ORCID Profile
0000-0003-4868-7166
Current Organisation
Evonetix
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Publisher: AIP Publishing
Date: 17-04-2006
DOI: 10.1063/1.2198013
Abstract: We report low-frequency charge noise measurement on silicon substrates with different phosphorus doping densities. The measurements are performed with aluminum single electron transistors (SETs) at millikelvin temperatures where the substrates are in the insulating regime. By measuring the SET Coulomb oscillations, we find a gate-voltage-dependent charge noise on the more heavily doped substrate. This charge noise is attributed to the electric-field-induced tunneling of electrons from their phosphorus donor potentials.
Publisher: AIP Publishing
Date: 18-02-2013
DOI: 10.1063/1.4792693
Abstract: Electrically detected ferromagnetic resonance is measured in microdevices patterned from ultra-thin Co/Pt bilayers. Spin pumping and rectification voltages are observed and distinguished via their angular dependence. The spin-pumping voltage shows an unexpected increase as the cobalt thickness is reduced below 2 nm. This enhancement allows more efficient conversion of spin to charge current.
Publisher: AIP Publishing
Date: 12-09-2016
DOI: 10.1063/1.4962811
Abstract: We study the energetics of a superconducting double dot, by measuring both the quantum capacitance of the device and the response of a nearby charge sensor. We observe different behaviour for odd and even charge states and describe this with a model based on the competition between the charging energy and the superconducting gap. We also find that, at finite temperatures, thermodynamic considerations have a significant effect on the charge stability diagram.
Publisher: American Physical Society (APS)
Date: 03-12-2015
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 11-2013
Publisher: Institution of Engineering and Technology (IET)
Date: 03-2019
Publisher: AIP Publishing
Date: 10-02-2014
DOI: 10.1063/1.4864399
Abstract: Current-induced torques in ultrathin Co/Pt bilayers were investigated using an electrically driven ferromagnetic resonance technique. The angle dependence of the resonances, detected by a rectification effect as a voltage, was analysed to determine the symmetries and relative magnitudes of the spin-orbit torques. Both anti-d ing (Slonczewski) and field-like torques were observed. As the ferromagnet thickness was reduced from 3 to 1 nm, the sign of the sum of the field-like torque and Oersted torque reversed. This observation is consistent with the emergence of a Rashba spin orbit torque in ultra-thin bilayers.
Publisher: AIP Publishing
Date: 04-08-2008
DOI: 10.1063/1.2968214
Abstract: A superconducting tunnel junction is used to directly extract quasiparticles from one of the leads of a single Cooper pair transistor. The consequent reduction in quasiparticle density causes a lower rate of quasiparticle tunneling onto the device. This rate is directly measured by radio-frequency reflectometry. Local cooling may be of direct benefit in reducing the effect of quasiparticles on coherent superconducting nanostructures.
Publisher: IOP Publishing
Date: 07-04-2008
DOI: 10.1088/0957-4484/19/19/195402
Abstract: We present low temperature charge sensing measurements of nanoscale phosphorus-implanted double dots in silicon. The implanted phosphorus forms two 50 nm diameter islands with source and drain leads, which are separated from each other by undoped silicon tunnel barriers. Occupancy of the dots is controlled by surface gates and monitored using an aluminium single-electron transistor which is capacitively coupled to the dots. We observe a charge stability diagram consistent with the designed many-electron double-dot system and this agrees well with capacitance modelling of the structure. We discuss the significance of these results to the realization of smaller devices which may be used as charge or spin qubits.
Publisher: American Physical Society (APS)
Date: 07-09-2006
Publisher: The Royal Society
Date: 15-07-2003
Abstract: Most experts agree that it is too early to say how quantum computers will eventually be built, and several nanoscale solid-state schemes are being implemented in a range of materials. Nanofabricated quantum dots can be made in designer configurations, with established technology for controlling interactions and for reading out results. Epitaxial quantum dots can be grown in vertical arrays in semiconductors, and ultrafast optical techniques are available for controlling and measuring their excitations. Single-walled carbon nanotubes can be used for molecular self-assembly of endohedral fullerenes, which can embody quantum information in the electron spin. The challenges of in idual addressing in such tiny structures could rapidly become intractable with increasing numbers of qubits, but these schemes are amenable to global addressing methods for computation.
