Showing papers by "Solid State Physics Laboratory published in 2021"
TL;DR: In this paper, the authors demonstrate high-fidelity coherent transport of an electron spin qubit between quantum dots in isotopically-enriched silicon and report a polarization transfer fidelity of 99.97% and an average coherent transfer fidelity was 99.4%.
Abstract: A fault-tolerant quantum processor may be configured using stationary qubits interacting only with their nearest neighbours, but at the cost of significant overheads in physical qubits per logical qubit. Such overheads could be reduced by coherently transporting qubits across the chip, allowing connectivity beyond immediate neighbours. Here we demonstrate high-fidelity coherent transport of an electron spin qubit between quantum dots in isotopically-enriched silicon. We observe qubit precession in the inter-site tunnelling regime and assess the impact of qubit transport using Ramsey interferometry and quantum state tomography techniques. We report a polarization transfer fidelity of 99.97% and an average coherent transfer fidelity of 99.4%. Our results provide key elements for high-fidelity, on-chip quantum information distribution, as long envisaged, reinforcing the scaling prospects of silicon-based spin qubits. Long-range coherent spin-qubit transfer between semiconductor quantum dots requires understanding and control over associated errors. Here, the authors achieve high-fidelity coherent state transfer in a Si double quantum dot, underpinning the prospects of a large-scale quantum computer.
46 citations
TL;DR: In the authors' bilayer graphene quantum dots, it is demonstrated that the valley g-factor gv, defined analogously to the spin g-Factor gs for valley splitting in a perpendicular magnetic field, is tunable by over a factor of 4 from 20 to 90, by gate voltage adjustments only.
Abstract: Quantum states in graphene are 2-fold degenerate in spins, and 2-fold in valleys. Both degrees of freedom can be utilized for qubit preparations. In our bilayer graphene quantum dots, we demonstrate that the valley g-factor gv, defined analogously to the spin g-factor gs for valley splitting in a perpendicular magnetic field, is tunable by over a factor of 4 from 20 to 90, by gate voltage adjustments only. Larger gv results from larger electronic dot sizes, determined from the charging energy. On our versatile device, bipolar operation, charging our quantum dot with charge carriers of the same or the opposite polarity as the leads, can be performed. Dots of both polarities are tunable to the first charge carrier, such that the transition from an electron to a hole dot by the action of the plunger gate can be observed. Addition of gates easily extends the system to host tunable double dots.
35 citations
TL;DR: In this article, the discovery of correlated electron-hole states in double-bilayer graphene torsion has been reported, and a correlated electron hole state was found in a single-layer double-bilayer graph.
Abstract: When twisted to angles near 1°, graphene multilayers provide a window on electron correlation physics. Here, we report the discovery of a correlated electron-hole state in double-bilayer graphene t...
28 citations
TL;DR: In this paper, a review of diffraction related phenomena/principles such as powder X-ray diffraction, and thin-film/grazing incidence Xray Diffraction (GIXRD) comprehensively for thin film samples which are used frequently in various branches of science and technology is presented.
Abstract: X-ray diffraction (XRD) techniques are powerful, non-destructive characterization tool with minimal sample preparation. XRD provides the first information about the materials phases, crystalline structure, average crystallite size, micro and macro strain, orientation parameter, texture coefficient, degree of crystallinity, crystal defects etc. XRD analysis provides information about the bulk, polycrystalline thin films, and multilayer structures, which is very important in various scientific and material engineering fields. This review discusses the diffraction related phenomena/principles such as powder X-ray diffraction, and thin-film/grazing incidence X-ray diffraction (GIXRD) comprehensively for thin film samples which are used frequently in various branches of science and technology. The review also covers few case studies on polycrystalline thin-film samples related to phase analysis, preferred orientation parameter (texture coefficient) analysis, stress evaluation in thin films and multilayer, multiphase content identification, bifurcation of multiphase on multilayer samples, depth profiling in thin-film/ multilayer structures, the impact of doping effect on structural properties of thin films etc., comprehensively using GIXRD/XRD.
