Research Topics
THz-frequency Magnons and Chiral Phonons in the Ferromagnetic Weyl Semimetal Co3Sn2S2
Kagome lattice provides a rich platform for exploring novel quantum states, emerging from the interplay between its frustrated corner-sharing triangular geometry and intriguing electronic structure. Co3Sn2S2 is a kagome lattice ferromagnet, exhibiting a unique interplay between its electronic wavefunction topology and magnetic spin configuration. This interaction results in several intriguing properties, including Weyl points, a colossal anomalous Hall effect, and a pronounced magneto-optical response. These properties collectively make Co3Sn2S2 a rich platform for exploring novel quantum phenomena and potential applications in spintronics and novel electronic devices.
1. Terahertz-frequency orbitally-coupled magnons in the kagome ferromagnet
In ferromagnetic materials, magnons - quanta of spin waves - typically resonate in the gigahertz range. Beyond conventional magnons, while theoretical studies have predicted magnons associated with orbital magnetic moments, their direct observation has remained challenging.
In this work, we studied coherent magnon dynamics in Co3Sn2S2 using time-resolved magneto-optical Kerr effect spectroscopy combined with in-plane strong magnetic fields and low temperatures. To our surprise, we directly observe two magnon modes in the terahertz range in the time domain (Fig. a,b). These frequencies exceed typical ferromagnetic resonance frequencies by 1-2 orders of magnitude, originating from its strong magnetic crystalline anisotropy.
The observation of two magnon modes is particularly intriguing, while only one coherent acoustic mode (Fig. c) is detectable in our experiment if only spin magnetic moment is considered. To investigate the origins of these two high-frequency magnon modes, we systematically varied the temperature and magnetic field, conducting thorough measurements and analyses. When we fitted the data to the Kittel equation of ferromagnetic resonance, we found that each mode is characterized by unique g-factors which notably deviate from the anticipated spin g-factor of 2. This surprising finding suggests that the observed magnon modes likely arise from the interplay between spin and orbital magnetic moments, facilitated by the strong spin-orbit coupling of Co3Sn2S2. To elucidate these findings, we proposed that these dual modes emerge from the low-energy collective excitations of coupled spin and orbit magnetic moments in the ferromagnetic ordered state (Fig. c,d). Although the orbital magnetic moment is small, it is the strong spin-orbit coupling that hybridizes the motions of spin and orbit magnetic moments, rendering the orbital magnons observable.
These findings unveil a novel category of magnons in a ferromagnet stemming from orbital magnetic moments, and position Co3Sn2S2 as a promising candidate for high-speed terahertz spintronic applications.
This work was in collaboration with Profs. Guang-Ming Zhang (Tsinghua), Zhe Yuan Group (Fudan), Yugui Yao Group (BIT), Enke Liu Group (IOP) and Zhiwei Wang Group (BIT).
2. Magnetic order induced chiral phonons
Chiral phonons are vibrational modes in a crystal that possess a well-defined handedness or chirality. They arise in systems that lack either inversion symmetry or time-reversal symmetry. Chiral phonons have been observed in materials with broken inversion symmetry, such as monolayer WSe2 and various chiral crystals. In systems where time-reversal symmetry is broken, external magnetic fields are typically necessary to induce energy splitting between chiral phonons of opposite handedness. Research exploring the intricate correlations between magnetic order and chiral phonons is still at an early stage.
Here we report the discovery of chiral phonon modes in Co3Sn2S2, a material that preserves inversion symmetry but breaks time-reversal symmetry. Using helicity-resolved magneto-Raman spectroscopy, we observe the spontaneous splitting of the doubly degenerate in-plane Eg modes into two distinct chiral phonon modes of opposite helicity when the sample is zero-field cooled below the Curie temperature (Fig. a,b), in the absence of an external magnetic field. When the magnetization is switched by the external out-of-plane magnetic field, the sign of the splitting switches (Fig. c). As we sweep the out-of-plane magnetic field, this Eg phonon splitting exhibits a well-defined hysteresis loop directly correlated with the material’s magnetization (Fig. d,e). The observed spontaneous splitting reaches up to 1.27 cm-1 at low temperatures, progressively diminishes with increasing temperature, and completely vanishes near the Curie temperature. Our findings highlight the role of the magnetic order in inducing chiral phonons, paving the way for novel methods to manipulate chiral phonons through magnetization and vice versa.