Publisher: American Physical Society (APS)
Date: 21-09-2016
Publisher: IOP Publishing
Date: 07-09-2011
Publisher: IOP Publishing
Date: 06-2021
DOI: 10.1088/2058-7058/34/04/35
Abstract: Primary-school children, and the rest of us too, are continuously being showered by unseen muons, a heavier relative of the more familiar electron. I was therefore excited to read about a successful US-based outreach project that allows members of the public to make muon detectors for less than $100 and observe these tiny particles for themselves.
Publisher: American Chemical Society (ACS)
Date: 14-06-2007
DOI: 10.1021/NL070949K
Abstract: We report the fabrication and measurement of silicon quantum dots with tunable tunnel barriers in a narrow-channel field-effect transistor. Low-temperature transport spectroscopy is performed in both the many-electron ( approximately 100 electrons) regime and the few-electron ( approximately 10 electrons) regime. Excited states in the bias spectroscopy provide evidence of quantum confinement. These results demonstrate that depletion gates are an effective technique for defining quantum dots in silicon.
Publisher: AIP Publishing
Date: 23-08-2010
DOI: 10.1063/1.3475771
Abstract: We present a study of the magnetoresistance (MR) of a Si metal-oxide-semiconductor field-effect-transistor (MOSFET) at the break-down regime when a magnetic field is applied perpendicular to the plane of the device. We have identified two different regimes where we observe a large and gate-voltage dependent MR. We suggest two different mechanisms which can explain the observed high MR. Moreover, we have studied how the MR of the MOSFET scales with the dimensions of the channel for gate voltages below the threshold. We observed a decrease in the MR by two orders of magnitude by reducing the dimensions of the channel from 50×280 μm2 to 5×5 μm2.
Publisher: Springer Science and Business Media LLC
Date: 20-01-2015
DOI: 10.1038/NCOMMS7084
Abstract: Quantum computation requires a qubit-specific measurement capability to readout the final state of in idual qubits. Promising solid-state architectures use external readout electrometers but these can be replaced by a more compact readout element, an in situ gate sensor. Gate-sensing couples the qubit to a resonant circuit via a gate and probes the qubit's radiofrequency polarizability. Here we investigate the ultimate performance of such a resonant readout scheme and the noise sources that limit its operation. We find a charge sensitivity of 37 μe Hz(-1/2), the best value reported for this technique, using the ex le of a gate sensor strongly coupled to a double quantum dot at the corner states of a silicon nanowire transistor. We discuss the experimental factors limiting gate detection and highlight ways to optimize its sensitivity. In total, resonant gate-based readout has advantages over external electrometers both in terms of reduction of circuit elements as well as absolute charge sensitivity.
Publisher: AIP Publishing
Date: 16-06-2003
DOI: 10.1063/1.1577826
Abstract: We report low-temperature electron transport behavior of trench-isolated silicon–germanium (SiGe) double quantum dots. By sweeping the potentials on side gates, we find a hexagonal charging diagram in the conductance measurements. It is also found that the gates allow the parameters of in idual tunnel barriers to be changed over a wide range. Charging effects may therefore be observed in different coupling regimes, for ex le, the two dots that comprise the double dot can be induced to merge together yielding a large single dot.
Publisher: Springer Science and Business Media LLC
Date: 03-07-2011
DOI: 10.1038/NMAT3053
Abstract: Spin currents--the flow of angular momentum without the simultaneous transfer of electrical charge--play an enabling role in the field of spintronics. Unlike the charge current, the spin current is not a conservative quantity within the conduction carrier system. This is due to the presence of the spin-orbit interaction that couples the spin of the carriers to angular momentum in the lattice. This spin-lattice coupling acts also as the source of d ing in magnetic materials, where the precessing magnetic moment experiences a torque towards its equilibrium orientation the excess angular momentum in the magnetic subsystem flows into the lattice. Here we show that this flow can be reversed by the three-magnon splitting process and experimentally achieve the enhancement of the spin current emitted by the interacting spin waves. This mechanism triggers angular momentum transfer from the lattice to the magnetic subsystem and modifies the spin-current emission. The finding illustrates the importance of magnon-magnon interactions for developing spin-current based electronics.
