蓝青铜CDW相变比热的连续绝热法测量

改进建立了一套连续绝热法测量材料比热测量材料比热随温度变化的装置。标准铜的测量结果证实了此装置的稳定可靠性。给出了两种准一维导体蓝青铜Ｋ０．３ＭｏＯ３ Ｔｌ０．３ＭｏＯ３的Ｐｅｉｅｒｌｓ－电荷密度波相变比煌测量结果。     

铊系超导单昌的低温生长

采用蠕爬型助熔剂ＣａＯ－ＣｕＯ和蒸发型复合助熔剂ＣａＯ－ＣｕＯ－ＮａＣｌ来制备Ｔｌ－Ｂａ－Ｃａ－Ｃｕ－Ｏ超导单晶，生长炉最高温度８９０℃和８５０℃，因而实现了铊系单晶的低温生工。生长出的单晶分别是典型尺寸为２．０×１．５×０．２ｍｍ＾３，Ｔｃ在１００Ｋ与１１９Ｋ之间的Ｔｌ－２２１２相单晶和尺寸为１．２×１．０×０．１ｍｍ＾３。Ｔｃ约为１１５Ｋ的Ｔｌ－２２２３相超导单晶。     

铊系超导单晶的低温生长

采用蠕爬型助熔剂ＣａＯ－ＣｕＯ和蒸发型复合助熔剂ＣａＯ－ＣｕＯ－ＮａＣｌ来制备Ｔｌ－Ｂａ－Ｃａ－ＣＵ－Ｏ超导单晶，生长炉最高温度分别为８９０℃和８５０℃，因而实现了铊系单晶的低温生长．生长出的单晶分别是典型尺寸为２．０×１．５×０．２ｍｍ３，Ｔｃ在１００Ｋ与１１９Ｋ之间的Ｔｌ－２２１２相单晶和尺寸为１．２×１．０×０．１ｍｍ３，Ｔｃ约为１１５Ｋ的Ｔｌ－２２２３相超导单晶．采用蠕爬型助熔剂可以降低熔点而不引进其它非组元杂质，但导致熔料蠕爬，对生长大块单晶不利．采用蒸发型复合助熔剂克服了熔料的蠕爬现象，减少了铊的损失，对生长多铜氧层的单晶有利．     

钾掺杂铊青铜Tl0.3MoO3的电输运性质研究

我们测量了几种成份钾掺杂铊青铜Ｔｌ０．３ＭｏＯ３单晶的电阻及热电势随温度变化的性质。结果显示，与未掺杂样品一样，无论是高于或低于Ｐｅｉｅｒｌｓ相变温度Ｔｐ，掺杂样品热电势的温度特性均满足一个经验公式Ｓ＝ＡＴ＋Ｂ／Ｔ。然而，由于掺杂，样品的电阻，热电势的绝对值以及相变温度Ｔｐ均减少；但其热电势符号变化的温度Ｔｓ却增加。我们在漂移散射和声子曳引的基础上，引入杂质的施主效应以及弱的链间偶合的影响讨论了上     

三层膜中特殊的内磁场效应

本文用直流溅射法在（１００）ＬａＡｌＯ３单晶基片上制备了ＬＳＭＯ／ＰＣＭＯ／ＬＳＭＯ三层膜，并研究了三层膜的电，磁特性。在零磁下，三层膜的电阻率随中间层Ｐｒ０．７Ｃａ０．３ＭｎＯ３＋δ厚度的增加而显著下降、转变温度向高温区移动。中间层ＰＣＭＯ的作用相当于提供了一个内磁场。     

钾钼青铜电子结构的XPS研究

用ＸＰＳ研究了紫青铜Ｋ０．９Ｍｏ６Ｏ１７和蓝青铜Ｋ０．３ＭｏＯ３的电子结构，根据测得的Ｍｏ３ｄ芯级电子谱表明，紫，蓝青铜分别含有Ｍｏ＾６＋，Ｍｏ＾５＋，Ｍｏ＾４＋和Ｍｏ＾６＋，Ｍｏ＾５＋离子，其平均价态数分别为５．５２和５．７３，通过对两种晶体的芯电子谱和价带谱的比较认为，不同化学计量比的Ｋ离子对它们的电子结构影响是十分敏感的。     

蓝青铜K_(0－3)MoO_3单晶Peierls相变研究

测量了蓝青铜Ｋ０３ＭｏＯ３单晶ＲＴ曲线，发现曲线在２８０Ｋ左右有异常变化，计算得到１８０Ｋ以下的半导体能隙为１３２０Ｋ（０１１ｅＶ）．液氮温度下测量了晶体的非线性导电性，得到电场阈值为０１２９Ｖ／ｃｍ．样品ＤＳＣ研究表明，样品在２４０Ｋ处经历一新的Ｐｅｉｅｒｌｓ相变，且为一级相变，据此对相变的微观性质进行了定量计算．１８０Ｋ附近ΔｃｐＴ曲线表明，１８０Ｋ处的相变为一个二级相变加一个一级相变     

