Nanoscale Electrostatic Control of Oxide Interfaces

We develop a robust and versatile platform to define nanostructures at oxide interfaces via patterned top gates. Using LaAlO$_3$/SrTiO$_3$ as a model system, we demonstrate controllable electrostatic confinement of electrons to nanoscale regions in the conducting interface. The excellent gate response, ultra-low leakage currents, and long term stability of these gates allow us to perform a variety of studies in different device geometries from room temperature down to 50 mK. Using a split-gate device we demonstrate the formation of a narrow conducting channel whose width can be controllably reduced via the application of appropriate gate voltages. We also show that a single narrow gate can be used to induce locally a superconducting to insulating transition. Furthermore, in the superconducting regime we see indications of a gate-voltage controlled Josephson effect.Comment: Version after peer review; includes additional data on superconductivit

Population-scale organization of cerebellar granule neuron signaling during a visuomotor behavior.

Granule cells at the input layer of the cerebellum comprise over half the neurons in the human brain and are thought to be critical for learning. However, little is known about granule neuron signaling at the population scale during behavior. We used calcium imaging in awake zebrafish during optokinetic behavior to record transgenically identified granule neurons throughout a cerebellar population. A significant fraction of the population was responsive at any given time. In contrast to core precerebellar populations, granule neuron responses were relatively heterogeneous, with variation in the degree of rectification and the balance of positive versus negative changes in activity. Functional correlations were strongest for nearby cells, with weak spatial gradients in the degree of rectification and the average sign of response. These data open a new window upon cerebellar function and suggest granule layer signals represent elementary building blocks under-represented in core sensorimotor pathways, thereby enabling the construction of novel patterns of activity for learning

Coherence of an optically illuminated single nuclear spin qubit

We investigate the coherence properties of individual nuclear spin quantum bits in diamond [Dutt et al., Science, 316, 1312 (2007)] when a proximal electronic spin associated with a nitrogen-vacancy (NV) center is being interrogated by optical radiation. The resulting nuclear spin dynamics are governed by time-dependent hyperfine interaction associated with rapid electronic transitions, which can be described by a spin-fluctuator model. We show that due to a process analogous to motional averaging in nuclear magnetic resonance, the nuclear spin coherence can be preserved after a large number of optical excitation cycles. Our theoretical analysis is in good agreement with experimental results. It indicates a novel approach that could potentially isolate the nuclear spin system completely from the electronic environment.Comment: 5 pages, 2 figure

Deep levels in a-plane, high Mg-content MgxZn1-xO epitaxial layers grown by molecular beam epitaxy

Deep level defects in n-type unintentionally doped a-plane MgxZn1−xO, grown by molecular beam epitaxy on r-plane sapphire were fully characterized using deep level optical spectroscopy (DLOS) and related methods. Four compositions of MgxZn1−xO were examined with x = 0.31, 0.44, 0.52, and 0.56 together with a control ZnO sample. DLOS measurements revealed the presence of five deep levels in each Mg-containing sample, having energy levels of Ec − 1.4 eV, 2.1 eV, 2.6 V, and Ev + 0.3 eV and 0.6 eV. For all Mg compositions, the activation energies of the first three states were constant with respect to the conduction band edge, whereas the latter two revealed constant activation energies with respect to the valence band edge. In contrast to the ternary materials, only three levels, at Ec − 2.1 eV, Ev + 0.3 eV, and 0.6 eV, were observed for the ZnO control sample in this systematically grown series of samples. Substantially higher concentrations of the deep levels at Ev + 0.3 eV and Ec − 2.1 eV were observed in ZnO compared to the Mg alloyed samples. Moreover, there is a general invariance of trap concentration of the Ev + 0.3 eV and 0.6 eV levels on Mg content, while at least and order of magnitude dependency of the Ec − 1.4 eV and Ec − 2.6 eV levels in Mg alloyed samples