Publisher: IOP Publishing
Date: 19-05-2008
DOI: 10.1088/0957-4484/19/26/265201
Abstract: We report a detailed study of low-temperature (mK) transport properties of a silicon double-dot system fabricated by phosphorous ion implantation. The device under study consists of two phosphorous nanoscale islands doped to above the metal-insulator transition, separated from each other and the source and drain reservoirs by nominally undoped (intrinsic) silicon tunnel barriers. Metallic control gates, together with an Al-AlO(x) single-electron transistor (SET), were positioned on the substrate surface, capacitively coupled to the buried dots. The in idual double-dot charge states were probed using source-drain bias spectroscopy combined with non-invasive SET charge sensing. The system was measured in linear (source-drain DC bias V(SD) = 0) and non-linear (V(SD) ≠ 0) regimes, allowing calculations of the relevant capacitances. Simultaneous detection using both SET sensing and source-drain current measurements was demonstrated, providing a valuable combination for the analysis of the system. Evolution of the triple points with applied bias was observed using both charge and current sensing. Coulomb diamonds, showing the interplay between the Coulomb charging effects of the two dots, were measured using simultaneous detection and compared with numerical simulations.
Publisher: IOP Publishing
Date: 27-11-2007
Publisher: IEEE
Date: 02-2008
Publisher: American Chemical Society (ACS)
Date: 26-09-2014
DOI: 10.1021/NL5023942
Abstract: We present a combined experimental-theoretical demonstration of the energy spectrum and exchange coupling of an isolated donor pair in a silicon nanotransistor. The molecular hybridization of the atomic orbitals leads to an enhancement of the one- and two-electron binding energies and charging energy with respect to the single donor case, a desirable feature for quantum electronic devices. Our hydrogen molecule-like model based on a multivalley central-cell corrected effective mass theory incorporating a full configuration interaction treatment of the 2-electron spectrum matches the measured data for an arsenic diatomic molecule with interatomic distance R = 2.3 ± 0.5 nm.
Publisher: Elsevier BV
Date: 04-2014
Publisher: American Physical Society (APS)
Date: 06-03-2008
Publisher: Elsevier BV
Date: 03-2005
Publisher: AIP Publishing
Date: 17-03-2008
DOI: 10.1063/1.2831664
Abstract: We report the demonstration of a silicon radio-frequency single electron transistor. The island is defined by electrostatically tunable tunnel barriers in a narrow channel field effect transistor. Charge sensitivities of better than 10μe∕Hz are demonstrated at megahertz bandwidth. These results demonstrate that silicon may be used to fabricate fast, sensitive electrometers.
Publisher: AIP Publishing
Date: 13-10-2014
DOI: 10.1063/1.4898704
Abstract: We electrically measure intrinsic silicon quantum dots with electrostatically defined tunnel barriers. The presence of both p- and n-type ohmic contacts enables the accumulation of either electrons or holes. Thus, we are able to study both transport regimes within the same device. We investigate the effect of the tunnel barriers and the electrostatically defined quantum dots. There is greater localisation of charge states under the tunnel barriers in the case of hole conduction, leading to higher charge noise in the p-type regime.
Publisher: American Physical Society (APS)
Date: 16-03-2015
Publisher: American Physical Society (APS)
Date: 09-10-2014
Publisher: Springer Science and Business Media LLC
Date: 10-11-2014
Abstract: The interplay between spin, charge and orbital degrees of freedom has led to the development of spintronic devices such as spin-torque oscillators and spin-transfer torque magnetic random-access memories. In this development, spin pumping represents a convenient way to electrically detect magnetization dynamics. The effect originates from direct conversion of low-energy quantized spin waves in the magnet, known as magnons, into a flow of spins from the precessing magnet to adjacent leads. In this case, a secondary spin-charge conversion element, such as heavy metals with large spin Hall angle or multilayer layouts, is required to convert the spin current into a charge signal. Here, we report the experimental observation of charge pumping in which a precessing ferromagnet pumps a charge current, demonstrating direct conversion of magnons into high-frequency currents via the relativistic spin-orbit interaction. The generated electric current, unlike spin currents generated by spin-pumping, can be directly detected without the need of any additional spin-charge conversion mechanism. The charge-pumping phenomenon is generic and gives a deeper understanding of its reciprocal effect, the spin orbit torque, which is currently attracting interest for their potential in manipulating magnetic information.
