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Register a new userPolar Rectification Effect in Electro-Fatigued SrTiO3 Based Junctions
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Rectifying semiconductor junctions are crucial to electronic devices. They convert alternating current into direct one by allowing unidirectional charge flows. In analogy to the current-flow rectification for itinerary electrons, here, a polar rectification that based on the localized oxygen vacancies (OVs) in a Ti/fatigued-SrTiO3 (fSTO) Schottky junction is first demonstrated. The fSTO with OVs is produced by an electro-degradation process. The different movability of localized OVs and itinerary electrons in the fSTO yield a unidirectional electric polarization at the interface of the junction under the coaction of external and built-in electric fields. Moreover, the fSTO displays a pre-ferroelectric state located between paraelectric and ferroelectric phases. The pre-ferroelectric state has three sub-states and can be easily driven into a ferroelectric state by external electric field. These observations open up opportunities for potential polar devices and may underpin many useful polar-triggered electronic phenomena.
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Anisotropic magnetoresistance and negative magnetoresistance for in-plane fields are compared for the LaAlO3 /SrTiO3 interface and the symmetric Nb-doped SrTiO3 heterostructure. Both effects are exceptionally strong in LaAlO3 /SrTiO3 . We analyze their temperature, magnetic field and gate voltage dependencies and find them to arise from a Rashba type spin-orbit coupling with magnetic scatterers that have two contributions to their potential: spin exchange and Coulomb interaction. Atomic spin-orbit coupling is sufficient to explain the small effects observed in Nb-doped SrTiO3 . These results clarify contradicting transport interpretations in SrTiO3 -based heterostructures.
Ferroelectric field-effect transistors employ a ferroelectric material as a gate insulator, the polarization state of which can be detected using the channel conductance of the device. As a result, the devices are of potential to use in non-volatile memory technology, but suffer from short retention times, which limits their wider application. Here we report a ferroelectric semiconductor field-effect transistor in which a two-dimensional ferroelectric semiconductor, indium selenide ({alpha}-In2Se3), is used as the channel material in the device. {alpha}-In2Se3 was chosen due to its appropriate bandgap, room temperature ferroelectricity, ability to maintain ferroelectricity down to a few atomic layers, and potential for large-area growth. A passivation method based on the atomic-layer deposition of aluminum oxide (Al2O3) was developed to protect and enhance the performance of the transistors. With 15-nm-thick hafnium oxide (HfO2) as a scaled gate dielectric, the resulting devices offer high performance with a large memory window, a high on/off ratio of over 108, a maximum on-current of 862 {mu}A {mu}m-1, and a low supply voltage.
The evolution of information technology has been driven by the discovery of new forms of large magnetoresistance (MR), such as giant magnetoresistance (GMR) and tunnelling magnetoresistance (TMR) in magnetic multilayers. Recently, new types of MR have been observed in much simpler bilayers consisting of ferromagnetic (FM)/nonmagnetic (NM) thin films; however, the magnitude of MR in these materials is very small (0.01 ~ 1%). Here, we demonstrate that NM/FM bilayers consisting of a NM InAs quantum well conductive channel and an insulating FM (Ga,Fe)Sb layer exhibit giant proximity magnetoresistance (PMR) (~80% at 14 T). This PMR is two orders of magnitude larger than the MR observed in NM/FM bilayers reported to date, and its magnitude can be controlled by a gate voltage. These results are explained by the penetration of the InAs two-dimensional-electron wavefunction into (Ga,Fe)Sb. The ability to strongly modulate the NM channel current by both electrical and magnetic gating represents a new concept of magnetic-gating spin transistors.
The dynamical Casimir effect is an intriguing phenomenon in which photons are generated from vacuum due to a non-adiabatic change in some boundary conditions. In particular, it connects the motion of an accelerated mechanical mirror to the generation of photons. While pioneering experiments demonstrating this effect exist, a conclusive measurement involving a mechanical generation is still missing. We show that a hybrid system consisting of a piezoelectric mechanical resonator coupled to a superconducting cavity may allow to electro-mechanically generate measurable photons from vacuum, intrinsically associated to the dynamical Casimir effect. Such an experiment may be achieved with current technology, based on film bulk acoustic resonators directly coupled to a superconducting cavity. Our results predict a measurable photon generation rate, which can be further increased through additional improvements such as using superconducting metamaterials.
The elegant simplicity of the device concept and the urgent need for a new transistor at the twilight of Moores law have inspired many researchers in industry and academia to explore the physics and technology of negative capacitance field effect transistor (NC-FET). Although hundreds of papers have been published, the validity of quasi-static NC and the frequency-reliability limits of NC-FET are still being debated. The concept of NC - if conclusively demonstrated - will have broad impacts on device physics and technology development. Here, the authors provide a critical review of recent progress on NC-FETs research and some starting points for a coherent discussion.
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