物理科學與技術學院學術報告:Novel metal-insulator transitions in disordered two-dimensional systems

報告題目:Novel metal-insulator transitions in disordered two-dimensional systems

報告人:汪 晨  電子科技大學電子科學與工程學院 cwangad@connect.ust.hk

報告時間:2019912日 上午 10:00-11:00

報告邀請人:陳垂針

報告地點:物理科技樓101

報告摘要:Disorders are ever-present。 The disorder-induced quantum phase transitions from extended states to localized states, known as the Anderson localization transitions, have been of fundamental importance in modern condensed matter physics after P。 W。 Anderson published his groundbreaking work in 1958。 For noninteracting closed Schrodinger systems, it is well-established that Anderson localization transitions exist (do not exist) in one-dimensional (three-dimensional) disordered systems。 However, whether Anderson localization transitions are allowed in the critical dimension, i。e。, two-dimension, has not yet been conclusive, which has also been drawn increasing attention in recent years。  In this talk, I will briefly discuss some current progress concerning the above issue。

The well-established one-parameter scaling theory predicts that all states are localized in two-dimensional systems except for those with time-reversal symmetry and spin-orbit coupling。 However, our numerical calculations show that extended states appear in systems without time-reversal symmetry (even at extremely weak magnetic fields) as well。 More strikingly, the form of metal-insulator transitions depends on the form of spin-orbit interactions: conventional Anderson localization transitions for uniform spin-orbit couplings but Berezinskii-Kosterlitz-Thouless transitions for random spin-orbit couplings。 In some specific systems, novel quantum phase transitions from diffusive metals to marginal metals, then to Anderson insulators is observed。

References:

[1] Anti-levitation in integer quantum Hall systems, C. Wang, Y. Avishai, Yigal Meir, and X. R. Wang, Phys. Rev. B 89, 045314 (2014).

[2] Band of Critical States in Anderson Localization in a Strong Magnetic Field with Random Spin-Orbit Scattering, C. Wang, Ying Su, Y. Avishai, Yigal Meir, and X. R. Wang, Phys. Rev. Lett. 114, 096803 (2015).

[3] Absence of localization in disordered two-dimensional electron gas at weak magnetic field and strong spin-orbit coupling, Ying Su, C. Wang, Y. Avishai, Yigal Meir, and X. R. Wang, Sci. Rep. 6, 33304 (2016).

[3] Anderson transition of two-dimensional spinful electrons in the Gaussian unitary ensemble. C. Wang and X. R. Wang, Phys. Rev. B 96, 104204 (2017).

[4] Unusual Metal to Marginal-Metal Transition in Two-Dimensional Ferromagnetic Electron Gases, Weiwei Chen, C. Wang, Qinwei Shi, Quanxiang Li, and X. R. Wang, arXiv:1907.12213.

報告人簡介:報告人汪晨于20119月獲得武漢大學物理學學士學位并于201611月獲得香港科技大學哲學博士(物理學)學位。在獲得博士學位后,報告人加入電子科技大學電子科學與工程學院從事博士后研究。報告人的研究方向主要包罗傳統二維系統和拓撲系統的安德森無序相變和自旋電子學。

 


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