Correlated Dirac Fermions in Organics

Date

Sep 30, 2019

Time

2:00 PM - 3:00 PM

Speaker

Dr. Michihiro Hirata

Affiliation

Institute for Materials Research (IMR), Tohoku University, Sendai, Japan

Language

en

Main Topic

Chemie

Other Topics

Chemie

Host

Dr. M. Baenitz

Description

In this talk, I will highlight the recent advances in understanding of the interaction effects of pseudo-relativistic electrons in solids, which has been one of the major interests in the study of topological quantum materials [1,2]. Focusing on the pressurized organic salt  (BEDT TTF)2I3 hosting interacting 2D massless Dirac fermions, we have characterized various correlation effects by 13C NMR in the temperature-pressure (T-P) phase diagram. Combined with numerical calculations at mean-field and renormalization-group levels, we have succeeded in providing basic frameworks for the excitation and correlation mechanisms in this compound. At high P of 2.3 GPa, fits to the data using the resulting interaction model elucidate notable correlation effects, ranging from a Dirac-cone reshaping and bandwidth renormalization to ferrimagnetic spin polarization [3]. We further observed additional spin fluctuations growing at low T, which according to our numerical studies correspond to incommensurate excitonic fluctuations developing as a precursor to a transition from massless to massive Dirac states [4]. With decreasing P, both the cone reshaping and the excitonic instability intensify, signaling a pronounced enhancement of the size of the electron-electron Coulomb interaction, in excellent agreement with supportive model calculations. Below a threshold P (~ 1.0 GPa), moreover, we find another instability to take over having a spin-singlet, commensurate charge structure, which is well understood based on our Hubbard-type model as a direct transition between the massless Dirac state and a stripe-charge ordered insulating state. These findings pave the new avenue not only for the exploration of the electronic instabilities in  (BEDT-TTF)2I3, but also for studies of many other topological quantum materials with complex interactions that stabilize and lead to competition of new phases of matter. [1] V. N. Kotov, B. Uchoa, V. M. Pereira, F. Guinea, and A. H. Castro Neto, Rev. Mod. Phys. 84, 1067 (2012). [2] T. O. Wehling, A. M. Black-Schaffer, and A. V. Balatsky, Adv. Phys. 63, 1 (2014). [3] M. Hirata, K. Ishikawa, K. Miyagawa, M. Tamura, C. Berthier, D. Basko, A. Kobayashi, G. Matsuno, and K. Kanoda, Nat. Commun. 7, 12666 (2016). [4] M. Hirata, K. Ishikawa, G. Matsuno, A. Kobayashi, K. Miyagawa, M. Tamura, C. Berthier, and K. Kanoda, Science (80-. ). 358, 1403 (2017).

Links

• MPI CPfS

Last modified: Oct 1, 2019, 12:09:21 AM