Ying Guo

We study the transport of the Josephson current in one-dimensional SF1F2F3S junctions, where S represents s-wave superconductors and F1, F2, and F3 denote ferromagnets with noncollinear magnetizations. The Josephson current displays distinct characteristics under various magnetization configurations as we vary the exchange fields (h1, h3) and thicknesses (d1, d3) of the F1 and F3 layers. Building on Eschrig's conversion mechanisms [Eschrig, Phys. Today 64(1), 43 (2011) and Eschrig, Rep. Prog. Phys. 78, 104501 (2015)], we rigorously derive the conversion and transport processes of spin-singlet and spin-triplet Cooper pairs as they traverse the ferromagnetic trilayers, which helps clarify the observed variations in the Josephson current. We demonstrate that opposite-spin Cooper pairs acquire an additional phase of Qjdj upon passing through each Fj layer (j = 1, 3). Here, Qj = 2hj/(ℏvF) represents the center-of-mass momentum of the Cooper pairs, where vF is the Fermi velocity. This result aligns with the description of these pairs provided in Eq. (73) of Eschrig [Rep. Prog. Phys. 78, 104501 (2015)]. The contributions of Qjdj to the Josephson current depend on the exchange field of the F2 layer and the magnetization directions of the F1 and F3 layers. When the F2 layer is a ferromagnet, the azimuthal angle difference (χ3 − χ1) between the F1 and F3 layers modulates the current amplitude. This angular difference has been previously discussed in Grein et al. [Phys. Rev. Lett. 102, 227005 (2009)] and Eschrig [Rep. Prog. Phys. 78, 104501 (2015)], and it has more recently been examined in detail in Schulz et al. [Phys. Rev. B 112, 104514 (2025) and Phys. Rev. B 112, 104515 (2025)]. In contrast, when the F2 layer is a half-metal, this angle difference induces a phase shift in the current without affecting its amplitude, consistent with the results presented in Eschrig and Löfwander [Nat. Phys. 4, 138 (2008)]. These findings open new possibilities for controlling long-range Josephson currents in practical applications.

First-principles quantum transport simulations reveal the potential of monolayer SnTe FETs for sub-5 nm applications, demonstrating competitive power-delay performance and energy efficiency among emerging two-dimensional semiconductor devices.

二维IV-VI硫族化合物MX（M=Sn、Ge；X=S、Se和Te）作为新型半导体材料，具有合适的带隙和优异的光电特性而引起广泛关注。本文基于密度泛函理论系统研究了层数对二维MX材料的能带结构、电子态密度和光吸收系数的影响。发现随着层数的增加（从1层增至5层），MX的带隙值不仅会减小，带隙类型也会随层数的增加而变化，其中GeSe由单层的直接带隙变为多层的间接带隙，GeS由单层的间接带隙变为多层的直接带隙，SnTe由1-4层的间接带隙变为5层的直接带隙。MX的吸收边随层数的增加向长波方向移动，光吸收系数的数量级从1层的10⁴ cm^-1增加到5层的10⁵ cm^-1。层数可以调控MX材料的光电性质，使MX作为后摩尔时代光电器件理想沟道材料成为可能。

Ultrathin oxide semiconductors are promising candidates for back-end-of-line (BEOL) compatible transistors and monolithic three-dimensional integration. Experimentally, ultrathin indium oxide (In₂O₃) field-effect transistors (FETs) with thicknesses down to 0.4 nm exhibit an extremely high drain current (10⁴ μA/μm) and transconductance (4000 μS/μm). Here, we employ ab initio quantum transport simulation to investigate the performance limit of sub-5 nm gate length (L_g) ultrathin In₂O₃ FETs. Based on the International Technology Roadmap for Semiconductors (ITRS) criteria for high-performance (HP) devices, the scaling limit of ultrathin In₂O₃ FETs can reach 2 nm in terms of on-state current, delay time, and power dissipation. The wide bandgap nature of ultrathin In₂O₃ (3.0 eV) renders it a suitable candidate for ITRS low-power (LP) electronics with L_g down to 3 nm. Notably, both the HP and LP ultrathin In₂O₃ FETs exhibit superior energy-delay products as compared to those of other common 2D semiconductors such as monolayer MoS₂ and MoTe₂. These findings unveil the potential of ultrathin In₂O₃ in HP and LP nanoelectronic device applications.

Over the past decade, two-dimensional semiconductors (2DSCs) have aroused wide interest due to their extraordinary electronic, magnetic, optical, mechanical, and thermal properties, which hold potential in electronic, optoelectronic, thermoelectric applications, and so forth. The field-effect transistor (FET), a semiconductor gated with at least three terminals, is pervasively exploited as the device geometry for these applications. For lack of effective and stable substitutional doping techniques, direct metal contact is often used in 2DSC FETs to inject carriers. A Schottky barrier (SB) generally exists in the metal–2DSC junction, which significantly affects and even dominates the performance of most 2DSC FETs. Therefore, low SB or Ohmic contact is highly preferred for approaching the intrinsic characteristics of the 2DSC channel. In this review, we systematically introduce the recent progress made in theoretical prediction of the SB height (SBH) in the 2DSC FETs and the efforts made both in theory and experiments to achieve low SB contacts. From the comparison between the theoretical and experimentally observed SBHs, the emerging first-principles quantum transport simulation turns out to be the most powerful theoretical tool to calculate the SBH of a 2DSC FET. Finally, we conclude this review from the viewpoints of state-of-the-art electrode designs for 2DSC FETs.

ML GeSe field-effect transistors have an excellent device performance, even at the 1 nm gate-length. The on-state current of the devices can fulfill the requirements of the International Technology Roadmap for Semiconductors (2013 version).

Selector device is critical in high-density cross-point resistive switching memory arrays for suppressing the sneak leakage current path. Ge x Se 1-x based ovonic threshold switch (OTS) selectors have recently demonstrated strong performance with high on-state current, nonlinearity and endurance. Detailed study of its reliability is still lacking and the understanding on the responsible mechanisms is limited. In this work, for the first time, the endurance degradation mechanism of Ge-rich Ge x Se 1-x OTS is identified. Accumulation of slow defects that remain delocalized at off-state and GeSe segregation/crystallization during cycling lead to the recoverable and non-recoverable leakage current, respectively. Most importantly, a refreshing program scheme is developed to recover and prevent the OTS degradation and the endurance can be therefore improved by more than five orders without adding additional material elements or process steps.