Photoemission studies of high-tc superconductors: the superconducting gap

Over the last several years there have been great improvements in the energy resolution and detection efficiency of angle-resolved photoemission spectroscopy. These improvements have made it possible to discover a number of fascinating features in the electronic structure of the high transition temperature (T(c)) superconductors: apparently bandlike Fermi surfaces, flat-band saddle points, and nested Fermi surface sections. Recent work suggests that these features, previously thought explainable only by one-electron band theory, may be better understood with a many-body approach. Furthermore, other properties of the high-T(c) superconductors, which are difficult to understand with band theory, are well described using a many-body picture. Angle-resolved photoemission spectroscopy has also been used to investigate the nature of the superconducting pairing state, revealing an anisotropic gap consistent with a d-wave order parameter and fueling the current debate over s-wave versus d-wave superconductivity.     

Electrical Resistivity and Stoichiometry of CaxC60 and SrxC60 Films

The temperature- and concentration-dependent resistivities of annealed CaxC(60) and SrxC(60) films were measured near room temperature. Resistivity minima were observed at x = 2 and 5. The resistivities of these films were rho(min) approximately 1 ohm-centimeter for x = 2 and rho(min) approximately 10(-2) ohm-centimeter for x = 5. This latter value is comparable to the resistivities found in similar experiments on K(3)C(60) films. There is a maximum in the resistivity between x = 2 and 3, and another at x approximately 7. The conductivity is activated over the whole range of compositions, and the activation energy scales with the logarithm of the resistivity. The results suggest that the conductivity and superconductivity observed in Ca(5)C(60) are associated with the population of bands derived from the t(1g) level of C(6O).     

Superconductivity at 40 K in the Oxygen-Defect Perovskites La2-xSrxCuO4-y

Structural, magnetic, and electronic properties of compounds in the series La2-xSrx CuO4-y for 0.05 相似文献   

Nodal quasiparticles and antinodal charge ordering in Ca2-xNaxCuO2Cl2

Understanding the role of competing states in the cuprates is essential for developing a theory for high-temperature superconductivity. We report angle-resolved photoemission spectroscopy experiments which probe the 4a0 x 4a0 charge-ordered state discovered by scanning tunneling microscopy in the lightly doped cuprate superconductor Ca2-xNaxCuO2Cl2. Our measurements reveal a marked dichotomy between the real- and momentum-space probes, for which charge ordering is emphasized in the tunneling measurements and photoemission is most sensitive to excitations near the node of the d-wave superconducting gap. These results emphasize the importance of momentum anisotropy in determining the complex electronic properties of the cuprates and places strong constraints on theoretical models of the charge-ordered state.     

Superconductivity-induced transfer of in-plane spectral weight in Bi2Sr2CaCu2O8+delta

Optical data are reported on a spectral weight transfer over a broad frequency range of Bi2Sr2CaCu2O8+delta, when this material became superconducting. Using spectroscopic ellipsometry, we observed the removal of a small amount of spectral weight in a broad frequency band from 10(4) cm(-1) to at least 2 x 10(4) cm(-1), due to the onset of superconductivity. We observed a blue shift of the ab-plane plasma frequency when the material became superconducting, indicating that the spectral weight was transferred to the infrared range. Our observations are in agreement with models in which superconductivity is accompanied by an increased charge carrier spectral weight. The measured spectral weight transfer is large enough to account for the condensation energy in these compounds.     

Pressure Dependence of Superconductivity in Single-Phase K3C60

The superconducting compound K(3)C(60) (with transition temperature T(c) = 19.3 kelvin at ambient pressure), formed as a single phase by reaction of alkali vapor with solids of the icosahedral C(60) molecule (buckminsterfullerene), shows a very large decrease of T(c) with increasing pressure. Susceptibility measurements on sintered pellets showing bulk superconductivity are reported up to 21 kilobars of pressure, where T(c) is already less than 8 kelvin. The results are consistent with a piling up of the density of states at the Fermi level.     

