A5070876029- Quantum and electron transport phenomena
- Semiconductor Quantum Structures and Devices
- GaN-based semiconductor devices and materials
- Physics of Superconductivity and Magnetism
- Rare-earth and actinide compounds
- Topological Materials and Phenomena
- Advancements in Semiconductor Devices and Circuit Design
- Semiconductor materials and devices
- ZnO doping and properties
- Ga2O3 and related materials
- Magnetic Properties of Alloys
- Surface and Thin Film Phenomena
- Graphene research and applications
- Molecular Junctions and Nanostructures
- Superconducting Materials and Applications
- Gas Sensing Nanomaterials and Sensors
- Gold and Silver Nanoparticles Synthesis and Applications
- Semiconductor materials and interfaces
- Advanced Chemical Sensor Technologies
- Advanced Condensed Matter Physics
- Analytical Chemistry and Sensors
- Microfluidic and Capillary Electrophoresis Applications
- Acoustic Wave Resonator Technologies
- Thermal properties of materials
- Mechanical and Optical Resonators
University of Michigan
2013-2023
Michigan United
2008
Virginia Commonwealth University
2006
Princeton University
1991-2002
Lawrence Berkeley National Laboratory
1997-2001
University of California, Berkeley
1997-2001
We study the transport properties of Kondo insulator SmB${}_{6}$ with a specialized configuration designed to distinguish bulk-dominated conduction from surface-dominated conduction. find that as material is cooled below 4 K, it exhibits crossover bulk surface fully insulating bulk. take robustness and magnitude conductivity, manifest in literature SmB${}_{6}$, be strong evidence for topological metallic states recently predicted this material.
In Kondo insulator samarium hexaboride SmB$_6$, strong correlation and band hybridization lead to an insulating gap a diverging resistance at low temperature. The divergence ends about 5 Kelvin, behavior recently demonstrated arise from the surface conductance. However, questions remain whether where topological state exists. Quantum oscillations have not been observed map Fermi surface. We solve problem by resolving Landau Level quantization topology using torque magnetometry. suggests two...
We present ac measurements of the diagonal conductivity ${\mathrm{\ensuremath{\sigma}}}_{\mathit{x}\mathit{x}}$, in integer quantum Hall regime for frequency f between 0.2 and 14 GHz temperature T\ensuremath{\ge}50 mK. Re(${\mathrm{\ensuremath{\sigma}}}_{\mathit{x}\mathit{x}}$) was obtained from measured attenuation a coplanar transmission line on sample surface. For f\ensuremath{\gtrsim}1 GHz, ${\mathrm{\ensuremath{\sigma}}}_{\mathit{x}\mathit{x}}$ peaks IQHE minima broaden as increases,...
A single-phase synthesis of thiolate monolayer-protected gold clusters (MPCs) is described. This method avoids the problem persistent ionic contamination from residual phase-transfer catalyst while retaining versatility associated with commonly used two-phase Brust synthesis. MPCs having alkyl, diphenylacetylene, ether, amide, or ester functionalities were prepared by this and characterized via 1H NMR, FT-IR, UV−vis absorption spectroscopy, TGA, STM, TEM. Comparisons products synthesized...
We have fabricated a two-dimensional array of Josephson junctions within 100 nm electron gas (2DEG) in GaAs/AlGaAs heterostructure. The screening provided by the 2DEG causes to show superconducting behavior despite large junction resistance. Varying resistance per square changes dissipation electrodynamic environment independently any other parameters system. As increases, current-voltage characteristics change from insulating character.
The inverted resistance method was used in this study to extend the bulk resistivity of [Formula: see text] a regime where surface conduction overwhelms bulk. Remarkably, regardless large off-stoichiometric growth conditions (inducing disorder by samarium vacancies, boron interstitials, etc.), shows an intrinsic thermally activated behavior that changes ∼7-10 orders magnitude, suggesting is ideal insulator immune disorder.
We study two kinds of quantum interference effects in transport--the Aharonov-Bohm effect and the weak-localization effect--in quasi-one-dimensional wires rings to address issues concerning phase-coherence length, spin-orbit scattering, flux cancellation mechanism which is predicted be present when elastic mean free path exceeds sample width. Our devices are fabricated on GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As pseudomorphic...
The recent conjecture of a topologically protected surface state in ${\mathrm{SmB}}_{6}$ and the verification robust conduction below 4 K have prompted large effort to understand states. Conventional Hall transport measurements allow current flow on all surfaces topological insulator, so such are influenced by contributions from multiple varying character. Instead, we study magnetotransport using Corbino geometry, which can directly measure conductivity single, independent surface. Both...
GaN-based high electron mobility transistors (HEMTs) have demonstrated frequency power amplification with considerably larger output densities than that available from amplifiers based on other material systems such as GaAs or InP. To further increase the operating while maintaining in HEMTs, gate-to-channel distance needs to be reduced significantly. This leads a two-dimensional gas (2DEG) density (ns) and (μ) Ga polar HEMT structures resulting sheet resistance. work demonstrates by proper...
