Profiles

Johan Carlström

Postdoktor

Visa sidan på svenska
Works at Department of Physics
Email johan.carlstrom@fysik.su.se
Visiting address Roslagstullsbacken 21
Room C5:3004
Postal address Fysikum 106 91 Stockholm

About me

I am currently working at Stockholm University with Emil Bergholtz. 

SCIENTIFIC INTERESTS

Statistical properties of Strongly correlated systems

I am currently exploring a new computational strategies for strongly correlated fermionic systems that is based on Diagrammatic Monte Carlo in combination with spin-charge transformation. Specifically, by mapping lattice fermion models onto spins and spin-less fermions, it is possible to construct dual models that exhibit much weaker interactions than the original models http://iopscience.iop.org/article/10.1088/1361-648X/aa7e1b/meta (IOP 2016). This makes it possible to apply diagrammatic techniques even in the strongly correlated regime https://arxiv.org/abs/1709.06415 (arXiv 2017)

 

Dynamics of strongly interacting systems 

An open fundamental question in quantum mechanics is the nature of propagation in an environment that posses a memory of particle trajectories. A basic example of this is a hole moving in a degenerate spin environment. This canonical problem has important connections to fundamental properties of strongly correlated systems, such as density of states. Recently we published the first large scale simulations exploring this topic http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.247202 (PRL 2016).

 

Interactions in Dirac systems

I am currently working with Emil Bergholtz on the role of interactions in Dirac systems like graphene, Weyl semi metals and 3D Dirac materials. Recently we found that in a wide range of semi-metallic systems, the nodal points are protected by symmetries in the presence of interactions https://arxiv.org/abs/1712.06610 (arXiv 2017). We are now exploring Coulomb interactions in Weyl semi-metals using diagrammatic Monte Carlo. 

 

Phase transitions in Multicomponent Superconductors

Multiband models support entropically stabilised states with additional superfluid channels. This is in stark contrast to the usual scenario where thermal fluctuations destroy superfluidity. This finding was awarded editors suggestion http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.055301 (PRL 2014) and was also featured in Nature Physics http://www.nature.com/nphys/journal/v10/n9/full/nphys3091.html.

 

Frustrated Superconductors

Transitions between broken and unbroken time-reversal symmetry in frustrated superconducting systems is associated with massless Leggett modes. The state with broken time-reversal symmetry also features a mass matrix that mixes the phase and amplitude sectors so that perturbations to amplitude necessitates perturbation to the phase differences and vice versa. This gives rise to a new mechanism for long range intervortex interaction http://journals.aps.org/prb/abstract/10.1103/PhysRevB.84.134518 (PRB 2011). 

Frustrated superconductors also support a new form of topological flux-carrying objects in the form of solitons http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.107.197001 (PRL 2011). These solitons exhibit a chirality, something which was awarded editors suggestion http://journals.aps.org/prb/abstract/10.1103/PhysRevB.87.014507 (PRB 2013).

 

Type-1.5 Superconductivity 

Non-monotonic intervortex forces resulting from the presence of additional length scales in multicomponent superconductors give rise to a new magnetic response in the form of the Semi-Meissner state. These systems cannot be categorised according to the Type-I/Type-II dichotomy http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.105.067003 (PRL 2010). 

 

COLLABORATORS

Emil J Bergholtz, Stockholm University, Sweden

Boris Svistunov UMASS, Amherst

Nikolay Prokof’ev UMASS, Amherst

Egor Babaev (Previous supervisor), KTH, Stockholm

Julien Garaud, University of Massachusetts, Amherst and KTH, Stockholm

Martin Speight, School of Mathematics, University of Leeds, UK

Mihail Silaev, IPM Russian Academy of Sciences and KTH, Stockholm

 

BRIEF CV

Postdoctoral research associate at Stockholm University, Sweden.

EDUCATION

Undergraduate studies: 2004-2009: Master, Engineering Physics, KTH, Stockholm.

