arXiv subjects

Nikhil Tilak

Publications and source records attributed to Nikhil Tilak.

4 recordsLinked to original sources

arXiv2024

Revealing the Charge Density Wave Proximity Effect in Graphene on 1T-TaS$_2$

The proximity-effect, whereby materials in contact appropriate each others electronic-properties, is widely used to induce correlated states, such as superconductivity or magnetism, at heterostructure interfaces. Thus far however, demonstrating the existence of proximity-induced charge-density-waves (PI-CDW) proved challenging. This is due to competing effects, such as screening or co-tunneling into the parent material, that obscured its presence. Here we report the observation of a PI-CDW in a graphene layer contacted by a 1T-TaS2 substrate. Using scanning tunneling microscopy (STM) and spectroscopy (STS) together with theoretical-modeling, we show that the coexistence of a CDW with a Mott gap in 1T-TaS2 coupled with the Dirac-dispersion of electrons in graphene, makes it possible to unambiguously demonstrate the PI-CDW by ruling out alternative interpretations. Furthermore, we find that the PI-CDW is accompanied by a reduction of the Mott gap in 1T-TaS2 and show that the mechanism underlying the PI-CDW is well-described by short-range exchange-interactions that are distinctly different from previously observed proximity effects.

cond-mat.mes-hall↗

arXiv2022

Moire Potential, Lattice Relaxation and Layer Polarization in Marginally Twisted MoS2 Bilayers

Artificially twisted heterostructures of semiconducting transition metal dichalcogenides (TMDs) offer unprecedented control over their electronic and optical properties via the spatial modulation of interlayer interactions and structural reconstruction. Here we study twisted MoS2 bilayers in a wide range of twist angles near 0° using Scanning Tunneling Microscopy/Spectroscopy. We investigate the twist angle-dependence of the moiré pattern which is dominated by lattice reconstruction for small angles (<2°) leading to large triangular domains with rhombohedral stacking. Local spectroscopy measurements reveal a large moiré-potential strength of 100-200 meV for angles <3°. In reconstructed regions we see a bias-dependent asymmetry between neighboring triangular domains which we relate to the vertical polarization which is intrinsic to rhombohedral stacked TMDs. This viewpoint is urther supported by spectroscopy maps and ambient Piezoresponse measurements. Our results provide a microscopic perspective on this new class of interfacial ferroelectrics and can offer clues for designing novel heterostructures which harness this effect.

cond-mat.mtrl-sci↗

arXiv2022

Revealing the Charge Density Wave Proximity Effect in Graphene on 1T-TaS2

Proximity effect is a very powerful approach and has been widely applied to induce electron correlations such as: superconductivity, magnetism and spin-orbit effects at the interface of heterostructure quantum materials. However, proximity induced charge density wave (CDW) state has remained elusive. We report the first observation of a novel proximity induced CDW within a graphene layer that is deposited on 1T-TaS2 crystal. By using scanning tunneling microscopy and spectroscopy to probe the interface of the graphene/1T-TaS2 heterostructure together with theoretical modeling, we show that the interactions between the Dirac-like carriers in graphene and the correlated electrons in 1T-TaS2 induce a periodic charge density modulation within graphene and modify the band structure at the surface of 1T-TaS2, resulting in a 7.5% reduction of its gap size. Our results provide a new platform to manipulate the electron charge correlations in heterostructures.

cond-mat.mes-hall↗

arXiv2021

Flat band carrier confinement in magic-angle twisted bilayer graphene

Magic angle twisted bilayer graphene has emerged as a powerful platform for studying strongly correlated electron physics, owing to its almost dispersionless low-energy bands and the ability to tune the band filling by electrostatic gating. Techniques to control the twist angle between graphene layers have led to rapid experimental progress but improving sample quality is essential for separating the delicate correlated-electron physics from disorder effects. Owing to the 2D nature of the system and the relatively low carrier density, the samples are highly susceptible to small doping inhomogeneity which can drastically modify the local potential landscape. This potential disorder is distinct from the twist-angle variation which has been studied elsewhere. Here, by using low temperature scanning tunneling spectroscopy and planar tunneling junction measurements, we demonstrate that flat bands in twisted bilayer graphene can amplify small doping inhomogeneity that surprisingly leads to carrier confinement, which in graphene could previously only be realized in the presence of a strong magnetic field.

cond-mat.mes-hall↗