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1.
Harpreet Kaur 《Pramana》1999,52(4):389-393
The beauty-conserving strangeness-changing decays ofB s meson are examined. In the charm sector, charm-conserving strangeness changing (Δc = 0, Δs ≠ 0) decays are Cabibbo suppressed and are governed by the CKM elementV us which is much smaller than the CKM diagonal elementV cs, so may be of little interest. On the other hand, in theb-sector, beauty-conserving strangeness changing (Δb = 0, Δs ≠ 0) decays are CKM allowed as the CKM matrix elementV us governing such decays is much larger thanV bc orV bu which govern respectively thebc orbu transitions. The phase space available, however, is too small for the decays considered here. The numerical estimates for the decay widths of two such modes ofB s meson are presented.  相似文献   

2.
We calculate the leptonic constant for the pseudoscalar ground state of the B c meson in the framework of a QCD-motivated potential model taking into account the two-loop anomalous dimension for the heavy quark current in nonrelativistic QCD as matched with full QCD.  相似文献   

3.
Kazuo Abe 《Pramana》2003,60(2):337-344
The Belle experiment continues to explore the origin of CP violation and test all aspects of standard model inB meson decays. Recent results on CP violating paramter sin2ф1 and other measurements are presented.  相似文献   

4.
We have investigated theoretically the Nernst effect in unconventional (d-wave) charge and spin density waves (UDW). In the presence of magnetic field, Landau levels are formed, and the gapless behaviour of the low energy excitations change into gapped behaviour. When additional electric field is applied, the quasiparticles drift with a velocity of E × B/B2, and carry entropy. From this, the Nernst coefficient can be calculated using the Kelvin relation. The present results account very nicely for the measured Nernst signal in the pseudogap phase of high Tc superconductor La2−xSrxCuO4 and Bi2Sr2−yLayCuO6. This indicates that the large Nernst effect is a clear signiture of UDW.  相似文献   

5.
杨白  沈保根  赵同云  孙继荣 《物理学报》2007,56(6):3527-3532
采用快淬方法制备了纳米晶复合Pr2Fe14B/α-Fe永磁薄带,研究了不同淬火速率对薄带织构和磁性的影响.通过改善快淬工艺,使得薄带中Pr2Fe14B相的晶粒在薄带的自由面形成显著的织构,Pr2Fe14B相晶粒易轴沿垂直于带面方向取向.分析了快淬凝固过程中Pr2Fe14B相的晶粒取向过程和机理,以及晶粒的大小和薄带结构的均匀性对薄带磁性的影响.对自由面有显著取向的薄带,进行酸蚀和打磨减薄处理,去除贴辊面未取向的部分,剩余部分为具有Pr2Fe14B相晶粒取向的各向异性薄带,Pr2Fe14B相取向使薄带的剩磁得到增强,矫顽力也有所提高. 关键词: 快淬 2Fe14B/α-Fe永磁薄带')" href="#">纳米晶复合Pr2Fe14B/α-Fe永磁薄带 织构 磁性能  相似文献   

6.
张彩霞  郭虹  杨致  骆游桦 《物理学报》2012,61(19):193601-193601
利用密度泛函理论和非平衡格林函数方法, 本文对小尺寸团簇Tan(B3N3H6)n+1 (n ≤ 4)的磁性和量子输运性质进行了系统的研究. 计算结果表明, 此类体系采用三明治结构作为其基态并且具有较高的稳定性. 体系的磁矩随团簇尺寸的增大而线性增大. 当把Tan(B3N3H6)n+1团簇耦合到Au电极上时, 形成的Au-Tan(B3N3H6)n+1-Au体系在有限偏压下展示出了较强的自旋过滤能力, 因而可以被看做是一类新型的低维自旋过滤器.  相似文献   

7.
B. Mawlong 《Pramana》2007,69(4):521-531
The charmless nonleptonic decay modes Bf 0 K(π) involving a scalar and a pseudoscalar meson in the final state are studied. The scalar meson f 0 is considered as a q̄q state, as favored by some recent studies. Using the generalized factorization approach, the branching ratios and CP violation parameters are computed for these modes. The form factors are calculated using the results from relativistic light front quark model and the ISGW2 model. It is found that the direct CP violation parameters in these modes are small. However, the obtained branching ratios are not in agreement with the experimental data. Therefore, these modes may be considered as possible probes for new physics.   相似文献   

