High-throughput identification of functional regulatory SNPs in systemic lupus erythematosus.

Genome-wide association studies implicate multiple loci in risk for systemic lupus erythematosus (SLE), but few contain exonic variants, rendering systematic identification of non-coding variants essential to decoding SLE genetics. We utilized SNP-seq and bioinformatic enrichment to interrogate 2180 single-nucleotide polymorphisms (SNPs) from 87 SLE risk loci for potential binding of transcription factors and related proteins from B cells. 52 SNPs that passed initial screening were tested by electrophoretic mobility shift and luciferase reporter assays. To validate the approach, we studied rs2297550 in detail, finding that the risk allele enhanced binding to the transcription factor Ikaros (IKZF1), thereby modulating expression of IKBKE. Correspondingly, primary cells from genotyped healthy donors bearing the risk allele expressed higher levels of the interferon / NF-κB regulator IKKϵ. Together, these findings define a set of likely functional non-coding lupus risk variants and identify a new regulatory pathway involving rs2297550, Ikaros, and IKKϵ implicated by human genetics in risk for SLE.

Identification of a regulatory pathway governing TRAF1 via an arthritis-associated non-coding variant.

TRAF1/C5 was among the first loci shown to confer risk for inflammatory arthritis in the absence of an associated coding variant, but its genetic mechanism remains undefined. Using Immunochip data from 3,939 patients with juvenile idiopathic arthritis (JIA) and 14,412 control individuals, we identified 132 plausible common non-coding variants, reduced serially by single-nucleotide polymorphism sequencing (SNP-seq), electrophoretic mobility shift, and luciferase studies to the single variant rs7034653 in the third intron of TRAF1. Genetically manipulated experimental cells and primary monocytes from genotyped donors establish that the risk G allele reduces binding of Fos-related antigen 2 (FRA2), encoded by FOSL2, resulting in reduced TRAF1 expression and enhanced tumor necrosis factor (TNF) production. Conditioning on this JIA variant eliminated attributable risk for rheumatoid arthritis, implicating a mechanism shared across the arthritis spectrum. These findings reveal that rs7034653, FRA2, and TRAF1 mediate a pathway through which a non-coding functional variant drives risk of inflammatory arthritis in children and adults.

Exciton-Dominated Ultrafast Optical Response in Atomically Thin PtSe2.

Strongly bound excitons are a characteristic hallmark of 2D semiconductors, enabling unique light-matter interactions and novel optical applications. Platinum diselenide (PtSe2 ) is an emerging 2D material with outstanding optical and electrical properties and excellent air stability. Bulk PtSe2 is a semimetal, but its atomically thin form shows a semiconducting phase with the appearance of a band-gap, making one expect strongly bound 2D excitons. However, the excitons in PtSe2 have been barely studied, either experimentally or theoretically. Here, the authors directly observe and theoretically confirm excitons and their ultrafast dynamics in mono-, bi-, and tri-layer PtSe2 single crystals. Steady-state optical microscopy reveals exciton absorption resonances and their thickness dependence, confirmed by first-principles calculations. Ultrafast transient absorption microscopy finds that the exciton dominates the transient broadband response, resulting from strong exciton bleaching and renormalized band-gap-induced exciton shifting. The overall transient spectrum redshifts with increasing thickness as the shrinking band-gap redshifts the exciton resonance. This study provides novel insights into exciton photophysics in platinum dichalcogenides.

Ultrafast Auger process in few-layer PtSe2.

Enhanced many-body interactions due to strong Coulomb interactions and quantum confinement are one of the most prominent features of two-dimensional systems. The Auger process is a representative many-body interaction typically observed in two-dimensional semiconductors, determining important physical properties of materials, such as carrier lifetime, photoconductivity, and emission quantum yield. Recently, platinum dichalcogenides, represented by PtSe2 and PtS2, have attracted great attention due to their superior air stability, thickness-dependent semimetal-to-semiconductor transition, and exotic magnetic characteristics. However, the Auger process in platinum dichalcogenides has not been investigated to date. Here, we utilized ultrafast optical-pump terahertz-probe spectroscopy to explore carrier dynamics in few-layer semiconducting PtSe2. Most of the excited carriers are trapped by defects within ∼10 ps after excitation due to high defect density. We overcome this challenge by raising the excitation intensity to saturate trap sites with carriers, and observed a many-body process involving the carriers that survived the rapid trapping. This process is not band-to-band Auger recombination, but rather defect-assisted Auger recombination in which free carriers interact with trapped carriers at defects. Theoretical simulations show that this three-body Auger process can be approximated as bimolecular recombination at the rate of ∼3.3 × 10-3 cm2 s-1. This work provides insights into the interplay between ultrafast many-body processes and defects in two-dimensional semiconductors.

