Search

MoS2 has recently emerged as a promising material for enabling quantum devices and spintronic applications. In this context, the demonstration of resistively detected electron spin resonance (RD-ESR) and the determination and improved physical understanding of the g factor are of great importance. However, its application and RD-ESR studies have been limited so far by Schotttky or high-resistance contacts to MoS2. Here, we exploit naturally n-doped few-layer MoS2 devices with ohmic tin (Sn) contacts that allow the electrical study of spin phenomena. Resonant excitation of electron spins and resistive detection is a possible path to exploit the spin effects in MoS2 devices. Using RD-ESR, we determine the g factor of few-layer MoS2 to be ~ 1.92 and observe that the g factor value is independent of the charge carrier density within the limits of our measurements., Comment: 4 figures, 7 pages

Integration of 2D materials in nanoelectromechanical systems (NEMS) marries the robustness of silicon-based materials with exceptional electrical controllability in 2D materials, drastically enhancing system performance which now is the key for many advanced applications in nanotechnology. Here, we experimentally demonstrate and theoretically analyze a powerful on-chip graphene integrated NEMS device consisting of a hybrid graphene/silicon-nitride membrane with metallic leads that enables an extremely large static and dynamic parameter regulation. When a static voltage is applied to the leads, the force induced by the thermal expansion difference between the leads and the membrane results in ultra-wide frequency tuning, deformation (post-buckling transition) and regulation of mechanical properties. Moreover, by injecting an alternating voltage to the leads, we can excite the resonator vibrating even far beyond its linear regime without a complex and space consuming actuation system. Our results prove that the device is a compact integrated system possessing mechanical robustness, high controllability, and fast response. It not only expands the limit of the application range of NEMS devices but also pushes multidimensional nanomechanical resonators into working in the nonlinear regime.

We propose an integrated nonlinear superconducting device based on a nanoelectromechanical shuttle. The system can be described as a qubit coupled to a bosonic mode. The topology of the circuit gives rise to an adjustable qubit/mechanical coupling, allowing the experimenter to tune between linear and quadratic coupling in the mechanical degrees of freedom. Owing to its flexibility and potential scalability, the proposed setup represents an important step towards the implementation of bosonic error correction with mechanical elements in large-scale superconducting circuits. We give preliminary evidence of this possibility by discussing a simple state-swapping protocol that uses this device as a quantum memory element., Comment: 20 pages, 4 figures

The physics of moir'e superlattices and the resulting formation of mini-bands in van der Waals materials have opened up an exciting new field in condensed matter physics. These systems exhibit a rich phase diagram of novel physical phenomena and exotic correlated phases that emerge in the low-dispersing bands. Transition metal dichalcogenides, in particular, molybdenum disulfide (MoS2), are potential candidates to extend the studies on moir'e electronics beyond graphene. Our transport spectroscopy measurements and analysis reveal a correlation-driven phase transition and the emergence of discrete mini-bands in MoS2 moir'e superlattices that remained elusive so far. We resolve these mini-bands arising from quantum mechanical tunneling through Schottky barriers between the MoS2 and its metallic leads. Energy scales deduced from a first approach exhibit an astounding agreement with our experimental observations. The behavior under thermal activation suggests a Lifshitz phase transition at low temperatures that is driven by a complete spin-valley symmetry breaking. These intriguing observations bring out the potential of twisted MoS2 to explore correlated electron states and associated physics.

This comment pertains the recent manuscript by Morissette {\it et al.} [arXiv:2206.08354v1]. The authors claim to have found signatures of collective excitations in electron spin resonance experiments that would be linked to the correlated structure of magic angle bilayer graphene. However, identical resonance features have already been reported in previous works on mono- and few-layer graphene, voiding their theoretical framework. A straight forward theoretical picture within the single-particle topologically non-trivial band structure of graphene delivers satisfactory explanations for the observation of the resonant features and applies as well to the data presented by Morissette {\it et al.}. However, this intuitive picture has been disregarded by the authors., Comment: 3 pages, 1 figure

