73 research outputs found
Bulk and local magnetic susceptibility of ErB12
High precision measurements of magnetoresistance Δρ/ρ = f(T,H) and magnetization M(T,H) were carried out on single crystals of rare-earth dodecaboride at temperatures in the interval 1.8-30 K in magnetic fields up to 70 kOe. The high accuracy of the experiments allowed us to perform numerical differentiation and analyze quantitatively the behavior of the derivative d(Δρ/ρ)/dH = f(T,H) and of the magnetic susceptibility χ(T,H) = dM/dH in paramagnetic and magnetically ordered (antiferromagnetic, ≈ 6.7 K and ≈ 5.85 K) phases of . It was shown that negative magnetoresistance anomalies observed in present study in paramagnetic state of may be consistently interpreted in the framework of a simple relation between resistivity and magnetization -Δρ/ρ ~
Hall effect in the vicinity of quantum critical point in Tm1-xYbxB12
The angular, temperature and magnetic field dependences of Hall resistance
roH for the rare-earth dodecaboride solid solutions Tm1-xYbxB12 have been
studied in a wide vicinity of the quantum critical point (QCP) xC~0.3. The
measurements performed in the temperature range 1.9-300 K on high quality
single crystals allowed to find out for the first time in these fcc compounds
both an appearance of the second harmonic contribution in ro2H at QCP and its
enhancement under the Tm to ytterbium substitution and/or with increase of
external magnetic field. When the Yb concentration x increases a negative
maximum of a significant amplitude was shown to appear on the temperature
dependences of Hall coefficient RH(T) for the Tm1-xYbxB12 compounds. Moreover,
a complicated activation type behavior of the Hall coefficient is observed at
intermediate temperatures for x>0.5 with activation energies Eg~200K and
Ea~55-75K in combination with the sign inversion of RH(T) at low temperatures
in the coherent regime. The density of states renormalization effects are
analyzed within the variation of Yb concentration and the features of the
charge transport in various regimes (charge gap formation, intra-gap manybody
resonance and coherent regime) are discussed in detail in Tm1-xYbxB12 solid
solutions.Comment: 38 pages including 10 figures, 70 reference
Structural basis for the interaction of a human small heat shock protein with the 14-3-3 universal signaling regulator
By interacting with hundreds of protein partners, 14-3-3 proteins coordinate vital cellular processes. Phosphorylation of the small heat shock protein, HSPB6, within its intrinsically disordered N-terminal domain activates its interaction with 14-3-3, ultimately triggering smooth muscle relaxation. After analyzing the binding of an HSPB6-derived phosphopeptide to 14-3-3 using isothermal calorimetry and X-ray crystallography, we have determined the crystal structure of the complete assembly consisting of the 14-3-3 dimer and full-length HSPB6 dimer and further characterized this complex in solution using fluorescence spectroscopy, small-angle X-ray scattering, and limited proteolysis. We show that selected intrinsically disordered regions of HSPB6 are transformed into well-defined conformations upon the interaction, whereby an unexpectedly asymmetric structure is formed. This structure provides the first atomic resolution snapshot of a human small HSP in functional state, explains how 14-3-3 proteins sequester their regulatory partners, and can inform the design of small-molecule interaction modifiers to be used as myorelaxants
Electron-phonon interaction and spectral weight transfer in FeCoSi
A comprehensive ellipsometric study was performed on FeCoSi
single crystals in the spectral range from 0.01 eV to 6.2 eV. Direct and
indirect band gaps of 73 meV and 10 meV, respectively, were observed in FeSi at
7 K. One of four infrared-active phonons that is energetically close to the
direct absorption edge is coupled both to the electrons and to the low-energy
phonon. This is evident from asymmetry in the phonon line shape and a reduction
of its frequency when the absorption edge shifts across the phonon energy due
to the temperature dependence of the direct band gap. As the temperature
increases, the indirect gap changes sign, which manifests as a transition from
