Showing papers by "Solid State Physics Laboratory published in 2015"
TL;DR: These experiments establish InAs/GaSb as a promising platform for the confinement of Majoranas into localized states, enabling future investigations of non-Abelian statistics and gate-tuning between edge-dominated and bulk-dominated regimes of superconducting transport.
Abstract: Topological superconductivity, a state that can support the formation of Majorana zero modes, can be induced in the edge state of a InAs/GaSb nanowire.
214 citations
TL;DR: In this article, the authors have developed a cheap and easy process for synthesizing heavily nitrogen doped graphene from non-mulberry silk cocoon membrane (Tassar, Antheraea mylitta) by pyrolyzing the cocoon at 400°C in argon atmosphere.
158 citations
TL;DR: In this article, a review of the mechanisms responsible for localized charge localization in nanoribbons is presented, and the consequences for physics and applications are discussed, such as multiple coupled sites of localized charge, cotunneling processes, and excited states.
Abstract: Graphene—two-dimensional carbon—is a material with unique mechanical, optical, chemical, and electronic properties. Its use in a wide range of applications was therefore suggested. From an electronic point of view, nanostructured graphene is of great interest due to the potential opening of a band gap, applications in quantum devices, and investigations of physical phenomena. Narrow graphene stripes called “nanoribbons” show clearly different electronical transport properties than micron-sized graphene devices. The conductivity is generally reduced and around the charge neutrality point, the conductance is nearly completely suppressed. While various mechanisms can lead to this observed suppression of conductance, disordered edges resulting in localized charge carriers are likely the main cause in a large number of experiments. Localized charge carriers manifest themselves in transport experiments by the appearance of Coulomb blockade diamonds. This review focuses on the mechanisms responsible for this charge localization, on interpreting the transport details, and on discussing the consequences for physics and applications. Effects such as multiple coupled sites of localized charge, cotunneling processes, and excited states are discussed. Also, different geometries of quantum devices are compared. Finally, an outlook is provided, where open questions are addressed.
106 citations
TL;DR: In this paper, structural, electrical, and light up conversion properties of Erbium (Er) substituted bismuth titanate (Bi4� xErxTi3O12) ceramics have been investigated.
98 citations
TL;DR: It is proposed that the temperature and humidity dependent electrical properties of the SCM could find applications in battery technology, bio-sensor, humidity sensor, steam engines and waste heat management.
Abstract: Silk cocoon membrane (SCM) is an insect engineered structure. We studied the electrical properties of mulberry (Bombyx mori) and non-mulberry (Tussar, Antheraeamylitta) SCM. When dry, SCM behaves like an insulator. On absorbing moisture, it generates electrical current, which is modulated by temperature. The current flowing across the SCM is possibly ionic and protonic in nature. We exploited the electrical properties of SCM to develop simple energy harvesting devices, which could operate low power electronic systems. Based on our findings, we propose that the temperature and humidity dependent electrical properties of the SCM could find applications in battery technology, bio-sensor, humidity sensor, steam engines and waste heat management.
66 citations
TL;DR: An explanation of the observed measurement-induced current based on strong capacitive coupling and energy dependent tunneling barriers, breaking the spatial symmetry in the unbiased system is presented.
Abstract: We present an electronic transport experiment in graphene where both classical and quantum mechanical charge detector back-action on a quantum dot are investigated. The device consists of two stacked graphene quantum dots separated by a thin layer of boron nitride. This device is fabricated by van der Waals stacking and is equipped with separate source and drain contacts to both dots. By applying a finite bias to one quantum dot, a current is induced in the other unbiased dot. We present an explanation of the observed measurement-induced current based on strong capacitive coupling and energy dependent tunneling barriers, breaking the spatial symmetry in the unbiased system. This is a special feature of graphene-based quantum devices. The experimental observation of transport in classically forbidden regimes is understood by considering higher-order quantum mechanical back-action mechanisms.
53 citations
TL;DR: In this paper, the authors investigated low-temperature electronic transport on InAs/GaSb double quantum wells, a system which promises to be electrically tunable from a normal to a topological insulator.
Abstract: We have investigated low-temperature electronic transport on InAs/GaSb double quantum wells, a system which promises to be electrically tunable from a normal to a topological insulator. Hall bars of $50\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$ in length down to a few micrometers gradually develop a pronounced resistance plateau near charge neutrality, which comes along with distinct nonlocal transport along the edges. Plateau resistances are found to be above or below the quantized value expected for helical edge channels. We discuss these results based on the interplay between imperfect edges and residual local bulk conductivity.
