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Publications

Quantum Spin Liquid Intertwining Nematic and Superconducting Order in Fese

Cornell Affiliated Author(s)
Author
J.-H. She
M.J. Lawler
Eun-Ah Kim
Abstract

Despite its seemingly simple composition and structure, the pairing mechanism of FeSe remains an open problem due to several striking phenomena. Among them are nematic order without magnetic order, nodeless gap and unusual inelastic neutron spectra with a broad continuum, and gap anisotropy consistent with orbital selection of unknown origin. Here we propose a microscopic description of a nematic quantum spin liquid that reproduces key features of neutron spectra. We then study how the spin fluctuations of the local moments lead to pairing within a spin-fermion model.

Journal
Physical Review Letters
Date Published
Group (Lab)
Michael Lawler Group

High Photoresponse in Conformally Grown Monolayer MoS2 on a Rugged Substrate

Cornell Affiliated Author(s)
Author
T.K. Nguyen
A.D. Nguyen
C.T. Le
F. Ullah
Z. Tahir
K.-I. Koo
Eun-Ah Kim
D.-W. Kim
J.I. Jang
Y.S. Kim
Abstract

Conformal growth of atomic-thick semiconductor layers on patterned substrates can boost up the performance of electronic and optoelectronic devices remarkably. However, conformal growth is a very challenging technological task, since the control of the growth processes requires utmost precision. Herein, we report on conformal growth and characterization of monolayer MoS2 on planar, microrugged, and nanorugged SiO2/Si substrates via metal-organic chemical vapor deposition.

Journal
ACS Applied Materials and Interfaces
Date Published
Group (Lab)

Coherent Superconductivity with a Large Gap Ratio from Incoherent Metals

Cornell Affiliated Author(s)
Author
A.A. Patel
M.J. Lawler
Eun-Ah Kim
Abstract

A mysterious incoherent metallic (IM) normal state with T-linear resistivity is ubiquitous among strongly correlated superconductors. Recent progress with microscopic models exhibiting IM transport has presented the opportunity for us to study new models that exhibit direct transitions into a superconducting state out of IM states within the framework of connected Sachdev-Ye-Kitaev "quantum dots." Here, local Sachdev-Ye-Kitaev interactions within a dot produce IM transport in the normal state, while local attractive interactions drive superconductivity.

Journal
Physical Review Letters
Date Published
Group (Lab)
Michael Lawler Group

MoS2 monolayers on Si and SiO2 nanocone arrays: Influences of 3D dielectric material refractive index on 2D MoS2 optical absorption

Cornell Affiliated Author(s)
Author
Eun-Ah Kim
J.-W. Cho
T.K. Nguyen
T.T.T. Nguyen
S. Yoon
J.-H. Choi
Y.C. Park
S.-K. Kim
Y.S. Kim
D.-W. Kim
Abstract

Heterostructures enable the control of transport and recombination of charge carriers, which are either injected through electrodes, or created by light illumination. Instead of full 2D-material-heterostructures in device applications, using hybrid heterostructures consisting of 2D and 3D materials is an alternative approach to take advantage of the unique physical properties of 2D materials. In addition, 3D dielectric nanostructures exhibit useful optical properties such as broadband omnidirectional antireflection effects and strongly concentrated light near the surface.

Journal
Nanoscale
Date Published
Group (Lab)

Pomeranchuk Instability of Composite Fermi Liquids

Cornell Affiliated Author(s)
Author
K. Lee
J. Shao
Eun-Ah Kim
F.D.M. Haldane
E.H. Rezayi
Abstract

Nematicity in quantum Hall systems has been experimentally well established at excited Landau levels. The mechanism of the symmetry breaking, however, is still unknown. Pomeranchuk instability of Fermi liquid parameter F≤-1 in the angular momentum =2 channel has been argued to be the relevant mechanism, yet there are no definitive theoretical proofs. Here we calculate, using the variational Monte Carlo technique, Fermi liquid parameters F of the composite fermion Fermi liquid with a finite layer width.