Publisher: American Physical Society (APS)
Date: 08-02-2002
Publisher: IOP Publishing
Date: 04-02-2009
Publisher: American Physical Society (APS)
Date: 29-12-2015
Publisher: AIP Publishing
Date: 27-02-2017
DOI: 10.1063/1.4977490
Abstract: We use ferromagnetic resonance to study the current-induced torques in YIG/heavy metal bilayers. YIG s les with thickness varying from 14.8 nm to 80 nm, with the Pt or Ta thin film on top, are measured by applying a microwave current into the heavy metals and measuring the longitudinal DC voltage generated by both spin rectification and spin pumping. From a symmetry analysis of the FMR lineshape and its dependence on YIG thickness, we deduce that the Oersted field dominates over spin-transfer torque in driving magnetization dynamics.
Publisher: AIP Publishing
Date: 24-06-2013
DOI: 10.1063/1.4812812
Abstract: We study experimentally the spin-current generation in yttrium iron garnet (YIG)/Pt bilayers based on YIG films with different thicknesses. Our results show that for all films with thicknesses exceeding a certain value, the spin current in the YIG/Pt system is enhanced at low frequencies. The cut-off frequencies, at which the enhancement starts, as well as the efficiency of the enhancement were found to increase with increasing film thickness. Good correlation between the cut-off frequency and the frequency at which the three-magnon splitting becomes allowed was observed. These findings prove that the latter process is responsible for the spin-current enhancement.
Publisher: American Chemical Society (ACS)
Date: 15-06-2015
DOI: 10.1021/ACS.NANOLETT.5B01306
Abstract: We report the dispersive readout of the spin state of a double quantum dot formed at the corner states of a silicon nanowire field-effect transistor. Two face-to-face top-gate electrodes allow us to independently tune the charge occupation of the quantum dot system down to the few-electron limit. We measure the charge stability of the double quantum dot in DC transport as well as dispersively via in situ gate-based radio frequency reflectometry, where one top-gate electrode is connected to a resonator. The latter removes the need for external charge sensors in quantum computing architectures and provides a compact way to readout the dispersive shift caused by changes in the quantum capacitance during inter-dot charge transitions. Here, we observe Pauli spin-blockade in the high-frequency response of the circuit at finite magnetic fields between singlet and triplet states. The blockade is lifted at higher magnetic fields when intra-dot triplet states become the ground state configuration. A line shape analysis of the dispersive phase shift reveals furthermore an intra-dot valley-orbit splitting Δvo of 145 μeV. Our results open up the possibility to operate compact complementary metal-oxide semiconductor (CMOS) technology as a singlet-triplet qubit and make split-gate silicon nanowire architectures an ideal candidate for the study of spin dynamics.
Publisher: AIP Publishing
Date: 18-12-2017
DOI: 10.1063/1.5009079
Abstract: We increase the isolation of a superconducting double dot from its environment by galvanically isolating it from any electrodes. We probe it using high frequency reflectometry techniques, find 2e-periodic behaviour, and characterise the energy structure of its charge states. By modelling the response of the device, we determine the time averaged probability that the device is poisoned by quasiparticles, and by comparing this with previous work, we conclude that quasiparticle exchange between the dots and the leads is an important relaxation mechanism.
Publisher: Elsevier BV
Date: 11-2013
Publisher: Elsevier BV
Date: 04-2006
Publisher: AIP Publishing
Date: 16-05-2016
DOI: 10.1063/1.4950976
Abstract: We present a reconfigurable metal-oxide-semiconductor multi-gate transistor that can host a quadruple quantum dot in silicon. The device consists of an industrial quadruple-gate silicon nanowire field-effect transistor. Exploiting the corner effect, we study the versatility of the structure in the single quantum dot and the serial double quantum dot regimes and extract the relevant capacitance parameters. We address the fabrication variability of the quadruple-gate approach which, paired with improved silicon fabrication techniques, makes the corner state quantum dot approach a promising candidate for a scalable quantum information architecture.
