CHAIR: Chris Jozwiak, CMJozwiak@LBL.GOV

Angle-Resolved Photoemission Spectroscopy (ARPES) is the premier tool to determine a quantum material’s momentum-dependent electronic states and their energy and lifetime renormalization due to many-body interactions. Nanoscale ARPES (nanoARPES) has recently greatly expanded the practical reach of ARPES to submicron samples. The MAESTRO nanoARPES instrument at the ALS has achieves ~100 nm resolution and has opened the door to a rapidly growing user community.

We propose a novel approach to push nanoARPES resolution beyond today’s practical limits to a fundamentally new regime, 10 nm and below. This ultimate nanoARPES will open a new frontier for understanding interactions and the understanding interactions and the electronic structure origin of emergent properties at the length scales where they develop. Particularly rewarding applications could include topological edge and anomalous quantum Hall states, states formed at lateral interfaces and heterostructures, and directly attacking classical problems such as defect-induced gap fluctuations in high Tc cuprates and other systems defined by electronic inhomogeneity. Confined to several nm and less, these states can today only be glimpsed by momentum-integrating probes, such as STM, but would become “ARPES-accessible” with Ultimate nanoARPES.

We further propose that by focusing the light to within a material’s electron coherence length, the ARPES process becomes fully coherent (FC-ARPES) and therefore sensitive to energy- and momentum-dependent electron phase within inhomogeneous materials. This sensitivity arises from the interference of photoemission from different points of the spatially varying electronic wavefunction within the beam spot (which itself has a coherent wavefront). Such interference will fluctuate at local potential barriers and have distinct spatial-, momentum- and energy-dependence. Similar to coherent ptychographical imaging in x-ray optics, these effects could be exploited to measure electronic phase variations in the complex nanoscale energy landscape of quantum materials.

The enabling technology will be a unique transmission geometry, in which the focused light passes through thin samples, generating photoelectrons that are collected from the opposite side. This optical arrangement allows a finer focus (>10x) than current world-record nanoARPES machines (≥100 nm). It also exploits forthcoming diffraction-limited synchrotrons whose unprecedented coherent flux at 2-5 nm wavelength will enable FC-ARPES spatial resolution to <10 nm.

In this session of the Innovation Forum, we would like to present this opportunity to the community and identify the range of scientific possibilities that could be rewarding targets of Ultimate nanoARPES. Several talks have been invited in order to introduce the concepts and start an active conversation. All participants are welcome and encouraged to engage in open discussion and present a slide with thoughts and potential science targets that can exploit these new opportunities.

CHAIR: Sujoy Roy, (SROY@LBL.GOV)

Complex interplay between spin, lattice and orbital degrees of freedom often gives rise to multifunctional properties and exotic phases in materials. Examples among many are spin/orbital ordering in colossal magnetorersistive materials, density waves, helical ordering giving rise to skyrmion phases in magnetic systems etc. There are equally many interesting and emerging phenomena that take place in buried interfaces and heterostructures. The ability to directly image the Bragg planes or surfaces where such order emerges would be a great boon in understanding how these phases and orders develop and how they effect material properties, butthere is currently no easy way to perform such measurements.

Existing techniques are typically designed for transmission geometry, requiring special sample fabrication and restricting the type of samples under investigation. While many specimens canbe prepared to work in transmission, others--particularly in materials physics--will require samples which are both extended and non-transmissive. The developmentof an imaging technique where imaging can happen at any selected reciprocal space will open up new and unique imaging capabilities.

In this forum we will discuss various imaging modalities to accomplish imaging in reflection and determineuniqueness, feasibility. As ALS-U is coming online in 5-6 years timeline, role of coherence should be a consideration in determining the methods. The forum will feature speakers followed by few single slide presentations and open discussions. 

CHAIR: Alpha N'Diaye (atndiaye@lbl.gov)

At ALS we are in a unique position to lead scientific projects. With the rich research environment at LBL and UCB, including ALS, the Molecular Foundry, NERSC, our collaborating colleagues at MSD, CSD and all other academic and industrial research activities of the Bay Area, we have a toolkit and a network at our fingertips which one is hard pressed to find almost anywhere else on the globe. Yet we often miss the opportunity to shape the scientific discussion. In order to shape the scientific discussion, we need to improve our ability to not join, but to initiate scientific collaborative projects from within our Thrust Areas.

In this session of the Innovation Forum, we would like to identify the enablers and roadblocks to such collaborations, as well as the opportunities which they may bring, such at follow-up funding, unique scientific output, or scientific visibility.