Showing papers by "Solid State Physics Laboratory published in 2004"
TL;DR: An algorithm to compute initial cluster centers for K-means clustering based on two observations that some of the patterns are very similar to each other and that is why they have same cluster membership irrespective to the choice of initial cluster center.
629 citations
TL;DR: In this paper, the physicochemical properties of MgO film obtained by using a precursor prepared by sol-gel technique are reported. And the results as obtained are encouraging to use MgOs as humidity sensor.
Abstract: The present paper reports the various physico-chemical properties of MgO film obtained by using a precursor prepared by sol–gel technique. The aim of this work is to produce films with nano size particles so as to employ them for sensor applications, as adsorption in such films increases many folds due to increase in surface area. Infra-red spectroscopic and thermal studies indicate the presence of solvent in the precursor, which perhaps helps in decomposition to nano-particles during the nucleation of the film. The films have been deposited on the glass rod bend in U-shape for humidity sensor. The results as obtained are encouraging to use MgO film as humidity sensor.
113 citations
TL;DR: In this article, a large and high-quality floating zone grown single crystals of boron carbide of the composition B∼4.3C were presented by Leithe-Jasper and Tanaka at the ISBB’99 in Dinard for the first time.
91 citations
TL;DR: In this paper, the authors compared the performance of QWIPs, QRIPs, and QDIPs based on physical analysis of the factors determining their operation, and they showed that the detectivity of QRPs can be much higher than the responsivity of WIPs; however, higher responsivity is inevitably accompanied by higher dark current.
Abstract: This paper deals with the comparison of quantum well, quantum wire and quantum dot infrared photodetectors (QWIPs, QRIPs and QDIPs, respectively) based on physical analysis of the factors determining their operation. The operation of the devices under consideration is associated with the intersubband (intraband) electron transitions from the bound states in QWs, QRs and QDs into the continuum states owing to the absorption of infrared radiation. The redistribution of the electric potential across the device active region caused by the photoionization of QWs, QRs and QDs affects the electron injection from the emitting contact. The injection current provides the effect of current gain. Since the electron thermoemission and capture substantially determine the electric potential distribution and, therefore, the injection current, these processes are also crucial for the device performance. To compare the dark current, responsivity and detectivity of QWIPs, QRIPs and QDIPs we use simplified but rather general semi-phenomenological formulae which relate these device characteristics to the rates of the thermoemission and photoemission of electrons from and their capture to the QWs and the QR and QD arrays. These rates are expressed via the photoemission cross-section, capture probability and so on, and the structural parameters. Calculating the ratios of the QWIP, QRIP and QDIP characteristics using our semi-phenomenological model, we show that: the responsivity of QRIPs and QDIPs can be much higher than the responsivity of QWIPs, however, higher responsivity is inevitably accompanied by higher dark current; the detectivity of QRIPs and QDIPs with low-density arrays of relatively large QRs and QDs is lower than that of QWIPs; the detectivity of QRIPs and QDIPs based on dense arrays can significantly exceed the detectivity of QWIPs.
87 citations
TL;DR: In this article, the effects of neutron irradiation on superconducting single crystals were investigated and the history dependence of the critical current density on the low-field side of the fishtail region was studied by measuring minor hysteresis loops and interpreted in terms of an order-disorder transition of the vortex lattice.
Abstract: We report on the effects of neutron irradiation in superconducting ${\mathrm{MgB}}_{2}$ single crystals. Transmission electron microscopy investigations reveal large radiation-induced defects with dimensions comparable to the superconducting coherence length. Accordingly, measurements of the magnetic moment show pronounced modifications of the reversible and irreversible properties after irradiation. In particular, we concentrate on the emergence of a second peak (fishtail), situated near ${H}_{c2}$ at low neutron fluences, but extending over a large part of the superconducting phase diagram at high doses. The history dependence of the critical current density on the low-field side of the fishtail region is studied by measuring minor hysteresis loops and interpreted in terms of an order-disorder transition of the vortex lattice.
73 citations
TL;DR: In this article, room temperature X-ray diffraction study reveals the formation of perovskite phase with tetragonal structure and dielectric measurements have been carried out at different frequencies as a function of temperature (RT to 235°C).
