TY  - JOUR
A1  - Pudell, Jan-Etienne
A1  - von Reppert, Alexander
A1  - Schick, D.
A1  - Zamponi, F.
A1  - Rössle, Matthias
A1  - Herzog, Marc
A1  - Zabel, Hartmut
A1  - Bargheer, Matias
T1  - Ultrafast negative thermal expansion driven by spin disorder
JF  - Physical review : B, Condensed matter and materials physics
N2  - We measure the transient strain profile in a nanoscale multilayer system composed of yttrium, holmium, and niobium after laser excitation using ultrafast x-ray diffraction. The strain propagation through each layer is determined by transient changes in the material-specific Bragg angles. We experimentally derive the exponentially decreasing stress profile driving the strain wave and show that it closely matches the optical penetration depth. Below the Neel temperature of Ho, the optical excitation triggers negative thermal expansion, which is induced by a quasi-instantaneous contractive stress and a second contractive stress contribution increasing on a 12-ps timescale. These two timescales were recently measured for the spin disordering in Ho [Rettig et al., Phys. Rev. Lett. 116, 257202 (2016)]. As a consequence, we observe an unconventional bipolar strain pulse with an inverted sign traveling through the heterostructure.
Y1  - 2019
U6  - https://doi.org/10.1103/PhysRevB.99.094304
SN  - 2469-9950
SN  - 2469-9969
VL  - 99
IS  - 9
PB  - American Physical Society
CY  - College Park
ER  -