Richard Louie

Followers

Following

Public Views

Uploads

Papers by Richard Louie

Annals of Physics, Feb 1, 1998

Certain zero-bias anomalies (ZBAs) in the voltage, temperature and magnetic field dependence of t... more Certain zero-bias anomalies (ZBAs) in the voltage, temperature and magnetic field dependence of the conductance G(V, T, H) of quenched Cu point contacts have previously been interpreted to be due to non-magnetic 2-channel Kondo (2CK) scattering from near-degenerate atomic two-level tunneling systems Ralph et al., 1994) and hence to represent an experimental realization of the non-Fermi-liquid physics of the T=0 fixed point of the 2-channel Kondo model. In this, the first in a series of three papers (I, II, III) devoted to 2-channel Kondo physics, we present a comprehensive review of the quenched Cu ZBA experiments and their 2CK interpretation, including new results on ZBAs in constrictions made from Ti or from metallic glasses. We first review the evidence that the ZBAs are due to electron scattering from stuctural defects that are not static, but possess internal dynamics. In order to distinguish between several mechanisms proposed to explain the experiments, we then analyze the scaling properties of the conductance at low temperature and voltage and extract from the data a universal scaling function 1(v). The theoretical calculation of the corresponding scaling function within the 2CK model is the subject of papers II and III. The main conclusion of our work is that the properties of the ZBAs, and most notably their scaling behavior, are in good agreement with the 2CK model and clearly different from several other proposed mechanisms.

Download

Development of Giant Magnetoresistive inspection system for detection of deep fatigue cracks under airframe fasteners

AIP Conference Proceedings, 2002

A redesign of the NASA Langley Research Center developed Giant Magnetoresistive-based Rotating Pr... more

Nanocontact Studies of Magnetic Field and Energy Dependent Electron Transport in Cu/co Composites and Multilayers

7th Joint MMM-Intermag Conference. Abstracts (Cat. No.98CH36275)

Response of Fe powder, purified and as-produced HiPco single-walled carbon nanotubes to flash exposure

Materials Science and Engineering: A, 2003

Over the past several years, carbon nanotubes (CNTs) have been a major focus of materials researc... more

Electron Transport Studies of Sputtered Magnetic Multilayers Using Nanofabricated Point Contacts

Nanofabrication techniques have been applied to form three-dimensional thin film "nanocontac... more Nanofabrication techniques have been applied to form three-dimensional thin film "nanocontacts" between a Cu film and a sputtered superlattice consisting of ferromagnetic and noble metal layers, with the minimum contact diameter ranging from 3 to 10 nm. The geometry and scale of these point-contact-like ballistic devices are such that they can be effectively employed for the detailed study of electronic

Asymmetry effects in 2-level Tunneling systems and Two-Channel Kondo Scattering

Previous experiments with quenched Cu nanoconstrictions have observed strong zero bias anomalies ... more Previous experiments with quenched Cu nanoconstrictions have observed strong zero bias anomalies that scale in a manner closely consistent with the predicted behavior of two-channel Kondo (TCK) scattering from two-level tunneling systems (TLS) in the nanoconstriction region. This scaling behavior has been considered somewhat surprising since any asymmetry in the TLS is expected to quench the temperature dependence of the

Low-energy restoration of Fermi-liquid behavior for two-channel Kondo scattering

Physical Review B, 1997

The origin of zero-bias anomalies ͑ZBA's͒ in pure metal nanoconstrictions is investigated. It is ... more The origin of zero-bias anomalies ͑ZBA's͒ in pure metal nanoconstrictions is investigated. It is shown that the ZBA's in titanium nanoconstrictions can be completely understood in terms of electron-assisted tunneling systems. The behavior of such a system is expected to depend on two distinct energy scales, a Kondo energy below which the electrons behave in a non-Fermi-liquid manner, and a splitting energy below which the Fermi-liquid behavior is restored. Titanium nanoconstrictions have been found to exhibit zero-bias anomalies that show both the non-Fermi-liquid behavior and the low-energy restoration of the Fermi liquid.

