Dr. Yan Zhang 张焱
张焱

Assistant Professor

Contact Info

Office:Physics Building W567, 物理楼西567

Tel:86-10-62766891

Email:yzhang85@pku.edu.cn

Personal Homepage:

 

Education

Degree

Year

Major     

Institution

Ph.D.

2007-2012

Condensed matter physics

Fudan University

B.S.

2003-2007

Physics

Fudan University

 

Professional Appointments

Year

Position

Institution

2012-2014

Postdoctoral Fellow

Stanford University

2014-

Assistant Professor

ICQM, School of Physics, Peking University

 

Research background:

In condensed matter physics, electrons play important roles. Under the interactions through charge, lattice, orbital, and spin, electrons evolve into many novel electronic states, such as high-temperature superconductivity, spin and charge density wave, magnetic and orbital ordering et al. The understanding of these electronic states not only deepens our understanding of the many-body physics and correlated electronic system, but also creates significant impact on the applications.

With angle-resolved photoemission spectroscopy (ARPES), we try to understand various novel electronic states in condensed matter physics. ARPES is one of the most powerful techniques to study the electronic state in materials. Based on the photoelectric effect, when a beam of monochromatized radiation is shined on a sample, electrons are emitted and escape to the vacuum (Fig.1). We then use a hemisphere energy analyzer to collect these photoelectrons. Through analysis, we could obtain various properties of the electrons in the solid, including Fermi surface, band dispersion, quasi-particle lifetime, electron-electron interaction, electron-boson interaction and so on (Fig.2). The ARPES technique is still in a fast development. The participation of the degrees of spin, time, and real space et al. in the future will make ARPES play more and more important roles in the research of condensed matter physics.

Fig.1:Illustration of the principle of ARPES. Fig.2:3D plot of the ARPES spetra.

Besides investigating the properties of electrons, we also try to design and tune the electronic states to make them practical, which is an important but also challenging issue. Typically, there are three ways to tune the electronic states. First, as to the bulk materials, we can change the temperature, pressure, carrier doping, magnetic field, and defects to tune their electronic states. Second, as to the thin films grown by Molecular Beam Epitaxy (MBE) or Pulsed Laser Deposition (PLD), we can modulate the growth conditions and substrates to tune the properties of the thin films and to obtain various non-equilibrium states. Finally, no matter for bulk materials or thin films, we can change their surface electronic states by gas absorption, ionic absorption, annealing, Electrochemical treatment and so on.

 

Research Interests

Novel electronic states and phase transitions:

1.        High-temperature superconductivity (Cuprates and Iron-based superconductors)

2.        Quantum phase transitions and quantum critical phenomenon

3.        Complex strong-correlated materials (charge/spin density wave, spin/orbit ordering)

Low-dimension electronic states:

1.        Topological insulator

2.        Surface and interface electronic states

 

Honors and Awards

Youth 1000 Talent Program Investigator

 

Selected Publications

1. Y. Zhang, Z. R. Ye, Q. Q. Ge, F. Chen, Juan Jiang, M. Xu, B. P. Xie, and D. L. Feng, “Nodal superconducting-gap structure in ferropnictide superconductor BaFe2(As0.7P0.3)2Nature Physics 8,371-375 (2012).

2. Y. Zhang, L. X. Yang, M. Xu , Z. R. Ye, F. Chen, C. He, H. C. Xu, J.Jiang, B. P. Xie, J. J. Ying, X. F. Wang, X. H. Chen, Jiangping Hu, M. Matsunami, S. Kimura, and D. L. Feng, “Nodeless superconducting gap in AxFe2Se2 (A =K, Cs) revealed by angle-resolved photoemission spectroscopy”, Nature Materials 10, 273-277 (2011).

3. Y. Zhang, L. X. Yang, F. Chen, B. Zhou, X. F. Wang, X. H. Chen, M. Arita, K. Shimada, H. Namatame, M. Taniguchi, J. P. Hu, B. P. Xie, and D. L. Feng, “Out-of-Plane Momentum and Symmetry-Dependent Energy Gap of the Pnictide Ba0.6K0.4Fe2As2 Superconductor Revealed by Angle-Resolved Photoemission Spectroscopy”, Phys. Rev. Lett. 105, 117003 (2010).

