Some consequences of electronic topological transition in 2D system on a square lattice: Excitonic ordered states

We study in a mean-field approximation the ordered “excitonic” states which develop around the quantum critical point (QCP) associated with the electronic topological transition (ETT) in a 2D electron system on a square lattice. We consider the case of hopping beyond nearest neighbors when ETT has an unusual character. We show that the amplitude of the order parameter (OP) and of the gap in the electron spectrum increase with increasing the distance from the QCP, , where and n is an electron concentration. Such a behavior is different from the ordinary case when OP and the gap decrease when going away from the point which is a motor for instability. We show that the chemical potential lies always inside the gap for wavevectors in a proximity of whatever is the doping concentration. The spectrum gets a characteristic flat shape as a result of hybridization effect in the vicinity of two different SP's. The shape of the spectrum as a function of and the angle dependence of the gap have a striking similarity with the features observed in the normal state of the underdoped high- cuprates. We discuss also details about the phase diagram and the behaviour of the density of states. Received 9 June 1999     

Origin of the Concentration Quenching of Luminescence in Zn2SiO4:Mn Phosphors

Physics of the Solid State - The analysis of the unified series of single-phase Zn2 – 2xMn2xSiO4 samples (x ≤ 0.2) has provided the possibility to determine the...     

Hydrothermal synthesis and microstructure of α-Zn<Subscript>2</Subscript>SiO<Subscript>4</Subscript>:V crystal phosphor

A morphologically uniform single-phase crystal phosphor α-Zn₂SiO₄:V was prepared by one-pot hydrothermal synthesis. Energy dispersive analysis showed that a zinc silicate-base solid solution was formed with a vanadium content of 10 ± 1 at %. Its luminescence spectrum was a broad luminescence band in the region 400–700 nm with a peak near 540 nm.     

The effect of the synthesis method on the morphological and luminescence characteristics of α-Zn<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>

A promising yellow phosphor, α-Zn₂V₂O₇, was synthesized at temperatures below the phase transition temperature (610 ± 5°C) by three different methods: solid-phase and microwave processes and thermolysis of a water–salt composition. According to powder X-ray diffraction, the structures of all samples belonged to space group C/2c. Depending on the method of synthesis, the particle size varied from 500 nm (thermolysis of a water–salt composition) to 5–8 μm (ceramic and microwave methods). The excitation spectra of all samples are in the UV region (220–400 nm) and the emission spectra are in the 400–750 nm wavelength range. The photoluminescence spectra of the samples are non-elementary, which is caused by specific features of the electronic charge transfer in the structural VO₄ tetrahedra.     

Doping evolution of the electronic properties of hole- and electron-doped high-T(c) cuprates: role of density wave correlations

We show that the presence of two topological quantum critical points (QCP's) in 2D electronic system on a square lattice imposes strong constraints on density-wave (DW) correlations in the high-T(c) cuprates. Electronic properties of the corresponding strongly correlated system are highly reminiscent of the experimental trends in the high-T(c) cuprates. The most interesting results are the existence at low doping of two single-particle gaps different by order of magnitude both increasing towards low doping and of the specific insulating state characterized by a small chemical potential jump.     

Spin dynamics of the electron-doped high-T(c) superconducting cuprates

We show that a basic difference between the electron- and hole-doped cuprates is their proximity to two different quantum critical points in a 2D free fermion system on a square lattice and that the spin dynamics observed recently for the first time in the electron-doped Nd2-xCexCuO4, very different from that in the hole-doped cuprates, can be understood as a consequence of this effect.     

Single-particle Green's function of a ferromagnet with single-ion anisotropy in the presence of a magnetic field of arbitrary direction

Theoretical and Mathematical Physics -