Broken Time-Reversal Symmetry in Superconducting Partially Filled Skutterudite Pr_(1-δ)Pt_4Ge_(12)

Time reversal symmetry(TRS)is a key symmetry for classification of unconventional superconductors,and the violation of TRS often results in a wealth of novel properties.Here we report the synthesis and superconducting properties of the partially filled skutterudite Pr_(1-δ)Pt_4Ge_(12).The results from x-ray diffraction and magnetization measurements show that the[Pt_4 Ge_(12)]cage-forming structure survives and bulk superconductivity is preserved below the superconducting transition temperature T_c = 7.80 K.The temperature dependence of both the upper critical field and the electronic specific heat can be described in terms of a two-gap model,providing strong evidence of multi-band superconductivity.TRS breaking is observed using zero Held muon-spin relaxation experiments,and the magnitude of the spontaneous field is nearly half of that in PrPt_4Ge_(12).     

Magnetic and Magnetocaloric Properties of Polycrystalline and Oriented Mn_(2-δ)Sn

Mn-based Heusler alloys have attracted significant research attention as half-metallic materials because of their giant magnetocr.ystalline anisotropy and magnetocaloric properties.We investigate the crystal structure and magnetic properties of polycrystalline,[101]-oriented,and[100]-oriented Mn_(2-δ) Sn prepared separately by arc melting,the Bridgeman method,and the flux method.All of these compounds crystallize in a Ni_2 In-type structure.In the Mn_(2-δ)Sn lattice,Mn atoms occupy all of the 2 a and a fraction of the 2 d sites.Site disorder exists between Mn and Sn atoms in the 2 c sites.In addition,these compounds undergo a re-entrant spin-glass-like transition at low temperatures,which is caused by frustration and randomness within the spin system.The magnetic properties of these systems depend on the crystal directions,which means that the magnetic interactions differ significantly along different directions.Furthermore,these materials exhibit a giant magnetocaloric effect near the Curie temperature.The largest value of maximum of magnetic entropy change(-△S_M)occurs perpendicular to the[100]direction.Specifically,at 252 K,maximum-△S_M is 2.91 and 3.64 J-kg~(-1)K~(-1) for a magnetic field of 5 and7 T,respectively.The working temperature span over 80 K and the relative cooling power reaches 302 J/kg for a magnetic field of 7 T,which makes the Mn_(2-δ)Sn compound a promising candidate for a magnetic refrigerator.     

Superconducting and elastic properties of (Dy1−xPrx)BaSrCu3O7−δ

Pr-substituted (Dy_1−xPr_x)BaSrCu₃O_7−δ (x=0.0, 0.1, 0.2, 0.4 and 0.7) has been investigated for its superconducting and elastic properties. Structural transition from orthorhombic to tetragonal symmetry is observed at x=0.1. Temperature-dependent sound velocity was measured using the pulse-echo overlap method. Elastic anomalies in the form of lattice stiffening with decreasing temperature were observed above 200 K. These anomalies were attributed to oxygen vacancy orderings in the Cu(1)O plane and also depended on the configurational state of oxygen orderings which is strongly influenced by Pr-doping.     

Superconducting Properties and Absence of Time Reversal Symmetry Breaking in the Noncentrosymmetric Superconducting Compounds TaxRe1-x(0.1≤x≤0.25)

Unconventional superconductivity,in particular,in noncentrosymmetric systems,has been a long-sought topic in condensed matter physics.Recently,Re-based superconductors have attracted great attention owing to the potential time-reversal symmetry breaking in their superconducting states.We report the superconducting properties of noncentrosymmetric compounds Ta_xRe_1-x with 0.1 ≤x≤0.25,and find that the superconducting transition temperature reaches a maximum of ~8 K at the optimal level x=0.15.Nevertheless,muon-spin rotation and relaxation measurements reveal no time-reversal symmetry breaking existing in its superconducting state,which is in sharp contrast to both centrosymmetric Re metal and many other noncentrosymmetric Re-based superconductors.     

Forming the Fe(Se1 –xTex) Superconducting Coatings on the Iron Surface

Technical Physics - The Fe(Se1 –xTex) superconducting coatings have been deposited onto the surface of strip and ribbon iron substrates from chalcogen vapors and chalcogenide melt. The...     

