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Atomically thin half-van der Waals metals enabled by confinement heteroepitaxy
摘要： Atomically thin two-dimensional (2D) metals may be key ingredients in next-generation quantum and optoelectronic devices. However, 2D metals must be stabilized against environmental degradation and integrated into heterostructure devices at the wafer scale. The high-energy interface between silicon carbide and epitaxial graphene provides an intriguing framework for stabilizing a diverse range of 2D metals. Here we demonstrate large-area, environmentally stable, single-crystal 2D gallium, indium and tin that are stabilized at the interface of epitaxial graphene and silicon carbide. The 2D metals are covalently bonded to SiC below but present a non-bonded interface to the graphene overlayer; that is, they are ‘half van der Waals’ metals with strong internal gradients in bonding character. These non-centrosymmetric 2D metals offer compelling opportunities for superconducting devices, topological phenomena and advanced optoelectronic properties. For example, the reported 2D Ga is a superconductor that combines six strongly coupled Ga-derived electron pockets with a large nearly free-electron Fermi surface that closely approaches the Dirac points of the graphene overlayer.
关键词： 2D metals,superconductivity,epitaxial graphene,quantum devices,silicon carbide
更新于2025-09-19 17:13:59
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Interplay of structure and charge order revealed by quantum oscillations in thin films of
摘要： The discovery of quantum oscillations in hole- and electron-doped cuprate families has underscored the importance of the Fermi surface in cuprate superconductivity. While the observed quantum oscillations in both families have revealed the presence of reconstructed Fermi surfaces, there remains an important distinction between the two. In hole-doped cuprates the oscillations are thought to arise from the effects of a charge density wave, while in the electron-doped cuprates it is thought that these oscillations occur from an antiferromagnetically reconstructed Fermi surface, despite the fact that the oscillations are observed in overdoped compounds, far from the putative antiferromagnetic critical point. In this work we study thin films of Pr2CuO4±δ, whose apparent doping can be finely tuned by annealing, allowing studies of quantum oscillations in samples straddling the critical point. We show that even though there is a mass enhancement of the quasiparticles, there are only small changes to the Fermi surface itself, suggesting that charge order is a more likely origin, with electronic correlations that are strongly dependent on the structural parameters.
关键词： antiferromagnetic critical point,Fermi surface,cuprate superconductivity,quantum oscillations,charge density wave
更新于2025-09-12 10:27:22
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Synthesis of heavy fermion CeCoIn5 thin film via pulsed laser deposition
摘要： CeCoIn5 (Co115) thin films have been grown on Al2O3 (000l) substrates through the pulsed laser deposition (PLD). The films are grown mainly along the c-axis, with CeIn3 and In-related alloys. The rock-salt type grains are nucleated, where Co115 grains mixed with excess indium are evenly distributed over the substrate. The electrical resistivity of the films shows a Kondo coherence peak near 47 K and the zero-resistance superconducting state at 1.8 K, which is the first observation in the PLD grown thin films of Co115. The Rietveld refinement of the thin films shows that the c/a ratio (tetragonality) is suppressed to 1.6312 from 1.6374 of single crystals, which is consistent with the linear relationship between the superconducting transition temperature and tetragonality. The good agreement indicates that the PLD could provide an alternative route to tune the 2D character of the critical spin fluctuations to understand the superconducting pairing mechanism of Co115.
关键词： Metal thin film,CeCoIn5 thin film,Heavy fermions,Superconductivity,Pulsed laser deposition
更新于2025-09-12 10:27:22
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Fano-Andreev effect in a parallel double quantum dot structure
摘要： We investigate the Andreev reflection in a parallel double quantum dot structure, by considering one metallic lead coupled to one s-wave superconductor through the quantum dots. It is found that if an arm of this system provides the reference channel for the Andreev reflection, the Fano line shapes will have opportunities to appear in the linear conductance spectra and can be reversed by adjusting the dot level or local magnetic flux. To present the underlying physics, we obtain the Fano form of the linear conductance expression. Despite the complicated structural parameters, the property of the Fano effect is clearly shown. We believe that the results of this work will help us to understand the Fano interference in the Andreev reflection process.
