TUNABLE PHASES IN CHARGE-DENSITY-WAVE HETEROEPITAXIAL DEVICES
Abstract
The PI aims to synthesize thin films of rare-earth telluride (RTex) compounds using molecular beam epitaxy and study the electronic and structural properties in pristine films and complex heteroepitaxial sequences. The epitaxy will take place in a unique apparatus where atomically flat substrates can be prepared in-situ using novel laser heating approaches. By using adsorption-controlled growth windows we will create high quality epitaxial layers and study their properties using in-situ and ex-situ diffraction tools, as well as surface measurements such as atomic force microscopy and scanning tunnelling microscopy. Having created high quality samples, we aim to utilize electronic instabilities such as charge density waves (CDW) to induce tunable symmetries in heteroepitaxial layers that are distinct from bulk samples. Firstly, the project will study for the first-time thin films down to the monolayer limit in order to explore electronic ground states that may compete with the CDW. This will be performed in concert with electrostatic tuning of the chemical potential via the electronic field-effect. In complex devices, the symmetries to be investigated include novel long-range orders, such as moiré interference patterns, and local inversion and/or mirror symmetry breaking at heterointerfaces. The parameter space is rich due to the tunable nature of the CDW wavelength which is correlated with the chemical pressure induced by the rare-earth element chosen to form the compound, and temperature. The PI will therefore study more than one type of RTex, with an initial focus on Dy and Gd as the rare-earth. By choosing compounds with dissimilar CDW wavelengths, to study interference patterns between atomic displacements at heterointerfaces by both electronic transport and diffraction methods. One goal is to modify the CDW order by tuning the experimental temperature to selectively implement such interference patterns, which, due to their long wavelength, may harbor emergent electronic bands that are weakly dispersing and hence strongly interacting. Furthermore, by layering rare-earth compounds with dissimilar electronegativities we aim to break inversion symmetry in bilayer or trilayer devices, rendering the system as a polar metal with incipient CDW order as the electronic ground state. Studying non-linear and nonreciprocal transport in such devices can offer insight into the electronic ground states and the broken symmetries that may emerge. The project aims to explore fundamentally new design principles for devices in this novel class of materials that is yet to be synthesized in thin-film form. The electronic gap sizes that are relevant are on the order of 100 meV, which is in the infra-red regime and hence the design principles may be useful for developing switchable detectors that are coupled to a CDW transition and tunable by electric field.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 20, 2023
- Source ID
- FA95502210463
Entities
People
- Joseph Falson
Organizations
- Air Force Office of Scientific Research
- California Institute of Technology
- United States Air Force