arXiv subjects

Margherita Melegari

Publications and source records attributed to Margherita Melegari.

3 recordsLinked to original sources

arXiv2026

Switchable giant room-temperature nonlinear Hall effect in Bilayer Graphene

Utilizing quantum second-order nonlinear transport for practical junction-free devices require materials with large and tunable nonlinearites at room temperature -- a current materials platform challenge. Here, we report the nonlinear Hall effect (NLHE) in double-ionic gated bilayer graphene devices that enable unusually strong inversion breaking. We observe NLHE that are readily switchable (on, off, and sign reversed) with second order nonlinear susceptibilities $χ^{(2)}_{yxx}$ that reaches giant room-temperature values of $3\,10^{-3}\,μ\mathrm{m}\,\mathrm{S/V}$, comparable to values commonly observed at low temperature in WTe$_2$ or in graphene-based moiré superlattices, and three-to-four orders of magnitude larger than values reported in material systems recently employed in search of a room-temperature NLHE. Our devices produce corresponding THz voltage responsivities $\simeq 4\,10^{4}\,\mathrm{V/W}$, comparable to commercially available Schottky diodes. These are orders of magnitude better than for previously reported room-temperature NLHE devices rendering double-ionic gated bilayer graphene a choice platform for junction-free nonlinear technology.

cond-mat.mes-hall↗

arXiv2026

Interband State Transfer in Double-Gated Bilayer Graphene at High Electric Field

The band structure of Bernal-stacked bilayer graphene can be tuned using double-gated transistors to apply a perpendicular electric field that generates an interlayer potential energy difference $Δ$. Dielectric breakdown limits the operation of conventional devices to the $Δ\ll t_\perp \simeq 360$ meV regime. We employ double ionic gating to reach fields past $ 1$ V/nm, for which $Δ> t_\perp$. We find that for $Δ\simeq t_\perp$, the evolution of the longitudinal resistance ($R_{xx}$) peak as a function of applied gate voltages undergoes a sharp change in slope, exhibiting a pronounced "knee". Increasing $Δ$ past the "knee" results in an unusual evolution transport properties: the peak in $R_{xx}$ decreases in magnitude, it exhibits a splitting concomitant with multiple sign reversals of the Hall resistance, and hysteresis in the peak position emerges. We explain the observed phenomenology in terms of in-gap bound states, whose energy strongly depends on the perpendicular electric field, and crosses the mid-gap level for sufficiently large $Δ> t_\perp$. The phenomenon causes large changes in the electronic density of in-gap states that profoundly affect the evolution of the chemical potential. Our experimental results and their interpretation reveal unique aspects of the physics of in-gap states in Bernal bilayer graphene and demonstrate that double ionic gating enables investigating the large-$Δ$ regime, which has remained experimentally inaccessible so far.

cond-mat.mes-hall↗

arXiv2023

Full control of solid-state electrolytes for electrostatic gating

Ionic gating is a powerful technique to realize field-effect transistors (FETs) enabling experiments not possible otherwise. So far, ionic gating has relied on the use of top-electrolyte gates, which pose experimental constraints and make device fabrication complex. Promising results obtained recently in FETs based on solid-state electrolytes remain plagued by spurious phenomena of unknown origin, preventing proper transistor operation, and causing limited control and reproducibility. Here we explore a class of solid-state electrolytes for gating (Lithium-ion conducting glass-ceramics, LICGCs), identify the processes responsible for the spurious phenomena and irreproducible behavior,and demonstrate properly functioning transistors exhibiting high density ambipolar operation with gate capacitance of ~20-50 $μ$F/cm$^2$ (depending on the polarity of the accumulated charges). Using two-dimensional semiconducting transition-metal dichalcogenides we demonstrate the ability to implement ionic-gate spectroscopy to determine the semiconducting bandgap, and to accumulate electron densities above 10$^{14}$ cm$^{-2}$, resulting in gate-induced superconductivity in MoS$_2$ multilayers. As LICGCs are implemented in a back-gate configuration, they leave the surface of the material exposed, enabling the use of surface-sensitive techniques (such as scanning tunneling microscopy and photoemission spectroscopy) impossible so far in ionic-liquid gated devices. They also allow double ionic gated devices providing independent control of charge density and electric field.

cond-mat.mtrl-sci↗