关键词： quantum dots,Andreev reflection,superconductivity,Fano effect,quantum interference
更新于2025-09-11 14:15:04
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Enhanced superconducting properties of a YGBCO/Gd-CeO2/YGBCO tri-layer film deposited by pulsed laser deposition
摘要： To evaluate the inhibition of the REBa2Cu3O7-δ (REBCO, where RE is rare earth) film thickness effect, a series of Y0.5Gd0.5Ba2Cu3O7-δ(YGBCO)/interlayer/YGBCO tri-layer films with Gd-Cerium oxide (CeO2) film were prepared under different experimental conditions in this study. The results illustrate that the electric current from the top YGBCO layer could transmit to the bottom YGBCO layer by adding Gd into the CeO2 interlayer with the approximate thicknesses limits of 10 nm. For further increase the electric current carrying capacity, a series of YGBCO/Gd-CeO2/YGBCO tri-layers were fabricated under different oxygen partial pressures and laser energies. The better crystallinity, and texture, and the smoother surface levels completely eliminated the thickness effect. However, the samples’ superconductivity declined sharply at low laser energies. Because the Gd particles deposited on the substrate were fully oxidized, this led to particle disappearance in the interlayer film. Additionally, YGBCO samples with a Gd-CeO2 interlayer were more likely to be damaged than a pure YGBCO sample in the measurement process, which could be solved by increasing the Gd content in the CeO2+Gd target. Hence, by depositing a Gd-CeO2 interlayer, YGBCO tri-layer films with high superconductivity and low damageability were obtained.
关键词： Gd-CeO2 interlayer,laser energy,superconductivity,damageability,oxygen partial pressure
更新于2025-09-11 14:15:04
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Broadening the IF band of a THz hot electron bolometer mixer by using a magnetic thin film
摘要： To expand the intermediate frequency (IF) band and improve the sensitivity of a hot electron bolometer mixer (HEBM), we proposed and examined a new HEBM structure using a magnetic thin film. We found that it was possible to suppress the superconductivity of the 5-nm thick niobium nitride (NbN) thin film by the addition of a 1.8-nm thick nickel (Ni) thin film. It was also confirmed that the superconductivity disappeared in the Au (70 nm)/Ni (1.8 nm)/NbN (5 nm) tri-layer for forming the electrodes of the HEBM. By using the magnetic thin film for the electrodes, we suggested that the superconductivity of the HEBM strip would be affected and that hot spots would form near the electrodes. This approach is effective for shortening the hot electron drift length and will lead to the expansion of the IF bandwidth. We think that the new structure lowers the required local oscillator (LO) power and improves the HEBM sensitivity by suppressing the proximity effect under the electrode. The IF bandwidth of the fabricated Ni-HEBMs was evaluated at 1.9 THz. We confirmed that the IF bandwidth expands, and the evaluated bandwidths were in the range of 5.1–5.7 GHz at 4 K. Ni-HEBMs with 0.1 μm strip length were also fabricated and evaluated. The IF bandwidth was about 6.9 GHz at 4 K.
关键词： hot electron bolometer mixer,THz,magnetic thin film,superconductivity,intermediate frequency band
更新于2025-09-11 14:15:04
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Proximity-induced supercurrent through topological insulator based nanowires for quantum computation studies
摘要： Proximity-induced superconducting energy gap in the surface states of topological insulators has been predicted to host the much wanted Majorana fermions for fault-tolerant quantum computation. Recent theoretically proposed architectures for topological quantum computation via Majoranas are based on large networks of Kitaev’s one-dimensional quantum wires, which pose a huge experimental challenge in terms of scalability of the current single nanowire based devices. Here, we address this problem by realizing robust superconductivity in junctions of fabricated topological insulator (Bi2Se3) nanowires proximity-coupled to conventional s-wave superconducting (W) electrodes. Milling technique possesses great potential in fabrication of any desired shapes and structures at nanoscale level, and therefore can be effectively utilized to scale-up the existing single nanowire based design into nanowire based network architectures. We demonstrate the dominant role of ballistic topological surface states in propagating the long-range proximity induced superconducting order with high IcRN product in long Bi2Se3 junctions. Large upper critical magnetic fields exceeding the Chandrasekhar-Clogston limit suggests the existence of robust superconducting order with spin-triplet cooper pairing. An unconventional inverse dependence of IcRN product on the width of the nanowire junction was also observed.
