2020 New's Items

Fermi-crossing Type-II Dirac fermions and topological surface states in NiTe2

S. Mukherjee
S. W. Jung
S. F. Weber
C. Xu
D. Qian
X. Xu
P. K. Biswas
T. K. Kim
L. C. Chapon
M. D. Watson
J. B. Neaton
C. Cacho
2020

Transition-metal dichalcogenides (TMDs) offer an ideal platform to experimentally realize Dirac fermions. However, typically these exotic quasiparticles are located far away from the Fermi level, limiting the contribution of Dirac-like carriers to the transport properties. Here we show that NiTe2 hosts both bulk Type-II Dirac points and topological surface states. The underlying mechanism is shared with other TMDs and based on the generic topological character of the Te p-orbital manifold. However, unique to NiTe2, a...

Signatures of possible surface states in TaAs

N. L. Nair
M.-E. Boulanger
F. Laliberté
S. M. Griffin
S. Channa
A. Legros
W. Tabis
J. B. Neaton
L. Taillefer
J. G. Analytis
2020

We study Shubnikov–de Haas oscillations in single crystals of TaAs and find a previously undetected two-dimensional quantum oscillation that does not belong to the bulk Fermi surface. We cannot find an impurity phase consistent with our observations, and extensive diffraction measurements have not shown the presence of known impurity phases. We conjecture that the frequency originates from surface states that are sensitive to surface disorder. One candidate is the interference of coherent quasiparticles traversing two distinct Fermi arcs on the [001] crystallographic surface. The...

Tunneling Spectroscopy in Carbon Nanotube-Hexagonal Boron Nitride-Carbon Nanotube Heterojunctions

Zhao S
Yoo SJ
Wang S
Lyu B
Kahn S
Wu F
Zhao Z
Cui D
Zhao W
Yoon Y
Utama MIB
Shi W
Watanabe K
Taniguchi T
Crommie MF
Shi Z
Zhou C
Wang F
2020

Electron tunneling spectroscopy is a powerful technique to probe the unique physical properties of one-dimensional (1D) single-walled carbon nanotubes (SWNTs), such as the van Hove singularities in the density of states or the power-law tunneling probability of a Luttinger liquid. However, little is known about the tunneling behavior between two 1D SWNTs over a large energy spectrum. Here, we investigate the electron tunneling behavior between two crossed SWNTs across a wide spectral window up to 2 eV in the unique carbon nanotube-hexagonal boron nitride-carbon nanotube...

Liquid-like Interfaces Mediate Structural Phase Transitions in Lead Halide Perovskites

Bischak CG
Lai M
Fan Z
Lu D
David P
Dong D
Chen H
Etman AS
Lei T
Sun J
Grünwald M
Limmer DT
Yang P
Ginsberg NS
2020

Microscopic pathways of structural phase transitions in metal halide perovskites are difficult to probe because they occur over disparate time and length scales and because electron-based microscopies typically used to directly probe nanoscale dynamics of phase transitions often damage metal halide perovskite materials. Using in situ nanoscale cathodoluminescence microscopy with low electron beam exposure, we visualize nucleation and growth in the thermally driven transition to the perovskite phase in hundreds of non-perovskite phase nanowires. In combination...

Evidence for a Magnetic-Field-Induced Ideal Type-II Weyl State in Antiferromagnetic Topological Insulator Mn ( Bi 1 − x Sb x ) 2 Te 4

Lee SH
Graf DE
Min L
Zhu Y
Hemian Y
Ciocys S
Wang Y
Choi ES
Basnet R
Fereidouni A
Wegner A
Zhao Y-F
Verlinde K
He J
Redwing R
Gopalan V
Churchill HOH
Lanzara A
Samarth N
Chang C-Z
Hu J
Mao ZQ
2020

The discovery of Weyl semimetals (WSMs) has fueled tremendous interest in condensed matter physics. The realization of WSMs requires the breaking of either inversion symmetry (IS) or time-reversal symmetry (TRS). WSMs can be categorized into type-I and type-II WSMs, which are characterized by untilted and strongly tilted Weyl cones, respectively. Type-I WSMs with breaking of either IS or TRS and type-II WSMs with solely broken IS have been realized experimentally, but a TRS-breaking type-II WSM still remains elusive. In this article, we report transport evidence for a TRS-breaking...

