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15TH INTERNATIONAL CONFERENCE ON NARROW GAP SYSTEMS (NGS15) Date: 1–5 August 2011 Location: Blacksburg (USA) ISBN: 978-0-7354-0993-4 Editor(s): Giti A. Khodaparast, Michael B. Santos, Christopher J. Stanton

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Preface: 15th International Conference on Narrow Gap Systems (NGS15)

Giti A. Khodaparast, Michael B. Santos, and Christopher J. Stanton

AIP Conf. Proc. 1416, pp. 1-1; doi:http://dx.doi.org/10.1063/1.3671684 (1 page)

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71.28.+d Narrow-band systems; intermediate-valence solids
71.20.Ps Other inorganic compounds
02.40.Pc General topology

A History of Narrow Gap Semiconductors and Systems: from Graphite to Graphene

Bruce D. McCombe

AIP Conf. Proc. 1416, pp. 9-13; doi:http://dx.doi.org/10.1063/1.3671685 (5 pages)

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A brief review of developments in narrow gap semiconductors and structures is provided based on tracing emphases in materials, physics and devices through the series of conferences bearing that designation (or some variant of it).
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71.28.+d Narrow-band systems; intermediate-valence solids
78.20.Ls Magneto-optical effects
73.21.Fg Quantum wells
73.43.Cd Theory and modeling
02.40.Pc General topology

First‐Principles Study of Surface States of Bi2Te3

Kyungwha Park

AIP Conf. Proc. 1416, pp. 14-18; doi:http://dx.doi.org/10.1063/1.3671686 (5 pages)

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Bi2Te3 is a topological insulator with time reversal symmetry possessing a single Dirac cone at a given surface. The surface states of topological insulators play a critical role in exotic physical phenomena and their applications. We investigate the surface states of thin films of Bi2Te3(111) using density‐functional theory including spin‐orbit coupling. Considering one to six quintuple layers (QLs) of Bi2Te3 films, we identify the surface states from calculated band structures using the decay length of the surface states and electron density plots. We show that the films of 1 and 2 QLs are too thin to hold the surface states protected topologically, and that for thicker films bands identified as surface states at Γ̄ lose their surface‐state features away from Γ̄. This method can be applied to other topological insulators.
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03.65.Pm Relativistic wave equations
71.23.An Theories and models; localized states
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
02.40.Pc General topology

Spin Polarization Phenomena and Pseudospin Quantum Hall Ferromagnetism in the HgTe Quantum Well

M. V. Yakunin, A. V. Suslov, S. M. Podgornykh, S. A. Dvoretsky, and N. N. Mikhailov

AIP Conf. Proc. 1416, pp. 19-22; doi:http://dx.doi.org/10.1063/1.3671687 (4 pages)

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The parallel field of a full spin polarization of the electron gas in a Γ8 conduction band of the HgTe quantum well was obtained from the magnetoresistance by three different ways in a zero and quasi‐classical range of perpendicular field component B⟂. In the quantum Hall range of B⟂ the spin polarization manifests in anticrossings of magnetic levels, which were found to strongly nonmonotonously depend on B⟂.
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76.70.Fz Double nuclear magnetic resonance (DNMR), dynamical nuclear polarization
71.10.Ca Electron gas, Fermi gas
71.70.Di Landau levels
75.30.Gw Magnetic anisotropy

Effect of Electron‐electron Interaction on Surface Transport in Three Dimensional Topological Insulators

Hridis K. Pal, Vladimir I. Yudson, and Dmitrii L. Maslov

AIP Conf. Proc. 1416, pp. 23-25; doi:http://dx.doi.org/10.1063/1.3671688 (3 pages)

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We study the effect of electron‐electron interaction on the temperature dependence of surface charge transport in three dimensional topological insulators. In conventional two dimensional materials at small temperatures, in the absence of umklapp scattering, the presence or absence of T2 dependence in the resistivity is found to depend on the Fermi surface geometry‐ whether it is concave or convex and whether it is simply or multiply connected. In the recently discovered three‐dimensional topological insulators such as Bi2Te3, Bi2Se3, and Sb2Te3, the Fermi surface of the two dimensional surface states, owing to hexagonal warping, changes shape from convex to concave as a function of energy. Electron‐electron interaction is therefore expected to affect the resistivity in these materials differently at different values of the Fermi energy. The expected behavior along with suggestions for experiments are presented.
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71.20.Be Transition metals and alloys
73.20.At Surface states, band structure, electron density of states
72.10.Di Scattering by phonons, magnons, and other nonlocalized excitations
02.40.Pc General topology

