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The rotational hydraulic damper has advantages in the design and control of rotational machines. This paper presents a novel hydraulic rotational damper with the characteristic of adjusting the damping coefficient. It is composed of a shell, a gap, a rotor shaft, sliding vanes, a valve, and a motor, just like a combination of a sliding pump system and a valve driven by a motor. A new cam ring slot designed to guide the radial motion of sliding vanes could reduce friction resistance force, which will also benefit the design of the sliding pump. The damping coefficient model of this damper is established based on dynamic analysis. Series of numerical simulations validate the impact of factors on the damping coefficient. Frictional resistances have little influence on the damping coefficient during most conditions. The total coefficient is positively correlative with the angular velocity and the valve angle. Therefore, changing the valve angle according to the rotor shaft’s angular speed could adjust the damping coefficient.

Weyl semimetal is the three-dimensional analog of graphene. According to quantum field theory, the appearance of Weyl points near the Fermi level will cause novel transport phenomena related to chiral anomaly. In the present paper, we report the experimental evidence for the long-anticipated negative magnetoresistance generated by the chiral anomaly in a newly predicted time-reversal-invariant Weyl semimetal material TaAs. Clear Shubnikov de Haas (SdH) oscillations have been detected starting from a very weak magnetic field. Analysis of the SdH peaks gives the Berry phase accumulated along the cyclotron orbits as π , indicating the existence of Weyl points.

The topological materials have attracted much attention for their unique electronic structure and peculiar physical properties. ZrTe 5 has host a long-standing puzzle on its anomalous transport properties manifested by its unusual resistivity peak and the reversal of the charge carrier type. It is also predicted that single-layer ZrTe 5 is a two-dimensional topological insulator and there is possibly a topological phase transition in bulk ZrTe 5 . Here we report high-resolution laser-based angle-resolved photoemission measurements on the electronic structure and its detailed temperature evolution of ZrTe 5 . Our results provide direct electronic evidence on the temperature-induced Lifshitz transition, which gives a natural understanding on underlying origin of the resistivity anomaly in ZrTe 5 . In addition, we observe one-dimensional-like electronic features from the edges of the cracked ZrTe 5 samples. Our observations indicate that ZrTe 5 is a weak topological insulator and it exhibits a tendency to become a strong topological insulator when the layer distance is reduced. To understand the anomalous electronic transport properties of ZrTe 5 remains an elusive puzzle. Here, Zhang et al . report direct electronic evidence to the origin of the resistivity anomaly and temperature induced Lifshitz transition in ZrTe 5 , indicating it being a weak topological insulator.

Unexpectedly, in superconducting iron chalcogenides, a second, much higher, maximum in the superconducting transition temperature emerges under increasing pressure. A second wind for iron superconductors Reports of superconductivity at up to 32 kelvin have boosted interest in a family of superconductors known as the iron chalcogenides. Pressure can have a significant role in the production and control of superconductivity in iron-based superconductors, and here Sun et al . report that as pressure on a system increases, superconductivity in the iron chalcogenides vanishes at first, then reappears in a second phase with a higher transition temperature at pressures above 11.5 gigapascals, or more than 110,000 atmospheres. This phenomenon could prove useful for manipulating the electronic and structural properties of materials without altering their chemistry. High-pressure studies are a useful method for investigating the mechanisms of superconductivity. Pressure has an essential role in the production 1 and control 2 , 3 of superconductivity in iron-based superconductors. Substitution of a large cation by a smaller rare-earth ion to simulate the pressure effect has raised the superconducting transition temperature T c to a record high of 55 K in these materials 4 , 5 . In the same way as T c exhibits a bell-shaped curve of dependence on chemical doping, pressure-tuned T c typically drops monotonically after passing the optimal pressure 1 , 2 , 3 . Here we report that in the superconducting iron chalcogenides, a second superconducting phase suddenly re-emerges above 11.5 GPa, after the T c drops from the first maximum of 32 K at 1 GPa. The T c of the re-emerging superconducting phase is considerably higher than the first maximum, reaching 48.0–48.7 K for Tl 0.6 Rb 0.4 Fe 1.67 Se 2 , K 0.8 Fe 1.7 Se 2 and K 0.8 Fe 1.78 Se 2 .

The Seebeck effect encounters a few fundamental constraints hindering its thermoelectric (TE) conversion efficiency. Most notably, there are the charge compensation of electrons and holes that diminishes this effect, and the Wiedemann-Franz (WF) law that makes independent optimization of the corresponding electrical and thermal conductivities impossible. Here, we demonstrate that in the topological Dirac semimetal Cd 3 As 2 the Nernst effect, i.e., the transverse counterpart of the Seebeck effect, can generate a large TE figure of merit z N T . At room temperature, z N T ≈ 0.5 in a small field of 2 T and it significantly surmounts its longitudinal counterpart for any field. A large Nernst effect is genetically expected in topological semimetals, benefiting from both the bipolar transport of compensated electrons and holes and their high mobilities. In this case, heat and charge transport are orthogonal, i.e., not intertwined by the WF law anymore. More importantly, further optimization of z N T by tuning the Fermi level to the Dirac node can be anticipated due to not only the enhanced bipolar transport, but also the anomalous Nernst effect arising from a pronounced Berry curvature. A combination of the topologically trivial and nontrivial advantages promises to open a new avenue towards high-efficient transverse thermoelectricity.

