Magnetic field-temperature phase diagram of the organic conductor α-(BEDT-TTF)2KHg(SCN)4

We present systematic magnetic torque studies of the “magnetic field-temperature” phase diagram of the layered organic conductor α-(BEDT-TTF)₂KHg(SCN)₄ at fields nearly perpendicular and nearly parallel to the highly conducting plane. The shape of the phase diagram is compared to that predicted for a charge-density-wave system in a broad field range.     

Superconductivity of κ-(BEDT-TTF)2Cu[N(CN)2]I under pressure

The insulating state of κ-(BEDT-TTF)₂Cu[N(CN)₂]I salt appearing at ambient pressure at low temperatures is suppressed by hydrostatic pressure. The resistive measurements showed that the emerging metallic state reveals superconductivity in high-quality crystals. The superconducting state with the transition temperature of about 8 K is stable at pressures higher than 0.1 GPa.     

Zeeman-driven phase transition within the superconducting state of κ-(BEDT-TTF)2Cu(NCS)2

(13)C nuclear magnetic resonance measurements were performed on κ-(BEDT-TTF)(2)Cu(NCS)(2), with the external field placed parallel to the quasi-2D conducting layers. The absorption spectrum is used to determine the electronic spin polarization M(s) as a function of external field H at a temperature T=0.35 K. A discontinuity in the derivative dM(s)/dH at an applied field of H(s)=213±3 kOe is taken as evidence for a Zeeman-driven transition within the superconducting state and stabilization of inhomogeneous superconductivity.     

准一维有机超导体(TMTSF)_2ClO_4的高精度温差电动势研究

测量了准一维有机超导体 (TMTSF) 2 ClO4 单晶a方向不同降温速率下的高精度温差电动势 (6— 2 80K) .高温下的温差电动势表现出线性行为 ,不能被正常的一维电子能带理论所解释 .在 2 4 0K左右观察到温差电动势斜率发生反常突变 .在 14 0K左右温差电动势向下逐渐偏离线性行为 ,这与 1D— 2D的维度渡越相关 .对阴离子有序—无序相变温度Ta(Ta=2 4K)附近的温差电动势结果与比热和电阻率的数据进行了比较 .对于极慢速降温的温差电动势 ,求导后可以看到相变的痕迹 .随着通过Ta 降温速率的增大 ,在Ta 之下的温差电动势数值出现了一个逐渐增大的整体抬高 .对此进行了讨论 .     

Diamagnetic evidence of superconductivity in the organic conductors β- (BEDT-TTF) 2IBr2 and β- (BEDT-TTF) 2AuI2

Replacement of the triiodide linear anion I₃^- by the symmetric linear anions IBr₂^- and AuI₂^- in the organic superconducting metal β- (BEDT-TTF) ₂I₃ results in an increase of the transition temperature from 1.2 to 1.9 and to 3.2 K respectively. Meissner effect measurements indicate that in all cases superconductivity is a volume property.     

配合物(PP)_2Cu和(PP)_3Fe的FT-Raman和FT-IR光谱研究(PP=2-(2-氧基-苯基)吡啶)

配合物（ＰＰ）２Ｃｕ和（ＰＰ）３Ｆｅ的ＦＴ┐Ｒａｍａｎ和ＦＴ┐ＩＲ光谱研究（ＰＰ＝２┐（２┐氧基┐苯基）吡啶）王悦姜世梅李艳芹（吉林大学超分子结构与谱学开放实验室长春１３００２１）ＦＴ┐ＲａｍａｎａｎｄＦＴ┐ＩＲＳｐｅｃｔｒａｏｆＣｕａｎｄＦｅＣｏｍ...     

