arXiv subjects

Yang Ji

Publications and source records attributed to Yang Ji.

46 records · Page 3Linked to original sources

arXiv2015

Spin-orbit torque in Pt/CoNiCo/Pt symmetric devices

Current induced magnetization switching by spin-orbit torques offers an energy-efficient means of writing information in heavy metal/ferromagnet (FM) multilayer systems. The relative contributions of field-like torques and damping-like torques to the magnetization switching induced by the electrical current are still under debate. Here, we describe a device based on a symmetric Pt/FM/Pt structure, in which we demonstrate a strong damping-like torque from the spin Hall effect and unmeasurable field-like torque from Rashba effect. The spin-orbit effective fields due to the spin Hall effect were investigated quantitatively and were found to be consistent with the switching effective fields after accounting for the switching current reduction due to thermal fluctuations from the current pulse. A non-linear dependence of deterministic switching of average Mz on the in-plane magnetic field was revealed, which could be explained and understood by micromagnetic simulation.

cond-mat.mes-hall↗

arXiv2014

Fully-automatic laser welding and micro-sculpting with universal in situ inline coherent imaging

Though new affordable high power laser technologies make possible many processing applications in science and industry, depth control remains a serious technical challenge. Here we show that inline coherent imaging, with line rates up to 312 kHz and microsecond-duration capture times, is capable of directly measuring laser penetration depth in a process as violent as kW-class keyhole welding. We exploit ICI's high speed, high dynamic range and robustness to interference from other optical sources to achieve fully automatic, adaptive control of laser welding as well as ablation, achieving micron-scale sculpting in vastly different heterogeneous biological materials.

physics.ins-det↗

arXiv2013

Tuning exciton and biexciton transition energies and fine structure splitting through hydrostatic pressure in single InGaAs quantum dots

We demonstrate that the exciton and biexciton emission energies as well as exciton fine structure splitting (FSS) in single (In,Ga)As/GaAs quantum dots (QDs) can be efficiently tuned using hydrostatic pressure in situ in an optical cryostat at up to 4.4 GPa. The maximum exciton emission energy shift was up to 380 meV, and the FSS was up to 180 $μ$eV. We successfully produced a biexciton antibinding-binding transition in QDs, which is the key experimental condition that generates color- and polarization-indistinguishable photon pairs from the cascade of biexciton emissions and that generates entangled photons via a time-reordering scheme. We perform atomistic pseudopotential calculations on realistic (In,Ga)As/GaAs QDs to understand the physical mechanism underlying the hydrostatic pressure-induced effects.

cond-mat.mes-hall↗

arXiv2009

Effect of Ka-band Microwave on the spin dynamics of electrons in a GaAs/Al0.35Ga0.65As heterostructure

We report experimental results of the effect of Ka-band microwave on the spin dynamics of electrons in a 2D electron system in a GaAs/Al0.35Ga0.65As heterostructure, via time-resolved Kerr rotation measurements. While the microwave reduces the transverse spin lifetime of the bulk GaAs when its frequency is close to the Zeeman splitting of the electrons in the magnetic field, it significantly increases that of electrons in the 2D electron system, from 745 ps to 1213 ps. Such a microwave-enhanced spin lifetime is ascribed to the microwave-induced electron scattering which leads to a motional narrowing of spins via DP mechanism.

cond-mat.mtrl-sci↗

arXiv2009

Spin dynamics of electrons in the first excited subband of a high-mobility low-density 2D electron system

We report on time-resolved Kerr rotation measurements of spin coherence of electrons in the first excited subband of a high-mobility low-density two-dimensional electron system in a GaAs/Al0.35Ga0.65As heterostructure. While the transverse spin lifetime (T2*) of electrons decreases monotonically with increasing magnetic field, it has a non-monotonic dependence on the temperature, with a peak value of 596 ps at 36 K, indicating the effect of inter-subband electron-electron scattering on the electron spin relaxation. The spin lifetime may be long enough for potential device application with electrons in excited subbands.

cond-mat.mtrl-sci↗

arXiv2008

Effect of electron-electron scattering on spin dephasing in a high-mobility low-density twodimensional electron gas

