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Abstract: Using molecular beam epitaxy, we study self-assembled InAs quantum dots (QDs) grown on GaAs (001) substrates by lowtemperature scanning tunneling microscopy. We compare two different growth processes, the well-known Stranski-Krastanow mode and the more recently studied droplet epitaxy mode. We show that, for the same amount of deposited indium, the shape of the dots shows similar anisotropic tendency, but the InAs coverage dependence of the density shows that the growth mechanisms are different at the initial stage of the QD formation. By scanning tunneling spectroscopy at low temperature, we succeed in mapping the local density of states (LDOS) of a single quantum dot grown by the droplet epitaxy. Maps of LDOS are consistent with those previously reported for the Stranski–Krastanow mode; however, energy spectrum of our QDs shows different peak structures. [Copyright &y& Elsevier]

K. Muraki, E. Ogo, H. Suefuji, H. Eto, C. Tsuji, C. Hattori, Y. Miyata, T. Abe, Poster: Physics track: Radiobiological and predictive modelling, and radiomics PO-1523: Predictive factors of over Grade 2 radiation pneumonitis for advanced non-small cell lung cancer. [Extracted from the article]

We investigate integer filling factor phases of many-N-electron vertically coupled semiconductor quantum dot artificial molecules when the inter-dot coupling is strong and weak. The experimental results are analyzed within local-spin density- functional theory. Maximum density droplets composed of electrons in both bonding and anti-bonding, or just bonding states are revealed. Interesting isospin physics (i.e., isospin transitions) can occur particularly when the inter-dot coupling is reduced. [Copyright &y& Elsevier]

We investigate the dissociation of few-electron circular vertical semiconductor double quantum dot artificial molecules at 0 T as a function of interdot distance. Slight mismatch introduced in the fabrication of the artificial molecules from materials with nominally identical constituent quantum wells induces localization. This offsets the energy levels in the quantum dots by up to 2 meV, and can play a crucial role in the appearance of the addition energy spectra as a function of coupling strength particularly in the weak coupling limit. [Copyright &y& Elsevier]

Abstract: We demonstrate a novel heterostructure for inducing 2D hole systems in (311)A GaAs–AlGaAs heterostructures that offers advantages over previous methods including low turn on voltages, easier fabrication and good interface roughness. The heterostructure incorporates a metallic p+-GaAs cap layer as an in situ top gate that pins the Fermi energy close to the valence band and can then be used to induce the 2D hole system at the GaAs/AlGaAs interface. [Copyright &y& Elsevier]

The tilting angular dependence of the energy gap was measured in the bilayer quantum Hall state at the Landau level filling ν=1 by changing the density imbalance between the two layers. The observed gap behavior shows a continuous transformation from the bilayer balanced density state to the monolayer state. Even a sample with 33 K tunneling gap shows the same activation energy anomaly reported by Murphy et al. (Phys. Rev. Lett. 72 (1994) 728). We discuss a possible relation between our experimental results and the quantum Hall ferromagnet of spins and pseudospins. [Copyright &y& Elsevier]

In a bilayer system, various phase transitions occur due to the competition among the cyclotron, Zeeman and tunneling energies. We investigate effects of an in-plane magnetic field B||, which couples subband and Landau levels with the same spin and modulate wave functions extended to both layers, on transitions of quantum Hall states in such a system. As B|| is applied, we observe that crossings between opposite spin levels as well as those between the same spin levels disappear in characteristic sequences. While anticrossings of single-particle levels are sufficient to explain the observed behavior for crossings at ν=4, the data at ν=6 are not understood in a single-particle picture, and suggest Coulomb-induced mixing of different spin levels. [Copyright &y& Elsevier]

We measured the magnetoresistance in bilayer quantum Hall (QH) state at fractional filling factor ν=2/3. Surprisingly, for different QH areas and two types of hysteresis were observed by controlling the total electron density and the density difference in two layers. Two QH areas and one type of hysteresis are novel characteristic of bilayer systems. [Copyright &y& Elsevier]

We demonstrate pulsed-mode control of nuclear-spin polarization in integer quantum Hall systems. Nuclear spins in a limited region along edge channels of a quantum Hall conductor are initially polarized through the hyperfine interaction with electron spins. The initialized nuclear-spin polarization is then manipulated with pulsed nuclear magnetic resonance using a micro-metal strip fabricated on top of the edge channels. The nuclear-spin polarization is probed by the Hall resistance. [Copyright &y& Elsevier]

We measured the activation energy of bilayer ν=1 quantum Hall states. By changing the density difference between layers, the tilting behavior of the pseudospin(P)-type activation energy at the equal density point gradually transforms into the spin(S)-type one at the monolayer density point. At the intermediate density difference, by increasing the tilting angle the activation energy starts to decrease as the P-type excitation gap and then increases as the S-type excitation gap. It is impossible to explain this behavior by the level crossing of the P- and S-type excitations. The result of the overall behavior indicates the excitation in a bilayer system is the simultaneous flip of spin and pseudospin. [Copyright &y& Elsevier]