Magnetic anisotropy and low-frequency dielectric response of weak ferromagnetic phase in κ-(BEDT-TTF)2Cu[N(CN)2]Cl, where BEDT-TTF is Bis(ethylenedithio)tetrathiafulvalene

We report a detailed characterization of the magnetism and AC transport in single crystals of the organic conductor -(BEDT-TTF)₂Cu[N(CN)₂]Cl by means of magnetic anisotropy measurements and low-frequency dielectric spectroscopy. Magnetic anisotropy obeys Curie-Weiss law with negative Curie-Weiss temperature in the temperature range 300 K-70 K. An antiferromagnetic transition with concomitant canted antiferromagnetic state is established at 22 K. A large hysteresis in the spin-flop transition and magnetic field reversal of the weak ferromagnetic magnetization are documented for the first time. A broad dielectric relaxation mode of moderate strength () emerges at 32 K, and weakens with temperature. The mean relaxation time, much larger than that expected for single-particle excitations, is thermally activated in a manner similar to the DC conductivity and saturates below 22 K. These features suggest the origin of the broad relaxation as an intrinsic property of the weak ferromagnetic ground state. We propose a charged domain wall in a random ferromagnetic domain structure as the relaxation entity. We argue that the observed features might be well described if Dzyaloshinsky-Moriya interaction is taken into account. A Debye relaxation with similar temperature dependence was also observed and seems to be related to an additional ferromagnetic-like, most probably, field-induced phase. We tentatively associate this phase, whose tiny contribution was sample dependent, with a Cu²⁺ magnetic subsystem. Received 15 June 1998 and Received in final form 1 February 1999     

α-Sr(HCOO)_2单晶的拉曼光谱研究

本文根据α-Sr(HCOO)_2的晶体结构分析了此种晶体的基本晶格振动,用商群分析方法计算了基本晶格振动的对称类型,在室温下记录α-Sr(HCOO)_2晶体的拉曼光谱,对750cm~(-1)—3000cm~(-1)频率范围内的一些谱线的归宿进行了分析。     

Temperature Dependence of the Critical Field of the Organic Superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br

JETP Letters - We present upper critical magnetic fields data for κ(BEDT-TTF)2Cu[N(CN)2]Br (hereafter k-Br), single crystals with the magnetic field applied either or perpendicular and...     

有机导体(TMTSF)_2PF_6的超导性

法国巴黎sud大学固体物理实验室的D.Jerome,A.Mazaud,M.Ribault和丹麦哥本哈根奥斯特研究所的 K.Bechgaard 在 1980年2月 15日的J.Phy-sique　 Letter上报道:他们发现有机导体“二-(四甲基四硒富瓦烯)-六氟磷化物” [di-(tetramethyltetraselena-fulvalene)-hexafluorophosphate,简写为(TMTSF)2PF6]存在超导性,12千巴静压力下超导转变温度Tc为0.9K.这是第一次发现在有机固体中存在超导(见图1). 早在1964年,美国斯坦福大学的W.A.Little就提出了有机超导体的设想; 973年有机导体“四硫富瓦烯(TTF)-四腈对苯醒二甲烷(TCNQ)”在58K…     

YBa_2(Cu_(1-x)Fe_x)_3O_(7-δ)超导体结构相变及其超导电性的研究

我们对YBa_2(Cu_(1-x)Fe_x)_3O_(7-δ)(0≤x≤0.07)超导体的结构相变与超导电性进行了系统研究。x射线衍射分析表明样品在x≈0.04时存在一个从正交晶到四方晶的结构相变过程,原胞体积随铁的组分增加而变大。R-T曲线测量得到零电阻温度随铁组分的增加迅速下降到液氮温度以下,零电阻温度T_c(O)随x增大而减小且在结构相变点没有突变。微结构分析表明从正交晶到四方晶的相变过程伴随着孪晶现象的消失。     

YBa_2(Cu_(1-x)Fe_x)_3O_(7-δ)超导体结构相变及其超导电性的研究

我们对YBa_2(Cu_(1-x)Fe_x)_3O_(7-δ)(0≤x≤0.07)超导体的结构相变与超导电性进行了系统研究。x射线衍射分析表明样品在x≈0.04时存在一个从正交晶到四方晶的结构相变过程,原胞体积随铁的组分增加而变大。R-T曲线测量得到零电阻温度随铁组分的增加迅速下降到液氮温度以下,零电阻温度T_c(O)随x增大而减小且在结构相变点没有突变。微结构分析表明从正交晶到四方晶的相变过程伴随着孪晶现象的消失。     