21 citations
TL;DR: In this article, the Kondo effect was observed in bilayer graphene quantum dots and its interplay with weak spin-orbit coupling was studied. But the authors focused on the interplay between spin and orbit interaction and the Kondrack effect, which can lead to a underscreened Kondo effects in quantum dots in bilayered graphene.
Abstract: The Kondo effect is a cornerstone in the study of strongly correlated fermions. The coherent exchange coupling of conduction electrons to local magnetic moments gives rise to a Kondo cloud that screens the impurity spin. Here we report on the interplay between spin–orbit interaction and the Kondo effect, that can lead to a underscreened Kondo effects in quantum dots in bilayer graphene. More generally, we introduce a different experimental platform for studying Kondo physics. In contrast to carbon nanotubes, where nanotube chirality determines spin–orbit coupling breaking the SU(4) symmetry of the electronic states relevant for the Kondo effect, we study a planar carbon material where a small spin–orbit coupling of nominally flat graphene is enhanced by zero-point out-of-plane phonons. The resulting two-electron triplet ground state in bilayer graphene dots provides a route to exploring the Kondo effect with a small spin–orbit interaction. The Kondo effect has been observed in a variety of systems, including carbon nanotube quantum dots and graphene in the presence of impurities. Here, the authors report the observation of the Kondo effect in bilayer graphene quantum dots and study its interplay with weak spin-orbit coupling.
17 citations
TL;DR: In this paper, the authors demonstrate that by applying hydrostatic pressure, an additional control of the band structure becomes possible due to the change of tunnel couplings between the layers, and they find that the flat bands and the gaps separating them can be drastically changed by pressures up to 2 GPa, in good agreement with theoretical simulations.
Abstract: Twisted two-dimensional structures open new possibilities in band structure engineering. At magic twist angles, flat bands emerge, which gave a new drive to the field of strongly correlated physics. In twisted double bilayer graphene dual gating allows changing of the Fermi level and hence the electron density and also allows tuning of the interlayer potential, giving further control over band gaps. Here, we demonstrate that by application of hydrostatic pressure, an additional control of the band structure becomes possible due to the change of tunnel couplings between the layers. We find that the flat bands and the gaps separating them can be drastically changed by pressures up to 2 GPa, in good agreement with our theoretical simulations. Furthermore, our measurements suggest that in finite magnetic field due to pressure a topologically nontrivial band gap opens at the charge neutrality point at zero displacement field.
15 citations
TL;DR: In this article, the transformation of the precursor MoO3 into two-dimensional MoSe2 in the synthesis using Chemical Vapor Deposition method is monitored using micro-Raman spectroscopy.
14 citations
TL;DR: In this article, metal oxide film humidity sensors were fabricated using SAW resonators of 433.92-MHz frequency to measure humidity in the range of 0%-98% relative humidity.
Abstract: The surface acoustic wave (SAW) humidity sensor may possess many attractive sensing characteristics such as high sensitivity, high resolution, high stability, frequency output, ease of interfacing, small size, and broad dynamic range. Mostly, the polymer materials are used for the SAW humidity sensor fabrication. But the polymer SAW sensors suffer from broad bandwidth, instability due to ambient temperature, nonlinearity, and small dynamic range. This article presents the fabrication of metal oxide film humidity sensors using SAW resonators of 433.92-MHz frequency. Five different SAW humidity sensors were fabricated by varying the deposited alumina film thickness to measure humidity in the range of 0%–98% relative humidity (RH). The hydrophilic films were formed by dip coating of alumina solution of different molar concentrations. The alumina film is thermally stable and inert. The static and dynamic response characteristics were determined from the shift in resonant peaks at different humidity using an HP 85046A vector network analyzer (VNA). The minimum sensitivity of the least sensitive sensor was found to be 2.51 kHz/%RH. The sensors show linear response ( $R^{2} \ge0.98$ ), high sensitivity (max. ~ 9 kHz/%RH), negligible hysteresis error (≤0.50%), wide dynamic range, and inexpensive fabrication due to the use of commercial resonators. The response parameters of the sensors were compared with the parameters of other oxide SAW sensors reported in the literature. Finally, the linear sensor was interfaced to the electronic and associated signal conditioning circuits to display humidity in %RH.