关键词： Topological insulators,Quantum computation,Nanowires,Majorana fermions,Ballistic topological surface states,Proximity-induced superconductivity,Spin-triplet cooper pairing
更新于2025-09-11 14:15:04
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Theoretical Model for Optical Spectrum and Structural Dynamics of La2-xSrxCuO4
摘要： Superconductivity in cuprates cannot be fully understood using free-electron theory and the BCS model. Experiments during the last thirty years have shown that structural dynamics and localization cannot be ignored. The Marcus model is applied here for a theoretical assignment of the optical spectra. Hubbard-U absorption at ≈2 eV is assigned as metal/metal (MM) charge transfer transition of type 2Cu(II) + hν → Cu(I) + Cu(III). The mid-infrared (MIR) sharp line at 0.35 eV in La2CuO4 is interpreted as a vibrational transition with intensity borrowing from the crossing Cu(I) + Cu(III) energy curve. Hole-doping decreases U, since holes become available as acceptors. The relationship between the pseudogap and U in the doped cuprate is discussed. The absorption at 0.13 eV and the activation energy at 0.035 eV, existing only after doping, are very likely due to vertical and adiabatic electron exchange of type Cu(III)+Cu(II)→ Cu(II)+Cu(III). The pseudogap involves two-electron states.
关键词： doping,metal-metal charge transfer,vibronic states,Cuprates,superconductivity (SC),MIR absorption,Hubbard-U,pseudogap
更新于2025-09-10 09:29:36
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Cavity quantum-electrodynamical polaritonically enhanced electron-phonon coupling and its influence on superconductivity
摘要： So far, laser control of solids has been mainly discussed in the context of strong classical nonlinear light-matter coupling in a pump-probe framework. Here, we propose a quantum-electrodynamical setting to address the coupling of a low-dimensional quantum material to quantized electromagnetic fields in quantum cavities. Using a prototypical model system describing FeSe/SrTiO3 with electron-phonon long-range forward scattering, we study how the formation of phonon polaritons at the two-dimensional interface of the material modifies effective couplings and superconducting properties in a Migdal-Eliashberg simulation. We find that through highly polarizable dipolar phonons, large cavity-enhanced electron-phonon couplings are possible, but superconductivity is not enhanced for the forward-scattering pairing mechanism due to the interplay between coupling enhancement and mode softening. Our results demonstrate that quantum cavities enable the engineering of fundamental couplings in solids, paving the way for unprecedented control of material properties.
关键词： phonon polaritons,electron-phonon coupling,superconductivity,cavity quantum electrodynamics,quantum materials
更新于2025-09-10 09:29:36
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Stable Structural Phase of Potassium-Doped <i>p</i> -Terphenyl and Its Semiconducting State
摘要： The potassium-doped p-terphenyl compounds were synthesized in recent experiments and the superconductivity with high transition temperatures were reported, but the atomic structure of potassium-doped p-terphenyl is unclear. In this paper, we studied the structural and electronic properties of potassium-doped p-terphenyl with various doping levels by the first-principles simulation. We first find out the low energy position of K atom in intralayer interstitial space of the molecular layer, then examine whether two rows of K atoms can be accommodated in this one space, at last the effect of the interlayer arrangement between adjacent two molecular layers on total energy is taken into account. Our results show that the doped K atoms prefer to stay at the bridge site of single C-C bond connected two phenyls instead of locating at the site above the phenyl ring, distinct from the situation of K-doped picene and phenanthrene. Among the possible structural phases of Kx-p-terphenyl, the K2-p-terphenyl phase with P212121 group symmetry is determined to be most appropriate, which is different from the one in recent report. The stable K2-p-terphenyl phase is semiconducting with an energy gap of 0.3 eV and the bands from the lowest unoccupied molecular orbitals are just fully filled by the electrons transferred from K atoms.
关键词： Plasmonics,First-principles simulation,Semiconducting state,Magnetic,Potassium-doped p-terphenyl,Superconductivity,Optical,Hybrid Materials
更新于2025-09-10 09:29:36