a semiconductor to a semimetal. The corresponding gain of the spectral weight
at low energies was recovered within an energy range of several eV. The present
findings strongly support the model indicating that FeCoSi can be
well described in an itinerant picture, taking into account self-energy
corrections.Comment: 12 pages, 12 figure
The energy gap of intermediate-valent SmB6 studied by point-contact spectroscopy
We have investigated the intermediate valence narrow-gap semiconductor SmB6
at low temperatures using both conventional spear-anvil type point contacts as
well as mechanically controllable break junctions. The zero-bias conductance
varied between less than 0.01 mikrosiemens and up to 1 mS. The position of the
spectral anomalies, which are related to the different activation energies and
band gaps of SmB6, did not depend on the the contact size. Two different
regimes of charge transport could be distinguished: Contacts with large zero -
bias conductance are in the diffusive Maxwell regime. They had spectra with
only small non-linearities. Contacts with small zero - bias conductance are in
the tunnelling regime. They had larger anomalies, but still indicating a finite
45 % residual quasiparticle density of states at the Fermi level at low
temperatures of T = 0.1 K. The density of states derived from the tunelling
spectra can be decomposed into two energy-dependent parts with Eg = 21 meV and
Ed = 4.5 meV wide gaps, respectively.Comment: 9 pages incl. 13 figure
The mechanism of SARS-CoV-2 nucleocapsid protein recognition by the human 14-3-3 proteins
The coronavirus nucleocapsid protein (N) controls viral genome packaging and contains numerous phosphorylation sites located within unstructured regions. Binding of phosphorylated SARS-CoV N to the host 14-3-3 protein in the cytoplasm was reported to regulate nucleocytoplasmic N shuttling. All seven isoforms of the human 14-3-3 are abundantly present in tissues vulnerable to SARS-CoV-2, where N can constitute up to ∼1% of expressed proteins during infection. Although the association between 14-3-3 and SARS-CoV-2 N proteins can represent one of the key host-pathogen interactions, its molecular mechanism and the specific critical phosphosites are unknown. Here, we show that phosphorylated SARS-CoV-2 N protein (pN) dimers, reconstituted via bacterial co-expression with protein kinase A, directly associate, in a phosphorylation-dependent manner, with the dimeric 14-3-3 protein, but not with its monomeric mutant. We demonstrate that pN is recognized by all seven human 14-3-3 isoforms with various efficiencies and deduce the apparent KD to selected isoforms, showing that these are in a low micromolar range. Serial truncations pinpointed a critical phosphorylation site to Ser197, which is conserved among related zoonotic coronaviruses and located within the functionally important, SR-rich region of N. The relatively tight 14-3-3/pN association could regulate nucleocytoplasmic shuttling and other functions of N via occlusion of the SR-rich region, and could also hijack cellular pathways by 14-3-3 sequestration. As such, the assembly may represent a valuable target for therapeutic intervention
Rattling-Induced Superconductiviy in the Beta-Pyrochlore Oxides AOs2O6
The superconducting properties of two beta-pyrochlore oxides, CsOs2O6 and
RbOs2O6, are studied by thermodynamic and transport measurements using
high-quality single crystals. It is shown that the character of
superconductivity changes systematically from weak coupling for CsOs2O6 to
moderately strong coupling for RbOs2O6, and finally to extremely strong
coupling with BCS-type superconductivity for KOs2O6, with increasing Tc.
Strong-coupling correction analyses of the superconducting properties reveal
that a low-energy rattling mode of the alkali metal ions is responsible for the
mechanism of the superconductivity in each compound. The large enhancement of
Tc from Cs to K is attributed to the increase in the electron-rattler coupling
with decreasing characteristic energy of the rattling and with increasing
anharmonicity. The existence of weak anisotropy in the superconducting gap or
in the electron-rattler interactions is found for the Cs and Rb compounds
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