共查询到20条相似文献,搜索用时 15 毫秒
1.
《中国物理 B》2021,30(7):75102-075102
We prepared the semimetals RAl Si(R = light rare earth), and systematically study their crystal structures and magnetic properties. X-ray diffractions confirm the coexistence of the site-disordered phase with group space of I41/amd and the noncentrosymmetrically ordered phase with space group of I41 md in RAl Si alloy. The ordered phase is the main phase in RAl Si alloy. RAl Si alloys show nonmagnetic character for R = La, low temperature ferromagnetic order for R = Ce, Pr, and paramagnetic character for R = Nd, respectively. Sm Al Si shows metamagnetic transition at 10 K and ferromagnetic order at 143 K, respectively. Sm Al Si follows the van Vleck paramagnetic model in its paramagnetic region. The magnetization curves of RAl Si(R = Ce, Pr, Sm) follow the mixed model of ferromagnetism and paramagnetism, and the fitted saturation moment MSdepends on the moment of trivalent rare earth. The paramagnetic susceptibility χ of RAl Si is going up with increasing the atomic order numbers of rare earth elements. This reveals that the magnetic property of RAl Si originates from the rare earth. 相似文献
2.
Using a novel approach to calculate optical properties of strongly correlated systems, we address the old question of the physical origin of the alpha--> gamma transition in Ce. We find that the Kondo collapse model, involving both the f and the spd electrons, describes the optical data better than a Mott transition picture involving the f electrons only. Our results compare well with existing experiments on thin films. We predict the full temperature dependence of the optical spectra and find the development of a hybridization pseudogap in the vicinity of the alpha--> gamma phase transition. 相似文献
3.
Rueff JP Itié JP Taguchi M Hague CF Mariot JM Delaunay R Kappler JP Jaouen N 《Physical review letters》2006,96(23):237403
We report on the most complete investigation to date of the -electron properties at the transition in elemental Ce by resonant inelastic x-ray scattering (RIXS). The Ce 2p3d-RIXS spectra were measured directly in the bulk material as a function of pressure through the transition. The spectra were simulated within the Anderson impurity model. The occupation number n(f) and f double occupancy were derived from the calculations in both gamma and alpha phases in the ground state. We find that the electronic structure changes result mainly from band formation of 4f electrons which concurs with reduced electron correlation and increased Kondo screening at high pressure. 相似文献
4.
Pressure induced structural phase transition of mono-antimonides of lanthanum, cerium, praseodymium and neodymium (LnSb, Ln=La, Ce, Pr and Nd) has been studied theoretically using an inter-ionic potential with modified ionic charge which parametrically includes the effect of Coulomb screening by the delocalized f electrons of rare earth (RE) ion. The anomalous structural properties of these compounds have been interpreted in terms of the hybridization of f electrons with the conduction band and strong mixing of f states of Ln ion with the p orbital of neighbouring antimonide ion. All the four compounds are found to undergo from their initial NaCl (B1) phase to body centered tetragonal (BCT) phase at high pressure and agree well with the experimental results. The body centered tetragonal phase is viewed as distorted CsCl structure and is highly anisotropic with c/a=0.82. The transition pressure of LnSb compounds is observed to increase with decreasing lattice constant in NaCl phase. The nature of bonds between the ions is predicted by simulating the ion-ion (Ln-Ln and Ln-Sb) distances at high pressure. The calculated values of elastic constants are also reported. 相似文献
5.
6.
We use a new updated algorithm scheme to investigate the critical behaviour of the two-dimensional ferromagnetic Ising model on a triangular lattice with the nearest neighbour interactions. The transition is examined by generating accurate data for lattices with L= 8, 10, 12, 15, 20, 25, 30, 40 and 50. The updated spin algorithm we employ has the advantages of both a Metropolis algorithm and a single-update method. Our study indicates that the transition is continuous at Tc= 3.6403({2}). A convincing finite-size scaling analysis of the model yields υ=0.9995(21), β /
υ = 0.12400({17}), γ / υ = 1.75223(22), γ '/υ=1.7555(22), α/υ= 0.00077(420) (scaling) and α / υ = 0.0010(42) (hyperscaling). The present scheme yields more accurate estimates for all the critical exponents than the Monte Carlo method, and our estimates are shown to be in excellent agreement with their predicted values. 相似文献
7.
