Electrical and terahertz magnetospectroscopy studies of laser-patterned micro- and nanostructures on InAs-based heterostructures

Nanostructures fabricated from narrow-gap semiconductors with strong spin-orbit interaction (SOI), such as InAs, can be used to filter momentum modes of electrons and offer the possibility to create and detect spin-polarized currents entirely by electric fields. Here, we present magnetotransport and THz magnetospectroscopy investigations of Hall-bars with back-gates made from in InGaAs/InAlAs quantum well structures with a strained 4 nm InAs inserted channel. The two-dimensional electron gas is at 53 nm depth and has a carrier density of about $6\times10^{11}$ cm$^{-2}$ and mobility of about $2\times10^{5}$ cm$^2$/Vs, after illumination. Electrical and THz optical transport measurements at low temperatures and in high magnetic fields reveal an effective mass of 0.038$m_{0}$ and an anisotropic $g$-factor of up to 20, larger than for bulk InAs or InAs-based heterostructures. We demonstrate that quasi-one-dimensional channels can be formed by micro-laser lithography. The population of subbands is controlled by in-plane gates. Contrary to previous reports symmetric and asymmetric in-plane gate voltages applied to quasi-one dimensional channels did not show indications of SOI-induced anomalies in the conductance.Comment: v1 did not contain references due to filename mix-up; v3 is revision following referee report; v4 is corrected version following acceptance; v5 is the published versio

Internal transitions of negatively charged magneto-excitons and many body effects in a two-dimensional electron gas

Spin-singlet and spin-triplet internal transitions of quasi-two-dimensional, negatively charged magneto-excitons (X-) and their evolution with excess electron density have been studied in GaAs/AlGaAs quantum-wells by optically detected resonance (ODR) spectroscopy. In the dilute electron limit, due to magnetic translational invariance, the ODR spectra are dominated by bound-to-continuum bands in contrast to the superficially similar negatively-charged-donor system D-, which exhibits strictly bound-to-bound transitions. With increasing excess electron density in the wells in the magnetic field region corresponding to Landau level filling factors nu < 2 the X- like transitions are blue-shifted; they are absent for nu > 2. The blue-shifted transitions are explained in terms of a new type of collective excitation -- magnetoplasmons bound to a mobile valence band hole, which demonstrates the many-body nature of "exciton-like" magnetoluminescence for nu < 2.Comment: 11 pages + 3 figures, final version accepted in PR

Aharanov-Bohm excitons at elevated temperatures in type-II ZnTe/ZnSe quantum dots

Optical emission from type-II ZnTe/ZnSe quantum dots demonstrates large and persistent oscillations in both the peak energy and intensity indicating the formation of coherently rotating states. Furthermore, the Aharanov-Bohm (AB) effect is shown to be remarkably robust and persists until 180K. This is at least one order of magnitude greater than the typical temperatures in lithographically defined rings. To our knowledge this is the highest temperature at which the AB effect has been observed in semiconductor structures

Above-Room-Temperature Ferromagnetism in GaSb/Mn Digital Alloys

Digital alloys of GaSb/Mn have been fabricated by molecular beam epitaxy. Transmission electron micrographs showed good crystal quality with individual Mn-containing layers well resolved; no evidence of 3D MnSb precipitates was seen in as-grown samples. All samples studied exhibited ferromagnetism with temperature dependent hysteresis loops in the magnetization accompanied by metallic p-type conductivity with a strong anomalous Hall effect (AHE) up to 400 K (limited by the experimental setup). The anomalous Hall effect shows hysteresis loops at low temperatures and above room temperature very similar to those seen in the magnetization. The strong AHE with hysteresis indicates that the holes interact with the Mn spins above room temperature. All samples are metallic, which is important for spintronics applications. * To whom correspondence should be addressed. E-mail: [email protected]

Terahertz dynamics of a topologically protected state: quantum Hall effect plateaus near cyclotron resonance in a GaAs/AlGaAs heterojunction

We measure the Hall conductivity of a two-dimensional electron gas formed at a GaAs/AlGaAs heterojunction in the terahertz regime close to the cyclotron resonance frequency by employing a highly sensitive Faraday rotation method coupled with electrical gating of the sample to change the electron density. We observe clear plateau-and step-like features in the Faraday rotation angle vs. electron density and magnetic field (Landau-level filling factor), which are the high frequency manifestation of quantum Hall plateaus - a signature of topologically protected edge states. The results are compared to a recent dynamical scaling theory.Comment: 18 pages, 3 figure

