Electron transport in Dirac and Weyl semimetals

Recently, the Dirac and Weyl semimetals have attracted extensive attention in condensed matter physics due to both the fundamental interest and the potential application of a new generation of electronic devices. Here we review the exotic electrical transport phenomena in Dirac andWeyl semimetals. Section 1 is a brief introduction to the topological semimetals（TSMs）. In Section 2 and Section 3, the intriguing transport phenomena in Dirac semimetals（DSMs） andWeyl semimetals（WSMs） are reviewed, respectively. The most widely studied Cd_3A_（s2） and the TaAs family are selected as representatives to show the typical properties of DSMs and WSMs, respectively. Beyond these systems, the advances in other TSM materials,such as ZrTe_5 and the MoTe_2 family, are also introduced. In Section 4, we provide perspectives on the study of TSMs especially on the magnetotransport investigations.

Autotoxicity of Water Extracts and Decomposition Liquids of Tumorous Stem Mustard(Brassica juncea var.tumida Tsen et Lee) Residues on Seed Germination and Seedling Growth of Tumorous Stem Mustard

[Objective] This study aimed to explore whether there is autotoxicity in tumorous stem mustard through studying the allelopathic effects of water extracts and decomposition liquids of tumorous stem mustard residues on seed germination and seedling growth of tumorous stem mustard.[Method] With Fuza No.2 as the experimental material,the effects of different concentrations of leaf extract,root extract,7-d decomposition liquid,15-d decomposition liquid of tumorous stem mustard on seed germination and seedling growth of tumorous stem mustard were investigated.[Result] Compared with those in the control,the four kinds of 100% treatment solutions all significantly reduced the seed germination rate,seed germination vigor,root length,plant height and fresh weight of tumorous stem mustard(P<0.05),and significantly increased the malondialdehyde(MDA) content,catalase(CAT) activity,peroxidase(POD) activity and superoxide dismutase(SOD) activity of young seedlings of tumorous stem mustard;the allelopathic effects of the four kinds of water extracts and decomposition liquids on seed germination and root length of tumorous stem mustard were weakened with the decreased concentration;for the four kinds of water extracts and decomposition liquids,low-concentration treatment solutions promoted the increase of plant height and fresh weight,while high-concentration treatment solutions inhibited the increase of plant height and fresh weight of young seedlings of tumorous stem mustard;the allelopathic effect of leaf extract on seed germination of tumorous stem mustard was stronger than those of root extract and decomposition liquids,the allelopathic effects of decomposition liquids on seedling growth of tumorous stem mustard were stronger than those of water extracts,the inhibitory effect of leaf extract on seed germination and seedling growth of tumorous stem mustard were stronger than that of root extract,and the inhibitory effect of 15-d decomposition liquid on seed germination and seedling growth of tumorous stem mustard was stronger than that of 7-d decomposition liquid.[Conclusion] The water extracts and decomposition liquids of tumorous stem mustard residues had certain autotoxicity on seed germination and seedling growth of tumorous stem mustard,and their allelopathic effects had a concentration-dependent manner.It could be presumed that the autotoxicity of tumorous stem mustard is the main cause of continuous cropping obstacle.

Discovery of tip induced unconventional superconductivity on Weyl semimetal

Weyl fermion is a massless Dirac fermion with definite chirality,which has been long pursued since 1929.Though it has not been observed as a fundamental particle in nature,Weyl fermion can be realized as low-energy excitation around Weyl point in Weyl semimetal,which possesses Weyl fermion cones in the bulk and nontrivial Fermi arc states on the surface. As a firstly discovered Weyl semimetal,Ta As crystal possesses 12 pairs of Weyl points in the momentum space,which are topologically protected against small perturbations. Here,we report for the first time the tip induced superconductivity on Ta As crystal by point contact spectroscopy. The zero bias conductance peak as well as a conductance plateau with double conductance peaks and sharp double dips are observed in the point contact spectra simultaneously,indicating unconventional superconductivity. Our further theoretical study suggests that the induced superconductivity may have nontrivial topology. The present work opens a new route in investigating the novel superconducting states based on Weyl materials.

