Darrell G. Schlom

F16. 00001: Superconducting Sr 2 RuO 4 thin films with record transition temperature up to 2 K by molecular-beam epitaxy

There is significant technological interest in developing ever faster switching between different electronic and magnetic states of matter. Manipulating properties at terahertz rates requires accessing the intrinsic timescales of both electrons and associated phonons, which is possible with short-pulse photoexcitation. However, in many Mott insulators, the electronic transition is accompanied by the nucleation and growth of percolating domains of the changed lattice structure, leading to empirical timescales dominated by slowly coarsening dynamics. Here we use time-resolved X-ray diffraction and reflectivity measurements to show that the photoinduced insulator-to-metal transition in an epitaxially strained Mott insulating thin film occurs without observable domain formation and coarsening effects, allowing the study of the intrinsic electronic and lattice dynamics. Above a fluence threshold, the initial electronic excitation …

S08. 00004: MBE synthesis and in situ ARPES of epitaxial thin films of the heavy fermion superconductor CeCoIn5

The coupling between ferroelectric and ferroelastic order parameters in transition metal oxide systems offer unique opportunities to employ strain as a tuning parameter of polar order at the nanoscale limit with large scale technological implications. KNbO 3 is an archetypal ferroelectric with a rich structural phase diagram in the bulk and provides the possibility of stabilising non-trivial phases through strain-engineering which are otherwise thermodynamically inaccessible. The ability to grow KNbO 3 thin films by sub-oxide molecular beam epitaxy allows the application of large strains with a high degree of control in epitaxial thin films. The new stabilised structure is probed through temperature dependent second harmonic generation, synchrotron-based x-ray reciprocal space mapping and transmission electron microscopy which reveals a giant enhancement in ferroelectric Tc, polarisation and nonlinear optical …

We report the use of suboxide molecular-beam epitaxy (S-MBE) to grow α-(AlxGa1− x) 2O3 films on (110) sapphire substrates over the 0< x< 0.95 range of aluminum content. In S-MBE, 99.98% of the gallium-containing molecular beam arrives at the substrate in a preoxidized form as gallium suboxide (Ga2O). This bypasses the rate-limiting step of conventional MBE for the growth of gallium oxide (Ga2O3) from a gallium molecular beam and allows us to grow fully epitaxial α-(AlxGa1− x) 2O3 films at growth rates exceeding 1 μm/h and relatively low substrate temperature (Tsub= 605±15○ C). The ability to grow α-(AlxGa1− x) 2O3 over the nominally full composition range is confirmed by Vegard’s law applied to the x-ray diffraction data and by optical bandgap measurements with ultraviolet–visible spectroscopy. We show that S-MBE allows straightforward composition control and bandgap selection for α-(AlxGa1− x …

FIG. 1. Γ-diagrams of β− Ga2O3 (201) and ϵ− Ga2O3 (001) on AlN (0001).(a) Γ of β− Ga2O3 (201) as a function of ϕGa. For MOCATAXY, ϕIn= 0.5 nm− 2 s− 1 was additionally supplied, resulting in a growth rate increase ΔΓ of β− Ga2O3 (201) as indicated in the figure. The expansion of the O-rich regime by MOCATAXY is indicated by ΔϕO at the corresponding stoichiometric points.(b) Γ of β− Ga2O3 (201) as a function of ϕGa2O= 1/2ϕGa by S-MBE and MBE. 30 The growth of Ga2O3 by S-MBE takes place in the adsorption-controlled regime with maximized Γ, whereas the growth of Ga2O3 by MBE is kinetically forbidden at the same ϕGa2O= 1/2ϕGa, indicated by ΔΓ in the figure.(c) Γ of β− Ga2O3 (201) and ϵ− Ga2O3 (001) as a function of TG by MBE and MOCATAXY. At ϕO= 3.0 nm− 2 s− 1, the gray and gray-dashed areas in panel (c) refer to the regime where β− Ga2O3 and ϵ− Ga2O3 can be synthesized by …

Single-crystal substrate materials with crystal structures and lattice parameters matching a desired epitaxial film are an enabling technology for many critical materials. Such substrates are best grown by bulk techniques that benefit from the substrate material being congruently melting. The shortage of congruently melting perovskites in critical lattice parameter ranges has been addressed herein by a search for new congruently melting compositions. A solid solution of two perovskites can be congruently melting at a minimum temperature under specified thermodynamic conditions where the coefficient matrix has a zero determinant. This is called an indifferent point. A wide variety of perovskite solid solutions were investigated to identify compounds that have an indifferent melting minimum and a cubic crystal structure with favorable lattice constants in the range of 0.390–0.412 nm. Solid solution pairs that form such …

Advancements of high-power laser sources in the THz frequency range have opened up opportunities for coherent intense excitation of infrared (IR)-active phonons in crystalline materials. The nonlinear phononics mechanism utilizes anharmonic coupling between driven IR-active modes and other lattice modes to induce changes in crystal structure and functional properties on picosecond timescales. Recent experimental and theoretical works have noted the potential for phonon-induced strains on these short time scales [npj Quantum Mater. 5, 95 (2020), PRL 129, 167401 (2022)]. A natural way to measure the response of the lattice due to these THz pulses is by employing X-ray diffraction to observe changes to the position and intensities of Bragg peaks.We show, using theory and first-principle calculations, that these lattice anharmonicities are responsible for the expansion of the c-axis in a biaxially strained thin …