第八届全国理论磁学会议

1. 第八届全国理论磁学会议 那日苏 荣建红 武晓霞 2005. 9. 30

2. Outline Introduction Recent Hot summery

3. Introduction 会议主要目的及内容： 旨在交流我国磁学理论研究方面的最新成果，探讨在磁学理论研究方面的新思想和新方法，推动我国磁学理论的进一步发展。会议安排了若干邀请报告介绍国内外磁学研究新进展。 • 会议日期：2005年7月22日—26日 • 主办单位：中国物理学会磁学专业委员会 • 承办单位：山西大学 • 会议地点：太谷梅苑山庄 邀请报告21个，16个口头报告。

4. 主题： • 1. 磁性量子理论和宏观量子现象 5 个报告 • 2. 自旋相关输运理论和自旋流 16个报告 • 3. 磁性纳米结构及低维磁性 7 个报告 • 4. 磁性第一原理计算与磁性材料计算模拟 6个报告

5. 会议顾问委员会： • 都有为 南京大学物理系 • 戴道生 北京大学物理系 • 金晓峰 复旦大学物理系 • 詹文山 中科院理化研究所 • 李伯臧 中科院物理研究所 • 李正中 南京大学物理系 • 林宗涵 北京大学物理系 • 梅良模 山东大学物理系 • 沈保根 中科院物理研究所 • 陶瑞宝 复旦大学物理系 • 杨应昌 北京大学物理系 • 姚凯伦 华中理工大学物理系 • 翟宏如 南京大学物理系

6. Recent Hot Spin electronics Electron + Charge Spin Microelectronics spintronics Spin dependent scattering Spin relaxation and spin dephasing are processes that lead to spin equilibration and are thus of great importance for spintronics. Dissipationless Spin current S.A. Wolf Science 294, (2001) 1488

7. Recent Hot • Electronic logic devices used charge property. • Energy scale for charge interaction is order of eV, energy scale for spin interaction is order of meV. • Spin-based electronic promises a logicoperations with much lower power consumption thanequivalent charge based logic operations. • Spin-based electronics promises a greater integration between logic and storage devices.

8. Recent Hot

9. Recent Hot Rev.Mod.Phys.76(2004)323-410

10. Recent Hot 1. Giant Magnetoresistance GMR Data density 170 Gbit/inch2

11. Recent Hot GMR效应的机理在于自旋极化电子在其相干长度范围内 在不同自旋取向膜层有不同的散射几率, 即不同的电阻。

12. Recent Hot 2. Tunneling Magnetoresistance TMR ‘0’ ‘1’ ‘1’ ‘0’ MRAM 256 Kbit Motorola S.A. Wolf Science 294, (2001) 1488

13. Spin polarized electron tunneling Magnon Phonon Temperature and bias voltage will reduce the Magnetoresistance. Cond-mat / 0405528 v1

14. Magnetic random access memory BL WWL MTJ GND RWL

15. 3. Spintronics devices In the spin FET, both the source and the drain are ferromagnetic. The source sends spin-polarized electrons into the channel, and this spin current flows easily if it reaches the drain unaltered (top). A voltage applied to the gate electrode produces an electric field in the channel, which causes the spins of fast-moving electrons to precess, or rotate (bottom). The drain impedes the spin current according to how far the spins have been rotated. Flipping spins in this way takes much less energy and is much faster than the conventional FET process of pushing charges out of the channel with a larger electric field. Appl. Phys. Lett. 56, 665–667,1990.

16. Spin diodes Magnetic bipolar transistor Phys. Rev.Lett. 88, 066603.2002

17. 4.Spin Hall Effect and Dissipationless Spin Current Spin Hall Effect PRL 83, 1834 (1999)

18. Dissipationless Spin Current Shou-Cheng ZhangScience 294, 823 (2001); 301, 1348 (2003)

19. Spin current - Dissipationless and arrow of time Charge current, broken time-reversal symmetry, dissipative transport Spin current , time-reversal symmetric, dissipationless transport. Ballistic, persistent or super-current 动画来自刘伍明研究员的报告

20. Experimental setup for detecting spin current

21. Intrinsic Spin Hall Effect A new effect in semiconductor spintronics that leads to dissipation less spin currents in paramagnetic spin-orbit coupled systems. In a high-mobility two-dimensional electron system with substantial Rashba spin-orbit coupling, a spin current that flows perpendicular to the charge current is intrinsic. In the usual case where both spin-orbit split bands are occupied, the intrinsic spin-Hall conductivity has a universal value for zero quasiparticle spectral broadening. PRL 92, 126603 (2004)

22. ？？？ (1) Is it the spin current is ill defined? Will the intrinsic spin Hall effect exactly cancelled by the intrinsic orbital-angular-momentum Hall effect? (2)

23. The spin-Hall effect predicted in [1,2] is fundamentally different from the extrinsic spin-Hall [4,5] effect due to Mott-type skew scattering by impurities. The intrinsic spin-Hall effect arises from the spin-orbit coupling of the host semiconductor band and has a finite value in the absence of impurities, while the extrinsic spin-Hall effect arises purely from the spin-orbit coupling to the impurity atoms; it is not a bulk effect like the ordinary Hall effect and its magnitude is typically many orders of magnitude smaller. The issue of impurity contributions to the spin-Hall effect has been intensively investigated theoretically. Remarkably, the authors of [6] calculated the vertex corrections due to impurity scattering in the Rashba model of the electron band in the context of the spin-Hall effect (other groups had also computed the vertex correction earlier [7,8]) and found that the vertex correction completely cancels the spin-Hall effect [9–11]. On the other hand, a number of numerical calculations show the spin-Hall effect independent of the disorder in the weak disorder limit [12,13]. The problem of the vertex correction does not occur in the Luttinger model of the hole band [14]. In fact, the vertex correction is identically zero, rendering the original prediction of [1] exact in the clean limit. Other work [15] claims that the spin accumulation at the edge of the sample due to spin current vanishes, due to the spin torque term that shows up in the transport equations. Their analysis is entirely in the ground state of the system (not in the presence of electric field) and also assumes no spin relaxation which is crucial to obtaining edge spin accumulation. PRL 95, 016801 (2005)

24. Persistent spin current in spin ring Spinon transport Quasi-classical picture of a spin-triplet excitation Quasi-classical picture of a spin-singlet excitation PRL 95, 066807 (2005)

25. Solid state quantum computation Quantum bits Science 294, 823 (2001); 301, 1348 (2003)

26. 4. Summary • New type of dissipationless quantum spin transport at room temperature. • Intrinsic spin injection in spintronics. • Spin injection without magnetic field or ferromagnet. • Spins created inside semiconductor, no issues withInterface. • Room temperature injection. • Quantum computation

27. Thanks for your attention