Earticle

The study of two-dimensional electron systems with extraordinarily low levels of disorder was, for a long time, the exclusive privilege of the epitaxial thin film research community. However, the successful isolation of graphene by mechanical exfoliation has truly disrupted this field. Furthermore, the assembly of heterostructures consisting of several layers of different 2D materials in arbitrary order by exploiting van der Waals forces has been a game-changer in the field of low-dimensional physics. This technique can be generalized to the large class of strictly 2D materials and offers unprecedented parameters to play with in order to tune electronic and other properties. It has led to a paradigm shift in the field of 2D condensed matter physics with bright prospects. In this review article, we discuss three device fabrication techniques towards high mobility devices: suspended structures, dry transfer, and pick-up transfer methods. We also address state-of-the-art device structures, which are fabricated by the van der Waals pick-up transfer method. Finally, we briefly introduce correlated ground states in the fractional quantum Hall regime.

2 K superfluid helium cryogenic system is the crucial component of many large accelerators. When the cryogenic system is operating at 2K@3129Pa, many room-temperature parts are connected to superfluid helium via tubes. Air Leakage in these connections may lead to air contamination of the cryogenic system. Air contamination may cause equipment failure in cryogenic systems and, in extreme cases, render the entire accelerator system inoperable. Helium guard is a technique that guards against air contamination of these sub-atmospheric pressure connections in 2 K superfluid helium cryogenic system. This paper introduces a typical 2 K cryogenic distribution design for large accelerators, and make risk analysis of air contamination. Finally, the analysis of specific leakage points and detailed engineering design are presented, which may be used as a reference when designing of a 2 K superfluid helium cryogenic distribution system.

In recent years, the interaction force between a permanent magnet and a closed superconductor coil has been gradually investigated in depth. The principle and application potential of an energy storage/convertor composed of a magnet and a closed superconducting coil have been proved. However, the study on the force between a magnet and a non-closed superconducting coil (superconducting roll stack) has hardly been reported in previous literature. The behavior of this kind of interaction and its influence to the interaction force between a permanent and a closed superconducting coil are also still unclear. In this paper, first we investigated the interaction force between a magnet and a superconducting roll stack. Then, a series of experiments were designed and conducted to clarify the factors affected the interaction force, including the geometrical parameters of the superconducting roll stack and the magnetic field density at the roll stack. Moreover, the comparison of the interaction forces between the magnet and roll stack or a closed coil was also introduced.

The International Electrotechnical Commission (IEC) 61788-26:2020 provides guidelines for measuring the critical current of Rare-earth barium copper oxide (REBCO) tapes using two methods: linear ramp and step-hold methods. The critical current measurement criterion, 1 or 0.1 μV/cm of electric field from IEC 61788-26 has been normally applied to REBCO coils or magnets. No-insulation (NI) winding technique has many advantages in aspects of electrical and thermal stability and mechanical integrity. However, the leak current from the NI REBCO coil can cause distortion in critical current measurement due to the characteristic resistance which causes the radial current flow paths. In this paper, we simulated the NI REBCO coil by applying both linear ramp and step-hold methods based on a simplified equivalent circuit model. Using the circuit analysis, we analyzed and evaluated both methods. By using the equivalent circuit model, we can evaluate the critical current of the NI REBCO coil, resulting in an estimation error within 0.1%. We also evaluate the accuracy of critical current measurement using both the linear ramp and step-hold methods. The accuracy of the linear ramp method is influenced by the inductive voltage, whereas the accuracy of the step-hold method depends on the duration of the hold-time. An adequate hold time, typically 5 to 10 times the time constant (τ), makes the step-hold method more accurate than the linear ramp method.