8.
In continuous magnetic fields H up to 28 T, we have studied the out-of-plane transport properties and tunneling characteristics of high-quality nondoped single crystals of the Bi-cuprate family: Bi2Sr2CuO6+δ (Bi2201), Bi2Sr2CaCu2O8+δ (Bi2212) and Bi2Sr2Ca2Cu3O10+δ (Bi2223) grown by an identical method. For all compounds the out-of-plane magnetotransport ρc(H) is negative in the temperature region where ρc(T) shows in the normal state a semiconducting-like temperature dependence. The negative magnetoresistance of ρc corresponds to the suppression of the semiconducting temperature dependence of ρc(T) which is found to be isotropic. For the Bi2201 compound, where the normal state can be reached in the available magnetic fields (28 T), a nearly complete suppression of the low-temperature upturn in ρc(T) is observed in the highest magnetic fields with a tendency towards a metallic behavior down to the lowest temperatures (0.4 K). Using the break-junction technique, especially for the Bi2212 and Bi2232 compounds, a clear superconducting gap structure can be observed. Both for temperatures above the critical temperature and for magnetic fields above the upper critical field, a pseudogap structure remains present in the tunneling spectra. The applied magnetic fields yield a stronger suppression of the superconducting state compared to that of the normal-state gap structures as manifested in ρc(T) transport and tunneling.  相似文献   

9.
密度泛函理论研究BnNi(n=6—12)团簇的结构和磁性   总被引:2,自引:0,他引:2       下载免费PDF全文
基于第一性原理,用密度泛函理论中的广义梯度近似(generalized gradient approximation,GGA)方法,在充分考虑自旋多重度的前提下,优化并得到了Bn(n=6—12)和BnNi(n=6—12)团簇的平衡构型,按照能量最低原理确定其基态结构. Bn团簇的计算结果与已有的理论结果相一致. 当Ni原子掺杂在Bn团簇 关键词nNi团簇')" href="#">BnNi团簇 基态结构 磁性  相似文献   

10.
Spin effects in the weak two-body hadronic decays of the B c and B c * mesons into J/ψ and ρ(π) mesons are considered within the model of hard one-gluon exchange between quarks at high momentum transfers. It is shown that the polarization of the J/ψ meson in the decays of the B c * meson differs substantially from that in the decays of the B c * meson. The decay widths of the B c * meson differ significantly from the widths of the B c * meson.  相似文献   

11.
We present a study of magnetization measurements performed on the single crystals of YNi2B2C and LuNi2B2C. For both the compounds, we find flux jumps in magnetisation values in the respective field regions, where the structural transitions in the flux line lattice symmetry have been reported in these systems via the small angle neutron scattering experiments. The magnetisation hysteresis loops and the AC susceptibility measurements show pronounced peak effect as well as second magnetisation peak anomaly for both YNi2B2C and LuNi2B2C. Based on these results, a vortex phase diagram has been constructed for YNi2B2C forH∥c depicting different glassy phases of the vortex matter.  相似文献   

12.
A new series of mixed oxide superconductors with the stoichiometric composition La2−x Dy x Ca y Ba2Cu4+y O z (x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La2−x (Y/Er) x Ca y Ba2Cu4+y O z series, show a strong dependence of T c on hole concentration (p sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum T c is obtained for x=0.5, y=1.0 sample (T c ∼ 75 K), for La1.5Dy0.5Ca1Ba2Cu5O z (La-2125).  相似文献   

13.
We have developed a terahertz time-domain spectroscopy (THz-TDS) system for reflectivity measurement with a temperature-controllable cryostat. For emission and detection of THz radiation, a Ti:Sapphire pulsed laser and photoconductive antennas are used. Two wire-grid polarizers enable us to carry out the polarized reflectivity measurements. Using our THz-TDS system, we measured the c-axis polarized reflectivity spectra for La2−xSrxCuO4 single crystals (x = 0.10 and 0.13) and observed sharp Josephson plasma edges for both samples below Tc. The reflectivity spectra of the x = 0.10 sample were in good agreement with those reported previously, which confirms the validity of the system. For the x = 0.13 sample, we discuss the anomolous features of the optical spectra.  相似文献   

14.
宋庆功  姜恩永  康建海 《物理学报》2008,57(5):3093-3099
根据密度波理论建立了stage-2有序LixTiS2(x=1/8,1/6,1/4,1/3,3/8,1/2)系统的晶胞模型.采用平面波赝势方法,对stage-2有序系统和stage-1有序LixTiS2(x=0,1/4,1/3,1/2,2/3,3/4,1)系统进行了几何结构优化和总能量计算,并进行了对比研究.发现stage-2晶胞的参量c(d关键词: xTiS2')" href="#">LixTiS2 阶梯结构 有序—无序相变 第一性原理计算  相似文献   