Download

Spin-Polarized transport across Ferromagnet-Superconductor interfaces

Nanocontacts with minimum diameter of 3-5nm have been formed between ferromagnetic and supercondu... more Nanocontacts with minimum diameter of 3-5nm have been formed between ferromagnetic and superconducting thin films. These nanocontacts have been employed in the study of spin dependent electron transport across the superconductor-ferromagnet interface. We will describe measurements which demonstrate that the spin polarization of conduction electrons in the ferromagnet reduces the Andreev reflection probability at the interface and discuss the use of this effect for examining spin-flip scattering at a ferromagnet- normal metal interface.

Microscale Cantilever Beam Resonators “Weigh” Individual Virus Particles

MRS Bulletin, 2004

Download

X-Rays Generated Using Graphite Nanofiber Cold Cathode with Copper Anode

MRS Bulletin, 2003

Last year, much of J.H. Schön's innovative work at Lucent on field-effect transistors made from s... more Last year, much of J.H. Schön's innovative work at Lucent on field-effect transistors made from self-assembled dithiol monolayers was judged to be fraudulent by an independent review committee. However, questions remained within the molecular electronics community as to which, if any, of the results of Schön's discredited research could be achieved. Recently, a group of researchers from IBM T.J. Watson Research Center have investigated Schön's system to elucidate the limitations and the key requirements necessary to fabricate molecular devices. While the researchers were unable to reproduce Schön's results, they identified some of the design rules necessary to fabricate molecular devices, which include the high purity of molecules for self-assembly and a thorough characterization of the surfaces at each step of the fabrication on both molecular and device-area levels. The researchers also determined that the molecular-device structure must be characterized both structurally and electrically. In addition, the research team explained that tunneling places a lower limit on channel length, and therefore molecular length, to ~3 nm. In addition, electrostatics requires gate dielectrics with thicknesses of less than 2/3 the molecular length, although they are also subject to tunneling limitations. As reported in the February issue of Nano Letters, C.R. Kagan and co-workers created prototypes of the devices having the structure of field-effect transistors ("trench" and planar Si structures) with self-assembled monolayers of 1,1'-biphenyl-4,4'-dithiol instead of an inorganic semiconductor. The prototypes were studied in detail after each step of preparation. The geometry of the devices on Si wafers was fabricated using lithography, reactive-ion etching, and anisotropic wet etching techniques. After this, a uniform film of gate dielectric was formed. Source and drain electrodes were prepared by collimated evaporation of Au and Ti on the gate dielectric. Self-assembled monolayers of dithiols formed on the source electrodes were characterized by local imaging probes such as scanning tunneling and atomic force microscopies as well as large area characterization by, for example, contact angle measurements and ellipsometry. The researchers found that biphenylmonothiol and biphenyldithiol form disordered layers with, at best, small (~10 Å) ordered regions, and that molecules such as alkanethiols assemble to form ordered domains separated by disordered boundaries. The devices made of the well-washed monolayers of 1,1'-biphenyl-4,4'-dithiol formed electrical shorts, contrary to the characteristics reported by Schön, but consistent with the expected physics for these disordered, short molecule assemblies. In efforts to uncover the origin of the I-V characteristics reported by Schön, the IBM research team formed molecular multilayers with longer channel lengths. The researchers, however, did not observe significant gate field effect; furthermore, they found that obtaining significant field effect and turning the device off are fundamentally impossible. Despite the evidence of recent misconduct, though, the research team said that "there is no scientific reason to lose faith in the tremendous promise of this field." An exploration of Schön's work was also carried out by a research team in The Netherlands; see the MRS website at www.mrs.org/gateway/matl -news.html. MAXIM NIKIFOROV

Download

$Research paper thumbnail of Simple Neutron Microscope Uses Refractive Aluminum Lenses$

