Dr. Yang Liu 刘阳
Dr. Yang Liu 刘阳

Assistant Professor

 

Contact Info

Office:Rm 544, 209 Chengfu Road, Haidian District, Beijing, 100871

Tel:17812704898

Email:liuyang02@pku.edu.cn

Personal Homepage:This person is very lazy. 

Resume

 

Education

Degree

Year

Major     

Institution

Ph.D.

2008-2014

Electric Engineering

Princeton University

M.S.

2006-2008

Electronics Engineering

Tsinghua University

B.S.

2002-2006

Electronics Engineering

Tsinghua University

 

Professional Appointments

Year

Position

Institution

2015-2018

Postdoctoral Fellow

Stanford University

2014-2015

Postdoctoral Fellow

Princeton University

 

Research Interests

Ultra-clean two-dimensional (2D) carrier systems in Modulation-doped GaAs/AlGaAs hetero-structures provide a nearly ideal testing ground for exploring quantum transport and other interaction-induced physics phenomena. This is indeed the cleanest system yet available where the electrons can travel coherently for as long as ~10 μm. At low temperatures and in the presence of a strong magnetic field, these systems exhibit fascinating, often unexpected, many-body states arising from the strong electron-electron interaction. Examples include the fractional quantum Hall liquid, the Wigner solid, and the newly discovered striped (nematic) and bubble phases in the higher Landau levels.

The rapid improvement of quantum computing technique and fast scaling of qubits put great demands on cryogenic electronic circuits operating at millikelvin temperatures. The high electron mobility transistors (HEMTs) based on high quality modulation-doped 2DES/2DHS, are the best candidates. They can be integrated with quantum devices such as qubits, SQUIDs, single-electron transistors, etc., work natively at T ≤ 4 K, have high cut-off frequency, and dissipate only a few μW of power. Moreover, the study of high mobility 2D systems reveals a rich family of quantum phenomenon and transitions such as quantum Hall effect, Wigner crystal, etc., which can be applied in developing new HEMTs.

Read the more detailed research plan.

 

Honors and Awards

2015 GLAM Postdoctoral Fellowship, Stanford University

2015 Finalist of Blavatnik Regional Awards

2014 Princeton EE Outstanding Dissertation Awards

2013 Chinese Government Award for Outstanding Self-Financed Students Abroad

2012 Princeton University Charlotte Elizabeth Procter Honorific Fellowship

 

Selected Publications:

  1. Yang Liu, Dominik K. Rastawicki, Warren Mar, Anna Miglio, Yan Sun, Alex W. Contryman, Lianhua He, Fang Liu, Aihui Zhou, Sorin Melinte, Jean-Christophe Charlier, Gian-Marco Rignanese, and Hari C. Manoharan,“Short-Range Isotopic Variation and Long-Range Hidden Charge Fluctuations Revealed through a Single Quantum Vibron”, manuscript in prepare.
  2. Yang Liu, M. A. Mueed, Md. Shafayat Hossain, S. Hasdermir, L.N. Pfeiffer, K.W. West, K.W. Baldwin, and M. Shayegan, “Morphing of 2D Hole Systems at ν=3/2 in Parallel Magnetic Fields: Compressible, Stripe, and Fractional Quantum Hall Phases”,Phys. Rev. B 94, 155312 (2016).
  3. Yang Liu, S. Hasdemir, L.N. Pfeifer, K.W. West, and K.W. Baldwin, M. Shayegan, “Observation of An Anisotropic Wigner Crystal”, Phys. Rev. Lett. 117, 106802 (2016).
  4. H. Deng, Yang Liu, I Jo, L.N. Pfeifer, K.W. West, K.W. Baldwin, and M. Shayegan, “Composite Fermions Waltz to the Tune of a Wigner Crystal”, Phys. Rev. Lett. 117, 096601 (2016).
  5. Yang Liu, S. Hasdemir, J. Shabani, M. Shayegan, L.N. Pfeifer, K.W. West, and K.W. Baldwin, “Multicomponent fractional quantum Hall states with subband and spin degrees of freedom”, Phys. Rev. B 92, 201101(R) (2015).
  6. Yang Liu,S. Hasdemir, Dobromir Kamburov, A.L. Graninger, M. Shayegan, L.N. Pfeiffer, K.W. West, K.W. Baldwin, and R. Winkler, “Even-denominator Fractional Quantum Hall State at a Landau Level Crossing”, Phys. Rev. B89, 165313 (2014).
  7. D. Kamburov, Yang Liu, M. A. Mueed, M. Shayegan, L. N. Pfeiffer, K. W. West, and K. W. Baldwin, “What Determines the Fermi Wave Vector of Composite Fermions?” Phys. Rev. Lett. 113, 196801 (2014).
  8. Yang Liu, D. Kamburov, S. Hasdemir, M. Shayegan, L.N. Pfeifer, K.W. West, K.W. Baldwin, “Fractional Quantum Hall Effect and Wigner Crystal of Two-Flux Composite Fermions”, Phys. Rev. Lett. 113, 246803 (2014).
  9. J. Shabani, Yang Liu, M. Shayegan, L. N. Pfeiffer, K. W. West, and K. W. Baldwin, “Phase diagrams for the stability of the ν=1/2 fractional quantum Hall effect in electron systems confined to symmetric, wide GaAs quantum wells”, Phys. Rev. B88, 245413 (2013).
  10. Yang Liu, J. Shabani, D. Kamburov, M. Shayegan, L. N. Pfeiffer, K. W. West, and K. W. Baldwin, “Evolution of the 7/2 Fractional Quantum Hall State in Two-Subband Systems”, Phys. Rev. Lett. 107, 266802 (2011).
  11. Yang Liu, J. Shabani, and M. Shayegan, “Stability of the q/3 Fractional Quantum Hall States”, Phys. Rev. B84, 195303 (2011).
  12. Yang Liu, L. Wang, C. Tian, M. Zhang, and Y. Liao, “Analysis and Optimization of the PGC Method in All Digital Demodulation Systems”, Journal of Lightwave Technology 26, pp. 3225-3233 (2008).

