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Flat-band physics of Moiré superlattices, originally discovered in the celebrated twisted bilayer graphene, have recently been intensively explored in multilayer graphene systems that can be further controlled by electric field. In this work, we experimentally find the evidence of correlated insulators at half filling of the electron moiré band of twisted monolayer-trilayer graphene with a twist angle around 1.2 degrees. Van Hove singularity (VHS), manifested as enhanced resistance and zero Hall voltage, is observed to be distinct in conduction and valence flat bands. It also depends on the direction and magnitude of displacement fields, consistent with the asymmetric crystal structure. While the resistance ridges at VHS can be enhanced by magnetic fields, when they cross commensurate fillings of the moiré superlattice in the conduction band, the enhancement is so strong that signatures of correlated insulator appear, which may further develop into an energy gap depending on the correlation strength. At last, Fermi velocity derived from temperature coefficients of resistivity is compared between conduction and valence bands with different displacement fields. It is found that electronic correlation has a negative dependence on Fermi velocity, which in turn could be used to quantify the correlation strength.

Ionic liquid gating has proved to be effective in inducing emergent quantum phenomena such as superconductivity, ferromagnetism, and topological states. The electrostatic doping at two-dimensional interfaces relies on ionic motion, which thus is operated at sufficiently high temperature. Here, we report the in situ tuning of quantum phases by shining light on an ionic liquid-gated interface at cryogenic temperatures. The light illumination enables flexible switching of the quantum transition in monolayer WS2 from an insulator to a superconductor. In contrast to the prevailing picture of photoinduced carriers, we find that in the presence of a strong interfacial electric field conducting electrons could escape from the surface confinement by absorbing photons, mimicking the field emission. Such an optical tuning tool in conjunction with ionic liquid gating greatly facilitates continuous modulation of carrier densities and hence electronic phases, which would help to unveil novel quantum phenomena and device functionality in various materials.

In transition metal dichalcogenides (TMDs), Ising superconductivity with an antisymmetric spin texture on the Fermi surface has attracted wide interest due to the exotic pairing and topological properties. However, it is not clear whether the

Highly controlled electronic correlation in twisted graphene heterostructures has gained enormous research interests recently, encouraging exploration in a wide range of moiré superlattices beyond the celebrated twisted bilayer graphene. Here we characterize correlated states in an alternating twisted Bernal bilayer–monolayer–monolayer graphene of ∼ 1.74°, and find that both van Hove singularities and multiple correlated states are asymmetrically tuned by displacement fields. In particular, when one electron per moiré unit cell is occupied in the electron-side flat band, or the hole-side flat band (i.e., three holes per moiré unit cell), the correlated peaks are found to counterintuitively grow with heating and maximize around 20 K – a signature of Pomeranchuk effect. Our multilayer heterostructure opens more opportunities to engineer complicated systems for investigating correlated phenomena.

Superconducting magnetic shielding (SMS) is crucial for superconducting electronic devices such as superconducting quantum interference devices (SQUIDs). Current magnetic shielding devices suffer from high construction price, poor mobility, and flexibility. The MgB2 SMS with cryocooler could be the potential the solution. In this work, a hybrid physical–chemical vapor deposition system, which is capable of depositing on a long cylindrical surface, is demonstrated. A dense and robust MgB2 film has successfully been deposited on the inside wall of a Φ50 × 120 mm 304 stainless steel tube. A microscopic image indicated that the deposited MgB2 showed a dendritic structure with cracks on it. Sample with different B2H6 flow rates has been made, current result showed a better performance with higher B2H6 flow rate. However, safety issue should be taken into consideration as we further increase the B2H6 concentration. The sample deposited with 10 sccm 25% B2H6 showed the best performance so far with a TC of 34.4 K. A SQUID testing system specifically for high-temperature SQUID with MgB2 SMS with a liquid-helium-free cryogenic system has been design and under construction for the future researches.

With the development of weak magnetic detection methods, the sensors, like superconducting quantum interference device (SQUID), become more and more sensitive. The magnetic shielding takes a more important part in weak signal detection systems than before. Traditional magnetic shielding methods are expensive, not flexible, and hard to prevent the low-frequency magnetic field clearly. For the superconducting magnetic shield, the operating temperature of a low critical temperature superconducting magnetic shield has high demand on refrigerating system. The high critical temperature superconducting magnetic shielding would introduce thermal magnetic noise. Due to the excellent superconductive property, the medium-temperature superconductor MgB2 has a huge potential to build the magnetic shielding system. In this article, we fabricate an MgB2 superconducting magnetic shielding cup with Mg Liquid Infiltration method. The highest TC of the sample is 39.4 K. The highest JC is 10 6 A/cm 2 at 4.2 K. The shielding effect of the cup has been tested at axial dc weak magnetic field and the shielding factor exceeds 2000.