Ultrafast relaxation dynamics in bimetallic plasmonic catalysts.

Combining a plasmonic metal, such as gold, with other popular catalysts, such as Ni or Pt, can extend its benefits to many energy-extensive reactions catalyzed by those metals. The efficiency of a plasmon-enhanced catalytic reaction is mainly determined by the light absorption cross section and the photoexcited charge carrier relaxation dynamics of the nanoparticles. We have investigated the charge carrier relaxation dynamics of gold/nickel (Au/Ni) and gold/platinum (Au/Pt) bimetallic nanoparticles. We found that the addition of Ni or Pt to gold can reduce light absorption in gold nanoparticles. However, electron-phonon coupling rates of Au/Ni and Au/Pt nanoparticles are significantly faster than that of pure Au nanoparticles. This is due to the fact that both Ni and Pt possess significantly larger electron-phonon coupling constants and higher densities of states near the Fermi level in comparison with Au. Additionally, the phonon-phonon coupling rate of bimetallic Au/Pt and Au/Ni nanoparticles was significantly different from that of pure gold nanoparticles, due to the acoustic impedance mismatch at the nanoparticle/substrate interface. Our findings provide important insights into the rational design of bimetallic plasmonic catalysts.

Light Polarization-Controlled Conversion of Ultrafast Coherent-Incoherent Exciton Dynamics in Few-Layer ReS2.

Coherent light-matter interaction can transiently modulate the quantum states of matter under nonresonant laser excitation. This phenomenon, called the optical Stark effect, is one of the promising candidates for realizing ultrafast optical switches. However, the ultrafast modulations induced by the coherent light-matter interactions usually involve unwanted incoherent responses, significantly reducing the overall operation speed. Here, by using ultrafast pump-probe spectroscopy, we suppress the incoherent response and modulate the coherent-to-incoherent ratio in the two-dimensional semiconductor ReS2. We selectively convert the coherent and incoherent responses of an anisotropic exciton state by solely using photon polarizations, improving the control ratio by 3 orders of magnitude. The efficient modulation was enabled by transient superpositions of differential spectra from two nondegenerate exciton states due to the light polarization dependencies. This work provides a valuable contribution toward realizing ideal ultrafast optical switches.

Generation, transport and detection of valley-locked spin photocurrent in WSe2-graphene-Bi2Se3 heterostructures.

Quantum optoelectronic devices capable of isolating a target degree of freedom (DoF) from other DoFs have allowed for new applications in modern information technology. Many works on solid-state spintronics have focused on methods to disentangle the spin DoF from the charge DoF1, yet many related issues remain unresolved. Although the recent advent of atomically thin transition metal dichalcogenides (TMDs) has enabled the use of valley pseudospin as an alternative DoF2,3, it is nontrivial to separate the spin DoF from the valley DoF since the time-reversal valley DoF is intrinsically locked with the spin DoF4. Here, we demonstrate lateral TMD-graphene-topological insulator hetero-devices with the possibility of such a DoF-selective measurement. We generate the valley-locked spin DoF via a circular photogalvanic effect in an electric-double-layer WSe2 transistor. The valley-locked spin photocarriers then diffuse in a submicrometre-long graphene layer, and the spin DoF is measured separately in the topological insulator via non-local electrical detection using the characteristic spin-momentum locking. Operating at room temperature, our integrated devices exhibit a non-local spin polarization degree of higher than 0.5, providing the potential for coupled opto-spin-valleytronic applications that independently exploit the valley and spin DoFs.

Publisher Correction: Ultrafast quantum beats of anisotropic excitons in atomically thin ReS2.

In the originally published HTML and PDF versions of this article, Figs. 3g and 4d contained typesetting errors affecting the way the data points were displayed. This has now been corrected in the HTML and PDF versions.

Anti-proliferative effect of Zea mays L. cob extract on rat C6 glioma cells through regulation of glycolysis, mitochondrial ROS, and apoptosis.

