Yaojia Wang

Integrated digital inverters based on two-dimensional anisotropic ReS2 field-effect transistors

Semiconducting two-dimensional transition metal dichalcogenides are emerging as top candidates for post-silicon electronics. While most of them exhibit isotropic behaviour, lowering the lattice symmetry could induce anisotropic properties, which are both scientifically interesting and potentially useful. Here we present atomically thin rhenium disulfide (ReS2) flakes with unique distorted 1T structure, which exhibit in-plane anisotropic properties. We fabricated monolayer and few-layer ReS2 field-effect transistors, which exhibit competitive performance with large current on/off ratios (∼107) and low subthreshold swings (100 mV per decade). The observed anisotropic ratio along two principle axes reaches 3.1, which is the highest among all known two-dimensional semiconducting materials. Furthermore, we successfully demonstrated an integrated digital inverter with good performance by utilizing two ReS2 anisotropic field-effect transistors, suggesting the promising implementation of large-scale two-dimensional logic circuits. Our results underscore the unique properties of two-dimensional semiconducting materials with low crystal symmetry for future electronic applications.

High responsivity phototransistors based on few-layer ReS2 for weak signal detection

Two-dimensional transition metal dichalcogenides are emerging with tremendous potential in many optoelectronic applications due to their strong light-matter interactions. To fully explore their potential in photoconductive detectors, high responsivity and weak signal detection are required. Here, we present high responsivity phototransistors based on few-layer rhenium disulfide (ReS2). Depending on the back gate voltage, source drain bias and incident optical light intensity, the maximum attainable photoresponsivity can reach as high as 88,600 A W-1, which is a record value compared to other two-dimensional materials with similar device structures and two orders of magnitude higher than that of monolayer MoS2. Such high photoresponsivity is attributed to the increased light absorption as well as the gain enhancement due to the existence of trap states in the few-layer ReS2 flakes. It further enables the detection of weak signals, as successfully demonstrated with weak light sources including a lighter and limited fluorescent lighting. Our studies underscore ReS2 as a promising material for future sensitive optoelectronic applications.

Raman vibrational spectra of bulk to monolayer ReS2 with lower symmetry

Lattice structure and symmetry of two-dimensional (2D) layered materials are of key importance to their fundamental mechanical, thermal, electronic and optical properties. Raman spectroscopy, as a convenient and nondestructive tool, however has its limitations on identifying all symmetry allowing Raman modes and determining the corresponding crystal structure of 2D layered materials with high symmetry like graphene and MoS2. Due to lower structural symmetry and extraordinary weak interlayer coupling of ReS2, we successfully identified all 18 first-order Raman active modes for bulk and monolayer ReS2. Without van der Waals (vdW) correction, our local density approximation (LDA) calculations successfully reproduce all the Raman modes. Our calculations also suggest no surface reconstruction effect and the absence of low frequency rigid-layer Raman modes below 100 cm-1. As a result, combining with Raman and LDA thus provides a general approach for studying the vibrational and structural properties of 2D layered materials with lower symmetry.

Gate-tunable negative longitudinal magnetoresistance in the predicted type-II Weyl semimetal WTe2

The progress in exploiting new electronic materials has been a major driving force in solid-state physics. As a new state of matter, a Weyl semimetal (WSM), in particular a type-II WSM, hosts Weyl fermions as emergent quasiparticles and may harbour novel electrical transport properties. Nevertheless, such a type-II WSM material has not been experimentally observed. In this work, by performing systematic magneto-transport studies on thin films of a predicted material candidate WTe2, we observe notable negative longitudinal magnetoresistance, which can be attributed to the chiral anomaly in WSM. This phenomenon also exhibits strong planar orientation dependence with the absence along the tungsten chains, consistent with the distinctive feature of a type-II WSM. By applying a gate voltage, we demonstrate that the Fermi energy can be in-situ tuned through the Weyl points via the electric field effect. Our results may open opportunities for implementing new electronic applications, such as field-effect chiral devices.

Gated tuned superconductivity and phonon softening in monolayer and bilayer MoS 2