The hyperfine interaction between the spins of electrons and nuclei is both a blessing and a curse. It can provide a wealth of information when used as an experimental probing technique but it can also be destructive when it acts as a dephasive perturbation on the electronic system. In this work, we fabricated large scale single and multilayer isotopically-purified $^{13}$C graphene Hall bars to search for interaction effects between the nuclear magnetic moments and the electronic system. We find signatures of nuclei with a spin in the analysis of the weak localization phenomenon that shows a significant dichotomy in the scattering times of monolayer $^{12}$C and $^{13}$C graphene close the Dirac point. Microwave-induced electron spin flips were exploited to transfer momentum to the nuclei and build-up a nuclear field. The presence of a very weak nuclear field is encoded in a modulation of the electron Zeeman energy which shifts the energy for resonant absorption and reduces the $g$-factor., Comment: 5 figures, 21 pages

Any departure from graphene's flatness leads to the emergence of artificial gauge fields that act on the motion of the Dirac fermions through an associated pseudomagnetic field. Here, we demonstrate the tunability of strong gauge fields in non-local experiments using a large planar graphene sheet that conforms to the deformation of a piezoelectric layer by a surface acoustic wave. The acoustic wave induces a longitudinal and a giant synthetic Hall voltage in the absence of external magnetic fields. The superposition of a synthetic Hall potential and a conventional Hall voltage can annihilate the sample's transversal potential at large external magnetic fields. Surface acoustic waves thus provide a promising and facile avenue for the exploit of gauge fields in large planar graphene systems.

Coupling graphene's excellent electron and spin transport properties with higher spin-orbit coupling material allows tackling the hurdle of spin manipulation in graphene, due to the proximity to van-der-Waals layers. Here we use magneto transport measurements to study the electron spin resonance on a combined system of graphene and MoS2 at 1.5K. The electron spin resonance measurements are performed in the frequency range of 18-33GHz, which allows us to determine the g-factor in the system. We measure average g-factor of 1.91 for our hybrid system which is a considerable shift compared to what is observed in graphene on SiO2. This is a clear indication of proximity induced SOC in graphene in accordance with theoretical predictions.

We investigate the sideband spectra of a driven nonlinear mode with its eigenfrequency being modulated at a low frequency (< 1 kHz). This additional parametric modulation leads to prominent antiresonance lineshapes in the sideband spectra, which can be controlled through the vibration state of the driven mode. We also establish a direct connection between the antiresonance frequency and the squeezing of thermal fluctuation in the system. Our work not only provides a simple and robust method for squeezing characterization but also opens a new possibility toward sideband applications.

Dirac electrons in graphene are to lowest order spin 1/2 particles, owing to the orbital symmetries at the Fermi level. However, anisotropic corrections in the $g$-factor appear due to the intricate spin-valley-orbit coupling of chiral electrons. We resolve experimentally the $g$-factor along the three orthogonal directions in a large-scale graphene sample. We employ a Hall bar structure with an external magnetic field of arbitrary direction, and extract the effective $g$-tensor via resistively-detected electron spin resonance. We employ a theoretical perturbative approach to identify the intrinsic and extrinsic spin orbit coupling and obtain a fundamental parameter inherent to the atomic structure of $^{12}$C, commonly used in ab-initio models., Comment: 5 pages, 4 figures

The generation of non-equilibrium electron spin polarization, spin transport, and spin detection are fundamental in many quantum devices. We demonstrate that a lattice of magnetic nanodots enhances the electron spin polarization in monolayer graphene via carrier exchange. We probed the spin polarization through a resistively-detected variant of electron spin resonance (ESR) and observed resonance amplification mediated by the presence of the nanodots. Each nanodot locally injects a surplus of spin-polarized carriers into the graphene, and the ensemble of all "spin hot spots" generates a non-equilibrium electron spin polarization in the graphene layer at macroscopic lengths. This occurs whenever the interdot distance is comparable or smaller than the spin diffusion length., Comment: Title of original submission "A nanomagnetic polarization amplifier for graphene" was changed

We demonstrate the interaction between surface acoustic waves and Dirac electrons in monolayer graphene at low temperatures and high magnetic fields. A metallic interdigitated transducer launches surface waves that propagate through a conventional piezoelectric GaAs substrate and couple to large-scale monolayer CVD graphene films resting on its surface. Based on the induced acousto-electric current, we characterize the frequency domains of the transducer from its first to the third harmonic. We find an oscillatory attenuation of the SAW velocity depending on the conductivity of the graphene layer. The acousto-electric current reveals additional fine structure that is absent in pure magnetotransport. In addition we find a shift between the acousto-electric longitudinal voltage and the velocity change of the SAW. We attribute this shift to the periodic strain field from the propagating SAW that slightly modifies the Dirac cone.