小麦8539高产系统模式栽培研究

采用播期（ｘ１）、密度（ｘ２）、氮肥（ｘ３）、磷肥（ｘ４）、钾肥（ｘ５）五元二次正交旋转回归组合设计,建立小麦８５３９高产栽培优化模型ｙ＝３５６．６４－３０．３１ｘ１＋１４．２３ｘ２＋３４．０８ｘ３＋７．５６ｘ４－１８．０７ｘ１ｘ２－１３．５１ｘ１ｘ３－１８．９８ｘ１ｘ４－８．６２ｘ４ｘ５＋１０．００ｘ５２。因子水平选优,当ｘ１取－２、ｘ２取２、ｘ３取２、ｘ４取２、ｘ５取－２时,获得产量１２０８５．８ｋｇ／ｈｍ２,比各因子取０水平时,净增６７４７．０ｋｇ／ｈｍ２,增产１２５．９２％,比四川小麦历史最高产量７５７５．０ｋｇ／ｈｍ２,增产８３．３８％。这是目前粮食作物高产模式栽培中罕见的增产效益。经大田验证,模型信度均达０．９５以上,具有较好的稳定性。模型的建立,对小麦８５３９的高产栽培和四川小麦上新台阶具有重要的指导作用。     

Tracking Cooper pairs in a cuprate superconductor by ultrafast angle-resolved photoemission

In high-temperature superconductivity, the process that leads to the formation of Cooper pairs, the fundamental charge carriers in any superconductor, remains mysterious. We used a femtosecond laser pump pulse to perturb superconducting Bi(2)Sr(2)CaCu(2)O(8+δ) and studied subsequent dynamics using time- and angle-resolved photoemission and infrared reflectivity probes. Gap and quasiparticle population dynamics revealed marked dependencies on both excitation density and crystal momentum. Close to the d-wave nodes, the superconducting gap was sensitive to the pump intensity, and Cooper pairs recombined slowly. Far from the nodes, pumping affected the gap only weakly, and recombination processes were faster. These results demonstrate a new window into the dynamical processes that govern quasiparticle recombination and gap formation in cuprates.     

浅析生产函数g(x)=a+bx+cx~2+ex~3(e<0)合理生产阶段的划分

生产函数g(x)可获取最佳利润的资源施用量应同时满足下述条件:①dy/dx=px/py;,②’py·g(x)-p_x·x>p~y·g(0);当a=0时,生产函数g(x)=a+bx+cx~2+ex~3(e<0)成为典型生产函数f(x)=bx+cx~2+ex~3(e<0)。这时,条件②’是式②p~yf(x)-p~x·x>0的一般形式;而式②是条件②’(当a=0时)的一个特例。生产函数g(x)=a+bx+ex~2+ex~3(e>0)当a≠0时,其合理生产阶段的起点不是边际产量最高点对应的资源施用量。对生产函数g(x)划分生产阶段时应先做变换:f(x)=g(x)-g(0),把g(x)变为典型生产函数f(x)的形式,然后对f(x)按传统方法划分阶段。生产函数g(x)与变换后的生产函数f(x)的合理生产阶段的起点完全相同。     

棉蚜防治指标的研究

通过三年多点田间小区对比试验,组建了棉蚜危害棉花1～3叶期、4～8叶期和伏蚜期棉花卷叶株率(x)和产量损失率(y)的回归式,分别为y=20.021e~(-8.9287/x)(n=29,r=0.8066,p<0.001)、y=19.925e~(-13.3779/x)(n=19,r=0.9006,p<0.001)和y=23.272e~(-12.2155/x)(n=12,r=0.7469,p<0.01)。结合目前我省棉花产量水平(亩产120～150斤皮棉)、防治费用等,提出上述三个时期棉蚜的防治指标分别为卷叶株率4～5%、7～8%和7～8%,均较我省过去的防治指标有所放宽。     

添加高铜对生长肥育猪组织铜残留量及病理学变化影响的研究

选用60头杂交猪(杜×长×约)研究日粮铜添加水平对生长肥育猪组织铜残留量和病理学变化的影响。试验采用单因子设计,分别设0、100、200、300、400 mgCu/kg饲粮的添加水平,试验从20 kg开始,100 kg结束。结果表明:添加100~400 mg/kg的铜不同程度地增加了组织中铜的残留量,试验猪肝脏和肾脏中的铜含量随着饲粮铜添加水平的增加极显著的增加,呈二次曲线的变化规律,肝脏铜含量(y1,mg/kg)和肾脏中铜的含量(y2,mg/kg)与饲粮铜添加水平(x,mg/kg)之间的回归方程分别为:y1=11.3963-0.2920x+0.0022x2(R2=0.814,P=0.036);y2=8.7583-0.0043x+0.0002x2(R2=0.975,P=0.025)。根据回归方程可知,为了保证肝脏或肾脏中铜的含量不超过10 mg/kg,饲粮铜添加水平应不高于127.76或90.27 mg/kg。饲粮铜添加水平与组织器官铜浓度之间相关关系依次为:肝脏>肾脏>脾脏>心脏。添加100~400 mg/kg的铜,对肝脏、肾脏、心脏和脾脏造成了不同程度的病理性损伤,主要表现为不同程度的细胞变性、炎性细胞浸润和毛细血管出血。     