51 citations
TL;DR: In this paper, large-area graphene films produced by chemical vapor deposition were grown directly on copper substrates or transferred on a gold substrate and their effect on the viability and proliferation of the Gram-positive bacteria Staphylococcus aureus and the Gramnegative bacteria Escherichia coli were assessed.
50 citations
TL;DR: In this article, a nanostructured hyper thin film sensor for the measurement of humidity in ppm level using the micro sized interdigitated electrode capacitive structure is presented, which can be useful for measuring moisture dispersion inside electronic gadgets and packages where the performance of the devices is deteriorated due to moisture entrapment.
Abstract: In this paper we present the development of a nanostructured hyper thin film sensor for the measurement of humidity in ppm level using the micro sized interdigitated electrode capacitive structure. The sensor electrode has been fabricated using the optical lithography technique on the oxide sensing film deposited on the quartz substrate. The nanoporous metal oxide thin film of γ-Al2O3 has been fabricated by simple sol–gel drop coating method. The electrical characteristics of the sensor have been determined in the moisture range from 175 to 625 ppm by Agilent 4294A impedance analyzer at 1 kHz, 50 kHz and100 kHz respectively. The sensor has excellent yield ratio because of complete avoidance of shorting problem of the electrode. The response time is very fast (Tr = 12 s) in comparison to the conventional commercial parallel plate gold electrode capacitive thin film aluminum oxide sensor. The proposed sensor can be useful for measuring moisture dispersion inside electronic gadgets and packages where the performance of the devices is deteriorated due to moisture entrapment.
49 citations
TL;DR: In this paper, structural and electrical properties of Lanthanum substituted barium bismuth titanate (BaBi4-xLaxTi4O15) ceramics prepared by conventional solid state reaction method have been investigated.
47 citations
TL;DR: In this article, the effect of co-doping of La and Ni in controlling the electrical leakage and enhancing the ferroelectric polarization in chemical solution processed BiFeO3 (BFO) thin films grown on Pt/Si substrates was reported.
TL;DR: It is shown that the commonly accepted explanation relying on light intensity confinement in high (low) dielectric constant regions at the red (blue) edge is challenged in the case of TiO2 inverse opals because of the sub-wavelength size of the material skeleton.
Abstract: Light harvesting enhancement by slow photons in photonic crystal catalysts or dye-sensitized solar cells is a promising approach for increasing the efficiency of photoreactions. This structural effect is exploited in inverse opal TiO2 photocatalysts by tuning the red edge of the photonic band gap to the TiO2 electronic excitation band edge. In spite of many experimental demonstrations, the slow photon effect is not fully understood yet. In particular, observed enhancement by tuning the blue edge has remained unexplained. Based on rigorous couple wave analysis simulations, we quantify light harvesting enhancement in terms of absorption increase at a specific wavelength (monochromatic UV illumination) or photocurrent increase (solar light illumination), with respect to homogeneous flat slab of equivalent material thickness. We show that the commonly accepted explanation relying on light intensity confinement in high (low) dielectric constant regions at the red (blue) edge is challenged in the case of TiO2 inverse opals because of the sub-wavelength size of the material skeleton. The reason why slow photons at the blue edge are also able to enhance light harvesting is the loose confinement of the field, which leads to significant resonantly enhanced field intensity overlap with the skeleton in both red and blue edge tuning cases, yet with different intensity patterns.
TL;DR: In this article, a homoepitaxial GaN nanowall network was grown on the GaN template using an ultra-high vacuum laser assisted molecular beam epitaxy system by ablating solid GaN target under a constant rf nitrogen plasma ambient.
