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Cornell University
LASSP -  Laboratory of Atomic and Solid State Physics

Cornell Laboratory for Atomic and Solid State Physics

Program - Summer School on Emergent Phenomena in Quantum Materials

Located at 120 Physical Sciences Building, Cornell University, Ithaca, NY.

Video to talks are linked below and on our YouTube channel YouTube.

Program at a glance:
program overview

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Monday 8/3
Morning Moderator: Eun-Ah Kim
8:00AM
Registration & Breakfast
9:00 - 9:10
Welcoming Remarks
9:10 - 10:10
Eugene Demler
PartI: Non equilibrium dynamics of many-body systems
In these lectures I will discuss several problems of non-equilibrium dynamics of many-body systems in response to sudden localized perturbations. In the first part I will focus on fermions and review Anderson orthogonality catastrophe. I will discuss two types of current experiments in which this type of dynamics is important: Radio-Frequency spectroscopy of ultracold Fermi atoms and resonant soft Xray scattering in high temperature superconductors. In the second lecture I will discuss polarons, i.e. mobile impurities coupled to bosonic baths such as electrons coupled to phonons or magnetic excitations. I will review non-perturbative techniques for calculating properties of polarons including renormalization group approach and variational wavefunctions. As a concrete example I will discuss implications of these results to experiments with impurity atoms in Bose condensates.
10:10 - 11:10
Abolhassan Vaezi
Watch YouTube | Slides
Part I: Universal Quantum Computation from Quantum Hall States
In the first talk, I will present a brief introduction to fractional quantum Hall physics and its relation to quantum computation. First, I will review the topological properties of quantum Hall states, their classifications and their low energy effective descriptions. Next, I will describe anyon excitations,fusion rules, and braid statistics. Finally, I will comment on how anyons can be utilized to store and process quantum information.
11:10 - 11:30
Break
11:30 - 12:30
Eugene Demler
PartI: Non equilibrium dynamics of many-body systems
In these lectures I will discuss several problems of non-equilibrium dynamics of many-body systems in response to sudden localized perturbations. In the first part I will focus on fermions and review Anderson orthogonality catastrophe. I will discuss two types of current experiments in which this type of dynamics is important: Radio-Frequency spectroscopy of ultracold Fermi atoms and resonant soft Xray scattering in high temperature superconductors. In the second lecture I will discuss polarons, i.e. mobile impurities coupled to bosonic baths such as electrons coupled to phonons or magnetic excitations. I will review non-perturbative techniques for calculating properties of polarons including renormalization group approach and variational wavefunctions. As a concrete example I will discuss implications of these results to experiments with impurity atoms in Bose condensates.
12:30 - 1:30
Lunch
1:30 - 2:30
Poster Session Group I
Afternoon Moderator: Erich Mueller
2:30 - 3:30
Abolhassan Vaezi
Watch YouTube | Slides
Part II: Universal Quantum Computation from Quantum Hall States
In the second talk, I will focus on two recently proposed quantum Hall systems that are capable of performing quantum computation. First, I will consider parafermion zero modes, their topological properties and how to realize them. Secondly, I will talk about Fibonacci anyons and why they are capable of universal quantum computation. Finally, I will show that these exotic anyons can be realized in bilayer fractional quantum Hall systems with 2/3 filling fraction.
3:30 - 3:45
Break
3:45 - 4:45
Bryan Clark
Talk I: A variational approach to strongly correlated systems.
Strongly correlated systems are often hard to treat analytically. In this talk, I will describe how variational techniques give a non-perturbative approach to accessing quantum many-body physics. The talk will focus on both the important variational forms as well as the numerical methods, such as quantum Monte Carlo and DMRG, used to optimize them. Physical examples may include spin liquids, many-body localization, and fractional chern insulators.
Tuesday 8/4
Morning Moderator: Tom Hartman
8:00AM
Breakfast
9:00 - 10:00
Andrei Bernevig
Watch YouTube
I will present theoretical and experimental advances in the study and detection of Majorana fermions. I will show that a new majorana fermion platform can give rise to basically self tuned topological superconductors. I will show experimental data that confirms these advances and show that the new platform can be used to look at the interacting classification of topological superconductors with a special time reversal symmetry. I will also show robust braiding schemes as well as calculations showing the possibility of realizing two dimensional superconductors in the same platform.
10:00 - 11:00
Subir Sachdev
Watch YouTube| Slides
Part I: The remarkable “normal” states of the high temperature superconductors
I will give an overview of the present understanding and open questions on the two metallic states of the cuprate superconductors, the pseudogap and the strange metal. Topics to be covered
  1. A quick overview of Fermi liquids
  2. Introduction to spin liquids and topological order
  3. The pseudogap metal as the co-existence of Fermi liquids and topological order
  4. A mean-field model of a strange metal
  5. More realistic models of strange metals.
11:00 - 11:30
Break
11:30 - 12:30
Subir Sachdev
Watch YouTube | Slides
Part II: The remarkable “normal” states of the high temperature superconductors
I will give an overview of the present understanding and open questions on the two metallic states of the cuprate superconductors, the pseudogap and the strange metal. Topics to be covered
  1. A quick overview of Fermi liquids
  2. Introduction to spin liquids and topological order
  3. The pseudogap metal as the co-existence of Fermi liquids and topological order
  4. A mean-field model of a strange metal
  5. More realistic models of strange metals.
12:30 - 1:30
Lunch
1:30 - 2:30
Poster Session Group I
Afternoon Moderator: Michael Lawler
2:30 - 3:30
Andrei Bernevig
Watch YouTube
I will present theoretical and experimental advances in the study and detection of Majorana fermions. I will show that a new majorana fermion platform can give rise to basically self tuned topological superconductors. I will show experimental data that confirms these advances and show that the new platform can be used to look at the interacting classification of topological superconductors with a special time reversal symmetry. I will also show robust braiding schemes as well as calculations showing the possibility of realizing two dimensional superconductors in the same platform.
3:30 - 3:45
Break
3:45 - 4:45
Bryan Clark
Talk II: Beyond explicitly representable variational ansatz
While the variational method is powerful, it is often restricted by the ingenuity of your variational manifold of wave-functions. In this talk, we will discuss quantum Monte Carlo methods, such as fixed-node quantum Monte Carlo and full configuration interaction quantum Monte Carlo which go beyond these ansatz. We will see that these many-body techniques allow us to accurately capture physics from both model as well as ab-initio systems.
Wednesday 8/5
Morning Moderator: Tom Hartman
8:00AM
Breakfast
9:00 - 10:00
Max Metlitski
Watch YouTube
Part I: Interaction effects on 3d topological insulators and superconductors

