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Publications

Quantum oscillations in insulators with neutral Fermi surfaces

Cornell Affiliated Author(s)
Author
I. Sodemann
Debanjan Chowdhury
T. Senthil
Abstract

We develop a theory of quantum oscillations in insulators with an emergent Fermi sea of neutral fermions minimally coupled to an emergent U(1) gauge field. As pointed out by Motrunich [Phys. Rev. B 73, 155115 (2006)PRBMDO1098-012110.1103/PhysRevB.73.155115], in the presence of a physical magnetic field the emergent magnetic field develops a nonzero value leading to Landau quantization for the neutral fermions. We focus on the magnetic field and temperature dependence of the analog of the de Haas-van Alphen effect in two and three dimensions.

Journal
Physical Review B
Date Published
Funding Source
DE-SC0008739
Group (Lab)
Debanjan Chowdhury Group

Fast Low-Current Spin-Orbit-Torque Switching of Magnetic Tunnel Junctions through Atomic Modifications of the Free-Layer Interfaces

Cornell Affiliated Author(s)
Author
Shengjie Shi
Yongxi Ou
Sriharsha Aradhya
D. Ralph
Robert Buhrman
Abstract

Future applications of spin-orbit torque will require new mechanisms to improve the efficiency of switching nanoscale magnetic tunnel junctions (MTJs), while also controlling the magnetic dynamics to achieve fast nanosecond-scale performance with low-write-error rates. Here, we demonstrate a strategy to simultaneously enhance the interfacial magnetic anisotropy energy and suppress interfacial spin-memory loss by introducing subatomic and monatomic layers of Hf at the top and bottom interfaces of the ferromagnetic free layer of an in-plane magnetized three-terminal MTJ device.

Journal
American Physical Society (APS)
Date Published
Funding Source
0335765

Band offset and electron affinity of MBE-grown SnSe2

Cornell Affiliated Author(s)
Author
Q. Zhang
M. Li
E.B. Lochocki
S. Vishwanath
X. Liu
R. Yan
H.-H. Lien
M. Dobrowolska
J. Furdyna
K.M. Shen
G. Cheng
A.R. Walker
D.J. Gundlach
H.G. Xing
N.V. Nguyen
Abstract

SnSe2 is currently considered a potential two-dimensional material that can form a near-broken gap heterojunction in a tunnel field-effect transistor due to its large electron affinity which is experimentally confirmed in this letter. With the results from internal photoemission and angle-resolved photoemission spectroscopy performed on Al/Al2O3/SnSe2/GaAs and SnSe2/GaAs test structures where SnSe2 is grown on GaAs by molecular beam epitaxy, we ascertain a (5.2 ± 0.1) eV electron affinity of SnSe2.

Journal
Applied Physics Letters
Date Published
Funding Source
1400432
1433490
NSF EFRI 1433490
Group (Lab)
Kyle Shen Group

Graphene-based bimorphs for micron-sized, tautonomous origami machines

Cornell Affiliated Author(s)
Author
M.Z. Miskin
K.J. Dorsey
B. Bircan
Y. Han
D.A. Muller
P.L. McEuen
Itai Cohen
Abstract

Origami-inspired fabrication presents an attractive platform for miniaturizing machines: thinner layers of folding material lead to smaller devices, provided that key functional aspects, such as conductivity, stiffness, and flexibility, are persevered. Here, we show origami fabrication at its ultimate limit by using 2D atomic membranes as a folding material. As a prototype, we bond graphene sheets to nanometer-thick layers of glass to make ultrathin bimorph actuators that bend to micrometer radii of curvature in response to small strain differentials.