Effect of Zn impurity in K0.8Fe(2-δ-x)Zn(x)Se2

A series of K(0.8)Fe(2-δ-x)Zn(x)Se(2) single-crystal samples with nominal compositions 0?≤?x?≤?0.05 were grown and their physical properties were measured in order to study the effect of Zn impurity. It is found that the Zn impurity (x?≤?0.02) does not affect the superconducting transition temperature T(c) significantly. Meanwhile the hump in resistivity which corresponds to the transition from the insulating to metallic phase quickly shifts towards low temperatures. The results imply that there should be a phase separation in this system and Zn impurity causes the enhancement of the insulating phase. The negligible effect of Zn impurity on T(c) suggests an s-wave pairing in the superconducting phase. Meanwhile there is a possibility that the Zn impurity may selectively enter into the insulting phase.     

Oxygen vacancy induced magnetism in BaTiO_(3-δ) and Nb:BaTiO_(3-δ) thin films

The unusual magnetic properties are observed in oxygen deficient BaTiO3-δ(BTO) and Nb:BaTiO3-δ(BNTO) thin films fabricated on SrTiO3 substrates by laser molecular beam epitaxy.The distinct magnetic hysteresis loops are observed in the oxygen deficient BTO and BNTO thin films in a temperature range of 5 to 300 K,whereas the diamagnetism is observed in both BTO and BNTO annealed at 1 atm of oxygen.The dopant Nb only enhances the magnetization in BNTO thin films,but has little effect on the coercivity.The magnetism of BTO and BNTO films is proposed to be the oxygen vacancies by origin.     

Spectral and Photophysical Properties of α-carboline (1-Azacarbazole) in Aqueous Solutions

The absorption and fluorescence spectra of α-carboline, 9H-pyrido[2,3-b]indole, AC, in organic aprotic solvents containing different water proportions and in acid/base aqueous solutions inside and outside the pH range have been examined. In the organic aprotic solvents, the addition of increasing concentrations of water sequentially quenches and shifts to the red the fluorescence spectra of AC. These spectral changes have been rationalized assuming the formation, at the lower water concentrations, of a discrete ground state non-cyclic weakly fluorescent AC hydrate emitting at 376 nm that, upon increasing the water concentrations, evolves to a higher order AC poly hydrate emitting at 397 nm. The changes of the AC absorption spectra in aqueous acid/basic solutions indicate the existence of three ground state prototropic species; the pyridinic protonated cation, C (pK_a?=?4.10?±?0.05), the neutral, N (pK_a?=?14.5?±?0.2), and the pyrrolic deprotonated anion, A. Conversely, the changes of the AC fluorescence spectra in these media indicate the existence of four excited state species emitting at 376 nm, 397 nm, 460 nm and 465 nm. Since the emissions at 376 nm and 397 nm satisfactorily match those of the hydrates observed in the organic-water mixtures, they were consistently assigned to two differently hydrated ground state N species. The remaining emissions at 460 nm and 465 nm have been assigned without ambiguity, on the basis of their excitation spectra, to the C and A species, respectively. The excited-state pK_as of the prototropic species of AC have been estimated by using the Förster-Weller cycle.     

Connection of Residual Losses of a Microwave Energy in Superconducting State of YBa2Cu3O7?δ Films on Sapphire Substrates with Their Resistance in a Normal State

In the work, the results of measurements of temperature dependence of the surface resistance Rs(T) of the YBa₂Cu₃O_– epitaxial films deposited on sapphire substrates have been presented. The films were obtained using the method of impulse laser deposition. The measurements of surface impedance Rs(T) have been carried out at a frequency of 135 GHz. It is shown that Rs(T) agrees with existing model, considering heterogeneity in the YBa₂Cu₃O_7– epitaxial films as the normal spherical domains. Analysis has been carried out for the set of specimens which were obtained at different technological regimes and have different critical parameters and geometry.     

纳米Ce_(1-x)(Fe_(0.5)La_(0.5)x)O_(2-δ)固溶体的水热合成及光谱分析

采用水热方法合成Ce1-x(Fe0.5La0.5)xO2-δ固溶体。利用X射线衍射技术(X-ray diffraction tech-nique,XRD)表征样品的相结构,并对固溶体的晶胞参数进行拟合,通过紫外可见漫反射光谱(UV-Vis dif-fraction spectrum)及拉曼光谱(Raman spectrum)表征其电子跃迁性能及由于双离子掺杂所引起的一系列掺杂效应。XRD结果表明,Ce1-x(Fe0.5La0.5)xO2-δ固溶体为CeO2立方萤石结构,当掺杂量增加到x=0.30时出现了微弱的Fe2O3杂相衍射峰;讨论了两种离子在晶格中不同的取代位置。晶胞参数随着掺杂量的增大而逐渐增大,当掺杂量达到x=0.18后保持基本不变。紫外漫反射光谱表明,随着掺杂量的增大,固溶体的带隙吸收边红移,即能隙逐渐减小,Fe离子在CeO2晶格中表现为+3价。Raman光谱F2g振动峰位逐渐向低波数方向移动,同时振动峰逐渐宽化,进一步证明了掺杂离子的影响效应。     

