The NQR picture of electronic phase separation in the lanthanum–barium cuprates

We report the results of Cu and La NQR investigations of the spin and charge separation in La_2−xBa_xCuO₄ compounds. For Ba doping inducing the low-temperature tetragonal phase our Cu–NQR measurements revealed three inequivalent Cu sites in CuO₂ planes. In terms of the stripe-phase picture we assign them to the charged stripe, to its neighborhood and to the AF correlated regions free of holes correspondingly. The last site corresponds to the ordered Cu magnetic moment of 0.29μ_B.     

Anomalies in magnetic susceptibility of nonstoichiometric Nd2NiO4+δ (δ=0.049, 0.065, 0.077, 0.234)

We have investigated the influence of oxygen excess on structural and physical properties of the Nd₂NiO_4+δ compounds. Using the citrate method and subsequent annealing in air and in a reducing atmosphere a various oxygen-doped compounds were prepared. X-ray diffraction at room temperature shows that structure is strongly oxygen excess dependent. Thus, by increasing δ by up to 0.077, the compounds adopt a tetragonal structure gradually with a biphasic domain between orthorhombic and tetragonal structures. And at higher δ values, the structure becomes orthorhombic. Moreover, Rietveld analysis shows that for δ<0.077 the presence of two crystalline phases with different oxygen excess: it should be the signature of interstitial oxygen, which is distributed in heterogeneous way. The biphasic products are composed of a stoichiometric Nd₂NiO₄ phase (orthorhombic structure) and a tetragonal Nd₂NiO_4.077 phase. Magnetic susceptibility shows a deviation from Curie-Weiss law for lower oxygen excess (δ?0.077). Moreover, some anomalies in dc magnetic susceptibility curves was observed at 45, 95 and 130 K for δ<0.077. These transitions are connected to the tetragonal phase, and were attributed, respectively, to an antiferromagnetic transition, possible charge ordering and structural transition.     

Patterning polycrystalline aluminum by electropolishing at low voltages

Highly ordered stripes with controllable spacing of the pattern lines are obtained during electropolishing aluminum (Al) foils at low voltage. The samples are investigated in detail with the Atomic Force Microscope (AFM). Stripes with similar spacing of the pattern lines are observed on the surface of Al sheets which are electropolished in the same electrolyte at various voltages. However, the spacing of the pattern lines is closer when there is more ethanol in the electrolyte at the same voltage. The formation mechanism of stripes with dissimilar spacing of the pattern lines in different electrolyte is discussed. We suggest that the spacing of the pattern lines depends on the concentration of the polar molecules (ethanol) in the electrolyte.     

Charge and spin inhomogeneity as a key to the physics of the high-Tc cuprates

We present a coherent scenario for the physics of cuprate superconductors, which is based on a charge-driven inhomogeneity, i.e. the “stripe phase”. We show that spin and charge critical fluctuations near the stripe instability of strongly correlated electron systems provide an effective interaction between the quasiparticles, which is strongly momentum, frequency, temperature and doping dependent. This accounts for the various phenomena occurring in the overdoped, optimally and underdoped regimes both for the normal and the superconducting phase.     

关于星和条的Ramsey数

令和．该文研究了广义Ramsey数n(K1,n1,…,K1,nt, m1K2,…,msK2)．当1≤■≤∑时,得到了它们的精确值;当∑>■时,得到了它们的上 界．     

Pseudospin solitons in the coherent stripe phase of a bilayer quantum Hall system

In the Hartree–Fock approximation and at total filling factor ν=4N+1, the ground state of the two-dimensional electron gas in a double quantum well system in a quantizing magnetic field is, in some range of interlayer distances, a coherent striped phase. This stripe phase has one-dimensional coherent channels that support charged excitations in the form of pseudospin solitons. In this work, we compute the transport gap of the coherent striped phase due to the creation of soliton–antisoliton pairs using a supercell microscopic unrestricted Hartree–Fock approach. We study the energy gap as a function of interlayer distance and tunneling amplitude. Our calculations confirm that the soliton–antisoliton excitation energy is lower than the corresponding Hartree–Fock electron–hole pair energy.     

Effects of in-plane oxygens on the magnetic response in cuprates

A brief analysis of ARPES, Raman, and neutron data is used to show the importance of the oxygen degree of freedom for the metallic phase of cuprate high-T_c superconductors. It is based on published results and a number of new calculations, relevant to Raman and neutron scattering in the metallic underdoped and optimally doped regime. They are placed in the context of a recently developed theoretical understanding of the microscopic interplay between metallicity and local valence-bond fluctuations in the cuprates. It is argued that the oxygen degree of freedom is dominantly responsible for the metallicity in the normal state. The coexistence of metallic oxygen-dominated states with localized copper-dominated states is a key experimental constraint on the microscopic understanding of the normal-state pseudogap proposed here, especially of its strong k-dependence.     

Spectral signatures of critical charge and spin fluctuations in cuprates

We discuss how Raman spectra of high temperature superconducting cuprates are affected by nearly critical spin and charge collective modes, which are coupled to charge carriers near a stripe quantum critical point. We find that specific fingerprints of nearly critical collective modes can be observed and that the selectivity of Raman spectroscopy in momentum space may be exploited to distinguish the spin and charge contribution. We apply our results to discuss the spectra of high-T_c superconducting cuprates finding that the collective modes should have masses with substantial temperature dependence in agreement with their nearly critical character. Moreover spin modes have larger masses and are more diffusive than charge modes indicating that in stripes the charge is nearly ordered, while spin modes are strongly overdamped and fluctuating with high frequency.     

Stripes and superconductivity in cuprates

Holes doped into the CuO₂ planes of cuprate parent compounds frustrate the antiferromagnetic order. The development of spin and charge stripes provides a compromise between the competing magnetic and kinetic energies. Static stripe order has been observed only in certain particular compounds, but there are signatures which suggest that dynamic stripe correlations are common in the cuprates. Though stripe order is bad for superconducting phase coherence, stripes are compatible with strong pairing. Ironically, magnetic-field-induced stripe order appears to enhance the stability of superconducting order within the planes.     

基于傅里叶变换的投影条纹非正弦性的研究

采用逆推法,计算出基于发散光路的三维测量中参考面上为标准的正弦性光场时的投影光栅函数,再将计算出的投影光栅,用投影仪投影到参考面上,从而获得了标准的正弦性光场,并利用傅里叶变换方法进行三维测量。实验研究表明,此方法可以有效地抑制变形条纹的频谱混叠,准确的提取其基频信息,从而提高三维测量的精度。仿真与实验均验证了提出方法的可行性与有效性。