The ability to create a robust and well-defined artificial atomic charge in graphene and understand its carrier-dependent electronic properties represents an important goal toward the development of graphene-based quantum devices. Herein, we devise a new pathway toward the atomically precise embodiment of point charges into a graphene lattice by posterior (N) ion implantation into a back-gated graphene device. The N dopant behaves as an in-plane proton-like charge manifested by formation of the characteristic resonance state in the conduction band. Scanning tunneling spectroscopy measurements at varied charge carrier densities reveal a giant energetic renormalization of the resonance state up to 220 meV with respect to the Dirac point, accompanied by the observation of gate-tunable long-range screening effects close to individual N dopants. Joint density functional theory and tight-binding calculations with modified perturbation potential corroborate experimental findings and highlight the short-range character of N-induced perturbation.
The quantum phase-coherent behavior of superconducting weak link (WL) is often masked by the heat dissipation and related thermal hysteresis. The latter can be reduced by improving heat evacuation and reducing the critical current, so that a phase-dynamic regime is obtained; however over a narrow bias-current and temperature range. Here we demonstrate that an inductive shunt with well-chosen shunt parameters introduces an unusual nonlinear dynamics that destabilizes an otherwise stable fixed point in the dissipative branch. This leads to a nonhysteretic behavior with large voltage oscillations in intrinsically hysteretic WL-based micron-size superconducting quantum interference devices. A dynamic thermal model describes quantitatively our observations and further allows us to elaborate on the optimal shunting conditions. Superconducting weak links (WL) [1] acting as Josephson junctions are of great interest for a range of quantum applications. A WL is usually probed with a dc current bias in the phase dynamic state [2] so that a dc voltage is measured. In particular, a WL-based micron-size superconducting quantum interference device (µ-SQUID) features then a flux-sensitive voltage [3] and can reach a magnetic moment resolution better than 1 µ B [4], which makes it an ultimate probe for quantum nanomagnetism [5][6][7][8]. The main limitation to µ-SQUIDs operation resides in the (thermal) hysteresis of their currentvoltage characteristics (IVCs) at low temperatures, due to poor heat evacuation from the WL to the bath [9][10][11][12]. A time-dependent Ginzburg-Landau approach capturing non-equilibrium effects on the order-parameter relaxation can model the hysteresis and the phase dynamic regime [13][14][15] in WLs. A more simple dynamic thermal model (DTM) successfully describes the same behavior by considering both the phase dynamics and the Joule heat evacuation [3,16]. A resistive shunt [17][18][19] placed close to a WL can remove thermal hysteresis down to certain temperature. However, for very low temperatures the required small resistor makes the voltage modulation in a µ-SQUID miniscule. Further, shunts with a large inductance lead to relaxation oscillations [20] due to substantial delay in current switching.In this Letter, we report on the striking effect of inductive shunting on the behavior of a WL-based µ-SQUID. When we use a shunt resistor with an adequate inductance in series, we observe reversible IVCs with large voltage modulations down to 1.3 K. The dynamic retrapping current increases with the inductance, leading to an increase in the temperature range of the reversible regime, up to a limiting value above which relaxation oscillations appear. The dynamic thermal model incorporating the nonlinear dynamics of temperature and current, quantitatively explains the observations. It is possible to observe a finite voltage state with phase-correlation across a WL such that the bias cur-rent across it is dynamically shared between a normal and super-current. In this dynamic regime, the WL does heat up abov...
We report an atomically-precise integration of individual nitrogen (N) dopant as an in-plane artificial nucleus in a graphene device by atomic implantation to probe its gate-tunable quantum states and correlation effects. The N dopant creates the characteristic resonance state in the conduction band, revealing a giant carrier-dependent energetic renormalization up to 350 meV with respect to the Dirac point, accompanied by the observation of long-range screening effects. Joint density functional theory and tight-binding calculations with modified perturbation potential corroborate experimental findings and highlight the short-range character of N-induced perturbation.
We introduce a computationally efficient method based on the path integral formalism to describe defect-modified graphene. By taking into account the entire Brillouin zone, our approach respects the lattice symmetry and can be used to investigate both short-range and long-range effects. The proposed method’s key advantage is that the computational complexity does not increase with the system size, scaling, instead, with the number of defects. Our aim is to make the quantum-field calculations in graphene accessible to the experimental community. We demonstrate our method’s capabilities by exploring the well-known graphene-mediated RKKY interaction and by performing a detailed study of the atomic collapse in the presence of defects.
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