199 research outputs found
Stacking-dependent electronic structure of trilayer graphene resolved by nanospot angle-resolved photoemission spectroscopy
The crystallographic stacking order in multilayer graphene plays an important
role in determining its electronic structure. In trilayer graphene,
rhombohedral stacking (ABC) is particularly intriguing, exhibiting a flat band
with an electric-field tunable band gap. Such electronic structure is distinct
from simple hexagonal stacking (AAA) or typical Bernal stacking (ABA), and is
promising for nanoscale electronics, optoelectronics applications. So far clean
experimental electronic spectra on the first two stackings are missing because
the samples are usually too small in size (um or nm scale) to be resolved by
conventional angle-resolved photoemission spectroscopy (ARPES). Here by using
ARPES with nanospot beam size (NanoARPES), we provide direct experimental
evidence for the coexistence of three different stackings of trilayer graphene
and reveal their distinctive electronic structures directly. By fitting the
experimental data, we provide important experimental band parameters for
describing the electronic structure of trilayer graphene with different
stackings
Vertical Ferroelectricity in Van der Waals Materials: Models and Devices
Ferroelectricity has a wide range of applications in functional electronics
and is extremely important for the development of next-generation information
storage technology, but it is difficult to achieve due to its special symmetry
requirements. In this letter, based on van derWaals stacking, a generic model
is proposed for realizing ferroelectric devices, where a freely movable center
layer is packaged in two fixed and symmetrically stacked layers. In this model,
the ferroelectric phase transition can be realized between the two equivalent
and eccentric ground stacking-states with opposite polarizations. By means of
first-principles calculations, taking the h-BN/h-BN/h-BN and h-BN/Graphene/h-BN
as feasible models, we carefully evaluate the magnitude of ferroelectricity.
The corresponding polarizations are estimated as 1.83 and 1.35 pC/m,
respectively, which are comparable to the sliding ferroelectricity. Such a new
tri-layer model of vertical ferroelectricity can be constructed by arbitrary
van derWaals semiconducting materials, and usually holds low switching barrier.
Optimized material combinations with remarkable polarization are highly
expectable to be discovered from the huge candidate set for future information
storage.Comment: 5 pages;4 figure
PTPRO-related CD8<sup>+</sup> T-cell signatures predict prognosis and immunotherapy response in patients with breast cancer
Background: Poor immunogenicity and extensive immunosuppressive T-cell infiltration in the tumor immune microenvironment (TIME) have been identified as potential barriers to immunotherapy success in “immune-cold” breast cancers. Thus, it is crucial to identify biomarkers that can predict immunotherapy efficacy. Protein tyrosine phosphatase receptor type O (PTPRO) regulates multiple kinases and pathways and has been implied to play a regulatory role in immune cell infiltration in various cancers. Methods: ESTIMATE and single-sample gene set enrichment analysis (ssGSEA) were performed to uncover the TIME landscape. The correlation analysis of PTPRO and immune infiltration was performed to characterize the immune features of PTPRO. Univariate and multivariate Cox analyses were applied to determine the prognostic value of various variables and construct the PTPRO-related CD8+ T-cell signatures (PTSs). The Kaplan–Meier curve and the receiver operating characteristic (ROC) curve were used to estimate the performance of PTS in assessing prognosis and immunotherapy response in multiple validation datasets. Results: High PTPRO expression was related to high infiltration levels of CD8+ T cells, as well as macrophages, activated dendritic cells (aDCs), tumor-infiltrating lymphocytes (TILs), and Th1 cells. Given the critical role of CD8+ T cells in the TIME, we focused on the impact of PTPRO expression on CD8+ T-cell infiltration. The prognostic PTS was then constructed using the TCGA training dataset. Further analysis showed that the PTS exhibited favorable prognostic performance in multiple validation datasets. Of note, the PTS could accurately predict the response to immune checkpoint inhibitors (ICIs). Conclusion: PTPRO significantly impacts CD8+ T-cell infiltration in breast cancer, suggesting a potential role of immunomodulation. PTPRO-based PTS provides a new immune cell paradigm for prognosis, which is valuable for immunotherapy decisions in cancer patients
Tunable Dirac Fermion Dynamics in Topological Insulators
Three-dimensional topological insulators are characterized by insulating bulk
state and metallic surface state involving Dirac fermions that behave as
massless relativistic particles. These Dirac fermions are responsible for
achieving a number of novel and exotic quantum phenomena in the topological
insulators and for their potential applications in spintronics and quantum
computations. It is thus essential to understand the electron dynamics of the
Dirac fermions, i.e., how they interact with other electrons, phonons and
disorders. Here we report super-high resolution angle-resolved photoemission
studies on the Dirac fermion dynamics in the prototypical Bi2(Te,Se)3
topological insulators. We have directly revealed signatures of the
electron-phonon coupling in these topological insulators and found that the
electron-disorder interaction is the dominant factor in the scattering process.
The Dirac fermion dynamics in Bi2(Te3-xSex) topological insulators can be tuned
by varying the composition, x, or by controlling the charge carriers. Our
findings provide crucial information in understanding the electron dynamics of
the Dirac fermions in topological insulators and in engineering their surface
state for fundamental studies and potential applications.Comment: 14 Pages, 4 Figure
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