Mechanism For Lo-phonon Temperature Overshoot In Gaas

Carrier relaxation and LO-phonon dynamics are investigated in GaAs crystals illuminated by picosecond laser pulses. It is evidenced that an overshoot of the LO-phonon quasitemperature above the electron quasitemperature can occur in the absence of intervalley scattering. This effect is ascribed to the screening of the polar optical interaction. © 1994 The American Physical Society.49117257726

Indication Of Unusual Pentagonal Structures In Atomic-size Cu Namwires

A study of the structural and quantum conductance properties of atomic-size copper nanowires generated by mechanical stretching was presented. The time-resolved electron microscopy observations and molecular dynamics simulations were used to derive the atomistic evolution. The quantum transport behavior was analyzed by means of conductance measurements and theoretical calculations. The formation of an unusual and highly pentagonal Cu nanowires with a diameter of ∼0.45 nm and ∼4.5 conductance quanta was also shown.93121261031-126103-4Agraït, N., Yeyati, A.L., Van Ruitenbeek, J.M., (2003) Phys. Rep., 377, p. 81Gulseren, O., Ercolessi, F., Tosatti, E., (1998) Phys. Rev. Lett., 80, p. 3775Kondo, Y., Takayanagi, K., (2000) Science, 289, p. 606Oshima, Y., Onga, A., Takayanagi, K., (2003) Phys. Rev. Lett., 91, p. 205503Ohnishi, H., Kondo, Y., Takayanagi, K., (1998) Nature (London), 395, p. 780Yanson, A.I., (1998) Nature (London), 395, p. 783Rodrigues, V., Fuhrer, T., Ugarte, D., (2000) Phys. Rev. Lett., 85, p. 4124Rego, L.G.C., Rocha, A.R., Rodrigues, V., Ugarte, D., (2003) Phys. Rev. B, 67, p. 045412Rodrigues, V., (2002) Phys. Rev. B, 65, p. 153402Krans, J.M., (1995) Nature (London), 375, p. 767Kondo, Y., Takayanagi, K., (1997) Phys. Rev. Lett., 79, p. 3455Rodrigues, V., Ugarte, D., (2003) Nanowires and Nanobelts, 1, p. 177. , edited by Z. L. Wang Kluwer, DordrechtRodrigues, V., Bettini, J., Silva, P.C., Ugarte, D., (2003) Phys. Rev. Lett., 91, p. 096801Marks, L.D., (1994) Rep. Prog. Phys., 57, p. 603Urban, J., (1998) Cryst. Res. Technol., 33, p. 1009Lisiecki, I., (2000) Phys. Rev. B, 61, p. 4968Emberly, E.G., Kirczenow, G., (1998) Phys. Rev. B, 58, p. 10911(1999) Phys. Rev. B, 60, p. 6028Reinhard, D., (1997) Phys. Rev. Lett., 79, p. 1459Sen, P., (2002) Phys. Rev. B, 65, p. 235433Cleri, F., Rosato, V., (1993) Phys. Rev. B, 48, p. 22Tomànek, D., Aligia, A.A., Balseiro, C.A., (1985) Phys. Rev. B, 32, p. 5051Coura, P.Z., (2004) Nano Lett., 4, p. 1187EPAPS Document No. E-PRLTAO-93-010436, E-PRLTAO-93-010436. , http://www.aip.org/pubservs/epaps.html)orfromftp.aip.orginthedirectory/ epaps, Figure 4 snapshot of a Cu nanowire being elongated along the [110] axis. A direct link to this document may be found in the online article's HTML reference section. The document may also be reached via the EPAPS homepage See the EPAPS homepage for more informatio

Calculation of nanowire thermal conductivity using complete phonon dispersion relations

The lattice thermal conductivity of crystalline Si nanowires is calculated. The calculation uses complete phonon dispersions, and does not require any externally imposed frequency cutoffs. No adjustment to nanowire thermal conductivity measurements is required. Good agreement with experimental results for nanowires wider than 35 nm is obtained. A formulation in terms of the transmission function is given. Also, the use of a simpler, nondispersive "Callaway formula", is discussed from the complete dispersions perspective.Comment: 4 pages, 3 figures. Accepted in Phys. Rev.

Phonon-mediated thermal conductance of mesoscopic wires with rough edges

We present an analysis of acoustic phonon propagation through long, free-standing, insulating wires with rough surfaces. Due to a crossover from ballistic propagation of the lowest-frequency phonon mode at $\omega <\omega _{1}=\pi c/W$ to a diffusive (or even localized) behavior upon the increase of phonon frequency, followed by re-entrance into the quasi-ballistic regime, the heat conductance of a wire acquires an intermediate tendency to saturate within the temperature range $T\sim \hbar \omega_{1}/k_{B}$.Comment: 4 pages, 3 figures included; minor changes and corrections, figures 1 and 2 replaced by better versions; to appear in PRB Brief Report

Resonant thermal transport in semiconductor barrier structures

I report that thermal single-barrier (TSB) and thermal double-barrier (TDB) structures (formed, for example, by inserting one or two regions of a few Ge monolayers in Si) provide both a suppression of the phonon transport as well as a resonant-thermal-transport effect. I show that high-frequency phonons can experience a traditional double-barrier resonant tunneling in the TDB structures while the formation of Fabry-Perot resonances (at lower frequencies) causes quantum oscillations in the temperature variation of both the TSB and TDB thermal conductances $\sigma_{\text{TSB}}$ and $\sigma_{\text{TDB}}$.Comment: 4 pages. 4 figure.