I will discuss recent progress in understanding the effect of interactions on topological insulators (TIs) and topological superconductors (TSCs) in 3d. There are three qualitatively new effects that interactions bring:

  1. Existence of new bulk TI and TSC phases absent in the non-interacting classification.
  2. Certain non-interacting bulk TSC phases become continuously connected in the presence of interactions.
  3. Existence of novel surface states. Unlike the surface states of non-interacting TIs and TSCs, which are always gapless or symmetry broken, these novel surface states are gapped and symmetry preserving at the cost of supporting fractional excitations.

Suggested reading:
T. Senthil, "Symmetry Protected Topological phases of Quantum Matter," arXiv:1405.4015 (and references therein).

10:00 - 10:30
Break
10:30 - 11:30
Max Metlitski
Watch YouTube
Part II: Interaction effects on 3d topological insulators and superconductors

I will discuss recent progress in understanding the effect of interactions on topological insulators (TIs) and topological superconductors (TSCs) in 3d. There are three qualitatively new effects that interactions bring:

  1. Existence of new bulk TI and TSC phases absent in the non-interacting classification.
  2. Certain non-interacting bulk TSC phases become continuously connected in the presence of interactions.
  3. Existence of novel surface states. Unlike the surface states of non-interacting TIs and TSCs, which are always gapless or symmetry broken, these novel surface states are gapped and symmetry preserving at the cost of supporting fractional excitations.

Suggested reading:
T. Senthil, "Symmetry Protected Topological phases of Quantum Matter," arXiv:1405.4015 (and references therein).

11:30 - 12:30
Kai Sun
Watch YouTube
Part I: Topological States in Strongly Correlated Systems
This lecture addresses the interplay between topological states of matter and strongly correlated materials, which are two of the major research areas in modern condensed matter physics. The lecture contains four parts. The first part reviews basic ideas about topology and topological states of matter, and the second part discusses basic concepts in strongly-correlated materials, using heavy fermion compounds as an example. The third part focuses on experimental techniques and summarizes key ingredients to identify a strongly-correlated topological material as well as its experimental signature. Finally, in the last part, we will review possible new phenomena that might arise in strongly correlated topological states.
12:30 - 1:30
Lunch
1:30 - 2:30
Poster Session Group II
Afternoon Moderator: Michael Lawler
2:30 - 3:30
Kristjan Haule
Watch YouTube
Part I: Understanding Correlated Electron Materials: The Functional Dynamical Mean Field Approach

Materials with strong electronic correlations have long resisted abinitio modeling due to their complexity arising from non-perturbative strength of the interaction. The Dynamical Mean Field Theory in combination with the Density Functional Theory has recently changed this position, and enabled detailed modeling of the electronic structure of many complex materials, such as the heavy fermions, transition metal oxides, iron superconductors, etc.