ELECTRONIC STRUCTURE AND CRYSTALLINE ELECTRIC FIELD IN Rco5(R= Y,La, Ce,Pr, Nd,Sm, Gd,and Tb) 下载免费PDF全文
Self consistent charge and spin polarized local spin-density approximation functional theory calculations based on the discrete variational method have been performed for RCo5(R=Y, La, Ce, Pr, Nd, Sm, Gd, and Tb) compounds. The partial density of states of the Pr atom in the PrCo6Co12 cluster is established to be strikingly similar to that of the Ce atom in the CeCo6Co12 cluster, supporting the suggestion that the Pr atom is valence fluctuating. The radii <r4f> and <r4f2> of the 4f electrons of the R atom from La to Tb, except Ce, show the lanthanide contraction. The crystalline electric field (CEF) parameter A02 at the R site is calculated using a real charge distribution ρ(R) in the cluster, except for Pr and Nd, and is in agreement with that evalu ated based on the single-ion model. This result shows that the CEF parameter A02 is mainly determined by the near electronic structure. There exists a hybridization in a certain degree between the light rare-earth R-4f and Co-3d orbitals in some single-electron-molecular-orbitals, which are n ear the Fermi energy level and occupied by electrons. For light rare-earths the R-4f electrons in R Co6Co12(R=Y, La, Ce, Pr, Nd, and Sm) clu sters are not localized entirely and a small amount of the R-4f electrons have itinerant properties. 相似文献
8.
A. Bredenstein S. Dittmaier M. Roth 《The European Physical Journal C - Particles and Fields》2005,44(1):27-49
The
electroweak radiative corrections to
within the electroweak standard model are calculated in double-pole approximation (DPA). Virtual corrections are treated in DPA, leading to a classification into factorizable and non-factorizable contributions, and real-photonic corrections are based on complete lowest-order matrix elements for
. Soft and collinear singularities appearing in the virtual and real corrections are combined alternatively in two different ways, namely by using the dipole subtraction method or by applying phase-space slicing. The radiative corrections are implemented in a Monte Carlo generator called Coffer
- the computer code can be obtained from the authors upon request - which optionally includes anomalous triple and quartic gauge-boson couplings in addition and performs a convolution over realistic spectra of the photon beams. A detailed survey of numerical results comprises
corrections to integrated cross sections as well as to angular, energy, and invariant-mass distributions. Particular attention is paid to the issue of collinear safety in the observables.Received: 3 June 2005, Published online: 5 August 2005 相似文献
9.
Lashley JC Lawson AC Cooley JC Mihaila B Opeil CP Pham L Hults WL Smith JL Schmiedeshoff GM Drymiotis FR Chapline G Basu S Riseborough PS 《Physical review letters》2006,97(23):235701
The gamma-->alpha isostructural transition in the Ce0.9-xLaxTh0.1 system is measured as a function of La alloying using specific heat, magnetic susceptibility, resistivity, thermal expansivity or striction measurements. A line of discontinuous transitions, as indicated by the change in volume, decreases exponentially from 118 K to close to 0 K with increasing La doping, and the transition changes from being first-order to continuous at a critical concentration, x(c) approximately 0.14. At the tricritical point, the coefficient of the linear T term in the specific heat gamma and the magnetic susceptibility increase rapidly near x(c) and approach large values at x=0.35 signifying that a heavy Fermi-liquid state evolves at large doping. The Wilson ratio reaches a value above 2 for a narrow range of concentrations near x(c), where the specific heat and susceptibility vary most rapidly with the doping concentration. 相似文献
10.
