arXiv subjects

Garen Avedissian

Publications and source records attributed to Garen Avedissian.

7 recordsLinked to original sources

arXiv2026

2D Theoretically Twistable Material Database

The study of twisted two-dimensional (2D) materials, where twisting layers create moiré superlattices, has created opportunities for investigating topological phases and strongly correlated physics. The broader potential of a seemingly infinite set of twistable 2D materials remains largely unexplored. Here, we define ''theoretically twistable materials'' as single- or multi-layer structures that allow for the construction of simple continuum models of their moiré structures. Our high-throughput algorithm systematically searches for theoretically twistable semimetals and insulators based on the Topological 2D Materials Database (2D-TQCDB). By analyzing key electronic properties, we identify thousands of candidate materials, propose representative twistable materials, and provide examples of crystal growth and exfoliation for several of them. Our results provide a resource for future experimental and theoretical studies of moiré systems.

cond-mat.mtrl-sci↗

arXiv2026

Rate Programmable Ionic-Redox Switching with Tunable Volatility in CuCrP2S6

Metal thiophosphates are emerging as a multifunctional material platform for neuromorphic electronics due to their accessible polar phases and ion dynamics on biologically relevant timescales. While resistive switching in these materials is frequently attributed to ferroelectric or antiferroelectric polarization, the intrinsic role of ion dynamics remains underexplored. Here, we isolate and demonstrate purely ion-driven resistive switching in paraelectric CuCrP2S6. Robust and reproducible resistive switching is observed in the absence of measurable ferroelectricity. The conductance can be tuned through both voltage amplitude and sweep rate, revealing a rate dependence characteristic of ion dynamics. The resulting resistance states exhibit controllable volatility, where switching rate determines the decay time constant of the readout current, attributed to ionic relaxation. Using either inert or reactive electrodes, we observe electrical evidence of solid-state redox activity associated with the interfacial reduction of native Cu+ ions, enabling controlled formation of filamentary conduction pathways. Analysis of this process allows extraction of the Cu+ diffusion coefficient, providing quantitative insight into the underlying transport kinetics. The understanding of ionic-redox based resistive switching in CuCrP2S6 is crucial for unleashing its full potential as a material platform for dual- or multi-mode operation.

cond-mat.mtrl-sci↗

arXiv2026

Ferroelectric hysteresis in singly aligned graphene-hBN moiré superlattices

Ferroelectric materials have the unique ability to maintain an electric polarization which can be reversed under an external applied electric field. This property makes them valuable for applications such as non-volatile random-access memories, transducers, actuators and electro optic modulators. Recently, emergent unconventional ferroelectricity has been demonstrated in moiré superlattices of bilayer graphene and hexagonal boron nitride (hBN) hosting non centrosymmetric stacking order. Whether this phenomenon is also present in noncentrosymmetric single layer graphene (SLG)-hBN moiré superlattices is still under debate. Here we demonstrate a ferroelectric response in an SLG-hBN moiré superlattice. Through Hall measurements, we pinpoint the origin of the hysteretic behavior to abnormal charge screening due to the moiré superlattice band and estimate the spontaneous polarization magnitude in the moiré superlattice structure. Temperature dependent measurements confirm that the hysteretic behavior persists from 2K up to room temperature, opening opportunities for high-mobility, ultrathin non-volatile devices

cond-mat.mes-hall↗

arXiv2025

Directional strong coupling at the nanoscale between hyperbolic polaritons and organic molecules

Strong coupling (SC) is a fundamental concept in physics that describes extreme interactions between light and matter. Recent experiments have demonstrated SC at the nanometer scale, where strongly confined polaritons, rather than photons, couple to quantum emitters or molecular vibrations. Coupling with the latter is generally referred to as vibrational SC (VSC) and is of significant fundamental and technological interest, as it can be an effective tool for modifying molecular properties. However, the implementation of VSC, especially at the nanoscale, depends on the development of tuning mechanisms that allow control over the coupling strength and, eventually, its directionality, opening the door for the selective coupling of specific molecular vibrations. Here we report the observation of directional VSC. Specifically, we show nanoscale images of propagating hyperbolic phonon polaritons (PhPs) coupled to pentacene molecules revealing that the fingerprint of VSC for propagating polaritons -- a marked anti-crossing in their dispersion at the vibrational resonance -- can be modulated as a function of the direction of propagation. In addition, we show that VSC can exhibit an optimal condition for thin molecular layers, characterized by a maximum coupling strength along one single direction. This phenomenon is understood by analysing the overlap of the polariton field with molecular layers of varying thicknesses. Apart from their fundamental importance, our findings promise novel applications for directional sensing or local directional control of chemical properties at the nanoscale.

