Novel material for nonvolatile ovonic unified memory (OUM)－Ag11In12Te26Sb51 phase change semiconductor

In this paper, Ag_{11}In_{12}Te_{26}Sb_{51} phase change semiconductor films have been prepared by dc sputtering. The crystallization behaviour of amorphous Ag_{11}In_{12}Te_{26}Sb_{51} thin films was investigated by using differential scanning calorimetry and x-ray diffraction. It was found that the crystallization temperature is about 483K and the melting temperature is 754.8K and the activation energy for crystallization, E_a, is 2.07eV. The crystalline Ag_{11}In_{12}Te_{26}Sb_{51} films were obtained using initializer. The initialization conditions have a great effect on the sheet resistance of Ag_{11}In_{12}Te_{26}Sb_{51} films. We found that the effect of the initialization condition on the sheet resistance can be ascribed to the crystallinity of Ag_{11}In_{12}Te_{26}Sb_{51} films. The sheet resistance of the amorphous (R_{amo}) film is found to be larger than 1×10^6Ω and that of the crystalline (R_{cry}) film lies in the range from about 10^3 to 10^4Ω. So we have the ratio R_{amo}/R_{cry}=10^2～10^3, which is sufficiently large for application in memory devices.     

Manipulation of intrinsic quantum anomalous Hall effect in two-dimensional MoYN2CSCl MXene

Quantum anomalous Hall effect (QAHE) is an innovative topological spintronic phenomenon with dissipationless chiral edge states and attracts rapidly increasing attention. However, it has only been observed in few materials in experiments. Here, according to the first-principles calculations, we report that the MXene MoYN$_{2}$CSCl shows a topologically nontrivial band gap of 37.3~meV, possessing QAHE with a Chern number of $C = 1$, which is induced by band inversion between $ {\rm d}_{xz}$ and ${\rm d}_{yz}$ orbitals. Also, the topological phase transition for the MoYN$_{2}$CSCl can be realized via strain or by turning the magnetization direction. Remarkably, MoYN$_{2}$CSCl shows the nodal-line semimetal state dependent on the electron correlation $U$. Our findings add an experimentally accessible and tunable member to the QAHE family, which stands a chance of enriching the applications in spintronics.     

Structural evolution and molecular dissociation of H2S under high pressures

Solid H$_{2}$S as the precursor for H$_{3}$S with incredible superconducting properties under high pressure, has recently attracted extensive attention. Here in this work, we propose two new phases of H$_{2}$S with $P$4$_{2}/n$ and $I$4$_{1}/a$ lattice symmetries in a pressure range of 0 GPa-30 GPa through first-principles structural searches, which complement the phase transition sequence. Further an $ab initio$ molecular dynamics simulation confirms that the molecular phase $P2/c$ of H$_{2}$S is gradually dissociated with the pressure increasing and reconstructs into a new $P$2$_{1}/m$ structure at 160 GPa, exhibiting the superconductivity with $T_{\rm c}$ of 82.5 K. Our results may provide a guidance for the theoretical study of low-temperature superconducting phase of H$_{2}$S.     

Isotopic effect of Cl2+ rovibronic spectra in the A-X system

This paper studies the isotopic effect of Cl2+ rovibronic spectra in the A2Πu(Ω=1/2) X 2Πg(Ω= 1/2) system.Based on the experimental results of the molecular constants of 35 Cl2+,it calculates the vibrational isotope shifts of the(2,7) and(3,7) band between the isotopic species 35 Cl+2,35 Cl 37 Cl+and 37 Cl2+,and estimates the rotational constants of both A 2 Π u and X 2 Π g states for the minor isotopic species 35 Cl 37 Cl+and 37 Cl2+.The experimental results of the spectrum of 35 Cl 37 Cl+(3,7) band proves the above mentioned theoretical calculation.The molecular constants and thus resultant rovibronic spectrum for 37 Cl2+ were predicted,which will be helpful for further experimental investigation.     

Superconductivity in CuIr2-xAlxTe4 telluride chalcogenides

The relationship between charge-density-wave (CDW) and superconductivity (SC), two vital physical phases in condensed matter physics, has always been the focus of scientists' research over the past decades. Motivated by this research hotspot, we systematically studied the physical properties of the layered telluride chalcogenide superconductors CuIr$_{2-x}$Al$_{x}$Te$_{4}$ ($0 \leqslant x \leqslant 0.2$). Through the resistance and magnetization measurements, we found that the CDW order was destroyed by a small amount of Al doping. Meanwhile, the superconducting transition temperature ($T_{\rm c}$) kept changing with the change of doping amount and rose towards the maximum value of 2.75 K when $x=0.075$. The value of normalized specific heat jump ($\Delta C/\gamma T_{\rm c}$) for the highest $T_{\rm c}$ sample CuIr$_{1.925}$Al$_{0.075}$Te$_{4}$ was 1.53, which was larger than the BCS value of 1.43 and showed the bulk superconducting nature. In order to clearly show the relationship between SC and CDW states, we propose a phase diagram of $T_{\rm c}$ vs. doping content.     