On the observation of intrinsic defects in (Co1-xInx)1-δO by PAC

We report on the results of Perturbed Angular Correlation measurements in polycrystalline (Co_1-xIn_x)_1-δO samples (x = 0.04 and 0.8 at.%) using ion-implanted ¹¹¹In tracers. The temperature and the oxygen activity (adjusted via a CO/CO₂ mixture) were chosen in such a way as to be able to observe defect trapping and detrapping in thermal equilibrium. The results are compared with those obtained for (Co_1-xIn_x)_1-δO (x= 0.04 at.%) rapidly cooled to 350 K and for CoO. This revised version was published online in August 2006 with corrections to the Cover Date.     

High-spin levels in138Ce and140Nd Observed in the (α, 4n γ) reactions

Levels of¹³⁸Ce and¹⁴⁰Nd have been studied using the¹³⁸Ba(α,4nγ)¹³⁸Ce and¹⁴⁰Ce(α, 4nγ)¹⁴⁰Nd reactions. Singleγ-ray spectra,γ-γ coincidence spectra, angular and time distributions with respect to the beam bursts have been measured. A number of higher excited states with excitation energies up to about 5 MeV and with spin value up to 12 are populated in both nuclei. The lower states with spins and parities 7^?, 5^?, 6^? and 10⁺ can be explained by two-quasiparticle neutron configurations of the types (h _11/2 ^?1 ,d _3/2 ^?1 ) 7^? , (h _11/2 ^?1 ,S _1/2 ^?1 ) 5^?, 6^? and (h _11/2 ^?2 ) 10⁺. Several high-spin states observed in¹³⁸Ce and¹⁴⁰Nd can be explained qualitatively as four-quasiparticle states with two-proton-two-neutron configurations. The 3^? state at an energy of 2,137.4 keV is observed in¹³⁸Ce. The evidence for the existence of the low-lying 3^? states in¹⁴⁰Nd at 2,124.0 keV is discussed. Beside the known 9.6 ms (7^?) isomeric state in¹³⁸Ce another state at 3,538.5keV (10⁺) with a half life of about 200 ns has been observed. The observed levels in the¹³⁸Ce and¹⁴⁰Nd nuclei are compared with theoretical predictions using delta force interaction.     

钙钛矿型氧载体SrCo_(0.8)Fe_(0.2)O_(3-δ)制氧性能的实验研究

钙钛矿型金属氧化物是优良的制备供富氧燃烧所需的O_2/CO_2的氧载体,本文采用柠檬酸法制备系列SrCo_(1-x)Fe_xO_(3-δ)(x=0.2,0.4,0.6,0.8)钙钛矿型氧化物,并采用X射线衍射分析来表征SrCo_(0.8)Fe_(0.2)O_(3-δ)(SCF182)反应前后的物相变化和晶体结构.同时在固定床上选择不同的运行条件对SCF182的释氧性能进行研究,包括吸附温度、吸附时间、脱附温度和循环特性.结果表明,SCF182的最佳吸附温度和脱附温度均为850℃,最佳吸附时间为1 h,循环性能良好,是可以为富氧燃烧提供稳定的O_2/CO_2循环气体的良好材料。     

Negative thermal expansion and photoluminescence in solid solution(HfSc)_(0.83)W_(2.25)P_(0.83)O_(12-δ)

A solid solution of(HfSc)_(0.83)W_(2.25)P_(0.83)O_(12-δ)is synthesized by the high-temperature, solid-state reaction and fastquenching method. It is shown that it possesses an orthorhombic structure with space group Pmmm(47) and exhibits negative thermal expansion(NTE) property with low anisotropy in thermal expansion. The coefficients of thermal expansion(CTEs) for a, b, and c axes are-1.41 × 10~(-6) K~(-1),-2.23 × 10~(-6) K-1, and-1.87 × 10~(-6) K-1, respectively. This gives rise to volume and linear CTEs of-3.10 × 10-6 K-1 and-1.03 × 10-6 K-1, respectively. Besides, it exhibits also intense photoluminescence from 360 nm to about 600 nm. The mechanism of NTE and the correlation of the PL with axial thermal expansion property are discussed.     

