Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userInducing Kondo Screening of Vacancy Magnetic Moments in Graphene with Gating and Local Curvature
145
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
In normal metals, the magnetic-moment of impurity-spins disappears below a characteristic Kondo temperature, TK. This marks the formation of a polarized cloud of conduction band electrons that screen the magnetic moment . In contrast, moments embedded in insulators remain unscreened at all temperatures. This raises the question about the fate of magnetic-moments in intermediate, pseudogap systems, such as graphene. In these systems coupling between the local moment and the conduction band electrons is predicted to drive a quantum phase-transition between a local-moment phase and a Kondo-screened singlet phase as illustrated in Fig. 1A. However, attempts to experimentally confirm these predictions and their intriguing consequences such as the ability to electrostatically tune magnetic-moments, have been elusive. Here we report the observation of Kondo screening and the quantum phase-transition between screened and unscreened phases of vacancy magnetic-moments in graphene. Using scanning-tunneling-microscopy (STM), spectroscopy (STS) and numerical-renormalization-group (NRG) calculations, we identified Kondo-screening by its spectroscopic signature and mapped the quantum phase-transition as a function of coupling strength and chemical potential. We show that the coupling strength can be tuned across this transition by variations in the local curvature and furthermore that the transition makes it possible to turn the magnetic-moment on and off with a gate voltage.
rate research
Read More
In normal metals, the magnetic moment of impurity spins disappears below a characteristic Kondo temperature, TK, where coupling with the conduction-band electrons produces an entangled state that screens the local moment. In contrast, moments embedded in insulators remain unscreened at all temperatures. This raises the question about the fate of magnetic moments in intermediate, pseudogap systems, such as graphene. In these systems theory predicts a quantum phase-transition at a critical coupling strength which separates a local magnetic-moment phase from a Kondo screened phase. However, attempts to experimentally confirm these predictions and their intriguing consequences such as the ability to electrostatically control magnetic moments, have thus far been elusive. Here we report the observation of Kondo screening and the quantum phase-transition between screened and unscreened phases of vacancy magnetic-moments in graphene. Using scanning tunneling microscopy (STM), spectroscopy (STS) and numerical renormalization group (NRG) calculations, we identified Kondo screening by its spectroscopic signature and mapped the phase-transition as a function of coupling strength and chemical potential. We show that this transition makes it possible to turn the magnetic-moment on and off electrostatically through a gate voltage or mechanically through variations in local curvature.
Herein we discuss the fabrication of ballistic suspended graphene nanostructures supplemented with local gating. Using in-situ current annealing, we show that exceptional high mobilities can be obtained in these devices. A detailed description is given of the fabrication of bottom and different top-gate structures, which enable the realization of complex graphene structures. We have studied the basic building block, the p-n junction in detail, where a striking oscillating pattern was observed, which can be traced back to Fabry-Perot oscillations that are localized in the electronic cavities formed by the local gates. Finally we show some examples how the method can be extended to incorporate multi-terminal junctions or shaped graphene. The structures discussed here enable the access to electron-optics experiments in ballistic graphene.
We intercalate a van der Waals heterostructure of graphene and hexagonal Boron Nitride with Au, by encapsulation, and show that Au at the interface is two dimensional. A charge transfer upon current annealing indicates redistribution of Au and induces splitting of the graphene bandstructure. The effect of in plane magnetic field confirms that splitting is due to spin-splitting and that spin polarization is in the plane, characteristic of a Rashba interaction with magnitude approximately 25 meV. Consistent with the presence of intrinsic interfacial electric field we show that the splitting can be enhanced by an applied displacement field in dual gated samples. Giant negative magnetoresistance, up to 75%, and a field induced anomalous Hall effect at magnetic fields < 1 T are observed. These demonstrate that hybridized Au has a magnetic moment and suggests the proximity to formation of a collective magnetic phase. These effects persist close to room temperature.
Electrostatic gating lies in the heart of modern FET-based integrated circuits. Usually, the gate electrode has to be placed very close to the conduction channel, typically a few nanometers, in order to achieve efficient tunability. However, remote control of a FET device through a gate electrode placed far away is always highly desired, because it not only reduces the complexity of device fabrication, but also enables designing novel devices with new functionalities. Here, a non-local gating effect in graphene using both near-field optical nano-imaging and electrical transport measurement is reported. With assistance of absorbed water molecules, the charge density of graphene can be efficiently tuned by a local-gate placed over 30 {mu}m away. The observed non-local gating effect is initially driven by an in-plane electric field established between graphene regions with different charge densities due to the quantum capacitance near the Dirac point in graphene. The nonlocality is further amplified and largely enhanced by absorbed water molecules through screening the in-plane electric field and expending the transition length. This research reveals novel non-local phenomenon of Dirac electrons, and paves the way for designing electronic devices with remote-control using 2D materials with small density of states.
The effect of electronic interactions in graphene with vacancies or resonant scatterers is investigated. We apply dynamical mean-field theory in combination with quantum Monte Carlo simulations, which allow us to treat non-perturbatively quantum fluctuations beyond Hartree-Fock approximations. The interactions narrow the width of the resonance and induce a Curie magnetic susceptibility, signaling the formation of local moments. The absence of saturation of the susceptibility at low temperatures suggests that the coupling between the local moment and the conduction electrons is ferromagnetic.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
