July 2005

New High-Resolution Electron-Energy Analyzer Installed on Beamline U13UB

The 1990s renaissance in the field of angle-resolved photoemission spectroscopy (ARPES) resulted from the combination of new parallel-detection (in energy and angle) photoelectron spectrometers with high-brightness VUV synchrotron beamlines. At the NSLS, such a beamline/endstation combination was constructed and commissioned at beamline U13UB in the late 1990s.

In FY2004, the original Scienta photoelectron spectrometer that had been used since 1998 was replaced by a higher-resolution instrument from the same company. Shown in Figure 1, the new instrument has a measured energy resolution of 0.7 meV, which is a significant improvement over the ~5meV resolution of the previous model. A photoelectron spectrum recorded at low temperature from an evaporated gold film in the vicinity of the Fermi edge is shown in Figure 2. The energy width of the Fermi edge in this spectrum is limited by the temperature of the sample.

Figure 1. Photograph of the U13UB experimental endstation, the heart of which is a very high resolution Scienta SES200 photoelectron spectrometer.

Figure 2. A photoelectron spectrum recorded at low temperature (~5 K) from an evaporated gold film in the vicinity of the Fermi edge, demonstrating the superior (sub meV) electron energy resolution of the new Scienta photoelectron spectrometer at beamline U13UB.

This new instrument has been used by U13UB PRT members and general users since late 2004. The U13UB PRT members (Brookhaven Lab's Physics Department, Boston University, Boston College, and Columbia University) are using the enhanced energy resolution of this new instrument to study detailed information on the electronic structure and dynamics of complex electronic systems. In particular, a recent study of the quasiparticle scattering rates around the Fermi surface of Sr₂RuO₄ was reported in Physical Review Letters by the Brookhaven group (PRL 94, 107003 (2005)). This study provided a microscopic picture of the origin of the crossover from non-Fermi liquid to Fermi liquid behavior observed in macroscopic transport measurements.