This work was in collaboration with Profs. Tiantian Zhang Group (IOTP), Feng Jin Group (IOP), Enke Liu Group (IOP) and Wanjun Jiang Group (Tsinghua).
References:
1. Discovery of terahertz-frequency orbitally-coupled magnons in a kagome ferromagnet.
Mengqian Che, Weizhao Chen, Maoyuan Wang, F. Michael Bartram, Liangyang Liu, Xuebin Dong, Jinjin Liu, Yidian Li, Hao Lin, Zhiwei Wang, Enke Liu, Yugui Yao, Zhe Yuan, Guang-Ming Zhang* and Luyi Yang*
Science Advances 11, eadw1182 (2025).
2. Magnetic order induced chiral phonons in a ferromagnetic Weyl semimetal.
Mengqian Che, Jinxuan Liang, Yunpeng Cui, Hao Li, Bingru Lu, Wenbo Sang, Xiang Li, Xuebin Dong, Le Zhao, Shuai Zhang, Tao Sun, Wanjun Jiang, Enke Liu, Feng Jin, Tiantian Zhang*, Luyi Yang*
Physical Review Letters 134, 196906 (2025).
Low-energy Collective Excitations in the Two-dimensional Antiferromagnet MnBi2Te4
The marriage between topology and magnetism can give birth to many exotic quantum phases and phenomena such as quantum anomalous Hall effect and axion electrodynamics. Recently, few-layer MnBi2Te4 crystals have emerged as a new platform for exploring these phases. We study ultrafast dynamics of low-energy collective excitations in this new class of two-dimensional (2D) topological magnetic material.
1. Ultrafast coherent interlayer phonon dynamics
In 2D van der Waals (vdW) materials, lattice vibrations, especially interlayer phonon modes, have not only provided unique capabilities in determining layer thickness, stacking order, and interface coupling strength, but have also played an important role in engineering novel electronic, thermal and magnetic properties in 2D vdW homo/heterostructures.
In this work, we report ultrafast optical pump-probe reflectivity measurements in few-layer MnBi2Te4, accompanied by ultralow frequency Raman data, of carrier and coherent interlayer phonon dynamics as a function of sample thickness, with the layer number varying from 4 to 25. Pronounced coherent phonon oscillations from the interlayer breathing mode are directly observed in the time domain. We find that the coherent oscillation frequency (50-300 GHz), the photocarrier and coherent phonon decay rates all depend sensitively on the sample thickness. The time-resolved measurements are complemented by ultralow-frequency Raman spectroscopy measurements, which both confirm the interlayer breathing mode and additionally enable observation of the interlayer shear mode.
These measurements not only uncover the interlayer coupling strengths but also provide crucial information on coherent phonon and carrier lifetimes and relaxation mechanisms. Our studies also pave the way for future light-driven topological and magnetic orders in few-layer topological magnetic materials, and ultrafast studies of nonequilibrium magnetic dynamics and nonequilibrium axion dynamics.
This work was in collaboration with Profs. Ping-Heng Tan Group (IOS, CAS), Jinsong Zhang Group (Tsinghua), Pu Yu Group (Tsinghua) and Yang Wu Group (Tsinghua).
2. Ultrafast magnetization and coherent magnon dynamics
Atomically thin van der Waals magnetic materials have not only provided a fertile playground to explore basic physics in the two-dimensional limit but also created vast opportunities for novel ultrafast functional devices.
