arXiv subjects

Peter Nemes-Incze

Publications and source records attributed to Peter Nemes-Incze.

9 recordsLinked to original sources

arXiv2022

Large-area nanoengineering of graphene corrugations for visible-frequency graphene plasmons

Quantum confinement of graphene carriers is an effective way to engineer its properties. It is commonly realized through physical edges that are associated with the deterioration of mobility and strong suppression of plasmon resonances. Here, we demonstrate a simple, large-area, edge-free nanostructuring technique, based on amplifying random nanoscale structural corrugations to a level where they efficiently confine carriers, without inducing significant inter-valley scattering. This soft confinement, allows the low-loss lateral ultra-confinement of graphene plasmons, scaling up their resonance frequency from native terahertz to commercially relevant visible range. Visible graphene plasmons localized into nanocorrugations mediate several orders of magnitude stronger light-matter interactions (Raman enhancement) than those previously achieved with graphene, enabling the detection of specific molecules from femtomolar solutions or ambient air. Moreover, nanocorrugated graphene sheets also support propagating visible plasmon modes revealed by scanning near-field optical microscopy observation of their interference patterns.

cond-mat.mes-hall↗

arXiv2021

Pressure-induced Superconductivity in dual-topological semimetal Pt2HgSe3

Recently monolayer jacutingaite (Pt2HgSe3), a naturally occurring exfoliable mineral, discovered in Brazil in 2008, has been theoretically predicted as a candidate quantum spin Hall system with a 0.5 eV band gap, while the bulk form is one of only a few known dual-topological insulators which may host different surface states protected by symmetries. In this work, we systematically investigate both structure and electronic evolution of bulk Pt2HgSe3 under high pressure up to 96 GPa. The nontrivial topology persists up to the structural phase transition observed in the high-pressure regime. Interestingly, we found that this phase transition is accompanied by the appearance of superconductivity at around 55 GPa and the critical transition temperature Tc increases with applied pressure. Our results demonstrate that Pt2HgSe3 with nontrivial topology of electronic states displays new ground states upon compression and raises potentials in application to the next-generation spintronic devices.

cond-mat.supr-con↗

arXiv2018

One-dimensional Si chains embedded in Pt(111)and protected by a hexagonal boron-nitride monolayer

Using scanning tunneling microscopy, we show that Si deposition on Pt(111) at 300K leads to a network of one-dimensional Si chains. On the bare Pt(111) surface, the chains, embedded into the Pt surface, are orientated along the <112>-direction. They disappear within a few hours in ultrahigh vacuum due to the presence of residual gas. Exposing the chains to different gases deliberately reveals that CO is largely responsible for the disappearance of the chains. The chains can be stabilized by a monolayer of hexagonal boron nitride, which is deposited prior to the Si deposition. The resulting Si chains are rotated by 30° with respect to the chains on the bare Pt(111) surface and survive even an exposure to air for 10 minutes.

cond-mat.mes-hall↗

arXiv2018

Large tunable valley splitting in edge-free graphene quantum dots on boron nitride

Coherent manipulation of binary degrees of freedom is at the heart of modern quantum technologies. Graphene offers two binary degrees: the electron spin and the valley. Efficient spin control has been demonstrated in many solid state systems, while exploitation of the valley has only recently been started, yet without control on the single electron level. Here, we show that van-der Waals stacking of graphene onto hexagonal boron nitride offers a natural platform for valley control. We use a graphene quantum dot induced by the tip of a scanning tunneling microscope and demonstrate valley splitting that is tunable from -5 to +10 meV (including valley inversion) by sub-10-nm displacements of the quantum dot position. This boosts the range of controlled valley splitting by about one order of magnitude. The tunable inversion of spin and valley states should enable coherent superposition of these degrees of freedom as a first step towards graphene-based qubits.

cond-mat.mes-hall↗

arXiv2017

Tuning the pseudospin polarization of graphene by a pseudo-magnetic field

One of the intriguing characteristics of honeycomb lattices is the appearance of a pseudo-magnetic field as a result of mechanical deformation. In the case of graphene, the Landau quantization resulting from this pseudo-magnetic field has been measured using scanning tunneling microscopy. Here we show that a signature of the pseudo-magnetic field is a local sublattice symmetry breaking observable as a redistribution of the local density of states. This can be interpreted as a polarization of graphene's pseudospin due to a strain induced pseudo-magnetic field, in analogy to the alignment of a real spin in a magnetic field. We reveal this sublattice symmetry breaking by tunably straining graphene using the tip of a scanning tunneling microscope. The tip locally lifts the graphene membrane from a SiO$_2$ support, as visible by an increased slope of the $I(z)$ curves. The amount of lifting is consistent with molecular dynamics calculations, which reveal a deformed graphene area under the tip in the shape of a Gaussian. The pseudo-magnetic field induced by the deformation becomes visible as a sublattice symmetry breaking which scales with the lifting height of the strained deformation and therefore with the pseudo-magnetic field strength. Its magnitude is quantitatively reproduced by analytic and tight-binding models, revealing fields of 1000 T. These results might be the starting point for an effective THz valley filter, as a basic element of valleytronics.