14 citations
TL;DR: This experimental observation of electron jetting has consequences for carrier transport in two-dimensional materials with a trigonally warped band structure in general, as well as for devices relying on ballistic and valley-selective transport.
Abstract: Graphene has evolved as a platform for quantum transport that can compete with the best and cleanest semiconductor systems. Here, we report on the observation of distinct electronic jets emanating from a narrow split-gate-defined channel in bilayer graphene. We find that these jets, which are visible via their interference patterns, occur predominantly with an angle of 60° between each other. This observation is related to the trigonal warping in the band structure of bilayer graphene, which, in conjunction with electron injection through a constriction, leads to a valley-dependent selection of momenta. This experimental observation of electron jetting has consequences for carrier transport in two-dimensional materials with a trigonally warped band structure in general, as well as for devices relying on ballistic and valley-selective transport.
14 citations
18 Jan 2021
TL;DR: In this article, the authors reported high TE performance in MCu3X4, reaching the figure of merit (ZT) above 2 at 1000 K, from first-principles calculations neglecting electron-phonon scattering, spin-orbit couplin...
Abstract: Few authors reported high TE performance in MCu3X4, reaching the figure of merit (ZT) above 2 at 1000 K, from first-principles calculations neglecting electron–phonon scattering, spin-orbit couplin...
13 citations
TL;DR: In this article, the effect of central metal atom on interaction behavior of a composite constituted of two materials, Single walled carbon nanotubes (SWCNT) and metal phthalocyanines (MPcs) with ammonia gas was analyzed.
Abstract: The present study deals with analysing the effect of central metal atom on interaction behaviour of a composite constituted of two materials, Single walled carbon nanotubes (SWCNT) and metal phthalocyanines (MPcs) (SWCNT-MPc) with ammonia gas. For this purpose, three metal phthalocyanines namely; Magnesium phthalocyanine (MgPc), Aluminum phthalocyanine hydroxide (AlPcOH) and Titanyl phthalocyanine (TiOPc) were taken and their variation in resistances with exposure of ammonia gas is taken as detection parameter. The central metal ions of MPcs were chosen so that valence electrons are in s, p and d orbitals respectively. The surface-interface interaction of pristine SWCNT towards ammonia gas was found to increase with better repeatability and stability after addition of MPcs. SWCNT-TiOPc composite exhibited maximum interaction with ammonia vapors (≈ 3 times pristine SWCNT) followed by SWCNT- MgPc (≈ 2 times pristine SWCNT), while AlPcOH had shown faster desorption (≈ 0.5 times faster) as compared to pristine SWCNT during recovery stage. The concept of charge transfer mechanism between SWCNT-MPcs and ammonia gas and varied orbital state accommodating ammonia lone pairs were used to explain interaction studies. Consistencies observed in physics and chemistry analysis highlighted the significance of both these fields to have complete understanding of the interaction phenomena between SWCNT-MPcs and ammonia gas.
TL;DR: In this paper, upconversion (UC) luminescence studies showed that the emission bands of the prepared Na3Y(PO4)2:Yb3+/Er3+ phosphors appear in the green and red regions under 980nm laser excitation.
TL;DR: In this article, the Coulomb repulsion allows an initial charge transition to induce subsequent charge transitions, inducing a cascade of electron hops, like toppling dominoes, to read out distant spins.
Abstract: The spin of a single electron in a semiconductor quantum dot provides a well-controlled and long-lived qubit implementation. The electron charge in turn allows control of the position of individual electrons in a quantum dot array, and enables charge sensors to probe the charge configuration. Here we show that the Coulomb repulsion allows an initial charge transition to induce subsequent charge transitions, inducing a cascade of electron hops, like toppling dominoes. A cascade can transmit information along a quantum dot array over a distance that extends by far the effect of the direct Coulomb repulsion. We demonstrate that a cascade of electrons can be combined with Pauli spin blockade to read out distant spins and show results with potential for high fidelity using a remote charge sensor in a quadruple quantum dot device. We implement and analyse several operating modes for cascades and analyse their scaling behaviour. We also discuss the application of cascade-based spin readout to densely-packed two-dimensional quantum dot arrays with charge sensors placed at the periphery. The high connectivity of such arrays greatly improves the capabilities of quantum dot systems for quantum computation and simulation.