彩棉三个品种的核型对比分析

采用常规压片法对滨彩2号(浅棕色)、99-55(深棕色)和滨绿1号(绿色)的染色体数目和核型进行了研究,得出结论:滨彩2号的染色体数目为2n=4x=52,核型公式为:k(2n)=4x=52=22m 18sm(2SAT) 12st,属于"2B"类型.染色体相对长度组成为2n=4x=52=10L 16M2 14M1 12S;99-55染色体数目为2n=4x=52,核型公式为:k(2n)=4x=52=26m(2SAT) 22sm 4st,属于"2B"类型.染色体相对长度组成为2n=4x=52=12L 10M2 22M1 8S;滨绿1号的染色体数目为2n=4x=52,核型公式为:k(2n)=4x=52=40m 12sm(2SAT),属于"1B"类型.染色体相对长度组成为2n=4x=52=8L 16M2 18M1 10s.     

Temperature Dependence of the Superconducting Gap Anisotropy in Bi2Sr2CaCu2O8+x

Detailed data on the momentum-resolved temperature dependence of the superconducting gap of Bi(2)Sr(2)CaCu(2)O(8+x) are presented, complemented by similar data on the intensity of the photoemission superconducting condensate spectral area. The gap anisotropy between the Gamma-Mand Gamma-X directions increases markedly with increasing temperature, contrary to what happens for conventional anisotropic-gap superconductors, such as lead. Specifically, the size of the superconducting gap along the Gamma-X direction decreases to values indistinguishable from zero at temperatures for which the gap retains virtually full value along the Gamma-M direction. These data rule out the simplest type of d-wave order parameter.     

砂梨品种等级果下降原因的研究Ⅱ采果前叶片矿质养分含量对果个大小及产量的影响

本试验以晚三吉、湘南和土任锦三个砂梨品种（ＰｙｒｕｓｐｙｒｉｆｏｌｉａＮａｋａｉ）的成年树为试材,研究其果实成熟采收前叶片氮、磷、钾含量与果个大小及产量的关系。结果表明：梨果成熟期叶片氨、磷含量与产量及单果重相关不显著;叶片含钾量在一定范围内与产量呈极显著负回归,湘南、晚三吉和土佐锦三个品种的回归方程分别为：Ｙ１＝８１．８１－７０．０２ｘ１,ｙ２＝１４２．８９－１２５．９７ｘ２,ｙ３＝９９．１９－１１４．６０ｘ３;叶片含钾量在一定范围内与单果重呈极显著正相关,三个品种的回归方程分别为：ｙ４＝２１．９３＋２４３．５２ｘ１,ｙ５＝－７５．８９＋２８４．４７ｘ２,和ｙ６＝－１０１．２４＋４３７．７５ｘ３。     

Oxygen Isotope Effect and Structural Phase Transitions in La2CuO4-Based Superconductors

The oxygen isotope effect on the superconducting transition temperature (alpha(o)) varies as a function of x in La2-xSrxCuO(4) and La2-xBaxCuO(4), with the maximum alpha(o) values (alpha(o) >/= 0.5) found for x near 0.12. This unusual x dependence implies that the isotope effect is influenced by proximity to the Abma --> P4(2)/ncm structural phase transition in these systems. Synchrotron x-ray difaction measurements reveal little change in lattice parameters or orthorhombicity due to isotope exchange in strontium-doped materials where alpha(o) > 0.5, eliminating static structural distortion as a cause of the large isotope effects. The anomalous behavior of alpha(o) in both strontium- and barium-doped materials, in combination with the previously discovered Abma --> P4(2)/ncm structural phase-transition in La(1.88)B(0.12)CuO(4), suggests that an electronic contribution to the lattice instability is present and maximizes at approximately 1/8 hole per copper atom. These observations indicate a dose connection between hole doping of the Cu-O sheets, tilting instabilities of the CuO(6) octahedra, and superconductivity in La(2)CuO(4)-based superconductors.     

Nonequilibrium phase transitions in cuprates observed by ultrafast electron crystallography

Nonequilibrium phase transitions, which are defined by the formation of macroscopic transient domains, are optically dark and cannot be observed through conventional temperature- or pressure-change studies. We have directly determined the structural dynamics of such a nonequilibrium phase transition in a cuprate superconductor. Ultrafast electron crystallography with the use of a tilted optical geometry technique afforded the necessary atomic-scale spatial and temporal resolutions. The observed transient behavior displays a notable "structural isosbestic" point and a threshold effect for the dependence of c-axis expansion (Deltac) on fluence (F), with Deltac/F = 0.02 angstrom/(millijoule per square centimeter). This threshold for photon doping occurs at approximately 0.12 photons per copper site, which is unexpectedly close to the density (per site) of chemically doped carriers needed to induce superconductivity.     

