- 标题
- 摘要
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- 实验方案
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Combination of OPSY and PhD-PHIP results in enhanced sensitivity in PHIP
摘要： Despite the large degree of polarization in PHIP experiments compared to the Boltzmann factor, the presence of a large amount of non-reacted molecules with thermal polarization is an important obstacle when dealing with very diluted samples. The feasibility of enhancing both sensitivity and resolution in a single experiment by combining two well established pulse sequences, OPSY and PHD-PHIP is presented. OPSY is used as a block for filtering the signals originated from thermally polarized protons. PhD-PHIP, on the other hand, is used as an acquisition block, increasing the resolution and further improving the sensitivity by preventing signal canceling in the presence of magnetic field inhomogeneities. Experiments in a complex sample with very low hyperpolarization levels are presented showing the excellent performance of the method.
关键词： Echo trains,PhD-PHIP,Spin dynamics,CPMG,J-spectroscopy,Hyperpolarization,Pulse sequences,Parahydrogen,SABRE,J-coupling,NMR,OPSY,PHIP
更新于2025-09-23 15:23:52
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Nuclear spin dynamics in [001] AlAs quantum well in the regime of integer and fractional quantum Hall effect
摘要： Relaxation of nuclear spins located in the vicinity of 2D electron system confined in a 16 nm [001] AlAs/AlGaAs quantum well was studied with the aid of electron spin resonance (ESR) in the regime of integer and fractional quantum Hall effect. Nuclear spin-lattice relaxation time τ was measured from the time decay of the Overhauser shift near different filling factors of the electron system. The resultant dependence of τ on filling factor turned out to be nontrivial. At the temperature 1.5 K τ reached its maximal value at the exact filling ν = 1 and decreased when ν was altered, yet this maximum vanished when the system was cooled down to 0.5 K. The fractional quantum Hall effect state at the filling of 2/3 was formed at the temperature of 0.5 K, and the development of this state was accompanied by the slowing of the nuclear spin relaxation. This observation suggests the enhancement of energy gap in the spin excitation spectrum of two-dimensional electrons at 2/3 state.
关键词： quantum wells,quantum Hall effect,spin dynamics,electron paramagnetic resonance
更新于2025-09-23 15:23:52
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Short range proximity effect induced by exchange interaction in tunnel-coupled CdTe and (Cd,Mn)Te quantum wells
摘要： The coherent spin dynamics of electrons in tunnel-coupled CdTe and (Cd,Mn)Te quantum wells (QWs) is studied by time-resolved pump-probe Kerr rotation. The coupled QWs have different thicknesses; the narrow one is doped by Mn2+ magnetic ions. A short range proximity effect between them is observed: the Zeeman splitting of electrons in the wide QW is given in addition to the intrinsic electron g factor by the exchange interaction with the Mn2+ ions mediated by electron tunneling into the narrow QW. The exchange interaction strength scales with the Cd0.88Mg0.12Te barrier thickness separating the QWs. The Kerr rotation signal measured on the wide QW shows two close frequencies of electron spin Larmor precession in a transverse magnetic field. These components have very different spin dephasing times, 50 ps and 1 ns. The two frequencies originate from electrons in the wide QW being either part of an exciton or being resident. The proximity effect of the exciton electron is smaller due to the binding by Coulomb interaction, which decreases the tunneling to the narrow well. The experimental data are in good agreement with model calculations.
关键词： Kerr rotation,proximity effect,quantum wells,exchange interaction,spin dynamics
更新于2025-09-23 15:21:01
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Rapid Optical Spin Initialization of a Quantum Dot in the Voigt Geometry Coupled to a Two-Dimensional Semiconductor
摘要： We study the interaction of a quantum dot in the Voigt con?guration with a laser pulse and particularly analyze the potential for rapid spin initialization by putting the quantum dot near a molybdenum disul?de (MoS2) monolayer. The MoS2 monolayer in?uences the spontaneous decay rates of the quantum dot, leading to anisotropically enhanced decay rates, for the quantum dot’s electric dipole moments parallel and perpendicular to the layer. By solving the relevant density matrix equations, we ?nd that high spin initialization ?delity is obtained at short times. The ?delity is signi?cantly higher than when the quantum dot is in free-space vacuum. We examine two different cases of the interaction of the quantum dot with the applied optical ?eld. First, we use a continuous wave laser ?eld and determine for various quantum dot—MoS2 layer distances the ?eld strength that leads to acceptable ?delity levels. The effect of the quality of the MoS2 material on the ?delity of spin initialization is also examined. We also study the interaction of the quantum dot with a laser pulse and apply numerical optimal control to obtain the time-dependent ?eld strength, which leads to maximum ?nal ?delity for short time intervals. The latter approach gives bene?cial results in comparison to the continuous wave ?eld excitation.
