超晶格與異質結構的自旋與軌道角動量之霍爾效應

Spin and Orbital Angular Momentum Hall Effect in Superlattice and Heterostructure

陳宗緯(Tsung-Wei Chen)

指導教授 ： 郭光宇

國立臺灣大學/理學院/物理研究所/博士(2007年)

https://doi.org/10.6342/NTU.2007.02861

摘要

考慮Rashba-Dresselhaus自旋軌道耦合效應的高遷移率之二維電子系統， 我們做了自旋與軌道角動量的霍爾效應之理論研究。 在研究自旋與軌道角動量流時， 我們引進了自旋矩與軌道矩的修正項。 我們發現到當兩個能帶皆佔據時， 自旋霍爾電導率仍然是一個常數 (也就是與載子的濃度無關)。 而且加入修正項之後， 所得出來的值與先前計算的結果相差一個負號。 自旋霍爾電導率一般來說在Rashba-Dresselhaus 系統下是無法互相抵消的。 軌道霍爾電導率也與載子濃度無關， 但是與Rashba 跟 Dresselhaus自旋耦合強度的比值有關。 這意謂我們可以藉由調整閘極電壓而改變總角動量霍爾效應的大小。 我們注意到， 在 Rashba 系統之下， 由於總角動量守恆， 所以軌道霍爾電導率會消除自旋霍爾電導率的貢獻。 但是由於電子的磁偶級矩是軌道的兩倍， 所以我們認為自旋仍可在邊界上造成累積而磁化。 我們也討論了由電場引發的軌道角動量流的來源。 最後我們也發現了自旋與軌道角動量電導率與 Berry 相位的緊密關係。 此研究已經發表在 Phys. Rev. B. 73, 235309 (2006)。

對於氮化銦鎵/氮化鎵(InGaN/GaN) 的超晶格系統， 我們計算了自旋霍爾電導率。 我們發現可以藉由調整由應變引起的內建電場的大小來調整自旋霍爾流。 計算結果顯示， 自旋霍爾電導率定性上與實驗吻合。 此研究已經發表在 Phys. Rev. Lett. 98, 136403 (2007)。

關鍵字

自旋霍爾效應 ； 軌道角動量霍爾效應 ； 自旋軌道耦合效應 ； 壓電效應 ； 氮化銦鎵/氮化鎵 ； 異質結構 ； 超晶格

並列摘要

The spin and orbital angular momentum (OAM) Hall effect in a high
mobility two-dimensional electron system with Rashba and
Dresselhuas spin-orbit coupling has been studied theoretically. We
introduce both the spin and OAM torque corrections, respectively,
to the spin and OAM currents. We find that when both bands are
occupied, the spin Hall conductivity is still a universal constant
(i.e., independent of the carrier density) which, however, has an
opposite sign to the previous value. The spin Hall conductivity in
general would not cancel the OAM Hall conductivity in
Rashba-Dresselhaus system. The OAM Hall conductivity is also
independent of the carrier density but depends on the strength
ratio of the Rashba to Dresselhaus spin-orbit coupling, suggesting
that one can manipulate the total Hall current through tuning the
Rashba coupling by a gate voltage. We note that in a pure Rashba
system, though the spin Hall conductivity is exactly cancelled by
the OAM Hall conductivity due to the angular momentum
conservation, the spin Hall effect could still manifest itself as
nonzero magnetization Hall current and finite magnetization at the
sample edges because the magnetic dipole moment associated with
the spin of an electron is twice as large as that of the OAM. We
also evaluate the electric field-induced OAM and discuss the
origin of the OAM Hall current. Finally, we find that the
conventional spin and OAM Hall conductivities are closely related
to the Berry vector (or gauge) potential. This work has been
published in Phys. Rev. B. 73, 235309 (2006).
In superlattice InGaN/GaN, the conventional spin Hall conductivity
has been calculated. We found that spin Hall current can be
manipulated by changing the built-in electric field which is due
to the tunable internal strain. The calculation result shows that
the conventional spin Hall conductivity is qualitatively
consistent with the experiment result. This work has been
published in Phys. Rev. Lett 98, 136403 (2007).

並列關鍵字

spin Hall effect ； orbital angular momentum Hall effect ； spin-orbit coupling ； piezoelectric effect ； InGaN/GaN ； heterostructure ； superlattices

參考文獻

C. Hong, W. C. Tsai, Y. F. Chen, and G. Y. Guo, Phy. Rev. Lett.

35. M. Cardona, N. E. Christensen, G. Fasol, Phys. Rev. B { f 38},

86. H. J. Chang, T. W. Chen, J. W. Chen, W.C. Hong, W.

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