 4.1.1. Lead-Acid Batteries 6483 4.1.2. Alkaline Batteries 6484 4.1.3. Lithium-Ion Batteries 6484 4.1.4. High-Temperature Sodium Batteries 6484 4.1.5. Liquid Flow Batteries 6485 4.1.6. Metal-Air Batteries 6485 4.2. Capacitors 6485 5. Chemical Energy Storage: Solar Fuels 6486 5.1. Solar Fuels in Nature 6486 5.2. Artificial Photosynthesis and General Considerations of Water Splitting 6486