 

Opening Positions

 Now hiring. 1-2 Ph.D candidates for 2018-2019, one postdoc position and one research staff position open. Please contact me at liuyang02@pku.edu.cn if you are interested in exploring the physics at low temperature and high magnetic field experimentally.

See the link for more information

量子材料中心研究员,助理教授,博士生导师

 

联系方式

Liuyang02(at)pku.edu.cn

北京大学物理学院西楼W544

实验室电话:待定

实验组主页

某人很懒,尚未准备。

个人简历

2002-2006

清华大学

电子工程系

工学学士

 

 

2006-2008

清华大学

电子工程系

工学硕士

干涉型光纤传感系统调制解调,激光诱导击穿光谱学

廖延彪

2008-2014

Princeton

电机工程系

哲学博士

GaAs宽量子阱中二维电子气

Mansour Shayegan

2014-2015

Princeton

电机工程系

博士后

GaAs宽量子阱中二维空穴气

Mansour Shayegan

2015-2018

Stanford

物理系

博士后

扫描隧道显微镜;原子/分子操控

Hari Manoharan

2018---

北京大学

量子材料科学中心

助理教授

低温+强磁场+二维电子气+多体物理+光学/探针/输运等测量手段

 

 

关键词

超高迁移率砷化镓异质结(Ultra-high-mobility GaAs heterostructure),二维电子气(Two-Dimensional electron/hole system),量子霍尔效应(quantum Hall effect),多体物理(many-body physics),稀释式制冷机(dilution refrigerator),低温强磁场输运测量(low-temperature high-magnetic-field transport measurement)

招生信息

计划招收博士研究生一至两名,计划招聘博士后一名,实验室助研一名,欢迎面谈。

欢迎一名二年级北大本科生参与科研工作。

研究兴趣和方向

半导体异质结结构不连续的能带结构会在界面处构成势阱,并在界面束缚大量的电子形成一个薄层。电子在垂直于界面方向的运动被势阱束缚而被量子化,而其平行于表面的运动仍然是自由的。这样的电子薄层被称为二维电子气(2DEG)。在极低温度下(~10 mK),极纯净半导体材料中,电子散射等非理想因素被降至极低。二维电子气的物理性质完全由电子的动能以及电子间库仑作用力所决定,并在强磁场的作用下呈现出一系列新颖的量子态。其中包括整数量子霍尔效应(Integer Quantum Hall Effect, IQHE, Klaus von Klitzing, et al. Nobel Physics,1985),分数量子霍尔效应(Fractional Quantum Hall Effect, FQHE,崔琦, et al. Nobel Physics, 1998),Wigner晶体,电荷密度波等等。我研究的主要内容将是探索这些量子态的物理特性以及单电子波函数的精细结构对这些量子态的影响。

分数量子霍尔效应是二维电子气展现的一种独特的多体量子态(many-body quantum state)。这种稳定的量子态完全由电子之间的相互作用引入。它的內在禀赋蕴含在电子与电子之间的相对拓扑结构。这种拓扑结构的宏观外在表现展示出超流的特征。尤为特殊的是位于朗道能级填充系数5/2的量子霍尔态。现有的实验和理论研究认为该量子态由Pfaffian波函数描述,其准粒子满足非阿贝尔统计特性,可以用于拓扑量子计算。分数量子霍尔态会继承电子的自旋、谷(valley)、能级(subband)等自由度。通过改变二维电子气的系统参数,我们可以观测到分数量子霍尔效应的相变。由于二维系统在平面内有微小的变化,在相变点附近,具有不同赝自旋的分数量子霍尔态可以被稳定在不同的区域内。我希望研究区域之间的边界线附近的赝自旋结构以及电子的跨边界运动性质,探索对量子霍尔态拓扑结构的测量和操作,从而在将来展开对拓扑量子计算的研究。