XPS和AES研究A3钢表面杂多酸钝化膜

通过比较多种杂多酸及铬酸盐等纯化剂的钝化效果，发现Ｈ３ＰＭｏ１２Ｏ４０是一种优良的纯化剂。在５５℃，ｐＨ１．０的条件下，Ａ３钢在２０ｇ／Ｌ的Ｈ３ＰＭｏ１２Ｏ４０溶液中能形成致密的耐蚀性保护膜。ＡＥＳ结合Ａｒ＾＋溅射测得膜的元素组成为：Ｐ１．９％，Ｍｏ１７．９％，Ｏ６９．６％，Ｆｅ１０．７％．ＸＰＳ测得膜中Ｍｏ以Ｍｏ（Ⅵ）、Ｍｏ（Ｖ）ｔ Ｍｏ（Ⅳ）三种氧化态存在。红外及Ｒａｍａｎ光谱表明，膜的主要振     

（110）取向La0.067Sr0.33—MnO3—δ外延膜的结构和磁电阻效应研究

采用直流磁控溅射法在（１１０）ＬａＡｌＯ３单晶基片上制备了Ｌａ０．６７Ｓｒ０．３３ＭｎＯ３－δ外延膜,系统地了样品的结构以及基片温度、外磁场对磁电阻效应的影响。     

异质外延生长钙钛矿结构氧化物薄膜

影响直接外延生长氧化物薄膜的因素有很多,最主要的是保证氧化物薄膜的正确成相和在单晶衬底上成核．直接外延生长时,衬底温度影响到薄膜的成相．衬底温度还影响薄膜的生长动力学,并因此影响薄膜的外延生长取向．由于薄膜是首先在衬底表面成核、成相并生长的,因此衬底材料晶格的影响是不容忽视的．衬底材料（或异质外延材料）与薄膜的相互作用是影响外延生长的最直接因素,而晶格常数失配会造成薄膜样品中存在应力并影响样品性质．利用脉冲激光淀积法,我们成功地外延生长了ＹＢａ２Ｃｕ３Ｏ７超导薄膜、Ｓｒ０．５Ｂａ０．５ＴｉＯ３铁电介电薄膜、Ｌａ０．７Ｃａ０．３ＭｎＯ３铁磁巨磁电阻薄膜、Ｌａ０．５Ｓｒ０．５ＣｏＯ３导电薄膜等多种具有钙钛矿结构的氧化物功能薄膜．以这些钙钛矿结构氧化物薄膜的外延生长为例,本文讨论影响氧化物薄膜异质外延生长的因素     

Pinning of charge density waves by irradiation induced defects in orthorhombic TaS3

Effects of electron irradiation induced damage on dc conductivity, threshold field and complex dielectric constant at 9 GHz are investigated in a wide temperature range. Whereas the single particle gap in the low temperature phase is not influenced by irradiation, transport properties associated with collective excitation of charge density waves (CDW) are sensitive to the presence of new pinning centres. The results are discussed in the framework of the semiclassical model of Grüner, Zawadowski and Chaikin. The pinning frequency determined from the threshold field agrees well with that of calculated from the complex dielectric constant.     

Amplification of ion-acoustic turbulence upon electron-cyclotron heating of plasma

In this paper, we present the results of the study of ion-acoustic turbulence upon electron-cyclotron heating of low-temperature plasma in a TAU-1 model setup. Two MI-167 magnetrons were used as microwave sources. The peak power of each magnetron was 1 kW, the pulse duration was 7.5 μs. An increase in the temperature of most electrons and an increase in the energy of nonthermal electrons were observed in experiments. Microwave field turning-on caused an increase by an order of magnitude in the spectral density of ion-acoustic noise in the entire frequency range from 0.3 to 3 MHz under study.     

Behavior features of phononless hopping conductivity in the vicinity of the crossover from the linear to quadratic frequency dependence

It was shown that the Coulomb interaction between electrons of “active” (resonance) pairs plays a major role in a wide frequency range. Therefore, the conventional approach to the calculation of the super-linearity of the frequency dependence of ac conductivity, based on the single-particle density of states with a Coulomb gap, is inapplicable to the calculation of high-frequency phononless conductivity. The observed superlinearity of the frequency dependence of the phononless hopping conductivity can manifest itself immediately in the region of the crossover from the linear to quadratic frequency dependence of the conductivity.     