Optical Excitation of Graphene, Population Inversion, and Terahertz Lasing

V. Ryzhii, M. Ryzhii, A. Satou, T. Otsuji, and V. Mitin

AIP Conf. Proc. 1416, pp. 26-30; doi:http://dx.doi.org/10.1063/1.3671689 (5 pages)

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We overview effects associated with the optical (infrared) pumping of graphene. Different scenarios of the photogenerated electrons and holes electron relaxation are considered.
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81.05.ue Graphene
07.77.Ka Charged-particle beam sources and detectors
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
07.20.Dt Thermometers

Coherent Phonons in Carbon Nanotubes and Graphene

G. D. Sanders, C. J. Stanton, J. H. Kim, K. J. Yee, M. H. Jung, B. H. Hong, L. G. Booshehri, E. H. Hàroz, and J. Kono

AIP Conf. Proc. 1416, pp. 31-33; doi:http://dx.doi.org/10.1063/1.3671690 (3 pages)

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We develop a theory for generation and detection of coherent phonons in graphene and carbon nanotubes. Coherent phonons are generated via phonon interactions with photogenerated carriers. Electronic states are treated in an extended tight binding model while phonon modes are treated using valence force field models. The amplitude for each coherent phonon mode satisfies a driven oscillator equation with a driving function that depends on the photoexcited carrier distributions.
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81.05.ue Graphene
73.22.Pr Electronic structure of graphene
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Electron Spin Alignment in InSb Type‐II Quantum Dots in an InAs Matrix

Mikhail S. Mukhin, Yakov V. Terent'ev, Leonid E. Golub, Mikhail O. Nestoklon, Boris Ya. Meltser, Alexey N. Semenov, Victor A. Solov'ev, Alexey A. Toropov, and Sergey V. Ivanov

AIP Conf. Proc. 1416, pp. 34-37; doi:http://dx.doi.org/10.1063/1.3671691 (4 pages)

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Electronic spin polarization up to 100 % has been observed in type‐II narrow‐gap heterostructures with InSb quantum dots in an InAs matrix via investigation of circular‐polarized photoluminescence at external magnetic field applied in Faraday geometry. Energy spectrum of holes confined in monolayer scale InSb∕InAs quantum well is calculated using tight‐binding approach. The observed effect is explained in terms of strong Zeeman splitting of electrons in InAs matrix due to their large intrinsic g‐factor and corresponding optical transition selection rules. Temperature dependence of polarization degree well fit obtained data providing its experimental verification of suggested model.
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76.70.Fz Double nuclear magnetic resonance (DNMR), dynamical nuclear polarization
71.28.+d Narrow-band systems; intermediate-valence solids
73.21.La Quantum dots
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Determination of Spin‐Orbit Coefficients and Phase Coherence Times in InGaAs∕InAlAs Quantum Wells

Takaaki Koga, Sebastien Faniel, Toru Matsuura, Shunsuke Mineshige, Yoshiaki Sekine, and H. Sugiyama

AIP Conf. Proc. 1416, pp. 38-41; doi:http://dx.doi.org/10.1063/1.3671692 (4 pages)

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We report the determination of the intrinsic spin‐orbit interaction (SOI) parameters and phase coherence times for In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As quantum wells (QWs) from the analysis of the weak antilocalization (WAL) measurements at dilution temperatures. We find that the Dresselhaus SOI is mostly negligible in this system and that the intrinsic parameters for the Rashba effect, aSO ≡ α/<Ez> is determined quantitatively to be aSOm∗/me  =  (1.46–1.51×10−17NS[m−2])emath2, where NS is the sheet carrier density. We also provide the values of the phase coherent time τϕ extracted from the WAL analysis and the transport mobility μ obtained from the Hall and Shubnikov‐de Haas (SdH) measurements.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
07.05.Kf Data analysis: algorithms and implementation; data management

Rashba Effect in Non‐Magnetic InGaAs∕GaAsSb Resonant Tunneling Diodes Enhanced By Transverse Magnetic Field

