27 research outputs found
THE TIGHT-BINDING APPROACH TO THE DIELECTRIC RESPONSE IN THE MULTIBAND SYSTEMS
Starting from the random phase approximation for the weakly coupled multiband
tightly-bounded electron systems, we calculate the dielectric matrix in terms
of intraband and interband transitions. The advantages of this representation
with respect to the usual plane-wave decomposition are pointed out. The
analysis becomes particularly transparent in the long wavelength limit, after
performing the multipole expansion of bare Coulomb matrix elements. For
illustration, the collective modes and the macroscopic dielectric function for
a general cubic lattice are derived. It is shown that the dielectric
instability in conducting narrow band systems proceeds by a common softening of
one transverse and one longitudinal mode. Furthermore, the self-polarization
corrections which appear in the macroscopic dielectric function for finite band
systems, are identified as a combined effect of intra-atomic exchange
interactions between electrons sitting in different orbitals and a finite
inter-atomic tunneling.Comment: 20 pages, LaTeX, no figure
The 2-Channel Kondo Model I: Review of Experimental Evidence for its Realization in Metal Nanoconstrictions
Certain zero-bias anomalies (ZBAs) in the voltage, temperature and magnetic
field dependence of the conductance of quenched Cu point contacts
have previously been interpreted to be due to non-magnetic 2-channel Kondo
(2CK) scattering from near-degenerate atomic two-level tunneling systems (Ralph
and Buhrman, 1992; Ralph et al. 1994), and hence to represent an experimental
realization of the non-Fermi-liquid physics of the T=0 fixed point of the
2-channel Kondo model. In this, the first in a series of three papers
(I,II,III) devoted to 2-channel Kondo physics, we present a comprehensive
review of the quenched Cu ZBA experiments and their 2CK interpretation,
including new results on ZBAs in constrictions made from Ti or from metallic
glasses. We first review the evidence that the ZBAs are due to electron
scattering from stuctural defects that are not static, but possess internal
dynamics. In order to distinguish between several mechanisms proposed to
explain the experiments, we then analyze the scaling properties of the
conductance at low temperature and voltage and extract from the data a
universal scaling function . The theoretical calculation of the
corresponding scaling function within the 2CK model is the subject of papers II
and III. The main conclusion of our work is that the properties of the ZBAs,
and most notably their scaling behavior, are in good agreement with the 2CK
model and clearly different from several other proposed mechanisms.Comment: 35 pages RevTeX, 19 encapsulated postscript figures; this final
published version features two additional authors, an additional section
reviewing recent experiments on Ti nanoconstrictions that agree very well
with the 2-channel Kondo model, 6 new figures (and is much shorter the
previous 53 page version, due to reformatting
A multi-ancestry genome-wide study incorporating gene-smoking interactions identifies multiple new loci for pulse pressure and mean arterial pressure
Elevated blood pressure (BP), a leading cause of global morbidity and mortality, is influenced by both genetic and lifestyle factors. Cigarette smoking is one such lifestyle factor. Across five ancestries, we performed a genome-wide gene–smoking interaction study of mean arterial pressure (MAP) and pulse pressure (PP) in 129 913 individuals in stage 1 and follow-up analysis in 480 178 additional individuals in stage 2. We report here 136 loci significantly associated with MAP and/or PP. Of these, 61 were previously published through main-effect analysis of BP traits, 37 were recently reported by us for systolic BP and/or diastolic BP through gene–smoking interaction analysis and 38 were newly identified (P < 5 × 10−8, false discovery rate < 0.05). We also identified nine new signals near known loci. Of the 136 loci, 8 showed significant interaction with smoking status. They include CSMD1 previously reported for insulin resistance and BP in the spontaneously hypertensive rats. Many of the 38 new loci show biologic plausibility for a role in BP regulation. SLC26A7 encodes a chloride/bicarbonate exchanger expressed in the renal outer medullary collecting duct. AVPR1A is widely expressed, including in vascular smooth muscle cells, kidney, myocardium and brain. FHAD1 is a long non-coding RNA overexpressed in heart failure. TMEM51 was associated with contractile function in cardiomyocytes. CASP9 plays a central role in cardiomyocyte apoptosis. Identified only in African ancestry were 30 novel loci. Our findings highlight the value of multi-ancestry investigations, particularly in studies of interaction with lifestyle factors, where genomic and lifestyle differences may contribute to novel findings