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为了准确计算稠密等离子体电离平衡,在理想Saha方程的基础上,加入了压致电离理论和德拜理论相结合的修正。此电离模型可以描述稠密等离子体内电离机制随着密度的增加由热电离转变为压致电离的现象。压致电离理论结合德拜理论修正的 Saha 方程的计算结果与其它电离模型结果作了对比和分析。电离气体区域采用完全电离等离子体模型计算电子弛豫时间,而在凝聚态区域采用电子平均自由程计算电子弛豫时间。提出了将两个区域平滑连接起来的公式,从而建立了一种可以计算从理想等离子体态到凝聚态物质的半经验电导率模型,半经验模型计算结果与实验数据作了对比。     

一种计算稠密等离子体电导率的半经验模型

为了准确计算稠密等离子体电离平衡,在理想Saha 方程的基础上,加入了压致电离理论和德拜理论相结合的修正。此电离模型可以描述稠密等离子体内电离机制随着密度的增加由热电离转变为压致电离的现象。压致电离理论结合德拜理论修正的Saha 方程的计算结果与其它电离模型结果作了对比和分析。电离气体区域采用完全电离等离子体模型计算电子弛豫时间,而在凝聚态区域采用电子平均自由程计算电子弛豫时间。提出了将两个区域平滑连接起来的公式,从而建立了一种可以计算从理想等离子体态到凝聚态物质的半经验电导率模型,半经验模型计算结果与实验数据作了对比。     

Metal-insulator transition in amorphous Si1−xCrx films

The electrical conductivity of the amorphous Si_1−xCr_x films prepared by vacuum evaporation and sputtering was measured down to 40mK. In both films we observed a continuous metal-insulator transition. The electrical conductivity at low temperatures and the critical behavior are explained in terms of the scaling theory for interacting electrons. Whereas, present results support neither the scaling law proposed by Möbius et al. nor the existance of σ_min reported in the same system.     

Heat transport in a strongly overdoped cuprate: Fermi liquid and a pure d-wave BCS superconductor

The transport of heat and charge in the overdoped cuprate superconductor Tl(2)Ba2CuO(6+delta) was measured down to low temperature. In the normal state, obtained by applying a magnetic field greater than the upper critical field, the Wiedemann-Franz law is verified to hold perfectly. In the superconducting state, a large residual linear term is observed in the thermal conductivity, in quantitative agreement with BCS theory for a d-wave superconductor. This is compelling evidence that the electrons in overdoped cuprates form a Fermi liquid, with no indication of spin-charge separation.     

Electron-hole droplet formation in direct-gap semiconductors observed by mid-infrared pump-probe spectroscopy.

Mid-infrared pump-probe measurements with subpicosecond time resolution reveal the existence of a metastable condensed phase of the electron-hole ensemble in a direct-gap semiconductor CuCl. High-density electrons and holes are directly created in a low-temperature state by the resonant femtosecond excitation of excitons above the Mott transition density. Strong metallic reflection with a plasma frequency Planck's over 2pi(omega)p approximately 0.5 eV builds up within 0.3 ps. Within a few picoseconds, the mid-infrared reflection spectrum is transformed from metalliclike into colloidlike. The observed resonance feature at Planck's over 2pi(omega)p/sqrt[3] allows us to obtain the carrier density in the metastable electron-hole droplets of 2x10(20) cm(-3).     

Microwave resonance of the bubble phases in 1/4 and 3/4 filled high Landau levels

We have measured the diagonal conductivity, sigma(xx), in the microwave regime of an ultrahigh mobility two dimensional electron system. We find a sharp resonance in Re[sigma(xx)] versus frequency when nu>4 and the partial filling of the highest Landau level, nu(*), is approximately 1/4 or 3/4 and temperatures <0.1 K. The resonance appears for a range of nu(*) from 0.20 to 0.38 and again from 0.64 to 0.80. The peak frequency f(pk) changes from approximately 500 to approximately 150 MHz as nu(*)=1/2 is approached. This range of f(pk) shows no dependence on nu where the resonance is observed. The quality factor, Q, of the resonance is maximum at about nu(*)=0.25 and 0.74. We interpret the resonance as due to a pinning mode of the bubble phase crystal.     

Der Einfluß der Unterlage auf die Struktur und Leitfähigkeit metallischer Aufdampfschichten

The influence of the substrate on the electrical conductance and on the structure of condensed metal films is investigated. Ag, Cu and Sn films are condensed at different temperatures onto two identical quartz plates. One of them was prenucleated at room temperature. At low condensation temperatures the influence of the metallic prenucleation on the structure of the film is very strong. Surprisingly we find the same influence if the prenucleation and the film are of the same metal. The influence of the nucleation on the electrical conductance of the film is not so strong. Gold films are condensed onto different dielectric substrates at room temperature. From measurements of the electrical conductivity we find that a fraction of the conduction electrons are specularly reflected at the boundaries of the film. This fraction depends on the substrate material and the annealing temperature of the film.