Abstract: We have grown homoepitaxial GaN nanowall networks on GaN template using an ultra-high vacuum laser assisted molecular beam epitaxy system by ablating solid GaN target under a constant rf nitrogen plasma ambient The effect of laser repetition rate in the range of 10 to 30 Hz on the structural properties of the GaN nanostructures has been studied using high resolution X-ray diffraction, field emission scanning electron microscopy and Raman spectroscopy The variation of the laser repetition rate affected the tip width and pore size of the nanowall networks The z-profile Raman spectroscopy measurements revealed the GaN nanowall network retained the same strain present in the GaN template The optical properties of these GaN nanowall networks have been studied using photoluminescence and ultrafast spectroscopy and an enhancement of optical band gap has been observed for the nanowalls having a tip width of 10–15 nm due to the quantum carrier confinement effect at the wall edges The electronic structure of the GaN nanowall networks has been studied using X-ray photoemission spectroscopy and it has been compared to the GaN template The calculated Ga/N ratio is largest (∼2) for the GaN nanowall network grown at 30 Hz Surface band bending decreases for the nanowall network with the lowest tip width The homoepitaxial growth of porous GaN nanowall networks holds promise for the design of nitride based sensor devices
TL;DR: In this paper, an enhancement in the value of magnetoelectric coupling coefficient was observed when lead zirconate titanate (PZT) ferroelectric material near morphotropic phase boundary (MPB) is mixed with small amount of high resistive nickel substituted cobalt ferrite (CNFO) phase in comparison to pure cobalt-ferrite (CFO).
TL;DR: In this paper, the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation, and it was shown that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature and of the superfluid density (ρs).
Abstract: The recent discovery of pressure (p) induced superconductivity in the binary helimagnet CrAs has raised questions on how superconductivity emerges from the magnetic state and on the mechanism of the superconducting pairing. In the present work the suppression of magnetism and the occurrence of superconductivity in CrAs were studied by means of muon spin rotation. The magnetism remains bulk up to p ≃ 3.5 kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at p ≃ 7 kbar. At 3.5 kbar superconductivity abruptly appears with its maximum Tc ≃ 1.2 K which decreases upon increasing the pressure. In the intermediate pressure region (3.5 < or ~ p < or ~ 7 kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature (Tc) and of the superfluid density (ρs). A scaling of ρs with Tc(3.2) as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs.
TL;DR: In this paper, the authors present evidence for a density wave in the compound CeRhIn5, the first for a so-called heavy-fermion metal where electrons have a very high effective mass.
Abstract: Strong electron correlations often lead to unusual electronic ground states. Here, the authors present evidence for a density wave in the compound CeRhIn5, the first for a so-called heavy-fermion metal where electrons have a very high effective mass.
TL;DR: In this article, the impact of the sputtering power on the properties of V2O5 films was analyzed by X-ray diffraction, XRD, field emission-scanning electron microscope (FE-SEM), atomic force microscopy (AFM), UV-vis spectroscopy and four point probe method (FPP) respectively.
TL;DR: In this paper, the authors review the theoretical basics of bilayer graphene and study the evolution of the band structure under the influence of external perturbations such as transverse electric fields or strain, and highlight their key role concerning the ease to experimentally probe the presence of a Lifshitz transition.
TL;DR: In this article, the effect of excess bismuth oxide Bi2O3 (2 − 10 ) for processing BaBi4Ti4O15 (BBT) ceramics by solid state reaction has been investigated.
TL;DR: In this paper, the structural phase transitions have been correlated with piezoelectric properties, which is attributed to the coexistence of rhombohedral and tetragonal phases and is confirmed by Raman spectroscopy.
Abstract: Lead free piezoelectrics [1-x{(Bi0.96La0.04)0.5Na0.5TiO3}−x(Ba0.90Ca0.10TiO3)] (BLNT-BCT) with compositions x ≤ 0.20 have been synthesized by a semi-wet route and the compositions around the MPB region have been systematically investigated using x-ray diffraction and Raman spectroscopy. X-ray diffraction analysis confirms phase formation without any traces of secondary phases. Rietveld refinement of x-ray diffraction data revealed different structural symmetry for a different range of compositions viz., (i) rhombohedral (R3c) [x ≤ 0.08] (ii) rhombohedral (R3c) + tetragonal (P4mm) (MPB) [0.10 ≤ x ≤ 0.15] (iii) tetragonal (P4mm) [0.15 < x ≤ 0.20], which is confirmed by Raman spectroscopy. The structural phase transitions have been correlated with piezoelectric properties and the composition with x = 0.12 depicts better piezoelectric properties amongst studied compositions, which is attributed to the coexistence of rhombohedral and tetragonal phases.
TL;DR: This work implements a mesoscopic coupled dot-cavity system in a high-mobility two-dimensional electron gas, and obtains an extended spin-singlet state in the regime of strong dot-Cavity coupling, presenting a viable route for nonlocal spin coupling that is applicable for quantum information processing.
