The metal insulator transition of nano-scaled $VO_2$ devices is drastically different from the smooth transport curves generally reported. The temperature driven transition occurs through a series of resistance jumps ranging over 2 decades in amplitude, indicating that the transition is caused by avalanches. We find a power law distribution of the jump amplitudes, demonstrating an inherent property of the $VO_2$ films. We report a surprising relation between jump amplitude and device size. A percolation model captures the general transport behavior, but cannot account for the statistical behavior.
In this work, we experimentally and theoretically explore voltage controlled oscillations occurring in micro-beams of vanadium dioxide. These oscillations are a result of the reversible insulator to metal phase transition in vanadium dioxide. Examining the structure of the observed oscillations in detail, we propose a modified percolative-avalanche model which allows for voltage-triggering. This model captures the periodicity and waveshape of the oscillations as well as several other key features. Importantly, our modeling shows that while temperature plays a critical role in the vanadium diox…
In this work we present a complete characterization and magnetic study of vanadium oxide/hexadecylamine nanotubes (VOx/Hexa NT's) doped with Co2+ and Ni2+ ions. The morphology of the NT's has been characterized by Transmission Electron Microscopy (TEM) while the metallic elements have been quantified by Instrumental Neutron Activation Analysis (INAA) technique. The static and dynamic magnetic properties were studied collecting data of magnetization as a function of magnetic field and temperature and by Electron Paramagnetic Resonance (EPR). We observed that the incorporation of metallic ions (…
We report the fabrication and characterization of superconducting quantum interference devices (SQUIDs) based on InAs nanowires and vanadium superconducting electrodes. These mesoscopic devices are found to be extremely robust against thermal cycling and to operate up to temperatures of $\sim2.5$~K with reduced power dissipation. We show that our geometry allows to obtain nearly-symmetric devices with very large magnetic-field modulation of the critical current. All these properties make these devices attractive for on-chip quantum-circuit implementation.
Many strongly correlated electronic materials, including high-temperature superconductors, colossal magnetoresistance and metal-insulator-transition (MIT) materials, are inhomogeneous on a microscopic scale as a result of domain structure or compositional variations. An important potential advantage of nanoscale samples is that they exhibit the homogeneous properties, which can differ greatly from those of the bulk. We demonstrate this principle using vanadium dioxide, which has domain structure associated with its dramatic MIT at 68 degrees C. Our studies of single-domain vanadium dioxide nan…
Recently, the possibility to tune the critical current of conventional metallic superconductors via electrostatic gating was shown in wires, Josephson weak-links and superconductor-normal metal-superconductor junctions. Here we exploit such a technique to demonstrate a gate-controlled vanadium-based Dayem nano-bridge operated as a \emph{half-wave} rectifier at $3$ K. Our devices exploit the gate-driven modulation of the critical current of the Josephson junction, and the resulting steep variation of its normal-state resistance, to convert an AC signal applied to the gate electrode into a DC on…
We present results from an experimental study of the equilibrium and non-equilibrium transport properties of vanadium oxide nanobeams near the metal-insulator transition (MIT). Application of a large electric field in the insulating phase across the nanobeams produces an abrupt MIT and the individual roles of thermal and non-thermal effects in driving the transition are studied. Transport measurements at temperatures ($T$) far below the critical temperature ($T_c$) of MIT, in several nanoscale vanadium oxide devices, show that both $T$ and electric field play distinctly separate, but critical …
We investigate the electronic and structural changes at the nanoscale in vanadium dioxide (VO2) in the vicinity of its thermally driven phase transition. Both electronic and structural changes exhibit phase coexistence leading to percolation. In addition, we observe a dichotomy between the local electronic and structural transitions. Nanoscale x-ray diffraction reveals local, non-monotonic switching of the lattice structure, a phenomenon that is not seen in the electronic insulator-to-metal transition mapped by near-field infrared microscopy.
We present an ab initio study of spin dependent transport in armchair carbon nanotubes with transition metal adsorbates, iron or vanadium. We neglect the effect of tube curvature and model the nanotube by graphene with periodic boundary conditions. A density functional theory based nonequilibrium Green's function method is used to compute the electronic structure and zero-bias conductance. The presence of the adsorbate causes a strong scattering of electrons of one spin type only. The scattering is shown to be due to coupling of the two armchair band states to the metal 3d orbitals with matchi…
Long regarded as a model system for studying insulator-to-metal phase transitions, the correlated electron material vanadium dioxide (VO$_2$) is now finding novel uses in device applications. Two of its most appealing aspects are its accessible transition temperature ($\sim$341 K) and its rich phase diagram. Strain can be used to selectively stabilize different VO$_2$ insulating phases by tuning the competition between electron and lattice degrees of freedom. It can even break the mesoscopic spatial symmetry of the transition, leading to a quasi-periodic ordering of insulating and metallic nan…
The standard treatment of quantum corrections to semiclassical electronic conduction assumes that charge carriers propagate many wavelengths between scattering events, and succeeds in explaining multiple phenomena (weak localization magnetoresistance (WLMR), universal conductance fluctuations, Aharonov-Bohm oscillations) observed in polycrystalline metals and doped semiconductors in various dimensionalities. We report apparent WLMR and conductance fluctuations in H$_{x}$VO$_{2}$, a poor metal (in violation of the Mott-Ioffe-Regel limit) stabilized by the suppression of the VO$_{2}$ metal-insul…
The metal-insulator transition (MIT) in vanadium dioxide (VO2) has the potential to lead to a number of disruptive technologies, including ultra-fast data storage, optical switches, and transistors which move beyond the limitations of silicon. For applications, VO2 films are deposited on crystalline substrates to prevent cracking observed in bulk VO2 crystals across the thermally driven MIT. Near the MIT, VO2 films exhibit nanoscale coexistence between metallic and insulating phases, which opens up further potential applications such as memristors, tunable capacitors, and optically engineered …
