Аннотация
In the copper oxide parent compounds of the high-transition-temperature
superconductors the valence electrons are localized—one per copper
site—by strong intra-atomic Coulomb repulsion. A symptom of this
localization is antiferromagnetism, where the spins of localized
electrons alternate between up and down. Superconductivity appears
when mobile ‘holes’ are doped into this insulating state, and it
coexists with antiferromagnetic fluctuations. In one approach to
describing the coexistence, the holes are believed to self-organize
into ‘stripes’ that alternate with antiferromagnetic (insulating)
regions within copper oxide planes, which would necessitate an unconventional
mechanism of superconductivity. There is an apparent problem with
this picture, however: measurements of magnetic excitations in superconducting
YBa2Cu3O6+x near optimum doping6 are incompatible with the naive
expectations for a material with stripes. Here we report neutron
scattering measurements on stripe-ordered La1.875Ba0.125CuO4. We
show that the measured excitations are, surprisingly, quite similar
to those in YBa2Cu3O6+x (that is, the predicted spectrum of magnetic
excitations is wrong). We find instead that the observed spectrum
can be understood within a stripe model by taking account of quantum
excitations. Our results support the concept that stripe correlations
are essential to high-transition-temperature superconductivity.
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