J. Silvano de Sousa, H. Detz, P. Klang, E. Gornik, G. Strasser, and J. Smoliner

AIP Conf. Proc. 1416, pp. 42-45; doi:http://dx.doi.org/10.1063/1.3671693 (4 pages)

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A large Rashba splitting enhanced by an in‐plane magnetic field is observed in non‐magnetic InGaAs∕GaAsSb∕InGaAs resonant tunneling diodes over a wide range of temperatures. The current resonances split by the Rashba effect reveal peak to valley ratios up to 2.5:1, the energy spacing between the split peaks reaches values up to 30 meV at B  =  5T. The observed peak splitting is robust and can be observed at temperatures as high as T  =  180K. The largest Rashba parameter determined from the split peak positions is α  =  0.78 eVmath. This value is consistent with literature values reported for InGaAs based devices.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.21.Fg Quantum wells
84.71.Ba Superconducting magnets; magnetic levitation devices

A New Generation of Interband Cascade Lasers

W. W. Bewley, C. S. Kim, M. Kim, C. D. Merritt, C. L. Canedy, I. Vurgaftman, J. Abell, and J. R. Meyer

AIP Conf. Proc. 1416, pp. 46-48; doi:http://dx.doi.org/10.1063/1.3671694 (3 pages)

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We report on recent antimonide‐based type‐II interband cascade lasers emitting at wavelengths from 3 μm to 5.5 μm, which display pulsed threshold current densities at 300 K as low as 170 A/cm2. Narrow ridge devices yield CW operation to 109 °C. Up to 158 mW of cw power and up to 13.5 % wallplug efficiency are observed at room temperature.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.25.Gy Edge and boundary effects; reflection and refraction
72.20.Pa Thermoelectric and thermomagnetic effects
78.55.Cr III-V semiconductors

Two Dimensional Integration of Ring Cavity Surface Emitting Quantum Cascade Lasers

Clemens Schwarzer, Elvis Mujagić, Tobias Zederbauer, Hermann Detz, Yu Yao, Aaron M. Andrews, Werner Schrenk, Jianxin Chen, Claire Gmachl, and Gottfried Strasser

AIP Conf. Proc. 1416, pp. 49-51; doi:http://dx.doi.org/10.1063/1.3671695 (3 pages)

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The continual improvements over the last fifteen years have made quantum cascade lasers reliable and versatile light sources in the mid infrared and the terahertz spectral regions. In this work we present our latest results regarding the implementation of these light sources for forming broad band emitting two‐dimensional laser arrays. A spectral tuning range of 180 cm−1 around the centered wavelength of 8.2 μm could be shown.
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42.72.Ai Infrared sources
42.79.Dj Gratings
06.30.Ft Time and frequency
42.82.Et Waveguides, couplers, and arrays

Quantum Dot IR Photodetectors and Solar Cells Enhanced by Built‐in Charge

V. Mitin, A. Sergeev, N. Vagidov, K. A. Sablon, and J. W. Little

AIP Conf. Proc. 1416, pp. 52-55; doi:http://dx.doi.org/10.1063/1.3671696 (4 pages)

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Electron transitions in the IR range, which correspond to transitions in the narrow bandgap semiconductors, are also realized in quantum‐dot structures. Quantum‐dot optoelectronic devices, which can replace devices based on narrow bandgap semiconductors, provide more flexibility for nanoscale engineering of photoelectron kinetics as well as improving coupling to IR radiation. Here, we report on radical improvement of quantum‐dot solar cells and quantum‐dot infrared photodetectors provided by Quantum dots with Built‐In Charge (Q‐BIC). We observed a 50% increase in the photovoltaic efficiency of n‐doped Q‐BIC solar cells with ∼ 6 electrons per dot. In this cell, the short circuit current density increases up to 24.30 mA/cm2, compared with 15.07 mA/cm2 in an undoped cell, without deterioration of the open circuit voltage. We also observed ∼25 times increase of the photoresponse of Q‐BIC IR photodetector when the built‐in charge increases from 1 electron to 6 electrons per dot.
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88.40.hj Efficiency and performance of solar cells
85.60.Gz Photodetectors (including infrared and CCD detectors)
72.40.+w Photoconduction and photovoltaic effects
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