Update or Wait: How to Keep Your Data Fresh

In this work, we study how to optimally manage the freshness of information updates sent from a source node to a destination via a channel. A proper metric for data freshness at the destination is the age-of-information, or simply age, which is defined as how old the freshest received update is since the moment that this update was generated at the source node (e.g., a sensor). A reasonable update policy is the zero-wait policy, i.e., the source node submits a fresh update once the previous update is delivered and the channel becomes free, which achieves the maximum throughput and the minimum delay. Surprisingly, this zero-wait policy does not always minimize the age. This counter-intuitive phenomenon motivates us to study how to optimally control information updates to keep the data fresh and to understand when the zero-wait policy is optimal. We introduce a general age penalty function to characterize the level of dissatisfaction on data staleness and formulate the average age penalty minimization problem as a constrained semi-Markov decision problem (SMDP) with an uncountable state space. We develop efficient algorithms to find the optimal update policy among all causal policies, and establish sufficient and necessary conditions for the optimality of the zero-wait policy. Our investigation shows that the zero-wait policy is far from the optimum if (i) the age penalty function grows quickly with respect to the age, (ii) the packet transmission times over the channel are positively correlated over time, or (iii) the packet transmission times are highly random (e.g., following a heavy-tail distribution)

Superconducting quantum point contact with split gates in the two dimensional LaAlO3/SrTiO3 superfluid

One of the hallmark experiments of quantum transport is the observation of the quantized resistance in a point contact formed with split gates in GaAs/AlGaAs heterostructures. Being carried out on a single material, they represent in an ideal manner equilibrium reservoirs which are connected only through a few electron mode channel with certain transmission coefficients. It has been a long standing goal to achieve similar experimental conditions also in superconductors, only reached in atomic scale mechanically tunable break junctions of conventional superconducting metals, but here the Fermi wavelength is so short that it leads to a mixing of quantum transport with atomic orbital physics. Here we demonstrate for the first time the formation of a superconducting quantum point contact (SQPC) with split gate technology in a superconductor, utilizing the unique gate tunability of the two dimensional superfluid at the LaAlO3/SrTiO3 (LAO/STO) interface. When the constriction is tuned through the action of metallic split gates we identify three regimes of transport: (i) SQPC for which the supercurrent is carried only by a few quantum transport channels. (ii) Superconducting island strongly coupled to the equilibrium reservoirs. (iii) Charge island with a discrete spectrum weakly coupled to the reservoirs. Our experiments demonstrate the feasibility of a new generation of mesoscopic all-superconductor quantum transport devices.Comment: 18 page

Gap Filler Induced Transition on the Mars Science Laboratory Heatshield

Detached Eddy Simulations have been performed to investigate the effects of high-fidelity turbulence modeling on roughness-induced transition to turbulence during Mars entry. Chemically reacting flow solutions will be obtained for a gap filler of Mars Science Laboratory at the peak heating condition

Growth and reproduction studies on gilthead seabream (Sparus aurata) in Beymelek Lagoon, Turkey

In the present study, age, growth, length-weight relationship and reproduction were investigated in gilthead seabream (Sparus aurata L., 1758) collected from Beymelek Lagoon (Antalya, Turkey) between February 2006 and July 2007. The age, total length and weight of samples ranged from 0+ to 4 years, 10.6 to 35.5cm, and 18 to 928g, respectively. Growth was described by the standard form of the von Bertalanffy growth equation and the estimated parameters were L∞ = 44.6cm, k = 0.394yr^-1 and t0 = -1.331yr. Length-weight relationship was determined as W=0.0174TL^2.9769 (R^2=0.965), and weight increased with size isometrically (b = 2.9769) for all fish. Sex inversion occurred mainly at 26 cm in total length and females reached sexual maturity at 28.5 cm. The spawning period was from December to February, while the gamete emission peaked in December

Testing of a lightweight SiC power module for avionic applications

Functional and performance tests of a three-phase, two-level power module based on CREE 1.2kV SiC MOSFETs for avionic applications is presented in this paper. SiC devices have superior properties over conventional Si devices at high voltage operations and these properties make SiC devices at-tractive for avionic industry in order to reduce size of power electronic converters while maintaining high efficiency. This paper starts with a brief explanation of thermo-mechanical de¬sign approach of SiC power module. Thermo-mechanical de¬sign is followed by test setup and experimental results for dif¬ferent load and switching frequency conditions. The module is tested up to 540V DC link voltage, 6kW output power with 100kHz switching frequency. Experimental results show that the module can be successfully operated with high efficiency at high switching frequencies