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  1. Abstract Nonlinear Hall effect (NLHE) is a new type of Hall effect with wide application prospects. Practical device applications require strong NLHE at room temperature (RT). However, previously reported NLHEs are all low-temperature phenomena except for the surface NLHE of TaIrTe 4 . Bulk RT NLHE is highly desired due to its ability to generate large photocurrent. Here, we show the spin-valley locked Dirac state in BaMnSb 2 can generate a strong bulk NLHE at RT. In the microscale devices, we observe the typical signature of an intrinsic NLHE, i.e. the transverse Hall voltage quadratically scales with the longitudinal current as the current is applied to the Berry curvature dipole direction. Furthermore, we also demonstrate our nonlinear Hall device’s functionality in wireless microwave detection and frequency doubling. These findings broaden the coupled spin and valley physics from 2D systems into a 3D system and lay a foundation for exploring bulk NLHE’s applications. 
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    Free, publicly-accessible full text available December 1, 2024
  2. Abstract

    Dirac and Weyl semimetals are a central topic of contemporary condensed matter physics, and the discovery of new compounds with Dirac/Weyl electronic states is crucial to the advancement of topological materials and quantum technologies. Here we show a widely applicable strategy that uses high configuration entropy to engineer relativistic electronic states. We take theAMnSb2(A= Ba, Sr, Ca, Eu, and Yb) Dirac material family as an example and demonstrate that mixing of Ba, Sr, Ca, Eu and Yb at theAsite generates the compound (Ba0.38Sr0.14Ca0.16Eu0.16Yb0.16)MnSb2(denoted asA5MnSb2), giving access to a polar structure with a space group that is not present in any of the parent compounds.A5MnSb2is an entropy-stabilized phase that preserves its linear band dispersion despite considerable lattice disorder. Although bothA5MnSb2andAMnSb2have quasi-two-dimensional crystal structures, the two-dimensional Dirac states in the pristineAMnSb2evolve into a highly anisotropic quasi-three-dimensional Dirac state triggered by local structure distortions in the high-entropy phase, which is revealed by Shubnikov–de Haas oscillations measurements.

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  3. Abstract

    The layered perovskite Ca3Mn2O7(CMO) is a hybrid improper ferroelectric candidate proposed for room temperature multiferroicity, which also displays negative thermal expansion behavior due to a competition between coexisting polar and nonpolar phases. However, little is known about the atomic-scale structure of the polar/nonpolar phase coexistence or the underlying physics of its formation and transition. In this work, we report the direct observation of double bilayer polar nanoregions (db-PNRs) in Ca2.9Sr0.1Mn2O7using aberration-corrected scanning transmission electron microscopy (S/TEM). In-situ TEM heating experiments show that the db-PNRs can exist up to 650 °C. Electron energy loss spectroscopy (EELS) studies coupled with first-principles calculations demonstrate that the stabilization mechanism of the db-PNRs is directly related to an Mn oxidation state change (from 4+ to 2+), which is linked to the presence of Mn antisite defects. These findings open the door to manipulating phase coexistence and achieving exotic properties in hybrid improper ferroelectric.

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  4. Exotic material properties and topological nontrivial surface states have been theoretically predicted to emerge in [111]-oriented perovskite layers. The realization of such [111]-oriented perovskite superlattices has been found challenging, and even the growth of perovskite oxide films along this crystallographic direction has been proven as a formidable task, attributed to the highly polar character of the perovskite (111) surface. Successful epitaxial growth along this direction has so far been limited to thin film deposition techniques involving a relatively high kinetic energy, specifically pulsed laser deposition and sputtering. Here, we report on the self-regulated growth of [111]-oriented high-quality SrVO3 by hybrid molecular beam epitaxy. The favorable growth kinetics available for the growth of perovskite oxides by hybrid molecular beam epitaxy on non-polar surfaces was also present for the growth of [111]-oriented films, resulting in high-quality SrVO3(111) thin films with residual resistivity ratios exceeding 20. The ability to grow high-quality perovskite oxides along energetically unfavorable crystallographic directions using hybrid molecular beam epitaxy opens up opportunities to study the transport properties of topological nontrivial and correlated electron systems.

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