关键词： spin initialization,quantum dot,Voigt geometry,optical pumping,Purcell effect,optimal control,spin dynamics
更新于2025-09-23 15:19:57
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Size- and Composition-Dependent Exciton Spin Relaxation in Lead Halide Perovskite Quantum Dots
摘要： The strong spin-orbital coupling in lead halide perovskites allows for facile spin injection for spintronics applications, but on the other hand also limits the lifetime of the injected spins. Full-dimensional confinement of the carriers using quantum dots (QDs) has been envisioned as an effective means to prolong the spin relaxation lifetime and has been explored for II-VI and III-V group QDs. Here we applied this idea to colloidal lead halide perovskite QDs and measured the exciton spin dynamics of QDs of varying sizes and compositions using circularly polarized transient absorption spectroscopy at room temperature. Interestingly, the spin lifetimes of CsPbI3 and CsPbBr3 QDs were prolonged and shortened, respectively, as compared to their bulk counterparts. Both CsPbI3 and CsPbBr3 QDs showed decreasing spin lifetime with decreasing QD size. Possible spin relaxation mechanisms, including those that are unique to these quantum-confined systems, were proposed, with important ramifications for the use of these perovskite QDs in spin-related applications.
关键词： lead halide perovskites,spin-orbital coupling,exciton spin dynamics,circularly polarized transient absorption spectroscopy,quantum dots
更新于2025-09-23 15:19:57
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[IEEE 2019 Compound Semiconductor Week (CSW) - Nara, Japan (2019.5.19-2019.5.23)] 2019 Compound Semiconductor Week (CSW) - Spin-conserved electron transport to InGaAs quantum dots through GaAs/AlGaAs superlattice
摘要： We report on the spin-conserved electron transport to self-assembled InGaAs quantum dots (QDs) through GaAs/AlGaAs superlattice (SL) by circularly polarized time-resolved photoluminescence spectroscopy of the QD excited states with the selective excitation for the SL minibands. The spin transport properties largely depend on the AlGaAs barrier thickness of the SL. The SL with a thinner barrier demonstrates a quantum spin transport to QDs with highly conserving the electron-spin polarization during the transport process through the SL minibands.
关键词： spin transport,superlattice,semiconductor quantum dot,spin dynamics
更新于2025-09-19 17:13:59
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Polarization-sensitive photoresponse of the CuSe/Se nanocomposite prepared by vacuum thermal deposition
摘要： We report on the generation of the polarization-sensitive photocurrent in the thin film of the CuSe/Se nanocomposite irradiated by femtosecond pulses of Ti:S laser. CuSe/Se bilayer consisting of nanocrystalline CuSe and amorphous Se films was obtained using successive deposition of Cu and Se on a glass substrate in the course of vacuum thermal evaporation. Synthesized bilayers were characterized using optical transmittance and Raman spectroscopy, optical, atomic force and scanning electron microscopy and X-ray diffractometry. It is demonstrated that in the longitudinal configuration, the photocurrent propagating along the plane of incidence is maximum for the p- and vanishes for the s-polarized excitation beam. In the transverse configuration, the photocurrent propagating perpendicular to the plane of incidence is an odd function of the polarization azimuth of the linearly polarized excitation beam and vanishes when it is either p- or s-polarized. We show that for an elliptically polarized excitation beam the polarity of the transverse photocurrent reverses when rotation direction of the electric field vector changes. Both longitudinal and transverse photocurrents are odd functions of the angle of incidence and can be explained in terms of the surface photogalvanic effect.
