Measurement of the dynamic charge response of materials using low-energy, momentum-resolved electron energy-loss spectroscopy (M-EELS)

Journal Article · Fri Oct 06 00:00:00 EDT 2017 · SciPost Physics Proceedings

DOI: https://doi.org/10.21468/SciPostPhys.3.4.026 · OSTI ID:1398288

Vig, Sean ^[1]; Kogar, Anshul ^[1]; Mitrano, Matteo  ^[1]; Husain, Ali  ^[1]; Venema, Luc ^[1]; Rak, Mindy ^[1]; Mishra, Vivek ^[2]; Johnson, Peter ^[3]; Gu, Genda ^[3]; Fradkin, Eduardo ^[1]; Norman, Michael ^[4]; Abbamonte, Peter ^[1]

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1. University of Illinois at Urbana Champaign
2. Oak Ridge National Laboratory
3. Brookhaven National Laboratory
4. Argonne National Laboratory

One of the most fundamental properties of an interacting electron system is its frequency- and wave-vector-dependent density response function, \chi({\bf q},\omega) . The imaginary part, \chi''({\bf q},\omega) , defines the fundamental bosonic charge excitations of the system, exhibiting peaks wherever collective modes are present. \chi $\chi$ quantifies the electronic compressibility of a material, its response to external fields, its ability to screen charge, and its tendency to form charge density waves. Unfortunately, there has never been a fully momentum-resolved means to measure \chi({\bf q},\omega) at the meV energy scale relevant to modern electronic materials. Here, we demonstrate a way to measure \chi $\chi$ with quantitative momentum resolution by applying alignment techniques from x-ray and neutron scattering to surface high-resolution electron energy-loss spectroscopy (HR-EELS). This approach, which we refer to here as “M-EELS”, allows direct measurement of \chi''({\bf q},\omega) with meV resolution while controlling the momentum with an accuracy better than a percent of a typical Brillouin zone. We apply this technique to finite-q excitations in the optimally-doped high temperature superconductor, Bi _2 ${}_2$ Sr _2 ${}_2$ CaCu _2 ${}_2$ O _{8+x} ${}_{8+x}$ (Bi2212), which exhibits several phonons potentially relevant to dispersion anomalies observed in ARPES and STM experiments. Our study defines a path to studying the long-sought collective charge modes in quantum materials at the meV scale and with full momentum control.

• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-98CH10886; SC0012368
• OSTI ID: 1398288
• Journal Information: SciPost Physics Proceedings, Journal Name: SciPost Physics Proceedings Journal Issue: 4 Vol. 3; ISSN 2542-4653
• Publisher: Stichting SciPostCopyright Statement
• Country of Publication: Netherlands
• Language: English