cond-mat.mtrl-sci↗

arXiv2024

Gate-tunable spin Hall effect in trilayer graphene/group-IV monochalcogenide van der Waals heterostructures

Spintronic devices require materials that facilitate effective spin transport, generation, and detection. In this regard, graphene emerges as an ideal candidate for long-distance spin transport owing to its minimal spin-orbit coupling, which, however, limits its capacity for effective spin manipulation. This problem can be overcome by putting spin-orbit coupling materials in close contact to graphene leading to spin-orbit proximity and, consequently, efficient spin-to-charge conversion through mechanisms such as the spin Hall effect. Here, we report and quantify the gate-dependent spin Hall effect in trilayer graphene proximitized with tin sulfide (SnS), a group-IV monochalcogenide which has recently been predicted to be a viable alternative to transition-metal dichalcogenides for inducing strong spin-orbit coupling in graphene. The spin Hall angle exhibits a maximum around the charge neutrality point of graphene up to room temperature. Our findings expand the library of materials that induce spin-orbit coupling in graphene to a new class, group-IV monochalcogenides, thereby highlighting the potential of two-dimensional materials to pave the way for the development of innovative spin-based devices and future technological applications.

cond-mat.mes-hall↗

arXiv2024

Gate-tunable Exchange Bias and Voltage-controlled Magnetization Switching in a van der Waals Ferromagnet

The discovery of van der Waals magnets has established a new domain in the field of magnetism, opening novel pathways for the electrical control of magnetic properties. In this context, Fe3GeTe2 (FGT) emerges as an exemplary candidate owing to its intrinsic metallic properties, which facilitate the interplay of both charge and spin degrees of freedom. Here, the bidirectional voltage control of exchange bias (EB) effect in a perpendicularly magnetized all-van der Waals FGT/O-FGT/hBN heterostructure is demonstrated. The antiferromagnetic O-FGT layer is formed by naturally oxidizing the FGT surface. The observed EB magnitude reaches 1.4 kOe with a blocking temperature (150 K) reaching close to the Curie temperature of FGT. Both the exchange field and the blocking temperature values are among the highest in the context of layered materials. The EB modulation exhibits a linear dependence on the gate voltage and its polarity, observable in both positive and negative field cooling (FC) experiments. Additionally, gate voltage-controlled magnetization switching, highlighting the potential of FGT-based heterostructures is demonstrated in advanced spintronic devices. These findings display a methodology to modulate the magnetism of van der Waals magnets offering new avenues for the development of high-performance magnetic devices.

cond-mat.mtrl-sci↗

arXiv2020

Robust ferroelectric properties of organic Croconic Acid films grown on spintronically relevant substrates

The discovery of stable room temperature ferroelectricity in Croconic Acid, an organic ferroelectric material, with polarization values on par with those found in inorganic ferroelectric materials and highest among organic ferroelectric materials, has opened up possibilities to realize myriads of nano-electronic and spintronic devices based on organic ferroelectrics. Such possibilities require an adequate understanding of the ferroelectric properties of Croconic Acid grown on surfaces that are commonly employed in device fabrication. While several macroscopic studies on relatively larger crystals of Croconic Acid have been performed, studies on thin films are only in their early stages. We have grown thin films of Croconic Acid on gold and cobalt surfaces, which are commonly used in spintronic devices as metallic electrodes, and studied the ferroelectric response of the films using ex-situ Piezoresponse Force Microscopy at room temperature. We show that the polarization reversal in Croconic Acid domains is sensitive to the substrate surface. Using the same experimental protocol, we observe the robust polarization reversal of a single, mostly in-plane electrical domain for a cobalt substrate, whereas polarization reversal is hardly observed for a gold substrate. We attribute this difference to the influence of substrates on the Croconic Acid molecular networks. Our study suggests that to realize devices one has to take care about the substrate on which Croconic Acid will be deposited. The fact that polarization switching is robust on cobalt surface can be used to fabricate multifunctional devices that utilize the cobalt-Croconic Acid interface.

cond-mat.mtrl-sci↗