arXiv subjects

Jean-Philippe Tetienne

Publications and source records attributed to Jean-Philippe Tetienne.

42 records · Page 3Linked to original sources

arXiv2016

Microwave-Free Nuclear Magnetic Resonance at Molecular Scales

The implementation of nuclear magnetic resonance (NMR) at the nanoscale is a major challenge, as conventional systems require relatively large ensembles of spins and limit resolution to mesoscopic scales. New approaches based on quantum spin probes, such as the nitrogen-vacancy (NV) centre in diamond, have recently achieved nano-NMR under ambient conditions. However, the measurement protocols require application of complex microwave pulse sequences of high precision and relatively high power, placing limitations on the design and scalability of these techniques. Here we demonstrate a microwave-free method for nanoscale NMR using the NV centre, which is a far less invasive, and vastly simpler measurement protocol. By utilising a carefully tuned magnetic cross-relaxation interaction between a subsurface NV spin and an external, organic environment of proton spins, we demonstrate NMR spectroscopy of $^1$H within a $\approx(10~{\rm nm})^3$ sensing volume. We also theoretically and experimentally show that the sensitivity of our approach matches that of existing microwave control-based techniques using the NV centre. Removing the requirement for coherent manipulation of either the NV or the environmental spin quantum states represents a significant step towards the development of robust, non-invasive nanoscale NMR probes.

cond-mat.mes-hall↗

arXiv2016

Quantum imaging of current flow in graphene

Since its first isolation in 2004, graphene has been found to host a plethora of unusual electronic transport phenomena, making it a fascinating system for fundamental studies in condensed-matter physics as well as offering tremendous opportunities for future electronic and sensing devices. However, to fully realise these goals a major challenge is the ability to non-invasively image charge currents in monolayer graphene structures and devices. Typically, electronic transport in graphene has been investigated via resistivity measurements, however, such measurements are generally blind to spatial information critical to observing and studying landmark transport phenomena such as electron guiding and focusing, topological currents and viscous electron backflow in real space, and in realistic imperfect devices. Here we bring quantum imaging to bear on the problem and demonstrate high-resolution imaging of current flow in graphene structures. Our method utilises an engineered array of near-surface, atomic-sized quantum sensors in diamond, to map the vector magnetic field and reconstruct the vector current density over graphene geometries of varying complexity, from mono-ribbons to junctions, with spatial resolution at the diffraction limit and a projected sensitivity to currents as small as 1 μA. The measured current maps reveal strong spatial variations corresponding to physical defects at the sub-μm scale. The demonstrated method opens up an important new avenue to investigate fundamental electronic and spin transport in graphene structures and devices, and more generally in emerging two-dimensional materials and thin film systems.

cond-mat.mes-hall↗

arXiv2016

Spin dynamics of diamond nitrogen-vacancy centres at the ground state level anti-crossing and all-optical low frequency magnetic field sensing

We investigate the photo-induced spin dynamics of single nitrogen-vacancy (NV) centres in diamond near the electronic ground state level anti-crossing (GSLAC), which occurs at an axial magnetic field around 1024 G. Using optically detected magnetic resonance spectroscopy, we first find that the electron spin transition frequency can be tuned down to 100 kHz for the \NV{14} centre, while for the \NV{15} centre the transition strength vanishes for frequencies below about 2 MHz owing to the GSLAC level structure. Using optical pulses to prepare and readout the spin state, we observe coherent spin oscillations at 1024 G for the \NV{14}, which originate from spin mixing induced by residual transverse magnetic fields. This effect is responsible for limiting the smallest observable transition frequency, which can span two orders of magnitude from 100 kHz to tens of MHz depending on the local magnetic noise. A similar feature is observed for the \NV{15} centre at 1024 G. As an application of these findings, we demonstrate all-optical detection and spectroscopy of externally-generated fluctuating magnetic fields at frequencies from 8 MHz down to 500 kHz, using a \NV{14} centre. Since the Larmor frequency of most nuclear spin species lies within this frequency range near the GSLAC, these results pave the way towards all-optical, nanoscale nuclear magnetic resonance spectroscopy, using longitudinal spin cross-relaxation.

cond-mat.mes-hall↗

arXiv2016

Wide-band, nanoscale magnetic resonance spectroscopy using quantum relaxation of a single spin in diamond