关键词： CuSe,Surfaces and interfaces,Spin dynamics,Electromotive force,Thin film
更新于2025-09-19 17:13:59
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[IEEE 2019 Compound Semiconductor Week (CSW) - Nara, Japan (2019.5.19-2019.5.23)] 2019 Compound Semiconductor Week (CSW) - Effects of growth temperature of a capping layer on excited spin properties of In <sub/>0.5</sub> Ga <sub/>0.5</sub> As quantum dots
摘要： We study effects of growth temperature of a capping layer on optical spin properties of In0.5Ga0.5As quantum dots (QDs) by photoluminescence (PL) spectroscopy including behaviors of the degree of circular polarization (CPD). The PL energy of the ground state shifts to lower energy with decreasing capping growth temperature, which is due to the increase of In composition inside QDs. The temperature dependence of PL intensity from the QD excited states shows the larger thermal activation energy with decreasing capping growth temperature, indicating the suppression of thermal escape of electrons from QDs to barriers. In addition, we observe the lower-energy shift of the CPD spectral peak, associated with decreasing PL energy, where the high CPD values can assure the high quality of these QDs grown with various capping growth temperatures.
关键词： capping layer,quantum dot,spin dynamics
更新于2025-09-11 14:15:04
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Theory of time-resolved Raman scattering in correlated systems: Ultrafast engineering of spin dynamics and detection of thermalization
摘要： Ultrafast characterization and control of many-body interactions and elementary excitations are critical to understanding and manipulating emergent phenomena in strongly correlated systems. In particular, spin interaction plays an important role in unconventional superconductivity, but efficient tools for probing spin dynamics, especially out of equilibrium, are still lacking. To address this question, we develop a theory for nonresonant time-resolved Raman scattering, which can be a generic and powerful tool for nonequilibrium studies. We also use exact diagonalization to simulate the pump-probe dynamics of correlated electrons in the square-lattice single-band Hubbard model. Different ultrafast processes are shown to exist in the time-resolved Raman spectra and dominate under different pump conditions. For high-frequency and off-resonance pumps, we show that the Floquet theory works well in capturing the softening of bimagnon excitation. By comparing the Stokes and anti-Stokes spectra, we also show that effective heating dominates at small pump fluences, while a coherent many-body effect starts to take over at larger pump amplitudes and frequencies on resonance to the Mott gap. Time-resolved Raman scattering thereby provides the platform to explore different ultrafast processes and design material properties out of equilibrium.
关键词： thermalization,Hubbard model,spin dynamics,correlated systems,time-resolved Raman scattering,Floquet theory
更新于2025-09-09 09:28:46
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Ultrafast electron and spin dynamics of strongly correlated NdNiO <sub/>3</sub>
摘要： Electron and spin dynamics of strongly correlated NdNiO3 are investigated across the metal–insulator transition with ultrafast optical spectroscopy at different temperatures, pump laser fluences, and laser polarizations. Transient differential reflectivity measurements on the insulating phase NdNiO3 show two characteristic electronic decay processes. The slow decay process, strongly dependent on coherent phonon excitation, is attributed to the electron–phonon interaction, while the fast decay process, to the electron-spin interaction. The temporal evolution of Kerr rotation reveals that net spin polarization can be induced by circularly polarized light in insulating NdNiO3 via electron excitation from the Ni t?2g to e?g orbital, and two net spin polarizations with opposite directions are observed given the antiferromagnetic ordering in insulating NdNiO3. At the insulator-to-metal transition, the transient differential reflectivity reverses its sign; the metallic phase NdNiO3 also shows two characteristic electronic decay processes, a typical metallic decay processes and a slow decay process; the slow decay process is attributed to the interaction between electrons and the low frequency coherent phonons (～2.45 THz). Our experiments demonstrate that the phase transition involves several processes upon continuous heating: the electron-spin interaction disappears at 9 K below the transition temperature; at the transition temperature, NdNiO3 transitions into the metallic phase and the antiferromagnetic ordering transitions into the paramagnetic ordering; at the transition temperature, the structure of NdNiO3 changes from a monoclinic structure ( P21/n) to a high temperature orthorhombic ( Pbmn) structure. Such a structure change results in the change in phonon vibrations, and subsequently, leads to the disappearance of the electron–phonon interactions due to the insulating phase NdNiO3 and the emergence of other types of electron–phonon interactions due to the metallic phase.
关键词： time-resolved Kerr rotation measurements,electron and spin dynamics,femtosecond transient reflectivity measurement,polymer-assisted deposition,strongly correlated oxide NdNiO3
更新于2025-09-09 09:28:46