Science | Shu Hayama

Shu Hayama
X-ray Spectroscopy

Shu Hayama Shusaku Hayama is the Beamline Scientist on the Versatile X-ray Absorption Spectroscopy beamline I20. Before joining Diamond, he was a beamline scientist at the Synchrotron Radiation Source (SRS), UK where he assisted in maintaining and operation of Station 9.3: Fast X-ray Absorption Spectroscopy and Station 16.5: Ultra-dilute X-ray Absorption Spectroscopy. His previous areas of study include semiconductor physics and structure determination of liquid metals and non-aqueous solutions.

Email: Shu Hayama
Tel: +44 (0) 1235 778625
Beamline I20: X-Ray Spectroscopy


Key Research Areas

X-ray spectroscopy studies of metals in graphite and other carbon-based systems, Structural studies of alkali metals in polarizable liquids, Optical properties of defects in Si and SiGe alloys.

Current Research Interests

With a team at University College London (UCL) and Tom Weller (ISIS), we are studying the behaviour of various metals as electron donors in graphite and other carbon-based systems.

Introducing metal atoms between the carbon layers can tune the interlayer spacing and charging of the graphite host by the valence electrons of intercalated metals. Low dimensionality of these systems makes them ideal candidates for high-temperature superconductors, and indeed the team at UCL [1] has recently discovered superconductivity in the binary graphite intercalates CaC6 and YbC6 which have the highest superconducting transition temperature Tc (Tc = 11.5K and 6.5K respectively) observed in a graphite-intercalated compound so far.

The exact mechanism through which superconductivity occurs in these compounds is not well understood and it is not clear if superconductivity arises from electron-phonon coupling or from electron-electron correlations. Furthermore, although all the guest atoms act as donors, no clear trend between the number of carriers transferred to the host layers and Tc has been observed. A systematic increase in Tc with pressure along the c-axis suggests layer-metal interactions play an important role in the superconductivity.

X-ray emission spectroscopy (XES), Resonant Inelastic X-ray Scattering (RIXS) and Extended X-ray Absorption Fine Structure (EXAFS) are powerful techniques with which to study the local electronic and geometric structures around the absorbing atom. We are therefore using these techniques to establish the electrical and structural changes that take place around the metal donor as a function of pressure and temperature. For example, Yb-compounds are known to primarily consist of a mixed valence of ytterbium ions Yb2+ and Yb3+, the former being non-magnetic whilst the latter is magnetic. However the exact population ratio of these two states is currently unknown. Since XES is a state-selective probe, it will be possible to obtain directly this type of information and shed new light on the charge transfer process.

[1] T E Weller, M Ellerby, S S Saxena, R P Smith and N T Skipper, Superconductivity in the intercalated graphite compounds C6Yb and C6Ca. Nature Physics, 1, 39-41 (2005).

Selected Publications

  1. "Photoluminescence studies of implantation damage centres in 30Si", Hayama S, Davies G., and Itoh KM, Journal of Applied Physics Letters, 96, 1754 (2004)
  2. "Liquid-liquid phase separation and microscopic structure in rubidium-ammonia solutions observed using X-ray absorption spectroscopy", Wasse JC, Hayama S, Skipper NT, Morrison D, Bowron DT, Journal of Physical Chemistry B, 107, 14452-14456 (2003)
  3. "X-ray diffraction studies of solutions of lithium in ammonia: The structure of the metal-nonmetal transition", Hayama S, Skipper NT, Wasse JC and Thompson H, Journal of Chemical Physics, 116, 2991-2996 (2002)
  4. "Structure of a metallic solution of lithium in ammonia", Wasse JC, Hayama S, Skipper NT and Fischer HE. Physical Review B, 61, 11993-11997 (2000)