Magnetization and magnetic phase diagrams of a spin-1/2 ferrimagnetic diamond chain at low temperature

We used the Jordan–Wigner transform and the invariant eigenoperator method to study the magnetic phase diagram and the magnetization curve of the spin-1/2 alternating ferrimagnetic diamond chain in an external magnetic field at finite temperature. The magnetization versus external magnetic field curve exhibits a 1/3 magnetization plateau at absolute zero and finite temperatures, and the width of the 1/3 magnetization plateau was modulated by tuning the temperature and the exchange interactions. Three critical magnetic field intensities H_(CB), H_(CE) and H_(CS) were obtained, in which the H_(CB) and H_(CE) correspond to the appearance and disappearance of the 1/3 magnetization plateau, respectively, and the higher H_(CS) correspond to the appearance of fully polarized magnetization plateau of the system. The energies of elementary excitation ωσ,k(σ = 1, 2, 3) present the extrema of zero at the three critical magnetic fields at 0 K, i.e., [hω_(3,k)(HCB)]_(min)= 0, [hω_(2,k)(H_(CE))]_(max)= 0 and [hω _(2,k)(H_(CS))]_(min)= 0, and the magnetic phase diagram of magnetic field versus different exchange interactions at 0 K was established by the above relationships. According to the relationships between the system's magnetization curve at finite temperatures and the critical magnetic field intensities, the magnetic field-temperature phase diagram was drawn. It was observed that if the magnetic phase diagram shows a three-phase critical point, which is intersected by the ferrimagnetic phase, the ferrimagnetic plateau phase, and the Luttinger liquid phase, the disappearance of the1/3 magnetization plateau would inevitably occur. However, the 1/3 magnetization plateau would not disappear without the three-phase critical point. The appearance of the 1/3 magnetization plateau in the low temperature region is the macroscopic manifestations of quantum effect.     

Electron tunnelling phase time and dwell time through an associated delta potential barrier

The electron tunnelling phase time τP and dwell time τD through an associated delta potential barrier U(x) = ξδ(x) are calculated and both are in the order of 10^-17～10^-16s. The results show that the dependence of the phase time on the delta barrier parameter ξ can be described by the characteristic length lc = h^2/meξ and the characteristic energy Ec=meξ^2/h^2 of the delta barrier, where me is the electron mass, lc and Ec are assumed to be the effective width and height of the delta barrier with lcEc=ξ, respectively. It is found that TD reaches its maximum and τD = τp as the energy of the tunnelling electron is equal to Ec/2, i.e. as lc =λDB, λDB is de Broglie wave length of the electron.     

Spin freezing in the van der Waals material Mn2Ga2S5

Geometrical frustration in low-dimensional magnetic systems has been an intriguing research aspect, where the suppression of conventional magnetic order may lead to exotic ground states such as spin glass or spin liquid. In this work we report the synthesis and magnetism study of the monocrystalline Mn$_2$Ga$_2$S$_5$, featuring both the van der Waals structure and a bilayered triangular Mn lattice. Magnetic susceptibility reveals a significant antiferromagnetic interaction with a Curie-Weiss temperature $\theta_{\rm w}\sim-260$ K and a high spin $S=5/2$ Mn$^{2+}$ state. However, no long range magnetic order has been found down to 2 K, and a spin freezing transition is found to occur at around 12 K well below its $\theta_{\rm w}$. This yields a frustration index of $f = -\theta_{\rm w}/T_{\rm f} \approx 22$, an indication that the system is highly frustrated. The absence of a double-peak structure in magnetic specific heat compared with the $TM_2$S$_4$ compounds implies that the spin freezing behavior in Mn$_2$Ga$_2$S$_5$ is a result of the competition between exchange interactions and the 2D crystalline structure. Our results suggest that the layered Mn$_2$Ga$_2$S$_5$ would be an excellent candidate for investigating the physics of 2D magnetism and spin disordered state.     

