X-rays uncover “hidden” quantum states

Elke Arenholz - CHESS

Quantum materials research involves manipulating and measuring the collective quantum states of electrons in materials. The NSF-funded user facilities at CHESS and the National High Magnetic Field Laboratory (aka the MagLab) have long been important resources in this pursuit.

unmodulated structure

Unmodulated structure which supports charge order within the Si(2)/Pt(2) planes.

We are now collaborating more closely than ever to address targeted questions about the quantum states of materials, as highlighted by a series of recent results involving measurements and/or co-authors from both labs. For example, research lead by by Jooseop Lee (IBS-CALDES) draws on collaborations with the Baumbach group at the MagLab and the QM2 program at CHESS to understand a previously-overlooked charge-density-wave phase in UPt2Si2.

Broader Impacts

Complex quantum phases of matter give rise to new kinds of fundamental excitations, and new kinds of emergent quantum particles. These new particles can have unique symmetries and transport properties, and open new avenues for information transfer, storage, and processing. Developing a full understanding of these phases is not trivial, and often requires many different complementary experimental techniques. The comprehensive experimental picture which is now being developed of subtle broken-symmetry phases in quantum materials will inform theory and accelerate materials discovery.

superlattice peaks and unmodulated structure
Left: Incommensurate superlattice peaks appear in the x-ray scattering from UPt2Si2 as the temperature is lowered through the heat capacity anomaly near room temperature. Right: Unmodulated structure which supports charge order within the Si(2)/Pt(2) planes.

Importance

Lee’s observation of incommensurate charge order in UPt2Si2 resolves a misunderstanding which has persisted in the literature for more than 15 years, regarding both the nature of the heat capacity anomaly which occurs slightly above room temperature in this material, and previous erroneous reports of “structural disorder” in the Si-Pt planes. This is important because it fundamentally alters the theoretical picture of the 5d electrons, which exhibit a complex interplay between tendencies towards magnetic and charge ordering, as well as a mixed character between localized and itinerant behavior. This also has important implications for the famous “hidden order” problem in the related compound URu2Si2.

Need for CHEXS Experimental Capabilities

CHESS researchers are at the forefront of observing and characterizing subtle symmetry breaking in quantum materials. The techniques in use at the QM2 beamline are optimized to discover the kinds of charge density wave phases that were observed by Lee et al. CHESS and the MagLab are actively seeking new opportunities in convergence research to develop a new holistic understanding of quantum materials.

Funding

Work at BNL was supported by DOE-BES under Contract No. DE-SC0012704. Some research was conducted at the High Flux Isotope Reactor, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. Research conducted at CHESS was supported by the NSF via Awards DMR-1332208 and DMR-1829070.

Reference:

J. Lee, K. Prokes, S. Park, I. Zaliznyak, S. Dissanayake, M. Matsuda, M. Frontzek, S. Stoupin, G. L. Chappell, R. E Baumbach, C. Park, J. A. Mydosh, G. E Granroth and J.P.C. Ruff.
Charge density wave with anomalous temperature dependence in UPt2Si2
Phys. Rev. B 102, 041112(R) (2020) DOI: 10.1103/PhysRevB.102.041112