In this work, we systematically investigate ultrafast magnetization dynamics and spin wave dynamics in few-layer topological antiferromagnetic MnBi2Te4 crystals as a function of layer number, temperature, and magnetic field. We observe laser-induced (de)magnetization processes that can be used to accurately track the distinct magnetic states in different magnetic field regimes, including showing clear odd-even layer number effects. In addition, strongly field-dependent antiferromagnetic magnon modes with tens of gigahertz frequencies are optically generated and directly observed in the time domain. Surprisingly, the magnetic state dependence and magnons are observed not only in time-resolved Kerr rotation and but also in time-resolved reflectivity measurements, indicating a strong correlation between the magnetic state and the electronic structure.
These measurements present the first comprehensive overview of ultrafast spin dynamics in this novel 2D antiferromagnet, paving the way for potential applications in 2D antiferromagnetic spintronics and magnonics as well as further studies of ultrafast control of both magnetization and topological quantum states.
This work was in collaboration with Profs. Shuo Yang Group, Yong Xu Group, Jinsong Zhang Group, Pu Yu Group and Yang Wu Group .
References:
1. Ultrafast coherent interlayer phonon dynamics in atomically thin layers of MnBi2Te4.
F. Michael Bartram, Yu-Chen Leng, Yongchao Wang, Liangyang Liu, Xue Chen, Huining Peng, Hao Li, Pu Yu, Yang Wu, Miao-Ling Lin, Jinsong Zhang, Ping-Heng Tan and Luyi Yang*
npj Quantum Materials 7, 84 (2022).
2. Real-time observation of magnetization and magnon dynamics in a two-dimensional antiferromagnet MnBi2Te4.
F. Michael Bartram#, Meng Li#, Liangyang Liu, Zhiming Xu, Yongchao Wang, Mengqian Che, Hao Li, Yang Wu, Yong Xu, Jinsong Zhang, Shuo Yang and Luyi Yang*
Science Bulletin 68, 2734-2742 (2023).
3. Fabrication-induced even-odd discrepancy of magnetotransport in few-layer MnBi2Te4.
Yaoxin Li, Yongchao Wang, Zichen Lian, Hao Li, Zhiting Gao, Liangcai Xu, Huan Wang, Rui’e Lu, Longfei Li, Yang Feng, Jinjiang Zhu, Liangyang Liu, Yongqian Wang, Bohan Fu, Shuai Yang, Luyi Yang, Yihua Wang, Tianlong Xia, Chang Liu, Shuang Jia, Yang Wu, Jinsong Zhang, Yayu Wang, and Chang Liu
Nature Communications 15, 3399 (2024).
Spin Dynamics and Exciton Transport in Metal Halide Perovskites
Over the past decade, metal halide perovskites have garnered great attention for their superior optoelectronic properties and high performance in solar cells and light-emitting devices. In addition, they are also a promising class of materials for semiconductor spintronics.
1. Spin dynamics
In metal halide perovskites, efficient spin injection has been demonstrated through optical pumping methods (Fig. a), and long spin coherence times from hundreds of picoseconds to over one nanosecond have been observed at cryogenic temperatures. However, most research of spin physics in perovskite semiconductors has been focusing on conventional lead-based systems. Their tin-based counterparts, which were synthesized recently with reasonably high quality, also provide a fertile playground to explore spin properties. Moreover, a complete understanding of the thermal evolution of the bandgap and the spin relaxation is still lacking.
Using time-resolved Faraday rotation spectroscopy combined with optical absorption and photoluminescence, we systematically studied ultrafast spin coherence, spin relaxation and bandgap revolution with temperature in two hybrid organic-inorganic perovskites MA0.3FA0.7PbI3 and MA0.3FA0.7Pb0.5Sn0.5I3 (abbreviated as Pb- and PbSn-perovskites). We observed contrasting spin lifetimes between the two samples (Fig. b), suggesting that the spin relaxation is likely due to scattering with defects via the Elliot-Yafet mechanism at low temperatures and the spin decoherence suffers from g-factor inhomogeneity due to impurities and vacancies. By measuring carrier spin lifetimes at elevated temperatures, we specify possible roles of defects and phonons in the spin relaxation channels. Temperature-dependent experiments show drastic changes of both electron and hole Landé g-factors (Fig. c,d). We propose that this effect is dominated by the enhancement of dynamic lattice distortions (lattice vibrations) with increasing temperature (Fig. e,f), resulting in strong modifications of not only the bandgap but also the interband transition matrix and the spin-orbit splitting gap. These results lay the foundation for further design and use of lead- and tin-based perovskites for spintronic applications.
