473 research outputs found
Electronic theory for the normal state spin dynamics in SrRuO: anisotropy due to spin-orbit coupling
Using a three-band Hubbard Hamiltonian we calculate within the
random-phase-approximation the spin susceptibility, , and
NMR spin-lattice relaxation rate, 1/T, in the normal state of the triplet
superconductor SrRuO and obtain quantitative agreement with
experimental data. Most importantly, we find that due to spin-orbit coupling
the out-of-plane component of the spin susceptibility becomes at
low temperatures two times larger than the in-plane one. As a consequence
strong incommensurate antiferromagnetic fluctuations of the
quasi-one-dimensional - and -bands point into the -direction. Our
results provide further evidence for the importance of spin fluctuations for
triplet superconductivity in SrRuO.Comment: revised versio
Phenomenology of the superconducting state in Sr2RuO4
The symmetry of the superconducting phase of Sr2RuO4 is identified as the
odd-parity pairing state d(k)=\hat{z}(k_x \pm i k_y) based on recent
experiments. The experimental evidence for the so-called orbital dependent
superconductivity leads to a single-band description of superconductivity based
on spin fluctuation mechanism. It is shown that the state \hat{z}(k_x \pm i
k_y) can be stabilized by the spin fluctuation feedback mechanism analogous to
the A-phase in 3He and by spin-orbit coupling effects.Comment: 7 pages, 1 figure, to be published in Proc. of the conference
"Anomalous Complex Superconductors" (Crete, 1998
Theory for Metal Hydrides with Switchable Optical Properties
Recently it has been discovered that lanthanum, yttrium, and other metal
hydride films show dramatic changes in the optical properties at the
metal-insulator transition. Such changes on a high energy scale suggest the
electronic structure is best described by a local model based on negatively
charged hydrogen (H) ions. We develop a many-body theory for the strong
correlation in a H ion lattice. The metal hydride is described by a large
-limit of an Anderson lattice model. We use lanthanum hydride as a prototype
of these compounds, and find LaH is an insulator with a substantial gap
consistent with experiments. It may be viewed either as a Kondo insulator or a
band insulator due to strong electron correlation. A H vacancy state in LaH
is found to be highly localized due to the strong bonding between the electron
orbitals of hydrogen and metal atoms. Unlike the impurity states in the usual
semiconductors, there is only weak internal optical transitions within the
vacancy. The metal-insulator transition takes place in a band of these vacancy
states.Comment: 18 pages, 16 figures and 6 tables. Submitted to PR
A Bioluminescent Sensor for Rapid Detection of PPEP-1, a Clostridioides difficile Biomarker
Current assays for Clostridioides difficile in nonhospital settings are outsourced and time-intensive, resulting in both delayed diagnosis and quarantining of infected individuals. We designed a more rapid point-of-care assay featuring a "turn-on " bioluminescent readout of a C. difficile-specific protease, PPEP-1. NanoLuc, a bright and stable luciferase, was "caged " with a PPEP-1-responsive peptide tail that inhibited luminescence. Upon proteolytic cleavage, the peptide was released and NanoLuc activity was restored, providing a visible readout. The bioluminescent sensor detected PPEP-1 concentrations as low as 10 nM. Sensor uncaging was achieved within minutes, and signal was captured using a digital camera. Importantly, the sensor was also functional at ambient temperature and compatible with fecal material, suggesting that it can be readily deployed in a variety of settings.Proteomic
Anisotropy in the Antiferromagnetic Spin Fluctuations of Sr2RuO4
It has been proposed that Sr_2RuO_4 exhibits spin triplet superconductivity
mediated by ferromagnetic fluctuations. So far neutron scattering experiments
have failed to detect any clear evidence of ferromagnetic spin fluctuations
but, instead, this type of experiments has been successful in confirming the
existence of incommensurate spin fluctuations near q=(1/3 1/3 0). For this
reason there have been many efforts to associate the contributions of such
incommensurate fluctuations to the mechanism of its superconductivity. Our
unpolarized inelastic neutron scattering measurements revealed that these
incommensurate spin fluctuations possess c-axis anisotropy with an anisotropic
factor \chi''_{c}/\chi''_{a,b} of \sim 2.8. This result is consistent with some
theoretical ideas that the incommensurate spin fluctuations with a c-axis
anisotropy can be a origin of p-wave superconductivity of this material.Comment: 5 pages, 3 figures; accepted for publication in PR
Electronic Structure of the Complex Hydride NaAlH4
Density functional calculations of the electronic structure of the complex
hydride NaAlH4 and the reference systems NaH and AlH3 are reported. We find a
substantially ionic electronic structure for NaAlH4, which emphasizes the
importance of solid state effects in this material. The relaxed hydrogen
positions in NaAlH4 are in good agreement with recent experiment. The
electronic structure of AlH3 is also ionic. Implications for the binding of
complex hydrides are discussed.Comment: 4 pages, 5 figure
The temperature-flow renormalization group and the competition between superconductivity and ferromagnetism
We derive a differential equation for the one-particle-irreducible vertex
functions of interacting fermions as a function of the temperature. Formally,
these equations correspond to a Wilsonian renormalization group scheme which
uses the temperature as an explicit scale parameter. Our novel method allows us
to analyze the competition between superconducting and various magnetic Fermi
surface instabilities in the one-loop approximation. In particular this
includes ferromagnetic fluctuations, which are difficult to treat on an equal
footing in conventional Wilsonian momentum space techniques. Applying the
scheme to the two-dimensional t-t' Hubbard model we investigate the RG flow of
the interactions at the van Hove filling with varying next-nearest neighbor
hopping t'. Starting at t'=0 we describe the evolution of the flow to strong
coupling from an antiferromagnetic nesting regime over a d-wave regime at
moderate t' to a ferromagnetic region at larger absolute values of t'. Upon
increasing the particle density in the latter regime the ferromagnetic
tendencies are cut off and the leading instability occurs in the triplet
superconducting pairing channel.Comment: 18 pages, 11 figure
Field dependence of the vortex structure in chiral p-wave superconductors
To investigate the different vortex structure between two chiral pairing p_x
+(-) i p_y, we calculate the pair potential, the internal field, the local
density of states, and free energy in the vortex lattice state based on the
quasiclassical Eilenberger theory, and analyze the magnetic field dependence.
The induced opposite chiral component of the pair potential plays an important
role in the vortex structure. It also produces H^{1/2}-behavior of the
zero-energy density of states at higher field. These results are helpful when
we understand the vortex states in Sr2RuO4.Comment: 11 pages, 10 figures, to be published in Phys. Rev.
Search for the decay in the momentum region
We have searched for the decay in the kinematic
region with pion momentum below the peak. One event was
observed, consistent with the background estimate of . This
implies an upper limit on
(90% C.L.), consistent with the recently measured branching ratio of
, obtained using the standard model
spectrum and the kinematic region above the peak. The
same data were used to search for , where is a weakly
interacting neutral particle or system of particles with .Comment: 4 pages, 2 figure
Vortex structure in chiral p-wave superconductors
We investigate the vortex structure in chiral p-wave superconductors by the
Bogoliubov-de Gennes theory on a tight-binding model. We calculate the spatial
structure of the pair potential and electronic state around a vortex, including
the anisotropy of the Fermi surface and superconducting gap structure. The
differences of the vortex structure between -wave
and -wave superconductors are clarified in the
vortex lattice state. We also discuss the winding case of the
-wave superconductivity.Comment: 10 pages, 8 figure
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