CM Journal Club

semester, 2017


Wednesday, January 18th 2017
4:30 pm:
CM Journal Club in PAN 120
There will be no journal club this week.

Wednesday, February 1st 2017
4:30 pm:
CM Journal Club in PAN 120
No JC this week.

Wednesday, February 8th 2017
4:30 pm:
CM Journal Club in PAN 120
To be announced.

Wednesday, February 22nd 2017
4:30 pm:
CM Journal Club in PAN 120
To be announced.

Wednesday, March 1st 2017
4:30 pm:
CM Journal Club in PAN 120
Subject: Short meeting

Wednesday, March 22nd 2017
4:30 pm:
CM Journal Club in PAN 120
Speaker: Xuzhe Ying
Subject: Commensurate Incommensurate transition

Wednesday, March 29th 2017
4:30 pm:
CM Journal Club in PAN 120
Speaker: Mengxing Ye
Subject: Kitaev Spin Liquid
Refreshments will be served.

I will follow Kitaev's original paper [1] and show how the Kitaev honeycomb model can be solved exactly by reduction to free fermions (in a static Z2 gauge field). It is also a good example to see how "quantum order", which pertains to quantum spin liquid, emerges in the spin system. I will try to make the talk friendly to junior graduate students, and the derivation only requires graduate level quantum mechanics.

[1] A. Kitaev, 'Anyons in an exactly solved model and beyond'


Wednesday, April 5th 2017
4:30 pm:
CM Journal Club in PAN 120
Speaker: Ruiqi Xing
Subject: The hunt for the pairing glue in the cuprates
Refreshments will be served.

To understand the microscopic mechanism of electrons forming cooper pairs in the high-Tc cuprates, in a recent(2016) paper[1], the authors made an attempt to quantitatively determine the pairing interactions for copper-oxide high-Tc superconductors through state-of-the-art laser-based angle-resolved photoemission(ARPES) measurements. I will talk about: (1)the key results they found (how they get the pairing interactions between electrons); (2) "loop current" theory, which they use to explain the experiments; how the idea
of marginal Fermi-liquid and loop current is developed by Chandra Varma et al. to explain phenomenon in cuprates; some concepts, some illustration through derivation (depending on the interest of audience) and current status of this theory.

Ref:
[1]Bok et al., "Quantitative determination of pairing interactions for high-temperature superconductivity in cuprates", Sci. Adv., 2,e150132(2016)
http://advances.sciencemag.org/content/2/3/e1501329
[2]Andrey V Chubukov, "The hunt for the pairing glue in the cuprates", http://www.condmatjournalclub.org/jccm-content/uploads/2016/03/JCCM_Mar_2016_01.pdf
[3]Vivek Aji, Arkady Shekhter, and C. M. Varma, "Theory of the coupling of quantum-critical fluctuations to fermions and d-wave superconductivity in cuprates", Phys. Rev. B 81, 064515(2010), etc.


Wednesday, April 12th 2017
4:30 pm:
CM Journal Club in PAN 120
Speaker: Konstantin Reich
Subject: Basics of Polymer Physics
Refreshments will be served.

Wednesday, April 19th 2017
4:30 pm:
CM Journal Club in PAN 120
Speaker: No CM Journal Club This Week

Wednesday, April 26th 2017
4:30 pm:
CM Journal Club in PAN 120
Subject: There will be no CM Journal club

Wednesday, May 3rd 2017
4:30 pm:
CM Journal Club in PAN 120
Speaker: Daniel Shaffer, University of Minnesota
Subject: Topological Superconductor
Refreshments will be served.

References:
1.Masatoshi Sato, Yoichi Ando, 'Topological superconductors: a review', https://arxiv.org/abs/1608.03395
2.Barry Simon, 'Holonomy, the Quantum Adiabatic Theorem, and Berry's Phase
', https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.51.2167
3.Edward Witten, 'Three Lectures On Topological Phases Of Matter', https://arxiv.org/abs/1510.07698


Wednesday, September 6th 2017
4:30 pm:
CM Journal Club in PAN 120
No journal club this week.

Wednesday, September 13th 2017
4:30 pm:
CM Journal Club in PAN 120
Speaker: To be announced.

Wednesday, September 20th 2017
4:30 pm:
CM Journal Club in PAN 120
Speaker: No CM Journal Club

Wednesday, October 4th 2017
4:30 pm:
CM Journal Club in PAN 120
There is no journal club this week.