71 citations
TL;DR: In this article, the FT-Raman spectra of 10B, 11B, and 13C isotope-enriched boron carbide of compositions B4.3C, B6.5C, and B10C have been measured in completion to the recently published IR-Phonon spectra.
64 citations
TL;DR: In this article, lead zirconate titanate (PZT) thin films with molar ratio of Zr:Ti::65/35 were deposited by pulsed laser deposition (PLD) and sol-gel technique.
Abstract: Lead Zirconate Titanate (PZT) thin films (with molar ratio of Zr:Ti::65/35) were deposited by pulsed laser deposition (PLD) and sol–gel technique on Pt/Si (1 1 1), and Pt/Si (1 0 0) substrates. A seed layer of PbTiO3 (0.1 μm) was coated by sol–gel on the substrates before depositing PZT by PLD and sol–gel. A metal/ferroelectric/metal (MFM) capacitor structure, formed by depositing gold electrode on top of the film, was used for C–V and P–E measurements. A large remnant polarization (Pr = 56.8 μC/cm2) was observed on Pt/Si (1 1 1) substrates for the films deposited by sol–gel. Comparison of properties of PZT film deposited by these two techniques is discussed.
60 citations
TL;DR: In this paper, the authors used the Mossbauer effect (MES) and X-ray photoelectron (XPS) spectroscopies to study antiferromagnetic CuFeS2, especially its Cu and Fe ground-state properties.
44 citations
TL;DR: In this paper, polycrystalline samples of the modified Pb(Zr1−x Tix)O3 (PZT) composition, with representative formula Pb0.92(LazBi1−z)0.98O3, a family of relaxor ferroelectrics, were prepared via the chemical route with z = 0.3, 0.6 and 0.9.
Abstract: Polycrystalline samples of the modified Pb(Zr1−x Tix)O3 (PZT) composition, with representative formula Pb0.92(LazBi1−z)0.08(Zr0.65Ti0.35)0.98O3 (PLBZT), a family of relaxor ferroelectrics, were prepared via the chemical route with z = 0.3, 0.6 and 0.9. Crystalline phases of powders calcined at different temperatures and the microstructure of the sintered pellets were investigated by x-ray diffraction (XRD) analysis and scanning electron microscopy, respectively. XRD confirms the result obtained by differential scanning calorimetry. The XRD profile shows that the samples having z = 0.9 and 0.6 do not exhibit a pyrochlore phase, whereas the samples with z = 0.3, have 3% of the pyrochlore phase. Microstructural analysis suggests that the shape of grains and intergranular residual pores are modified upon La doping. The dielectric constant and dielectric losses were measured as a function of frequency at room temperature for different frequencies starting from 0.1 kHz to 1 MHz. The dielectric constant was found to be strongly influenced by frequency whereas the Curie temperature remained almost the same. Finally, we conclude that the dielectric constant, loss and activation energy of PLBZT strongly suggest that these compounds are suitable for the preparation of high value capacitors and may be good candidates for device applications.
41 citations
TL;DR: In this paper, the reversible mixed-state properties of superconducting materials are summarized and discussed in terms of new results and evaluations, which take the two band character of the material explicitly into account.
Abstract: The reversible mixed-state properties of superconducting ${\mathrm{MgB}}_{2}$ are summarized and discussed in terms of new results and evaluations, which take the two band character of the material explicitly into account. The magnetic field dependence of the reversible magnetization is analyzed within Ginzburg Landau theory which, however, fits only either at high or at low fields. The resulting parameters (e.g., characteristic fields, lengths, and anisotropy) are quite different in these two regimes. We find large anisotropies of about 4.6 at high fields and low temperatures, but values close to 1 at low fields. Finally, we present neutron irradiation experiments, where new defects, leading to strong irreversibility but also to a modification of the reversible properties, are induced.
TL;DR: In this paper, the authors presented the results of directional point-contact measurements in single crystals, in magnetic fields up to 9 T parallel to the c axis, with a generalized Blonder-Tinkham-Klapwijk model.
