A New Analyzer for Spin Photoemission Experiments

In our laboratory we are developing a novel analyzer for Spin-ARPES experiments (see photo at right). This analyzer employs a new concept for spin detection, based on a Time of Flight analyzer (which is 10 times more efficient than dispersive analyzers) and coupled with a high-efficiency spin detector utilizing exchange scattering (about 50-100 times more efficient for spin detection than using spin-orbit interaction as in Mott detectors).

Spin-ARPES is a fundamental probe for understanding magnetic materials. It is in fact the only experimental tool that can directly probe the spin-resolved band structure of materials.  So far this technique has been poorly used because of its limited energy and momentum resolution.

Our goal at present is to push spin-photoemission to a similar level of improvement as ARPES today. Our new system will allow us to perform spin-ARPES experiments with unprecedented energy resolution (5-10 meV compared to the 50 meV of current setups).

We have successfully tested the TOF portion of the detector (see photo at right) and are now testing the full setup.  The system is expected to be fully operational within the next six months.

The spin-sensitive, time-of-flight electron analyzer, fully assembled in our laboratory at LBNL.

Testing the full Spin-ARPES detector at Beamline 12 of LBNL's Advanced Light Source in August 2005.

The new MERLIN beamline at the ALS

We are involved in the construction of the new sub-meV Resolution Line (MERLIN) at the Advanced Light Source, to be ready in 2007. The new line has two fixed branches dedicated to ultra-high resolution experiments, in ARPES and Resonant IXS.  The third branch is a roll-over branch and will be mostly dedicated to Spin-ARPES experiments. The MERLIN line will cover a photon energy range between 15eV and 150 eV and is an Elliptically Polarized Undulator line.

This program is a joint project with:  Z. Hasan (Princeton), T. C. Chiang (Univ. Illinois, Urbana Champaign), D. Dessau (University Colorado), Z. Hussain (ALS), Z. Qui (UC Berkeley), G. Sawatzky (UBC), Z. X. Shen (Stanford) and N. Smith (ALS).