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Controlling charge density in two-dimensional (2D) materials is a powerful approach for engineering new electronic phases and properties. This control is traditionally realized by electrostatic gating. Here, we report an optical approach for generation of high carrier densities using transition metal dichalcogenide heterobilayers, WSe₂/MoSe₂, with type II band alignment. By tuning the optical excitation density above the Mott threshold, we realize the phase transition from interlayer excitons to charge-separated electron/hole plasmas, where photoexcited electrons and holes are localized to individual layers. High carrier densities up to 4 x 10¹⁴ cm^–2 can be sustained under both pulsed and continuous wave excitation conditions. These findings open the door to optical control of electronic phases in 2D heterobilayers.

Local thermal magnetization fluctuations in Li-doped MnTe are found to increase its thermopower α strongly at temperatures up to 900 K. Below the Néel temperature (T_N ~ 307 K), MnTe is antiferromagnetic, and magnon drag contributes α_md to the thermopower, which scales as ~T³. Magnon drag persists into the paramagnetic state up to >3 x T_N because of long-lived, short-range antiferromagnet-like fluctuations (paramagnons) shown by neutron spectroscopy to exist in the paramagnetic state. The paramagnon lifetime is longer than the charge carrier–magnon interaction time; its spin-spin spatial correlation length is larger than the free-carrier effective Bohr radius and de Broglie wavelength. Thus, to itinerant carriers, paramagnons look like magnons and give a paramagnon-drag thermopower. This contribution results in an optimally doped material having a thermoelectric figure of merit ZT > 1 at T > ~900 K, the first material with a technologically meaningful thermoelectric energy conversion efficiency from a spin-caloritronic effect.

Author(s): Yi Li, Tomas Polakovic, Yong-Lei Wang, Jing Xu, Sergi Lendinez, Zhizhi Zhang, Junjia Ding, Trupti Khaire, Hilal Saglam, Ralu Divan, John Pearson, Wai-Kwong Kwok, Zhili Xiao, Valentine Novosad, Axel Hoffmann, and Wei Zhang

A new design for a cavity spintronic device obtains a strong photon-magnon coupling with a magnet that is over 1000 times smaller than previously used magnets.

[Phys. Rev. Lett. 123, 107701] Published Tue Sep 03, 2019

Author(s): Zhijun Jiang, Charles Paillard, David Vanderbilt, Hongjun Xiang, and L. Bellaiche

First-principles calculations are performed to investigate the effect of epitaxial strain on energetic, structural, electrical, electronic, and optical properties of 1×1 AlN/ScN superlattices. This system is predicted to adopt four different strain regions exhibiting different properties, including ...

[Phys. Rev. Lett. 123, 096801] Published Wed Aug 28, 2019

Author(s): Ziwei Wang and Erik Luijten

Spontaneous pattern formation plays an important role in a wide variety of natural phenomena and materials systems. A key ingredient for the occurrence of modulated phases is the presence of competing interactions, generally of different physical origins. We demonstrate that in dipolar films, a prot...

[Phys. Rev. Lett. 123, 096101] Published Wed Aug 28, 2019

Author(s): Hongyi Sun, Bowen Xia, Zhongjia Chen, Yingjie Zhang, Pengfei Liu, Qiushi Yao, Hong Tang, Yujun Zhao, Hu Xu, and Qihang Liu

As a paradigmatic phenomenon in condensed matter physics, the quantum anomalous Hall effect (QAHE) in stoichiometric Chern insulators has drawn great interest for years. Using model Hamiltonian analysis and first-principles calculations, we establish a topological phase diagram and map different 2D ...

[Phys. Rev. Lett. 123, 096401] Published Wed Aug 28, 2019

Author(s): Jeremias Aguilera Damia, Shamit Kachru, Srinivas Raghu, and Gonzalo Torroba

Significant effort has been devoted to the study of “non-Fermi-liquid” (NFL) metals: gapless conducting systems that lack a quasiparticle description. One class of NFL metals involves a finite density of fermions interacting with soft order parameter fluctuations near a quantum critical point. The p...

[Phys. Rev. Lett. 123, 096402] Published Thu Aug 29, 2019

Author(s): M. R. Molas, A. O. Slobodeniuk, T. Kazimierczuk, K. Nogajewski, M. Bartos, P. Kapuściński, K. Oreszczuk, K. Watanabe, T. Taniguchi, C. Faugeras, P. Kossacki, D. M. Basko, and M. Potemski

Monolayers of semiconducting transition metal dichalcogenides are two-dimensional direct-gap systems which host tightly bound excitons with an internal degree of freedom corresponding to the valley of the constituting carriers. Strong spin-orbit interaction and the resulting ordering of the spin-spl...

[Phys. Rev. Lett. 123, 096803] Published Fri Aug 30, 2019

Author(s): T. M. R. Wolf, J. L. Lado, G. Blatter, and O. Zilberberg

Twisted graphene bilayers provide a versatile platform to engineer metamaterials with novel emergent properties by exploiting the resulting geometric moiré superlattice. Such superlattices are known to host bulk valley currents at tiny angles (α≈0.3°) and flat bands at magic angles (α≈1°). We show t...

[Phys. Rev. Lett. 123, 096802] Published Fri Aug 30, 2019

Nonideal current–voltage characteristics make the mobility that truly reflects the device performance hard to be extracted. A fundamental understanding is necessary to overcome this issue. Herein, the observed nonideal behaviors of organic field‐effect transistors are summarized and analyzed, and solutions for future device engineering toward ideal organic field‐effect transistors are provided.

Abstract

Over the past three decades, the mobility of organic field‐effect transistors (OFETs) has been improved from 10⁻⁵ up to over 10 cm² V⁻¹ s⁻¹, which reaches or has already satisfied the requirements of demanding applications. However, pronounced nonideal behaviors in current–voltage characteristics are commonly observed, which indicates that the reported mobilities may not truly reflect the device properties. Herein, a comprehensive understanding of the origins of several observed nonidealities (downward, upward, double‐slope, superlinear, and humped transfer characteristics) is summarized, and how to extract comparatively reliable mobilities from nonideal behaviors in OFETs is discussed. Combining an overview of the ideal and state‐of‐the‐art OFETs, considerable possible approaches are also provided for future OFETs.

The marriage of single metal atoms and 2D materials yields powerful nanoplatforms. The unique advantages, how to synthesize and characterize various 2D material‐supported metal single‐atoms and their diverse applications in chemical production, energy, and the environment are reviewed. The recent advances and research gaps of this emerging field are also summarized.

Abstract

Recently, emerging 2D material‐supported metal single‐atom catalysts (SACs) are receiving enormous attention in heterogeneous catalysis. Due to their well‐defined, precisely located metal centers, unique metal–support interaction and identical coordination environment, these catalysts serve as excellent models for understanding the fundamental issues in catalysis as well as exhibiting intriguing practical applications. Understanding the correlations between metal–support combinations and the catalytic performance at the atomic level can be achieved on the SACs@2D materials nanoplatforms. Herein, recent advances of metal SACs on various types of 2D materials are reviewed, especially their exciting applications in the fields of chemicals, energy, and the environment. Based on the summary and perspectives, this work should contribute to the rational design of perfect metal SACs with versatile properties.