Linjun Li

Zhejiang University | ZJU · Department of Optical Engineering

2D perovskites hold immense promise in optoelectronics due to their strongly bound electron-hole pairs (i.e., excitons). While exciton polaron from interplay between exciton and lattice has been established in 2D lead-based perovskites, the exciton nature and behavior in the emerging 2D tin-based perovskites remains unclear. By combining spin-resol...

Enhancement and active control of light-matter interactions at the atomic scale is important for developing next-generation nanophotonic and quantum optical devices. Here, we demonstrate electric control of both excitonic strong coupling and electroluminescence by integrating semiconductor monolayers into a nanometer gap of electrically driven nano...

The discovery of various primary ferroic phases in atomically-thin van der Waals crystals have created a new two-dimensional wonderland for exploring and manipulating exotic quantum phases. It may also bring technical breakthroughs in device applications, as evident by prototypical functionalities of giant tunneling magnetoresistance, gate-tunable...

Two-dimensional single crystal metals, in which the behavior of highly confined optical modes is intertwined with quantum phenomena, are highly sought after for next-generation technologies. Here, we report large area (>10⁴ μm²), single crystal two-dimensional gold flakes (2DGFs) with thicknesses down to a single nanometer level, employing an atomi...

The development of neuromorphic visual systems has recently gained momentum due to their potential in areas such as autonomous vehicles and robotics. However, current machine visual systems based on silicon technology usually contain photosensor arrays, format conversion, memory and processing modules. As a result, the redundant data shuttling betw...

Narrow bandgap materials have garnered significant attention within the field of broadband photodetection. However, the performance is impeded by diminished absorption near the bandgap, resulting in a rapid decline in photoresponsivity within the mid‐wave infrared (MWIR) and long‐wave infrared (LWIR) regions. Furthermore, they mostly worked in cryo...

2D charge density wave (CDW) materials receive much attention for high responsivity and broadband photodetection in recent years due to their collective electron transport and narrow bandgap. However, the high dark current density problem hinders their real application. Here, a sharp CDW transition in quasi-1D (TaSe4)2I is reported and applied for...

2D charge density wave (CDW) materials receive much attention for high responsivity and broadband photodetection in recent years due to their collective electron transport and narrow bandgap. However, the high dark current density problem hinders their real application. Here, a sharp CDW transition in quasi‐1D (TaSe 4 ) 2 I is reported and applied...

Ultrafast interfacing of electrical and optical signals at the nanoscale is highly desired for on-chip applications including optical interconnects and data processing devices. Here, we report electrically driven nanoscale optical sources based on metal-insulator-graphene tunnel junctions (MIG-TJs), featuring waveguided output with broadband spectr...

We report coordinated studies of flux pinning behavior and structural inhomogeneity in BaFe1.8Co0.2As2 single crystals with superconducting transition temperature at 24 K, in order to understand the flux pinning mechanism in the iron-based superconducting materials. Static and dynamic behavior of vortices are investigated by transport, bulk magneti...

Single crystals of BaFe2-xCoxAs2 synthesized by FeAs flux method were studied by variable temperature magnetic force microscopy (VT-MFM). The nominal Co doping concentrations range from underdoped region (x˜0.1) to optimum doped region (x˜0.2) of the superconducting dome. Sharp superconducting transitions (˜1K) indicate good sample quality. Individ...

Two-dimensional (2D) material heterostructures have attracted considerable attention owing to their interesting and novel physical properties, which expand the possibilities for future optoelectronic, photovoltaic, and nanoelectronic applications. A portable, fast, and deterministic transfer technique is highly needed for the fabrication of heteros...

2D ferroelectric β-InSe/graphene heterostructure was fabricated by mechanical exfoliation, and the carrier dynamics crossing the heterostructure interface has been systematically investigated by Raman, photoluminescence and transient absorption measurements. Due to the efficient interfacial photo excited electron transfer and photogating effect fro...

As basic building blocks for next-generation information technologies devices, high-quality p-n junctions based on van der Waals (vdW) materials have attracted widespread interest. Compared to traditional two-dimensional (2D) heterojunction diodes, the emerging homojunctions are more attractive owing to their intrinsic advantages, such as continuou...

2D Ruddlesden-Popper perovskites with chiral organic ligands are emerging as the promising candidates for circularly polarized light (CPL) detection, which has important applications in quantum communication and opto-spintronics. However, the...

Interface interactions in 2D vertically stacked heterostructures play an important role in optoelectronic applications, and photodetectors based on graphene/InSe heterostructures show promising performance nowadays. However, nonlinear optical property studies based on the graphene/InSe heterostructure are insufficient. Here, we fabricated a graphen...

