Competing phases in the cuprates: Charge vs spin order

We have investigated magnetic and charge instabilities of the cuprates within the Gutzwiller approximation RPA (GA+RPA). Interestingly, in GA the dressed Hubbard U is not a single parameter, but has different forms in the spin and charge responses, with distinct doping dependencies. While there are a number of competing magnetic instabilities for hole-doped cuprates, we fail to find any purely electronic charge density waves. The dominant magnetic instabilities are associated with ‘double nesting’, and the phase diagrams are material dependent, with LSCO differing from other cuprates.     

Magnetic order and spin dynamics in ferroelectric HoMnO3

Hexagonal HoMnO3 is a frustrated antiferromagnet (T(N)=72 K) ferroelectric (T(C)=875 K) in which these two order parameters are coupled. Our neutron measurements of the spin-wave dispersion for the S=2 Mn3+ on the layered triangular lattice are well described by a two-dimensional nearest-neighbor Heisenberg exchange J=2.44 meV, and an anisotropy D that is 0.28 meV above the spin-reorientation transition at 40 K and 0.38 meV below. For H parallel c the magnetic structures and phase diagram have been determined, and reveal additional transitions below 8 K where the ferroelectrically displaced Ho3+ ions are ordered magnetically.     

Spin gaps and spin dynamics in superconducting cuprates

Spin gap effects, consisting of a declining uniform susceptibility and spin paramagnetic NMR shift at low temperaturesin the normal state and associatedT ₁ behavior, are discussed and documented in several cuprate superconductors. Dynamic spin magnetism in these systems is further reviewed in the light of mean-field models, where we note that detailed results from the model by Millis, Monien, and Pines are not borne out in recent neutron data on YBa₂Cu₃O_6.92.T ₁ data on¹⁷O in La_1.85Sr_0.15CuO₄ are presented, showing consistency with neutron dynamic susceptibility data forT≧80 K, but exhibiting a strong spin gap character below 80 K which is not present in the neutron data. Data for Zn-doped YBCO withT _c≈60 K are also presented, showing strong RKKY broadening from localized moments in the planes, but no spin gap effect such as that found in theT _c=60 K oxygen-deficient phase.     

Time reversal symmetry breaking in cuprates induced by the spiral spin order

We propose a new interpretation of the spontaneous time reversal symmetry breaking (TRSB) observed recently in a pseudogap state of cuprates (Kaminsky et al.). It is shown that the TRSB dichroism in an ARPES signal may be related to the local spin spiral structures in the system. It may be caused by a spin-orbit interaction and by spin polarization of electrons at various sections of the Fermi surface in the spiral state. The angular dependence of the dichroism signal is studied in a schematic KKR approximation. Tests are proposed to check the existence of the local spiral spin structure and to distinguish it from the TRSB state with microcurrents constructed by Varma.     

Chiral order and electromagnetic dynamics in one-dimensional multiferroic cuprates

We show by unbiased numerical calculations that the ferromagnetic nearest-neighbor exchange interaction stabilizes a vector spin chiral order against the quantum fluctuation in a frustrated spin-1/2 chain relevant to multiferroic cuprates, LiCu2O2 and LiCuVO4. Our realistic semiclassical analyses for LiCu2O2 resolve controversies on the helical magnetic structure and unveil the pseudo-Nambu-Goldstone modes as the origin of experimentally observed electromagnons.     

Nuclear Magnetic Resonance in Industry

It is the author's intention to demonstrate progress in the application of nuclear magnetic resonance (NMR) in industry over a period of nearly 30 years.     

Charge modulation, spin response, and dual Hofstadter butterfly in high-Tc cuprates

The modulated density of states observed in recent STM experiments in underdoped cuprates is argued to be a manifestation of the charge-density wave of Cooper pairs (CPCDW). CPCDW formation is due to superconducting phase fluctuations enhanced by Mott-Hubbard correlations near half-filling. The physics behind the CPCDW is related to a Hofstadter problem in a dual superconductor. It is shown that CPCDW does not impact nodal fermions at the leading order. An experiment is proposed to probe coupling of the CPCDW to the spin carried by nodal quasiparticles.     

Charge dynamics in electron-underdoped high-Tc cuprates

We investigate charge dynamics in the antiferromagnetic (AF) phase of electron-doped cuprates by using numerically exact diagonalization technique for an electron-doped t-t′-J model. When AF correlation develops with decreasing temperature, a gap-like behavior emerges in the optical conductivity accompanied by the enhancement of the coherent motion of carriers due to the same sublattice hoppings. This is a remarkable contrast to the behavior of a hole-doped t-t′-J model.     