X-ray diffraction study of effect of deposition conditions on α--β phase transition and stress evolution in sputter-deposited W coatings 下载免费PDF全文
Pure W and W-Cu-W trilayer coatings were deposited on an Fe substrate by d.c. magnetron sputtering. The α-β phase evolution, intragranular stress evolution in sputter-deposited W layer were investigated by x-ray diffraction. They are directly related to the film microstructure, density and adhesion. Therefore, control of the film stress and phase component transition is essential for its applications. The phase component transition from β-W to α-W and intragranular stress evolution from tensile to compressive strongly depend on the deposition parameters and can be induced by lowering Ar pressure and rising target power. The compressively stressed films with α-W phase have a dense microstructure and high adhesion to Fe substrate. 相似文献
11.
We present a complete one-loop study of the process
and the predicted cross section in a
Linear Collider. A suitable numerical code, PLATONlc, valid for any set of real MSSM parameters, is released. This study and code are complementary to those suitable for dark matter detection through the inverse process
describing neutralino-neutralino annihilation at rest, which were presented previously. If SUSY is realized in nature, both codes should be very helpful in future astrophysical and collider studies of the neutralino sector.Received: 6 November 2003, Published online: 9 January 2004Programme dActions Intégrées Franco-Hellenique, Platon 04100 UM. 相似文献
12.
Pépin C 《Physical review letters》2007,98(20):206401
We show within the slave-boson technique that the Anderson lattice model exhibits a Kondo breakdown quantum critical point where the hybridization goes to zero at zero temperature. At this fixed point, the f electrons experience as well a selective Mott transition separating a local-moment phase from a Kondo-screened phase. The presence of a multiscale quantum critical point in the Anderson lattice in the absence of magnetism is discussed in the context of heavy fermion compounds. This study is the first evidence for a selective Mott transition in the Anderson lattice. 相似文献
13.
A. Bredenstein S. Dittmaier M. Roth 《The European Physical Journal C - Particles and Fields》2004,36(3):341-363
We have constructed a Monte Carlo generator (the corresponding FORTRAN code can be obtained from the authors upon request) for lowest-order predictions for the processes
and
in the standard model and extensions thereof by an effective
coupling as well as anomalous triple and quartic gauge-boson couplings. Polarization is fully supported, and a realistic photon beam spectrum can be taken into account. For the processes
all helicity amplitudes are explicitly given in a compact form. The presented numerical results contain, in particular, a survey of cross sections for representative final states and their comparison to results obtained with the program package Whizard/Madgraph. The impact of a realistic beam spectrum on cross sections and distributions is illustrated. Moreover, the size of various contributions to cross sections, such as from weak charged- or neutral-current, or from strong interactions, is analyzed. Particular attention is paid to W-pair production channels
where we investigate the impact of background diagrams, possible definitions of the W-pair signal, and the issue of gauge-invariance violation caused by finite gauge-boson widths. Finally, the effects of triple and quartic anomalous gauge-boson couplings on cross sections as well as the possibility to constrain these anomalous couplings at future
colliders are discussed.Received: 19 May 2004, Published online: 16 July 2004 相似文献
14.
Effect of R substitution on magnetic properties and magnetocaloric effects of La1-xRxFe11.5Si1.5 compounds with R=Ce, Pr and Nd 下载免费PDF全文
<正>Magnetic properties and magnetocaloric effects of La1-xRxFe1105 Si9105)(R=Pr,(0≤x≤0.5);R = Ce and Nd, (0≤x≤0.3)) compounds are investigated.Partially replacing La with R = Ce,Pr and Nd in La1-xRxFe11.5Si1.5 leads to a reduction in Curie temperature due to the lattice contraction.The substitution of R for La causes an enhancement in field-induced itinerant electron metamagnetic transition,which leads to a remarkable increase in magnetic entropy change△Sm and also in hysteresis loss.However,a high effective refrigerant capacity RCeff is still maintained in La1-xRxFe11.5Si1.5.In the present samples,a large△Sm and a high RCeff have been achieved simultaneously. 相似文献
15.