The influence of collision energy on magnetically tuned 6Li-6Li Feshbach resonance

The effect of collision energy on the magnetically tuned $^{6}$Li-$^{6}$Li Feshbach resonance (FR) is investigated theoretically by using the coupled-channel (CC) method for the collision energy ranging from 1 μ$ {\rm K} \cdot {k}_{\rm B}$ to 100 μ$ {\rm K} \cdot {k}_{\rm B}$. At the collision energy of 1 μ$ {\rm K} \cdot {k}_{\rm B}$, the resonance positions calculated are 543.152 Gs (s wave, the unit $1 {\rm Gs}=10^{-4} {\rm T}$), 185.109 Gs (p wave $|m_{l}| = 0$), and 185.113 Gs (p wave $|m_{l}| = 1$), respectively. The p-wave FR near 185 Gs exibits a doublet structure of 4 mGs, associated with dipole-dipole interaction. With the increase of the collision energy, it is found that the splitting width remains the same (4 mGs), and that the resonance positions of s and p waves are shifted to higher magnetic fields with the increase of collision energy. The variations of the other quantities including the resonance width and the amplitude of the total scattering section are also discussed in detail. The thermally averaged elastic rate coefficients at $T=10$, 15, 20, 25 K are calculated and compared.     

Superconducting properties of the C15-type Laves phase ZrIr2 with an Ir-based kagome lattice

We report systematic studies on superconducting properties of the Laves phase superconductor ZrIr$_2$. It crystallizes in a C15-type (cubic MgCu$_2$-type, space group $Fd\overline{3}m$) structure in which the Ir atoms form a kagome lattice, with cell parameters $a=b=c=7.3596(1)$ Å. Resistivity and magnetic susceptibility measurements indicate that ZrIr$_2$ is a type-II superconductor with a transition temperature of 4.0 K. The estimated lower and upper critical fields are 12.8 mT and 4.78 T, respectively. Heat capacity measurements confirm the bulk superconductivity in ZrIr$_2$. ZrIr$_2$ is found to possibly host strong-coupled s-wave superconductivity with the normalized specific heat change $\Delta C_{\rm e}/\gamma T_{\rm c} \sim 1.86$ and the coupling strength $\Delta_0/k_{\rm B}T_{\rm c} \sim 1.92$. First-principles calculations suggest that ZrIr$_2$ has three-dimensional Fermi surfaces with simple topologies, and the states at Fermi level mainly originate from the Ir-5d and Zr-4d orbitals. Similar to SrIr$_2$ and ThIr$_2$, spin--orbit coupling has dramatic influences on the band structure in ZrIr$_2$.     

Growth,characterization, and Raman spectra of the 1T phases of TiTe2, TiSe2, and TiS2

High-quality large 1$T$ phase of Ti$X_2$ ($X ={\rm Te}$, Se, and S) single crystals have been grown by chemical vapor transport using iodine as a transport agent. The samples are characterized by compositional and structural analyses, and their properties are investigated by Raman spectroscopy. Several phonon modes have been observed, including the widely reported $A_{1g}$ and $E_g$ modes, the rarely reported $E_u$ mode ($\sim$183 cm$^{-1}$ for TiTe$_2$, and $\sim$185 cm$^{-1}$ for TiS$_2$), and even the unexpected $K$ mode ($\sim$85 cm$^{-1}$) of TiTe$_2$. Most phonons harden with the decrease of temperature, except that the $K$ mode of TiTe$_2$ and the $E_u$ and "$A_{2u}$/Sh" modes of TiS$_2$ soften with the decrease of temperature. In addition, we also found phonon changes in TiSe$_2$ that may be related to charge density wave phase transition. Our results on Ti$X_2$ phonons will help to understand their charge density wave and superconductivity.     

Deposition and characterization of YBCO/CeO2/YSZ/CeO2 multilayers on biaxially textured Ni substrates

CeO2/YSZ/CeO2 buffer layers were deposited on biaxially textured Ni substrates by pulsed laser deposition. The influence of the processing parameters on the texture development of the seed layer CeO2 was investigated. Epitaxial films of YBCO were then grown in situ on the CeO2/YSZ （yttria-stabilized ZrO2）/CeO2-buffered Ni substrates. The resulting YBCO conductors exhibited self-fleld critical current density Jc of more than 1 MA/cm^2 at 77K and superconducting transition temperature Tc of about 91K.     

Potential energy curves and analytical potential energy functions of the metastable states of B2^＋＋

The multi-reference configuration interaction method and aug-cc-pvqz （AVQZ） have been used to calculate potential energy curves （PECs） of the singlet and triplet states of the riu and rig symmetry of B2＋＋. All of the four states （^l∏u, ^1∏g, ^3∏u and ^3∏g） are found to be metastable states, though the potential well of ^3∏u symmetry is very shallow. Based on the PECs, the analytical potential energy functions （APEFs） of these states have been fitted using the least square fitting method and two models of function. The spectroscopic parameters of each state are also calculated, and are compared with other investigations in the literature. The credibility and veracity of the two functions are evaluated. Some ideas to improve the fitting accuracy are presented. Also the vibrational levels for each state are predicted by solving the SchrSdinger equation of nuclear motion.     