Abstract: We present the results of directional point-contact measurements in ${\mathrm{MgB}}_{2}$ single crystals, in magnetic fields up to 9 T parallel to the c axis. By fitting the conductance curves of our point contacts---showing clear Andreev-reflection features---with a generalized Blonder-Tinkham-Klapwijk model, we extracted the values of the two gaps ${\ensuremath{\Delta}}_{\ensuremath{\sigma}}$ and ${\ensuremath{\Delta}}_{\ensuremath{\pi}}.$ The resulting ${\ensuremath{\Delta}}_{\ensuremath{\sigma}}(B)$ and ${\ensuremath{\Delta}}_{\ensuremath{\pi}}(B)$ curves agree very well with the predictions of the two-band model in dirty limit when the $\ensuremath{\pi}$-band diffusivity is a few times greater than the $\ensuremath{\sigma}$-band one. This result concurs with other experimental and theoretical findings in indicating that, even in the best crystals, the $\ensuremath{\pi}$ band is moderately dirty.
TL;DR: In this paper, structural, dielectric, ferroelectric and piezoelectric properties of lead magnesium niobate-lead titanate, PMN-PT (66:34), prepared at different sintering temperatures (1150-1250°C) are discussed for actuator applications.
Abstract: Structural, dielectric, ferroelectric and piezoelectric properties of lead magnesium niobate–lead titanate, PMN–PT (66:34), prepared at different sintering temperatures (1150–1250°C) are discussed for actuator applications. System sintered at 1200 and 1250°C showed better perovskite phase stabilization and higher values of dielectric constant (er). Remnant polarization (Pr) was found to be higher (45 µC/cm2) for the system sintered at 1250°C. The piezoelectric coefficients, d33, d31, dh and strain induced in the system by a large electric field were found to be sintering temperature dependent. Hysteresis free strain behavior of the system sintered at 1200°C showed the suitability of this material for actuator applications.
TL;DR: Li-Zn-Ti ferrite substituted with vanadium having the general formula Li 05+ t Zn 2 Ti 02 V t Fe 21−2 t O 4 with 000≤ t ≤025 in steps of 005 were synthesized by the standard ceramic technique X-ray diffraction (XRD) analysis showed all the samples to be single-phase with spinel structure as discussed by the authors.
TL;DR: In this paper, the Kondo effect in a many-electron quantum ring as a function of the magnetic field is investigated in terms of the energy spectrum of the ring and the parametrically changing tunnel coupling.
Abstract: The Kondo effect is investigated in a many-electron quantum ring as a function of the magnetic field. For fields applied perpendicular to the plane of the ring a modulation of the Kondo effect with the Aharonov-Bohm period is observed. This effect is discussed in terms of the energy spectrum of the ring and the parametrically changing tunnel coupling. In addition, we use gate voltages to modify the ground-state spin of the ring. The observed splitting of the Kondo-related zero-bias anomaly in this configuration is tuned with an in-plane magnetic field.
TL;DR: In this article, the excitation of B4.3C with an Ar-laser ( ℏω=2.4 eV ) yields a photoluminescence spectrum between about 1.56 and 1.58 eV with its main maximum at 1.563 eV and a weaker maximum at1.572 eV.
TL;DR: In this paper, the magnetic penetration depth of polycrystalline superconductors with different boron isotopes was investigated by transverse field muon spin rotation and it was shown that there is no effect on the penetration depth.
Abstract: The magnetic penetration depth $\ensuremath{\lambda}(0)$ in polycrystalline ${\mathrm{MgB}}_{2}$ for different boron isotopes $(^{10}\mathrm{B}∕^{11}\mathrm{B})$ was investigated by transverse field muon spin rotation. No boron isotope effect on the penetration depth $\ensuremath{\lambda}(0)$ was found within experimental error: $\ensuremath{\Delta}\ensuremath{\lambda}(0)∕\ensuremath{\lambda}(0)=0.8(8)%$, suggesting that ${\mathrm{MgB}}_{2}$ is an adiabaic superconductor. This is in contrast to the substantial oxygen isotope effect on $\ensuremath{\lambda}(0)$ observed in cuprate high-temperature superconductors.
TL;DR: In this article, compositional dependence of initial permeability (μ i ), the frequency dispersion of initial permutation and the corresponding loss, tan ǫ δ μ have been studied.