High Operability 1024×1024 Long Wavelength Infrared Focal Plane Array Base on Type‐II InAs∕GaSb Superlattice

A. Haddadi, S. R. Darvish, G. Chen, A. M. Hoang, B.‐M. Nguyen, and M. Razeghi

AIP Conf. Proc. 1416, pp. 56-58; doi:http://dx.doi.org/10.1063/1.3671697 (3 pages)

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Fabrication and characterization of a high performance 1024×1024 long wavelength infrared type‐II superlattice focal plane array are described. The FPA performs imaging at a continous rate of 15.00 frames/sec. Each pixel has pitch of 18μm with a fill factor of 71.31%. It demonstrates excellent operability of 95.8% and 97.4% at 81 and 68K operation temperature. The external quantum efficiency is ∼81% without any antireflective coating. Using F∕2 optics and an integration time of 0.13ms, the FPA exhibits an NEDT as low as 27 and 19mK at operating temperatures of 81 and 68K respectively.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.79.Pw Imaging detectors and sensors
76.40.+b Diamagnetic and cyclotron resonances
02.60.Pn Numerical optimization

New Approaches to Direct Bandgap III‐V Materials for LWIR Detector Applications

W. L. Sarney, S. P. Svensson, H. Hier, D. Donetsky, D. Wang, L. Shterengas, S. Suchalkin, and G. Belenky

AIP Conf. Proc. 1416, pp. 59-61; doi:http://dx.doi.org/10.1063/1.3671698 (3 pages) | Cited 1 time

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Infrared (IR) detector materials based on III‐V semiconductors are an affordable alternative to HgCdTe, which is the current material of choice for most high performance IR focal plane array systems fielded in the Army. Based on the assumption that III‐V compounds do not have an inherently small bandgap enabling operation out to 10 μm, the long wave infrared (LWIR) range, there has been substantial research investment in superlattice (SL) approaches. For this reason, quantum structures such as quantum well IR photodetectors (QWIPs) and type‐II strained‐layer superlattices (SLS) are grown to take advantage of confinement effects and to induce an effective bandgap in the desired range. The drawbacks of these approaches include inherently low quantum efficiencies and operating temperature for QWIPs, and very short minority carrier lifetimes for SLS detectors. In this presentation, we will discuss approaches for developing III‐V, direct bandgap, dilute N and Bi alloys grown by molecular beam epitaxy (MBE) for LWIR applications.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.21.Fg Quantum wells
73.21.Cd Superlattices

Negative‐Band‐Gap Quantum Dots

Natalia Malkova and Garnett W. Bryant

AIP Conf. Proc. 1416, pp. 62-67; doi:http://dx.doi.org/10.1063/1.3671699 (6 pages)

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The spectrum of quantum dots (QDs) made from semiconductors like HgTe and HgS changes from negative gap to positive gap with decreasing size. Furthermore, intrinsic surface states, which are not related to dangling bonds, appear in the negative gap regime. We investigate theoretically the evolution of the spectrum of HgS QDs with decreasing size and show how states evolve from a negative gap to a positive gap as confinement is increased. The lowest confined electron level evolves into an intrinsic surface state with increasing size. This surface state is not derived from a bulk HgS bands. We demonstrate that surface states found do not have characteristic topological properties.
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02.40.Pc General topology
71.15.Nc Total energy and cohesive energy calculations
71.28.+d Narrow-band systems; intermediate-valence solids
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Correlation Between Bands Structure and Magneto‐Transport Properties in n‐type HgTe∕CdTe Superlattice with Relatively Thin CdTe Barrier

M. Braigue, A. Nafidi, H. Chaib, Devki N. Talwar, A. Tirbiyine, J. Hemine, A. Idbaha, A. Boulkassim, T. El Gouti, M. Massaq, and M. SrinivasaVinod

AIP Conf. Proc. 1416, pp. 68-71; doi:http://dx.doi.org/10.1063/1.3671700 (4 pages)

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Theoretical calculations of the electronic properties of n‐type HgTe∕CdTe superlattices (SLs) in the envelope function formalism have provided a reasonable agreement with the experimental data on the magneto‐transport behavior. Numerical results of the band energies E(d2), E(kz) and E(kp) in the direction of growth and in plane of the SLs predict that the system retains semiconductor characteristics for d1/d2  =  2.69 and d2<10 nm. For d2  =  3.2 nm the calculated effective band gap (Eg(Γ,4.2 K)  =  48 meV) suggests that the material sample is a two‐dimensional modulated nanostructure and a potential candidate to be used for the far infrared detection applications.
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71.28.+d Narrow-band systems; intermediate-valence solids
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.20.Ls Magneto-optical effects
72.20.My Galvanomagnetic and other magnetotransport effects