Two-electron and one-photon transitions in highly charged nickel-like ions

This paper calculates the transition wavelengths and probabilities of the two-electron and one-photon (TEOP) transition from the $(3{\rm s}^{-1}_{1/2}4{\rm d}_{j})_{J=1,2}$ to $(3{\rm p}^{-1}_{3/2}4{\rm s}_{1/2})_{J=1}$ and the $(3{\rm p}^{-1}_{1/2}4{\rm s}_{1/2})_{J=1}$ to $(3{\rm d}^{-1}_{j}4{\rm d}_{j'})_{J=1,2}$ for highly charged Ni-like ions with atomic number $Z$ in the range $47\leq Z\leq92$. In the calculations, the multi-configuration Dirac--Fock method and corresponding program packages GRASP92 and REOS99 were used, and the relativistic effects, correlation effects and relaxation effects were considered systematically. It is found that the TEOP transitions are very sensitive to the correlation of electrons, and the probabilities will be enhanced sharply in some special $Z$ regions along the isoelectronic sequence. The present TEOP transition wavelengths are compared with the available data from some previous publications, good agreement is obtained.     

Incommensurate-commensurate magnetic phase transition in double tungstate Li2Co(WO4)2

Magnetic susceptibility, specific heat, and neutron powder diffraction measurements have been performed on polycrystalline Li$_{2}$Co(WO$_{4}$)$_{2}$ samples. Under zero magnetic field, two successive magnetic transitions at $T_{\rm N1}\sim 9.4$ K and $T_{\rm N2}\sim 7.4$ K are observed. The magnetic ordering temperatures gradually decrease as the magnetic field increases. Neutron diffraction reveals that Li$_{2}$Co(WO$_{4}$)$_{2}$ enters an incommensurate magnetic state with a temperature dependent $\bm k$ between $T_{\rm N1}$ and $T_{\rm N2}$. The magnetic propagation vector locks-in to a commensurate value $\bm k = (1/2, 1/4, 1/4)$ below $T_{\rm N2}$. The antiferromagnetic structure is refined at 1.7 K with Co$^{2+}$ magnetic moment 2.8(1) $\mu_{\rm B}$, consistent with our first-principles calculations.     

Ru thickness-dependent interlayer coupling and ultrahigh FMR frequency in FeCoB/Ru/FeCoB sandwich trilayers

The antiferromagnetic (AFM) interlayer coupling effective field in a ferromagnetic/non-magnetic/ferromagnetic (FM/NM/FM) sandwich structure, as a driving force, can dramatically enhance the ferromagnetic resonance (FMR) frequency. Changing the non-magnetic spacer thickness is an effective way to control the interlayer coupling type and intensity, as well as the FMR frequency. In this study, FeCoB/Ru/FeCoB sandwich trilayers with Ru thickness ($t_{\rm Ru}$) ranging from 1 Å to 16 Å are prepared by a compositional gradient sputtering (CGS) method. It is revealed that a stress-induced anisotropy is present in the FeCoB films due to the B composition gradient in the samples. A $t_{\mathrm{Ru}}$-dependent oscillation of interlayer coupling from FM to AFM with two periods is observed. An AFM coupling occurs in a range of $2 {\rm Å} \le t_{\rm Ru} \le 8 {\rm Å}$ and over 16 $\mathrm{Å}$, while an FM coupling is present in a range of $t_{\rm Ru}< 2$ Å and $9 {\rm Å} \le t_{\rm Ru} \le 14.5 Å$. It is interesting that an ultrahigh optical mode (OM) FMR frequency in excess of 20 GHz is obtained in the sample with ${t}_{\mathrm{Ru}}= 2.5 \mathrm{Å}$ under an AFM coupling. The dynamic coupling mechanism in trilayers is simulated, and the corresponding coupling types at different values of $t_{\mathrm{Ru}}$ are verified by Layadi's rigid model. This study provides a controllable way to prepare and investigate the ultrahigh FMR films.     

