Peter S. Riseborough

Observation of a kink in the dispersion of f-electrons

Strong interactions in correlated electron systems may result in the formation of heavy quasiparticles that exhibit kinks in their dispersion relation. Spectral weight is incoherently shifted away from the Fermi energy, but Luttingers theorem requires the Fermi volume to remain constant. Our angle-resolved photoemission study of USb2 reveals a kink in a noncrossing 5f band, representing the first experimental observation of a kink structure in f-electron systems. The kink energy scale of 21 meV and the ultra-small peak width of 3 meV are observed. We propose the novel mechanism of renormalization of a point-like Fermi surface, and that Luttingers theorem remains applicable.

Heavy-Fermion Superconductivity

When the BCS theory appeared in 1957, Bernd Matthias felt it did not do everything. He thought that it worked for the p-electron superconductors such as lead and tin, but the transition metal superconductors such as niobium and vanadium were still unexplained. Aside from his instinct, it was that here the isotope effect was all over the map. This led him to uranium, where his student Hunter Hill did the isotope effect for uranium and found that the orthorhombic α-phase had a backward mass squared dependence and that the cubic γ-phase looked BCS-like. This was Hunter’s thesis work, and the experiment was difficult enough that those who did not like the result could ignore it. Bernd was also drawn to the U6 X superconducting compound with X = Mn, Co, Fe, and Ni. In these compounds, the T c scaled with the moments, that is, they followed the Slater-Pauling curve. These were the first superconductors discovered that formed with 3d magnetic elements.

Unusual Magnetic Field-Dependence of the Electronic Dispersion Relations in a Hidden Ordered Phase.

and orbital density wave state in the underscreened Anderson Lattice Model. The spin-flip part of the Hund’s rule coupling stabilizes a spontaneous spin-dependent mixing of 5f quasiparticle bands that, in the normal state, have pure orbital characters. The transition breaks the spin-rotational invariance and leads to an asymmetric pseudo-gap which forms in the density of states. When a magnetic field is applied, the electronic dispersion relations become dependent on the relative orientation of the field and the spontaneously-chosen quantization axis. We argue that this may result in the magnetic susceptibility of the low-temperature phase becoming anisotropic, but without the development of a static magnetization.

The Korteweg–de Vries equation: its place in the development of nonlinear physics

This article puts Korteweg and de Vriess manuscript (published in the Philosophical Magazine in 1895) in historical context. The article highlights the importance of the Korteweg–de Vries equation in the development of concepts used in nonlinear physics and also mentions some of their recent applications.

Influence of magnetic fields on structural martensitic transitions

We propose a model which suggests that structural martensitic transitions are related to significant changes in the electronic structure, and are effected by high-magnetic fields. The magnetic field dependence is considered unusual as many influential investigations of martensitic transitions have emphasized that the structural transitions are primarily lattice dynamical and are driven by the entropy due to the phonons. We provide a theoretical framework which can be used to describe the effect of high magnetic field on the transition and lattice dynamics in which the field dependence originates from the dielectric constant. The model is compared with some recent experimental results.