在常见半导体(比如Si,Ge,GaAs,AlAs等)中,电子能级来源于原子的s-轨道,因此二维电子气具有相对简单的色散和自旋结构以及朗道能级波函数。与此同时,半导体中的空穴来源于原子的p-轨道,从而拥有更加复杂的能带和自旋结构。宽量子阱GaAs空穴同时包含了重空穴态和轻空穴态。空穴中的强自旋轨道耦合使得二维空穴气的色散和自旋特性及其复杂。我们可以通过外建电场对空穴的色散和自旋特性进行调控,进而在二维空穴气中引入新的量子态。我研究的一个重心会集中在二维空穴材料中量子态及其相变,特别是系统性的探索强自旋轨道耦合导致的自旋相关物理现象。我希望我的实验研究能够发现并理解自旋轨道耦合系统中复杂的物理现象, 拓展对该类型系统中量子态进行精确操控的能力。 

代表性科研成果:

  • 在国际上首次实验发现复合费米子的Wigner晶体。
  • 在国际上首次完成GaAs宽量子阱中的SU(4)对称性相关实验观测。
  • 在国际上首先用实验方法实现了对Wigner晶体晶体结构的检测。
  • 在国际上首次实验发现空穴系统中最低朗道能级的交错并对相关量子态展开实验。

代表性论文

  1. Yang Liu, Dominik K. Rastawicki, Warren Mar, Anna Miglio, Yan Sun, Alex W. Contryman, Lianhua He, Fang Liu, Aihui Zhou, Sorin Melinte, Jean-Christophe Charlier, Gian-Marco Rignanese, and Hari C. Manoharan,“Short-Range Isotopic Variation and Long-Range Hidden Charge Fluctuations Revealed through a Single Quantum Vibron”, manuscript in prepare.
  2. Yang Liu, M. A. Mueed, Md. Shafayat Hossain, S. Hasdermir, L.N. Pfeiffer, K.W. West, K.W. Baldwin, and M. Shayegan, “Morphing of 2D Hole Systems at ν=3/2 in Parallel Magnetic Fields: Compressible, Stripe, and Fractional Quantum Hall Phases”,Phys. Rev. B 94, 155312 (2016).
  3. Yang Liu, S. Hasdemir, L.N. Pfeifer, K.W. West, and K.W. Baldwin, M. Shayegan, “Observation of An Anisotropic Wigner Crystal”, Phys. Rev. Lett. 117, 106802 (2016).
  4. H. Deng, Yang Liu, I Jo, L.N. Pfeifer, K.W. West, K.W. Baldwin, and M. Shayegan, “Composite Fermions Waltz to the Tune of a Wigner Crystal”, Phys. Rev. Lett. 117, 096601 (2016).
  5. Yang Liu, S. Hasdemir, J. Shabani, M. Shayegan, L.N. Pfeifer, K.W. West, and K.W. Baldwin, “Multicomponent fractional quantum Hall states with subband and spin degrees of freedom”, Phys. Rev. B 92, 201101(R) (2015).
  6. Yang Liu,S. Hasdemir, Dobromir Kamburov, A.L. Graninger, M. Shayegan, L.N. Pfeiffer, K.W. West, K.W. Baldwin, and R. Winkler, “Even-denominator Fractional Quantum Hall State at a Landau Level Crossing”, Phys. Rev. B89, 165313 (2014).
  7. D. Kamburov, Yang Liu, M. A. Mueed, M. Shayegan, L. N. Pfeiffer, K. W. West, and K. W. Baldwin, “What Determines the Fermi Wave Vector of Composite Fermions?” Phys. Rev. Lett. 113, 196801 (2014).
  8. Yang Liu, D. Kamburov, S. Hasdemir, M. Shayegan, L.N. Pfeifer, K.W. West, K.W. Baldwin, “Fractional Quantum Hall Effect and Wigner Crystal of Two-Flux Composite Fermions”, Phys. Rev. Lett. 113, 246803 (2014).
  9. J. Shabani, Yang Liu, M. Shayegan, L. N. Pfeiffer, K. W. West, and K. W. Baldwin, “Phase diagrams for the stability of the ν=1/2 fractional quantum Hall effect in electron systems confined to symmetric, wide GaAs quantum wells”, Phys. Rev. B88, 245413 (2013).
  10. Yang Liu, J. Shabani, D. Kamburov, M. Shayegan, L. N. Pfeiffer, K. W. West, and K. W. Baldwin, “Evolution of the 7/2 Fractional Quantum Hall State in Two-Subband Systems”, Phys. Rev. Lett. 107, 266802 (2011).
  11. Yang Liu, J. Shabani, and M. Shayegan, “Stability of the q/3 Fractional Quantum Hall States”, Phys. Rev. B84, 195303 (2011).
  12. Yang Liu, L. Wang, C. Tian, M. Zhang, and Y. Liao, “Analysis and Optimization of the PGC Method in All Digital Demodulation Systems”, Journal of Lightwave Technology 26, pp. 3225-3233 (2008).