arXiv subjects

Z. -P. Li

Publications and source records attributed to Z. -P. Li.

7 recordsLinked to original sources

arXiv2022

Coherent dynamics of multi-spin $\rm V_B^-$ centers in hexagonal boron nitride

Hexagonal boron nitride (hBN) has recently been demonstrated to contain optically polarized and detected electron spins that can be utilized for implementing qubits and quantum sensors in nanolayered-devices. Understanding the coherent dynamics of microwave driven spins in hBN is of crucial importance for advancing these emerging new technologies. Here, we demonstrate and study the Rabi oscillation and related dynamical phenomena of the negatively charged boron vacancy ($\rm V_B^-$) spins in hBN. We report on different dynamics of the $\rm V_B^-$ spins at weak and strong magnetic fields. In the former case the defect behaves like a single electron spin system, while in the latter case it behaves like a multi-spin system exhibiting the multiple-frequency dynamical oscillation like clear beat in Ramsey fringes. We also carry out theoretical simulations for the spin dynamics of $\rm V_B^-$ and reveal that the nuclear spins can be driven via the strong electric-nuclear coupling existing in $\rm V_B^-$ center, which can be modulated by the magnetic field and microwave field.

quant-ph↗

arXiv2022

Generation of Spin Defects by Ion Implantation in Hexagonal Boron Nitride

Optically addressable spin defects in wide-bandage semiconductors as promising systems for quantum information and sensing applications have attracted more and more attention recently. Spin defects in two-dimensional materials are supposed to have unique superiority in quantum sensing since their atomatic thickness. Here, we demonstrate that the negatively boron charged vacancy (V$ _\text{B}^{-} $) with good spin properties in hexagonal boron nitride can be generated by ion implantation. We carry out optically detected magnetic resonance measurements at room temperature to characterize the spin properties of V$ _\text{B}^{-} $ defects, showing zero-filed splitting of $ \sim $ 3.47 GHz. We compare the photoluminescence intensity and spin properties of V$ _\text{B}^{-} $ defects generated by different implantation parameters, such as fluence, energy and ion species. With proper parameters, we can create V$ _\text{B}^{-} $ defects successfully with high probability. Our results provide a simple and practicable method to create spin defects in hBN, which is of great significance for integrated hBN-based devices.

quant-ph↗

arXiv2021

Temperature-dependent energy-level shifts of Spin Defects in hexagonal Boron Nitride

Two-dimensional hexagonal boron nitride (hBN) has attracted large attentions as platforms for realizations for integrated nanophotonics and collective effort has been focused on the spin defect centers. Here, the temperature dependence of the resonance spectrum in the range of 5-600 K is investigated. The zero-field splitting (ZFS) parameter D is found to decrease monotonicly with increasing temperature and can be described by Varshni empirical equation perfectly, while E almost does not change. We systematically study the differences among different hBN nanopowders and provide an evidence of edge effects on ODMR of VB- defects. Considering the proportional relation between D and reciprocal of lattice volume, the thermal expansion might be the dominant reason for energy-level shifts. We also demonstrate that the VB- defects still exist stably at least at 600 K. Moreover, we propose a scheme for detecting laser intensity using the VB- defects in hBN nanopowders, which is based on the obvious dependence of its D value on laser intensity. Our results are helpful to gain insight into the spin properties of VB- and for the realizations of miniaturized, integrated thermal sensor.

quant-ph↗

arXiv2008

Resonant Spin-Transfer-Driven Switching of Magnetic Devices Assisted by Microwave Current Pulses

The torque generated by the transfer of spin angular momentum from a spin-polarized current to a nanoscale ferromagnet can switch the orientation of the nanomagnet much more efficiently than a current-generated magnetic field, and is therefore in development for use in next-generation magnetic random access memory (MRAM). Up to now, only DC currents and square-wave current pulses have been investigated in spin-torque switching experiments. Here we present measurements showing that spin transfer from a microwave-frequency pulse can produce a resonant excitation of a nanomagnet and lead to improved switching characteristics in combination with a square current pulse. With the assistance of a microwave-frequency pulse, the switching time is reduced and achieves a narrower distribution than when driven by a square current pulse alone, and this can permit significant reductions in the integrated power required for switching. Resonantly excited switching may also enable alternative, more compact MRAM circuit architectures.

cond-mat.other↗

arXiv2008

Strong linewidth variation for spin-torque nano-oscillators as a function of in-plane magnetic field angle

We measure the microwave signals produced by spin-torque-driven magnetization dynamics in patterned magnetic multilayer devices at room temperature, as a function of the angle of a magnetic field applied in the sample plane. We find strong variations in the frequency linewidth of the signals, with a decrease by more than a factor of 20 as the field is rotated from the magnetic easy axis to the in-plane hard axis. Based on micromagnetic simulations, we identify these variations as due to a transition from spatially incoherent to coherent precession.

cond-mat.other↗

arXiv2002

Pion photoproduction on the nucleon in the quark model

We present a detailed quark-model study of pion photoproduction within the effective Lagrangian approach. Cross sections and single-polarization observables are investigated for the four charge channels, $γp\to π^+ n$, $γn\to π^- p$, $γp\to π^0 p$, and $γn\to π^0 n$. Leaving the $πNΔ$ coupling strength to be a free parameter, we obtain a reasonably consistent description of these four channels from threshold to the first resonance region. Within this effective Lagrangian approach, strongly constrainted by the quark model, we consider the issue of double-counting which may occur if additional {\it t}-channel contributions are included.

nucl-th↗

arXiv2002

Quark model approach to the $η$ meson electroproduction on the proton

A recently developed quark model approach to pseudoscalar meson photoproduction is extended to electroproduction process for the $η$ meson in the kinematics of momentum transfer $Q^2 \leq$ 4 (GeV/c)$^2$ and total center of mass energy $W \leq$ 1.6 GeV. Existing data are well reproduced and the roles of the $S_{11}(1535)$ and $D_{13}(1520)$ resonances are closely investigated. In the study of the longitudinal excitation of the $S_{11}(1535)$ resonance, a reliable constraint on the $S_{11}(1535)$ properties is obtained by cleanly removing the electromagnetic transition from the $γ_{(v)} p \to S_{11}(1535) \to ηp$ amplitude. Thus, the fitted quantities can be determined with an uncertainty of about 15%. This could be the first direct constraint on the $S_{11}(1535)$ properties in theory.

nucl-th↗