Mildred S. Dresselhaus

Bio: Mildred S. Dresselhaus is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Carbon nanotube & Raman spectroscopy. The author has an hindex of 136, co-authored 762 publications receiving 112525 citations. Previous affiliations of Mildred S. Dresselhaus include University of California, Los Angeles & Universidade Federal de Minas Gerais.

Magnetic properties of Heisenberg antiferromagnetic EuTe/PbTe superlattices

Abstract: Bulk EuTe is a type II Heisenberg antiferromagnet (AF2) with a single magnetic phase transition temperature at 9.6 K. However, for several isolated EuTe (111) monolayers (MLs) as can be achieved in a superlattice (SL) structure, both ferrimagnetic-like and antiferromagnetic-like phase transitions can take place, depending on the SLs configuration. The temperature-dependent magnetizationM(T) of such SLs has been studied near the transition temperature (Tc) by SQUID magnetometry. The functional forms ofM(T) atT ≤ Tc can be described by mean-field theory for SLs with 3, 4 and 5 EuTe MLs per SL cell. The magnetic transition temperatures obtained by mean-field analysis, using bulk exchange coupling values, are in close agreement with observedTc values for SLs with 2, 3, 4 and 5 EuTe MLs. The qualitative behavior of the surface specific heat can be deduced fromM(T) data for SLs with three EuTe monolayers.

Characterization of nanographite and carbon nanotubes by polarization dependent optical spectroscopy

Abstract: The optical absorption for ? electrons as a function of the electron wavevector k is investigated by first order perturbation theory in graphite and single wall carbon nanotubes (SWNTs). The matrix element connecting two states in the valence and conduction bands is found to be significantly anisotropic in k-space and polarization dependent. In the case of graphite, the absorption shows a node around the equi-energy contour, and in the case of SWNTs we obtain selection rules that allow only transitions between certain pairs of subbands. The strength of the optical absorption is not only diameter dependent but also chirality dependent. The implications of the optical absorption matrix element on the resonant conditions are discussed.

New Method to Detect the Transport Scattering Mechanisms of Graphene Carriers

Abstract: Detecting the carrier scattering mechanisms in a materials system is important for transport related science and engineering. The approaches of fast laser process and electrical conductivity matching were used in previous literature, which do not give accurate information on scattering relaxation time as a function of carrier energy for intrinsic photon-free transport. Graphene is considered as a model system in materials science studying for its simple atomic and electronic structures. Here we have developed a new methodology to detect the scattering relaxation time as a function of carrier energy, which can be used to infer the carrier scattering mechanisms at different temperatures. Our method utilizes the measured values of optimal Seebeck coefficient, for both P-type and N-type materials. This new approach can eliminate the influence from photon-carrier scattering in the fast-laser method, and avoid the over-fitting issue in the electrical conductivity matching method. We have then applied the new approach in the SiO2 substrated graphene system, and discovered that the Dirac carriers are mainly scattered by short-range interactions at 40 K. The scatter strength of long-range Coulomb interaction increases with temperature. At 300 K, the long-range and short-range interactions scatter the Dirac carriers with almost comparable strengths.

Resonant tunneling and intrinsic bistability in twisted graphene structures

Abstract: We predict that vertical transport in heterostructures formed by twisted graphene layers can exhibit a unique bistability mechanism. Intrinsically bistable $I\text{\ensuremath{-}}V$ characteristics arise from resonant tunneling and interlayer charge coupling, enabling multiple stable states in the sequential tunneling regime. We consider a simple trilayer architecture, with the outer layers acting as the source and drain and the middle layer floating. Under bias, the middle layer can be either resonant or nonresonant with the source and drain layers. The bistability is controlled by geometric device parameters easily tunable in experiments. The nanoscale architecture can enable uniquely fast switching times.

Electric Field Effect in Atomically Thin Carbon Films

Abstract: We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions, metallic, and of remarkably high quality. The films are found to be a two-dimensional semimetal with a tiny overlap between valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in concentrations up to 10 13 per square centimeter and with room-temperature mobilities of ∼10,000 square centimeters per volt-second can be induced by applying gate voltage.

Helical microtubules of graphitic carbon

Abstract: THE synthesis of molecular carbon structures in the form of C60 and other fullerenes1 has stimulated intense interest in the structures accessible to graphitic carbon sheets. Here I report the preparation of a new type of finite carbon structure consisting of needle-like tubes. Produced using an arc-discharge evaporation method similar to that used for fullerene synthesis, the needles grow at the negative end of the electrode used for the arc discharge. Electron microscopy reveals that each needle comprises coaxial tubes of graphitic sheets, ranging in number from 2 up to about 50. On each tube the carbon-atom hexagons are arranged in a helical fashion about the needle axis. The helical pitch varies from needle to needle and from tube to tube within a single needle. It appears that this helical structure may aid the growth process. The formation of these needles, ranging from a few to a few tens of nanometres in diameter, suggests that engineering of carbon structures should be possible on scales considerably greater than those relevant to the fullerenes. On 7 November 1991, Sumio Iijima announced in Nature the preparation of nanometre-size, needle-like tubes of carbon — now familiar as 'nanotubes'. Used in microelectronic circuitry and microscopy, and as a tool to test quantum mechanics and model biological systems, nanotubes seem to have unlimited potential.

The rise of graphene

Abstract: Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

The electronic properties of graphene

Abstract: This article reviews the basic theoretical aspects of graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations. The Dirac electrons can be controlled by application of external electric and magnetic fields, or by altering sample geometry and/or topology. The Dirac electrons behave in unusual ways in tunneling, confinement, and the integer quantum Hall effect. The electronic properties of graphene stacks are discussed and vary with stacking order and number of layers. Edge (surface) states in graphene depend on the edge termination (zigzag or armchair) and affect the physical properties of nanoribbons. Different types of disorder modify the Dirac equation leading to unusual spectroscopic and transport properties. The effects of electron-electron and electron-phonon interactions in single layer and multilayer graphene are also presented.