Nuclear Magnetic Resonance Studies in Gases

There are several reasons why nuclear magnetic resonance (NMR) studies in gases are important. At low pressures the interactions in the gas phase are essentially governed by two body collisions. It is therefore possible to study the intermolecular forces between two molecules approaching one another during collision from their influence on the chemical shifts of the nuclei of the molecules under considerations. The experimental measurements allow one to learn how the chemical shift is perturbed because of the presence of other molecules. This knowledge can then be transferred to interpret solvent effects in condensed phases and for detection of any solvent-solute interactions in such systems.     

核磁共振技术在生物质转化中的应用

生物质结构的精确分析研究有利于其各个组分的转化利用,而核磁共振（NMR）技术是生物质解聚及结构演变分析中重要的表征技术.本文主要介绍了¹H NMR、¹³C NMR、³¹P NMR和2D HSQC四种NMR技术在生物质结构、产物定性和定量分析、反应路径和催化解聚机理探究中的应用,然后讨论了NMR技术应用于生物质研究中存在的主要问题,并进行了展望.     

Two-Dimensional Frequency-Relaxation Nuclear Magnetic and Nuclear Quadrupole Resonance Spectroscopies

Russian Physics Journal -     

核磁共振岩屑含油饱和度分析技术的实验研究

含油饱和度是油田勘探开发中的重要油层物理参数之一,目前油田现场岩屑常规录井方法只能定性给出岩屑的含油级别,无法给出岩屑含油饱和度的定量结果. 提出了利用核磁共振技术进行现场岩屑含油饱和度快速定量分析. 在室内实验基础上,采用添加弛豫试剂的方法进行了岩屑含油饱和度的核磁共振定量分析,研究摸索了一套利用核磁共振技术进行现场岩屑含油饱和度分析的方法,给出了弛豫试剂的优选方案,同时给出了核磁共振岩屑含油饱和度的测量精度.     

铁基超导体中的反铁磁序和自旋动力学

类似于其他非常规超导材料,铁基高温超导电性通常出现在静态长程反铁磁序被抑制之后,并且强烈的自旋涨落始终与超导电性相伴相生,因此理解磁性相互作用是建立铁基超导微观机理的重要前提.中子散射作为研究凝聚态物质中磁性相互作用的有力工具,在揭示铁基超导电性的磁性起源方面起到了关键作用.本文系统总结了近十年来铁基超导材料的中子散射研究结果,包括铁基超导材料中的静态磁结构、磁性相变、动态磁激发、电子向列相等,并探讨它们与超导电性之间的关系.     

核磁共振与相关诺贝尔奖

概要介绍了核磁共振原理及其应用，并对与之相关的诺贝尔奖也做了介绍．     

Charge current driven by spin dynamics in disordered Rashba spin-orbit system

Pumping of charge current by spin dynamics in the presence of the Rashba spin-orbit interaction is theoretically studied. Considering a disordered electron, the exchange coupling and spin-orbit interactions are treated perturbatively. It is found that the dominant current induced by spin dynamics is interpreted as a consequence of the conversion from spin current via the inverse spin Hall effect. We also find that the current has an additional component from a fictitious conservative field. The results are applied to the case of a moving domain wall.     

固体核磁共振技术在锡硅分子筛表征中的应用

生物质等绿色资源的高效转化利用是催化科学的重要发展方向.锡硅分子筛因具有优良的催化性能而得到相关研究者的普遍关注.准确构建催化剂活性中心结构/酸性与催化反应性能之间的构效关系是新型高效催化剂设计与研发的基础.固体核磁共振（NMR）是研究分子筛活性中心局域结构、酸特性与催化反应机理的重要手段.本文简述了近年来固体NMR技术在锡硅分子筛研究领域的一系列主要进展,并进行了展望.     

基于时域核磁共振技术的木材吸湿过程研究

木材吸湿会对其力学性能和尺寸稳定性产生影响,深入了解木材吸湿过程中水分状态的变化有重要意义.利用时域核磁共振(TD-NMR)技术,以美国黄杨木和红橡木作为研究对象,对木材吸湿过程中水分状态和弛豫特性进行研究.结果显示:吸湿过程的前4h,两种木材试件结合水峰面积迅速增大,自由水峰面积无明显增长,说明在吸湿初期,增加的水分主要以结合水为主;在达到吸湿平衡后,红橡木试件内自由水峰面积约为黄杨木试件内自由水峰面积的2倍,这是由于与黄杨木相比,红橡木管孔孔径较大,因此在吸湿过程中,红橡木的自由水吸湿速度较快,吸湿量大于黄杨木.