有机材料(EDT-DSDTFVO)_2FeCl_4和(EDT-DSDTFVO)_2GaCl_4的磁电阻分析

有机材料(EDT-DSDTFVO)2FeCl4和(EDT-DSDTFVO)2GaCl4的输送实验结果,显示出这两类盐的电阻率对温度的依赖性以及压力效果十分相似,但是两种盐的磁电阻率却表现出很大的不同,FeCl4盐为负磁电阻,而GaCl4盐为正磁电阻。我们认为这种输送现象的差异性起源于π-d相互作用。我们用EDT-DSDTFVO表示ethylenedithiodiselenadithiafulvalenothioquinone-1,3-dithiole methide。     

Point-contact spectra of the organic metal β-(BEDT-TTF)2I3

The d²U/dI²-characteristics of point-contacts between the organic superconductor β-(BEDT-TTF)₂I₃ in the normal metallic state and a normal metal (copper) are measured and found to be quite similar to those of point-contacts between normal metals which are well known to be correlated with the electron phonon coupling and the phonon density of states.     

K_2H(IO_3)_2Cl单晶中子衍射结构分析

利用中子四圆衍射仪收集了K_2H(IO_3)_2Cl单晶的衍射数据共481个,其中独立衍射351个。利用SHELX程序做了Fourier合成及差值Fourrer合成,并用OR XFLS4程序做了最小二乘法修正(其中包括各向同性及各向异性消光修正),R因子达到3.3％,确定了结构中氢原子的位置,肯定了氢键的存在。     

MgB2超导体的同位素效应

本基于双带模型，通过引入非电子—声子相互作用并利用自洽近似方法在贴理论框架内讨论了硼化镁超导体的同位素效应，并探讨了非电子。声子相互作用对体系超导电性的作用。     

KBr:(Ag~-)_2发光的磁场效应

通过测量偏振度和发光衰减时间的磁场效应,研究了KBr中Ag~-离子对的弛豫激发态(RES),产生发光的RES是~3∑_u~+,并进一步在D_2h晶场中劈裂成三个支能级B_(2u)B_(3u)和,A_u。KBr∶(Ag~-)_2中这些支能级之间的能量间隔,由偏振度和发光的衰减时间的温度关系估计为0.13meV和0.52meV。 采用-N_2莱塞在(Ag~-)_2中心的X_1吸收带激发磷光体。观察发光是在激光的前进     

Femtosecond carrier relaxation dynamics and photoinduced phase separation in κ-(BEDT-TTF)2Cu[N(CN)2]X (X=Br,Cl)

We investigate the relaxation dynamics of nonequilibrium carriers in organic conductors κ-(BEDT-TTF)(2)Cu[N(CN)(2)]X (X=Br and Cl) using ultrafast time-resolved optical spectroscopy. The dynamics for both salts show similar temperature dependences, which is well characterized by the carrier relaxation across the pseudogap (PG) of the magnitude Δ(PG) ≈ 16 meV for Br salt and 7.0 meV for Cl salt. On the other hand, only the Br salt shows an abrupt increase of the decay time at low temperature, indicating an additional decay component associated with the superconducting (SC) gap below T(c). The fluence dependent dynamics at low temperature evidences the superposition of the SC component onto the PG component. These results indicate a metallic-insulating phase separation in the Br salt triggered by photoexcited nonequilibrium carriers.     

Thermal expansion of the organic conductor β-(BEDT-TTF)2I3

We report hiogh resolution thermal expansion measurements between 1.2 and 300 K along the c¹-axis in the organic conductor β-(BEDT-TTF)₂I₃ where the superconducting properties are strongly dependent on the way the system is prepared in the pressure-temperature diagram. We clearly observed a strong anomaly at 172 K related to the structural phase transition and the resistivity anomalies reported by several groups. The temperature analysis in the low temperature regime is coherent with a phonon dominant contribution. Finally, the presence of small hysteresis in a large region around the transitions seem to indicate why both the pressure and the temperature cycling may stabilize small regions of the high-T_c phase of the system, as observed.