Superconductors at the atomic two-dimensional limit are the focus of an enduring fascination in the condensed matter community. This is because, with reduced dimensions, the effects of disorders, fluctuations, and correlations in superconductors become particularly prominent at the atomic two-dimensional limit; thus such superconductors provide opportunities to tackle tough theoretical and experimental challenges. Here, based on the observation of ultrathin two-dimensional superconductivity in monolayer and bilayer molybdenum disulfide (MoS2) with electric-double-layer gating, we found that the critical sheet carrier density required to achieve superconductivity in a monolayer MoS2 flake can be as low as 0.55 × 1014 cm−2, which is much lower than those values in the bilayer and thicker cases in previous report and also our own observations. Further comparison of the phonon dispersion obtained by ab initio calculations indicated that the phonon softening of the acoustic modes around the M point plays a key role in the gate-induced superconductivity within the Bardeen–Cooper–Schrieffer theory framework. This result might help enrich the understanding of two-dimensional superconductivity with electric-double-layer gating.Superconductivity: Tunable superconductivity in two-dimensional materialsExperiments show that a softening of phonon modes aids gate-induced superconductivity in two-dimensional materials. As a material’s dimensions are reduced, the role of disorder and electronic correlations in defining the electronic properties become more prominent, and as the density of charge carriers is much lower, superconductivity is less likely to emerge. An international team of researchers led by Feng Mio and Baigeng Wang from Nanjing University and Harold Hwang from SLAC National Accelerator laboratory and Stanford University use an ionic liquid-based setup, which allows for high gate voltages to be applied, to demonstrate gate-induced superconductivity in monolayers and bilayers of a transition metal dichalcogenide. They show that a softening of the acoustic phonon modes allows for superconductivity to be realized in single layers with a lower carrier density than that needed in multilayers.

Gate-Induced Interfacial Superconductivity in 1T-SnSe2

Layered metal chalcogenide materials provide a versatile platform to investigate emergent phenomena and two-dimensional (2D) superconductivity at/near the atomically thin limit. In particular, gate-induced interfacial superconductivity realized by the use of an electric-double-layer transistor (EDLT) has greatly extended the capability to electrically induce superconductivity in oxides, nitrides, and transition metal chalcogenides and enable one to explore new physics, such as the Ising pairing mechanism. Exploiting gate-induced superconductivity in various materials can provide us with additional platforms to understand emergent interfacial superconductivity. Here, we report the discovery of gate-induced 2D superconductivity in layered 1T-SnSe2, a typical member of the main-group metal dichalcogenide (MDC) family, using an EDLT gating geometry. A superconducting transition temperature Tc ≈ 3.9 K was demonstrated at the EDL interface. The 2D nature of the superconductivity therein was further confirmed based on (1) a 2D Tinkham description of the angle-dependent upper critical field Bc2, (2) the existence of a quantum creep state as well as a large ratio of the coherence length to the thickness of superconductivity. Interestingly, the in-plane Bc2 approaching zero temperature was found to be 2-3 times higher than the Pauli limit, which might be related to an electric field-modulated spin-orbit interaction. Such results provide a new perspective to expand the material matrix available for gate-induced 2D superconductivity and the fundamental understanding of interfacial superconductivity.

Low-Temperature Eutectic Synthesis of PtTe2 with Weak Antilocalization and Controlled Layer Thinning

Metallic transition metal dichalcogenides (TMDs) have exhibited various exotic physical properties and hold the promise of novel optoelectronic and topological devices applications. However, the synthesis of metallic TMDs is based on gas-phase methods and requires high temperature condition. As an alternative to the gas-phase synthetic approach, lower temperature eutectic liquid-phase synthesis presents a very promising approach with the potential for larger-scale and controllable growth of high-quality thin metallic TMDs single crystals. Herein, we report the first realization of low-temperature eutectic liquid-phase synthesis of type-II Dirac semimetal PtTe2 single crystals with thickness ranging from 2 to 200 nm. The electrical measurement of synthesized PtTe2 reveals a record-high conductivity of as high as 3.3*106 S/m at room temperature. Besides, we experimentally identify the weak antilocalization behavior in the type-II Dirac semimetal PtTe2 for the first time. Furthermore, we develop a simple and general strategy to obtain atomically-thin PtTe2 crystal by thinning as-synthesized bulk samples, which can still retain highly crystalline and exhibits excellent electric conductivity. Our results of controllable and scalable low-temperature eutectic liquid-phase synthesis and layer-by-layer thinning of high-quality thin PtTe2 single crystals offer a simple and general approach for obtaining different thickness metallic TMDs with high-melting point transition metal.

THU0281 Long-term prognosis and predictingfactors of chinese patients with systemic lupus erythematosus: a multi-center cohort study from cstar registry

Objectives To investigate the long-term outcomes, both mortality and damage, and related prognostic factors of patients with systemic lupus erythematosus (SLE) in the CSTAR (Chinese SLE Treatment and Research group) registry cohort. Methods All of the patients were enrolled from April 2009 to February 2010. They were followed up at clinic and were telephone interviewed at the endpoint. Demographic data, clinical manifestations, activity (SLEDAI-2K), damage scores (SLLIC/Damage Index), and medications were collected. Data were censored at the last clinic visit or telephone interview. Survival rates were studied by Kaplan-Meier method, and COX proportional hazard model was adopted to perform the analysis of predicting factors for mortality. Results A total of 2104 patients were recruited at baseline, and 1494 patients were successfully followed up. The cumulative 1, 3 and 5-year survival ratesfrom diagnosis were 99.0%, 98.1% and 97.1%. 78 patients died during follow-up, and the main death causes were infection (34.6%), active disease (26.9%), cardiovascular and cerebrovascular events (6.41%) and malignancy (5.13%). At entry, 247 patients presented with irreversible organ damage and it increased to 398 patients at the endpoint. The major accumulated organ damages were renal (25.9%), musculoskeletal (20.2%), neuropsychiatric (12.4%), and pulmonary (10.8%) damage. Cox regressionshowed that male, late onset age (≥50y), onset to diagnosis time ≥1 year, previous organ damage, renal involvement, pulmonary arterial hypertension, neuropsychiatric involvement, serositis and the number of involved organ systems ≥3predict for higher mortality. Conclusions Long-term survival rates have improved for Chinese SLE patients. Early diagnosis, preventing fromthe emerging systemic organ involvements and organ damagecould be the treating target for the management of SLE patients in China. Disclosure of Interest None declared