Im HJ Ito T Kim HD Kimura S Lee KE Hong JB Kwon YS Yasui A Yamagami H 《Physical review letters》2008,100(17):176402
Ce 4d-4f resonant angle-resolved photoemission spectroscopy was carried out to study the electronic structure of strongly correlated Ce 4f electrons in a quasi-two-dimensional nonmagnetic heavy-fermion system CeCoGe1.2Si0.8. For the first time, dispersive coherent peaks of an f state crossing the Fermi level, the so-called Kondo resonance, are directly observed together with the hybridized conduction band. Moreover, the experimental band dispersion is quantitatively in good agreement with a simple hybridization-band picture based on the periodic Anderson model. The obtained physical quantities, i.e., coherent temperature, Kondo temperature, and mass enhancement, are comparable to the results of thermodynamic measurements. These results manifest an itinerant nature of Ce 4f electrons in heavy-fermion systems and clarify their microscopic hybridization mechanism. 相似文献
16.
The chirality-asymmetry macroscopic force mediated by light
pseudoscalar particles between α -quartz and some achiral
matter is studied. If this force between achiral source mass and
α -quartz with some chirality is attractive, it will become
repulsive when the chirality of the α -quartz crystal is
changed. According to the tested limits of the coupling constant
gs gp /\hbar c< 1.5× 10-24 at the
Compton wavelength λ = 10-3 m, the force (F) between
a 0.08× 0.08× 0.002 m3 block of α -quartz
and a 0.08× 0.08× 0.01 m3 copper block with a
separation being 0.5× 10-3 \mbox{m} in between, is
estimated from the published data at less than 4.64× 10-24 N, i.e. F < 4.64× 10-24 N. 相似文献
17.
为了研究稀土掺杂对单层MoS2电子结构的影响,文章基于密度泛函理论框架下的第一性原理,采用平面波赝势方法分别计算了本征及La,Ce,Nd掺杂单层MoS2的晶格参数、能带结构、态密度和差分电荷密度.计算发现,稀土掺杂所引起的晶格畸变与杂质原子的共价半径大小有关,La杂质附近的键长变化最大,Nd杂质附近的键长变化最小.能带结构分析表明,La掺杂可以在MoS2的禁带中引入3个能级,Ce掺杂可以形成6个新能级,Nd掺杂可以形成4个能级,并对杂质能级属性进行了初步分析.差分电荷密度分布显示,稀土掺杂可以使单层MoS2中的电子分布发生改变,尤其是f电子的存在会使差分电荷密度呈现出反差极大的物理图象. 相似文献
18.
A favored interpretation of the gamma <--> alpha phase transition in cerium postulates the transformation of the localized 4f state in gamma-Ce to a weakly correlated itinerant 4f band in alpha-Ce. However, results of high-energy neutron inelastic scattering measurements, presented here, show clearly that the magnetic susceptibility response from alpha-Ce follows the Ce3+ form factor despite the large, 30-fold, increase in its spectral width relative to that in gamma-Ce. This observation provides, for the first time, indisputable evidence for the localized character of the 4f state in the alpha phase. The present findings appear consistent with recent calculations combining dynamical mean-field theory with the local density approximation that indicate a strongly correlated 4f state in alpha-Ce. The localized 4f state is also fundamental to the Kondo volume collapse theories for the gamma <--> alpha phase transition in cerium. 相似文献
19.
This paper provides an investigation of the phase
transition and spalling characteristic induced during shock loading
and unloading in the pure iron and the FeMnNi alloy. The impact for
the pure iron is symmetric and with same-thickness for both the
flyer and the target plate. It is found that an abnormal multiple
spalling happens in the pure iron sample as the pressure exceeds the
$\alpha -\varepsilon $ transition threshold of 13 GPa. In the
symmetric and same-thickness impact and reverse impact experiments
of the FeMnNi alloy, two abnormal tension regions occur when the
pressure exceeds the $\alpha -\varepsilon $ transition threshold of
6.3~GPa, and the reverse phase transition $\varepsilon -\alpha $
begins below 4.2~GP. The experimental process is simulated
successfully from the non-equilibrium mixture phase and Boettger's
model. Such abnormal spalling phenomena are believed to relate to
the shocked $\alpha -\varepsilon $ phase transition. The possible
reasons for the abnormal multiple spalling, which occurs during the
symmetric and same-thickness impact experiments of pure iron and
FeMnNi alloy, are discussed. 相似文献