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Publications

Spectral and spatial isolation of single tungsten diselenide quantum emitters using hexagonal boron nitride wrinkles

Cornell Affiliated Author(s)
Author
R.S. Daveau
T. Vandekerckhove
A. Mukherjee
Z. Wang
J. Shan
K.F. Mak
Nick Vamivakas
Gregory Fuchs
Abstract

Monolayer WSe2 hosts bright single-photon emitters. Because of its compliance, monolayer WSe2 conforms to patterned substrates without breaking, thus creating the potential for large local strain, which is one activation mechanism of its intrinsic quantum emitters. Here, we report an approach to creating spatially isolated quantum emitters from WSe2 monolayers that display clean spectra with little detrimental background signal.

Journal
APL Photonics
Date Published
Funding Source
FA9550-18-1-0480
DMR-1719875
DMR-1553788
NNCI-1542081
FA9550-19-1-0074
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Strain relaxation induced transverse resistivity anomalies in SrRu O3 thin films

Cornell Affiliated Author(s)
Author
L. Miao
N.J. Schreiber
H.P. Nair
B.H. Goodge
S. Jiang
J.P. Ruf
Y. Lee
M. Fu
B. Tsang
Y. Li
Cyrus Zeledon
J. Shan
K.F. Mak
L.F. Kourkoutis
D.G. Schlom
K.M. Shen
Abstract

Here, we report a magnetotransport study of high-quality SrRuO3 thin films with high residual resistivity ratios grown by reactive oxide molecular-beam epitaxy. The transverse resistivity exhibits clear anomalies which are typically believed to be signatures of the topological Hall effect and the presence of magnetic skyrmions.

Journal
Physical Review B
Date Published
Funding Source
1709255
DMR-1539918
DMR-1709255
DE-SC0019414
FA9550-15-1-0474
GBMF3850
DMR-1719875
NNCI-1542081
Group (Lab)
Jie Shan Group
Kin Fai Mak Group
Kyle Shen Group

Gate-tunable spin waves in antiferromagnetic atomic bilayers

Cornell Affiliated Author(s)
Author
X.-X. Zhang
L. Li
D. Weber
J. Goldberger
K.F. Mak
J. Shan
Abstract

Remarkable properties of two-dimensional (2D) layer magnetic materials, which include spin filtering in magnetic tunnel junctions and the gate control of magnetic states, were demonstrated recently1–12. Whereas these studies focused on static properties, dynamic magnetic properties, such as excitation and control of spin waves, remain elusive. Here we investigate spin-wave dynamics in antiferromagnetic CrI3 bilayers using an ultrafast optical pump/magneto-optical Kerr probe technique.

Journal
Nature Materials
Date Published
Funding Source
DMR-1807810
1420451
1719875
1807810
FA9550-19-1-0390
DMR-1719875
DMR-1420451
WE6480/1
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Simulation of Hubbard model physics in WSe2/WS2 moiré superlattices

Cornell Affiliated Author(s)
Author
Y. Tang
L. Li
T. Li
Y. Xu
S. Liu
K. Barmak
K. Watanabe
T. Taniguchi
A.H. MacDonald
J. Shan
K.F. Mak
Abstract

The Hubbard model, formulated by physicist John Hubbard in the 1960s1, is a simple theoretical model of interacting quantum particles in a lattice. The model is thought to capture the essential physics of high-temperature superconductors, magnetic insulators and other complex quantum many-body ground states2,3. Although the Hubbard model provides a greatly simplified representation of most real materials, it is nevertheless difficult to solve accurately except in the one-dimensional case2,3.

Journal
Nature
Date Published
Funding Source
N00014-18-1-2368
TBF1473
DE-SC0013883
DE-SC0019481
DMR-1420634
JPMJCR15F3
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Magneto-Memristive Switching in a 2D Layer Antiferromagnet

Cornell Affiliated Author(s)
Author
H.H. Kim
S. Jiang
B. Yang
S. Zhong
S. Tian
C. Li
H. Lei
J. Shan
K.F. Mak
A.W. Tsen
Abstract

Memristive devices whose resistance can be hysteretically switched by electric field or current are intensely pursued both for fundamental interest as well as potential applications in neuromorphic computing and phase-change memory. When the underlying material exhibits additional charge or spin order, the resistive states can be directly coupled, further allowing electrical control of the collective phases. The observation of abrupt, memristive switching of tunneling current in nanoscale junctions of ultrathin CrI3, a natural layer antiferromagnet, is reported here.