Publisher: AIP Publishing
Date: 22-02-2010
DOI: 10.1063/1.3318463
Abstract: We report charge sensing measurements on a silicon quantum dot with a nearby silicon single electron transistor (SET) acting as an electrometer. The devices are electrostatically formed in bulk silicon using surface gates. We show that as an additional electron is added onto the quantum dot, a charge is induced on the SET of approximately 0.2e. These measurements are performed in the many electron regime, where we can count in excess of 20 charge additions onto the quantum dot.
Publisher: AIP Publishing
Date: 18-08-2008
DOI: 10.1063/1.2960356
Abstract: We report electrically detected magnetic resonance of phosphorus donors in a silicon field-effect transistor. An on-chip transmission line is used to generate the oscillating magnetic field allowing broadband operation. At millikelvin temperatures, continuous wave spectra were obtained up to 40GHz, using both magnetic field and microwave frequency modulation. The spectra reveal the hyperfine-split electron spin resonances characteristic for Si:P and a central feature which displays the fingerprint of spin-spin scattering in the two-dimensional electron gas.
Publisher: IOP Publishing
Date: 21-02-2012
Publisher: American Physical Society (APS)
Date: 21-07-2020
Publisher: American Chemical Society (ACS)
Date: 16-02-2016
DOI: 10.1021/ACS.NANOLETT.5B04356
Abstract: Quantum mechanical effects induced by the miniaturization of complementary metal-oxide-semiconductor (CMOS) technology h er the performance and scalability prospects of field-effect transistors. However, those quantum effects, such as tunneling and coherence, can be harnessed to use existing CMOS technology for quantum information processing. Here, we report the observation of coherent charge oscillations in a double quantum dot formed in a silicon nanowire transistor detected via its dispersive interaction with a radio frequency resonant circuit coupled via the gate. Differential capacitance changes at the interdot charge transitions allow us to monitor the state of the system in the strong-driving regime where we observe the emergence of Landau-Zener-Stückelberg-Majorana interference on the phase response of the resonator. A theoretical analysis of the dispersive signal demonstrates that quantum and tunneling capacitance changes must be included to describe the qubit-resonator interaction. Furthermore, a Fourier analysis of the interference pattern reveals a charge coherence time, T2 ≈ 100 ps. Our results demonstrate charge coherent control and readout in a simple silicon transistor and open up the possibility to implement charge and spin qubits in existing CMOS technology.
Publisher: American Physical Society (APS)
Date: 09-06-2017
Publisher: AIP Publishing
Date: 11-2009
DOI: 10.1063/1.3258206
Abstract: The authors demonstrate readout of electrically detected magnetic resonance at radio frequencies by means of a LCR tank circuit. Applied to a silicon field-effect transistor at millikelvin temperatures, this method shows a 25-fold increased signal-to-noise ratio of the conduction band electron spin resonance and a higher operational bandwidth of & kHz compared to the kilohertz bandwidth of conventional readout techniques. This increase in temporal resolution provides a method for future direct observations of spin dynamics in the electrical device characteristics.
Publisher: AIP Publishing
Date: 15-11-2006
DOI: 10.1063/1.2364664
Abstract: We report on milli-Kelvin charge sensing measurements of a silicon double-dot system fabricated by phosphorus ion implantation. An aluminum single-electron transistor is capacitively coupled to each of the implanted dots enabling the charging behavior of the double-dot system to be studied independent of current transport. Using an electrostatic gate, the interdot coupling can be tuned from weak to strong coupling. In the weak interdot coupling regime, the system exhibits well-defined double-dot charging behavior. By contrast, in the strong interdot coupling regime, the system behaves as a single dot.
Publisher: AIP Publishing
Date: 08-05-0001
DOI: 10.1063/1.2203740
Abstract: We demonstrate electrical control of Si:P double dots in which the potential is defined by nanoscale phosphorus-doped regions. Each dot contains approximately 600 phosphorus atoms and has a diameter close to 30nm. On application of a differential bias across the dots, electron transfer is observed, using single electron transistors in both dc and rf modes as charge detectors. With the possibility to scale the dots down to a few and even single atoms these results open the way to a new class of precision-doped quantum dots in silicon.
