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We report a comprehensive study on a layered-structure compound of NaZn4As3, which has been predicted to be an ideal topological semimetal (TSM) candidate. It is found that NaZn4As3 undergoes a structural transformation from high temperature rhombohedral to a low temperature monoclinic phase. The electric resistivity exhibits a metal-to-insulator-like transition at around 100 K, and then develops a plateau at low temperature, which might be related to the protected topologically conducting surface states. Our first-principles calculation confirms further that NaZn4As3 is a topological insulator (TI) for both different phases rather than a previously proposed TSM. The Hall resistivity reveals that the hole carriers dominate the transport properties for the whole temperature range investigated. Furthermore, an obvious kink possibly associated to the structure transition has been detected in thermopower around ~ 170 K. The large thermopower and moderate κ indicate that NaZn4As3 and /or its derivatives can provide a good platform for optimizing and studying the thermoelectric performance.

In this work, an immersion freezing system was proposed to shorten the total freezing time and improve the quality of frozen food. The thermal performance of the refrigerant liquid prepared for using in the immersion freezing system was evaluated. A three-dimensional model (3D) was developed to investigate the dynamic characteristics of food freezing process. The effects of the refrigerant liquid inlet flow rate, inlet temperature, total freezing time and freezing rate of chicken breast, velocity and temperature distribution in the immersion freezing system were investigated. In addition, the freezing rates of food using traditional air-blast freezing and the proposed immersion freezing were evaluated. The results showed that the freezing rate of food in immersion freezing was approximately 12.85 times higher than that of the traditional air-blast freezing. When the flow rate increased from 0.11 kg·s-1 to 0.63 kg·s-1, the total freezing time shortened by 36.9%. When the temperature decreased from -25 ºC to -40 ºC, the total freezing time shortened by 35.5%. However, the temperature of the refrigerant liquid should not be too low, which will lead to high viscosity of the liquid, thus resulting in increasing in the overall power consumption of the proposed system.

Using 2% percent of iron dopants as reaction active sites yields a series of single crystals of 1,10-phenanthroline intercalated NiPS3, via solution reaction with aniline chloride, not possible by direct reaction. Experimental magnetic susceptibility measurements demonstrate that 1,10-phenanthroline intercalation suppresses the anti-ferromagnetism ordering at around 150 K in Fe0.02Ni0.98PS3, and gives rise to a ferrimagnetic phase transition at the temperature around 75 K. A intercalation mechanism is proposed for the reaction, and this dopant seeding method provides a new approach for intercalation into layered materials.\ud \ud

Magnetic Weyl semimetals (MWSM) have attracted significant attention due to their intriguing physical properties and potential applications in spin-electronic devices. Here we report the characterization of NdAlSi including transport, magnetization, and heat capacity on single crystals, as well as band structure calculation. It is a newly proposed MWSM candidate which breaks both time-reversal and spacial inversion symmetries. A temperature-magnetic field phase diagram is experimentally established. Remarkably, on the angular magnetoresistance (AMR), a two-fold symmetric sharp peak instead of a smooth variation is observed in the field-induced ferrimagnetic phase. We argue that the tunability of both the topological and magnetic properties in NdAlSi is crucial for realizing such a behavior. Our results indicate that 4f-electron-based MWSM can provide a unique platform to explore new and intriguing quantum phenomena arising from the interaction between magnetism and topology., 24 pages, 12 figures

Finding promising materials that show large thermoelectricity at low temperatures is crucial for low-temperature refrigeration applications. Here, we report a significantly large thermoelectric power factor ( PF) up to 50 μW cm−1 K−2 at an extremely low temperature of ∼8 K in a quasi-one-dimensional (Q1D) antiferromagnet KMn6Bi5, in which highly electrical conductivity and dramatic enhancement of Seebeck coefficient may favor its occurrence. In addition, a giant Nernst signal has also been detected with a maximum value of 24 μV K−1 T−1 at ∼5 K. All these intriguing characteristics observed in KMn6Bi5 can be attributed to the manifestation of the unusually strong coupling among spin, charge, lattice, and one dimensionality in KMn6Bi5. Our findings provide fundamental insight into the thermal transport in Q1D antiferromagnets and should stimulate further experimental exploration of thermal transport in such Q1D family for possible thermoelectric applications at extremely low temperatures.