Gliomas are one of the most common types of primary brain tumors, characterized by rapid proliferation and infiltration into normal brain tissue. Corncob is the most plentiful byproducts of Zea mays L., of which anti-cancer effect has not been reported. Therefore, we aimed to examine the anti-proliferative effect of a high-pressure hot-water extract of corncob on glioma cells and elucidated the underlying mechanism. The high-pressure hot-water corncob extract contained approximately 94.8 mg/g and 1.82 µg/g of total phenol and catechin, respectively. Glioma cell treated with different concentrations of high-pressure hot-water corncob extract was shown to be suppressed in growth during three days of culture. In parallel, corncob extract reduced the glioma cell viability and induced cell cycle arrest in G0/G1 phase by upregulating the expression level of cyclin-dependent kinase inhibitor p21. Decreased proliferation and viability in glioma cells treated with corncob extract can be attributed to reduced reactive oxygen species (ROS), antiapoptotic Bcl-2 protein, and a lactate transporter monocarboxylate transporter 1 of which levels are higher than those in normal cells. Based on its inhibitory effects on proliferation and viability of C6 glioma cells, a high-pressure hot-water corncob extract has the potential to be used for glioma treatment.

Control over Electron-Phonon Interaction by Dirac Plasmon Engineering in the Bi2Se3 Topological Insulator.

Understanding the mutual interaction between electronic excitations and lattice vibrations is key for understanding electronic transport and optoelectronic phenomena. Dynamic manipulation of such interaction is elusive because it requires varying the material composition on the atomic level. In turn, recent studies on topological insulators (TIs) have revealed the coexistence of a strong phonon resonance and topologically protected Dirac plasmon, both in the terahertz (THz) frequency range. Here, using these intrinsic characteristics of TIs, we demonstrate a new methodology for controlling electron-phonon interaction by lithographically engineered Dirac surface plasmons in the Bi2Se3 TI. Through a series of time-domain and time-resolved ultrafast THz measurements, we show that, when the Dirac plasmon energy is less than the TI phonon energy, the electron-phonon coupling is trivial, exhibiting phonon broadening associated with Landau damping. In contrast, when the Dirac plasmon energy exceeds that of the phonon resonance, we observe suppressed electron-phonon interaction leading to unexpected phonon stiffening. Time-dependent analysis of the Dirac plasmon behavior, phonon broadening, and phonon stiffening reveals a transition between the distinct dynamics corresponding to the two regimes as the Dirac plasmon resonance moves across the TI phonon resonance, which demonstrates the capability of Dirac plasmon control. Our results suggest that the engineering of Dirac plasmons provides a new alternative for controlling the dynamic interaction between Dirac carriers and phonons.

Ultrafast quantum beats of anisotropic excitons in atomically thin ReS2.

Quantum beats, periodic oscillations arising from coherent superposition states, have enabled exploration of novel coherent phenomena. Originating from strong Coulomb interactions and reduced dielectric screening, two-dimensional transition metal dichalcogenides exhibit strongly bound excitons either in a single structure or hetero-counterpart; however, quantum coherence between excitons is barely known to date. Here we observe exciton quantum beats in atomically thin ReS2 and further modulate the intensity of the quantum beats signal. Surprisingly, linearly polarized excitons behave like a coherently coupled three-level system exhibiting quantum beats, even though they exhibit anisotropic exciton orientations and optical selection rules. Theoretical studies are also provided to clarify that the observed quantum beats originate from pure quantum coherence, not from classical interference. Furthermore, we modulate on/off quantum beats only by laser polarization. This work provides an ideal laboratory toward polarization-controlled exciton quantum beats in two-dimensional materials.

Selectively tunable optical Stark effect of anisotropic excitons in atomically thin ReS2.

The optical Stark effect is a coherent light-matter interaction describing the modification of quantum states by non-resonant light illumination in atoms, solids and nanostructures. Researchers have strived to utilize this effect to control exciton states, aiming to realize ultra-high-speed optical switches and modulators. However, most studies have focused on the optical Stark effect of only the lowest exciton state due to lack of energy selectivity, resulting in low degree-of-freedom devices. Here, by applying a linearly polarized laser pulse to few-layer ReS2, where reduced symmetry leads to strong in-plane anisotropy of excitons, we control the optical Stark shift of two energetically separated exciton states. Especially, we selectively tune the Stark effect of an individual state with varying light polarization. This is possible because each state has a completely distinct dependence on light polarization due to different excitonic transition dipole moments. Our finding provides a methodology for energy-selective control of exciton states.

