Group

Bryan Clark

Email: bkclark@illinois.edu
Office: 2111 ESB

I am an assistant professor at the University of Illinois and have the opportunity to collaborate with many talented and passionate graduate students and postdocs.



Graduate Students


Xiongjie Yu
Xiongjie has many interests but has recently focused on many-body localization. He has worked on the development of two new DMRG-style algorithms (ES-DMRG and SIMPS) for excited states. These algorithms find eigenstates in the middle of a many-body spectrum in the MBL phase. This increases the system size accessible to study many-body localization by one to two orders of magnitude. Using these algorithms, Xiongjie has shown for large systems that entanglement saturates as a function of system size, that ETH breaks down and how to build many local excitations.

In addition, Xiongjie has found bimodality of entanglement in the MBL critical region as well as identified a universal one-parameter family of curves in this region. He has also developed a new observable to examine MBL with (the cut-averaged entanglement entropy) which has the property that it is smooth even for a single disorder realization!

Xiongjie also looked at an eigenstate phase transition in MBL in a random energy model finding the first instance where the finite size transition to the ergodic phase happens from the MBL side.


Dmitrii Kochkov
Dmitrii works on frustrated magnetism and is an expert on exact-diagonalization techniques (having written a highly scalable parallel code).

Dmitrii recently posted a result on the XXZ Hamiltonian on the kagome lattice. He showed that the macroscopically degenerate XXZ0 point was connected to a number of phases on the kagome lattice including the q=0 state, the sqrt(3) x sqrt(3) state, a ferromagnetic state and (probably) two spin-liquids. In addition, Dmiitrii made a compelling case that the KAHF is actually a critical point between two phases instead of a spin-liquid.

More recently, Dmitrii has been thinking about the phase diagram of the stuffed honeycomb lattice which he spoke about at the most recent March Meeting.

Dmitrii has won the physic departments Jordan Asketh Award, which recognizes one of the year’s outstanding European graduate students.


Benjamin Correa
Benjamin works in the area of many-body localization. He is currently focused on exploring MBL states in dimensions greater then one as well as establishing what information the one-body density matrix can reveal about the MBL phase.


Jahan Claese
Jahan recently has published a paper which generalizes the variational Monte Carlo approach to finite temperature. This generalization allows us to use, at finite temperature, the full machinery of variational wave-functions that have been developed over the last thirty years.

More recently, Jahan has been thinking about problems in superconductivity, and particularly, the nature of pair and spin density waves.

Jahan received an Honorable Mention in the NSF graduate research fellowship program.


Eli Chertkov
Eli is interested in machine learning, inverse problems and superconductivity. Eli got a 2017 NSF Grad Fellowship Honorable Mention as well one of the departments Scott Anderson Outstanding Graduate Assistant Awards for 2017.


Ryan Levy
Ryan has recently joined the group and is interested in superconductivity.


Di Luo
Di Luo has recently joined the group.



Postdocs



Alumni


David Luitz (former postdoc)
David Luitz was a graduate student with Fakher Assad, a postdoc with Fabien Alet and was an ICMT postdoc at University of Illinois. David Luitz is now in Munich as a Marie Skłodowska Curie Fellow. He works on entanglement and many-body localization. In our group he has found bimodality of entanglement in the MBL critical region as well as identified a universal one-parameter family of curves in this region.


Hitesh Changlani (former postdoc)
Hitesh was a graduate student with Chris Henley at Cornell University and a postdoc with myself, David Ceperley, Lucas Wagner and Shinshei Ryu at UIUC (he is a prolific collaborator). Hitesh has moved now to a postdoc at Johns Hopkins. He is an expert in, among other things, frustrated magnetism and downfolding.

One project he worked on with me is the development of new methodological approaches for combining quantum Monte Carlo and DMRG. These new approaches allow us to go beyond what can be computed with either method individually.

More recently, Hitesh has discovered a new chiral spin liquid phase in the the 2/3 magnetic plateau on the kagome lattice as well as the existence of a macroscopically degenerate point which likely controls much of the physics on frustrated magnets on lattices of triangles.


Michael Kolodrubetz (former student)
As a graduate student at Princeton, Michael was (unofficially) co-advised by myself and David Huse. Since then he has gone on to postdocs with Anatoli Polkovnikov and Anders Saandvik at Boston University and, more recently, Joel Moore at UC Berkeley.

Michael is an expert on quantum dynamics and interacting with experimentalists. In his thesis, Michael developed new versions of FCIQMC, including partial-node FCIQMC; showed in what cases the fermion sign problem is affected by moving from first to second quantization; and worked on numerous projects looking at critical scaling in dynamic quantum systems.


Copyright © Bryan Clark 2016