Search

Magnetic materials with noncolinear spin configurations have engendered significant interest in condensed matter physics due to their intriguing physical properties. In this study, we direct our attention towards the magnetic properties and critical behavior of single-crystal SmMn$_{2}$Ge$_{2}$, an itinerant magnet with numerous temperature-dependent magnetic phase transitions. Notably, SmMn$_{2}$Ge$_{2}$ displays significant magnetic anisotropy with easy magnetization direction switching from the $ c $ axis to the $ab$ plane as temperature decreases. The critical behavior of the ferromagnetic transition occurring above room temperature is thoroughly examined. Reliable and self-consistent critical exponents, including $ \beta = 0.292(2) $, $ \gamma=0.924(8) $, and $ \delta = 4.164(6)$, along with the Curie temperature, $T_{\rm c}=347$ K, are extracted through various methods, which provide evidence for the coexistence of multiple magnetic interactions in SmMn$_{2}$Ge$_{2}$. Further analysis reveals that the magnetic interaction of SmMn$_{2}$Ge$_{2}$ is a long-range type with the interaction distance decaying as $ J(r)\sim r^{-4.35} $.

As known, the piezoelectric polarization effect makes GaN HEMT have unique electrical characteristics and wider applications compared with other III-V semiconductor devices. In this letter, a novel electromechanical coupling theory is proposed and verified for the first time for the GaN HEMT heterojunction structure by applying the mechanical clamping boundary conditions in piezoelectric constitutive equations. The total piezoelectric polarization defined as P couple in this new electromechanical coupling theory consist of three parts: the spontaneous polarization P sp, the strain-induced piezoelectric polarization P strain due to lattice mismatch in growth, and the bias-dependent piezoelectric polarization . The output and transfer characteristics of GaN HEMT have been simulated based on the new electromechanical coupling theory and verified in agreement with the experimental results in trend. This theory helps to extend the understanding of the basic physical mechanism of the AlGaN/GaN interface and is of great significance to device design and application for GaN-based materials.

This vision summarizes the recent advancement of nanostructured steels for advanced structural applications, foresees possible challenges and pinpoints future directions as well as opportunities in this new era of industrial revolution 4.0.

Extremely large magnetoresistance (XMR) has been explored in many nonmagnetic topologically nontrivial/trivial semimetals, while it is experimentally ambiguous which mechanism should be responsible in a specific material due to the complex electronic structures. In this paper, the magnetoresistance origin of single crystal CaAl4 with C2/m structure at low temperature is investigated, exhibiting unsaturated magnetoresistance of ∼ 3000% at 2.5 K and 14 T as the fingerprints of XMR materials. By the combination of ARPES and the first-principles calculations, we elaborate multiband features and anisotropic Fermi surfaces, which can explain the mismatch of isotropic two-band model. Although the structural phase transition from I4/mmm to C2/m has been recognized, the subtle impact on electronic structure is revealed by our ARPES measurements. Considering that both charge compensation and potential topologically nontrivial band structure exist in CaAl4, our findings report CaAl4 as a new reference material for exploring the XMR phenomena.

We report the tip-induced superconductivity on the topological semimetal NbSb2, similar to the observation on TaAs2 and NbAs2. Belonging to the same family of MPn 2, all these materials possess similar band structures, indicating that the tip-induced superconductivity may be closely related to their topological nature and share a common mechanism. Further analysis suggests that a bulk band should play the dominant role in such local superconductivity most likely through interface coupling. In addition, the compatibility between the induced superconductivity and tips’ ferromagnetism gives an evidence for its unconventional nature. These results provide further clues to elucidate the mechanism of the tip-induced superconductivity observed in topological materials.

We report an investigation of the structural, magnetic and electronic properties of Ba(Fe(1-x)V(x))2As2 using x-ray, transport, magnetic susceptibility and neutron scattering measurements. The vanadium substitutions in Fe sites are possible up to 40\%. Hall effect measurements indicate strong hole-doping effect through V doping, while no superconductivity is observed in all samples down to 2K. The antiferromagnetic and structural transition temperature of BaFe2As2 is gradually suppressed to finite temperature then vanishes at x=0.245 with the emergence of spin glass behavior, suggesting an avoided quantum critical point (QCP). Our results demonstrate that the avoided QCP and spin glass state which were previously reported in the superconducting phase of Co/Ni-doped BaFe2As2 can also be realized in non-superconducting Ba(Fe(1-x)V(x))2As2., Comment: 5 pages, 6 figures

We report the synthesis of single crystals of α -ZrSb 2 / α -HfSb 2 and their magneto-transport properties. Both of α -ZrSb 2 and α -HfSb 2 exhibit metallic behavior. The T 3 behavior of zero-field resistivity for both compounds below 30 K indicates interband electron-phonon scattering. The magnetoresistance (MR) is found to obey Kohler's rule for ZrSb 2 while the MR of HfSb 2 deviates from this rule. A possible explanation for the results of Kohler's plot is considered, which is confirmed with the results of the Hall effect. The positive linear Hall resistivity of ZrSb 2 suggests hole-type carriers and a mobility of , while the existence of two types of carriers in HfSb 2 is confirmed from the nonlinear Hall resistivity.