TL;DR: In this article, a cubic zinc-blend structure with (111) preferred orientation and nearly stoichiometric composition was obtained for a ZnS thin film developed on the mercury cadmium telluride (HgCdTe) substrate using the thermal evaporation technique.
TL;DR: In this article, a strain balanced InAs/GaSb type-II superlattice structures have been grown using molecular beam epitaxy, where InSb like interfaces have been introduced at both InAs on GaSb and InAs surfaces using migration enhanced epitaxy to compensate the tensile strain between the constituent binaries of the super-link.
TL;DR: In this paper, an extensive Victory TCAD-based assessment to evaluate the device performance under heavy ion particle strike induced single event effects (SEEs) has been presented, where the impact of SEEs on π-shaped AlGaN/GaN HEMT architecture has been compared with conventional HEMTs.
Abstract: This paper presents an extensive Victory TCAD based assessment to evaluate the device performance under heavy ion particle strike induced single event effects (SEEs). The impact of SEEs on π-shaped AlGaN/GaN HEMT architecture has been compared with conventional AlGaN/GaN HEMT. For validation of simulation, models have been calibrated against the experimental data of in-house fabricated GaN HEMTs on SiC wafers, after which π-shaped architecture is realized using Silvaco’s Victory Process simulation tools. Comparisons demonstrate that π-Gate HEMT architecture is a SEE hardened device under different heavy ion particle strike conditions. Further, due to the step modification in the electric field itself, the π-Gate HEMT also exhibits SEE hardened operation under different ambient temperatures. The effect of angled heavy ion particle strike has also been studied for evaluating the device performance with regards to SEE.
TL;DR: In this article, the authors use multilayer gate technology to create a device based on two distinct phases in adjustable regions of a magic-angle twisted bilayer graphene (MATBG) device.
Abstract: In situ electrostatic control of two-dimensional superconductivity1 is commonly limited due to large charge carrier densities, and gate-defined Josephson junctions are therefore rare2,3. Magic-angle twisted bilayer graphene (MATBG)4–8 has recently emerged as a versatile platform that combines metallic, superconducting, magnetic and insulating phases in a single crystal9–14. Although MATBG appears to be an ideal two-dimensional platform for gate-tunable superconductivity9,11,13, progress towards practical implementations has been hindered by the need for well-defined gated regions. Here we use multilayer gate technology to create a device based on two distinct phases in adjustable regions of MATBG. We electrostatically define the superconducting and insulating regions of a Josephson junction and observe tunable d.c. and a.c. Josephson effects15,16. The ability to tune the superconducting state within a single material circumvents interface and fabrication challenges, which are common in multimaterial nanostructures. This work is an initial step towards devices where gate-defined correlated states are connected in single-crystal nanostructures. We envision applications in superconducting electronics17,18 and quantum information technology19,20. In situ electrostatic control of two-dimensional superconductivity is commonly limited due to large charge carrier densities. Now, by means of local gates, electrostatic gating can define a Josephson junction in a magic-angle twisted bilayer graphene device, a single-crystal material.
TL;DR: In this paper, the authors have reported the compositional effect of BCT concentration on structure, surface morphology, dielectric properties and energy storage capacity of BZT-xBCT ceramics.
TL;DR: In this article, the authors reviewed the origins of residual stress in MEMS fabrication processes and different techniques involved in testing and characterization of residual stresses are reviewed, and a brief overview of the possible route to minimize the residual stresses is also presented.
Abstract: Micro-electro-mechanical system (MEMS) technology has radically changed the scale, performance, and cost of a wide variety of sensors and actuators by taking advantage of batch fabrication. The multidisciplinary nature of MEMS employs knowledge of diverse technical areas to realize improved and novel transducer systems. This also brings various associated challenges that are otherwise being ignored in a simple macro-dimensional system. MEMS devices typically comprise several deposited thick and thin films as well as bonded of dissimilar materials (like silicon, metal, glass, etc.). Residual stress is one of the most common outcomes during this integration/stacking of distinctly different materials for the fabrication of novel MEMS structures. The residual stress may significantly affect the performance and reliability of the fabricated devices. Thus, the evaluation and regulation of residual stress are one of the crucial aspects to assess the functioning of modern-day MEMS devices. This paper reviewed the origins of residual stress in MEMS fabrication processes. Different techniques involved in testing and characterization of the residual stresses are reviewed. Few important case studies are discussed to highlight the effect of residual stress (generated during various fabrication processes) on characteristics of different MEMS structures. The brief overview of the possible route to minimize the residual stresses is also presented.
