6 research outputs found
Monolayer 1T-NbSe2 as a 2D-correlated magnetic insulator
Monolayer group V transition metal dichalcogenides in their 1T phase have recently emerged as a platform to
investigate rich phases of matter, such as spin liquid and ferromagnetism, resulting from strong electron correla-
tions. Newly emerging 1T-NbSe2 has inspired theoretical investigations predicting collective phenomena such as
charge transfer gap and ferromagnetism in two dimensions; however, the experimental evidence is still lacking.
Here, by controlling the molecular beam epitaxy growth parameters, we demonstrate the successful growth of
high-quality single-phase 1T-NbSe2. By combining scanning tunneling microscopy/spectroscopy and ab initio
calculations, we show that this system is a charge transfer insulator with the upper Hubbard band located above
the valence band maximum. To demonstrate the electron correlation resulted magnetic property, we create a
vertical 1T/2H NbSe2 heterostructure, and we find unambiguous evidence of exchange interactions between the
localized magnetic moments in 1T phase and the metallic/superconducting phase exemplified by Kondo reso-
nances and Yu-Shiba-Rusinov–like bound states.Center for Dynamics and Control of Materials: an NSF MRSEC under cooperative agreement
no. DMR-1720595. J.L. and F.G. were supported by the Robert A. Welch Foundation under
award number F-1990-20190330. Other supports were from NSF grant nos. DMR-1808751 and
DMR-1949701, the Welch Foundation F-1672, F-1814, and the National Natural Science
Foundation of China (grant nos. 11774268 and 11974012).Center for Dynamics and Control of Material
Atomistic Control in Molecular Beam Epitaxy Growth of Intrinsic Magnetic Topological Insulator MnBi2Te4
Intrinsic magnetic topological insulators have emerged as a promising
platform to study the interplay between topological surface states and
ferromagnetism. This unique interplay can give rise to a variety of exotic
quantum phenomena, including the quantum anomalous Hall effect and axion
insulating states. Here, utilizing molecular beam epitaxy (MBE), we present a
comprehensive study of the growth of high-quality MnBi2Te4 thin films on Si
(111), epitaxial graphene, and highly ordered pyrolytic graphite substrates. By
combining a suite of in-situ characterization techniques, we obtain critical
insights into the atomic-level control of MnBi2Te4 epitaxial growth. First, we
extract the free energy landscape for the epitaxial relationship as a function
of the in-plane angular distribution. Then, by employing an optimized
layer-by-layer growth, we determine the chemical potential and Dirac point of
the thin film at different thicknesses. Overall, these results establish a
foundation for understanding the growth dynamics of MnBi2Te4 and pave the way
for the future applications of MBE in emerging topological quantum materials.Comment: 20 pages, 4 figure
Recommended from our members
Confined monolayer Ag as a large gap 2D semiconductor and its momentum resolved excited states
2D materials have intriguing quantum phenomena that are distinctively different
from their bulk counterparts. Recently, epitaxially synthesized wafer-scale 2D metals,
composed of elemental atoms, are attracting attention not only for their potential
applications but also for exotic quantum effects such as superconductivity. By mapping
momentum-resolved electronic states using time-resolved and angle-resolved photoemission
spectroscopy (ARPES), we reveal that monolayer Ag confined between bilayer graphene and
SiC is a large gap (> 1 eV) 2D semiconductor, consistent with GW-corrected density
functional theory. The measured valence band dispersion matches the DFT-GW
quasiparticle band. However, the conduction band dispersion shows an anomalously large
effective mass of 2.4 m0. Possible mechanisms for this large enhancement in the “apparent
mass” are discussed.This work was primarily supported by the National Science Foundation through the Center for
Dynamics and Control of Materials: an NSF MRSEC under Cooperative Agreement No. DMR-
1720595. Other supports include NSF Grant Nos. DMR-1808751, and the Welch Foundation F-
1672. Support for synthesis comes from The Penn State Center for Nanoscale Science (NSF
Grant DMR-2011839) and the Penn State 2DCC-MIP (NSF DMR-1539916).Center for Dynamics and Control of Material
Visualizing the interplay of Dirac mass gap and magnetism at nanoscale in intrinsic magnetic topological insulators
In intrinsic magnetic topological insulators, Dirac surface state gaps are
prerequisites for quantum anomalous Hall and axion insulating states.
Unambiguous experimental identification of these gaps has proved to be a
challenge, however. Here we use molecular beam epitaxy to grow intrinsic
MnBi2Te4 thin films. Using scanning tunneling microscopy/spectroscopy, we
directly visualize the Dirac mass gap and its disappearance below and above the
magnetic order temperature. We further reveal the interplay of Dirac mass gaps
and local magnetic defects. We find that in high defect regions, the Dirac mass
gap collapses. Ab initio and coupled Dirac cone model calculations provide
insight into the microscopic origin of the correlation between defect density
and spatial gap variations. This work provides unambiguous identification of
the Dirac mass gap in MnBi2Te4, and by revealing the microscopic origin of its
gap variation, establishes a material design principle for realizing exotic
states in intrinsic magnetic topological insulators.Comment: 18 pages, 4 figure
Factors for achieving target serum uric acid levels after initiating urate-lowering therapy in patients with gout: results from the ULTRA registry
Abstract Achieving target serum uric acid (SUA) levels is important in gout management. Guidelines recommend lowering SUA levels to < 6 mg/dL; however, many patients fail to reach this target, even with uric acid-lowering therapy (ULT). This study investigated clinical characteristics of target SUA achievers among Korean patients with gout. This study used data from the ULTRA registry, a nationwide inception cohort established in September 2021 that enrolls patients with gout who initiate ULT. Demographic, clinical, and laboratory data were collected at baseline; the 6-month follow-up. Patients were divided into two groups: target achievers (SUA level < 6 mg/dL at 6 months) and non-achievers. The mean participant (N = 117) age was 56.1 years, and 88.0% were male. At 6 months, 83 patients (70.9%) reached target SUA levels. Target achievers had better drug adherence (≥ 80%) to ULT (97.6% vs. 76.5%; p < 0.01) than non-achievers. Target non-achievers had a higher percentage of a family history of gout (32.4% vs. 10.8%; p < 0.01) and less antihypertensive agent use (38.2% vs. 59.0%; p = 0.03) than target achievers. Multivariate regression analysis revealed that good adherence to ULT, the absence of a family history of gout, and antihypertensive agent use were key factors associated with achieving target SUA levels at 6 months
Recommended from our members
Tuning commensurability in twisted van der Waals bilayers
Moiré superlattices based on van der Waals bilayers1-4 created at small twist angles lead to a long wavelength pattern with approximate translational symmetry. At large twist angles (θt), moiré patterns are, in general, incommensurate except for a few discrete angles. Here we show that large-angle twisted bilayers offer distinctly different platforms. More specifically, by using twisted tungsten diselenide bilayers, we create the incommensurate dodecagon quasicrystals at θt = 30° and the commensurate moiré crystals at θt = 21.8° and 38.2°. Valley-resolved scanning tunnelling spectroscopy shows disparate behaviours between moiré crystals (with translational symmetry) and quasicrystals (with broken translational symmetry). In particular, the K valley shows rich electronic structures exemplified by the formation of mini-gaps near the valence band maximum. These discoveries demonstrate that bilayers with large twist angles offer a design platform to explore moiré physics beyond those formed with small twist angles