We synthesized single crystals of β-MoTe2 by the chemical vapor transport (CVT) method. Resistivity and magnetoresistivity (MR) have been measured. The MR displays H 2 behavior at low field and linear field dependence at high field, which is different from the quadratic behavior in the sample obtained from the NaCl-flux method. It is suggested that the observed linear MR may originate from disorder. The quality and low-temperature property of β-MoTe2 clearly depend on the growth method. Moreover, the angular-dependent MR reveals the two-fold symmetry of Fermi surface.

Photoluminescence (PL) and Raman spectra under uniaxial strain were measured in mono- and bi-layer MoSe2 to comparatively investigate the evolution of excitonic gaps and Raman phonons with strain. We observed that the strain dependence of excitonic gaps shows a nearly linear behavior in both flakes. One percent of strain increase gives a reduction of ~ 42 meV (~ 35 meV) in A-exciton gap in monolayer (bilayer) MoSe2. The PL width remains little changed in monolayer MoSe2 while it increases rapidly with strain in the bilayer case. We have made detailed discussions on the observed strain-modulated results and compared the difference between monolayer and bilayer cases. The hybridization between 4d orbits of Mo and 4p orbits of Se, which is controlled by the Se–Mo–Se bond angle under strain, can be employed to consistently explain the observations. The study may shed light into exciton physics in few-layer MoSe2 and provides a basis for their applications.

In this paper we developed two types of chitosan-based microspheres with and without biomimetic apatite coatings and compared their potential as injectable scaffolds for bone regeneration. The microspheres were obtained by emulsion cross-linking (E0) and coacervate precipitation (C0), respectively. They were then biomimetically coated with apatite to become E1 and C1 microspheres. The physicochemical properties and biocompatibility of the microspheres were characterized. Both E0 and C0 microspheres presented favorable ranges of diameter, density and Rockwell hardness. However, there were differences in the degree of cross-linking, shape, morphology, degradation rate, swelling rate, pH value after PBS immersion and the biocompatibility between E0 and C0. The apatite coating was successfully prepared for both C0 and E0, which enhanced the attachment, proliferation and differentiation of MC3T3-E1 cells. In conclusion, our results suggest the feasibility of using chitosan microspheres as a potential injectable scaffold. Both the preparation method and the biomimetic apatite coating contribute to their biological properties.

We report both 23Na and 75As nuclear magnetic resonance (NMR) studies on hole-doped Ca1?xNaxFe2As2 superconducting single crystals (x ? 0.67) with the superconducting temperature Tc = 32 K. Singlet superconductivity is suggested by a sharp drop of the Knight shift 75K below Tc. The spin-lattice relaxation rate 1/T1 does not show the Slichter?Hebel coherence peak, which suggests an unconventional pairing. The penetration depth is estimated to be 0.24 ?m at temperature T = 2 K. Here 1/75T1T shows an anisotropic behavior and a prominent low-temperature upturn, with 75T1 denoting the 75As spin-lattice relaxation time and T the temperature, which indicates strong low-energy antiferromagnetic spin fluctuations and supports a magnetic origin of superconductivity.

Raman spectra have been measured on iron-based quaternary CeO$_{1-x}$F$_x$FeAs and LaO$_{1-x}$F$_x$FeAs with varying fluorine doping at room temperatures. A group analysis has been made to clarify the optical modes. Based on the first principle calculations, the observed phonon modes can be assigned accordingly. In LaO$_{1-x}$F$_x$FeAs, the E$_g$ and A$_{1g}$ modes related to the vibrations of La, are suppressed with increasing F doping. However F doping only has a small effect on the E$_g$ and A$_{1g}$ modes of Fe and As. The Raman modes of La and As are absent in rare-earth substituted CeO$_{1-x}$F$_x$FeAs, and the E$_g$ mode of oxygen, corresponding to the in-plane vibration of oxygen, moves to around 450 cm$^{-1}$ and shows a very sharp peak. Electronic scattering background is low and electron-phonon coupling is not evident for the observed phonon modes. Three features are found above 500 cm$^{-1}$, which may be associated with multi-phonon process. Nevertheless it is also possible that they are related to magnetic fluctuations or interband transitions of d orbitals considering their energies., Comment: 12 pages, 3 figures, 2 tables