Wednesday, October 11th 2017
4:30 pm:
CM Journal Club in PAN 120
To be announced.

Tuesday, October 17th 2017
3:30 pm:
CM Journal Club in Tate-301-20
Speaker: Laxman Raju Thoutam, CEMS, University of Minnesota
Subject: Research update: Conductivity and beyond at the LAO/STO interface
Please note change of time, room and day for the seminar, this week only.

Wednesday, October 25th 2017
4:30 pm:
CM Journal Club in Tate 201-20
Speaker: Ruiqi Xing
Subject: Machine Learning circumvents sign problem in Quantum Monte Carlo

The journal club talk will be about the paper [1]. I will first introduce the famous fermion sign problem [2] in Determinantal Quantum Monte Carlo(DQMC) [3], and then discuss how to circumvent it using a method developed in machine learning community, convolutional neural networks. Introduction to neural networks [4] will be given. In the end, A successful application of this method to distinguish phases and to identify quantum phase transitions will be presented.

[1]Machine learning quantum phases of matter beyond the fermion sign problem
[2]Sign problem in the numerical simulation of many-electron systems
[3]Monte Carlo calculations of coupled boson-fermion systems. I
[4]Neural Networks and Deep Learning


Wednesday, November 1st 2017
4:30 pm:
CM Journal Club in Tate 201-20
Speaker: Dmitry Chichinadze
Subject: Quantum tunneling and dynamics in dissipative systems

This week we are going to discuss effects of dissipation on quantum tunneling. The main part of the talk will be devoted to the Caldeira-Leggett model [1], which describes a quantum-mechanical system coupled to an ensemble of oscillators. We will also discuss some specific cases of CL model, which involve two-state systems [2]. The plan of talk is as follows: we first introduce model, discuss experimental relevance and derive general formalism to describe dissipative dynamics. In the second part we will apply this formalism to two-state system and discuss possible applications. Literature: First two references are the renowned papers. The last reference is a good (and very detailed) book on quantum dissipative systems in general.
[1] Caldeira, A. O., & Leggett, A. J. (1983). Quantum tunnelling in a dissipative system. Annals of physics, 149(2), 374-456.
[2] Leggett, A. J., Chakravarty, S. D. A. F. M. G. A., Dorsey, A. T., Fisher, M. P., Garg, A., & Zwerger, W. (1987). Dynamics of the dissipative two-state system. Reviews of Modern Physics, 59(1), 1.
[3] Weiss, U. (2012). Quantum dissipative systems (Vol. 13). World scientific.


Tuesday, November 14th 2017
3:30 pm:
CM Journal Club in Tate 301-20
Speaker: Morten Christensen
Subject: The physics of quantum materials

The paper to be discussed is The physics of quantum materials by B. Keimer and J. E. Moore. Reading it before the journal club meeting is strongly encouraged.
https://www.nature.com/nphys/journal/v13/n11/full/nphys4302.html


Wednesday, November 29th 2017
4:30 pm:
CM Journal Club in Tate Hall 201-20
Speaker: Mengxing Ye
Subject: Deconfined quantum criticality

I will give an overview of the theory of deconfined quantum criticality following [1]. As an example, it shows that the quantum phase transition of the S=1/2 square lattice antiferromagnet between the Neel state (which breaks spin rotation symmetry) and the paramagnetic valence bond crystal (which preserves spin rotation but breaks lattice symmetry) is second order without fine-tuning. To achieve it, the field theory at the quantum critical point cannot be described by order parameters of either phases. I will focus on the physical picture and briefly discuss how the low energy field theory is formulated. A look at the less technical overview paper [2] is recommended.

[1] Quantum criticality beyond the Landau-Ginzburg-Wilson paradigm
[2] Deconfined Quantum Critical Points


Wednesday, December 6th 2017
4:30 pm:
CM Journal Club in Tate 201-20
Speaker: Bo Xiong
Subject: Topological field theory treatment to quantum hall liquids

Following Ref.[1] and [2], I am going to introduce the approach of Chern-Simons theory to quantum hall liquids, focusing on fractional quantum hall effect. Classification of Abelian quantum hall states will be given at the end.

[1] Zee, A. "Quantum hall fluids." Field theory, topology and condensed matter physics. Springer, Berlin, Heidelberg, 1995. 99-153.
[2] Wen, Xiao-Gang. "Topological orders and edge excitations in fractional quantum Hall states." Advances in Physics 44.5 (1995): 405-473.

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