Utilizing time-resolved Kerr rotation techniques, we have investigated the spin dynamics of a high mobility, low density two dimensional electron gas in a GaAs/Al0:35Ga0:65As heterostructure in dependence on temperature from 1.5 K to 30 K. It is found that the spin relaxation/dephasing time under a magnetic field of 0.5 T exhibits a maximum of 3.12 ns around 14 K, superimposed on an increasing background with rising temperature. The appearance of the maximum is ascribed to that at the temperature where the crossover from the degenerate to the nondegenerate regime takes place, electron-electron Coulomb scattering becomes strongest, and thus inhomogeneous precession broadening due to D'yakonov-Perel'(DP) mechanism becomes weakest. These results agree with the recent theoretical predictions [Zhou et al., PRB 75, 045305 (2007)], verifying the importance of electron-electron Coulomb scattering to electron spin relaxation/dephasing.

cond-mat.other↗

arXiv2003

An Electronic Mach-Zehnder Interferometer

Double-slit electron interferometers, fabricated in high mobility two-dimensional electron gas (2DEG), proved to be very powerful tools in studying coherent wave-like phenomena in mesoscopic systems. However, they suffer from small fringe visibility due to the many channels in each slit and poor sensitivity to small currents due to their open geometry. Moreover, the interferometers do not function in a high magnetic field, namely, in the quantum Hall effect (QHE) regime, since it destroys the symmetry between left and right slits. Here, we report on the fabrication and operation of a novel, single channel, two-path electron interferometer that functions in a high magnetic field. It is the first electronic analog of the well-known optical Mach-Zehnder (MZ) interferometer. Based on single edge state and closed geometry transport in the QHE regime the interferometer is highly sensitive and exhibits very high visibility (62%). However, the interference pattern decays precipitously with increasing electron temperature or energy. While we do not understand the reason for the dephasing we show, via shot noise measurement, that it is not a decoherence process that results from inelastic scattering events.

cond-mat.mes-hall↗

arXiv2001

Charge Distribution in a Kondo Correlated Quantum Dot

We report here on a direct and non-invasive measurement of the charge and its distribution in a Kondo correlated quantum dot (QD). A non-invasive potential-sensitive detector in proximity with the QD reveals that even though the conductance of the QD is significantly enhanced as it enters the Kondo regime the net charge in the QD remains unaffected. This demonstrates the separation between spin and charge degrees of freedom in the Kondo effect. We find however, under certain experimental conditions, that an abrupt redistribution of the charge in the QD is taking place simultaneously with the onset of Kondo correlation. This suggests that the spin-charge separation in the Kondo effect does not always hold.

cond-mat.mes-hall↗

arXiv2001

Transmission Phase of a Quantum Dot with Kondo Correlation Near the Unitary Limit

The complex transmission amplitude -- both magnitude and phase -- of a quantum dot (QD) with Kondo correlation was measured near the unitary limit. Contrary to previous phase measurements, performed far from this limit [Ji et al., Science 290, 779 (2000)], the transmission phase was observed to evolve linearly over a range of about 1.5 pi when the Fermi energy was scanned through a Kondo pair -- a pair of spin degenerate energy levels. Moreover, the phase in Coulomb blockade (CB) peak, adjancent to the Kondo pair, retained a memory of the Kondo correlation and did not exhibit the familiar behavior in the CB regime. These results do not agree with theoretical predictions, suggesting that a full explanation may go beyond the framework of the Anderson model.

cond-mat.mes-hall↗

arXiv2000

Phase Evolution in a Kondo Correlated System

The coherence and phase evolution of electrons in a mesoscopic system in the Kondo correlated regime were studied. The Kondo effect, in turn, is one of the most fundamental many-body effects where a localized spin interacts with conduction electrons in a conductor. Results were obtained by embedding a quantum dot (QD) in a double path electronic interferometer and measuring interference of electron waves. The Phase was found to evolve in a range twice as large as the theoretically predicted one. Moreover, the phase proved to be highly sensitive to the onset of Kondo correlation, thus serving as a new fingerprint of the Kondo effect.

cond-mat.mes-hall↗