We present an ultrafast single sub-micron particle detection method based on a half-bowtie coplanar waveguide. The method is capable of resolving the translocation of these particles at a bandwidth greater than 30MHz. We compare experimentally the simultaneous use of our radio- frequency technique with conventional DC based resistive pulse recordings and find that our method has a throughput that is enhanced by two orders of magnitude. The technique incorporates a microfluidic circuit and has potential to be employed for screening nano particles and biopolymers such as DNA at frequencies in excess of 1 GHz.

In 2005 Kane & Mele[C. L. Kane and E. J. Mele, Phys. Rev. Lett. 95, 226801 (2005)], predicted that at sufficiently low energy, graphene exhibits a topological state of matter with an energy gap generated by the atomic spin-orbit interaction. However, this intrinsic gap has not been measured to this date. In this letter, we exploit the chirality of the low energy states to resolve this gap. We probe the spin states experimentally, by employing low temperature microwave excitation in a resistively detected electron spin resonance on graphene. The structure of the topological bands is reflected in our transport experiments, where our numerical models allow us to identify the resonance signatures. We determine the intrinsic spin-orbit bulk gap to be exactly 42.2 {\mu}eV. Electron-spin resonance experiments can reveal the competition between the intrinsic spin-orbit coupling and classical Zeeman energy that arises at low magnetic fields and demonstrate that graphene remains to be a material with surprising properties., Comment: 5 pages, 4 figures

The precise value of the $g$-factor in graphene is of fundamental interest for all spin-related properties and their application. We investigate monolayer graphene on a Si/SiO2 substrate by resistively detected electron spin resonance (ESR). Surprisingly, the magnetic moment and corresponding g-factor of 1.952+/-0.002 is insensitive to charge carrier type, concentration, and mobility., Comment: 5 pages, 3 figures

We describe a method for transferring ultra large-scale CVD-grown graphene sheets. These samples can be fabricated as large as several cm$^2$ and are characterized by magneto-transport measurements on SiO$_2$ substrates. The process we have developed is highly effective and limits damage to the graphene all the way through metal liftoff, as shown in carrier mobility measurements and the observation of the quantum Hall effect. The charge-neutral point is shown to move drastically to near-zero gate voltage after a 2-step post-fabrication annealing process, which also allows for greatly diminished hysteresis., Comment: 5 pages, 5 figures. Revision includes updated title, figures updated with extra labels and to be compatible with black and white printing, and various minor edits. Added publication information

An advanced system of sensors/actuators should allow the direct feedback of a sensed signal into an actuation, e.g., an action potential propagation through an axon or a special cell activity might be sensed and suppressed by an actuator through voltage stimulation or chemical delivery. Such a complex procedure of sensing and stimulation calls for direct communication among these sensors and actuators. In addition, minimizing the sensor/actuator to the size of a biological cell can enable the cell-level automatic therapy. For this objective, we propose such an approach to form a peer-to-peer network of \emph{in vivo} sensors/actuators (S/As) that can be deployed with or even inside biological cells. The S/As can communicate with each other via electromagnetic waves of optical frequencies. In comparison with the comparable techniques including the radio-frequency identification (RFID) and the wireless sensor network (WSN), this technique is well adapted for the cell-level sensing-actuating tasks considering the requirements on size, actuation speed, signal-collision avoidance, etc., Comment: 16 pages, 16 figures

Earlier theory and measurements show that nanomechanical electron shuttles can work as ratchets for radio-frequency rectification, but its performance was hard to predict so far. This paper focuses on the coupled shuttles which can potentially break symmetry better than a single shuttle. We propose a full stochastic model of coupled shuttles, where the mechanical motion of nanopillars and the incoherent electronic tunneling are modeled as a Markov chain. A linear master equation is constructed. In particular, the interaction of the their randomness is taken into account. This model favors analyzing the symmetry breaking that results in the observed rectification current~\cite{Kim2010_PRL}. Further, based on the model we propose the deterministic equations of mean physical variables by assuming multivariate Gaussian distribution, which enables complex device simulation and design.