We demonstrate a wide-band all-optical method of nanoscale magnetic resonance (MR) spectroscopy under ambient conditions. Our method relies on cross-relaxation between a probe spin, the electronic spin of a nitrogen-vacancy centre in diamond, and target spins as the two systems are tuned into resonance. By optically monitoring the spin relaxation time ($T_1$) of the probe spin while varying the amplitude of an applied static magnetic field, a frequency spectrum of the target spin resonances, a $T_1$-MR spectrum, is obtained. As a proof of concept, we measure $T_1$-MR spectra of a small ensemble of $^{14}$N impurities surrounding the probe spin within the diamond, with each impurity comprising an electron spin 1/2 and a nuclear spin 1. The intrinsically large bandwidth of the technique and probe properties allows us to detect both electron spin transitions -- in the GHz range -- and nuclear spin transitions -- in the MHz range -- of the $^{14}$N spin targets. The measured frequencies are found to be in excellent agreement with theoretical expectations, and allow us to infer the hyperfine, quadrupole and gyromagnetic constants of the target spins. Analysis of the strength of the resonances obtained in the $T_1$-MR spectrum reveals that the electron spin transitions are probed via dipole interactions, while the nuclear spin resonances are dramatically enhanced by hyperfine coupling and an electron-mediated process. Finally, we investigate theoretically the possibility of performing $T_1$-MR spectroscopy on nuclear spins without hyperfine interaction and predict single-proton sensitivity using current technology. This work establishes $T_1$-MR as a simple yet powerful technique for nanoscale MR spectroscopy, with broadband capability and a projected sensitivity down to the single nuclear spin level.

quant-ph↗

arXiv2015

Scanning nano-spin ensemble microscope for nanoscale magnetic and thermal imaging

Quantum sensors based on solid-state spins provide tremendous opportunities in a wide range of fields from basic physics and chemistry to biomedical imaging. However, integrating them into a scanning probe microscope to enable practical, nanoscale quantum imaging is a highly challenging task. Recently, the use of single spins in diamond in conjunction with atomic force microscopy techniques has allowed significant progress towards this goal, but generalisation of this approach has so far been impeded by long acquisition times or by the absence of simultaneous topographic information. Here we report on a scanning quantum probe microscope which solves both issues, by employing a nano-spin ensemble hosted in a nanodiamond. This approach provides up to an order of magnitude gain in acquisition time, whilst preserving sub-100 nm spatial resolution both for the quantum sensor and topographic images. We demonstrate two applications of this microscope. We first image nanoscale clusters of maghemite particles through both spin resonance spectroscopy and spin relaxometry, under ambient conditions. Our images reveal fast magnetic field fluctuations in addition to a static component, indicating the presence of both superparamagnetic and ferromagnetic particles. We next demonstrate a new imaging modality where the nano-spin ensemble is used as a thermometer. We use this technique to map the photo-induced heating generated by laser irradiation of a single gold nanoparticle in a fluid environment. This work paves the way towards new applications of quantum probe microscopy such as thermal/magnetic imaging of operating microelectronic devices and magnetic detection of ion channels in cell membranes.

cond-mat.mes-hall↗

arXiv2015

Magneto-optical imaging of thin magnetic films using spins in diamond

Imaging the fields of magnetic materials provides crucial insight into the physical and chemical processes surrounding magnetism, and has been a key ingredient in the spectacular development of magnetic data storage. Existing approaches using the magneto-optic Kerr effect (MOKE), x-ray and electron microscopy have limitations that constrain further development, and there is increasing demand for imaging and characterisation of magnetic phenomena in real time with high spatial resolution. In this work, we show how the magneto-optical response of an array of negatively-charged nitrogen-vacancy spins in diamond can be used to image and map the sub-micron stray magnetic field patterns from thin ferromagnetic films. Using optically detected magnetic resonance, we demonstrate wide-field magnetic imaging over 100x100 μm^2 with a diffraction-limited spatial resolution of 440 nm at video frame rates, under ambient conditions. We demonstrate a novel all-optical spin relaxation contrast imaging approach which can image magnetic structures in the absence of an applied microwave field. Straightforward extensions promise imaging with sub-μT sensitivity and sub-optical spatial and millisecond temporal resolution. This work establishes practical diamond-based wide-field microscopy for rapid high-sensitivity characterisation and imaging of magnetic samples, with the capability for investigating magnetic phenomena such as domain wall and skyrmion dynamics and the spin Hall effect in metals.

cond-mat.mes-hall↗