Strain tuning in microstructured quantum materials F

The application of strain to quantum materials is a powerful technique for tuning electronic correla-tions and the balance between interaction parameters by favoring specific electronic phases over al-most degenerate competing orders via breaking underlying crystal symmetries. For example, it can promote a long-range charge-ordered state over high-temperature superconductivity in cuprates [1,2] or induce a chiral state in Kagome metals [3].
To maximize surface strains, we exploit the enhanced yield strain of micron-scale materials, well-stud-ied in materials science [4]. State-of-the-art microfabrication using focused ion beam techniques allow precise design of crystalline samples, achieving desired strain fields such as uniaxial stress or more complex strain gradients [5]. We microcarve the entire sample into a flexible cantilever without a sub-strate and then bend it, enabling arbitrary and especially out-of-plane tensile strain even in layered quantum materials [6].
Raman scattering directly probes long-wavelength phonon modes, which are highly sensitive to lattice strain. With submicrometer spatial resolution, it provides a direct measure of strain variations. ... mehrIt also detects local symmetry breaking and gives access to electronic, magnetic, and orbital excitations, prob-ing the electronic ground state. Even without a change in lattice symmetry under stress, the phonon mode frequency serves as an extremely sensitive probe, determined with high energy resolution.
The layered crystal structure of delafossite PdCoO2, with weak interlayer coupling, makes it an ideal candidate for studying out-of-plane tensile strain. Its exceptional purity [7] minimizes extrinsic disorder effects. Among the various Raman modes allowed by group theory, the fully symmetric A1g phonon, consisting of oxygen ion vibrations along the c-direction [8], is particularly interesting. Finite element simulations guide the design of a cantilever manufactured from high-quality single crystals of PdCoO2. Together with DFT-calculations our Micro-Raman measurements confirm quantitively the spatial strain distribution on the cantilever. Furthermore, we investigate the role of the amorphous layer thickness for Raman spectra.
[1] Kim, H. H. et al. Uniaxial pressure control of competing orders in a high-temperature superconductor. Science 362, 1040-1044, doi:10.1126/science.aat4708 (2018).
[2] Kim, H. H. et al. Charge Density Waves in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.67}$ Probed by Resonant X-Ray Scattering under Uniaxial Compression. Physical Review Letters 126, 037002, doi:10.1103/PhysRevLett.126.037002 (2021).
[3] Guo, C. et al. Switchable chiral transport in charge-ordered kagome metal CsV3Sb5. Nature 611, 461-466, doi:10.1038/s41586-022-05127-9 (2022).