I will give basic foundation of this theory from the functional point of view, and an overview on the recent advances in this field, such as the exact double-counting, and stationary implementation of the total free energy, which opens the door for structural optimizations at finite temperatures.

3:30 - 3:45
Break
3:45 - 4:45
Kristjan Haule
Watch YouTube
Part II: Understanding Correlated Electron Materials: The Functional Dynamical Mean Field Approach

Materials with strong electronic correlations have long resisted abinitio modeling due to their complexity arising from non-perturbative strength of the interaction. The Dynamical Mean Field Theory in combination with the Density Functional Theory has recently changed this position, and enabled detailed modeling of the electronic structure of many complex materials, such as the heavy fermions, transition metal oxides, iron superconductors, etc.

I will give basic foundation of this theory from the functional point of view, and an overview on the recent advances in this field, such as the exact double-counting, and stationary implementation of the total free energy, which opens the door for structural optimizations at finite temperatures.

Thursday 8/6
Morning Moderator: Erich Mueller
8:00AM
Breakfast
9:00 - 10:00
Kai Sun
Watch YouTube
Part II: Topological States in Strongly Correlated Systems
This lecture addresses the interplay between topological states of matter and strongly correlated materials, which are two of the major research areas in modern condensed matter physics. The lecture contains four parts. The first part reviews basic ideas about topology and topological states of matter, and the second part discusses basic concepts in strongly-correlated materials, using heavy fermion compounds as an example. The third part focuses on experimental techniques and summarizes key ingredients to identify a strongly-correlated topological material as well as its experimental signature. Finally, in the last part, we will review possible new phenomena that might arise in strongly correlated topological states.
10:00 - 11:00
Garnet Chan
Watch YouTube
Matrix product states, DMRG, and tensor networks

I will give a general introduction to the subject of tensor networks, using matrix product states as the introductory example, and developing towards tensor networks such as PEPS and MERA.

11:00 - 11:30
Break
11:30 - 12:30
Garnet Chan
Watch YouTube
Numerical aspects of DMRG, quantum embedding, and the realistic description of strongly correlated materials

I will discuss numerical aspects of DMRG calculations, the extension to ab-initio Hamiltonians, and its combination with quantum embedding techniques such as density matrix embedding theory to give a description of realistic correlated materials.

12:30 - 1:30
Lunch
1:30 - 2:30
Poster Session Group II
Afternoon Moderator: Eun-Ah Kim
2:30 - 3:30
Maissam Barkeshli
Watch YouTube
Part I: Boundaries, defects, and exotic zero modes in topological phases of matter
I will describe recent progress over the last few years regarding the study of various extrinsic line and point defects in 2+1 D topological phases of matter. The line defects include the possibility of topologically distinct boundaries of a given topological phase of matter, or of distinct interfaces between different topological states. These line defects couple to the topological properties in non-trivial ways, and allow the possibility of (1) directly coupling electrons from an external system to fractionalized excitations of a topological state, and (2) creating high genus surfaces in an experimentally realizable manner. The extrinsic point-like defects localize exotic zero modes and give rise to topologically protected degeneracies, giving them some of the properties of non-abelian quasiparticles, even though they are not elementary excitations of the phase. I will describe various physical systems, such as fractional quantum Hall states, where such defects can be created.
3:30 - 3:45
Break
3:45 - 4:45
Maissam Barkeshli
Watch YouTube
Part II: Boundaries, defects, and exotic zero modes in topological phases of matter
I will describe recent progress over the last few years regarding the study of various extrinsic line and point defects in 2+1 D topological phases of matter. The line defects include the possibility of topologically distinct boundaries of a given topological phase of matter, or of distinct interfaces between different topological states. These line defects couple to the topological properties in non-trivial ways, and allow the possibility of (1) directly coupling electrons from an external system to fractionalized excitations of a topological state, and (2) creating high genus surfaces in an experimentally realizable manner. The extrinsic point-like defects localize exotic zero modes and give rise to topologically protected degeneracies, giving them some of the properties of non-abelian quasiparticles, even though they are not elementary excitations of the phase. I will describe various physical systems, such as fractional quantum Hall states, where such defects can be created.
4:45 - 5:00
Wrap Up