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Publications

Manipulation of the van der Waals Magnet Cr2Ge2Te6 by Spin–Orbit Torques

Author
Vishakha Gupta
Thow Cham
Gregory Stiehl
Arnab Bose
Joseph Mittelstaedt
Kaifei Kang
Shengwei Jiang
Kin Mak
Jie Shan
Robert Buhrman
Daniel Ralph
Abstract

We report measurements of current-induced thermoelectric and spin-orbit torque effects within devices in which multilayers of the semiconducting two-dimensional van der Waals magnet Cr2Ge2Te6 (CGT) are integrated with Pt and Ta metal overlayers. We show that the magnetic orientation of the CGT can be detected accurately either electrically (using an anomalous Hall effect) or optically (using magnetic circular dichroism) with good consistency.

Journal
American Chemical Society (ACS)
Date Published
Funding Source
1719875
2776.047
DMR-1719875
N00014-18-1-2368
NNCI-2025233
DE-SC0017671
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Electrical switching of valley polarization in monolayer semiconductors

Cornell Affiliated Author(s)
Author
L. Li
S. Jiang
Z. Wang
K. Watanabe
T. Taniguchi
J. Shan
K.F. Mak
Abstract

Achieving on-demand control of the valley degree of freedom is essential for valley-based information science and technology. Optical and magnetic control of the valley degree of freedom in monolayer transition-metal dichalcogenide (TMD) semiconductors has been studied extensively. However, electrical control of the valley polarization has remained a challenge. Here we demonstrate switching of the valley polarization in monolayer WSe2 by electrical gating. This is achieved by coupling a WSe2 monolayer to a two-dimensional (2D) layered magnetic insulator CrI3.

Journal
Physical Review Materials
Date Published
Funding Source
DMR-1807810
FA9550-18-1-0480
DMR-1719875
JPMJCR15F3
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Probing magnetic exchange fields by quantum emitters in a gate-tunable WSe2/ferromagnet-coupled system

Cornell Affiliated Author(s)
Author
A. Mukherjee
K. Shayan
N. Liu
S. Strauf
K.F. Mak
J. Shan
Nick Vamivakas
Abstract

Solid-state quantum emitters can be used as nanoscale optical transducers in quantum metrology. Here, we present a technique to probe voltage controlled magnetic exchange fields with a quantum emitter embedded in a WSe2/ferromagnet heterostrucutre. © OSA 2020.

Conference Name
.
Date Published
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

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