arXiv subjects

R. Yang

Publications and source records attributed to R. Yang.

50 records · Page 3Linked to original sources

arXiv2011

Anomalous differential conductance of In-Bi2Te3 contact

The differential conductance of In/Bi2Te3 contact under cryogenic temperature is investigated. Anomalous zero/finite bias differential conductance has been observed. The dependence of the observed anomalous differential conductance on magnetic field and temperature is studied. Data analysis indicates that the anomalous differential conductance is caused by the peculiar transport properties of the superconducting Indium/Bi2Te3 interface where Andreev reflection plays a key role.

cond-mat.mtrl-sci↗

arXiv2010

Weak field magnetoresistance of narrow-gap semiconductor InSb

The weak antilocalization effect of InSb film in perpendicular as well as tilted magnetic field is investigated. It is found that the InSb film has quasi-two-dimensional feature and the Nyquist mechanism dominates decoherence. The two dimensionality is also verified further and the influence of roughness effect and Zeeman effect on weak antilocalization effect is studied by systematically investigating the anisotropy of weak field magnetoresistance with respect to magnetic field. It is also found that the existence of in-plane field can effectively suppress the weak antilocalization effect of InSb film and the roughness effect plays an important role in the anisotropy.

cond-mat.mtrl-sci↗

arXiv2010

Weak antilocalization effect in LPE-grown p-Hg0.8Cd0.2Te thin film and the evidence of Te-precipitation

The weak antilocalization effect is observed in a p-type Hg0.8Cd0.2Te thin film with thickness ~10 micrometers. Based on the analysis of composition, carrier species and excellent fitting of data with a model concerning weak antilocalization effect in Te crystal, the most plausible explanation is that the observed weak antilocalization effect is caused by Te-precipitation.

cond-mat.mtrl-sci↗

arXiv2010

Density of states and zero Landau level probed through capacitance of graphene

We report capacitors in which a finite electronic compressibility of graphene dominates the electrostatics, resulting in pronounced changes in capacitance as a function of magnetic field and carrier concentration. The capacitance measurements have allowed us to accurately map the density of states D, and compare it against theoretical predictions. Landau oscillations in D are robust and zero Landau level (LL) can easily be seen at room temperature in moderate fields. The broadening of LLs is strongly affected by charge inhomogeneity that leads to zero LL being broader than other levels.

cond-mat.mes-hall↗

arXiv2010

Weak field magnetoresistance of narrow-gap semiconductors InSb

The magnetoresistance of InSb has been intensively investigated. The experiments we perform here focus on weak field magnetoresistance of InSb thin film. We investigate the magnetoresistance of InSb films in perpendicular, tilted as well as parallel magnetic field. Our results verify the previous observations concerning weak localization effect in InSb thin film. Moreover, we systematically study the anisotropy of magnetoresistance of InSb. We find that the existence of in-plane field can effectively suppress the weak localization effect of InSb film. We fit the experimental data with two types of models, the match between data and model is excellent. From the fitting procedure, we get information about phase coherence time, spin-orbit scattering time. The information about Zeeman effect and sample roughness are also extracted from the fitting procedure.

cond-mat.mtrl-sci↗

arXiv2010

On resonant scatterers as a factor limiting carrier mobility in graphene

We show that graphene deposited on a substrate has a non-negligible density of atomic scale defects. This is evidenced by a previously unnoticed D peak in the Raman spectra with intensity of about 1% with respect to the G peak. We evaluated the effect of such impurities on electron transport by mimicking them with hydrogen adsorbates and measuring the induced changes in both mobility and Raman intensity. If the intervalley scatterers responsible for the D peak are monovalent, their concentration is sufficient to account for the limited mobilities achievable in graphene on a substrate.

cond-mat.mes-hall↗

arXiv2009

Scaling of the quantum-Hall plateau-plateau transition in graphene

The temperature dependence of the magneto-conductivity in graphene shows that the widths of the longitudinal conductivity peaks, for the N=1 Landau level of electrons and holes, display a power-law behavior following $Δν\propto T^κ$ with a scaling exponent $κ= 0.37\pm0.05$. Similarly the maximum derivative of the quantum Hall plateau transitions $(dσ_{xy}/dν)^{max}$ scales as $T^{-κ}$ with a scaling exponent $κ= 0.41\pm0.04$ for both the first and second electron and hole Landau level. These results confirm the universality of a critical scaling exponent. In the zeroth Landau level, however, the width and derivative are essentially temperature independent, which we explain by a temperature independent intrinsic length that obscures the expected universal scaling behavior of the zeroth Landau level.

