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Publications

Valley magnetoelectricity in single-layer MoS 2

Cornell Affiliated Author(s)
Author
J. Lee
Z. Wang
H. Xie
K.F. Mak
J. Shan
Abstract

The magnetoelectric (ME) effect, the phenomenon of inducing magnetization by application of an electric field or vice versa, holds great promise for magnetic sensing and switching applications. Studies of the ME effect have so far focused on the control of the electron spin degree of freedom (DOF) in materials such as multiferroics and conventional semiconductors. Here, we report a new form of the ME effect based on the valley DOF in two-dimensional Dirac materials.

Journal
Nature Materials
Date Published
Funding Source
DESC0013883
DMR-1420451
DMR-1410407
FA9550-14-1-0268
FA9550-16-1-0249
S2017A040300024
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Thickness dependence of spin-orbit torques generated by WTe2

Cornell Affiliated Author(s)
Author
David MacNeill
Gregory Stiehl
Marcos Guimarães
Neal Reynolds
Robert Buhrman
Daniel Ralph
Abstract

We study current-induced torques in WTe2/permalloy bilayers as a function of WTe2 thickness. We measure the torques using both second-harmonic Hall and spin-torque ferromagnetic resonance techniques for samples with WTe2 thicknesses that span from 16 nm down to a single monolayer. We confirm the existence of an out-of-plane antidamping torque, and we show directly that the sign of this torque component is reversed across a monolayer step in the WTe2.

Journal
American Physical Society (APS)
Date Published
Funding Source
DMR-1406333
ECCS-1542081
DMR-1120296
680-50-1311

Emergent magnetic anisotropy in the cubic heavy-fermion metal CeIn3

Cornell Affiliated Author(s)
Author
P.J.W. Moll
T. Helm
S.-S. Zhang
C.D. Batista
N. Harrison
R.D. McDonald
L.E. Winter
B.J. Ramshaw
M.K. Chan
Fedor Balakirev
Bertram Batlogg
E.D. Bauer
F. Ronning
Abstract

Metals containing cerium exhibit a diverse range of fascinating phenomena including heavy fermion behavior, quantum criticality, and novel states of matter such as unconventional superconductivity. The cubic system CeIn3 has attracted significant attention as a structurally isotropic Kondo lattice material possessing the minimum required complexity to still reveal this rich physics.

Journal
npj Quantum Materials
Date Published
Funding Source
DMR-1157490
MO 3077/1-1
Group (Lab)
Brad Ramshaw Group

Formation pathways of mesoporous silica nanoparticles with dodecagonal tiling

Cornell Affiliated Author(s)
Author
Y. Sun
K. Ma
T. Kao
K.A. Spoth
H. Sai
D. Zhang
L.F. Kourkoutis
V. Elser
U. Wiesner
Abstract

Considerable progress in the fabrication of quasicrystals demonstrates that they can be realized in a broad range of materials. However, the development of chemistries enabling direct experimental observation of early quasicrystal growth pathways remains challenging. Here, we report the synthesis of four surfactant-directed mesoporous silica nanoparticle structures, including dodecagonal quasicrystalline nanoparticles, as a function of micelle pore expander concentration or stirring rate.

Journal
Nature Communications
Date Published
Funding Source
0966188
0966188
1332208
Group (Lab)
Veit Elser Group

Protocol to engineer Fulde-Ferrell-Larkin-Ovchinnikov states in a cold Fermi gas

Cornell Affiliated Author(s)
Author
S. Dutta
E.J. Mueller
Abstract

We propose a two-step experimental protocol to directly engineer Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states in a cold two-component Fermi gas loaded into a quasi-one-dimensional trap. First, one uses phase imprinting to create a train of domain walls in a superfluid with equal number of ↑- and ↓-spins. Second, one applies a radio-frequency sweep to selectively break Cooper pairs near the domain walls and transfer the ↑-spins to a third spin state, which does not interact with the ↑- and ↓-spins.