TL;DR: In this article, a linear quantum dot array is used to simulate a Heisenberg chain of four spins, dialing in homogeneous exchange couplings, and probing the low-energy antiferromagnetic eigenstate with singlet-triplet correlation measurements.
Abstract: Quantum-mechanical correlations of interacting fermions result in the emergence of exotic phases. Magnetic phases naturally arise in the Mott-insulator regime of the Fermi-Hubbard model, where charges are localized and the spin degree of freedom remains. In this regime the occurrence of phenomena such as resonating valence bonds, frustrated magnetism, and spin liquids are predicted. Quantum systems with engineered Hamiltonians can be used as simulators of such spin physics to provide insights beyond the capabilities of analytical methods and classical computers. To be useful, methods for the preparation of intricate many-body spin states and access to relevant observables are required. Here we show the quantum simulation of magnetism in the Mott-insulator regime with a linear quantum dot array. We characterize a Heisenberg chain of four spins, dial in homogeneous exchange couplings, and probe the low-energy antiferromagnetic eigenstate with singlet-triplet correlation measurements. The methods and control presented here open new opportunities for the simulation of quantum magnetism benefiting from the flexibility in tuning and layout of gate-defined quantum dot arrays.
15 Apr 2021
TL;DR: In this article, the authors investigated the conduction band of three-layer MoS by means of magneto-transport experiments and found the lowest band minima at the K point of the first Brillouin zone.
Abstract: The authors investigate the conduction band of three-layer MoS${}_{2}$ by means of magneto-transport experiments and find the lowest band minima at the K point of the first Brillouin zone.
TL;DR: In this paper, the authors reported the synthesis of monolayer MoS2 flakes at atmospheric pressure using a home-built CVD setup, where a wide range of shapes are grown from triangular shapes to many point stars via in-between shapes such as four and six-point stars, using the weight ratio variation of MoO3 and S precursors at different growth temperatures.
Abstract: Monolayer MoS2 has received special consideration owing to its intriguing properties and its potential to revolutionize modern technologies. Atmospheric pressure chemical vapor deposition (APCVD) is the traditional method to grow uniform and high-quality MoS2 flakes in a controlled manner. Little is known, however, about their synthesis mechanism and shape evolution. Herein, we report the synthesis of monolayer MoS2 flakes at atmospheric pressure using a home-built CVD setup. A wide range of shapes are grown from triangular shapes to many point stars, via in-between shapes such as four and six-point stars, using the weight ratio variation of MoO3 and S precursors at different growth temperatures. Further, the properties of the as-grown MoS2 flakes are probed by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), Raman spectroscopy, photoluminescence (PL), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS), confirming that they are regular and good in quality. Moreover, the synthesis pathway and different shape formations are explained on the basis of the fluid model and the growing rate of Mo, S zigzag edges. Thus, this work provides a better insight into the synthesis mechanism of monolayer MoS2 and represents a significant step towards realizing potential future applications.
TL;DR: In this article, a quantum dot was used as a quantum sensor to characterize the position and activation energy of individual shallow defects on the nanoscale, and the defect positions and activation energies were characterized by modeling the experimental data.
Abstract: The optical and electronic properties of semiconductors are strongly affected by structural and stoichiometric defects. The precise incorporation of dopants and the control of impurities are essentially what makes semiconductors useful materials for a broad range of devices. The standard defect and impurity characterization methods are sensitive only on a macroscopic scale, like the most widely used method of deep-level transient spectroscopy (DLTS). We perform time-resolved measurements of the resonance fluorescence of a single self-assembled $(\mathrm{In},\mathrm{Ga})$$\mathrm{As}$ quantum dot (QD) at low temperatures ($4.2\phantom{\rule{0.2em}{0ex}}\mathrm{K}$). By pulsing the applied gate voltage, we are able to selectively occupy and unoccupy individual defects in the vicinity of the dot. We address the exciton transition of the QD with a tunable diode laser. Our time-resolved measurements exhibit a shift of the resonance energy of the optical transition. We attribute this to a change of the electric field in the dot's vicinity, caused by electrons tunneling from a reservoir to the defect sites. Furthermore, we are able to characterize the defects concerning their position and activation energy by modeling our experimental data. Our results thus demonstrate how a quantum dot can be used as a quantum sensor to characterize the position and activation energy of individual shallow defects on the nanoscale.