Experiments reveal a host of unusual magnetic behaviors in the recently discovered layered magnetic topological insulator MnBi${}_{2}$Te${}_{4}$, paving the way for further study of its quantum properties.

Electronic correlation in a flat band has been a longstanding interest because of emergent phenomena such as Mott insulator and superconductivity. Besides recent Moiré superlattice, transition metal dichalcogenides (TMDs) may directly, e.g. by forming a charge density wave in 1T-TaS2, reconstruct a narrow band that exhibits a correlated insulator. Here we report an emergent insulator in electron doped monolayer WSe2, a prototypical TMDs with direct bandgaps. By detailed mapping a cascade of phases “band insulator-superconductor-emergent insulator-metal”, we can identify, besides the superconducting dome, a narrow miniband split from the conduction band, half filling of which coincides with the insulating state. The correlation picture is supported by a density wave that possesses an isolated flat band. Finally, through evolutionary changes within the same class of materials, multivalley population is suggested to account for enhanced superconductivity and the insulator. Our finding provides new opportunities to explore correlated physics within traditionally non-correlated materials.

HT C SQUID has a great potential in ultra-weak magnetic signal detections due to its advantages of energy saving and volume reduction of the overall system, including the cryogenics. However, the application of HT C SQUID is limited because lack of proper magnetic shielding. Superconducting magnetic shielding is an efficient way for HT C SQUID. In this work, we fabricate MgB 2 thick film on a stainless steel cylinder using HPCVD to make a preliminary attempt for SMS with MgB 2 films. High quality MgB 2 film is deposited on the inner side of a hollowed cylinder. The transition temperature of the film is 37.5 K, and the critical current density is 7.6 × 10 6 A⋅cm −2 at 10 K and 4.6 × 10 6 A⋅cm −2 at 20 K, which is comparable with the planar films. The shielding effectiveness of the cylindrical MgB 2 film is numerical simulated. Height and thickness of the cylindrical magnetic shielding designed according to the simulation result was calculated and a corresponding shielding effectiveness of 65 dB is obtained. The numerical result shows the feasibility of using MgB 2 film as magnetic shielding.

Magnetic shielding has been a key factor in the measurement of ultra-weak magnetic fields, especially for shielding from low frequency electromagnetic noise. With the recent development of superconducting quantum interference devices, superconducting magnetic shielding has become an important area of research. MgB2 has shown great potential in magnetic shielding for its remarkable superconducting properties, the feasibility of its use in this capacity having been demonstrated by MgB2 bulk samples. However, the potential for application of such bulk samples is limited. In this work, we have investigated the possibility of the fabrication of MgB2 films on three-dimensional (3D) structures using a hybrid physical−chemical vapor deposition system. MgB2 films 10 μm thick have been fabricated on the outer surface of a polycrystalline Al2O3 cylinder. The deposited film showed a transition temperature (TC) of 39 K and J C of 5.1 × 105 A cm−2, which are comparable to those of planar MgB2 films. This work shows the feasibility of depositing MgB2 films onto a 3D structure, and sheds light on the potential use of MgB2 films in superconducting magnetic shielding.

Lumped element kinetic inductance detectors (LEKIDs) are made from a single layer superconducting thin film. Because of their low noise and highly multiplexibility, LEKIDs provide a sensitive technology for the detection of millimeter and submillimeter waves. In this work, a 5-pixel 50-nm-thick MgB2 array is made. The microwave properties of the array are measured under dark conditions. We show that the loaded quality factor Q of the resonant circuit is 30 000 at 7.5 K, which is comparable to that of lower-operating-temperature (usually several hundred mK) LEKIDs made from superconductors such as Al and Nb. Moreover, the temperature dependence of resonance frequency gives the two-gap character of MgB2, Δπ (0) = 2.58 meV and Δσ (0) = 8.26 meV. The gap frequency (f = 2Δ/h) indicates that MgB2 LEKIDs have a promising application on terahertz detection.