Nodeless superconducting gaps in Ca_(10)(Pt_(4-δ)As_8)((Fe_(1-x)Pt_x)_2As_2)_5 probed by quasiparticle heat transport

The in-plane thermal conductivity of the iron-based superconductor Ca10(Pt_(4-δ)As_8)((Fe_(1-x)Pt_x)_2As_2)_5 single crystal("10-4-8", T c= 22 K) was measured down to 80 m K. In a zero field, the residual linear term κ_0/T is negligible, suggesting the nodeless superconducting gaps in this multiband compound. In the magnetic fields, κ_0/T increases rapidly, which mimics the multiband superconductor Nb Se_2 and Lu Ni_2B_2 C with highly anisotropic gap. Such a field dependence of κ_0/T is an evidence for the multiple superconducting gaps with quite different magnitudes or highly anisotropic gap. Compared with the London penetration depth results of the Ca10(Pt_(4-δ)As_8)((Fe_(1-x)Pt_x)_2As_2)_5("10-3-8") compound, the 10-4-8 and 10-3-8 compounds may have a similar superconducting gap structure.     

Correlated giant dielectric peaks and antiferromagnetic transitions near room temperature in pure and alkali-doped BaMnO(3-δ)

We report structural, magnetic, dielectric and thermal properties of single-crystal BaMnO(2.99) and its derivatives BaMn(0.97)Li(0.03)O(3) and Ba(0.97)K(0.03)MnO(3). The hexagonal 15R-BaMnO(2.99) perovskite phase is a known antiferromagnetic insulator that orders at a Néel temperature T(N) = 220 K. We find dilute Li and K doping change the ratio of cubic to hexagonal layers and cause drastic changes in the dielectric and magnetic properties. Unusually large high-temperature magnetoelectric shifts (up to 85%) are observed near temperatures at which pronounced peaks in the dielectric constant are observed for applied electric fields along either the c or a axis, respectively. The temperatures of the dielectric peaks are strongly correlated with anomalies in the c- or a-axis magnetic susceptibility and the specific heat for all compositions studied. All our data suggest that the strongly anisotropic magnetic and dielectric anomalies (which occur near, or above room temperature) originate from the same Mn ion sites, which implies these materials form an exceptional class of magnetoelectrics.     

Spin glassy behavior and large exchange bias effect in cubic perovskite Ba_(0.8)Sr_(0.2)FeO_(3-δ)

A single-phase iron oxideBa_(0.8)Sr_(0.2)FeO_(3-δ)with a simple cubic perovskite structure in Pm-3 m symmetry is successfully synthesized by a solid-state reaction method in O_2 flow. The oxygen content is determined to be about 2.81, indicating the formation of mixed Fe~(3+)and Fe~(4+)charge states with a disorder fashion. As a result, the compound shows small-polaron conductivity behavior, as well as spin glassy features arising from the competition between the ferromagnetic interaction and the antiferromagnetic interaction. Moreover, the competing interactions also give rise to a remarkable exchange bias effect in Ba_(0.8 )Sr_(0.2 )FeO_(2.81), providing an opportunity to use it in spin devices.     

Hall effect of FeTe and Fe(Se1–xTex) thin films

The Hall effect is investigated in thin-film samples of iron–chalcogenide superconductors in detail. The Hall coefficient (R_H) of FeTe and Fe(Se_1–xTe_x) exhibits a similar positive value around 300 K, indicating that the high-temperature normal state is dominated by hole-channel transport. FeTe exhibits a sign reversal from positive to negative across the transition to the low-temperature antiferromagnetic state, indicating the occurrence of drastic reconstruction in the band structure. The mobility analysis using the carrier density theoretically calculated reveals that the mobility of holes is strongly suppressed to zero, and hence the electric transport looks to be dominated by electrons. The Se substitution to Te suppresses the antiferromagnetic long-range order and induces superconductivity instead. The similar mobility analysis for Fe(Se_0.4Te_0.6) and Fe(Se_0.5Te_0.5) thin films shows that the mobility of electrons increases with decreasing temperature even in the paramagnetic state, and keeps sufficiently high values down to the superconducting transition temperature. From the comparison between FeTe and Fe(Se_1–xTe_x), it is suggested that the coexistence of ‘itinerant’ carriers both in electron and hole channels is indispensable for the occurrence of superconductivity.