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arXiv2026

Molecular Beam Epitaxy of AgTaO3

We report the first synthesis of single-crystal AgTaO3 thin films using molecular-beam epitaxy (MBE). High-quality epitaxial AgTaO3 films were grown on both (001)- and (111)-oriented SrTiO3 substrates using sequential deposition of atomic silver and TaO2 layers under an ozone/oxygen atmosphere (80 % O3 + 20 % O2). X-ray diffrac- tion and reciprocal space mapping demonstrate that the films are coherently strained to the SrTiO3 substrates with sharp rocking curves comparable to the substrates, indicating high structural perfection. High-angle annular dark-field scanning trans- mission electron microscopy (HAADF-STEM) confirms coherent, low defect growth for (001)pc-oriented films. For (111)pc-oriented films, initial coherent growth proceeds up to 10 nm before transitioning into a Ta-rich surface region. Energy-dispersive X-ray spectroscopy (EDX) reveals a narrow cation intermixing region at the sub- strate interface for both orientations. This work demonstrates an effective synthesis route for single-crystal AgTaO3 thin films, providing a platform to investigate strain engineering and emergent interfacial properties in silver-based tantalates.

cond-mat.mtrl-sci↗

arXiv2026

Constraint Analysis and Quantization of Anomalous 2-D Thomas-Whitehead Gravity

The two-dimensional effective Polyakov action is often realized as the anomalous contributions of string theories and fermions coupled to gravity in two dimensions. However, as a result of the reparametrization invariance, one finds that the effective action produces vanishing Hamiltonians as constraints even in disparate gauges such as the dynamical light-cone and the Arnowitt-Deser-Misner (ADM) formalism of the metric. On the other hand, two-dimensional gravitational theories naturally arise as geometric actions on the coadjoint orbits of the Virasoro algebra. The Thomas-Whitehead gravity formalism extends the effective Polyakov action in such a way that the defining coadjoint element for the orbit becomes a dynamical field, viz. the diffeomorphism field. In this work, we examine the role the diffeomorphism field plays through the well-understood quantization of the two-dimensional anomalous contributions to gravity. This is first done in the dynamical light-cone and then with the ADM formalism of the metric. To examine a dynamical diffeomorphism field, the constraint analysis is then repeated in a Minkowski background, where the dynamics of the diffeomorphism field arise from the Thomas-Whitehead action. Adding dynamics to the diffeomorphism field appears to remove the vanishing Hamiltonians; however, expressing the diffeomorphism in terms of the P-tensor recovers the Hamiltonian constraint. One can compare this investigation to that of a gauge Wess-Zumino-Witten action where the gauge field has become dynamical through the inclusion of a Yang-Mills term.

gr-qc↗