arXiv subjects

Valeria Demontis

Publications and source records attributed to Valeria Demontis.

9 recordsLinked to original sources

arXiv2026

Optically Tunable Threshold Switching and Thermally Activated Transport in Planar Ag/MAPbI$_3$ Thin Single-Crystal Devices

Halide perovskites have enabled major advances in optoelectronics, extending well beyond photovoltaics. Their mixed ionic-electronic conduction, once regarded as detrimental to device stability, is increasingly viewed as a functional degree of freedom for memory and neuromorphic-inspired devices, especially when coupled to external stimuli such as light. Specifically, single crystals are attractive models because they suppress grain-boundary effects and microstructural disorder that can mask intrinsic transport and interfacial mechanisms in polycrystalline films. Here, we report the growth of thin methylammonium lead iodide (MAPbI$_3$) single crystals by a space-confined method and their integration into planar two-terminal devices with directly deposited Ag contacts. At room temperature, the devices exhibit ultra-low dark currents ($10^{-13}-10^{-12}$ A) and negligible hysteresis in the dark. Under illumination, the current increases due to photogeneration and the I-V characteristics develop a pronounced polarity-dependent hysteresis and a threshold-like transition between two conductance states. Temperature-dependent dark measurements (300-400 K) show thermionically activated, contact-influenced transport and a weakly varying normalized hysteresis metric. Together with the back-to-back Schottky-diode analysis and control devices using more inert contact materials, these results support a transport model in which Ag/perovskite interfaces play a central role and the hysteretic response is influenced by coupled interfacial and ionic processes.

cond-mat.mtrl-sci↗

arXiv2026

Magnetically Induced Switching-Current Jumps in InAs/Al Josephson Junctions

We report Barkhausen-like switching at millitesla fields in an $n$-doped InAs/Al nanowire Josephson junction, which serves as an interferometric probe of intrinsic magnetic reconfigurations, as evidenced by discrete switching-current jumps. At $T=30$~mK the device displays a Fraunhofer-like modulation with $I_{\mathrm{sw}}(0)\approx 0.24~μ\mathrm{A}$ and an abrupt transition at $|B|\approx 3~\mathrm{mT}$ between two branches differing by $ΔI_{\mathrm{sw}}\approx 0.13~μ\mathrm{A}$. By tracking the characteristic field scales from $30$ to $900$~mK, we find that the jump field is essentially temperature-independent, whereas the superconducting critical field decreases with temperature, as expected for thin Al films. The sharp discontinuity, sweep-direction asymmetry, and reproducibility across repeated scans point to avalanche-like switching between metastable magnetic configurations of the local magnetic texture, which are directly coupled to the weak link. Within an effective-field framework, each reconfiguration modifies a local field offset, thereby reshaping the interference response and leading to an abrupt reorganization of the switching-current pattern.

cond-mat.mes-hall↗

arXiv2024

InAs Nanowire-Based Twin Electrical Sensors enabling Simultaneous Gas Detection Measurements: Nanodevice Engineering, Testing and Signal Fluctuation Analysis

Epitaxially grown InAs NWs are relevant for electrical sensing applications due to Fermi level pinning at NW surface, thus very sensitive to surrounding environment. While a single NW growth batch consists of millions virtually identical replicas of the same NW, real samples display subtle differences in NW size, shape, structure which may affect the detection performance. Here, electrical gas detection is investigated the in two NW-based nominally identical or twin devices fabricated starting from the same NW growth batch. Two individual wurtzite InAs NWs are placed onto a fabrication substrate at 2 micrometers distance with 90 degrees relative orientation, each NW is electrically contacted, and the nanodevices are exposed to humidity and NO$_2$ flux diluted in synthetic air. Electrical signal versus time is measured simultaneously in each nanodevice, upon different gases and concentrations. Observed detection limit is 2 ppm for NO$_2$, 20% for relative humidity. Correlation analysis method is exploited by calculating auto- and cross-correlation functions for the experimental signal pairs, indicating lack of cross-correlation in the signal noise of the two nanodevices, suggesting that signal differences could be ascribed mainly to nonidealities of fabrication protocol and nanoscopic differences in the two nanostructures, rather than different environmental conditions.

cond-mat.mes-hall↗

arXiv2024

Engineering nanowire quantum dots with iontronics

Achieving stable, high-quality quantum dots has proven challenging within device architectures rooted in conventional solid-state device fabrication paradigms. In fact, these are grappled with complex protocols in order to balance ease of realization, scalability, and quantum transport properties. Here, we demonstrate a novel paradigm of semiconductor quantum dot engineering by exploiting ion gating. Our approach is found to enable the realization and control of a novel quantum dot system: the iontronic quantum dot. Clear Coulomb blockade peaks and their dependence on an externally applied magnetic field are reported, together with the impact of device architecture and confinement potential on quantum dot quality. Devices incorporating two identical quantum dots in series are realized, addressing the reproducibility of the developed approach. The iontronic quantum dot represents a novel class of zero-dimensional quantum devices engineered to overcome the need for thin dielectric layers, facilitating single-step device fabrication. Overall, the reported approach holds the potential to revolutionize the development of functional quantum materials and devices, driving rapid progress in solid state quantum technologies

cond-mat.mes-hall↗

arXiv2022

Giant reduction of thermal conductivity in twinning superlattice InAsSb nanowires