Preparation,Mechanical and Biological Properties of Inkjet Printed Alginate/Gelatin Hydrogel

3D printing has made remarkable progress in soft tissue reconstruction enabling the custom design of complex material implants with patient specific geometry.The aim of this study was to inkjet print mechanically reinforced biocompatible hydrogels.Here,we developed a double crosslinked ink by optimizing the rheological properties of solutions of sodium alginate(NaAlg),NaAlg/transglutaminase(TG),CaCl_(2)and gelatin/CaCl_(2).The results showed that a two-component ink system comprising NaAlg(4%w/v)/TG(0.8%w/v)and gelatin(4%w/v)/CaCl_(2)(3%w/v)gave optimum printability.The mechanical and biological properties of printed alginate/gelatin hydrogels prepared from inks with different gelatin contents,and incorporated fibroblasts,were characterized by Scanning Electron Microscope(SEM),mechanical testing and laser confocal microscopy.The compressive moduli of alginate/gelatin hydrogels could be adjusted from 19.2 kPa±1.2 kPa to 65.9 kPa±3.3 kPa by increasing the content of gelatin.After incubation for 7 d,fibroblasts had permeated all printed hydrogels and the rate of proliferation increased with increasing gelatin content.The highest cell proliferation rate(497%)was obtained in a hydrogel containing 4.5%(w/v)gelatin.This study offers a new strategy for the fabrication of 3D structures used to mimic the function of native tissues.

3D Bioprinted Skin Substitutes for Accelerated Wound Healing and Reduced Scar

The shortage of skin for grafting continues to be a major problem in the treatment of serious skin injuries.3D bioprinting provides a new way to solve this problem.However,current 3D printed skin is less effective in treatment of large wounds because of severe shrinkage and scarring.In this study,bionically designed bilayer skin was fabricated using an extrusion-based bioprinter and a gelatin/sodium alginate/gelatin methacrylate hydrogel with excellent physical and biological properties.Full-thickness skin wounds were created in the back of nude mice and treated with bioprinted skin or hydrogel.Bioprinted skin accelerated wound healing,reduced wound contraction and scarring,and facilitated wound skin epithelialization compared with the bioprinted hydrogel or untreated wound.The skin from the wound was collected 28 days after grafting for histology and immunofluorescence analysis.The thickness of the dermis and epidermis of the bioprinted skin was similar to that of nude mice.Microvascular formation in the dermis and dense keratinocytes in the epidermis of the bioprinted skin were observed.This study provides a potential treatment strategy for reducing skin contraction and scar in large skin wounds.

Log-periodic quantum oscillations in topological or Dirac materials

As a manifestation of the underlying physical nature, quailtum oscillations with the applied magnetic field (B) are one of the most important topics in condensed matter physics. The research history can be tracked to 1930 when Lev Shubnikov and W. J. de Haas observed Shubnikov-de Haas (SdH) oscillations in the magnetoresistance (MR) of bismuth crystals. Since then, researchers have observed quantum oscillations in diverse materials, including metals, metallic compounds, semimetals, semiconductors and even insula tors, as well as in artificial mesoscopic microstructures . Nowadays, quantum oscillation detec ted by magneto transport investigation has been a powerful tool to detect the physical properties in solid-state systems.

High thermoelectric performance of ZrTe_(2)/SrTiO_(3) heterostructure

Achieving high thermoelectric pe rformance in thin fiIm heterostructures is essental for integrated and minlatured ther moelectric device applcations.In this work,we d emonstrate a mechansm and device performance of enh anced themoelectnic perfomance induced by interfuclal effect in a tansitdon metal dichalcogenides SrTiO_(3)(STO)heterpstructure Owing to the fomed conductive interface and elevated conductivity.the ZrTe_(2)/STO he teras tructure presents large thermoelectric power factor of 3.7×10^(5)μWcm^(-1)K^(-2) at 10 K.Fomat ion of quasi-wo dimensional conductance at the interface s atributed for the lage Seebeck coffcent and high electnical conductivity leading to high thermoelectric perfor mance which is demonstrated by a prototype device attaining 3 K cooling with 100 mA current input to this heterostructure This supenior themoelectnic property makes this he teros tructure a promtsing candidate for future thermoelectric device.