This work was in collaboration with Prof. Hairen Tan group (Nanjing Univ.) and Yong Xu Group (Tsinghua).
2. Exciton transport
Photogenerated carrier transport and recombination in metal halide perovskites are critical to device performance. Despite considerable efforts, sample quality issues and measurement techniques have limited the access to their intrinsic physics. To date, a clear understanding of the transport properties in halide perovskites remains elusive, and the contributions from different phonon modes have yet to be fully delineated.
In this work, by utilizing high-purity CsPbBr3 single crystals and contact-free transient grating spectroscopy, we directly monitor exciton diffusive transport from low temperature to room temperature. Fig. a shows the exciton diffusion coefficient and diffusion length extracted from transient grating measurements. We converted the diffusion into an effective exciton mobility (μ) using the Einstein relation. As the temperature (T) increases, the mobility decreases rapidly below 100 K with a μ~T-3.0 scaling, and then follows a more gradual μ~T-1.7 trend at higher temperatures (Fig. b). First-principles calculations perfectly reproduce this experimental trend and reveal that optical phonon scattering governs carrier mobility shifts over the entire temperature range, with a single longitudinal optical mode dominating room-temperature transport. Our findings unambiguously resolve previous theory-experiment discrepancies, providing benchmarks for future optoelectronic design.
This work was in collaboration with Prof. Qihua Xiong group (Tsinghua), Sheng Meng Group (IOP) and Ping-Heng Tan Group (IOS).
References:
1. Spin coherence and spin relaxation in hybrid organic-inorganic lead- and mixed lead-tin-perovskites.
Haochen Zhang, Zehua Zhai, Zhixuan Bi, Han Gao, Meng Ye, Yong Xu, Hairen Tan, Luyi Yang*
Nano Letters 23, 7914–7920 (2023).
2. Revealing unusual bandgap shifts with temperature and bandgap renormalization effect in phase-stabilized metal halide perovskite thin films.
Haochen Zhang#, Zhixuan Bi#, Zehua Zhai#, Han Gao, Meng Ye, Xuanzhang Li, Haowen Liu, Yuegang Zhang, Hairen Tan*, Yong Xu*, and Luyi Yang*
Advanced Functional Materials 34, 2302214 (2024).
3. Intrinsic exciton transport and recombination in single-crystal lead bromide perovskite.
Zhixuan Bi, Yunfei Bai, Ying Shi, Tao Sun, Heng Wu, Haochen Zhang, Yuhang Cui, Danlei Zhu, Yubing Wang, Miao-Ling Lin, Yaxian Wang, Dongxin Ma, Ping-Heng Tan, Sheng Meng*, Qihua Xiong*, Luyi Yang*
ACS Nano 19, 19989-20000 (2025).
Magneto-optical Kerr Effect in Ferromagnetic SrRuO3 Thin Films
SrRuO3 is a canonical spin-orbit coupled ferromagnet, which is of great interest in incorporating magnetic functionality into oxide devices.
1. Control of magnetism by ionic liquid gating in SrRuO3 thin films
In this work, we demonstrated that the magnetic properties in ferromagnetic SrRuO3 thin films can be controlled by ionic liquid gating (ILG). ILG is a cutting-edge technique for accumulating large carrier densities at a surface. However, it is technically challenging to perform optical measurements at cryogenic temperatures with this technique. We overcame all the experimental challenges and did systematic MOKE studies of ionic liquid gated samples. We showed an efficient and reversible control of an exotic ferromagnetic to paramagnetic phase transition via ILG. We envision that electric-field controlled protonation opens up a pathway to explore novel electronic states and material functionalities in protonated material systems. This work was in collaboration with Prof. Pu Yu's group.