We report the experimental results of magnetotransport on the single crystal ${\mathrm{MoGe}}_{2}$, which was theoretically predicated to be a topological insulator. The resistivity of ${\mathrm{MoGe}}_{2}$ exhibits a metallic behavior at zero field, while with magnetic fields applied along the $z$ axis and perpendicular to current, ${\mathrm{MoGe}}_{2}$ presents an upturn resistivity behavior and unsaturated quadratic large magnetoresistance (MR). The analysis of Hall effect shows that ${\mathrm{MoGe}}_{2}$ is a compensated semimetal with high mobilities at low temperatures, which is the origin of resistivity upturn and unsaturated large MR. As magnetic fields parallel to current, ${\mathrm{MoGe}}_{2}$ shows a weak antilocalization effect at low fields and a pronounced negative MR at higher fields, which is analogous to the picture of the Adler-Bell-Jackiw axial anomaly. Our results indicate that ${\mathrm{MoGe}}_{2}$ is a topological semimetal rather than a topological insulator, and will encourage further theoretical and experimental investigations on this compound.

We report the magnetotransport properties and the electronic structure of $\mathrm{Na}{\mathrm{Cd}}_{4}{\mathrm{As}}_{3}$ single crystal. The electric resistivity of $\mathrm{Na}{\mathrm{Cd}}_{4}{\mathrm{As}}_{3}$ exhibits a metallic behavior. Clear Shubnikov--de Haas (SdH) oscillations have been observed at low temperatures and high magnetic fields. A single fundamental frequency and small cyclotron effective mass are obtained from the analysis of SdH oscillations, which originate from an ellipsoidal Fermi surface. The Hall resistivity reveals the multiband nature at low temperature and the electron carriers dominate the transport properties. First-principles calculations show that the electronic structure of $\mathrm{Na}{\mathrm{Cd}}_{4}{\mathrm{As}}_{3}$ undergoes a topological phase transition from topological crystalline insulator (TCI) to topological insulator (TI) induced by the structural phase transition. The breaking of mirror symmetry is considered to play a key role in the topological phase transition. Our findings show that $\mathrm{Na}{\mathrm{Cd}}_{4}{\mathrm{As}}_{3}$ is a suitable platform to study the effect of mirror symmetry on the band topology of TCI.

We report a comprehensive high-pressure study on the monoclinic TlFeSe2 single crystal, which is an antiferromagnetic insulator with quasi-one-dimensional crystal structure at ambient pressure. It is found that TlFeSe2 undergoes a pressure-induced structural transformation from the monoclinic phase to an orthorhombic structure above P c ≈ 13 GPa, accompanied with a large volume collapse of ΔV/V 0 = 8.3%. In the low-pressure monoclinic phase, the insulating state is easily metallized at pressures above 2 GPa; while possible superconductivity with T c onset ∼ 2 K is found to emerge above 30 GPa in the high-pressure phase. Such a great tunability of TlFeSe2 under pressure indicates that the ternary AFeSe2 system (A = Tl, K, Cs, Rb) should be taken as an important platform for explorations of interesting phenomena such as insulator-metal transition, dimensionality crossover, and superconductivity.

Interfaces between materials with different electronic ground states have become powerful platforms for creating and controlling novel quantum states of matter, in which inversion symmetry breaking and other effects at the interface may introduce additional electronic states. Among the emergent phenomena, superconductivity is of particular interest. Here, by depositing metal films on a newly identified topological semimetal tungsten carbide (WC) single crystal, interfacial superconductivity is obtained, evidenced from soft point-contact spectroscopy. This very robust phenomenon is demonstrated for a wide range of metal/WC interfaces, involving both nonmagnetic and ferromagnetic films, and the superconducting transition temperatures are surprisingly insensitive to the magnetism of thin films. This method offers an opportunity to explore the long-sought topological superconductivity and has potential applications in topological-state-based spin devices.

This paper dealt with the fracture failure of a GCr15 steel ball screw nut. Through testing and analysis of hardness, microstructure, scanning electron microscopy and energy dispersive spectrum meter, it was found that there are local carbide network, few oversized carbide particles and metallic inclusions. The analysis showed that carbide network was failed to be eliminated through spheroidizing annealing treatment, while the presence of non-uniform carbide particles and metallic inclusions easily induced the crack and consequently led to the fracture of the nut.