We demonstrate embedded growth of cortical mouse neurons in dense arrays of semiconductor microtubes. The microtubes, fabricated from a strained GaAs/InGaAs heterostructure, guide axon growth through them and enable electrical and optical probing of propagating action potentials. The coaxial nature of the microtubes -- similar to myelin -- is expected to enhance the signal transduction along the axon. We present a technique of suppressing arsenic toxicity and prove the success of this technique by overgrowing neuronal mouse cells., Comment: 3 pages, 4 figures

We demonstrate single electron shuttling through two coupled nanomechanical pendula. The pendula are realized as nanopillars etched out of the semiconductor substrate. Coulomb blockade is found at room temperature, allowing metrological applications. By controlling the mechanical shuttling frequency we are able to validate the different regimes of electron shuttling.

We present spontaneous symmetry breaking in a nanoscale version of a setup prolific in classical mechanics: two coupled nanomechanical pendulums. The two pendulums are electron shuttles fabricated as nanopillars and placed between two capacitor plates in a homogeneous electric field. Instead of being mechanically coupled through a spring they exchange electrons, i.e. they shuttle electrons from the source to the drain 'capacitor plate'. Nonzero DC current through this system by external AC excitation is caused via dynamical symmetry breaking. This symmetry-broken current appears at sub- and superharmonics of the fundamental mode of the coupled system.

We observe direct mechanical mixing in nanoelectromechanical transistors fabricated in semiconductor materials operating in the radio frequency band of 10-1000 MHz. The device is made of a mechanically flexible pillar with a length of 240 nm and a diameter of 50 nm, placed between two electrodes in an impedance matched coplanar wave guide. We find a non-linear IV-characteristic, which enables radio frequency mixing of two electromagnetic signals via the nanomechanical transistor. Potential applications for this mixer are ultrasensitive displacement detection or signal processing in communication electronic circuits requiring high-throughput insulation., Comment: 3 pages, 4 figures. This article has been published by Applied Physics Letters. You can find this article online at http://apl.aip.org in Oct. 2007

We present measurements on direct radio-frequency pumping of ion channels and pores bound in bilipid membranes. We make use of newly developed microcoaxes, which allow delivering the high frequency signal in close proximity to the membrane bound proteins and ion channels. We find rectification of the radio-frequency signal, which is used to pump ions through the channels and pores., Comment: 18 pages, 4 figures

We report on strongly enhanced electron multiplication in thin silicon membranes. The device is configured as a transmission-type membrane for electron multiplication. A sub-threshold electric field applied on the emission side of the membrane enhances the number of electrons emitted by two orders of magnitude. This enhancement stems from field emitted electrons stimulated by the incident particles, which suggests that stacks of silicon membranes can form ultra-sensitive electron multipliers., Comment: 4 pages, 3 figures, submit to Appl. phys. Lett. (2007)

A new transmission-type electron multiplier was fabricated from silicon-on-insulator (SOI) material by integrating an array of one dimensional (1D) silicon nanopillars onto a two dimensional (2D) silicon membrane. Primary electrons are injected into the nanopillar-membrane system from the flat surface of the membrane, while electron emission from the other side is probed by an anode. The secondary electron yield (SEY) from nanopillars is found to be about 1.8 times that of plane silicon membrane. This gain in electron number is slightly enhanced by the electric field applied from the anode. Further optimization of the dimensions of nanopillars and membrane and application of field emission promise an even higher gain for detector applications and allow for probing of electronic/mechanical excitations in nanopillar-membrane system excited by incident particles or radiation., Comment: 4 figures