Abstract: Li–Zn–Ti ferrite samples, with compositional formula Li 0.5+ t Zn 0.2 Ti 0.2 V t Fe 2.1−2 t O 4, ‘ t ’ ranging from 0.0 to 0.25 in steps of 0.05 were prepared by the ceramic route. XRD results confirmed the single-phase spinel structure of the samples. SEM photomicrographs have revealed the grain size of the samples. B–H loops have been traced for all the samples and the various hysteresis parameters like coercivity, remanence and remanence ratio have been studied as a function of composition. Compositional dependence of initial permeability (μ i ), the frequency dispersion of initial permeability and the corresponding loss, tan δ μ have been studied. The possible mechanisms involved are discussed.
TL;DR: In this paper, the microstructural and dielectric behavior of glass ceramics in the system [SrO.yBaO] with varying y, have been investigated.
TL;DR: In this paper, the conductance of a finite quantum dot network is studied as a function of interdot coupling, where Coulomb resonances with on average increasing charging energies are observed.
Abstract: The conductance through a finite quantum dot network is studied as a function of interdot coupling. As the coupling is reduced, the system undergoes a transition from the antidot regime to the tight binding limit, where Coulomb resonances with on average increasing charging energies are observed. Percolation models are used to describe the conduction in the open and closed regime and contributions from different blockaded regions can be identified. A strong negative average magnetoresistance in the Coulomb blockade regime is in good quantitative agreement with theoretical predictions for magnetotunneling between individual quantum dots.
TL;DR: In this article, the effect of pH of the precursor sol on the electrical and optical properties of the platinised silicon (Pt/TiN/SiO2/Si) and fused quartz substrates has been investigated.
TL;DR: In this paper, magnetization data on crystalline and polycrystalline MgB2 before and after irradiation with ~1 MeV protons was presented, where the critical current density is below our noise floor of 103 A cm−2 over most of the field range.
Abstract: We present magnetization data on crystalline and polycrystalline MgB2 before and after irradiation with ~1 MeV protons. In the virgin crystal the critical current density is below our noise floor of 103 A cm−2 over most of the field range. However, after irradiation a peak occurs in the current density as a function of applied magnetic field as the upper critical field Hc2 is approached. After subsequent ageing over a time period of three months, the peak effect is greatly enhanced, exhibiting much stronger pinning over a wide field range, and the upper critical field is approximately doubled, accompanied by a 2 K reduction in transition temperature. Similar studies were made on polycrystalline fragments, where irradiation leads to an increased irreversibility field (Jc is enhanced at high fields but decreased at low fields) and a suppression in transition temperature. However, after two years of ageing both parameters returned towards those of the virgin sample.
TL;DR: In this paper, three-terminal tunnelling experiments on quantum dots in the Coulomb-blockade regime allow a quantitative determination of the coupling strength of individual quantum states to the leads.
Abstract: Three-terminal tunnelling experiments on quantum dots in the Coulomb-blockade regime allow a quantitative determination of the coupling strength of individual quantum states to the leads. Exploiting this insight, we have observed independent fluctuations of the coupling strengths as a function of electron number and magnetic field due to changes in the shape of the wave function in the dot. Such a detailed understanding and control of the dot-lead coupling can be extended to more complex systems such as coupled dots, and are essential for building functional quantum electronic systems.
TL;DR: In this article, the effect of variation of beam size on X-ray rocking curve and its FWHM value was investigated in graphite crucible CZT ingots.
TL;DR: In this paper, the authors highlight the advantages of using point-contact spectroscopy (PCS) in multigap superconductors like MgB2, both as a fundamental research tool and as a non-destructive diagnostic technique for the optimization of thin-film characteristics.
Abstract: In this paper we highlight the advantages of using point-contact spectroscopy (PCS) in multigap superconductors like MgB2, both as a fundamental research tool and as a non-destructive diagnostic technique for the optimization of thin-film characteristics. We first present some results of crucial fundamental interest obtained by directional PCS in MgB2 single crystals, for example the temperature dependence of the gaps and of the critical fields, and the effect of a magnetic field on the gap amplitudes. Then, we show how PCS can provide useful information about the surface properties of MgB2 thin films (e.g., Tc, gap amplitude(s), clean-?or dirty-limit conditions) in view of their optimization for the fabrication of tunnel and Josephson junctions for applications in superconducting electronics.