4. Y. Zhang, J.Wei, H.W. Ou, J. F. Zhao, B. Zhou, F. Chen, M. Xu, C. He, G.Wu, H. Chen, M. Arita, K. Shimada, H. Namatame, M. Taniguchi, X. H. Chen, and D. L. Feng, “Unusual Doping Dependence of the Electronic Structure and Coexistence of Spin-Density-Wave and Superconductor Phases in Single Crystalline Sr1-xKxFe2As2”, Phys. Rev. Lett. 102, 127003 (2009).

5. Y. Zhang, C. He, Z. R. Ye, J. Jiang, F. Chen, M. Xu, Q. Q. Ge, B. P. Xie, J. Wei, M. Aeschlimann, X. Y. Cui, M. Shi, J. P. Hu, and D. L. Feng, “Symmetry breaking via orbital-dependent reconstruction of electronic structure in detwinned NaFeAs”, Phys. Rev. B 85, 085121 (2012). This paper has been selected as the “Editor’s suggestion”

6. Y. Zhang, B. Zhou, F. Chen, J. Wei, M. Xu, L. X. Yang, C. Fang, W. F. Tsai, G. H. Cao, Z. A.Xu, M. Arita, C.H. Hong, K. Shimada, H. Namatame, M. Taniguchi, J. P. Hu, and D. L. Feng, “The orbital characters of bands in iron-based superconductor BaFe1.85Co0.15As2”, Phys. Rev. B 83, 054510 (2011). This paper has been selected as the “Editor’s suggestion”

 

Open Positions

We plan to recruit 1-2 Ph. D. students each year. Postdoc position is open.

 

Experimental facilities:

ARPES system(in progress)

Single-crystal synthesis system

MBE system(in progress)

Enjoy your journey into the world of electrons.

助理教授、研究员、博士生导师

北京大学量子材料科学中心

 

电话:010-62766891

Email:yzhang85@pku.edu.cn

 

个人简介:

2007年、2012年在复旦大学分别获得理学学士、博士学位。2010年1月至4月,为日本广岛大学同步辐射实验室青年访问学者。博士期间在Nature Physics、Nature Materials、Physical Review Letters等国际一流物理期刊发表论文30余篇(其中第一作者或通讯作者9篇),引用次数超过600次。2012年7月,作为中国优秀博士研究生代表,参加德国林岛诺贝尔奖获得者大会。2012年12月至2014年9月,在美国斯坦福大学开展博士后研究。2014年9月,被聘为北京大学量子材料科学中心助理教授、研究员、博士生导师。

研究背景简介:

在凝聚态物理中,电子扮演着很重要的角色。材料中的电子在电荷、晶格、轨道、自旋等各种自由度的相互作用下衍生出多种奇异的电子态,例如高温超导、自旋和电荷密度波、磁和轨道有序等等。这些奇异电子态表现出丰富的物理性质,并成为各种实用的功能材料。

本课题组利用角分辨光电子能谱技术来研究凝聚态体系中各种奇异的电子态,并对电子态进行设计和调控。角分辨能谱(ARPES)是研究材料微观电子态性质的强大实验手段。利用光电效应的原理,我们用深紫外光照射样品,并探测出射的光电子(图一)。通过分析光电子的动量和能量等信息,我们可以获得体系内部电子态的各种性质。这其中包括材料的费米面、能带色散关系、准粒子寿命、电子电子相互作用、 电子波色子相互作用等等(图二)。目前这一技术仍在快速发展中,自旋、时间、实空间等各种维度的加入和发展,将会使角分辨光电子能谱技术在凝聚态物理中扮演越来越重要的角色。

图一:角分辨光电子能谱原理示意图。 图二:测量得到的材料电子结构3D示意图。

除了理解电子态的各种奇异性质,如何适当的调控,使之成为实用的功能材料是十分重要也是十分困难的问题。由于材料中各种相互作用的竞争,一点点的扰动会对电子态产生巨大的影响。电子态的调控通常通过三种方式进行,首先,对于块体材料,我们可以利用温度、压力、载流子掺杂、磁场、缺陷等方法调控电子态的性质。其次,利用分子束外延生长系统(MBE)进行薄膜生长,可以精密的控制薄膜的生长速度,达到单层控制级别的生长。同时由于其外延生长的特性,可以利用衬底来调控薄膜性质,生长出各种所需要的非稳定相。最后,在块材或薄膜的表面,我们可以进行气体吸附、离子吸附、气氛退火、电化学等处理方法,来改变其性质,对表面处的低维电子态进行调节。