Growth and characterization of superconducting Ca1-xNaxFe2As2 single crystals by NaAs-flux method

High-quality superconducting Ca$_{1-x}$Na$_x$Fe$_2$As$_2$ single crystals have been successfully grown by the NaAs-flux method, with sodium doping level $x = 0.4$-0.64. The typical sizes of these crystals are more than 10 mm in $ab$-plane and $\sim 0.1$ mm along $c$-axis in thickness. X-ray diffraction, resistance and magnetization measurements are carried out to characterize the quality of these crystals. While no signature of magnetic phase transitions is detected in the normal state, bulk superconductivity is found for these samples, with a sharp transition at $T_{\rm c}$ ranging from 19.8 K ($x = 0.4$) to 34.8 K ($x = 0.64$). The doping dependences of the $c$-axis parameter and $T_{\rm c}$ are consistent with previous reports, suggesting a possible connection between the lattice parameters and superconductivity.     

Ab initio calculations on the α^3∑u^＋ state properties of dimer ^7Li2

The comparison between single-point energy scanning （SPES） and geometry optimization （OPT） in determining the equilibrium geometry of the α^3∑u^＋ state for ^7Li2 is made at numerous basis sets such as 6-311＋＋G（2df）, cc-PVTZ, 6-311＋＋G（2df, p）, 6-311G（3df,3pd）, 6-311＋＋G（2df,2pd）, D95（3df,3pd）, 6-311＋＋G, DGDZVP, 6-311＋＋G（3df,2pd）, 6-311G（2df,2pd）, D95V＋＋, CEP-121G, 6-311＋＋G（d,p）, 6-311＋＋G（2df, pd） and 6-311＋＋G（3df,3pd） in full active space using a symmetry-adapted-cluster/ symmetry-adapted-cluster configuration-interaction （SAC/SAC=CI） method presented in Gaussian03 program package. The difference of the equilibrium geometries obtained by SPES and by OPT is reported. Analyses show that the results obtained by SPES are more reasonable than those obtained by OPT. We have calculated the complete potential energy curves at those sets over a wide internuclear distance range from about 3.0α0 to 37.0α0, and the conclusion is that the basis set cc-PVTZ is the most suitable one. With the potential obtained at ccopVTZ, the spectroscopic data （Te, De, D0, ωe,ωeХe, αe and Be） are computed and they are 1.006 eV, 338.71 cm^-1, 307.12 cm^-1, 64.88 cm^-1, 3.41 cm^-1, 0.0187 cm^-1 and 0.279 cm^-1, respectively, which are in good agreement with recent measurements. The total 11 vibrational states are found at J=0. Their corresponding vibrational levels and classical turning points are computed and compared with available RKR data, and good agreement is found. One inertial rotation constant （By） and six centrifugal distortion constants （Dr Hv, Lv, My, Nv, and Ov） are calculated. The scattering length is calculated to be -27.138α0, which is in good accord with the experimental data.     

Alloying and magnetic disordering effects on phase stability of Co2 YGa (Y=Cr,V, and Ni) alloys: A first-principles study

The alloying and magnetic disordering effects on site occupation, elastic property, and phase stability of Co$_{2}Y$Ga ($Y={\rm Cr}$, V, and Ni) shape memory alloys are systematically investigated using the first-principles exact muffin-tin orbitals method. It is shown that with the increasing magnetic disordering degree $y$, their tetragonal shear elastic constant $C'$ (i.e., $(C_{11}-C_{12})/2$) of the $L2_{1}$ phase decreases whereas the elastic anisotropy $A$ increases, and upon tetragonal distortions the cubic phase gets more and more unstable. Co$_{2}$CrGa and Co$_{2}$VGa alloys with $y\geq0.2$ thus can show the martensitic transformation (MT) from $L2_{1}$ to $D0_{22}$ as well as Co$_{2}$NiGa. In off-stoichiometric alloys, the site preference is controlled by both the alloying and magnetic effects. At the ferromagnetism state, the excessive Ga atoms always tend to take the $Y$ sublattices, whereas the excessive Co atom favor the $Y$ sites when $Y={\rm Cr}$, and the excessive $Y$ atoms prefer the Co sites when $Y={\rm Ni}$. The Ga-deficient $Y={\rm V}$ alloys can also occur the MT at the ferromagnetism state by means of Co or V doping, and the MT temperature $T_{\rm M}$ should increase with their addition. In the corresponding ferromagnetism $Y={\rm Cr}$ alloys, nevertheless, with Co or Cr substituting for Ga, the reentrant MT (RMT) from $D0_{22}$ to $L2_{1}$ is promoted and then $T_{\rm M}$ for the RMT should decrease. The alloying effect on the MT of these alloys is finally well explained by means of the Jahn-Teller effect at the paramagnetic state. At the ferromagnetism state, it may originate from the competition between the austenite and martensite about their strength of the covalent banding between Co and Ga as well as $Y$ and Ga.