Ultrasensitive mechanical detection of magnetic moment using a commercial disk drive write head

Sensitive detection of weak magnetic moments is an essential capability in many areas of nanoscale science and technology, including nanomagnetism, quantum readout of spins, and nanoscale magnetic resonance imaging. Here, we show that the write head of a commercial hard drive may enable significant advances in nanoscale spin detection. By approaching a sharp diamond tip to within 5 nm from the pole and measuring the induced diamagnetic moment with a nanomechanical force transducer, we demonstrate a spin sensitivity of 0.032 Bohr magnetons per root Hz, equivalent to 21 proton magnetic moments. The high sensitivity is enabled in part by the pole's strong magnetic gradient of up to 28 million Tesla per meter and in part by the absence of non-contact friction due to the extremely flat writer surface. In addition, we demonstrate quantitative imaging of the pole field with about 10 nm spatial resolution. We foresee diverse applications for write heads in experimental condensed matter physics, especially in spintronics, ultrafast spin manipulation, and mesoscopic physics.Comment: 21 pages, 6 figure

Minimalist AdaBoost for blemish identification in potatoes

We present a multi-class solution based on minimalist Ad- aBoost for identifying blemishes present in visual images of potatoes. Using training examples we use Real AdaBoost to rst reduce the fea- ture set by selecting ve features for each class, then train binary clas- siers for each class, classifying each testing example according to the binary classier with the highest certainty. Against hand-drawn ground truth data we achieve a pixel match of 83% accuracy in white potatoes and 82% in red potatoes. For the task of identifying which blemishes are present in each potato within typical industry dened criteria (10% coverage) we achieve accuracy rates of 93% and 94%, respectively

Persistent spin texture enforced by symmetry

Persistent spin texture (PST) is the property of some materials to maintain a uniform spin configuration in the momentum space. This property has been predicted to support an extraordinarily long spin lifetime of carriers promising for spintronics applications. The PST is known to emerge when the strengths of two dominant spin-orbit couplings, the Rashba and linear Dresselhaus, are equal. This condition, however, is not trivial to achieve and requires tuning the Rashba and Dresselhaus parameters, as has been demonstrated with semiconductor quantum-well structures. Here we predict that there exist a class of non-centrosymmetric bulk materials where the PST is enforced by the non-symmorphic space group symmetry of the crystal. Around certain high symmetry points in the Brillouin zone, the sublattice degrees of freedom impose a constraint on the effective spin-orbit field, which remains independent of the momentum orientation and thus maintains the PST. We illustrate this behavior using density-functional theory calculations for a handful of promising candidates accessible experimentally. Among them is the ferroelectric oxide BiInO3-a wide band gap semiconductor which sustains a PST around the conduction band minimum. Our results broaden the range of materials, which can be employed in spintronics

Persistent spin texture enforced by symmetry

Persistent spin texture (PST) is the property of some materials to maintain a uniform spin configuration in the momentum space. This property has been predicted to support an extraordinarily long spin lifetime of carriers promising for spintronics applications. Here, we predict that there exists a class of noncentrosymmetric bulk materials, where the PST is enforced by the nonsymmorphic space group symmetry of the crystal. Around certain high symmetry points in the Brillouin zone, the sublattice degrees of freedom impose a constraint on the effective spin–orbit field, which orientation remains independent of the momentum and thus maintains the PST. We illustrate this behavior using density-functional theory calculations for a handful of promising candidates accessible experimentally. Among them is the ferroelectric oxide BiInO3—a wide band gap semiconductor which sustains a PST around the conduction band minimum. Our results broaden the range of materials that can be employed in spintronics

Two-dimensional type-II Dirac fermions in a LaAlO3/LaNiO3/LaAlO3 quantum well

The type-II Dirac fermions that are characterized by a tilted Dirac cone and anisotropic magnetotransport properties have been recently proposed theoretically and confirmed experimentally. Here, we predict the emergence of two-dimensional (2D) type-II Dirac fermions in LaAlO3/LaNiO3/LaAlO3 quantum-well structures. Using first-principles calculations and model analyses, we show that the Dirac points are formed at the crossing between the dx2−y2 and dz2 bands protected by the mirror symmetry. The energy position of the Dirac points can be tuned to appear at the Fermi energy by changing the quantum-well width. For the quantum-well structure with a two-unit-cell-thick LaNiO3 layer, we predict the coexistence of the type-II Dirac point and the closed nodal line. The results are analyzed and interpreted using a tight-binding model and symmetry arguments. Our findings offer a practical way to realize 2D type-II Dirac fermions in oxide heterostructures

Spin-orbit dependence of anisotropic current-induced spin polarization

Studies of the current-induced spin polarization (CISP) have been recently reinvigorated due to the discoveries of CISP in some burgeoning materials such as oxide interfaces, van der Waals, and topological quantum materials. Here, we investigate the CISP in two-dimensional systems for different types of spin-orbit coupling (SOC) using the Boltzmann transport theory. We find an anisotropic response of CISP to the current direction which strongly depends on the type of SOC. We demonstrate that the CISP is nonlinear with respect to the SOC magnitude, depends on the Fermi energy, and exhibits two different transport regimes for low or high carrier density. Finally, we propose a magnetoresistance device which can exploit the predicted CISP anisotropy

Two-dimensional type-II Dirac fermions in a LaAlO3/LaNiO3/LaAlO3 quantum well

The type-II Dirac fermions that are characterized by a tilted Dirac cone and anisotropic magneto-transport properties have been recently proposed theoretically and confirmed experimentally. Here, we predict the emergence of two-dimensional type-II Dirac fermions in LaAlO3/LaNiO3/LaAlO3 quantum-well structures. Using first-principles calculations and model analysis, we show that the Dirac points are formed at the crossing between the dx2-y2 and dz2 bands protected by the mirror symmetry. The energy position of the Dirac points can be tuned to appear at the Fermi energy by changing the quantum-well width. For the quantum-well structure with a two-unit cell thick LaNiO3 layer, we predict the coexistence of the type-II Dirac points and the Dirac nodal line. The results are analyzed and interpreted using a tight-binding model and symmetry arguments. Our findings offer a practical way to realize the 2D type-II Dirac fermions in oxide heterostructures