Magnetic properties of lightly doped antiferromagnetic YBa2_{2}Cu3_{3}Oy_{y}

The present work addresses YBa$_{2}$Cu$_{3}$O$_{y}$ at doping below x=6% where the compound is a collinear antiferromagnet. In this region YBa$_{2}$Cu$_{3}$O$_{y}$ is a normal conductor with a finite resistivity at zero temperature. The value of the staggered magnetization at zero temperature is 0.6\mu_B, the maximum value allowed by spin quantum fluctuations. The staggered magnetization is almost independent of doping. On the other hand, the Neel temperature decays very quickly from T_N=420K at x=0 to practically zero at x = 0.06. The present paper explains these remarkable properties and demonstrates that the properties result from the physics of a lightly doped Mott insulator with small hole pockets. Nuclear quadrupole resonance data are also discussed. The data shed light on mechanisms of stability of the antiferromagnetic order at x < 6%

Conductance anomalies in a one-dimensional quantum contact

Short length quantum wires (quantum contacts) exhibit a conductance structure at the value of conductance close to 0.7 \times 2e^2/h. The structure is also called the conductance anomaly. In longer contacts the structure evolves to the lower values of conductance. We demonstrate that this structure is related to the development of charge density waves within the contact. This is a precursor for Wigner crystallization. Many-body Hartree-Fock calculations of conductance are performed. The results are in agreement with experimental data.Comment: 11 pages, 10 Fig

A one-dimensional spin-orbit interferometer

We demonstrate that the combination of an external magnetic field and the intrinsic spin-orbit interaction results in nonadiabatic precession of the electron spin after transmission through a quantum point contact (QPC). We suggest that this precession may be observed in a device consisting of two QPCs placed in series. The pattern of resonant peaks in the transmission is strongly influenced by the non-abelian phase resulting from this precession. Moreover, a novel type of resonance which is associated with suppressed, rather than enhanced, transmission emerges in the strongly nonadiabatic regime. The shift in the resonant transmission peaks is dependent on the spin-orbit interaction and therefore offers a novel way to directly measure these interactions in a ballistic 1D system.Comment: 8 pages, 5 figure

Nuclear time-reversal violation and the Schiff moment of 225Ra

We present a comprehensive mean-field calculation of the Schiff moment of the nucleus 225Ra, the quantity which determines the static electric dipole moment of the corresponding atom if time-reversal (T) invariance is violated in the nucleus. The calculation breaks all possible intrinsic symmetries of the nuclear mean field and includes, in particular, both exchange and direct terms from the full finite-range T-violating nucleon-nucleon interaction, and the effects of short-range correlations. The resulting Schiff moment, which depends on three unknown T-violating pion-nucleon coupling constants, is much larger than in 199Hg, the isotope with the best current experimental limit on its atomic electric-dipole moment.Comment: 4 pages, 2 figures; this version (references added) to be published in PR

Few interacting particles in a random potential

We study the localization length of few interacting particles in a random potential. Concentrating on the case of three particles we show that their localization length is strongly enhanced comparing to the enhancement for two interacting particles.Comment: latex 10 pages, 1 figur

Violation of the Spin Statistics Theorem and the Bose-Einstein Condensation of Particles with Half Integer Spin

We consider the Bose condensation of particles with spin 1/2. The condensation is driven by an external magnetic field. Our work is motivated by ideas of quantum critical deconfinement and bosonic spinons in spin liquid states. We show that both the nature of the novel Bose condensate and the excitation spectrum are fundamentally different from that in the usual integer spin case. We predict two massive ("Higgs") excitations and two massless Goldstone excitations. One of the Goldstone excitations has a linear excitation spectrum and another has quadratic spectrum. This implies that the Bose condensate does not support superfluidity, the Landau criterion is essentially violated. We formulate a "smoking gun" criterion for searches of the novel Bose condensation