cond-mat.mes-hall↗

arXiv2016

Electrostatically confined monolayer graphene quantum dots with orbital and valley splittings

The electrostatic confinement of massless charge carriers is hampered by Klein tunneling. Circumventing this problem in graphene mainly relies on carving out nanostructures or applying electric displacement fields to open a band gap in bilayer graphene. So far, these approaches suffer from edge disorder or insufficiently controlled localization of electrons. Here we realize an alternative strategy in monolayer graphene, by combining a homogeneous magnetic field and electrostatic confinement. Using the tip of a scanning tunneling microscope, we induce a confining potential in the Landau gaps of bulk graphene without the need for physical edges. Gating the localized states towards the Fermi energy leads to regular charging sequences with more than 40 Coulomb peaks exhibiting typical addition energies of 7-20 meV. Orbital splittings of 4-10 meV and a valley splitting of about 3 meV for the first orbital state can be deduced. These experimental observations are quantitatively reproduced by tight binding calculations, which include the interactions of the graphene with the aligned hexagonal boron nitride substrate. The demonstrated confinement approach appears suitable to create quantum dots with well-defined wave function properties beyond the reach of traditional techniques.

cond-mat.mes-hall↗

arXiv2014

Room temperature magnetic order on zigzag edges of narrow graphene nanoribbons

Magnetic order emerging in otherwise non-magnetic materials as carbon is a paradigmatic example of a novel type of s-p electron magnetism predicted to be of exceptional high-temperature stability. It has been demonstrated that atomic scale structural defects of graphene can host unpaired spins. However, it is still unclear under which conditions long-range magnetic order can emerge from such defect-bound magnetic moments. Here we propose that in contrast to random defect distributions, atomic scale engineering of graphene edges with specific crystallographic orientation, comprising edge atoms only from one sub-lattice of the bipartite graphene lattice, can give rise to a robust magnetic order. We employ a nanofabrication technique based on Scanning Tunneling Microscopy to define graphene nanoribbons with nanometer precision and well-defined crystallographic edge orientations. While armchair ribbons display quantum confinement gap, zigzag ribbons narrower than 7 nm reveal a bandgap of about 0.2 - 0.3 eV, which can be identified as a signature of interaction induced spin ordering along their edges. Moreover, a semiconductor to metal transition is revealed upon increasing the ribbon width, indicating the switching of the magnetic coupling between opposite ribbon edges from antiferromagnetic to ferromagnetic configuration. We found that the magnetic order on graphene edges of controlled zigzag orientation can be stable even at room temperature, raising hope for graphene-based spintronic devices operating under ambient conditions.

cond-mat.mes-hall↗

arXiv2012

Breakdown of continuum mechanics for nanometer-wavelength rippling of graphene

Understanding how the mechanical behavior of materials deviates at the nanoscale from the macroscopically established concepts is a key challenge of particular importance for graphene, given the complex interplay between its nanoscale morphology and electronic properties. In this work, the (sub-) nanometer wavelength periodic rippling of suspended graphene nanomembranes has been realized by thermal strain-engineering and investigated using Scanning Tunneling Microscopy. This allows us to explore the rippling of a crystalline membrane with wavelengths comparable to its lattice constant. The observed nanorippling mode violates the predictions of the continuum model, and evidences the breakdown of the plate idealization of the graphene monolayer. Nevertheless, microscopic simulations based on a quantum mechanical description of the chemical binding accurately describe the observed rippling mode and elucidate the origin of the continuum model breakdown. Spatially resolved tunneling spectroscopy measurements indicate a substantial influence of the nanoripples on the local electronic structure of graphene and reveal the formation of one-dimensional electronic superlattices.

cond-mat.mes-hall↗

arXiv2009

Tuning the electronic structure of graphene by ion irradiation

Mechanically exfoliated graphene layers deposited on SiO2 substrate were irradiated with Ar+ ions in order to experimentally study the effect of atomic scale defects and disorder on the low-energy electronic structure of graphene. The irradiated samples were investigated by scanning tunneling microscopy and spectroscopy measurements, which reveal that defect sites, besides acting as scattering centers for electrons through local modification of the on-site potential, also induce disorder in the hopping amplitudes. The most important consequence of the induced disorder is the substantial reduction in the Fermi velocity, revealed by bias-dependent imaging of electron-density oscillations observed near defect sites.

cond-mat.mes-hall↗