HPLC法检测复合维生素片中叶酸和维生素B_(12)的含量

[目的]建立应用高效液相法测定复合维生素片中叶酸和维生素B12含量的方法。[方法]色谱柱用菲罗门lunaC18(4.6×250 mm,5μm),流动相为甲醇-0.028 mol/L磷酸氢二钠水溶液(用磷酸调pH到3.5)(21∶79),流速1.0 ml/min,检测波长为361 nm,进样量为20μl,柱温为25℃。[结果]维生素B12在6.65～66.50 ng范围内呈现良好的线性关系,回归方程是y=0.495 1x+1.342 8(R2=0.999 4,n=6),平均回收率为96.83%,RSD为0.82%(n=6)。叶酸在80～800 ng范围内呈现良好的线性关系,回归方程是y=0.021 1 x+0.661 1(R2=0.998 8,n=6),平均回收率为95.56%,RSD为1.54%(n=6)。[结论]高效液相色谱法灵敏度高,操作简便,重现性好,结果准确,可以用于复合维生素片中叶酸和维生素B12的含量测定。     

西葫芦LAI动态模拟模型的初步建立与检验

对春提早、秋延后和越冬茬西葫芦的叶面积指数(LAI)及生育期的有效积温进行归一化处理,分别将最大的LAI和出苗至开花的有效积温定为1,以相对LA(I0～1)和相对有效积温(0～1)为参数,进行LAI动态模拟,筛选、建立了一个适用于这3个茬口西葫芦的相对LAI动态模拟模型:y=(a+bx)(/1+cx+dx2)。其中,春提早为y=(-0.040 0+0.087 5x)/(1-1.473 8x+0.588 2x2)(r=0.992 2**,n=50);秋延后为y=(0.035 5+0.060 0x)(/1-1.390 5x+0.543 1x2)(r=0.991 9**,n=22);越冬茬为y=(-0.046 4+0.146 4x)(/1-1.377 9x+0.559 0x2)(r=0.988 7**,n=70)。准确度(以k表示)分别为0.999 6,1.000 7和1.000 5,精确度(以R2表示)分别为0.983 9,0.982 3和0.976 9。西葫芦LAI动态模型从三叶一心期就能够比较准确地进行西葫芦LAI动态预测。     

Uranium-series dating of sediments from searles lake: differences between continental and marine climate records

One of the major unresolved questions in Pleistocene paleoclimatology has been whether continental climatic transitions are consistent with the glacial delta(18)O marine record. Searles Lake in California, now a dry salt pan, is underlain by sediment layers deposited in a succession of lakes whose levels and salinities have fluctuated in response to changes in climate over the last 3 x 10(6) years. Uraniumseries dates on the salt beds range from 35 x 10(3) to 231x 10(3) years. This range of dates allows identification of lake-sediment horizons that are time correlatives of the boundaries of marine isotope stages from the recent 3/4 boundary back to the 8/9 boundary. The 5/6 boundary coincided with a deepening of the lake, but the analogous 1/2 boundary coincided with desiccation. The 3/4, 4/5, 6/7, 7/8, and 8/9 boundaries correspond in age to horizons that record little or no change in sedimentation or climate. These hydrologic results demonstrate that the continental paleoclimate record at this mid-latitude site does not mimic the marine record.     

Caloris Basin: An Enhanced Source for Potassium in Mercury's Atmosphere

Enhanced abundances of neutral potassium (K) in the atmosphere of Mercury have been found above the longitude range containing Caloris Basin. Results of a large data set including six elongations of the planet between June 1986 and January 1988 show typical K column abundances of approximately 5.4 x 10(8) K atoms/cm(2). During the observing period in October 1987, when Caloris Basin was in view, the typical K column was approximately 2.7 x 10(9) K atoms/cm(2). Another large value (2.1 x 10(9) K atoms/cm(2)) was seen over the Caloris antipode in January 1988. This enhancement is consistent with an increased source of K from the well-fractured crust and regolith associated with this large impact basin. The phenomenon is localized because at most solar angles, thermal alkali atoms cannot move more than a few hundred kilometers from their source before being lost to ionization by solar ultraviolet radiation.