Dresden 2026 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 26: Poster II
HL 26.52: Poster
Wednesday, March 11, 2026, 09:30–11:30, P1
Ultrafast negative thermal expansion in NbO2 — •Florian Baltrusch1, Marc Herzog1, Florin Boariu2, Matthias Rössle2, Jutta Schwarzkopf3, and Matias Bargheer1,2 — 1Institut für Physik und Astronomie, Universität Potsdam, Potsdam, Germany — 2Helmholtz-Zentrum Berlin, Berlin, Germany — 3Leibniz-Institut für Kristallzüchtung, Berlin, Germany
Niobium dioxide (NbO2) exhibits negative thermal expansion (NTE), meaning it contracts upon heating rather than expanding like most materials. Below 200 K, bulk NbO2 shows a monotonic contraction of the tetragonal c-axis, while the a/b-axes expand. This behaviour not only enables zero-expansion composites but also provides an unconventional elastic driving mechanism for magneto-elastic materials on picosecond timescales.
In epitaxial thin films, however, the lattice response is modified by substrate constraints via the Poisson effect. Temperature-dependent XRD measurements show that the film response depends strongly on the thermal-expansion mismatch between film and substrate during equilibrium heating.
Using ultrafast X-ray diffraction (UXRD), we directly observe ultrafast NTE in NbO2 thin films. On picosecond timescales, the substrate remains effectively "frozen", allowing us to isolate the intrinsic response of the NbO2 layer. This enables us to determine the timescale of contraction, which provides crucial insights about its driving mechanism.
Keywords: Negative thermal expansion, NbO2