Nano-thick metallic transition metal dichalcogenides such as VS$_{2}$ are essential building blocks for constructing next-generation electronic and energy-storage applications, as well as for exploring unique physical issues associated with the dimensionality effect. However, such 2D layered materials have yet to be achieved through either mechanical exfoliation or bottom-up synthesis. Herein, we report a facile chemical vapor deposition route for direct production of crystalline VS$_{2}$ nanosheets with sub-10 nm thicknesses and domain sizes of tens of micrometers. The obtained nanosheets fea…
We use apertureless scattering near-field optical microscopy (SNOM) to investigate the nanoscale optical response of vanadium dioxide (VO2) thin films through a temperature-induced insulator-to-metal transition (IMT). We compare images of the transition at both mid-infrared (MIR) and terahertz (THz) frequencies, using a custom-built broadband THz-SNOM compatible with both cryogenic and elevated temperatures. We observe that the character of spatial inhomogeneities in the VO2 film strongly depends on the probing frequency. In addition, we find that individual insulating (or metallic) domains ha…
We present the model of an ultrasensitive mid-infrared (mid-IR) photodetector operating in the mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) domains consisting of a hybrid heterostructure made of nanopatterned graphene (NPG) and vanadium dioxide (VO$_2$) which exhibits a large responsivity of $R\sim 10^4$ V/W, a detectivity exceeding $D^*\sim 10^{10}$ J, and a sensitivity in terms of noise-equivalent power $\mathrm{NEP}\sim 100$ fW/$\sqrt{\rm Hz}$ close to room temperature by taking advantage of the phase change of a thin VO$_2$ film. Our proposed photodetector can reach a…
Subwavelength modulators play an indispensable role in integrated photonic-electronic circuits. Due to weak light-matter interactions, it is always a challenge to develop a modulator with a nanometer scale footprint, low switching energy, low insertion loss and large modulation depth. In this paper, we propose the design of a vanadium dioxide dual-mode plasmonic waveguide electroabsorption modulator using a metal-insulator-VO$_2$-insulator-metal (MIVIM) waveguide platform. By varying the index of vanadium dioxide, the modulator can route plasmonic waves through the low-loss dielectric insulato…
We present a hierarchical quantum master equation (HQME) approach, which allows the numerically exact evaluation of higher-order current cumulants in the framework of full counting statistics for nonequilibrium charge transport in nanosystems. The novel methodology is exemplarily applied to a model of vibrationally coupled electron transport in a molecular nanojunction. We investigate the influence of cotunneling on avalanche-like transport, in particular in the nonresonant transport regime, where we find that inelastic cotunneling acts as trigger process for resonant avalanches. In this regim…
We report on the fabrication and characterization of microSQUID devices based on nanoscale vanadium/copper/vanadium Josephson weak links. Magnetically driven quantum interference patterns have been measured for temperatures in the 0.24 - 2 K range. As magnetometers, these devices obtain flux-to-voltage transfer function values as high as 450 microV/Phi_0 leading to promising magnetic flux resolution Phi_N < 3 microPhi_0 / Hz^(1/2), being here limited by the room temperature preamplification stage. Significant improvements in the flux noise performance figures, which are already competitive wit…
Silicon single-photon avalanche diode (SPAD) is a core device for single-photon detection in the visible and the near-infrared range, and widely used in many applications. However, due to limits of the structure design and device fabrication for current silicon SPADs, the key parameters of detection befficiency and timing jitter are often forced to compromise. Here, we propose a nanostructured silicon SPAD, which achieves high detection efficiency with excellent timing jitter simultaneously over a broad spectral range. The optical and electric simulations show significant performance enhanceme…
Nanophotonic (nanoplasmonic) structures confine, guide, and concentrate light on the nanoscale. Advancement of nanophotonics critically depends on active nanoscale control of these phenomena. Localized control of the insulator and metallic phases of vanadium dioxide (VO2) would open up a universe of applications in nanophotonics via modulation of the local dielectric environment of nanophotonic structures allowing them to function as active devices. Here we show dynamic reversible control of VO2 insulator-to-metal transition (IMT) locally on the scale of 15 nm or less and control of nanoantenn…
Motivated by recent experiments on the finite temperature Mott transition in VO2 films, we propose a classical coarse-grained dielectric breakdown model where each degree of freedom represents a nanograin which transitions from insulator to metal with increasing temperature and voltage at random thresholds due to quenched disorder. We describe the properties of the resulting non-equilibrium metal-insulator transition and explain the universal characteristics of the resistance jump distribution. We predict that by tuning voltage, another critical point is approached, which separates a phase of …
Vanadium dioxide (VO2) has been widely studied for its rich physics and potential applications, undergoing a prominent insulator-metal transition (IMT) near room temperature. The transition mechanism remains highly debated, and little is known about the IMT at nanoscale dimensions. To shed light on this problem, here we use ~1 nm wide carbon nanotube (CNT) heaters to trigger the IMT in VO2. Single metallic CNTs switch the adjacent VO2 at less than half the voltage and power required by control devices without a CNT, with switching power as low as ~85 $μW$ at 300 nm device lengths. We also obta…
We have systematically studied a variety of vanadium dioxide (VO2) crystalline forms, including bulk single crystals and oriented thin films, using infrared (IR) near-field spectroscopic imaging techniques. By measuring the IR spectroscopic responses of electrons and phonons in VO2 with sub-grain-size spatial resolution (~20 nm), we show that epitaxial strain in VO2 thin films not only triggers spontaneous local phase separations but also leads to intermediate electronic and lattice states that are intrinsically different from those found in bulk. Generalized rules of strain and symmetry depen…
