Bandwidth Control and Symmetry Breaking in a Mott-Hubbard Correlated Metal

In Mott materials strong electron correlation yields a spectrum of complex electronic structures. Recent synthesis advancements open realistic opportunities for harnessing Mott physics to design transformative devices. However, a major bottleneck in realizing such devices remains the lack of control over the electron correlation strength. This stems from the complexity of the electronic structure, which often veils the basic mechanisms underlying the correlation strength. Here, we present control of the correlation strength by tuning the degree of orbital overlap using picometer-scale lattice engineering. We illustrate how bandwidth control and concurrent symmetry breaking can govern the electronic structure of a correlated $SrVO_3$ model system. We show how tensile and compressive biaxial strain oppositely affect the $SrVO_3$ in-plane and out-of-plane orbital occupancy, resulting in the partial alleviation of the orbital degeneracy. We derive and explain the spectral weight redistribution under strain and illustrate how high tensile strain drives the system towards a Mott insulating state. Implementation of such concepts will drive correlated electron phenomena closer towards new solid state devices and circuits. These findings therefore pave the way for understanding and controlling electron correlation in a broad range of functional materials, driving this powerful resource for novel electronics closer towards practical realization

Unveiling the mixed nature of polaritonic transport: From enhanced diffusion to ballistic motion approaching the speed of light

In recent years it has become clear that the transport of excitons and charge carriers in molecular systems can be enhanced by coherent coupling with photons, giving rise to the formation of hybrid excitations known as polaritons. Such enhancement has far-reaching technological implications, however, the enhancement mechanism and the transport nature of these composite light-matter excitations in such systems still remain elusive. Here we map the ultrafast spatiotemporal dynamics of surface-bound optical waves strongly coupled to a self-assembled molecular layer and fully resolve them in energy/momentum space. Our studies reveal intricate behavior which stems from the hybrid nature of polaritons. We find that the balance between the molecular disorder and long-range correlations induced by the coherent mixing between light and matter leads to a mobility transition between diffusive and ballistic transport, which can be controlled by varying the light-matter composition of the polaritons. Furthermore, we directly demonstrate that the coupling with light can enhance the diffusion coefficient of molecular excitons by six orders of magnitude and even lead to ballistic flow at two-thirds the speed of light

Indirectly Heated Switch as a Platform for Nanosecond Probing of Phase Transition Properties in Chalcogenides

Although phase-change materials (PCMs) have been studied for more than 50 years, temperature-dependent characterization of the phase transition dynamics remains challenging due to the lack of nanosecond-nanoscale thermometry. In this article, we utilize the four-terminal, indirectly heated phase-change switch (IPCS), which was originally designed for nonvolatile radio frequency (RF) applications, as an ultrafast electrothermal platform to study PCM. We propose a novel experimental setup that allows nanosecond probing of the transient resistance of the PCM, beyond the melting temperature (>1100 K), due to the built-in electrical isolation between the PCM path and the thermal actuation path of the IPCS. The embedded metallic heater can induce reversible phase transitions between the crystalline and amorphous phases of the PCM. Our platform enables simultaneous measurements of the dynamics of PCM resistance (as a probe for the phase of the material) and heater temperature, during the application of heating pulses. Furthermore, we map the surface temperature of the IPCS at steady state by scanning thermal microscopy (SThM) and show the effect of cooling by electrodes in devices with overlap between the heater and PCM contacts. Our method can be used to study chalcogenides and other amorphous semiconductors for reconfigurable electronics and neuromorphic hardware

Low-Temperature Molecular Vapor Deposition of Ultrathin Metal Oxide Dielectric for Low-Voltage Vertical Organic Field Effect Transistors

We demonstrate a low-temperature layer-by-layer formation of a metal-oxide-only (AlO_<i>x</i>) gate dielectric to attain low-voltage operation of a self-assembly based vertical organic field effect transistor (VOFET). The AlO_<i>x</i> deposition method results in uniform films characterized by high quality dielectric properties. Pin-hole free ultrathin layers with thicknesses ranging between 1.2 and 24 nm feature bulk dielectric permittivity, ε_AlO<i>x</i>, of 8.2, high breakdownfield (>8 MV cm^–1), low leakage currents (<10^–7A cm^–2 at 3MV cm^–1), and high capacitance (up to 1 μF cm^–2). We show the benefits of the tunable surface properties of the oxide-only dielectric utilized here, in facilitating the subsequent nanostructuring steps required to realize the VOFET patterned source electrode. Optimal wetting properties enable the directional block-copolymer based self-assembly patterning, as well as the formation of robust and continuous ultrathin metallic films. Supported by computer modeling, the vertical architecture and the methods demonstrated here offer a simple, low-cost, and free of expensive lithography route for the realization of low-voltage (<i>V</i>_GS/DS ≤ 3 V), low-power, and potentially high-frequency large-area electronics