Publisher: Springer Science and Business Media LLC
Date: 16-04-2018
DOI: 10.1038/S41563-018-0058-9
Abstract: Unlike conventional spin-singlet Cooper pairs, spin-triplet pairs can carry spin
Publisher: Public Library of Science (PLoS)
Date: 29-04-2015
Publisher: American Physical Society (APS)
Date: 16-02-2016
Publisher: AIP Publishing
Date: 05-02-2015
DOI: 10.1063/1.4907694
Abstract: We demonstrate, at room temperature, the strong coupling of the fundamental and non-uniform magnetostatic modes of an yttrium iron garnet ferrimagnetic sphere to the electromagnetic modes of a co-axial cavity. The well-defined field profile within the cavity yields a specific coupling strength for each magnetostatic mode. We experimentally measure the coupling strength for the different magnetostatic modes and, by calculating the expected coupling strengths, we are able to identify the modes themselves.
Publisher: AIP Publishing
Date: 03-09-2012
DOI: 10.1063/1.4750251
Abstract: We report the fabrication and electrical characterization of an electrostatically defined aluminum-gated SET on a lightly doped SOI etched nanowire based on MOSFET structures. The tunability of the device is achieved via two sets of electrically isolated aluminum surface gates. The results demonstrate a reproducible constant charging energy of 2 meV for a large range of gate voltages as well as tunable tunneling resistance. The controllable tunnel barriers permit transport spectroscopy of subthreshhold features.
Publisher: SPIE
Date: 23-02-2005
DOI: 10.1117/12.583293
Publisher: AIP Publishing
Date: 09-05-2016
DOI: 10.1063/1.4948921
Abstract: We investigate magnetization dynamics in a spin-Hall oscillator using a direct current measurement as well as conventional microwave spectrum analysis. When the current applies an anti-d ing spin-transfer torque, we observe a change in resistance which we ascribe mainly to the excitation of incoherent exchange magnons. A simple model is developed based on the reduction of the effective saturation magnetization, quantitatively explaining the data. The observed phenomena highlight the importance of exchange magnons on the operation of spin-Hall oscillators.
Publisher: AIP Publishing
Date: 17-10-2011
DOI: 10.1063/1.3652911
Abstract: We use both parallel and perpendicular parametric pumping techniques to excite short-wavelength spin waves in an yttrium iron garnet film and study the spin current generation from spin waves excited by these pumping methods with the help of the inverse spin-Hall effect in the adjacent Pt layer. We observed clear spin current generations for these pumping techniques and find that the efficiency is nearly independent of the magnitude and the direction of the wave vectors of excited spin waves. These experimental results are important for future spintronic devices operated by short-wavelength spin waves.
Publisher: Elsevier BV
Date: 10-2012
Publisher: American Physical Society (APS)
Date: 25-08-2006
Publisher: Springer Science and Business Media LLC
Date: 16-05-2016
DOI: 10.1038/NPHYS3772
Publisher: American Chemical Society (ACS)
Date: 17-02-2014
DOI: 10.1021/NL403659X
Abstract: A metallic double dot is measured with radio frequency reflectometry. Changes in the total electron number of the double dot are determined via single electron tunnelling contributions to the complex electrical impedance. Electron counting experiments are performed by monitoring the impedance, demonstrating operation of a single electron ammeter without the need for external charge detection.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2012
End Date: 2013
Funder: Royal Society
View Funded ActivityStart Date: 2016
End Date: 2019
Funder: Engineering and Physical Sciences Research Council
View Funded ActivityStart Date: 2009
End Date: 2012
Funder: Leverhulme Trust
View Funded ActivityStart Date: 2010
End Date: 2013
Funder: Engineering and Physical Sciences Research Council
View Funded ActivityStart Date: 2016
End Date: 2021
Funder: Engineering and Physical Sciences Research Council
View Funded ActivityStart Date: 2009
End Date: 2014
Funder: Engineering and Physical Sciences Research Council
View Funded ActivityStart Date: 2015
End Date: 2020
Funder: European Research Council
View Funded Activity