12,127 research outputs found
Kondo Breakdown and Hybridization Fluctuations in the Kondo-Heisenberg Lattice
We study the deconfined quantum critical point of the Kondo-Heisenberg
lattice in three dimensions using a fermionic representation for the localized
spins. The mean-field phase diagram exhibits a zero temperature quantum
critical point separating a spin liquid phase where the hybridization vanishes
and a Kondo phase where it does not. Two solutions can be stabilized in the
Kondo phase, namely a uniform hybridization when the band masses of the
conduction electrons and the spinons have the same sign, and a modulated one
when they have opposite sign. For the uniform case, we show that above a very
small temperature scale, the critical fluctuations associated with the
vanishing hybridization have dynamical exponent z=3, giving rise to a
resistivity that has a T log T behavior. We also find that the specific heat
coefficient diverges logarithmically in temperature, as observed in a number of
heavy fermion metals.Comment: new Figure 2, new results on spin susceptibility, some minor changes
to tex
Odd Parity and Line Nodes in Heavy Fermion Superconductors
Group theory arguments have demonstrated that a general odd parity order
parameter cannot have line nodes in the presence of spin-orbit coupling. In
this paper, it is shown that these arguments do not hold on the
zone face of a hexagonal close packed lattice. In particular, three of the six
odd parity representations vanish identically on this face. This has potential
relevance to the heavy fermion superconductor .Comment: 5 pages, revte
Novel results in STM, ARPES, HREELS, Nernst, neutron, Raman, and isotope substitution experiments and their relation to bosonic modes and charge inhomogeneity, from perspective of negative-Ueff boson-fermion modelling of HTSC
This paper seeks to synthesize much recent work on the HTSC materials around
the latest STM results from Davis and coworkers. The conductance diffuse
scattering results in particular are used as point of entry to discuss bosonic
modes, both of condensed and uncondensed form. The bosonic mode picture is
essential to understanding an ever growing range of observations within the
HTSC field. The work is expounded within the context of the negative-U,
boson-fermion modelling long advocated by the author. This general approach is
presently seeing much theoretical development, into which I have looked to
couple many of the experimental advances. While the formal theory is not yet
sufficiently detailed to cover adequately all the experimental complexities
presented by the real cuprate systems, it is clear that it affords very
appreciable support to the line taken. An attempt is made throughout to say why
and how it is that these events are tied so very closely to this particular set
of materials.Comment: 36 pages pdf with 3 figures and 1 table included, Submitted to J.
Phys. Cond. Mat
Multi-scale fluctuations near a Kondo Breakdown Quantum Critical Point
We study the Kondo-Heisenberg model using a fermionic representation for the
localized spins. The mean-field phase diagram exhibits a zero temperature
quantum critical point separating a spin liquid phase where the f-conduction
hybridization vanishes, and a Kondo phase where it does not. Two solutions can
be stabilized in the Kondo phase, namely a uniform hybridization when the band
masses of the conduction electrons and the f spinons have the same sign, and a
modulated one when they have opposite sign. For the uniform case, we show that
above a very small Fermi liquid temperature scale (~1 mK), the critical
fluctuations associated with the vanishing hybridization have dynamical
exponent z=3, giving rise to a specific heat coefficient that diverges
logarithmically in temperature, as well as a conduction electron inverse
lifetime that has a T log T behavior. Because the f spinons do not carry
current, but act as an effective bath for the relaxation of the current carried
by the conduction electrons, the latter result also gives rise to a T log T
behavior in the resistivity. This behavior is consistent with observations in a
number of heavy fermion metals.Comment: 17 pages, 10 figure
Electron Spin Dynamics in Semiconductors without Inversion Symmetry
We present a microscopic analysis of electron spin dynamics in the presence
of an external magnetic field for non-centrosymmetric semiconductors in which
the D'yakonov-Perel' spin-orbit interaction is the dominant spin relaxation
mechanism. We implement a fully microscopic two-step calculation, in which the
relaxation of orbital motion due to electron-bath coupling is the first step
and spin relaxation due to spin-orbit coupling is the second step. On this
basis, we derive a set of Bloch equations for spin with the relaxation times
T_1 and T_2 obtained microscopically. We show that in bulk semiconductors
without magnetic field, T_1 = T_2, whereas for a quantum well with a magnetic
field applied along the growth direction T_1 = T_2/2 for any magnetic field
strength.Comment: to appear in Proceedings of Mesoscopic Superconductivity and
Spintronics (MS+S2002
Half‐Space Neutron Transport with Linearly Anisotropic Scattering
The method developed by Case is used to solve four time‐independent, one‐speed problems for neutron transport in a homogeneous medium where the scattering function is linear in the cosine of the scattering angle. The solutions to the albedo, Milne, Green's function, and constant isotropic source problems for a half‐space are facilitated by the use of half‐range bi‐orthogonality relations between the eigenfunctions of the homogeneous transport equation. Expressions are also derived for the emerging angular densities and the densities and net currents on the surface of the half‐space.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70296/2/JMAPAQ-6-12-1939-1.pd
Metformin in polycystic ovary syndrome: systematic review and meta-analysis
The original publication may be found at www.bmj.comObjective To assess the effectiveness of metformin in improving clinical and biochemical features of polycystic ovary syndrome. Design Systematic review and meta-analysis. Data sources Randomised controlled trials that investigated the effect of metformin compared with either placebo or no treatment, or compared with an ovulation induction agent. Selection of studies 13 trials were included for analysis, including 543 women with polycystic ovary syndrome that was defined by using biochemical or ultrasound evidence. Main outcome measure Pregnancy and ovulation rates. Secondary outcomes of clinical and biochemical features of polycystic ovary syndrome. Results Meta-analysis showed that metformin is effective in achieving ovulation in women with polycystic ovary syndrome, with odds ratios of 3.88 (95% confidence interval 2.25 to 6.69) for metformin compared with placebo and 4.41 (2.37 to 8.22) for metformin and clomifene compared with clomifene alone. An analysis of pregnancy rates shows a significant treatment effect for metformin and clomifene (odds ratio 4.40, 1.96 to 9.85). Metformin has an effect in reducing fasting insulin concentrations, blood pressure, and low density lipoprotein cholesterol. We found no evidence of any effect on body mass index or waist:hip ratio. Metformin was associated with a higher incidence of nausea, vomiting, and other gastrointestinal disturbance. Conclusions Metformin is an effective treatment for anovulation in women with polycystic ovary syndrome. Its choice as a first line agent seems justified, and there is some evidence of benefit on variables of the metabolic syndrome. No data are available regarding the safety of metformin in long term use in young women and only limited data on its safety in early pregnancy. It should be used as an adjuvant to general lifestyle improvements and not as a replacement for increased exercise and improved diet.Jonathan M Lord, Ingrid H K Flight, Robert J Norma
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