Journal
Physical Review A
Date Published
Funding Source
1508300
PHY-1508300

Orbital superconductivity, defects, and pinned nematic fluctuations in the doped iron chalcogenide FeSe0.45Te0.55

Cornell Affiliated Author(s)
Author
S. Sarkar
J. Van Dyke
P.O. Sprau
F. Massee
U. Welp
W.-K. Kwok
J.C.S. Davis
D.K. Morr
Abstract

We demonstrate that the differential conductance, dI/dV, measured via spectroscopic imaging scanning tunneling microscopy in the doped iron chalcogenide FeSe0.45Te0.55, possesses a series of characteristic features that allow one to extract the orbital structure of the superconducting gaps. This yields nearly isotropic superconducting gaps on the two holelike Fermi surfaces, and a strongly anisotropic gap on the electronlike Fermi surface.

Journal
Physical Review B
Date Published
Group (Lab)
J.C. Seamus Davis Group

Frictional Magneto-Coulomb Drag in Graphene Double-Layer Heterostructures

Cornell Affiliated Author(s)
Author
Xiaomeng Liu
Lei Wang
Kin Fong
Yuanda Gao
Patrick Maher
Kenji Watanabe
Takashi Taniguchi
James Hone
Cory Dean
Philip Kim
Abstract

Coulomb interaction between two closely spaced parallel layers of conductors can generate the frictional drag effect by interlayer Coulomb scattering. Employing graphene double layers separated by few‐layer hexagonal boron nitride, we investigate density tunable magneto- and Hall drag under strong magnetic fields. The observed large magnetodrag and Hall-drag signals can be related with Laudau level filling status of the drive and drag layers.

Journal
Physical Review Letters
Date Published
Group (Lab)
Xiaomeng Liu Group

Electronic in-plane symmetry breaking at field-tuned quantum criticality in CeRhIn 5

Cornell Affiliated Author(s)
Author
F. Ronning
T. Helm
K.R. Shirer
Maja Bachmann
L. Balicas
M.K. Chan
B.J. Ramshaw
R.D. McDonald
Fedor Balakirev
M. Jaime
E.D. Bauer
P.J.W. Moll
Abstract

Electronic nematic materials are characterized by a lowered symmetry of the electronic system compared to the underlying lattice, in analogy to the directional alignment without translational order in nematic liquid crystals. Such nematic phases appear in the copper-A nd iron-based high-temperature superconductors, and their role in establishing superconductivity remains an open question. Nematicity may take an active part, cooperating or competing with superconductivity, or may appear accidentally in such systems.

Journal
Nature
Date Published
Funding Source
100T
MO 3077/1-1
DMR-1157490
DE-SC0002613
Group (Lab)
Brad Ramshaw Group

Reconstructing three-dimensional protein crystal intensities from sparse unoriented two-axis X-ray diffraction patterns

Cornell Affiliated Author(s)
Author
T.-Y. Lan
J.L. Wierman
M.W. Tate
H.T. Philipp
V. Elser
Sol Gruner
Abstract

Recently, there has been a growing interest in adapting serial microcrystallography (SMX) experiments to existing storage ring (SR) sources. For very small crystals, however, radiation damage occurs before sufficient numbers of photons are diffracted to determine the orientation of the crystal. The challenge is to merge data from a large number of such 'sparse' frames in order to measure the full reciprocal space intensity. To simulate sparse frames, a dataset was collected from a large lysozyme crystal illuminated by a dim X-ray source.

Journal
Journal of Applied Crystallography
Date Published
Group (Lab)
Sol M. Gruner Group
Veit Elser Group

Robust spin correlations at high magnetic fields in the harmonic honeycomb iridates

Cornell Affiliated Author(s)
Author
K. Modic
B. Ramshaw
Jon Betts
Nicholas Breznay
James Analytis
Ross McDonald
Arkady Shekhter
Abstract

The complex antiferromagnetic orders observed in the honeycomb iridates are a double-edged sword in the search for a quantum spin-liquid: both attesting that the magnetic interactions provide many of the necessary ingredients, while simultaneously impeding access. Focus has naturally been drawn to the unusual magnetic orders that hint at the underlying spin correlations. However, the study of any particular broken symmetry state generally provides little clue about the possibility of other nearby ground states.

Journal
Nature Communications
Date Published
Funding Source
DR20160085
DMR-1157490
1157490
GBMF4374
DE-AC02-05CH11231
Group (Lab)
Brad Ramshaw Group