arXiv subjects

Robert H. Blick

Publications and source records attributed to Robert H. Blick.

At least 19 recordsLinked to original sources

arXiv2026

Epitaxy of strained, nuclear-spin free $^{76}$Ge quantum wells from solid source materials

Germanium quantum well heterostructures have rapidly emerged as a leading platform for solid-state quantum information processing; however, material quality limits scalability, and higher structural quality, higher purity, as well as zero nuclear spin, are required. Here, we address these problems by employing the heaviest of Ge isotopes, by evaporating high-purity $^{76}$Ge radiation detector material, as utilized in fundamental neutrino particle physics experiments, to fabricate $^{76}$Ge/$^{28}$Si$^{76}$Ge quantum wells for quantum applications and explore the respective challenges. Specifically, we demonstrate improved results on strain-relaxed virtual Si$_{0.2}$Ge$_{0.8}$ substrates, forward graded from Si, with a dislocation density below 3.7$\cdot$10$^{5}$ cm$^{-2}$, explore nuclear spin-free solid-source molecular beam epitaxy, and demonstrate first quantum transport in $^{76}$Ge quantum wells. We demonstrate a record-level quantum well interface width of 0.3 nm by X-ray reflectivity, and quantitatively compare it to atom probe tomography and scanning transmission electron microscopy. The grown layer reveals nuclear-spin-bearing impurity concentrations below 10$^{19}$ cm$^{-3}$ and chemical impurity levels below 10$^{18}$ cm$^{-3}$, except for residual carbon attributed to the graphite crucible of the Ge source, which may reach up to 10$^{19}$ cm$^{-3}$. Low-temperature magneto-transport measurements yield electron mobilities of 6.1$\cdot$10$^4$ cm$^2$V$^{-1}$s$^{-1}$ at 15 mK with a carrier density of 2.2$\cdot$10$^{11}$ cm$^{-2}$, indicating that residual carbon is the dominant scattering mechanism.

physics.app-ph↗

arXiv2025

Resistively detected electron spin resonance and g-factor in few-layer exfoliated MoS2 devices

MoS2 has recently emerged as a promising material for enabling quantum devices and spintronic applications. In this context, an improved physical understanding of the g-factor of MoS2 depending on device geometry is of great importance. Resistively detected electron spin resonance (RD-ESR) could be employed to and the determine the g-factor in micron-scale devices However, its application and RD-ESR studies have been limited by Schottky 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.

cond-mat.mes-hall↗

arXiv2024

A hybrid graphene-siliconnitride nanomembrane as a versatile and ultra-widely tunable mechanical device

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.

cond-mat.mes-hall↗

arXiv2024

Hybrid optomechanical superconducting qubit system

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.

quant-ph↗

arXiv2023

Addressing the spin-valley flavors in moir'e mini-bands of MoS2

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.

cond-mat.mes-hall↗

arXiv2022

Acoustically Induced Giant Synthetic Hall Voltages in Graphene

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.

cond-mat.mes-hall↗

arXiv2022

Comment on "Electron spin resonance and collective excitations in magic-angle twisted bilayer graphene"

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.

cond-mat.mes-hall↗

arXiv2022

Nuclear-induced dephasing and signatures of hyperfine effects in isotopically purified $^{13}$C graphene

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.

cond-mat.mes-hall↗

arXiv2021

Mechanically Modulated Sideband and Squeezing Effects of Membrane Resonators

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.

physics.class-ph↗

arXiv2021

Polarization amplification by spin-doping in nanomagnetic/graphene hybrid systems

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.

cond-mat.mes-hall↗

arXiv2019

Acoustically driven Dirac electrons in monolayer graphene

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.

cond-mat.mes-hall↗

arXiv2018

Intrinsic spin-orbit coupling gap and the evidence of a topological state in graphene

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 μeV. 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.

cond-mat.mes-hall↗

arXiv2018

A tank-circuit for ultrafast single particle detection in micropores

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.

physics.app-ph↗

arXiv2017

Upscaling High-Quality CVD Graphene Devices to 100 Micron-Scale and Beyond

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.

cond-mat.mtrl-sci↗

arXiv2016

Probing Electron Spin Resonance in Monolayer Graphene

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.

cond-mat.mtrl-sci↗

arXiv2015

Coupled Nanomechanical Electron Shuttles: Full Stochastic Modeling and Device-Level Simulation

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.

quant-ph↗

arXiv2014

In-vivo Network of Sensors and Actuators

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.

eess.SY↗

arXiv2013

Guided Neuronal Growth on Arrays of Biofunctionalized GaAs/InGaAs Semiconductor Microtubes

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.

cond-mat.soft↗