198,267 research outputs found
Effective range expansion in various scenarios of EFT(\notpi)
Using rigorous solutions, we compare the ERE parameters obtained in three
different scenarios of EFT(\notpi) in nonperturbative regime. A scenario with
unconventional power counting (like KSW) is shown to be disfavored by the PSA
data, while the one with elaborate prescription of renormalization but keeping
conventional power counting intact seems more promising.Comment: 6 pages, 3 tables, no figure, revtex4-1, minor revisions, to appear
in EP
One-Dimensional Transition Metal-Benzene Sandwich Polymers: Possible Ideal Conductors for Spin Transport
We investigate the electronic and magnetic properties of the proposed
one-dimensional transition metal (TM=Sc, Ti, V, Cr, and Mn)-benzene (Bz)
sandwich polymers by means of density functional calculations.
[V(Bz)] is found to be a quasi-half-metallic ferromagnet and
half-metallic ferromagnetism is predicted for [Mn(Bz)]. Moreover, we
show that stretching the [TM(Bz)] polymers could have dramatic
effects on their electronic and magnetic properties. The elongated
[V(Bz)] displays half-metallic behavior, and [Mn(Bz)]
stretched to a certain degree becomes an antiferromagnetic insulator. The
possibilities to stabilize the ferromagnetic order in [V(Bz)] and
[Mn(Bz)] polymers at finite temperature are discussed. We suggest
that the hexagonal bundles composed by these polymers might display intrachain
ferromagnetic order at finite temperature by introducing interchain exchange
coupling
Electronic, Mechanical, and Piezoelectric Properties of ZnO Nanowires
Hexagonal [0001] nonpassivated ZnO nanowires are studied with density
functional calculations. The band gap and Young's modulus in nanowires which
are larger than those in bulk ZnO increase along with the decrease of the
radius of nanowires. We find ZnO nanowires have larger effective piezoelectric
constant than bulk ZnO due to their free boundary. In addition, the effective
piezoelectric constant in small ZnO nanowires doesn't depend monotonously on
the radius due to two competitive effects: elongation of the nanowires and
increase of the ratio of surface atoms
Antiferromagnetic Alignment and Relaxation Rate of Gd Spins in the High Temperature Superconductor GdBa_2Cu_3O_(7-delta)
The complex surface impedance of a number of GdBaCuO
single crystals has been measured at 10, 15 and 21 GHz using a cavity
perturbation technique. At low temperatures a marked increase in the effective
penetration depth and surface resistance is observed associated with the
paramagnetic and antiferromagnetic alignment of the Gd spins. The effective
penetration depth has a sharp change in slope at the N\'eel temperature, ,
and the surface resistance peaks at a frequency dependent temperature below 3K.
The observed temperature and frequency dependence can be described by a model
which assumes a negligibly small interaction between the Gd spins and the
electrons in the superconducting state, with a frequency dependent magnetic
susceptibility and a Gd spin relaxation time being a strong function
of temperature. Above , has a component varying as , while below it increases .Comment: 4 Pages, 4 Figures. Submitted to Phys. Rev.
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