Dynamic semiconductor diode generators (DDGs) offer a potential portable and miniaturized energy source, with the advantages of high current density, low internal impedance, and independence of the rectification circuit. However, the output voltage of DDGs is generally as low as 0.1–1 V, owing to energy loss during carrier transport and inefficient...

Recently, the spin entropy related to magnetic‐order transition, which contributes to thermoelectric power is attracting more and more attention. Here, it is demonstrated that the photo‐thermoelectric (PTE) response can be reshaped when Ca3Ru2O7 undergoes a meta‐magnetic phase (MMP) transition driven by both temperature and magnetic field. First, a...

Nanoparticle-on-mirror plasmonic nanocavities, capable of extreme optical confinement and enhancement, have triggered state-of-the-art progress in nanophotonics and development of applications in enhanced spectroscopies and molecular detection. However, the optical quality factor and thus performance of these nanoconstructs are undermined by the gr...

There is a rising prospective in harvesting energy from the environment, as in situ energy is required for the distributed sensors in the interconnected information society, among which the water flow energy is the most potential candidate as a clean and abundant mechanical source. However, for microscale and unordered movement of water, achieving...

Two-dimensional (2D) heterostructure materials have attracted increasing attention in ultrafast nonlinear optical applications due to their intriguing properties. Here, we fabricate a graphene/α-In2Se3 heterostructure by dropping α-In2Se3 dispersion onto the surface of few-layered graphene film and investigate its nonlinear optical responses. We sh...

Topological materials and topological phases have recently become a hot topic in condensed matter physics. In this work, we report an In-intercalated transition-metal dichalcogenide InxTaSe2 (named 112 system), a topological nodal-line semimetal in the presence of both charge density wave (CDW) and superconductivity. In the x = 0.58 sample, the 2×3...

There is a rising prospective in harvesting energy from water droplets, as microscale energy is required for the distributed sensors in the interconnected human society. However, achieving a sustainable direct-current generating device from water flow is rarely reported, and the quantum polarization principle of the water molecular remains uncovere...

Topological materials and topological phases have recently become a hot topic in condensed matter physics. In this work, we report a topological nodal-line semimetal InxTaSe2, in the presence of both charge density wave (CDW) and superconductivity. In the x = 0.58 samples, the 2 * /3 commensurate CDW (CCDW) and the 2 * 2 CCDW are observed below 116...

Optical microfibers drawn from conventional fibers have attracted considerable interests and have found many novel applications. Here, we review recent advances in ultrafast fiber lasers based on optical microfibers. Starting with characteristics and fabrication of optical microfibers, which are closely related to ultrafast fiber lasers, we show th...

Controllability of collective electron states has been a long-sought scientific and technological goal and promises development of new devices. Herein, we investigate the tuning of charge density wave (CDW) in 1T-TaS2 via a 2D van der Waals heterostructure of 1T-TaS2/BP. Unusual gate-dependent conductance oscillations were observed in 1T-TaS2 nano-...

Spatially tailored pseudo-magnetic fields (PMFs) can give rise to pseudo-Landau levels and the valley Hall effect in graphene. At an experimental level, it is highly challenging to create the specific strain texture that can generate PMFs over large areas. Here, we report that superposing graphene on multilayer black phosphorus creates shear-strain...

The superconductor to insulator transition(SIT) has been intensively studied in thin-film superconductors for a few decades by tuning their thickness,disorder or external magnetic field.It is now established that, when the normal-state conductance is high, superconductivity systematically gives way to an anomalous quantum metallic state(AQM).In hig...

TaSe$_2$ has several different polytypes and abundant physical properties such as superconductivity and charge density waves (CDW), which had been investigated in the past few decades. However, there is no report on the physical properties of 4$Ha$ polytype up to now. Here we report the crystal growth and discovery of superconductivity in tantalum...

TaSe$_2$ has several different polytypes and abundant physical properties such as superconductivity and charge density waves (CDW), which had been investigated in the past few decades. However, there is no report on the physical properties of 4$Ha$ polytype up to now. Here we report the crystal growth and discovery of superconductivity in the tanta...

2D materials are known for their highly susceptible to environmental influence. Here we show the influence of different substrates to the exciton/trion related bandgap engineering of two typical materials, MoS2 and WS2 nanosheets.

Atomically thin molybdenum disulfide (MoS2), a direct-band-gap semiconductor, is promising for applications in electronics and optoelectronics but the scalable synthesis of highly-crystalline film remains challenging. Here we report the successful epitaxial growth of a continuous, uniform, highly-crystalline monolayer MoS2 film on hexagonal boron n...

