Quantensysteme

Advanced Seminar on Condensed Matter Physics

Sommersemester 2019

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INF 227, SR 1.403
Friday 11:00 h

26.4.2019 11:00 h
Prof. Dr. A.K. Raychaudhuri, S.N. Bose National Centre in Basic Sciences JD Block, Salt lake Sector III, Kolkata 700098
INF 227, SR 1.403
17.5.2019 11:00 h
Dr. Pascal Reiss, University of Oxford
INF 227, SR 1.403

When a continuous phase transition (such as ferromagnetism or antiferromagnetism) is suppressed from some finite temperature to zero Kelvin by means of an external tuning parameter, a quantum critical point can be reached. As a consequence, it has been observed in many different electronic systems that unconventional superconductivity often emerges in the proximity of such quantum critical points. This raises the fundamental question about the role of critical fluctuations in mediating a superconducting pairing interaction.
Recently, electronic nematic fluctuations have been identified as a candidate for enhancing superconductivity in various unconventional superconductors, most prominently in the iron-based superconductors. However, the often encountered coexistence with long-range magnetic order has hindered detailed studies of nematic criticality. To address this challenge, a member of the 11 family of iron-based superconductors, FeSe, is particularly suited. We use a combination of iso-electronic chemical substitution in FeSe1-xSx to suppress long-range magnetic order, and physical pressure to study the uncovered, nematic quantum phase transition. Using magneto-transport and quantum oscillations measurements, we trace the strength of electronic correlations and their role played in promoting superconductivity. We demonstrate that electronic correlations remain finite, the Fermi surface suffers a Lifshitz transition, and superconductivity is weakened across the nematic quantum phase transition. We interpret these results in light of recent theoretical and experimental advances.

14.6.2019 11:00 h
Aljoscha Auer
INF 227, SR 1.403
16.7.2019 11:00 h
Prof. Dr. Alexander Vassiliev, Moscow State (Lomonosov) University
INF 227, SB1
16.7.2019 12:00 h
Dr. Olga Maximova, Moscow State (Lomonosov) University
INF 227, SR 1.403