2. Anomalous Kerr signals in SrRuO3 thin films
There has been considerable recent activity in understanding the anomalous Hall effect (AHE) in SrRuO3 which exhibits strange “bumps” upon traversing the magnetic hysteresis loop. In particular, a lively debate over the past year on the origin of such “bumps” has led to two alternative explanations: a two-channel model where two distinct magnetic regions occur with slightly different AHE hysteresis loops, or a topological skyrmion model with an additional real space Berry curvature contribution to the Hall effect.
Our work presents the very first observation of a related anomaly in the optical frequency regime (the magneto-optical Kerr signal) for thin films of SrRuO3. In contrast to previous work, our samples (30 nm to 200 nm thick) are far from the ultrathin limit, so the interfacial Dzyaloshinskii-Moriya interaction, skyrmions, and atomic layer inhomogeneities, are not expected to play an important role. Remarkably, even in this regime, we discover bump-like anomalies in the MOKE signal over wide ranges of temperature, magnetic field, and frequencies, while the magnetization exhibits normal square-like hysteresis loops. Significantly, this observation contradicts the well-established lore that the polar Kerr rotation is linearly proportional to the macroscopic magnetization in ferromagnetic thin films. We also provide a concrete and semi-quantitative theoretical explanation of our data which has been lacking thus far for the AHE.
This work was in collaboration with Prof. Pu Yu's group and Prof. Arun Paramekanti's group (UofT).
References:
1. Reversible manipulation of the magnetic state in SrRuO3 through electric-field controlled proton evolution.
Zhuolu Li#, Shengchun Shen#, Zijun Tian#, Kyle Hwangbo#, M. Wang, Y. Wang, F. Michael Bartram, Liqun He, Y. Lyu, Y. Dong, G. Wan, H. Li, N. Lu, J. Zang, H. Zhou, E. Arenholz, Q. He, Luyi Yang*, Weidong Luo* & Pu Yu*
Nature Comm. 11, 184 (2020).
2. Anomalous Kerr effect in SrRuO3 thin films.
F. Michael Bartram#, Sopheak Sorn#, Zhuolu Li#, Kyle Hwangbo, Shengchun Shen, Felix Frontini, Liqun He, Pu Yu*, Arun Paramekanti*, and Luyi Yang*
Phys. Rev. B 102, 140408(R) (2020).
3. Resonant optical topological Hall conductivity from skyrmions.
Sopheak Sorn, Luyi Yang and Arun Paramekanti
Phys. Rev. B 104, 134419 (2021)
Spin and valley dynamics in atomically-thin semiconductors
The recently-discovered monolayer MoS2 and related atomically-thin transition metal dichalcogenides (TMDs) are analogous to graphene in that they are 2D materials with hexagonal honeycomb structure, but with an extremely important difference:unlike graphene, TMDs possess a semiconductor bandgap. This makes TMDs useful for a variety of opto-electronic applications, including solar applications, light-emitting diodes, and semiconductor electronics, spintronics, and valleytronics. For example, besides the real electron spin, information can also be encoded in the “valley pseudospin”, i.e. whether the electron resides in the K or K’ valley of the materials’ hexagonal Brillouin zone (or, a quantum superposition of K and K’). Although a robust valley degree of freedom in TMDs has been inferred from photoluminescence (PL) experiments, the exploration of spin-valley coupled dynamics and decoherence of resident electrons in electron-doped material is still at a very early stage.