Simple Neutron Microscope Uses Refractive Aluminum Lenses

MRS Bulletin, 2003

Download

Doped PMMA Used For 3D Multilayered Optical Memory

MRS Bulletin, 2005

x), these nanostructures with rectangular cross sections and triangular tips result from high-tem... more x), these nanostructures with rectangular cross sections and triangular tips result from high-temperature pyrolysis of polyureasilazane in the presence of an FeCl 2 catalyst and N 2 vapor. A powder precursor formed by curing the polyureasilazane and ball-milling it with the catalyst material was annealed at 1450ºC, yielding nanobelts 50-100 nm thick, 400-1000 nm wide, and ranging in length from hundreds of microns to several millimeters. Energy-dispersive spectrum analysis confirmed that the nanobelts consisted only of Si and N. High-resolution transmission electron microscopy revealed that the belts were perfectly crystalline α-Si 3 N 4 with both [011] and [100] growth directions. Investigation of the structure using x-ray diffraction verified the presence of α-Si 3 N 4 , and a broad underlying diffraction peak was interpreted to come from an amorphous precursor that remained under the nanobelts.

Download

Nanomanipulation and lithography for carbon nanotube based nondestructive evaluation sensor development

2002 SEM Annual …, 2002

Carbon nanotubes (CNTs) offer great potential for advanced sensor development due to the unique e... more

Download

Spin filtering by ultrathin ferromagnetic films

Applied Physics Letters, 1999

Spin filtering of ballistic electrons by ultrathin cobalt films of thicknesses ranging from 0.2 t... more Spin filtering of ballistic electrons by ultrathin cobalt films of thicknesses ranging from 0.2 to 3.5 nm has been studied experimentally using nonmagnetic metal–ferromagnet–superconductor nanocontacts. In such systems the flow of electrons with energies below the superconducting gap is very sensitive to any net spin polarization of the electron current. This effect was used to quantitatively measure the transmission rates of up and down spin electrons passing through an individual ferromagnetic layer of nanometer thickness.

Download

The 2-Channel Kondo Model

Annals of Physics, 1999

Recent experiments by Ralph and Buhrman on zero-bias anomalies in quenched Cu nanoconstrictions (... more Recent experiments by Ralph and Buhrman on zero-bias anomalies in quenched Cu nanoconstrictions (reviewed in a preceding paper, I) are in accord with the assumption that the interaction between electrons and nearly degenerate two-level systems in the constriction can be described, for sufficiently small voltages and temperatures (V, T < TK), by the 2-channel Kondo (2CK) model. Motivated by these experiments, we introduce a generalization of the 2CK model, which we call the nanoconstriction 2-channel Kondo model (NTKM), that takes into account the complications arising from the non-equilibrium electron distribution in the nanoconstriction. We calculate the conductance G(V, T ) of the constriction in the weakly non-equilibrium regime of V, T ≪ TK by combining concepts from Hershfield's Y -operator formulation of non-equilibrium problems and Affleck and Ludwig's exact conformal field theory (CFT) solution of the 2CK problem (CFT technicalities will be discussed in a subsequent paper, III). Finally, we extract from the conductance a universal scaling curve Γ(v) and compare it with experiment. Combining our results with those of Hettler, Kroha and Hershfield, we conclude that the NTKM achieves quantitative agreement with the experimental scaling data.

Download

Probing Ferromagnets with Andreev Reflection

Physical Review Letters, 1998

High transmissivity, ferromagnet-superconductor thin film nanocontacts are studied experimentally... more High transmissivity, ferromagnet-superconductor thin film nanocontacts are studied experimentally. Compared to nonmagnetic metal-superconductor contacts, Andreev reflection is strongly suppressed due to the spin polarization of conduction electrons in the ferromagnet. This effect is used to measure both the transparency of the interface and spin polarization of the direct current in the ferromagnet in contrast to the spin polarization of the tunneling current previously measured in ferromagnet-insulatorsuperconductor systems. [S0031-9007(98)

Download

Richard Louie

Uploads

Papers by Richard Louie

Log In