Restructuring of the phonon spectra of the MCT and MZT alloy at the Dirac point singularity

J. Cebulski and E. M. Sheregii

AIP Conf. Proc. 1416, pp. 72-76; doi:http://dx.doi.org/10.1063/1.3671701 (5 pages)

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The singularity in the energy band‐structure which is the zero‐gap state (Dirac point) in the HgCdTe or ZnHgTe alloys, causes a discontinuity in the temperature dependence of the transverse optical phonon frequency, as shown in the optical reflectivity experiments.
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71.20.Be Transition metals and alloys
78.40.Kc Metals, semimetals, and alloys
03.65.Pm Relativistic wave equations
07.20.Dt Thermometers

Photoluminescence, Photoreflectance and Optical Absorption of Hg0.5Cd0.5Se

David A. Miranda, S. A. López‐Rivera, J. J. Prías‐Barragan, and M. de los Ríos

AIP Conf. Proc. 1416, pp. 77-80; doi:http://dx.doi.org/10.1063/1.3671702 (4 pages)

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Radiative recombination spectra of Hg0.5Cd0.5Se in the temperature range 11–110 K at different excitation power were investigated. A blue shift in the photoluminescence spectra that exposes the peculiarities of the electronic band structure of these alloys was observed. This phenomena could be associated to an atypical radiative recombination process in which high energetic photons have a higher probability of emission than low energetic ones. Furthermore, photoreflectance and optical absorption measured at 300K showed a higher value for band gap than suggested by photoluminescence at low temperature. A slight differance was observed between the values of the band gap obtained from optical absorption and photoreflectance.
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07.20.Dt Thermometers
71.20.Gj Other metals and alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.60.Lc Optically stimulated luminescence

Magneto Optical Response in Hg(Cd)MnTe Semiconducting Alloys

Devki N. Talwar and Z. C. Feng

AIP Conf. Proc. 1416, pp. 81-83; doi:http://dx.doi.org/10.1063/1.3671703 (3 pages)

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In the presence of high magnetic fields we have used an effective medium approach within the Voigt geometry to study the two‐component p‐polarized far‐infrared magneto‐plasma reflectivity spectra of doped CdHgTe and HgMnTe alloys—providing valuable information of the phonons, plasmons and cyclotron resonance frequencies.
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78.40.Kc Metals, semimetals, and alloys
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
76.40.+b Diamagnetic and cyclotron resonances
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Detection of a Coherent Longitudinal Optical Phonon in a GaAs Buffer Layer Optically Covered with a GaSb Top Epitaxial Layer Using Terahertz Spectroscopy

Hideo Takeuchi, Syuichi Tsuruta, and Masaaki Nakayama

AIP Conf. Proc. 1416, pp. 84-87; doi:http://dx.doi.org/10.1063/1.3671704 (4 pages)

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We demonstrate that, in a GaSb∕GaAs epitaxial structure, the coherent longitudinal optical (LO) phonon in the GaAs layer optically covered with the GaSb top layer is observed utilizing terahertz spectroscopy. In the terahertz‐wave measurement, the Fourier power spectrum of the terahertz waveform exhibits both the GaAs and the GaSb LO phonons; namely, the coherent LO phonon in the optically covered GaAs buffer layer is observed in the terahertz‐wave measurement. This fact demonstrates that the instantaneous surface potential modulation originating from the impulsive carrier excitation by the pump pulses reaches the GaAs buffer layer. This surface potential modulation generates the coherent GaAs LO phonon.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
72.40.+w Photoconduction and photovoltaic effects
72.10.Di Scattering by phonons, magnons, and other nonlocalized excitations
42.60.Rn Relaxation oscillations and long pulse operation

Synchronized Mid‐Infrared Beam Characterization of Narrow Gap Semiconductors

L. J. Olafsen, I. K. Eaves, and J. S. Olafsen

AIP Conf. Proc. 1416, pp. 88-90; doi:http://dx.doi.org/10.1063/1.3671705 (3 pages)