Semiconductor nanostructures hold great promise for high-efficiency waste heat recovery exploiting thermoelectric energy conversion, a technological breakthrough that could significantly contribute to providing environmentally friendly energy sources as well as in enabling the realization of self-powered biomedical and wearable devices. A crucial requirement in this field is the reduction of the thermal conductivity of the thermoelectric material without detrimentally affecting its electrical transport properties. In this work we demonstrate a drastic reduction of thermal conductivity in III-V semiconductor nanowires due to the presence of intentionally realized periodic crystal lattice twin planes. The electrical and thermal transport of these nanostructures, known as twinning superlattice nanowires, have been probed and compared with their twin-free counterparts, showing a one order of magnitude decrease of thermal conductivity while maintaining unaltered electrical transport properties, thus yielding a factor ten enhancement of the thermoelectric figure of merit, ZT. Our study reports for the first time the experimental measurement of electrical and thermal properties in twinning superlattice nanowires, which emerge as a novel class of nanomaterials for high efficiency thermoelectric energy harvesting.

cond-mat.mtrl-sci↗

arXiv2020

Orbital Tuning of Tunnel Coupling in InAs/InP Nanowire Quantum Dots

We report results on the control of barrier transparency in InAs/InP nanowire quantum dots via the electrostatic control of the device electron states. Recent works demonstrated that barrier transparency in this class of devices displays a general trend just depending on the total orbital energy of the trapped electrons. We show that a qualitatively different regime is observed at relatively low filling numbers, where tunneling rates are rather controlled by the axial configuration of the electron orbital. Transmission rates versus filling are further modified by acting on the radial configuration of the orbitals by means of electrostatic gating, and the barrier transparency for the various orbitals is found to evolve as expected from numerical simulations. The possibility to exploit this mechanism to achieve a controlled continuous tuning of the tunneling rate of an individual Coulomb blockade resonance is discussed.

cond-mat.mes-hall↗

arXiv2019

Microwave-Assisted Tunneling in Hard-Wall InAs/InP Nanowire Quantum Dots

With downscaling of electronic circuits, components based on semiconductor quantum dots are assuming increasing relevance for future technologies. Their response under external stimuli intrinsically depend on their quantum properties. Here we investigate single-electron tunneling in hard-wall InAs/InP nanowires in the presence of an off-resonant microwave drive. Our heterostructured nanowires include InAs quantum dots (QDs) and exhibit different tunnel-current regimes. In particular, for source-drain bias up to few mV Coulomb diamonds spread with increasing contrast as a function of microwave power and present multiple current polarity reversals. This behavior can be modelled in terms of voltage fluctuations induced by the microwave field and presents features that depend on the interplay of the discrete energy levels that contribute to the tunneling process.

cond-mat.mes-hall↗

arXiv2019

Thermoelectric conversion at 30K in InAs/InP nanowire quantum dots

We demonstrate high-temperature thermoelectric conversion in InAs/InP nanowire quantum dots by taking advantage of their strong electronic confinement. The electrical conductance G and the thermopower S are obtained from charge transport measurements and accurately reproduced with a theoretical model accounting for the multi-level structure of the quantum dot. Notably, our analysis does not rely on the estimate of co-tunnelling contributions since electronic thermal transport is dominated by multi-level heat transport. By taking into account two spin-degenerate energy levels we are able to evaluate the electronic thermal conductance K and investigate the evolution of the electronic figure of merit ZT as a function of the quantum dot configuration and demonstrate ZT ~ 35 at 30 K, corresponding to an electronic effciency at maximum power close to the Curzon- Ahlborn limit.

cond-mat.mes-hall↗

arXiv2018

Ionic liquid gating of InAs nanowire-based field effect transistors

We report the operation of a field-effect transistor based on a single InAs nanowire gated by an ionic liquid. Liquid gating yields very efficient carrier modulation with a transconductance value thirty time larger than standard back gating with the SiO2 /Si++ substrate. Thanks to this wide modulation we show the controlled evolution from semiconductor to metallic-like behavior in the nanowire. This work provides the first systematic study of ionic-liquid gating in electronic devices based on individual III-V semiconductor nanowires: we argue this architecture opens the way to a wide range of fundamental and applied studies from the phase-transitions to bioelectronics.

cond-mat.mes-hall↗