Search Results
Sub-nanometre resolution of atomic motion during electronic excitation in phase-change materials
2016, Mitrofanov, Kirill V., Fons, Paul, Makino, Kotaro, Terashima, Ryo, Shimada, Toru, Kolobov, Alexander, V., Tominaga, Junji, Bragaglia, Valeria, Giussani, Alessandro, Calarco, Raffaella, Riechert, Henning, Sato, Takahiro, Katayama, Tetsuo, Ogawa, Kanade, Togashi, Tadashi, Yabashi, Makina, Wall, Simon, Brewe, Dale, Hase, Muneaki
Phase-change materials based on Ge-Sb-Te alloys are widely used in industrial applications such as nonvolatile memories, but reaction pathways for crystalline-to-amorphous phase-change on picosecond timescales remain unknown. Femtosecond laser excitation and an ultrashort x-ray probe is used to show the temporal separation of electronic and thermal effects in a long-lived (>100 ps) transient metastable state of Ge2Sb2Te5 with muted interatomic interaction induced by a weakening of resonant bonding. Due to a specific electronic state, the lattice undergoes a reversible nondestructive modification over a nanoscale region, remaining cold for 4 ps. An independent time-resolved x-ray absorption fine structure experiment confirms the existence of an intermediate state with disordered bonds. This newly unveiled effect allows the utilization of non-thermal ultra-fast pathways enabling artificial manipulation of the switching process, ultimately leading to a redefined speed limit and improved energy efficiency and reliability of phase-change memory technologies.
Mirror-symmetric Magneto-optical Kerr Rotation using Visible Light in [(GeTe)2(Sb2Te3)1]n Topological Superlattices
2014, Bang, Do, Awano, Hiroyuki, Tominaga, Junji, Kolobov, Alexander V., Fons, Paul, Saito, Yuta, Makino, Kotaro, Nakano, Takashi, Hase, Muneaki, Takagaki, Yukihiko, Giussani, Alessandro, Calarco, Raffaella, Murakami, Shuichi
Interfacial phase change memory (iPCM), that has a structure of a superlattice made of alternating atomically thin GeTe and Sb2Te3 layers, has recently attracted attention not only due to its superior performance compared to the alloy of the same average composition in terms of energy consumption but also due to its strong response to an external magnetic field (giant magnetoresistance) that has been speculated to arise from switching between topological insulator (RESET) and normal insulator (SET) phases. Here we report magneto-optical Kerr rotation loops in the visible range, that have mirror symmetric resonances with respect to the magnetic field polarity at temperatures above 380 K when the material is in the SET phase that has Kramers-pairs in spin-split bands. We further found that this threshold temperature may be controlled if the sample was cooled in a magnetic field. The observed results open new possibilities for use of iPCM beyond phase-change memory applications.