Robust Magnetic Polarons in Type-II (Zn,Mn)Te Quantum Dots

We present evidence of magnetic ordering in type-II (Zn, Mn) Te quantum dots. This ordering is attributed to the formation of bound magnetic polarons caused by the exchange interaction between the strongly localized holes and Mn within the dots. In our photoluminescence studies, the magnetic polarons are detected at temperatures up to ~ 200 K, with a binding energy of ~ 40 meV. In addition, these dots display an unusually small Zeeman shift with applied field (2 meV at 10 T). This behavior is explained by a small and weakly temperature-dependent magnetic susceptibility due to anti-ferromagnetic coupling of the Mn spins

Terahertz Magneto Optical Polarization Modulation Spectroscopy

We report the development of new terahertz techniques for rapidly measuring the complex Faraday angle in systems with broken time-reversal symmetry using the cyclotron resonance of a GaAs two-dimensional electron gas in a magnetic field as a system for demonstration of performance. We have made polarization modulation, high sensitivity (< 1 mrad) narrow band rotation measurements with a CW optically pumped molecular gas laser, and by combining the distinct advantages of terahertz (THz) time domain spectroscopy and polarization modulation techniques, we have demonstrated rapid broadband rotation measurements to < 5 mrad precision.Comment: 25 pages including 7 figures, introduces use of rotating polarizer with THz TDS for Complex Faraday Angle determinatio

Increased Immunoreactivity to Two Overlapping Peptides of Myelin Proteolipid Protein in Multiple Sclerosis

We tested the proliferative responses of peripheral blood mononuclear cells from 61 patients with multiple sclerosis, 56 healthy control subjects and 52 patients with other neurological diseases to seven synthetic peptides of myelin proteolipid protein (PLP) and 19 synthetic peptides of myelin basic protein (MBP). Increased proliferative responses to two overlapping PLP peptides, PLP184-199 and PLP190-209, were found significantly more frequently in blood from patients with relapsing-remitting or secondary progressive multiple sclerosis (52.3%), but not from those with primary progressive multiple sclerosis (18.2%), than in that from healthy control subjects (8.9%) and patients with other neurological diseases (20.8%). Reactivity to these PLP peptides was most frequently seen in blood from patients with multiple sclerosis of 6-15 years duration and with moderate to severe disability (Kurtzke's Expanded Disability Status Scale > 4.0); the blood from 15 of 19 patients in this group reacted to one or both of the peptides. Both peptides could be recognized by short-term T-cell lines specific for whole PLP, and lines specific for one or other of the two overlapping peptides were able to recognize whole PLP, indicating that these peptides can be processed naturally from the intact molecule. This region of PLP is encephalitogenic in a number of strains of mice. Samples from multiple sclerosis patients did not react more frequently to any of the MBP peptides than those from healthy control subjects. The proportions of patients with other neurological diseases whose blood responded to the MBP peptides that most frequently elicited responses in blood from multiple sclerosis patients were significantly lower than the proportions of multiple sclerosis patients and healthy control subjects whose blood responded to these peptides

Is there evidence for accelerated polyethylene wear in uncemented compared to cemented acetabular components? A systematic review of the literature

Joint arthroplasty registries show an increased rate of aseptic loosening in uncemented acetabular components as compared to cemented acetabular components. Since loosening is associated with particulate wear debris, we postulated that uncemented acetabular components demonstrate a higher polyethylene wear rate than cemented acetabular components in total hip arthroplasty. We performed a systematic review of the peer-reviewed literature, comparing the wear rate in uncemented and cemented acetabular components in total hip arthroplasty. Studies were identified using MEDLINE (PubMed), EMBASE and the Cochrane Central Register of Controlled Trials. Study quality was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. The search resulted in 425 papers. After excluding duplicates and selection based on title and abstracts, nine studies were found eligible for further analysis: two randomised controlled trials, and seven observational studies. One randomised controlled trial found a higher polyethylene wear rate in uncemented acetabular components, while the other found no differences. Three out of seven observational studies showed a higher polyethylene wear in uncemented acetabular component fixation; the other four studies did not show any differences in wear rates. The available evidence suggests that a higher annual wear rate may be encountered in uncemented acetabular components as compared to cemented components