Abstract: Quantum engineering requires controllable artificial systems with quantum coherence exceeding the device size and operation time. This can be achieved with geometrically confined low-dimensional electronic structures embedded within ultraclean materials, with prominent examples being artificial atoms (quantum dots) and quantum corrals (electronic cavities). Combining the two structures, we implement a mesoscopic coupled dot-cavity system in a high-mobility two-dimensional electron gas, and obtain an extended spin-singlet state in the regime of strong dot-cavity coupling. Engineering such extended quantum states presents a viable route for nonlocal spin coupling that is applicable for quantum information processing.
TL;DR: The results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature and of the superfluid density (ρs).
Abstract: The recent discovery of pressure induced superconductivity in the binary helimagnet CrAs has attracted much attention. How superconductivity emerges from the magnetic state and what is the mechanism of the superconducting pairing are two important issues which need to be resolved. In the present work, the suppression of magnetism and the occurrence of superconductivity in CrAs as a function of pressure ($p$) were studied by means of muon spin rotation. The magnetism remains bulk up to $p\simeq3.5$~kbar while its volume fraction gradually decreases with increasing pressure until it vanishes at $p\simeq$7~kbar. At 3.5 kbar superconductivity abruptly appears with its maximum $T_c \simeq 1.2$~K which decreases upon increasing the pressure. In the intermediate pressure region ($3.5\lesssim p\lesssim 7$~kbar) the superconducting and the magnetic volume fractions are spatially phase separated and compete for phase volume. Our results indicate that the less conductive magnetic phase provides additional carriers (doping) to the superconducting parts of the CrAs sample thus leading to an increase of the transition temperature ($T_c$) and of the superfluid density ($\rho_s$). A scaling of $\rho_s$ with $T_c^{3.2}$ as well as the phase separation between magnetism and superconductivity point to a conventional mechanism of the Cooper-pairing in CrAs.
TL;DR: In this paper, the authors demonstrate theoretically and experimentally the case of bichromatic driving creating fundamental relations between commensurability and symmetry properties in a double quantum dot driven two-level system.
Abstract: The current through a driven two-level system, here realized in a double quantum dot, is determined by the phases acquired between avoided crossings. As a function of the detuning and the driving amplitude, it exhibits a characteristic interference pattern both in real space and in Fourier space. The authors demonstrate theoretically and experimentally the case of bichromatic driving creating fundamental relations between commensurability and symmetry properties.
TL;DR: In this paper, a novel rapid sol-gel thin-film porous metal-oxide-based surface acoustic wave (SAW) humidity sensor has been proposed, and the device has been configured in a high-frequency oscillator circuit to explore the frequency response in the presence of water vapor.
Abstract: In this paper, we are proposing a novel rapid sol–gel thin-film porous metal–oxide-based surface acoustic wave (SAW) humidity sensor. For the SAW sensor, the center frequency of 433.92 MHz has been selected, and the device has been configured in a high-frequency oscillator circuit to explore the frequency response in the presence of water vapor. The sensitive thin film of sol–gel $\gamma $ -Al2O3 coated with a drop dry method offers very high surface-to-volume ratio with the distribution of micropores making the sensor highly sensitive for moisture detection. Pore morphologies of the film have been studied by field emission scanning electron microscope and atomic force microscopy. The $\gamma $ phase of alumina of the film has been characterized with X-ray diffraction. The sensor has been tested from 3% relative humidity (RH) to 85% RH. The proposed sensor has very fast ( $T_{r}= 1$ s) response time and excellent yield ratio in comparison with the conventional commercial capacitive aluminum oxide sensor. The sensitivity (3%–20% RH) and the hysteresis (3%–85% RH) are found to be 120-Hz/% RH and 0.3%, respectively. The sensor can be useful for different applications, including moisture dispersion inside electronic gadgets, dryers, ovens, textile production, semiconductor device processing, food processing, medicine, and sealed packages.
TL;DR: In this paper, a new method was devised for obtaining fast NO2 gas sensing characteristics by using detuned SnO2/SAW sensor oscillator, which showed XRD reflections corresponding to (1.0) and (2.1) planes of rutile structure.
