Mechanical Mixing in Nonlinear Nanomechanical Resonators

Nanomechanical resonators, machined out of Silicon-on-Insulator wafers, are operated in the nonlinear regime to investigate higher-order mechanical mixing at radio frequencies, relevant to signal processing and nonlinear dynamics on nanometer scales. Driven by two neighboring frequencies the resonators generate rich power spectra exhibiting a multitude of satellite peaks. This nonlinear response is studied and compared to $n^{th}$-order perturbation theory and nonperturbative numerical calculations.Comment: 5 pages, 7 figure

Superposition of photon- and phonon- assisted tunneling in coupled quantum dots

We report on electron transport through an artificial molecule formed by two tunnel coupled quantum dots, which are laterally confined in a two-dimensional electron system of an Al$_x$Ga$_{1-x}$As/GaAs heterostructure. Coherent molecular states in the coupled dots are probed by photon-assisted tunneling (PAT). Above 10 GHz, we observe clear PAT as a result of the resonance between the microwave photons and the molecular states. Below 8 GHz, a pronounced superposition of phonon- and photon-assisted tunneling is observed. Coherent superposition of molecular states persists under excitation of acoustic phonons.Comment: 5 pages, 4 figure

Bilateral renal angiomyolipomas with invasion of the renal vein: A case report

An angiomyolipoma (AML) is usually a benign, rare, and, more commonly, a unilateral renal tumour. Bilateral tumours are very rare, particularly in the absence of tuberous sclerosis complex. Only in a few isolated cases have features of malignancy been associated with an AML. We present a unique case of bilateral AMLs mimicking invasive tumours in the absence of any other features of tuberous sclerosis complex

Spin blockade in ground state resonance of a quantum dot

We present measurements on spin blockade in a laterally integrated quantum dot. The dot is tuned into the regime of strong Coulomb blockade, confining ~ 50 electrons. At certain electronic states we find an additional mechanism suppressing electron transport. This we identify as spin blockade at zero bias, possibly accompanied by a change in orbital momentum in subsequent dot ground states. We support this by probing the bias, magnetic field and temperature dependence of the transport spectrum. Weak violation of the blockade is modelled by detailed calculations of non-linear transport taking into account forbidden transitions.Comment: 4 pages, 4 figure

Microwave spectroscopy on a double quantum dot with an on-chip Josephson oscillator

We present measurements on microwave spectroscopy on a double quantum dot with an on-chip microwave source. The quantum dots are realized in the two-dimensional electron gas of an AlGaAs/GaAs heterostructure and are weakly coupled in series by a tunnelling barrier forming an 'ionic' molecular state. We employ a Josephson oscillator formed by a long Nb/Al-AlO$_x$/Nb junction as a microwave source. We find photon-assisted tunnelling sidebands induced by the Josephson oscillator, and compare the results with those obtained using an externally operated microwave source.Comment: 6 pages, 4 figure

Anaplastic, T-cell, Non-Hodgkin's Lymphoma Presenting with Haematuria

Non-Hodgkin's lymphoma (NHL) represents about 3% of new cancer cases[1]. Bladder involvement has been found in approximately 3-13% of NHL patients when studied at postmortem[2]. Although accounting for only 0.2% of all primary bladder tumours, the majority of bladder lymphomas are B-cell lymphomas. T-cell lymphoma of the bladder is incredibly rare. We describe a case of anaplastic, T-cell lymphoma presenting with haematuria and loin pain, with unilateral upper tract obstruction

Nuclear spin relaxation probed by a single quantum dot

We present measurements on nuclear spin relaxation probed by a single quantum dot in a high-mobility electron gas. Current passing through the dot leads to a spin transfer from the electronic to the nuclear spin system. Applying electron spin resonance the transfer mechanism can directly be tuned. Additionally, the dependence of nuclear spin relaxation on the dot gate voltage is observed. We find electron-nuclear relaxation times of the order of 10 minutes

Nanomechanical resonators operating as charge detectors in the nonlinear regime

We present measurements on nanomechanical resonators machined from Silicon-on-Insulator substrates. The resonators are designed as freely suspended Au/Si beams of lengths on the order of 1 - 4 um and a thickness of 200 nm. The beams are driven into nonlinear response by an applied modulation at radio frequencies and a magnetic field in plane. The strong hysteresis of the magnetomotive response allows sensitive charge detection by varying the electrostatic potential of a gate electrode.Comment: 8 pages, 6 figure

Fano resonances and Aharonov-Bohm effects in transport through a square quantum dot molecule

We study the Aharonov-Bohm effect in a coupled 2$\times$2 quantum dot array with two-terminals. A striking conductance dip arising from the Fano interference is found as the energy levels of the intermediate dots are mismatched, which is lifted in the presence of a magnetic flux. A novel five peak structure is observed in the conductance for large mismatch. The Aharonov-Bohm evolution of the linear conductance strongly depends on the configuration of dot levels and interdot and dot-lead coupling strengths. In addition, the magnetic flux and asymmetry between dot-lead couplings can induce the splitting and combination of the conductance peak(s).Comment: 15 pages, 7 figures, Revtex, to be published in Phys. Rev.