We directly probed the coupled spin and valley dynamics in electron- (or hole-) doped monolayer MoS2 and WSe2 using techniques based on optically-induced Kerr rotation spectroscopy. In contrast to PL studies, these techniques directly probe the spin and valley polarizations of electrons alone (rather than excitons), which can persist long after recombination with photoexcited holes. Using these Kerr-effect methods, we directly and unambiguously measured very long intrinsic electron spin relaxation timescales ns-μs, which is 2-6 orders of magnitude longer than the exciton recombination time. Measurements as a function of applied magnetic fields indicate that electrons ‘see’ a strong effective magnetic field due to the large spin-orbit coupling in these 2D materials, and that electrons undergo rapid intervalley scattering between the K and K’ valleys of the materials’ hexagonal Brillouin zone. Additionally, a long-lived oscillatory signal is observed at lower energies, indicating that some electrons are localized and exhibit robust spin coherence. These studies provide direct insight into the intrinsic physics underpinning spin and valley dynamics of resident electrons in TMDs.
References:
1. Long-lived nanosecond spin relaxation and spin coherence of electrons in monolayer MoS2 and WS2.
Luyi Yang, N. A. Sinitsyn, W. Chen, J. Yuan, J. Zhang, J. Lou, and S. A. Crooker
Nature Physics 11, 830 (2015).
2. Spin coherence and dephasing of localized electrons in monolayer MoS2.
Luyi Yang, W. Chen, K. M. McCreary, B. T. Jonker, J. Lou and S. A. Crooker
Nano Letters 15, 8250 (2015).
3. Gate controlled spin-valley locking of resident carriers in WSe2 monolayers.
P. Dey, Luyi Yang, C. Robert, G. Wang, B. Urbaszek, X. Marie, S. A. Crooker
Phys. Rev. Lett. 119, 137401 (2017).
"Listen" to spin fluctuations
In magnetic systems, fundamental noise can exist in the form of intrinsic and random spin fluctuations. Passively “listening” to these fluctuations using sensitive optical magnetometry forms the basis of spin noise spectroscopy (SNS), wherein dynamic properties about the system (such as relaxation and coherence times) are inferred from the noise alone while in thermal equilibrium. The fluctuation-dissipation theorem supports this approach.
1. Two-color spin noise spectroscopy: Using spin fluctuation correlations to reveal homogeneous linewidths within quantum dot ensembles
Inhomogeneous broadening is ubiquitous in the sciences, occurring whenever a collection of nominally-equivalent constituents differ in, e.g., size, shape, or composition. However, the homogeneous linewidth γh is usually the quantity of interest, since γh reveals coherence times. Unfortunately, γh is generally inaccessible in inhomogenously-broadened ensembles using conventional low-power/linear optical spectroscopic techniques. Single-particle or non-linear methods are typically required. Here we develop a novel low-power technique – two-color spin noise spectroscopy – to reveal the underlying γh of singly-charged (In,Ga)As quantum dots (QD) in an otherwise inhomogeneously-broadened QD ensemble. (Quantum dots are nanometer-scale, “zero-dimensional” materials useful for electronics, photonics, and potential quantum computing applications.)
As the name suggests, two-color spin noise spectroscopy utilizes two different probe lasers to measure spin fluctuations at different wavelengths. Correlations between these two fluctuation signals form the basis for this new methodology. When the two lasers have the same wavelength, they are sensitive to the same quantum dots in the ensemble and their spin fluctuation signals are correlated. In contrast, two lasers that are widely detuned from each other measure different subsets of quantum dots, leading to uncorrelated fluctuations. Measuring the noise correlation versus laser detuning directly reveals the quantum homogeneous linewidth even in the presence of a strong inhomogeneous broadening.
2. Two-color spin noise spectroscopy: Cross-correlation spin noise spectroscopy of interacting multi-component spin systems
Interacting multi-component spin systems are ubiquitous in semiconductor spintronics; e.g. carrier-mediated ferromagnetism in magnetic semiconductors, or electronic spin coupling to nuclear spin baths. Traditionally, inter-species spin interactions are studied by experimental methods that are necessarily perturbative: e.g., by intentionally polarizing or depolarizing one spin species and detecting the response of the other(s).