Quantum energy flow in mesoscopic dielectric structures

We investigate the phononic energy transport properties of mesoscopic, suspended dielectric wires. The Landauer formula for the thermal conductance is derived and its universal aspects discussed. We then determine the variance of the energy current in the presence of a steady state current flow. In the final part, some initial results are presented concerning the nature of the temperature fluctuations of a mesoscopic electron gas thermometer due to the absorption and emission of wire phonons.Comment: 20 pages, 2 figures. Submitted to Phys. Rev.

One-dimensional quantum channel and Hawking radiation of the Kerr and Kerr-Newman black holes

In this paper, we review the one-dimensional quantum channel and investigate Hawking radiation of bosons and fermions in Kerr and Kerr-Newman black holes. The result shows the Hawking radiation can be described by the quantum channel. The thermal conductances are derived and related to the black holes' temperatures.Comment: V2, 12 pages. Typo correcte

First-principles quantum transport modeling of thermoelectricity in single-molecule nanojunctions with graphene nanoribbon electrodes

We overview nonequilibrium Green function combined with density functional theory (NEGF-DFT) modeling of independent electron and phonon transport in nanojunctions with applications focused on a new class of thermoelectric devices where a single molecule is attached to two metallic zigzag graphene nanoribbons (ZGNRs) via highly transparent contacts. Such contacts make possible injection of evanescent wavefunctions from ZGNRs, so that their overlap within the molecular region generates a peak in the electronic transmission. Additionally, the spatial symmetry properties of the transverse propagating states in the ZGNR electrodes suppress hole-like contributions to the thermopower. Thus optimized thermopower, together with diminished phonon conductance through a ZGNR/molecule/ZGNR inhomogeneous structure, yields the thermoelectric figure of merit ZT~0.5 at room temperature and 0.5<ZT<2.5 below liquid nitrogen temperature. The reliance on evanescent mode transport and symmetry of propagating states in the electrodes makes the electronic-transport-determined power factor in this class of devices largely insensitive to the type of sufficiently short conjugated organic molecule, which we demonstrate by showing that both 18-annulene and C10 molecule sandwiched by the two ZGNR electrodes yield similar thermopower. Thus, one can search for molecules that will further reduce the phonon thermal conductance (in the denominator of ZT) while keeping the electronic power factor (in the nominator of ZT) optimized. We also show how often employed Brenner empirical interatomic potential for hydrocarbon systems fails to describe phonon transport in our single-molecule nanojunctions when contrasted with first-principles results obtained via NEGF-DFT methodology.Comment: 20 pages, 6 figures; mini-review article prepared for the special issue of the Journal of Computational Electronics on "Simulation of Thermal, Thermoelectric, and Electrothermal Phenomena in Nanostructures", edited by I. Knezevic and Z. Aksamij

Multi-charged Acceptor Centers In P-doped Si/si1 -xgex/si Quantum Wells In The Presence Of A Magnetic Field

Neutral (A0) and positively charged (A+) shallow acceptor centers in p-doped SiGe/Si nanostructures are investigated in the presence of an external magnetic field. The band mixing of valence states, the confinement potential and the magnetic field are responsible for an increase in the binding energy of the system. The properties of the lower-energy states of the A+ are studied and their binding energies calculated for a Si0.87Ge0.13 quantum well. It is shown that the ground state of the A+ complex has a singlet-like parity configuration up to magnetic fields as high as 12 T. The effects of hole-hole repulsive interaction and hole-impurity attractive potential on the A+ spectra are considered. © 1998 Published by Elsevier Science B.V. All rights reserved.21-4785788Shields, A.J., Pepper, M., Ritchie, D.A., Simmons, M.Y., Jones, G.A.C., (1995) Phys. Rev. B, 51, p. 18049Ryu, S.R., Jiang, Z.X., Li, W.J., McCombe, B.D., (1996) Phys. Rev. B, 54, pp. R11086MacDonald, A.H., (1992) Solid State Commun., 84, p. 109Hawrylak, P., (1993) Solid State Commun., 88, p. 475Broido, D., Sham, L.J., (1985) Phys. Rev. B, 31, p. 888Bir, G.L., Pikus, G.E., (1974) Symmetry and Strain-Inducted Effects in Semiconductors, , Wiley, New YorkMadelung, O., (1987) Landolt&Bernstein: Semiconductors, Physics of Group IV and III-V Compounds, 3-17 A. , Springer, BerlinRego, L.G.C., Hawrylak, P., Brum, J.A., Wojs, A., (1997) Phys. Rev. B, 55, p. 15694Wagner, M., Merket, U., Chaplik, A.V., (1992) Phys. Rev. B, 45, p. 1951Ashoori, R.C., Stormer, H.L., Weiner, J.S., Pfeiffer, L.N., Baldwin, K.W., West, K.W., (1993) Phys. Rev. Lett., 71, p. 61