TL;DR: In this paper, two color-band photodetectors on n-type GaAs have been fabricated and reported for the first time, and they are used for two-dimensional (2D) MoSe2-Cu2-xS nanocomposite-based heterojunction.
Abstract: Two-dimensional (2D) MoSe2–Cu2–xS nanocomposite-based heterojunction two color-band photodetectors on n-type GaAs have been fabricated and are reported for the first time. MoSe2–Cu2–xS nanocomposit...
08 Feb 2021
TL;DR: In this article, the authors investigated the impact of AlN buffer layer growth parameters for developing highly single crystalline AlGaN films, where the growth conditions need to be amended to maximize the incorporation ability of adatoms and minimize defect density.
Abstract: We have investigated the impact of AlN buffer layer growth parameters for developing highly single crystalline AlGaN films The low mobility of Al adatoms and high temperature for compound formation are amongst the major causes that affects the growth quality of AlGaN films Thus, proper optimization need to be carried out for achieving high quality AlGaN due to an augmented tendency of defect generation compared to GaN films Thus, growth conditions need to be amended to maximize the incorporation ability of adatoms and minimize defect density So, this study elaborates the growth optimization of AlGaN/AlN/Si (111) heterostructure with varied AlN buffer growth temperature (760 to 800 °C) It was observed that the remnant Al in low temperature growth of AlN buffer layer resist the growth quality of AlGaN epitaxial films A highly single crystalline AlGaN film with comparatively lowest rocking curve FWHM value (~ 061°) and smooth surface morphology with least surface defect states was witnessed when AlN buffer was grown at 780 °C From the Vegard’s law, the photoluminescence analysis unveils Aluminium composition of 315% with significantly reduced defect band/NBE band ratio to 03 The study demonstrates good crystalline quality AlGaN film growth with Aluminium content variation between ~ 30–39% in AlGaN/AlN heterostructure on Si(111) substrate leading to a bandgap range which is suitable for next-generation solar-blind photodetection applications
TL;DR: In this paper, the structural, optical, and electrical characteristics of AlN thin films on Si (111) substrate grown by DC magnetron sputtering technique for MEMS applications are presented.
TL;DR: In this paper, a temperature programmed desorption (TPD) on an uncoated surface acoustic wave (SAW) device has been explored for selectivity studies of chemical warfare agents (CWA).
Abstract: In this article a temperature programmed desorption (TPD) on an uncoated surface acoustic wave (SAW) device has been explored for selectivity studies of chemical warfare agents (CWA). High sensitivity to mass change on SAW device surface was exploited to study desorption patterns in a novel way. CWA Simulants 2-chloroethyl ethyl sulfide (CEES), Methyl Salicylate (MS) and Dimethyl Methyl phosphonate (DMMP) were investigated at different concentrations. SAW device was cooled and exposed to simulant vapours resulting in physical adsorption of gas molecules on device surface and subsequently by ramp heating the device, vapours were desorbed. The change in SAW oscillation frequency, due to desorption, was monitored during the temperature ramping and desorption spectrum was obtained. Desorption spectra were statistically analyzed using Principal Component Analysis (PCA) and our results indicate that all the three compounds investigated produced distinct desorption patterns independent of concentrations. Through this work we aim to develop a reliable methodology for subsequent development of a hand held TDP-SAW detector for field applications.
TL;DR: In this paper, the energy band gap of nano-composites of MWCNTs and Ni0.5Zn0.4/MWCNTs nano-particles was calculated and the dielectric parameters and EMI shielding effectiveness were carried out by Vector Network Analyzer in the Xband frequency region.