Graduate studies: 2009-2014: Department of Theoretical Physics, Statistical Physics group, KTH. Thesis title: Multicomponent Superconductivity: Vortex Matter and Phase Transitions. Supervisor: Egor Babaev.

 

POSTDOCTORAL APPOINTMENTS 

Sep. 2017 - Present: Postdoctoral research associate at the Dept. of Physics, Stockholm University,  Sweden.

Jan. 2015 - May 2017: Postdoctoral research associate at the Dept. of Physics, University of Massachusetts,  Amherst, USA.

 

GRANTS

2014: The Wenner-Gren Foundations in Stockholm, 2 year postdoctoral fellowship.

2014: Stiftelsen Olle Engkvist Byggmästare, 2 year postdoctoral fellowship (declined).

 

ARTICLES IN PEER REVIEWED JOURNALS  

1) Type-1.5 Superconducting State from an Intrinsic Proximity Effect in Two-Band Superconductors, Babaev, Carlström, and Speight, Phys. Rev. Lett. 105, 067003 (2010).

 

2) Type-1.5 Superconductivity in Two-Band Systems, (proceedings of the Vortex VI conference, featured in top 25 downloaded articles of Physics C), Babaev and Carlström, Physica C: Superconductivity, Volume 470, Issue 19, 1 October 2010, Pages 717–721.

 

3) Type-1.5 Superconductivity in Multiband Systems: Effects of Interband Couplings, Carlström, Babaev and Speight, Phys. Rev. B 83, 174509 (2011).

 

4) Semi-Meissner State and Nonpairwise Intervortex Interactions in Type-1.5 Superconductors, Carlström, Garaud, and Babaev, Phys. Rev. B 84, 134515 (2011).

 

5) Length Scales, Collective Modes, and Type-1.5 Regimes in Three-Band Superconductors, Carlström, Garaud, and Babaev, Phys. Rev. B 84, 134518 (2011).

 

6) Topological Solitons in Three-Band Superconductors with Broken Time Reversal Symmetry, Garaud, Carlström, and Babaev, Phys. Rev Lett, 107, 197001 (2011).

 

7) Type-1.5 superconductivity in Multiband systems: Magnetic response, Broken Symmetries and Microscopic Theory – A brief overview, Babaev, Carlström, Garaud, Silaev and Speight, Volume 479, September 2012, Pages 2–14.

 

8) Chiral CP2 skyrmions in Three-Band Superconductors, Garaud, Carlström, Babaev, and Speight, Phys. Rev. B 87, 014507 (2013), (Editors suggestion).

 

9) Entropy- and Flow-induced Superfluid States, Carlström and  Babaev, Phys. Rev. Lett, 113, 055301 (2014), (Editors suggestion), also featured in Nature Physics. 

 

10) Spontaneous breakdown of time-reversal symmetry induced by thermal fluctuations, Carlström and Babaev, Phys. Rev. B 91 140504(R) (Rapid Communication) (2015). 

 

11) Quantum Walk in Degenerate Spin Environments, Carlström, Prokof’ev, and Svistunov, Phys. Rev. Lett. 116, 247202 (2016)

 

12) Type-1.5 superconductivity in multicomponent systems, Babaev, Carlström, Silaev and Speight, PHYSC 1253076 (2016). 

 

13) Spin-charge transformation of lattice fermion models: duality approach for diagrammatic simulation of strongly correlated systems, Carlström, Journal of Physics: Condensed Matter 29 (38), 385602.

 

PREPRINTS

1) Diagrammatic Monte Carlo procedure for the spin-charge transformed Hubbard model, Johan Carlström, arXiv:1709.06415 (2017)

 

2) Symmetry Enforced Stability of Interacting Weyl and Dirac Semimetals, Carlström, Bergholtz, arXiv:1712.06610 (2017)

 

BOOKS

1)    Superconductors at the nanoscale: From basic research to applications, De Gruyter (ISBN 978-3-11-045680-6) (*Coauthored chapter 4). 

 

Last updated: May 7, 2018

Bookmark and share Tell a friend