主要研究方向:

材料中奇异电子态的形成机理和相变机制:

  • 高温超导材料(铜氧化物和铁基高温超导体)
  • 量子相变和量子临界现象
  • 复杂强关联材料(电荷密度波、磁有序、轨道序)

薄膜、界面和表面上的低维奇特电子态:

  • 拓扑绝缘体
  • 表面电子态调控和诱导

实验设备:

角分辨光电子能谱系统(搭建中)

样品生长和处理系统

分子束外延薄膜生长系统(搭建中)

代表性论文:

  1. Y. Zhang, Z. R. Ye, Q. Q. Ge, F. Chen, Juan Jiang, M. Xu, B. P. Xie, and D. L. Feng*, “Nodal superconducting-gap structure in ferropnictide superconductor BaFe2(As0.7P0.3)2', Nature Physics 8,371-375 (2012).
  2. Y. Zhang, L. X. Yang, M. Xu , Z. R. Ye, F. Chen, C. He, H. C. Xu, J.Jiang, B. P. Xie, J. J. Ying, X. F. Wang, X. H. Chen, Jiangping Hu, M. Matsunami, S. Kimura, and D. L. Feng*, “Nodeless superconducting gap in AxFe2Se2 (A =K, Cs) revealed by angle-resolved photoemission spectroscopy', Nature Materials 10, 273-277 (2011).
  3. Y. Zhang, L. X. Yang, F. Chen, B. Zhou, X. F. Wang, X. H. Chen, M. Arita, K. Shimada, H. Namatame, M. Taniguchi, J. P. Hu, B. P. Xie, and D. L. Feng*, “Out-of-Plane Momentum and Symmetry-Dependent Energy Gap of the Pnictide Ba0.6K0.4Fe2As2 Superconductor Revealed by Angle-Resolved Photoemission Spectroscopy', Phys. Rev. Lett. 105, 117003 (2010).
  4. Y. Zhang, J.Wei, H.W. Ou, J. F. Zhao, B. Zhou, F. Chen, M. Xu, C. He, G.Wu, H. Chen, M. Arita, K. Shimada, H. Namatame, M. Taniguchi, X. H. Chen, and D. L. Feng*, “Unusual Doping Dependence of the Electronic Structure and Coexistence of Spin-Density-Wave and Superconductor Phases in Single Crystalline Sr1-xKxFe2As2', Phys. Rev. Lett. 102, 127003 (2009).
  5. Y. Zhang, C. He, Z. R. Ye, J. Jiang, F. Chen, M. Xu, Q. Q. Ge, B. P. Xie, J. Wei, M. Aeschlimann, X. Y. Cui, M. Shi, J. P. Hu, and D. L. Feng*, “Symmetry breaking via orbital-dependent reconstruction of electronic structure in detwinned NaFeAs', Phys. Rev. B 85, 085121 (2012). This paper has been selected as the “Editor’s suggestion'
  6. Y. Zhang, B. Zhou, F. Chen, J. Wei, M. Xu, L. X. Yang, C. Fang, W. F. Tsai, G. H. Cao, Z. A.Xu, M. Arita, C.H. Hong, K. Shimada, H. Namatame, M. Taniguchi, J. P. Hu, and D. L. Feng*, “The orbital characters of bands in iron-based superconductor BaFe1.85Co0.15As2', Phys. Rev. B 83, 054510 (2011). This paper has been selected as the “Editor’s suggestion'

研究生培养情况:

目前课题组有博士后一名。拟计划每年招收博士研究生1~2名。

课题组处于起步阶段,欢迎本科生、博士生和博士后的加入。精密超高真空系统的搭建、国外大型同步辐射光源的实验、新样品的合成和处理、各种复杂物相的理解与探索都可以让你接触到凝聚态物理的前沿,学习和发展新的实验技术。

Enjoy your journey into the world of electrons.