Magnetic-Field Dependence of Tunnel Couplings in Carbon Nanotube Quantum Dots

By means of sequential and cotunneling spectroscopy, we study the tunnel couplings between metallic leads and individual levels in a carbon nanotube quantum dot. The levels are ordered in shells consisting of two doublets with strong- and weak-tunnel couplings, leading to gate-dependent level renormalization. By comparison to a one- and two-shell model, this is shown to be a consequence of disorder-induced valley mixing in the nanotube. Moreover, a parallel magnetic field is shown to reduce this mixing and thus suppress the effects of tunnel renormalization.Comment: 5 pages, 3 figures; revised version as publishe

Interplay between one-dimensional confinement and crystallographic anisotropy in ballistic hole quantum wires

We study the Zeeman splitting in induced ballistic 1D quantum wires aligned along the [233] and [011] axes of a high mobility (311)A undoped heterostructure. Our data shows that the g-factor anisotropy for magnetic fields applied along the high symmetry [011] direction can be explained by the 1D confinement only. However when the magnetic field is along [233] there is an interplay between the 1D confinement and 2D crystal anisotropy. This is highlighted for the [233] wire by an unusual non-monotonic behavior of the g-factor as the wire is made narrower

Pyrazine-Fused Triterpenoids Block the TRPA1 Ion Channel in Vitro and Inhibit TRPA1-Mediated Acute Inflammation in Vivo

TRPA1 is a nonselective cation channel, most famously expressed in nonmyelinated nociceptors. In addition to being an important chemical and mechanical pain sensor, TRPA1 has more recently appeared to have a role also in inflammation. Triterpenoids are natural products with anti-inflammatory and anticancer effects in experimental models. In this paper, 13 novel triterpenoids were created by synthetically modifying betulin, an abundant triterpenoid of the genus Betula L., and their TRPA1-modulating properties were examined. The Fluo 3-AM protocol was used in the initial screening, in which six of the 14 tested triterpenoids inhibited TRPA1 in a statistically significant manner. In subsequent whole-cell patch clamp recordings, the two most effective compounds (pyrazine-fused triterpenoids 8 and 9) displayed a reversible and dose- and voltage-dependent effect to block the TRPA1 ion channel at submicromolar concentrations. Interestingly, the TRPA1 blocking action was also evident in vivo, as compounds 8 and 9 both alleviated TRPA1 agonist-induced acute paw inflammation in mice. The results introduce betulin-derived pyrazine-fused triterpenoids as promising novel antagonists of TRPA1 that are potentially useful in treating diseases with a TRPA1-mediated adverse component

Electrically-Controlled Nuclear Spin Polarization and Relaxation by Quantum-Hall states

We investigate interactions between electrons and nuclear spins by using the resistance (Rxx) peak which develops near filling factor n = 2/3 as a probe. By temporarily tuning n to a different value, ntemp, with a gate, the Rxx peak is shown to relax quickly on both sides of ntemp = 1. This is due to enhanced nuclear spin relaxation by Skyrmions, and demonstrates the dominant role of nuclear spin in the transport anomaly near n = 2/3. We also observe an additional enhancement in the nuclear spin relaxation around n = 1/2 and 3/2, which suggests a Fermi sea of partially-polarized composite fermions.Comment: 6 pages, 3 figure

Dissociation of vertical semiconductor diatomic artificial molecules

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 nominally identical constituent quantum wells induces localization by offsetting the energy levels in the quantum dots by up to 2 meV, and this plays a crucial role in the appearance of the addition energy spectra as a function of coupling strength particularly in the weak coupling limit.Comment: Accepted for publication in Phys. Rev. Let

Magnetization of a two-dimensional electron gas with a second filled subband

We have measured the magnetization of a dual-subband two-dimensional electron gas, confined in a GaAs/AlGaAs heterojunction. In contrast to two-dimensional electron gases with a single subband, we observe non-1/B-periodic, triangularly shaped oscillations of the magnetization with an amplitude significantly less than $1 \mu_{\mathrm{B}}^*$ per electron. All three effects are explained by a field dependent self-consistent model, demonstrating the shape of the magnetization is dominated by oscillations in the confining potential. Additionally, at 1 K, we observe small oscillations at magnetic fields where Landau-levels of the two different subbands cross.Comment: 4 pages, 4 figure