The interplay of magnetic interactions, the dimensionality of the crystal structure and electronic correlations in producing superconductivity is one of the dominant themes in the study of the ...electronic properties of complex materials. Although magnetic interactions and two-dimensional structures were long thought to be detrimental to the formation of a superconducting state, they are actually common features of both the high transition-temperature (Tc) copper oxides and low-Tc material Sr2RuO4, where they appear to be essential contributors to the exotic electronic states of these materials. Here we report that the perovskite-structured compound MgCNi3 is superconducting with a critical temperature of 8 K. This material is the three-dimensional analogue of the LnNi2B2C family of superconductors, which have critical temperatures up to 16 K (ref. 2). The itinerant electrons in both families of materials arise from the partial filling of the nickel d-states, which generally leads to ferromagnetism as is the case in metallic Ni. The high relative proportion of Ni in MgCNi3 suggests that magnetic interactions are important, and the lower Tc of this three-dimensional compound-when compared to the LnNi2B2C family-contrasts with conventional ideas regarding the origins of superconductivity.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
First-principles calculations of the electronic band structure and lattice dynamics for the new superconductor MgB (2) are carried out and found to be in excellent agreement with our inelastic ...neutron scattering measurements. The numerical results reveal that the E(2g) in-plane boron phonons near the zone center are very anharmonic and strongly coupled to the planar B sigma bands near the Fermi level. This giant anharmonicity and nonlinear electron-phonon coupling is key to quantitatively explaining the observed high T(c) and boron isotope effect in MgB (2).
We studied the pressure and temperature dependence of the electrical resistivity of the superconducting compound magnesium diboride (MgB2). The superconducting transition temperature decreases ...monotonically with pressure, being parabolic or linear, depending on samples. The rate of decrease under pressure is higher than in conventional superconductors. We discuss our results in terms of the semimetallic character of the electronic band structure of (MgB2).
The new superconductor MgCNi3 with a TC8 K is an interesting candidate for non-conventional superconductivity as it is in the borderline of ferromagnetism. We have performed a systematic study of ...several samples of this compound under pressures up to 25 GPa, measuring the electrical resistivity between 1 and 300 K. We observe a slight increase of the critical superconducting transition temperature at high pressures. Our results are compared with the evolution under pressure of the calculated electronic band structure.
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