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The near‐ and mid‐infrared output from the idler of an optical parametric oscillator (OPO) and from antimonide‐based narrow gap semiconductors is imaged using an infrared camera that yields 30 Hz (interlaced) and 60 Hz (deinterlaced) images. These images are collected in free‐running, synchronized, and slow phase slip modes utilizing hardware and software platforms for synchronization of the camera with the 10 Hz, 4 ns output from the OPO. This method is useful for analyzing mid‐infrared semiconductor output as well as correlating that output with characteristics of the optical pump used to stimulate mid‐infrared emission.
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42.65.Yj Optical parametric oscillators and amplifiers
71.28.+d Narrow-band systems; intermediate-valence solids
07.05.Hd Data acquisition: hardware and software
05.45.Xt Synchronization; coupled oscillators

Spin‐orbit Splitting Anisotropy in n‐type InGaAs Inversion Layers

M. A. Toloza Sandoval, A. Ferreira da Silva, E. A. de Andrada e Silva, and G. C. La Rocca

AIP Conf. Proc. 1416, pp. 91-94; doi:http://dx.doi.org/10.1063/1.3671706 (4 pages)

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Using a recently developed spin‐dependent variational theory for the heterojunction electronic structure, we investigate the spin‐orbit (SO) splitting in InGaAs two dimensional electron gases (2DEGs). We discuss in particular its anisotropy, determined by the relative strength of the Rashba and Dresselhaus SO terms. The envelope function formalism is employed analytically, using the 8‐band k⋅p Kane model for the bulk and spin‐dependent variational functions for the Rashba split conduction subbands. The Dresselhaus contribution is included via quasi‐degenerate first order perturbation theory and the total spin‐splitting at the Fermi level is calculated as a function of the Fermi wave‐vector direction and of the 2DEG carrier density. Contrary to what it is usually assumed regarding InGaAs quantum wells, we find significant Dresselhaus contribution and corresponding spin‐orbit anisotropy in the conduction subbands.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses
75.30.Gw Magnetic anisotropy
81.07.St Quantum wells
73.20.At Surface states, band structure, electron density of states

Probing Spin‐Relaxation Anisotropy in 1D InSb Wires by Weak Anti‐Localization

P. A. R. D. Jayathilaka, S. Cairns, J. Keay, S. Q. Murphy, C. K. Gaspe, T. D. Mishima, and M. B. Santos

AIP Conf. Proc. 1416, pp. 95-99; doi:http://dx.doi.org/10.1063/1.3671707 (5 pages)

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Arrays of quasi‐one‐dimensional wires were fabricated in symmetrically doped AlInSb∕InSb heterostructures to investigate the dimensional suppression of electron spin relaxation. Using weak localization analysis, it was discovered that the spin relaxation length in 300nm wide wires was enhanced by 40% relative to the two‐dimensional value. Moreover, wires aligned along the <100> direction showed spin relaxation lengths ∼30% longer than for wires aligned along <110>. This anisotropy is consistent with the additional influence of the cubic Dresselhaus interaction along the <110> direction which is predicted to be unaffected by dimensional confinement.
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76.30.Pk Conduction electrons
73.20.Fz Weak or Anderson localization
71.28.+d Narrow-band systems; intermediate-valence solids
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Spin polarization of a Ferromagnetic Narrow Gap p‐(In,Mn)As Obtained from Andreev Reflection Spectroscopy

T. Akazaki, H. Munekata, T. Yokoyama, Y. Tanaka, and H. Takayanagi

AIP Conf. Proc. 1416, pp. 100-104; doi:http://dx.doi.org/10.1063/1.3671708 (5 pages)

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Spin‐polarized carrier transport across Nb∕p‐(In,Mn)As junctions has been studied. Suppressions of conductance in the superconductor sub‐gap region and conductance peaks at the bias voltage around the edge of the sub‐gap are observed. These features are well reproduced by a newly modified BTK model including both spin polarization and the inverse proximity effect. The value of spin polarization in p‐(In,Mn)As extracted by the calculation is P  =  0.725 at 0.5 K with Z  =  0.25
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
85.25.Am Superconducting device characterization, design, and modeling
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.28.+d Narrow-band systems; intermediate-valence solids
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