TL;DR: In this article, a two-dimensional electron gas in the quantum Hall regime has been investigated by tuning the local potential with the metallic tip of a scanning force microscope, and the longitudinal four-terminal resistance of the Hall bar structure was recorded while the tip was scanned above.
Abstract: A two-dimensional electron gas in the quantum Hall regime has been investigated by tuning the local potential with the metallic tip of a scanning force microscope. The longitudinal four-terminal resistance of the Hall bar structure was recorded while the tip was scanned above. The resulting resistance images exhibit local features that show a $1∕B$-periodicity. These features line up along the Hall bar edges resembling the formation of edge channels. At certain filling factors they develop a subtle fine structure indicating the intricate microscopic variations of states in real space.
TL;DR: Aharonov-Bohm oscillations are studied in the magnetoconductance of a micron-sized open quantum ring coupled capacitively to a Coulomb-blockaded quantum dot as mentioned in this paper.
Abstract: Aharonov-Bohm oscillations are studied in the magnetoconductance of a micron-sized open quantum ring coupled capacitively to a Coulomb-blockaded quantum dot. As the plunger gate of the dot is modulated and tuned through a conductance resonance, the amplitude of the Aharonov-Bohm oscillations in the transconductance of the ring displays a minimum. We demonstrate that the effect is due to a single-electron screening effect, rather than to dephasing. Aharonov-Bohm oscillations in a quantum ring can thus be used for the detection of single charges.
TL;DR: In this article, spectroscopic data on the electronic structure of YbS under pressure is presented. But the accuracy of these estimates is enhanced by a combined analysis of emission spectra measured as a function of the incident and emitted energy.
Abstract: We present spectroscopic data on the electronic structure of YbS under pressure. From resonant x-ray emission and x-ray absorption spectra in the high-resolution partial fluorescence yield mode, we find that the Yb valence increases from 2.3 at ambient pressure to 2.6 at 360 kbar. The accuracy of these estimates is enhanced by a combined analysis of emission spectra measured as a function of the incident and emitted energy. The spectral line shapes reflect the mixed character of the electronic states, intermediate between atomic and bandlike.
TL;DR: Magnetization and muon spin relaxation were measured as a function of the applied magnetic field at $2\phantom{\rule{0.3em}{0ex}}\mathrm{K} as mentioned in this paper.
Abstract: Magnetization and muon spin relaxation on $\mathrm{Mg}{\mathrm{B}}_{2}$ were measured as a function of the applied magnetic field at $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Both indicate an inverse-squared penetration depth strongly decreasing with increasing field $H$ below about $1\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. Magnetization also suggests the anisotropy of the penetration depth increases with increasing $H$, interpolating between a low ${H}_{c1}$ and a high ${H}_{c2}$ anisotropy. Measurements of the torque as a function of the angle between the field and the $c$ axis of the crystal are in agreement with this finding, while also ruling out drastic differences between the mixed state anisotropies of the two basic length scales penetration depth and coherence length.
TL;DR: In this article, a surface acoustic wave-based polymer-coated sensor for the detection of hidden explosives is described, and the preliminary results indicated that the carbowax 1000 could be a very good chemical interface to sense low levels of chemical signature of explosive material.
Abstract: The explosive charge within a landmine is the source for a mixture of chemical vapours that form a distinctive chemical signature indicative of a landmine. The concentrations of these compounds in the air over landmines is extremely low (parts-per-trillion or lower), well below the minimum detection limits of most field-portable chemical sensors. This paper describes a portable surface acoustic wave-based polymer-coated sensor for the detection of hidden explosives. The sensitivity and selectivity of polymer-based sensors depend on several factors including the chemo-selective coating used, the physical properties of the vapour(s) of interest, the selected transducers, and the operating conditions. The polymer-based sensor was calibrated in the laboratory using the explosive vapour generator. The preliminary results indicated that the carbowax 1000 could be a very good chemical interface to sense low levels of chemical signature of explosive material. Response for 50 ppb of TNT vapours was observed to be 400 Hz for an exposure of 2 min.