Disorder, Metal-Insulator crossover and Phase diagram in high-Tc cuprates

We have studied the influence of disorder induced by electron irradiation on the normal state resistivities $\rho(T)$ of optimally and underdoped YBa2CuOx single crystals, using pulsed magnetic fields up to 60T to completely restore the normal state. We evidence that point defect disorder induces low T upturns of rho(T) which saturate in some cases at low T in large applied fields as would be expected for a Kondo-like magnetic response. Moreover the magnitude of the upturns is related to the residual resistivity, that is to the concentration of defects and/or their nanoscale morphology. These upturns are found quantitatively identical to those reported in lower Tc cuprates, which establishes the importance of disorder in these supposedly pure compounds. We therefore propose a realistic phase diagram of the cuprates, including disorder, in which the superconducting state might reach the antiferromagnetic phase in the clean limit.Comment: version 2 with minor change

Magnetically-induced electric polarization in an organo-metallic magnet

The coupling between magnetic order and ferroelectricity has been under intense investigation in a wide range of transition-metal oxides. The strongest coupling is obtained in so-called magnetically-induced multiferroics where ferroelectricity arises directly from magnetic order that breaks inversion symmetry. However, it has been difficult to find non-oxide based materials in which these effects occur. Here we present a study of copper dimethyl sulfoxide dichloride (CDC), an organo-metallic quantum magnet containing $S = 1/2$ Cu spins, in which electric polarization arises from non-collinear magnetic order. We show that the electric polarization can be switched in a stunning hysteretic fashion. Because the magnetic order in CDC is mediated by large organic molecules, our study shows that magnetoelectric interactions can exist in this important class of materials, opening the road to designing magnetoelectrics and multiferroics using large molecules as building blocks. Further, we demonstrate that CDC undergoes a magnetoelectric quantum phase transition where both ferroelectric and magnetic order emerge simultaneously as a function of magnetic field at very low temperatures

High-field Hall resistivity and magnetoresistance in electron-doped Pr_2-xCe_xCuO_{4-\delta}

We report resistivity and Hall effect measurements in electron-doped Pr$_{2-x}$Ce$_{x}$CuO$_{4-\delta}$ films in magnetic field up to 58 T. In contrast to hole-doped cuprates, we find a surprising non-linear magnetic field dependence of Hall resistivity at high field in the optimally doped and overdoped films. We also observe a crossover from quadratic to linear field dependence of the positive magnetoresistance in the overdoped films. A spin density wave induced Fermi surface reconstruction model can be used to qualitatively explain both the Hall effect and magnetoresistance.Comment: PRL in pres

On the extreme variants of nuclear fusion realization

The canonic reaction of helium synthesis as a result of deuterium and tritium interaction can take place both in high-temperature and low-temperature variants. In both cases, the nuclei draw together so closely that Coulomb’s barrier becomes enough transparent for tunneling. In the case of high-temperature synthesis the energy of chaotic thermal motion is needed to overcome the energy of electrostatic repulsion of «bare» nuclei. As a contrary, in the low-temperature variant, when deuterium and tritium nuclei replace protons in partially ionized hydrogen molecule, and negatively charged μ-meson replaces the only electron, electromagnetic interaction of nuclei with μ-meson provides nuclei approach each other to the critical distance of Rс ≈ 5 ∙ 10–13 m. A hypothesis on appearance of intermedium quasi-molecular states (IQS) when negatively charged ions collide is formulated. It is supposed that in such states the nuclei can draw together due to effective attraction to the group of negatively charged electrons having higher mass and charge as compared with individual electron. The value Rс ≈ 5 ∙ 10–13 m guarantees the tunneling only for light nuclei; therefore, the focus is made on ions’ collision with α-clustered nuclei (having compositions divisible to α-particles compositions). It is expected that the new nuclei synthesis will take place in the presence of oncoming tunneling of relatively weakly connected α-particles from α-clustered nuclei. For IQS formation, the energy acquired by colliding ions in external fields has to be comparable with the energy of their entire ionization. It was shown that the energies (not exceeding 1 keV) of oxygen ions in experiments with electrolysis of water, were accompanied by appearance of mainly carbon, silicon and iron, which meet this condition. These facts testify for the existence of IQS that have to be considered as one of the necessary conditions of low-energy nuclear reactions. In the Conclusion the program of further research is briefly stated. © 2017, Institute for Metals Superplasticity Problems of Russian Academy of Sciences. All rights reserved

Quantum Oscillations in the Underdoped Cuprate YBa2Cu4O8

We report the observation of quantum oscillations in the underdoped cuprate superconductor YBa2Cu4O8 using a tunnel-diode oscillator technique in pulsed magnetic fields up to 85T. There is a clear signal, periodic in inverse field, with frequency 660+/-15T and possible evidence for the presence of two components of slightly different frequency. The quasiparticle mass is m*=3.0+/-0.3m_e. In conjunction with the results of Doiron-Leyraud et al. for YBa2Cu3O6.5, the present measurements suggest that Fermi surface pockets are a general feature of underdoped copper oxide planes and provide information about the doping dependence of the Fermi surface.Comment: Contains revisions addressing referees' comments including a different Fig 1b. 4 pages, 4 figure