Ferroelectronics Lab

Understanding and utilizing non-volatile properties of materials

New Publication! “Two-dimensional charge order stabilized in clean polytype heterostructures”

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Abstract

Compelling evidence suggests distinct correlated electron behavior may exist only in clean 2D materials such as 1T-TaS2. Unfortunately, experiment and theory suggest that extrinsic disorder in free standing 2D layers disrupts correlation-driven quantum behavior. Here we demonstrate a route to realizing fragile 2D quantum states through endotaxial polytype engineering of van der Waals materials. The true isolation of 2D charge density waves (CDWs) between metallic layers stabilizes commensurate long-range order and lifts the coupling between neighboring CDW layers to restore mirror symmetries via interlayer CDW twinning. The twinned-commensurate charge density wave (tC-CDW) reported herein has a single metal–insulator phase transition at ~350 K as measured structurally and electronically. Fast in-situ transmission electron microscopy and scanned nanobeam diffraction map the formation of tC-CDWs. This work introduces endotaxial polytype engineering of van der Waals materials to access latent 2D ground states distinct from conventional 2D fabrication.

Full text available from nature communications

New Publication! “Superconductivity in a quintuple-layer square-planar nickelate”

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Abstract

Since the discovery of high-temperature superconductivity in copper oxide materials1, there have been sustained efforts to both understand the origins of this phase and discover new cuprate-like superconducting materials2. One prime materials platform has been the rare-earth nickelates and, indeed, superconductivity was recently discovered in the doped compound Nd0.8Sr0.2NiO2 (ref. 3). Undoped NdNiO2 belongs to a series of layered square-planar nickelates with chemical formula Ndn+1NinO2n+2 and is known as the ‘infinite-layer’ (n = ∞) nickelate. Here we report the synthesis of the quintuple-layer (n = 5) member of this series, Nd6Ni5O12, in which optimal cuprate-like electron filling (d8.8) is achieved without chemical doping. We observe a superconducting transition beginning at ~13 K. Electronic structure calculations, in tandem with magnetoresistive and spectroscopic measurements, suggest that Nd6Ni5O12 interpolates between cuprate-like and infinite-layer nickelate-like behaviour. In engineering a distinct superconducting nickelate, we identify the square-planar nickelates as a new family of superconductors that can be tuned via both doping and dimensionality.

Full text available from Nature Materials

New Publication! “Magnetoelectrics and multiferroics: Materials and opportunities for energy-efficient spin-based memory and logic”

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Abstract:

With the explosion of Internet traffic, the rise of large data centers, and smart technologies on the horizon, forecasts of the global energy consumption from information, and communications technologies are expected to rise from ~ 8% in 2020 to ~ 21% in 2030. The future demand will challenge the supply of electricity and has technology makers looking for ways to improve the efficiency of information and communication devices. In recent years, advances in magnetoelectric and multiferroic materials now provide the basis for nonvolatile spin-based logic and memory elements that have a projected energy efficiency orders of magnitude larger than the complementary metal-oxide semiconductor transistor. The possibilities are exciting, yet significant challenges remain. This article summarizes key materials, recent advancements, and current challenges in electric-field-controlled magnetism for realizing these potentially transformational devices. A perspective and potential considerations are given.

Full text available from MRS Bulletin

New Publication! “A Narrowband Spintronic Terahertz Emitter Based on Magnetoelastic Heterostructures”

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Abstract:

Narrowband terahertz (THz) radiation is crucial for high-resolution spectral identification, but a narrowband THz source driven by a femtosecond (fs) laser has remained scarce. Here, it is computationally predicted that a metal/dielectric/magnetoelastic heterostructure enables converting a fs laser pulse into a multicycle THz pulse with a narrow linewidth down to ∼1.5 GHz, which is in contrast to the single-cycle, broadband THz pulse from the existing fs-laser-excited emitters. It is shown that such narrowband THz pulse originates from the excitation and long-distance transport of THz spin waves in the magnetoelastic film, which can be enabled by a short strain pulse obtained from fs laser irradiation of the metal film when the thicknesses of the metal and magnetoelastic films both fall into a specific range. These results therefore reveal an approach to achieving optical generation of narrowband THz pulse based on heterostructure design, which also has implications in the design of THz magnonic devices.

Full text available from ACS Publications

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Ferroelectronics Lab
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E: jtheron@umich.edu