We show that multi-probe spin noise spectroscopy can reveal interspecies spin-spin interactions – under conditions of strict thermal equilibrium – by cross-correlating the stochastic fluctuation signals exhibited by each of the constituent spin species. As a proof of principle, we compare the results with an experimental study of a well-understood interacting spin system – a mixture of warm Rb and Cs vapors – by applying the two-color spin noise spectroscopy. Noise correlations directly reveal the presence of inter-species spin exchange interactions.
These non-invasive and noise-based techniques also hold promise for studies of correlations in interacting systems, such as coupled quantum dot or nanocrystal systems, or spin interactions in chemical and biological systems. Advanced optical measurement methods combined with effects of magnetic fields and manipulation of spins in solids could lead toward new physics with potential applications in energy security and information processing technology.
References:
1. Two-colour spin noise spectroscopy and fluctuation correlations reveal homogeneous linewidths within quantum-dot ensembles.
Luyi Yang, P. Glasenapp, A. Greilich, D. Reuter, A. D. Wieck, M. Bayer, D. R. Yakovlev, and S. A. Crooker
Nature Comm. 5, 4949 (2014).
2. Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems.
D. Roy, Luyi Yang, S. A. Crooker, and N. A. Sinitsyn
Sci. Rep. 5, 9573 (2015).
Spin propagation in a two-dimensional electron gas
In this work, we developed a powerful new optical technique, Doppler spin velocimetry, for probing the motion of spin polarization. This technique is capable of resolving displacements of spin polarization at the level of 1 nm on a picosecond time scale. We applied this technique to measure the motion of a current-driven persistent spin helix, which is a spin texture that can be formed in GaAs quantum wells in the presence of spin-orbit coupling. In the experiments a periodic wave of spin is photoinjected into a two-dimensional electron gas (2DEG) drifting under the influence of an in-plane electric field. Transfer of momentum from the propagating electron sea pushes the spin density wave (SDW) along. To measure the resulting velocity, we detected the Doppler shift of light that is diffracted from the SDW.
Measuring the Doppler shift of light from moving SDWs allowed us to report several surprising aspects of the basic physics that underlies spin propagation in a 2DEG. All of these results are highly relevant to the development of spin logic devices – some with quite favourable implications while others pose challenges that need to be faced and overcome. In the latter category, we discovered that coherent spin precession within a propagating SDW is lost at temperatures near 150 K. This finding is critical to understanding why room temperature operation of devices based on electrical gate control of spin current has so far remained elusive. On the favourable side, at all temperatures, electron spin polarization co-propagates with the high-mobility electron sea, even when this requires an unusual form of separation of spin density from photoinjected electron density. Furthermore, although the spin packet co-propagates with the 2DEG, spin diffusion is strongly suppressed by electron-electron interactions, leading to remarkable resistance to diffusive spreading of the drifting pulse of spin polarization.
References:
1. Doppler velocimetry of spin propagation in a two-dimensional electron gas.
Luyi Yang, J. D. Koralek, J. Orenstein, D. R. Tibbetts, J. L. Reno, and M. P. Lilly
Nature Physics 8, 153 (2012).
2. Coherent propagation of spin helices in a quantum-well confined electron gas.
Luyi Yang, J. D. Koralek, J. Orenstein, D. R. Tibbetts, J. L. Reno, and M. P. Lilly
Phys. Rev. Lett. 109, 246603 (2012).
3. Measurement of electron-hole friction in an n-doped GaAs/AlGaAs quantum well using optical transient grating spectroscopy.
Luyi Yang, J. D. Koralek, J. Orenstein, D. R. Tibbetts, J. L. Reno, and M. P. Lilly
Phys. Rev. Lett. 106, 247401 (2011).
4. Random walk approach to spin dynamics in a two-dimensional electron gas with spin-orbit coupling.
Luyi Yang, J. Orenstein, and D.-H. Lee
Phys. Rev. B 82, 155324 (2010).