SAT0482 Clinical and Serological Features of Patients with Dermatomyositis Complicated by Spontaneous Pneumomediastinum

Background Interstitial lung disease (ILD) is a common complication and is associated with the prognosis of dermatomyositis (DM). The respiratory function deteriorate quickly and leads to poor prognoses in some individuals, a condition known as rapidly progressive ILD (RP-ILD). Some patients with DM associated RP-ILD present characteristic cutaneous rash of DM but have not clinically significant muscle weakness, a subgroup of DM designated as clinically amyopathic dermatomyositis (CADM) [1]. Recent studies have demonstrated that most patients with DM and RP-ILD are positive for anti-melanoma differentiation-associated gene 5 (MDA5). Spontaneous pneumomediastinum (PNM) is a rare but devastating illness in DM-ILD. Albeit that previous studies have revealed that some patients with DM and PNM have mild muscle involvement and are anti-MDA5 positive [2], the clinical and serological features of this severe entity have not been fully elucidated. Objectives To explore the clinical and serological features of patients with DM and PNM. Methods A total of 93 (68 classic DM and 25 CADM) patients were recruited. Anti-MDA5 antibodies were detected using ELISA [3]. Variables were compared between patients with and without PNM. Multivariate analysis was performed using a multivariate logistic regression model. The following variables were assessed as potential factors associated with spontaneous PNM in DM: presence of RP-ILD, DM subgroup (classic DM or CADM), presence of skin ulcers and presence of anti-MDA5 antibodies. Results A total of 11 patients (7 man and 4 women) developed PNM. Seven patients were diagnosed with CADM while 4 patients were diagnosed with classic DM. Despite being treated with the combination of glucocorticoids and immunosuppressants, during the follow-up period, 6 patients died of respiratory failure, with a varied interval after the occurrence of PNM ranged from 3 to 48 weeks. Compared with DM patients without PNM, DM patients with PNM had significantly higher frequencies of RP-ILD (63.6% vs 24.4%, P =0.01), anti-MDA5 antibodies (90.9% vs 52.4%, P =0.02), CADM diagnoses (63.6% vs 22.0%, P =0.007) and cutaneous ulcers (36.4% vs 10.2%, P =0.04), but significantly lower creatine kinase (CK) levels (58.5 vs 284 ng/ml, P =0.04). The logistic multivariate analysis indicated that cutaneous ulcer was the only independent risk factor for the occurrence of PNM in DM (OR =5.98, 95% CI 1.12–31.98, P=0.037). Conclusions Spontaneous PNM is a refractory complication and tends to occur in DM patients with RP-ILD, anti-MDA5 antibody, CADM diagnosis and low CK level, especially in patients with cutaneous ulcers. References Sato S, Kuwana M (2010) Clinically amyopathic dermatomyositis. Curr Opin Rheumatol 22:639-643. doi:10.1097/BOR.0b013e32833f1987 Le Goff B, Cherin P, Cantagrel A, Gayraud M, Hachulla E, Laborde F, Papo T, Sibilia J, Zabraniecki L, Ravaud P, Puechal X (2009) Pneumomediastinum in interstitial lung disease associated with dermatomyositis and polymyositis. Arthritis Rheum 61 (1):108-118. doi:10.1002/art.24372 Sato S, Hoshino K, Satoh T, Fujita T, Kawakami Y, Fujita T, Kuwana M (2009) RNA helicase encoded by melanoma differentiation-associated gene 5 is a major autoantigen in patients with clinically amyopathic dermatomyositis: Association with rapidly progressive ILD. Arthritis Rheum 60:2193-2200. doi:10.1002/art.24621 Disclosure of Interest None declared

Results of relaxation function theory for the NMR measurements in La2CuO4

Abstract The spin-lattice relaxation rates and the spin-echo decay rates for the two-dimensional Heisenberg model are interpreted in a framework of a self-consistent relaxation function theory. The results are compared with the experiments on La2CuO4 and the numerical simulations of quantum Monte Carlo method.