1s-intraexcitonic dynamics in monolayer MoS2 probed by ultrafast mid-infrared spectroscopy.

The 1s exciton--the ground state of a bound electron-hole pair--is central to understanding the photoresponse of monolayer transition metal dichalcogenides. Above the 1s exciton, recent visible and near-infrared investigations have revealed that the excited excitons are much richer, exhibiting a series of Rydberg-like states. A natural question is then how the internal excitonic transitions are interrelated on photoexcitation. Accessing these intraexcitonic transitions, however, demands a fundamentally different experimental tool capable of probing optical transitions from 1s 'bright' to np 'dark' states. Here we employ ultrafast mid-infrared spectroscopy to explore the 1s intraexcitonic transitions in monolayer MoS2. We observed twofold 1s→3p intraexcitonic transitions within the A and B excitons and 1s→2p transition between the A and B excitons. Our results revealed that it takes about 0.7 ps for the 1s A exciton to reach quasi-equilibrium; a characteristic time that is associated with a rapid population transfer from the 1s B exciton, providing rich characteristics of many-body exciton dynamics in two-dimensional materials.

Ultra-high modulation depth exceeding 2,400% in optically controlled topological surface plasmons.

Modulating light via coherent charge oscillations in solids is the subject of intense research topics in opto-plasmonics. Although a variety of methods are proposed to increase such modulation efficiency, one central challenge is to achieve a high modulation depth (defined by a ratio of extinction with/without light) under small photon-flux injection, which becomes a fundamental trade-off issue both in metals and semiconductors. Here, by fabricating simple micro-ribbon arrays of topological insulator Bi2Se3, we report an unprecedentedly large modulation depth of 2,400% at 1.5 THz with very low optical fluence of 45 µJ cm(-2). This was possible, first because the extinction spectrum is nearly zero due to the Fano-like plasmon-phonon-destructive interference, thereby contributing an extremely small denominator to the extinction ratio. Second, the numerator of the extinction ratio is markedly increased due to the photoinduced formation of massive two-dimensional electron gas below the topological surface states, which is another contributor to the ultra-high modulation depth.

Controllable synthesis of molybdenum tungsten disulfide alloy for vertically composition-controlled multilayer.

The effective synthesis of two-dimensional transition metal dichalcogenides alloy is essential for successful application in electronic and optical devices based on a tunable band gap. Here we show a synthesis process for Mo1-xWxS2 alloy using sulfurization of super-cycle atomic layer deposition Mo1-xWxOy. Various spectroscopic and microscopic results indicate that the synthesized Mo1-xWxS2 alloys have complete mixing of Mo and W atoms and tunable band gap by systematically controlled composition and layer number. Based on this, we synthesize a vertically composition-controlled (VCC) Mo1-xWxS2 multilayer using five continuous super-cycles with different cycle ratios for each super-cycle. Angle-resolved X-ray photoemission spectroscopy, Raman and ultraviolet-visible spectrophotometer results reveal that a VCC Mo1-xWxS2 multilayer has different vertical composition and broadband light absorption with strong interlayer coupling within a VCC Mo1-xWxS2 multilayer. Further, we demonstrate that a VCC Mo1-xWxS2 multilayer photodetector generates three to four times greater photocurrent than MoS2- and WS2-based devices, owing to the broadband light absorption.

Ultrafast biexciton spectroscopy in semiconductor quantum dots: evidence for early emergence of multiple-exciton generation.

Understanding multiple-exciton generation (MEG) in quantum dots (QDs) requires in-depth measurements of transient exciton dynamics. Because MEG typically faces competing ultrafast energy-loss intra-band relaxation, it is of central importance to investigate the emerging time-scale of the MEG kinetics. Here, we present ultrafast spectroscopic measurements of the MEG in PbS QDs via probing the ground-state biexciton transients. Specifically, we directly compare the biexciton spectra with the single-exciton ones before and after the intra-band relaxation. Early emergence of MEG is evidenced by observing transient Stark shift and quasi-instantaneous linewidth broadening, both of which take place before the intra-band relaxation. Photon-density-dependent study shows that the broadened biexciton linewidth strongly depends on the MEG-induced extra-exciton generation. Long after the intra-band relaxation, the biexciton broadening is small and the single-exciton state filling is dominant.