15.
Gobinda Majumder 《Pramana》2004,62(3):587-590
Semileptonic decays ofBX u lv have great importance both from theoretical and experimental point of view, as they are useful for extracting the magnitude ofV ub, one of the tiniest elements of CKM matrix. Similarly measurement ofB √ Ds×u can be used to calculateV ub The Belle Collaboration has measured these branching ratios and extractedV ub for various theoretical models.  相似文献   

16.
Manoranjan Kar  S Ravi 《Pramana》2002,58(5-6):1009-1012
Electron-doped (Ba1−x La x )MnO3 compounds were prepared for x=0−0.5. Measurements of X-ray diffraction (XRD) at room temperature and temperature variation of dc electrical resistivity down to 20 K were carried out. Samples with x=0.2–0.5 exhibit metal-insulator (M-I) transition. The maximum M-I transition temperature (T c) of 289 K was observed for 30% of La doping (x=0.3). XRD patterns of these samples (x=0.2−0.5) were analyzed using Rietveld refinement. These samples are found to be mostly in single-phase form with orthorhombic symmetry (space group Pbnm). We have found strong correlation between Mn-O-Mn bond angles and T c of M-I transition. The resistivity data below T c could be fitted to the expression ρ=ρ 1+ρ 2 T 2 and this shows that double exchange interaction plays a major role even in Mn4+-rich compound. Above T c the resistivity data were fitted to variable range hopping and small polaron models.  相似文献   

17.
RR Kothawale  BN Dole  SS Shah 《Pramana》2002,58(5-6):871-875
We have investigated the superconducting properties of the Bi1.7 Pb0.3Sr2Ca2−xCe x Cu3O10+δ system with x=0.00, 0.02, 0.04, 0.08 and 0.1 by X-ray diffraction and magnetic susceptibility. The substitution of Ce for Ca has been found to drastically change the superconducting properties of the system. X-ray diffraction studies on these compounds indicate decrease in the c-parameter with increased substitution of Ce at Ca site and volume fraction of high T c (2 : 2 : 2 : 3) phase decreases and low T c phase increases. The magnetic susceptibility of this compound shows that the diamagnetic on set superconducting transition temperature (onset) varies from 109 K to 51 K for x=0.00, 0.02, 0.04, 0.08 and 0.1. These results suggest the possible existence of Ce in a tetravalent state rather than a trivalent state in this system; that is, Ca2+ → Ce4+ replacement changes the hole carrier concentration. Hole filling is the cause of lowering T c of the system.  相似文献   

18.
单丹  朱珺钏  金灿  陈小兵 《物理学报》2009,58(10):7235-7240
采用了传统的固相烧结工艺,制备了不同Zr和Hf掺杂量的SrBi4Ti4-xZrxO15x=000,003, 006,010,020)和SrBi4Ti4-xHfxO15x=000,0005, 0015,0030,0060)的陶瓷 关键词: 4Ti4-xZrxO15')" href="#">SrBi4Ti4-xZrxO15 4Ti4-xHfxO15')" href="#">SrBi4Ti4-xHfxO15 铁电性能 介电性能  相似文献   

19.
We investigate the effect of the restoration of chiral symmetry on the quark potential in a quark–meson plasma by considering meson exchanges in the two flavor Nambu–Jona-Lasinio model at finite temperature and density. There are two possible oscillations in the chiral restoration phase; one is the Friedel oscillation due to the sharp quark Fermi surface at high density, and the other is the Yukawa oscillation driven by the complex meson poles at high temperature. The quark–meson plasma is strongly coupled in the temperature region 1≤T/T c≤3, with T c being the critical temperature of the chiral phase transition. The maximum coupling in this region is located at the phase transition point.  相似文献   

20.
Effects of a combined substitute of Yb and Nd on Y site on the superconducting properties of YBa2Cu3Oy have been studied. We synthesized Y1−x(Yb0.9Nd0.1)xBa2Cu3Oz compound with x = 0.2, 0.4, 0.6, 0.8 and 1.0. Here, the ratio of Yb–Nd was fixed to be 9:1 for obtaining 123 phase without secondary phases. The melt processing thermal profiles for Y1−x(Yb0.9Nd0.1)xBa2Cu3Oz with x = 0.2 and 0.4 and the addition of 40 mol% {Y1−x(Yb0.9Nd0.1)x}2BaCuO5 and 0.5 wt% Pt in air were determined on the basis of the thermal analysis results. All samples showed a low grain growth rate, particularly for high x values, which may be partially ascribed to un-optimized thermal schedules. Although almost all the samples exhibited low Jc values, the sample with x = 0.2 exhibited Tc of 88.8 K and a relatively high Jc value of 16,000 A/cm2 at 77 K for H//c-axis.  相似文献   

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