cond-mat.mes-hall↗

arXiv2009

Influence of metal contacts and charge inhomogeneity on transport properties of graphene near the neutrality point

There is an increasing amount of literature concerning electronic properties of graphene close to the neutrality point. Many experiments continue using the two-probe geometry or invasive contacts or do not control samples' macroscopic homogeneity. We believe that it is helpful to point out some problems related to such measurements. By using experimental examples, we illustrate that the charge inhomogeneity induced by spurious chemical doping or metal contacts can lead to large systematic errors in assessing graphene's transport properties and, in particular, its minimal conductivity. The problems are most severe in the case of two-probe measurements where the contact resistance is found to strongly vary as a function of gate voltage.

cond-mat.mes-hall↗

arXiv2009

Effect of high-k environment on charge carrier mobility in graphene

It is widely assumed that the dominant source of scattering in graphene is charged impurities in a substrate. We have tested this conjecture by studying graphene placed on various substrates and in high-k media. Unexpectedly, we have found no significant changes in carrier mobility either for different substrates or by using glycerol, ethanol and water as a top dielectric layer. This suggests that Coulomb impurities are not the scattering mechanism that limits the mean free path currently attainable for graphene on a substrate.

cond-mat.mes-hall↗

arXiv2008

Quantum resistance metrology in graphene

We have performed a metrological characterization of the quantum Hall resistance in a 1 $μ$m wide graphene Hall-bar. The longitudinal resistivity in the center of the $ν=\pm 2$ quantum Hall plateaus vanishes within the measurement noise of 20 m$Ω$ upto 2 $μ$A. Our results show that the quantization of these plateaus is within the experimental uncertainty (15 ppm for 1.5$ μ$A current) equal to that in conventional semiconductors. The principal limitation of the present experiments are the relatively high contact resistances in the quantum Hall regime, leading to a significantly increased noise across the voltage contacts and a heating of the sample when a high current is applied.

cond-mat.mes-hall↗

arXiv2007

Chaotic Dirac billiard in graphene quantum dots

We report on transport characteristics of quantum dot devices etched entirely in graphene. At large sizes, they behave as conventional single-electron transistors, exhibiting periodic Coulomb blockade peaks. For quantum dots smaller than 100 nm, the peaks become strongly non-periodic indicating a major contribution of quantum confinement. Random peak spacing and its statistics are well described by the theory of chaotic neutrino (Dirac) billiards. Short constrictions of only a few nm in width remain conductive and reveal a confinement gap of up to 0.5eV, which demonstrates the in-principle possibility of molecular-scale electronics based on graphene.

cond-mat.mes-hall↗

arXiv2007

Making graphene visible

Microfabrication of graphene devices used in many experimental studies currently relies on the fact that graphene crystallites can be visualized using optical microscopy if prepared on top of silicon wafers with a certain thickness of silicon dioxide. We study graphene's visibility and show that it depends strongly on both thickness of silicon dioxide and light wavelength. We have found that by using monochromatic illumination, graphene can be isolated for any silicon dioxide thickness, albeit 300 nm (the current standard) and, especially, approx. 100 nm are most suitable for its visual detection. By using a Fresnel-law-based model, we quantitatively describe the experimental data without any fitting parameters.

cond-mat.mes-hall↗

arXiv2004

The Center of Activity in the CSS Superluminal Source 3C 138

We present the results from the first quasi-simultaneous multi-frequency (2.3, 5.0, 8.4 and 15 GHz) Very Long Baseline Interferometry (VLBI) observations of a compact steep spectrum (CSS) superluminal source 3C138. For the first time, the spectral distribution of the components within its central 10 milli-arcsecond (mas) region was obtained. This enables us to identify the component at the western end as the location of the nuclear activity on the assumption that the central engine is associated with one of the detected components. The possibility that none of these visible components is the true core is also discussed. The new measurements further clarify the superluminal motions of its inner jet components. The multi-frequency data reveal a convex spectrum in one jet component, inferring the existence of free-free absorption by the ambient dense plasma.

astro-ph↗

arXiv2003

A First Mass Production of Gas Electron Multipliers

We report on the manufacture of a first batch of approximately 2,000 Gas Electron Multipliers (GEMs) using 3M's fully automated roll to roll flexible circuit production line. This process allows low-cost, reproducible fabrication of a high volume of GEMs of dimensions up to 30$\times$30 cm$^{2}$. First tests indicate that the resulting GEMs have optimal properties as radiation detectors. Production techniques and preliminary measurements of GEM performance are described. This now demonstrated industrial capability should help further establish the prominence of micropattern gas detectors in accelerator based and non-accelerator particle physics, imaging and photodetection.

hep-ex↗