اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدPositron annihilation spectroscopy for the pure and Niobium doped ZrCo$_2$Sn Heusler compound
326
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We perform spin-polarized two-dimensional angular correlation of annihilation radiation (2D-ACAR) calculations for the recently predicted ZrCo$_2$Sn-Weyl Heusler compound within the density functional theory using the generalized gradient approximation (GGA) and its extension GGA+U. We confirm that within the GGA+U method, a pair of Weyl-points are revealed, and that by doping with Niobium, for the composition Nb$_{0.3}$Zr$_{0.7}$Co$_2$Sn, the Weyl points are reaching the Fermi level. Our 2D-ACAR results indicate the existence of the Weyl points, however, within the present calculation, it is uncertain if the smearing at the Fermi level can be attributed to the positron wave function.
قيم البحث
اقرأ أيضاً
We investigated in detail the optical properties of several Cu(1-delta)Mg(delta)GeO3 (with delta=0,0.01), and CuGe(1-x)B(x)O3 with B=Si (x=0,0.007,0.05,0.1), and Al (x=0,0.01) single crystals, in the frequency range 20-32000 cm^-1. We report temperat
ure dependent reflectivity and transmission measurements, performed with polarized light in order to probe the anisotropy of the crystals along the b and c axes, and optical conductivity spectra obtained by Kramers-Kronig transformation or direct inversion of the Fresnel formula. Special emphasis is given to the far-infrared phonon spectra. The temperature dependence of the phonon parameters is presented and discussed in relation to the soft mode issue in CuGeO3. For T<Tsp we could detect zone boundary folded modes activated by the spin-Peierls phase transition. Following the temperature dependence of these modes, which shows the second order character of the phase transition, we were able to study the effect of doping on Tsp. Moreover, in transmission experiments we detected a direct singlet-triplet excitation at 44 cm^-1, across the magnetic gap, which is not understandable on the basis of the magnetic excitation spectrum so far assumed for CuGeO3. The optical activity of this excitation and its polarization dependence confirm the existence of a second (optical) magnetic branch, recently suggested on the basis of inelastic neutron scattering data. The anisotropy in the magnetic exchange constants along the b axis, necessary for the optical triplet mode to gain a finite intensity, and the strong effect of Si substitution on the phonon spectra are discussed in relation to the alternative space group P2(1)2(1)2(1), recently proposed for CuGeO3 in the high temperature uniform phase.
We present magnetoresistivity measurements in high-quality single crystals of the Nowotny chimney ladder compound Ru$_2$Sn$_3$. We find a linear and nonsaturating magnetoresistance up to 20 T. The magnetoresistance changes with the magnetic field ori
entation at small magnetic fields, from a positive to a negative curvature. Above 5 T, the magnetoresistance shows no sign of saturation up to 20 T for any measured angle. The shape of the anisotropy in the magnetoresistance remains when increasing temperature and Kohlers rule is obeyed. We associate the linear and nonsaturating magnetoresistance to a small Fermi surface with hot spots, possibly formed as a consequence of the structural transition. We discuss the relevance of electron-electron interactions under magnetic fields and aspects of the topologically nontrivial properties expected in Ru$_2$Sn$_3$.
We present a comprehensive study of vacancy and vacancy-impurity complexes in InN combining positron annihilation spectroscopy and ab-initio calculations. Positron densities and annihilation characteristics of common vacancy-type defects are calculat
ed using density functional theory and the feasibility of their experimental detection and distinction with positron annihilation methods is discussed. The computational results are compared to positron lifetime and conventional as well as coincidence Doppler broadening measurements of several representative InN samples. The particular dominant vacancy-type positron traps are identified and their characteristic positron lifetimes, Doppler ratio curves and lineshape parameters determined. We find that In vacancies and their complexes with N vacancies or impurities act as efficient positron traps, inducing distinct changes in the annihilation parameters compared to the InN lattice. Neutral or positively charged N vacancies and pure N vacancy complexes on the other hand do not trap positrons. The predominantly introduced positron trap in irradiated InN is identified as the isolated In vacancy, while in as-grown InN layers In vacancies do not occur isolated but complexed with one or more N vacancies. The number of N vacancies per In vacancy in these complexes is found to increase from the near surface region towards the layer-substrate interface.
We present results of single crystal neutron diffraction experiments on the rare-earth, half-Heusler antiferromagnet (AFM) NdBiPt. This compound exhibits an AFM phase transition at $T_{mathrm N}=2.18$~K with an ordered moment of $1.78(9)$~$mu_{mathrm
B}$ per Nd atom. The magnetic moments are aligned along the $[001]$-direction, arranged in a type-I AFM structure with ferromagnetic planes, alternating antiferromagnetically along a propagation vector $tau$ of $(100)$. The $R$BiPt ($R$= Ce-Lu) family of materials has been proposed as candidates of a new family of antiferromagnetic topological insulators (AFTI) with magnetic space group that corresponds to a type-II AFM structure where ferromagnetic sheets are stacked along the space diagonal. The resolved structure makes it unlikely, that NdBiPt qualifies as an AFTI.
We investigated the far- and mid-infrared reflectivity (20-6000 wavenumber) of several pure and doped CuGeO3 single crystals. The b-axis and c-axis optical response is presented for different temperatures between 4 K and 300 K. Moreover, a full group
theoretical analysis of the lattice vibrational modes of CuGeO3 in the high temperature undistorted phase as well as in the low temperature spin-Peierls phase is reported and compared to the experimental results. We observe the activation of zone boundary phonons along the b axis of the crystal below the spin-Peierls transition temperature.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