Journal
Advanced Materials
Date Published
Funding Source
2016YFA0300504
ER17-13-199
W911NF-19-10267
N00014-18-1-2368
1807810
FA9550-18-1-0480
11574394
11774423
11822412
NRF-2017K1A3A1A12073407
15XNLQ07
18XNLG14
19XNLG17
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Pressure-controlled interlayer magnetism in atomically thin CrI3

Cornell Affiliated Author(s)
Author
T. Li
S. Jiang
N. Sivadas
Z. Wang
Y. Xu
D. Weber
J.E. Goldberger
K. Watanabe
T. Taniguchi
C.J. Fennie
Fai Mak
J. Shan
Abstract

Stacking order can influence the physical properties of two-dimensional van der Waals materials1,2. Here we applied hydrostatic pressure up to 2 GPa to modify the stacking order in the van der Waals magnetic insulator CrI3. We observed an irreversible interlayer antiferromagnetic-to-ferromagnetic transition in atomically thin CrI3 by magnetic circular dichroism and electron tunnelling measurements. The effect was accompanied by a monoclinic-to-rhombohedral stacking-order change characterized by polarized Raman spectroscopy.

Journal
Nature Materials
Date Published
Funding Source
1719875
N00014-18-1-2368
W911NF-17-1-0605
DMR-1719875
DMR-1420451
WE6480/1
JPMJCR15F3
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Layer-dependent spin-orbit torques generated by the centrosymmetric transition metal dichalcogenide β−MoTe2

Cornell Affiliated Author(s)
Author
Gregory Stiehl
Ruofan Li
Vishakha Gupta
Ismail Baggari
Shengwei Jiang
Hongchao Xie
Lena Kourkoutis
Kin Mak
Jie Shan
Robert Buhrman
Daniel Ralph
Abstract

Single-crystal materials with sufficiently low crystal symmetry and strong spin-orbit interactions can be used to generate novel forms of spin-orbit torques on adjacent ferromagnets, such as the out-of-plane antidamping torque previously observed in WTe2/ferromagnet heterostructures. Here, we present measurements of spin-orbit torques produced by the low-symmetry material β-MoTe2, which, unlike WTe2, retains bulk inversion symmetry.

Journal
American Physical Society (APS)
Date Published
Funding Source
1429155
1542081
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Evidence of high-temperature exciton condensation in two-dimensional atomic double layers

Cornell Affiliated Author(s)
Author
Z. Wang
D.A. Rhodes
K. Watanabe
T. Taniguchi
J.C. Hone
J. Shan
K.F. Mak
Abstract

A Bose–Einstein condensate is the ground state of a dilute gas of bosons, such as atoms cooled to temperatures close to absolute zero1. With much smaller mass, excitons (bound electron–hole pairs) are expected to condense at considerably higher temperatures2–7. Two-dimensional van der Waals semiconductors with very strong exciton binding are ideal systems for the study of high-temperature exciton condensation. Here we study electrically generated interlayer excitons in MoSe2–WSe2 atomic double layers with a density of up to 1012 excitons per square centimetre.

Journal
Nature
Date Published
Funding Source
DE-SC0013883
DE-SC0019481
DMR-1420634
JPMJCR15F3
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Long valley lifetime of dark excitons in single-layer WSe2

Cornell Affiliated Author(s)
Author
Y. Tang
K.F. Mak
J. Shan
Abstract

Single-layer transition metal dichalcogenides provide a promising material system to explore the electron’s valley degree of freedom as a quantum information carrier. The valley degree of freedom can be directly accessed by means of optical excitation. However, rapid valley relaxation of optically excited electron-hole pairs (excitons) through the exchange interaction has been a major roadblock. Theoretically such valley relaxation is suppressed in dark excitons, suggesting a potential route for long valley lifetimes.

Journal
Nature Communications
Date Published
Funding Source
DE-SC0019481
-SC0019481
DESC0013883
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Evolution of interlayer and intralayer magnetism in three atomically thin chromium trihalides

Cornell Affiliated Author(s)
Author
H.H. Kim
B. Yang
S. Li
S. Jiang
C. Jin
Z. Tao
G. Nichols
F. Sfigakis
S. Zhong
C. Li
S. Tian
D.G. Cory
G.-X. Miao
J. Shan
K.F. Mak
H. Lei
K. Sun
L. Zhao
A.W. Tsen
Abstract

We conduct a comprehensive study of three different magnetic semiconductors, CrI3, CrBr3, and CrCl3, by incorporating both few-layer and bilayer samples in van der Waals tunnel junctions. We find that the interlayer magnetic ordering, exchange gap, magnetic anisotropy, and magnon excitations evolve systematically with changing halogen atom. By fitting to a spin wave theory that accounts for nearest-neighbor exchange interactions, we are able to further determine a simple spin Hamiltonian describing all three systems.

Journal
Proceedings of the National Academy of Sciences of the United States of America
Date Published
Funding Source
1749774
1807810
DMR-1749774
DMR-1807810
N00014-18-1-2368
ER17-13-199
RGPIN-2017-03815
11574394
11774423
11822412
NRF-2017K1A3A1A12073407
RGPIN-04178
2016YFA0300504
Group (Lab)
Jie Shan Group
Kin Fai Mak Group