Johan Fredrik Carlström
About me
I am currently working at Stockholm University with an independent research position funded by the Swedish research council.
SCIENTIFIC INTERESTS
Exact techniques for Strongly correlated systems fermions
Recently, I have worked on developing diagrammatic methods for the strongly correlated regime. I have also used worm techniques for this purpose.
https://www.nature.com/articles/s42005-020-00408-z
https://journals.aps.org/prb/abstract/10.1103/PhysRevB.97.075119
https://arxiv.org/abs/1909.00816
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 the 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 semimetals, 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 stabilized 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 are 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 categorized 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
Emil Blomquist, 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.
CURRENT POSITION
Researcher at Stockholm University with a starting grant from VR.
CURRENT GROUP
Tommaso Bertolini, PhD student.
Carlos Naya Rodriguez, Postdoc
Ilaria Maccari, Postdoc
POSTDOCTORAL APPOINTMENTS
Sep. 2017 - 2019: 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
2020: Carl Tryggers stiftelse, Project grant of 600,000 sek over 2 years.
2020: Olle Engkvists stiftelse, Project grant of 620,000 sek over 2 years.
2019: Swedish research council, Stating grant of 3000,000 sek (~310,000 $) over 4 years.
2014: The Wenner-Gren Foundations in Stockholm, 2 year postdoctoral fellowship.
2014: Stiftelsen Olle Engkvist Byggmästare, 2 year postdoctoral fellowship.