We report the fast growth of high-quality millimeter-size monolayer MoSe2 crystals on molten glass using an ambient pressure CVD system. We found that the isotropic surface of molten glass suppresses nucleation events and greatly improves the growth of large crystalline domains. Triangular monolayer MoSe2 crystals with sizes reaching ∼2.5 mm, and w...

The fabrication of crystalline 2D conjugated polymers with well-defined repeating units and in-built porosity presents a significant challenge to synthetic chemists. Yet they present an appealing target because of their desirable physical and electronic properties. Here we report the preparation of a 2D conjugated aromatic polymer synthesized via C...

We report the fast growth of high-quality millimeter-size monolayer molybdenum selenide (MoSe2) crystals on molten soda-lime-silica glass using an ambient pressure CVD system. We found that the isotropic surface of molten glass suppresses nucleation events and greatly improves the growth of large crystalline domains. Triangular monolayer MoSe2 crys...

Exhibiting thickness-dependent change in the critical temperature (T c) for the onset of superconductivity, Mo2C has emerged as an important new member in the family of two-dimensional atomic crystals. Controllable growth in terms of morphology and thickness is necessary to elucidate its intrinsic properties at the 2D limit. Here we demonstrate the...

Layered transition metal dichalcogenides (TMDs) provide an ideal platform for exploring the effects of dimensionality on correlated electronic phases such as charge density wave (CDW) order. When TMDs are reduced in thickness to the 2-D limit, it is expected that the substrates will exert considerable influence on the electron states. Here we repor...

To understand the complex physics of a system with strong electron–electron interactions, the ideal is to control and monitor its properties while tuning an external electric field applied to the system (the electric-field effect). Indeed, complete electric-field control of many-body states in strongly correlated electron systems is fundamental to...

Intrinsic electrical and excitonic properties of monolayer transition-metal dichalcogenides can be revealed on CYTOP fluoropolymer substrates with greatly suppressed unintentional doping and dielectric screening. Ambipolar transport behavior is observed in monolayer WS2 by applying solid-state back gates. The excitonic properties of monolayer MoS2...

Systematic acsusceptibilitymeasurements have been performed to investigate the vortex dynamics in a BaFe1.9Ni0.1As2single crystal as a function of temperature, frequency, ac field amplitude, and dc magnetic field. The complex activation energyU(T,B,j) is derived in the framework of thermally activated flux creep theory and can be expressed in one s...

Intrinsic electrical and excitonic properties of monolayer transition metal dichalcogenides are studied on CYTOP fluoropolymer substrates with greatly suppressed unintentional doping and dielectric screening. Ambipolar transport behavior is observed in monolayer WS2 by applying solid states backdates. The excitonic properties of monolayer MoS2 and...

The chemical vapor deposition (CVD) of graphene on Cu has attracted much attention because of its industrial scalability. Herein, we report inductively coupled plasma-assisted CVD of epitaxially grown graphene on (111)-textured Cu film alloyed with a small amount of Ni, where large area high quality graphene film can be grown in less than 5 min at...

Pure electric field control of many-body states in strongly correlated electron systems is fundamental to the next generation of condensed matter research and devices1-3. The advent of two-dimensional (2D) materials made this possible due to the absence of dynamical screening in 2D and the ultimate control over charge carrier density by gating. 1T-...

High-quality large-sized hexagoal WSe2 crystals can be grown on dielectric substrates using atmospheric chemical vapor deposition in the presence of hydrogen gas. These hexagonal crystals (lateral width >160 um) have a carrier mobility of 100 cm(2) V(-1) s(-1) and a photoresponsivity of ≈1100 mA W(-1) , which is comparable to that of exfoliated fla...

Layer-by-layer-stacked chemical vapour deposition (CVD) graphene films find applications as transparent and conductive electrodes in solar cells, organic light-emitting diodes and touch panels. Common to lamellar-type systems with anisotropic electron delocalization, the plane-to-plane (vertical) conductivity in such systems is several orders lower...

K. P. Loh and co‐workers develop a method to synthesize wafer scale, high‐quality, fewlayer, hexagonal boron nitride (h‐BN) films. On page 731, they use a remotely discharged plasma beam source in high vacuum. Lithographic patterning of layer‐by‐layer stacked h‐BN and graphene films enables the fabrication of a (h‐BN‐G)n disk array, which can exhib...

Vertical integration of hexagonal boron nitride (h‐BN) and graphene for the fabrication of vertical field‐effect transistors or tunneling diodes has stimulated intense interest recently due to the enhanced performance offered by combining an ultrathin dielectric with a semi‐metallic system. Wafer scale fabrication and processing of these heterostru...

Parent compound of DyFeAsO was successfully synthesized by solid-state reaction under ambient pressure and superconductivity was induced by partial substitution of trivalent Dy³⁺ ions with tetravalent Th⁴⁺ in Dy1-xThx FeAsO. In the undoped parent compound, an anomaly in the resistivity appears around 140 K which corresponds to the structural phase...

