Direct observation of elastic softening immediately after femtosecond-laser excitation in a phase-change material

Tomoya Kawaguchi, Kazuya Tokuda, Seiya Okada, Makina Yabashi, Tetsu Ichitsubo, Noboru Yamada, Eiichiro Matsubara

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

The generation and propagation of photoexcited elastic waves in crystalline Ge2Sb2Te5 were analyzed by picosecond time-resolved X-ray diffraction using a femtosecond-laser pump and an X-ray free-electron laser probe technique. The crystalline lattice anisotropically expanded initially in approximately 20 ps after the excitation. This was followed by a periodic oscillation of the lattice strain. The elastic stiffness along the cubic (111) direction had significantly softened during the initial expansion, and the strain magnitude was the largest in the (100) and (110) directions. This indicates that femtosecond-laser excitation creates a shallower interlayer potential between the Te and Ge-Sb layers and eventually leads to softening of the elastic stiffness along the cubic (111) direction. Furthermore, this softened state increases the system's sensitivity to an external stress field. This residual internal stress in a thin film enhances the selective formation of a particular type of variant during the symmetry change from cubic to rhombohedra. This causes the subsequent anisotropic expansion. These phenomena are quite interesting and align with the ultrafast amorphization of this material.

Original languageEnglish
Article number060302
JournalPhysical Review B
Volume101
Issue number6
DOIs
Publication statusPublished - 2020 Feb 1
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

Fingerprint

Dive into the research topics of 'Direct observation of elastic softening immediately after femtosecond-laser excitation in a phase-change material'. Together they form a unique fingerprint.

Cite this