Abstract: A new method has been devised for obtaining fast NO2 gas sensing characteristics by using detuned SnO2/SAW sensor oscillator. The deposited SnO2 thin films were polycrystalline showing XRD reflections corresponding to (1 0 1) and (2 1 1) planes of rutile structure. The frequency of the sensor remained tuned for SnO2 layer of small thickness (
TL;DR: A novel algorithm for selection of an optimal set of surface acoustic wave (SAW) sensors for an E-Nose from a given set of available gas sensors is proposed, independent of the choice of the pattern recognition engine.
Abstract: Electronic noses (E-Nose) are devices used to substitute human or canine olfactory systems in detecting gases or chemical substances. The success of an E-Nose in detecting a set of target gases depends on how optimal is the choice of the gas sensors. This paper proposes a novel algorithm for selection of an optimal set of surface acoustic wave (SAW) sensors for an E-Nose from a given set of available gas sensors. The sensor performance is quantified in terms of separability of data obtained from them. A similarity measure specifying how similar the responses of sensors are when exposed to a set of gases, is also defined. The sensor selection algorithm is then specified as an optimization problem in terms of separability of target gases and similarity of sensor responses. The advantage of the proposed method lies in its performance being independent of the choice of the pattern recognition engine.
TL;DR: In this paper, single phase polycrystalline lithium ferrites modified with Zn and Mn were synthesized by solid state reaction method and the prepared samples exhibit a markedly increased value in real part of dielectric constant ( e ) and a lowest loss tangent (tan δ ) for x = 0.04 measured in the frequency range 70-Hz to 1-MHz.
TL;DR: In this paper, ZnO/Quartz based surface acoustic wave (SAW) sensors have been fabricated for the detection of DMMP (di-methyl methyl phosphonate) at room temperature.
Abstract: ZnO/Quartz based surface acoustic wave (SAW) sensors have been fabricated for the detection of DMMP (di-methyl methyl phosphonate) at room temperature The as-deposited ZnO thin films are c-axis oriented The sensitivity of the sensor toward DMMP vapors increases with increase in the thickness of ZnO thin films A change in elasticity of ZnO films with exposure to DMMP vapors is the dominant sensing mechanism Various properties of ZnO thin films (roughness, porosity, crystallite size, bond strength etc) responsible for elastic changes are analyzed by depositing the films under different processing conditions The ZnO/SAW sensor is also highly selective toward DMMP vapors as compared to other interferants The results throw light into the elasticity mechanism for SAW sensing along with the possibility of utilizing ZnO/SAW sensor for DMMP detection
TL;DR: In this paper, the authors focus on two frequently used etching techniques, namely, O2 plasma ashing and O2+Ar reactive ion etching (RIE), and find that the latter creates defective graphene in the exposed trenches, resulting in instabilities in the ribbon transport.
Abstract: Most graphene nanoribbons in the experimental literature are patterned using plasma etching. Various etching processes induce different types of defects and do not necessarily result in the same electronic and structural ribbon properties. This study focuses on two frequently used etching techniques, namely, O2 plasma ashing and O2 + Ar reactive ion etching (RIE). O2 plasma ashing represents an alternative to RIE physical etching for sensitive substrates, as it is a more gentle chemical process. We find that plasma ashing creates defective graphene in the exposed trenches, resulting in instabilities in the ribbon transport. These are probably caused by more or larger localized states at the edges of the ashed device compared to the RIE defined device.
TL;DR: In this article, a spin precession frequency that in an external magnetic field is linear in the spatial separation of the spin mode was measured in a diffusive two-dimensional electron gas without the need for processing the sample structure, applying electrical currents or resolving the spatial pattern of spin mode.
Abstract: A method is presented that enables the measurement of spin-orbit coefficients in a diffusive two-dimensional electron gas without the need for processing the sample structure, applying electrical currents or resolving the spatial pattern of the spin mode. It is based on the dependence of the average electron velocity on the spatial distance between local excitation and detection of spin polarization, resulting in a variation of spin precession frequency that in an external magnetic field is linear in the spatial separation. By scanning the relative positions of the exciting and probing spots in a time-resolved Kerr rotation microscope, frequency gradients along the [100] and [010] crystal axes of GaAs/AlGaAs QWs are measured to obtain the Rashba and Dresselhaus spin-orbit coefficients, α and β. This simple method can be applied in a variety of materials with electron diffusion for evaluating spin-orbit coefficients.