Berry phase and band structure analysis of the Weyl semimetal NbP.

Weyl semimetals are often considered the 3D-analogon of graphene or topological insulators. The evaluation of quantum oscillations in these systems remains challenging because there are often multiple conduction bands. We observe de Haas-van Alphen oscillations with several frequencies in a single crystal of the Weyl semimetal niobium phosphide. For each fundamental crystal axis, we can fit the raw data to a superposition of sinusoidal functions, which enables us to calculate the characteristic parameters of all individual bulk conduction bands using Fourier transform with an analysis of the temperature and magnetic field-dependent oscillation amplitude decay. Our experimental results indicate that the band structure consists of Dirac bands with low cyclotron mass, a non-trivial Berry phase and parabolic bands with a higher effective mass and trivial Berry phase.

Analyses of treatment variables for patients with childhood craniopharyngioma--results of the multicenter prospective trial KRANIOPHARYNGEOM 2000 after three years of follow-up.

BACKGROUND: Controversies surround various treatment variables for patients with childhood craniopharyngioma such as growth hormone (GH) replacement, which some believe can exacerbate recurrence/progression. We prospectively assessed the risk of tumor recurrence/progression in survivors of childhood craniopharyngioma. METHODS: Multivariable analyses of risk factors (age at diagnosis, degree of resection, irradiation, GH treatment and gender) and descriptive analyses of overall survival (OS) and event-free survival (EFS) rates were performed in 117 patients, recruited prospectively and evaluated after 3 years of follow-up in the German, Austrian and Swiss multicenter trial KRANIOPHARYNGEOM 2000. RESULTS: We observed a 3-year OS of 0.97 and a 3-year EFS of 0.46, indicating high recurrence rates after complete resection (CR) (n = 47; 3-year-EFS: 0.64) and high progression rates after incomplete resection (IR) (n = 64; 3-year EFS: 0.31). The risk of an event decreased by 80% after CR compared to IR (hazard ratio = 0.20; p < 0.001). Irradiation had protective effects on EFS: irradiated patients had an 88% lower risk of recurrence/progression compared to patients without/before irradiation (hazard ratio = 0.12; p < 0.001). GH treatment had no impact on 3-year EFS rates. CONCLUSIONS: Tumor recurrences/progressions are frequent and occur early after initial treatment of childhood craniopharyngioma. A radical resection preserving the integrity of hypothalamic structures appears optimal at original diagnosis. Irradiation was efficient in preventing recurrences/progressions. GH treatment had no impact on the low 3-year EFS observed in our study. However, further conclusions on the influence of GH on recurrence rates have to be refined to long-term follow-up studies of patients with childhood craniopharyngioma.