Journal
Proceedings of the National Academy of Sciences of the United States of America
Date Published
Funding Source
FA2386-13-1-4118
1719875
DMR-1429155
ECCS-0335765
DMR-1719875
Group (Lab)
Itai Cohen Group
Paul McEuen Group

Characterization of chromium compensated GaAs as an X-ray sensor material for charge-integrating pixel array detectors

Cornell Affiliated Author(s)
Author
J. Becker
M.W. Tate
K.S. Shanks
H.T. Philipp
J.T. Weiss
P. Purohit
Darol Chamberlain
Sol Gruner
Abstract

We studied the properties of chromium compensated GaAs when coupled to charge integrating ASICs as a function of detector temperature, applied bias and X-ray tube energy. The material is a photoresistor and can be biased to collect either electrons or holes by the pixel circuitry. Both are studied here. Previous studies have shown substantial hole trapping. This trapping and other sensor properties give rise to several non-ideal effects which include an extended point spread function, variations in the effective pixel size, and rate dependent offset shifts.

Journal
Journal of Instrumentation
Date Published
Funding Source
DMR-1332208
DE-SC0004079
DE-SC0016035
DE-SC0017631
1332208
Group (Lab)
Sol M. Gruner Group

Electrical Tuning of Interlayer Exciton Gases in WSe2 Bilayers

Cornell Affiliated Author(s)
Author
Z. Wang
Y.-H. Chiu
K. Honz
K.F. Mak
J. Shan
Abstract

van der Waals heterostructures formed by stacking two-dimensional atomic crystals are a unique platform for exploring new phenomena and functionalities. Interlayer excitons, bound states of spatially separated electron-hole pairs in van der Waals heterostructures, have demonstrated potential for rich valley physics and optoelectronics applications and been proposed to facilitate high-temperature superfluidity. Here, we demonstrate highly tunable interlayer excitons by an out-of-plane electric field in homobilayers of transition metal dichalcogenides.

Journal
Nano Letters
Date Published
Funding Source
DMR-1420451
DESC0012635
DESC0013883
DMR-1460920
Group (Lab)
Jie Shan Group
Kin Fai Mak Group

Measuring and Manipulating the Adhesion of Graphene

Cornell Affiliated Author(s)
Author
M.Z. Miskin
C. Sun
Itai Cohen
W.R. Dichtel
P.L. McEuen
Abstract

We present a technique to precisely measure the surface energies between two-dimensional materials and substrates that is simple to implement and allows exploration of spatial and chemical control of adhesion at the nanoscale. As an example, we characterize the delamination of single-layer graphene from monolayers of pyrene tethered to glass in water and maximize the work of separation between these surfaces by varying the density of pyrene groups in the monolayer. Control of this energy scale enables high-fidelity graphene-transfer protocols that can resist failure under sonication.

Journal
Nano Letters
Date Published
Funding Source
ECCS-1542081
1719875
DMR-1719875
Group (Lab)
Itai Cohen Group
Paul McEuen Group

Benchmark problems for phase retrieval

Cornell Affiliated Author(s)
Author
V. Elser
T.-Y. Lan
T. Bendory
Abstract

In recent years, the mathematical and algorithmic aspects of the phase retrieval problem have received considerable attention. Many papers in this area mention crystallography as a principal application. In crystallography, the signal to be recovered is periodic and comprised of atomic distributions arranged homogeneously in the unit cell of the crystal. The crystallographic problem is both the leading application and one of the hardest forms of phase retrieval. We have constructed a graded set of benchmark problems for evaluating algorithms that perform this type of phase retrieval.

Journal
SIAM Journal on Imaging Sciences
Date Published
Funding Source
DE-SC0005827
Group (Lab)
Veit Elser Group

Direct visualization of sulfur cathodes: New insights into Li-S batteries via operando X-ray based methods

Cornell Affiliated Author(s)
Author
S.-H. Yu
X. Huang
K. Schwarz
R. Huang
Tomas Arias
J.D. Brock
H.D. Abruña
Abstract

As the need for the development of "beyond lithium" ion battery technologies continues unabated, lithium sulfur batteries have attracted widespread attention due to their very high theoretical energy density of 2600 W h kg-1. However, despite much effort, the detailed reaction mechanism remains poorly understood. In this study, we have combined operando X-ray diffraction and X-ray microscopy along with X-ray tomography, to visualize the evolution of both the morphology and crystal structure of the materials during the entire battery cycling (discharging/charging) process.

Journal
Energy and Environmental Science
Date Published
Funding Source
DMR-1332208
2015R1A6A3A03020354
Group (Lab)
Tomas Arias Group