Charge transport of topological semimetals is the focus of intensive investigations because of their nontrivial band topology. Heat transport of these materials, on the other hand, is largely unexplored and remains elusive. Here, we report on an observation of unprecedented, giant magnetic quantum oscillations of thermal conductivity in the prototypical Weyl semimetal TaAs. The oscillations are antiphase with the quantum oscillating electronic density of states of a Weyl pocket, and their amplitudes amount to 2 orders of magnitude of the estimation based on the Wiedemann-Franz law. Our analyses show that all the conventional heat-transport mechanisms through diffusions of propagating electrons, phonons, and electron-hole bipolar excitations are far inadequate to account for these phenomena. Taking further experimental facts that the parallel field configuration favors much-higher magnetothermal conductivity, we propose that the newly proposed chiral zero sound provides a reasonable explanation to these exotic phenomena. More work focusing on other topological semimetals along the same line is badly called for.

The search for topological superconductivity (TSC) is currently an exciting pursuit, since non-trivial topological superconducting phases could host exotic Majorana modes. However, the difficulty in fabricating proximity-induced TSC heterostructures, the sensitivity to disorder and stringent topological restrictions of intrinsic TSC place serious limitations and formidable challenges on the materials and related applications. Here, we report a new type of intrinsic TSC, namely intrinsic surface topological superconductivity (IS-TSC) and demonstrate it in layered AuSn 4 with T c of 2.4 K. Different in-plane and out-of-plane upper critical fields reflect a two-dimensional (2D) character of superconductivity. The two-fold symmetric angular dependences of both magneto-transport and the zero-bias conductance peak (ZBCP) in point-contact spectroscopy (PCS) in the superconducting regime indicate an unconventional pairing symmetry of AuSn 4 . The superconducting gap and surface multi-bands with Rashba splitting at the Fermi level ( E F ), in conjunction with first-principle calculations, strongly suggest that 2D unconventional SC in AuSn 4 originates from the mixture of p- wave surface and s- wave bulk contributions, which leads to a two-fold symmetric superconductivity. Our results provide an exciting paradigm to realize TSC via Rashba effect on surface superconducting bands in layered materials. The authors study the layered superconductor AuSn 4 ( T c  = 2.4 K) and reveal a two-fold symmetric angular dependence, consistent with unconventional pairing. They argue that the two-fold symmetry results from the Rashba-driven mixture of p -wave surface and s -wave bulk contributions.

Recently, as a novel technique, electronic double-layer transistors (EDLTs) with ionic liquids have shown strong potential for tuning the electronic states of correlated systems. EDLT induced local carrier doping can always lead to dramatic changes in physical properties when compared to parent materials, e.g. insulating-superconducting (SC) transition. Generally, the modification of gate voltage (VG) in EDLT devices produces a direct change on the doping level. Here, we report that the processing temperature (TG) also plays a dominant role in the electric field induced superconductivity in layered ZrNBr single crystals. When applying VG at T G ≥ 250 K, the induced SC state is irreversible in the material, which is confirmed in the zero resistance and diamagnetism after long-time relaxation at room temperature and/or by applying reverse voltage, whereas the solid/liquid interface induced reversible insulating-SC transition occurs at T G ≤ 235 K. These experimental facts support another electrochemical mechanism that electric field induced partial deintercalation of Br ions could cause permanent electron doping into the system. Our findings in this study will extend the potential of electric fields for tuning bulk electronic states in low-dimension systems.

The quantum geometric Berry curvature results in an anomalous correction to the band velocity of crystal electrons with a corresponding transverse (thermo)electric conductivity. However, time‐reversal symmetry typically constrains the direct observation and exploitation of anomalous transport to magnetic compounds. Here, it is demonstrated the anomalous Hall and Nernst conductivities are essential for describing the optoelectronic transport in thin films of the non‐magnetic, weakly gapped semimetal HfTe5 subject to an external magnetic field. A focused photoexcitation adresses the symmetries of the local Nernst conductivity, which unveils a hitherto hidden, anomalous photo‐Nernst effect of three‐dimensional (3D) massive Dirac fermions. The experimental temperature and density dependencies are compared with a semiclassical Boltzmann transport model. For HfTe5 thin films with the Fermi level close to the gap, the model suggests that the anomalous photo‐Nernst currents originate from an intrinsic Berry curvature mechanism, where the Zeeman interaction effectively breaks time‐reversal symmetry of the massive Dirac fermions already at moderate external magnetic fields.

Strange-metal phenomena often develop at the border of antiferromagnetic order in strongly correlated metals1. Previous work established that they can originate from the fluctuations anchored by the quantum-critical point associated with a continuous quantum phase transition out of the antiferromagnetic order2–4. What is still unclear is how these phenomena can be associated with a potential new phase of matter at zero temperature. Here, we show that magnetic frustration of the 4f local moments in the distorted kagome intermetallic compound cerium palladium aluminium gives rise to such a paramagnetic quantum-critical phase. Our discovery motivates a design principle for strongly correlated metallic states with unconventional excitations.