The dream of every surfer is an extremely steep wave propagating at the highest speed possible. The best waves for this would be shock waves, but are very hard to surf. In the nanoscopic world the same is true: the surfers in this case are electrons riding through nanomechanical devices on acoustic waves [1]. Naturally, this has a broad range of applications in sensor technology and for communication electronics for which the combination of an electronic and a mechanical degree of freedom is essential. But this is also of interest for fundamental aspects of nano-electromechanical systems (NEMS), when it comes to quantum limited displacement detection [2] and the control of phonon number states [3]. Here, we study the formation of shock waves in a NEMS resonator with an embedded two-dimensional electron gas using surface acoustic waves. The mechanical displacement of the nano-resonator is read out via the induced acoustoelectric current. Applying acoustical standing waves we are able to determine the anomalous acoustocurrent. This current is only found in the regime of shock wave formation. We ontain very good agreement with model calculations., Comment: 14 Pages including 4 figures

Self excitation is a mechanism which is ubiquitous for electromechanical power devices such as electrical generators. This is conventionally achieved by making use of the magnetic field component in electrical generators [1], where a good example are the overall visible wind farm turbines [2]. In other words, a static force, like wind acting on the rotor blades, can generate a resonant excitation at a certain mechanical frequency. For nanomechanical systems [3,4,5] such a self excitation (SE) mechanism is highly desirable as well, since it can generate mechanical oscillations at radio frequencies by simply applying a DC bias voltage. This is of great importance for low-power signal communication devices and detectors, as well as for mechanical computing elements. For a particular nanomechanical system - the single electron shuttle - this effect was predicted some time ago by Gorelik et al. [6]. Here, we use a nano-electromechanical single electron transistor (NEMSET) to demonstrate self excitation for both the soft and hard regime, respectively. The ability to use self excitation in nanomechanical systems may enable the detection of quantum mechanical backaction effects [7] in direct tunneling, macroscopic quantum tunneling [8], and rectification [9]. All these effects have so far been over shadowed by the large driving voltages, which had to be applied., Comment: 19 pages including 4 figures

We present a new generation of nano-electromechanical systems (NEMS), which are realized by doping the semiconductor base material. In contrast to the traditional approach these doped NEMS (D-NEMS) do not require a metallization layer. This makes them far lighter and hence increases resonance frequency and quality factor. Additionally, D-NEMS can be tuned from the conductive state into an insulating one. This will enable a host of new device designs, like mechanically tunable pin-junctions and nanomechanical single electron switches. We demonstrate D-NEMS fabrication and operation from the intrinsic, to the light, and to the heavy regime of doping., Comment: 4 pages, 4 figures

In quantum dot circuits, screening electron clouds in strongly-coupled leads will hybridize with the states of the artificial atom. Using a three-terminal geometry, we directly probe the atomic structure of a quantum dot with Kondo coupling. Our measurements reveal that this hybrid system behaves as a non-linear entity with orbital degeneracy. Geometric distortion reduces the symmetry, lowers the energy, and lifts the degeneracy--the Jahn-Teller effect., Comment: 4 pages, 4 figures

Relaxation of single defects in a nanometer sized resonator is observed by coupling surface acoustic waves to a freely suspended beam. The surface waves act on the resonator as driving forces being able to modify the internal friction in the beam. In analogy to classical experiments on internal friction in macroscopic samples, we perform frequency, amplitude, and temperature dependent experiments on the nano resonator and find a scenario which is consistent with the observation of single defect relaxation., Comment: 5 pages, 4 figures

We demonstrate the formation of confinement potentials in suspended nanostructures induced by the geometry of the devices. We then propose a setup for measuring the resulting geometric phase change of electronic wave functions in such a mechanical nanostructure. The device consists of a suspended loop through which a phase coherent current is driven. Combination of two and more geometrically induced potentials can be applied for creating mechanical quantum bit states.

We present measurements on nanomechanical resonators operating in the radio frequency range. We apply a setup which allows the comparison of two schemes of displacement detection for mechanical resonators, namely conventional power reflection measurements of a probing signal and direct detection by capacitive coupling via a gate electrode. For capacitive detection, we employ an on-chip preamplifier, which enables direct measurements of the resonator's displacement. We observe that the response of the mechanical resonator depends on the detection technique applied, which is verified in model calculations. We show results on the detection of subharmonics.-Paper withdrawn, Comment: 8 pages, 3 figures