Trigonal polymorph of Li 2 Mn O 3

Xia B
Cheng J
Arengo M
Rajput N
Janssen Y
Neilson JR
Persson KA
Simonson JW
2020

We report the discovery of a trigonal polymorph of the prospective Li-ion battery material ${\mathrm{Li}}_{2}\mathrm{Mn}{\mathrm{O}}_{3}$ and its synthesis in bulk, single-crystal form. Crystal growth of trigonal ${\mathrm{Li}}_{2}\mathrm{Mn}{\mathrm{O}}_{3}$ is strongly dependent upon the quality of a polycrystalline $\mathrm{Li}\mathrm{Mn}{\mathrm{O}}_{2}$ precursor consumed in the synthesis process. The crystal structure of the trigonal phase is composed of ordered honeycomb layers of $\mathrm{Li}{\mathrm{O}}_{6}$ and $\mathrm{Mn}{\mathrm{O}}_{6}$ octahedra segregated by layers of...

A generic electroluminescent device for emission from infrared to ultraviolet wavelengths

Zhao Y
Wang V
Lien DH
Javey A
2020

The range of luminescent materials that can be used in electroluminescent devices is limited due to material processing challenges and band alignment issues. This impedes the development of electroluminescent devices at extreme wavelengths and hinders the use of electroluminescence spectroscopy as an analytical technique. Here, we show that a two-terminal device that uses an array of carbon nanotubes as the source contact can excite electroluminescence from various materials independent of their chemical composition. Transient band bending, created by applying an a.c. gate voltage,...

Cu-Ag Tandem Catalysts for High-Rate CO2 Electrolysis toward Multicarbons

Chen C
Li Y
Yu S
Louisia S
Jin J
Li M
Ross MB
Yang P
2020

Tandem electrocatalysis decouples individual steps within a chemically complicated pathway via multicomponent catalyst design. Such a concept is attractive for CO2 electro-conversion to multicarbons (C2+), especially at high rates. Here, we show that a Cu-Ag tandem catalyst on a gas diffusion electrode (GDE) can enhance the C2+ production rate from CO2 through CO2 reduction to CO on Ag and subsequent carbon coupling on Cu. With added Ag, the C...

Anisotropic reticular chemistry

Xu W
Tu B
Liu Q
Shu Y
Liang CC
Diercks CS
Yaghi OM
Zhang YB
Deng H
Li Q
2020

Reticular chemistry has been focused on making simple structures in which a few kinds of components are linked to make crystals such as metal–organic frameworks (MOFs). While this chemistry has grown into a large field, a more extensive area with fascinating directions is emerging through the introduction of multiplicity and variation into the components of MOFs. When the MOF backbone is composed of more than two kinds of components, the resulting backbone multiplicity is regular repeats of those units. However, when variations involve multiple functionalization of the organic...

Single-molecule diffusometry reveals no catalysis-induced diffusion enhancement of alkaline phosphatase as proposed by FCS experiments

Chen Z
Shaw A
Wilson H
Woringer M
Darzacq X
Marqusee S
Wang Q
Bustamante C
2020

Theoretical and experimental observations that catalysis enhances the diffusion of enzymes have generated exciting implications about nanoscale energy flow, molecular chemotaxis, and self-powered nanomachines. However, contradictory claims on the origin, magnitude, and consequence of this phenomenon continue to arise. To date, experimental observations of catalysis-enhanced enzyme diffusion have relied almost exclusively on fluorescence correlation spectroscopy (FCS), a technique that provides only indirect, ensemble-averaged measurements of diffusion behavior. Here, using an anti-...