The low magnetic field vortex patterns nucleation and evolution in a high-quality two-gap superconductor MgB2 single crystal have been investigated by low-temperature scanning Hall probe microscopy. Large areas have been imaged with single-vortex resolution while changing systematically the thermodynamic parameters for field and temperature. The ob...

The structural properties of electron-doped compound BaFe1.8Ni0.2As2 are investigated by the synchrotron X-ray powder diffraction at high pressures ranged from 1 bar to 24.0 GPa at room temperature. The compound BaFe1.8Ni0.2As2 holds a tetragonal structure (space group I4/mmmI4/mmm) at ambient condition. Upon compression, the lattice parameter a fi...

Superconducting microstructures prepared by advanced nanofabrication methods can be used to address long-standing, fundamental questions concerning vortex motion, including vortex tunneling and the Aharonov-Casher effect of vortices. The observation of these phenomena requires devices with minimal disorder and the fewest dissipative normal electron...

The distribution of vortices at low magnetic fields in single crystals of multiband BaFe2-xNixAs2 (x = 0.1 and x = 0.16) superconductors is studied by Bitter decoration. Highly inhomogeneous vortex patterns, including vortex stripes and vortex clusters, are observed. The origin of these inhomogeneous vortex arrays is likely to be due to strong flux...

Transport properties of Ni-doped BaFe2-xNixAs2 single crystals have been investigated and the electronic phase diagram is derived. Tc reaches 20K at the optimal doping level x=0.10. There is a small doping range around x=0.055 where superconductivity and spin-density wave order coexist. The Hall coefficient shows a strong temperature dependence at...

We report measurements of structural phase transition of four parent compounds RFeAsO (R=La, Sm, Gd, and Tb) by means of low-temperature x-ray diffraction (XRD). Magnetic transition temperatures associated with Fe ions (TN1) are also determined from the temperature dependence of resistivity. As R is changed from La, through Sm and Gd, to Tb, both t...

We studied the electric field effect on superconductivity in atomically thin flakes of NbSe2 prepared by mechanical exfoliation. We found that these NbSe2 flakes are superconducting down to a thickness of a single unit cell consisting of two molecular layers of NbSe2 with an onset superconducting transition temperature (Tc) up to 2.5 K. We demonstr...

Temperature dependence of the upper critical magnetic field (Hc2) near Tc of 20 K in a BaFe1.9Ni0.1As2 single crystal is determined via magneto-resistance measurements, for the out-plane (H⊥ab) and in-plane (H || ab) directions in magnetic fields of up to 8 T. The upper critical fields at zero temperature estimated by the Werthamer-Helfand-Hohenber...

We report the realization of superconductivity by an isovalent doping with phosphorus in LaFeAsO. X-ray diffraction shows that, with the partial substitution of P for As, the Fe2As2 layers are squeezed while the La2O2 layers are stretched along the c-axis. Electrical resistance and magnetization measurements show emergence of bulk superconductivity...

We report Zn-doping effect in the parent and F-doped LaFeAsO oxy-arsenides. Slight Zn doping in LaFe1- xZnxAsO drastically suppresses the resistivity anomaly around 150 K associated with the antiferromagnetic (AFM) spin density wave (SDW) in the parent compound. The measurements of magnetic susceptibility and thermopower confirm further the effect...

We use inelastic neutron scattering to study magnetic excitations of the FeAs-based superconductor BaFe1.9Ni0.1As2 above and below its T_{c} (=20 K). In addition to gradually open a spin gap at the in-plane antiferromagnetic ordering wave vector (1, 0, 0), the effect of superconductivity is to form a three-dimensional resonance with clear dispersio...

There have been many studies on superconducting properties in two dimensional films. However, a detailed study of superconducting properties in the two-dimensional limit when crystallinity is still retained, which will allow the probing of band dependent superconductivity in 2D, has not been performed. Due to concerns over defects in ultra thin fil...

We use neutron spectroscopy to determine the nature of the magnetic excitations in superconducting BaFe$_{1.9}$Ni$_{0.1}$As$_{2}$ ($T_{c}=20$ K). Above $T_{c}$ the excitations are gapless and centered at the commensurate antiferromagnetic wave vector of the parent compound, while the intensity exhibits a sinusoidal modulation along the c-axis. As t...

A series of Th and F co-doped superconductors Sm1–xThxFeAsO1–yFy are synthesized and the variation of superconductivity with the doping level is investigated. At the fixed Th doping level x = 0.1, the superconducting transition temperature Tc increases monotonically with F content, and finally Tc reaches a maximum of about 55K around y = 0.1, and s...