Journal
Physical Review Letters
Date Published
Group (Lab)

Enhancing the Performance of Surface Plasmon Resonance Biosensor via Modulation of Electron Density at the Graphene–Gold Interface

Cornell Affiliated Author(s)
Author
K. Chung
J.S. Lee
Eun-Ah Kim
K.-E. Lee
K. Kim
J. Lee
D. Kim
S.O. Kim
S. Jeon
H. Park
D.-W. Kim
D.H. Kim
Abstract

Surface plasmons at a metal/dielectric interface resonate with incident light, generating an evanescent field at the interface, which is highly sensitive to the change in refractive index of the medium. These characteristics are utilized as the basis for surface plasmon resonance-based sensors with Kretschmann configuration, providing label-free and real-time monitoring of binding interaction between probe and target moieties.

Journal
Advanced Materials Interfaces
Date Published
Funding Source
2015R1D1A1A0105791
2017R1A2A1A05022387
NRF-2015R1A2A1A10052826
2015R1A3A2033061
Group (Lab)

Machine Learning Out-of-Equilibrium Phases of Matter

Cornell Affiliated Author(s)
Author
J. Venderley
V. Khemani
Eun-Ah Kim
Abstract

Neural-network-based machine learning is emerging as a powerful tool for obtaining phase diagrams when traditional regression schemes using local equilibrium order parameters are not available, as in many-body localized (MBL) or topological phases. Nevertheless, instances of machine learning offering new insights have been rare up to now. Here we show that a single feed-forward neural network can decode the defining structures of two distinct MBL phases and a thermalizing phase, using entanglement spectra obtained from individual eigenstates.

Journal
Physical Review Letters
Date Published
Group (Lab)

Quantum limit transport and destruction of the Weyl nodes in TaAs

Cornell Affiliated Author(s)
Author
B. Ramshaw
K. Modic
Arkady Shekhter
Yi Zhang
Eun-Ah Kim
Philip Moll
Maja Bachmann
M. Chan
Jon Betts
Fedor Balakirev
A. Migliori
N. Ghimire
E. Bauer
F. Ronning
R. McDonald
Abstract

Weyl fermions are a recently discovered ingredient for correlated states of electronic matter. A key difficulty has been that real materials also contain non-Weyl quasiparticles, and disentangling the experimental signatures has proven challenging. Here we use magnetic fields up to 95 T to drive the Weyl semimetal TaAs far into its quantum limit, where only the purely chiral 0th Landau levels of the Weyl fermions are occupied.

Journal
Nature Communications
Date Published
Funding Source
DR20160085
DMR-1308089
LDRD 20160616ECR
1157490
1308089
715730
Group (Lab)
Brad Ramshaw Group

Interference-Enhanced Broadband Absorption of Monolayer MoS2 on Sub-100 nm Thick SiO2/Si Substrates: Reflection and Transmission Phase Changes at Interfaces

Cornell Affiliated Author(s)
Author
Eun-Ah Kim
J.-W. Cho
B.R. Kim
T.T.T. Nguyen
Y.-H. Nam
S.-K. Kim
S. Yoon
Y.S. Kim
J.-H. Lee
D.-W. Kim
Abstract

The optical characteristics of MoS2 monolayers on SiO2/Si substrates with an SiO2 thickness ranging from 40 to 130 nm are investigated. The measured Raman and optical reflection spectra of the MoS2 monolayers vary considerably depending on the SiO2 thickness. The Raman peak intensity of the MoS2 monolayer on the substrate with an 80 nm thick SiO2 layer is four times larger than those in the cases of 40- and 130 nm thick SiO2 layers, indicating a significant difference in the absorption at the excitation wavelength.

Journal
Advanced Materials Interfaces
Date Published
Group (Lab)

Non-Abelian fermionization and fractional quantum Hall transitions

Cornell Affiliated Author(s)
Author
A. Hui
M. Mulligan
Eun-Ah Kim
Abstract

There has been a recent surge of interest in dualities relating theories of Chern-Simons gauge fields coupled to either bosons or fermions within the condensed matter community, particularly in the context of topological insulators and the half-filled Landau level. Here, we study the application of one such duality to the long-standing problem of quantum Hall interplateaux transitions.

Journal
Physical Review B
Date Published
Group (Lab)