1,188 research outputs found
K. Alex M\"uller and his important role in ferroelectricity
In this review we concentrate on the work of K. Alex M\"uller in connection
with his activities on oxide perovskites and ferroelectrics which were central
to his research career long before he successfully discovered the first high
temperature superconductor (HTSC) together with J. G. Bednorz in 1986. Not
accidentally, but taking his long experience in perovskite ferroelectrics into
account, the first HTSC was an oxide perovskite which had never been considered
before to be superconducting.Comment: 8 pages, 4 figure
Tuning the structural instability of SrTiO_3 by Eu doping: The phase diagram of Sr_1-xEu_xTiO_3
The phase diagram of Sr_1-xEu_xTiO_3 is determined experimentally by electron
paramagnetic resonance and resistivity measurements and analyzed theoretically
within the self-consistent phonon approximation as a function of x
([0.03-1.0]). The transition temperature of the structural instability of the
system increases nonlinearly to higher temperatures with increasing x. This is
interpreted theoretically by a substantial alteration in the dynamics caused by
a change in the double-well potential from broad and shallow to narrow and
deep.Comment: 15 pages, 5 figure
Stressor-Induced Increase in Muscle Fatigability of Young Men and Women is Predicted by Strength but Not Voluntary Activation
This study investigated mechanisms for the stressor-induced changes in muscle fatigability in men and women. Participants performed an isometric-fatiguing contraction at 20% maximal voluntary contraction (MVC) until failure with the elbow flexor muscles. Study one (n = 55; 29 women) involved two experimental sessions: 1) a high-stressor session that required a difficult mental-math task before and during a fatiguing contraction and 2) a control session with no mental math. For some participants (n = 28; 14 women), cortical stimulation was used to examine mechanisms that contributed to muscle fatigability during the high-stressor and control sessions. Study two (n = 23; nine women) determined the influence of a low stressor, i.e., a simple mental-math task, on muscle fatigability. In study one, the time-to-task failure was less for the high-stressor session than control (P \u3c 0.05) for women (19.4%) and men (9.5%): the sex difference response disappeared when covaried for initial strength (MVC). MVC force, voluntary activation, and peak-twitch amplitude decreased similarly for the control and high-stressor sessions (P \u3c 0.05). In study two, the time-to-task failure of men or women was not influenced by the low stressor (P \u3e 0.05). The greater fatigability, when exposed to a high stressor during a low-force task, was not exclusive to women but involved a strength-related mechanism in both weaker men and women that accelerated declines in voluntary activation and slowing of contractile properties
Stressor-Induced Increase in Muscle Fatigability of Young Men and Women is Predicted by Strength but Not Voluntary Activation
This study investigated mechanisms for the stressor-induced changes in muscle fatigability in men and women. Participants performed an isometric-fatiguing contraction at 20% maximal voluntary contraction (MVC) until failure with the elbow flexor muscles. Study one (n = 55; 29 women) involved two experimental sessions: 1) a high-stressor session that required a difficult mental-math task before and during a fatiguing contraction and 2) a control session with no mental math. For some participants (n = 28; 14 women), cortical stimulation was used to examine mechanisms that contributed to muscle fatigability during the high-stressor and control sessions. Study two (n = 23; nine women) determined the influence of a low stressor, i.e., a simple mental-math task, on muscle fatigability. In study one, the time-to-task failure was less for the high-stressor session than control (P \u3c 0.05) for women (19.4%) and men (9.5%): the sex difference response disappeared when covaried for initial strength (MVC). MVC force, voluntary activation, and peak-twitch amplitude decreased similarly for the control and high-stressor sessions (P \u3c 0.05). In study two, the time-to-task failure of men or women was not influenced by the low stressor (P \u3e 0.05). The greater fatigability, when exposed to a high stressor during a low-force task, was not exclusive to women but involved a strength-related mechanism in both weaker men and women that accelerated declines in voluntary activation and slowing of contractile properties
Evidence for Coexistence of Bulk Superconductivity and Itinerant Antiferromagnetism in the Heavy Fermion System CeCo(InCd)
In the generic phase diagram of heavy fermion systems, tuning an external
parameter such as hydrostatic or chemical pressure modifies the superconducting
transition temperature. The superconducting phase forms a dome in the
temperature-tuning parameter phase diagram, which is associated with a maximum
of the superconducting pairing interaction. Proximity to antiferromagnetism
suggests a relation between the disappearance of antiferromagnetic order and
superconductivity. We combine muon spin rotation, neutron scattering, and x-ray
absorption spectroscopy techniques to gain access to the magnetic and
electronic structure of CeCo(InCd) at different time scales.
Different magnetic structures are obtained that indicate a magnetic order of
itinerant character, coexisting with bulk superconductivity. The suppression of
the antiferromagnetic order appears to be driven by a modification of the
bandwidth/carrier concentration, implying that the electronic structure and
consequently the interplay of superconductivity and magnetism is strongly
affected by hydrostatic and chemical pressure.Comment: Article + Supplementary information 33 pages, 13 figure
Direct evidence for the emergence of a pressure induced nodal superconducting gap in the iron-based superconductor Ba_0.65Rb_0.35Fe_2As_2
Identifying the superconducting (SC) gap structure of the iron-based
high-temperature superconductors (Fe-HTS's) remains a key issue for the
understanding of superconductivity in these materials. In contrast to other
unconventional superconductors, in the Fe-HTS's both -wave and extended
s-wave pairing symmetries are close in energy, with the latter believed to be
generally favored over the former. Probing the proximity between these very
different SC states and identifying experimental parameters that can tune them,
are of central interest. Here we report high-pressure muon spin rotation
experiments on the temperature-dependent magnetic penetration depth (lambda) in
the optimally doped Fe-HTS Ba_0.65Rb_0.35Fe_2As_2. At ambient pressure this
material is known to be a nodeless s-wave superconductor. Upon pressure a
strong decrease of (lambda) is observed, while the SC transition temperature
remains nearly constant. More importantly, the low-temperature behavior of
(1/lambda^{2}) changes from exponential saturation at zero pressure to a
power-law with increasing pressure, providing unambiguous evidence that
hydrostatic pressure promotes nodal SC gaps. Comparison to microscopic models
favors a d-wave over a nodal s^{+-}-wave pairing as the origin of the nodes.
Our results provide a new route of understanding the complex topology of the SC
gap in Fe-HTS's.Comment: 33 pages and 12 figures (including supplementary information
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