Spin-orbit coupling is studied using the quantum interference corrections to conductance in ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}∕\mathrm{AlN}∕\mathrm{GaN}$ two-dimensional electron systems where carrier density controlled by persistent photoconductivity effect. All samples exhibit a weak antilocalization feature with spin-orbit field of around $1.8\phantom{\rule{0.3em}{0ex}}\mathrm{mT}$. The zero-field spin splitting energies extracted from measurements are found...
We report on high electric field stress measurements at room temperature InAlN/AlN/GaN heterostructure effect transistor structures. The degradation rate as a function of the average electron density in GaN channel (as determined by gated Hall bar for particular gate biases used), has minimum densities around 1×1013 cm−2, and tends to follow hot phonon lifetime dependence density. observations are consistent with buildup longitudinal optical phonons their ultrafast decay about same channel....
Temperature-dependent resistivity and Hall measurements were performed on a heavily Sn-doped (010) β-Ga2O3 substrate grown by edge-defined film-fed method. At room temperature, the electron mobility was 77.7 cm2 V−1 s−1. A maximum of 95.2 s−1 achieved at T = 185 K. Because doping concentration is near Mott critical value 2.48 × 1018 cm−3, data analyzed using two-band model, which considers transport through both conduction band an impurity band. > 200 K, charge limited free carriers in The...
We study low-frequency noise in selectively doped ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ quantum point contact and Hall bar structures. Experiments are carried out at 4.2 K constant magnetic fields where both diagonal voltages is measured using a four-terminal lock-in technique. In all cases, for low currents frequencies, we find the size of excess voltage power to be quadratic current and, furthermore, field....
We have used rapid thermal annealing to investigate the influence of N interstitials on electronic properties GaAsN alloys. Nuclear reaction analysis reveals an annealing-induced decrease in interstitial concentration, while total composition remains constant. Corresponding signatures for reduced concentration are apparent Raman spectra. Following annealing, both room-T carrier n, and mobility increase. At higher measurement-Ts, a thermally activated increase n suggests presence trap near...
The performance of arrays small, densely integrated chemiresistor (CR) vapor sensors with electron-beam patterned interface layers thiolate-monolayer-protected gold nanoparticles (MPNs) is explored. Each CR in the array consists a 100-μm2 interdigital electrode separated from adjacent devices by 4 μm. Initial studies involved four separate arrays, each containing CRs coated one different MPNs, which were calibrated five vapors before and after MPN-film patterning. MPNs derived n-octanethiol...
Fundamental research aside, studying three-dimensional topological insulators (3D TIs) is important for realizing advanced electronics, such as dissipationless transistors and spintronic devices. In characterizing 3D TIs, one difficulty comes from the fact that both surface bulk conduction exist, are markedly different. When dominates, in SmB${}_{6}$, value impeded. This study offers a technique to access conductivity surface-dominated regime. method expected see wide use in-depth transport...
We have investigated the effects of N on electronic properties Si-doped GaAs1−xNx alloy films and AlGaAs∕GaAsN modulation-doped heterostructures. For bulk-like films, electron mobility is independent free carrier concentration arsenic species, decreases with increasing composition. Thus, N-related defects are main source scattering in dilute nitride alloys. heterostructures, gated illuminated magnetoresistance measurements reveal a two-dimensional gas which increases to constant value....
Use of electron-beam induced crosslinking to pattern films monolayer-protected gold nanoparticles (MPNs) onto a chemiresistor (CR) sensor array is described. Each the four CRs comprises 100 µm2 set interdigital electrodes (IDEs) with nm widths and spaces, separated from adjacent devices by 4 µm. Films MPNs, each different thiolate monolayer, were successively patterned on IDEs. Vapor exposures yield rapid, reversible changes in CR resistances differential vapor sensitivities comparable those...
We have investigated the N composition, $x$, and temperature, $T$, dependence of electron effective mass, ${m}^{\ensuremath{\ast}}$, ${\text{GaAs}}_{1\ensuremath{-}x}{\text{N}}_{x}$ films with sufficiently low carrier concentration that carriers are expected to be confined near bottom conduction-band edge (CBE). Using Seebeck Hall measurements, in conjunction assumptions parabolic bands Fermi-Dirac statistics, we find a nonmonotonic ${m}^{\ensuremath{\ast}}$ on $x$ an increasing $T$ $x$....
After the theoretical prediction that ${\mathrm{SmB}}_{6}$ is a topological Kondo insulator, there has been an explosion of studies on surface. However, not yet agreement even most basic quantities such as surface carrier density and mobility. In this paper, we carefully revisit Corbino disk magnetotransport to find those transport parameters. We first show subsurface cracks exist in crystals, arising both from preparation during crystal growth. provide evidence these hidden are additional...