ConQuMat - TRR360

Steering Committee Meeting
2024-05-14 12:00 - 13:00 (Europe/Berlin)

TRR 360 Seminar: Altermagnetism: spin symmetry prediction and photoemission observation Libor Šmejkal
2024-05-07 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Altermagnetism: spin symmetry prediction and photoemission observation

Libor ŠmejkalUniversity of Mainz

Venue

TRR 360 Seminar: Quantum criticality on compressed lattices Markus Garst
2024-04-24 14:00 - 15:00 | Technical University Munich + Zoom
Quantum criticality on compressed lattices
Prof. Dr. Markus Garst
Karlsruher Institut für Technologie

At a quantum phase transition, the ground state of a system changes as a function of a non-thermal control parameter. In a solid, the associated quantum critical degrees of freedom generically couple to the crystal lattice. This coupling is potentially able to change the universality class of the quantum critical point. We discuss various scenarios where this is realised. The coupling is necessarily non-perturbative when the order parameter couples bilinearly to strain as it is the case for quantum critical endpoints or nematic quantum criticality [1]. If the strain couples only to the square of the order parameter, it is non-perturbative at weak coupling if the effective dimension d+z, with the spatial dimension d and the dynamical exponent z, is smaller than 2/ν, where ν is the correlation length exponent. This criterion is, for example, marginally fulfilled at a Lifshitz transition of a two-dimensional metal like Sr2RuO4 [2]. We discuss in detail the quantum phase transition in the O(N) universality class with dynamical exponent z=1, and we show that non-perturbative effects might also arise if this criterion is not fulfilled but the coupling exceeds a critical threshold [3].
[1] I. Paul and M. Garst, Phys. Rev. Lett. 118, 227601 (2017).[2] H. M. L. Noad et al. Science 382, 447 (2023)[3] S. Sarkar, L. Franke, N. Grivas and M. Garst, Phys. Rev. B 108 235126 (2023).

Venue

TRR 360 Sonderseminar: Magnetic field versus temperature phase diagram of an effective spin-1/2 zigzag chain in a magnetic semiconductor YbCuS2 Takahiro Onimaru
2024-03-11 11:30 - 12:30 | University of Augsburg, Room S-288 + Zoom
Magnetic field versus temperature phase diagram of an effective spin-1/2 zigzag chain in a magnetic semiconductor YbCuS2
Prof. Dr. Takahiro Onimaru
Graduate School of Advanced Science and Engineering, Hiroshima University, Japan

Venue

2. Steering Committee Meeting
2024-02-19 13:00 - 16:00 | Zoom Conference

TRR 360 Seminar: Controlled quantum materials Daniele Fausti
2024-01-30 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Controlled quantum materials
D. Fausti 1,2,3
1 Department of Physics, University of Trieste, Trieste
2 Elettra Sincrotrone Trieste S.c.p.a., Trieste
3 Department of Physics, University of Erlangen Nuremberg
The rich phase diagrams of many transition metal oxides (TMOs) is the result of the intricate interplay between electrons, phonons, and magnons. This makes TMOs very susceptible to external parameters such as pressure, doping, magnetic field, and temperature which in turn can be used to finely tune their properties. The same susceptibility makes TMOs the ideal playground to design experiments where the interaction between tailored electromagnetic fields and matter can trigger the formation of new, sometimes exotic, physical properties. This aspect has been explored in time domain studies [1] and has led to the demonstration that ultrashort mid-IR light pulses can “force” the formation of quantum coherent states in matter, disclosing a new regime of physics where thermodynamic limits may be bridged and quantum effects can, in principle, appear at ambient temperatures.
In this presentation I will review our recent results in archetypal strongly correlated cuprate superconductors and demonstrate the feasibility of a light-based control of quantum phases in real materials [2,3,4]. I will then introduce our new approaches to time domain spectroscopy going beyond mean photon number observables [5-10] and show that the statistical features of light can provide information on superconducting fluctuations beyond standard linear and non-linear optical spectroscopies [11]. Finally, I will elaborate on our current research effort to use cavity electrodynamics to control fluctuations in matter and thereby the onset of quantum coherent states in complex materials [12].
References:
[1] Advances in Physics 65, 58-238, 2016
[2] Science 331, 189-191 (2011)
[3] Phys. Rev. Lett. 122, 067002 (2019)
[4] Nature Physics 17, 368–373 (2021)
[5] Phys. Rev. Lett. 119, 187403 (2017)
[6] New J. Phys. 16 ,043004 (2014)
[7] Nat. Commun. 6, 10249 (2015)
[8] PNAS March 19, 116 (12) 5383-5386 (2019)
[9] J. of Physics B 53, 145502 (2019)
[10] Optics Letters 45, 3498 (2020)
[11] Light: Science & Applications 11, # 44 (2022)
[12] Nature 622, 487–492 (2023)

Venue

1. Steering Committee Meeting
2024-01-25 11:00 - 12:00 | Zoom Conference

TRR 360 Seminar: Broadband optical studies of kagome metals Ece Uykur
2024-01-16 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Broadband optical studies of kagome metals: Electronic correlations, localized
carriers and phonons
Ece Uykur
Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum
Dresden-Rossendorf, 01328, Dresden, Germany

Kagome metals attract a lot of attention as materials that combine two extreme features in their
electronic structure: Massless Dirac fermions with linear band dispersion and flat bands hosting massive
localized electrons. Topological nature of the former and strongly correlated nature of the latter lead to
multitude of exotic phenomena, including quantum anomalous Hall effect and novel states, such as axion insulators. The electron dynamics of these systems is the key for understanding the proposed exotic phenomena.
To this end, we employed broadband infrared and ultrafast pump-probe spectroscopy studies on
series of kagome metals. In this talk, I will summarize the optical fingerprints of itinerant and localized
carriers, signatures of electronic correlations, and the interplay between unconventional carriers and
phonons in these systems.

Venue

TRR 360 Seminar: Magneto-optical detection of topological contributions to the anomalous Hall effect in kagome magnets Sándor Bordács
2023-12-05 16:00 - 17:00 | University of Augsburg, Room S-288 + Zoom
Venue

Young Researchers Forum 2023
2023-11-28 10:00 - 2023-11-29 16:00 | University of Augsburg, Universitätsstr. 2, Augsburg, 86159
This 2-day event will be used as an ice breaker for the members of the MGK. The young researcher get the chance to get to know each other. First young researchers present topics related to their work. The Ö-project gives a presentation about Educational Escape Games and ideas of the young researchers for the Quantum Escape Game of the Ö-projects shall be discussed.

TRR 360 Sonderseminar: The unusual electron transport in metallic Kagome nets Philip J. W. Moll
2023-11-08 17:00 - 18:00 | University of Augsburg, Room S-288 + Zoom
The unusual electron transport in metallic Kagome nets
Prof. Dr. Philip J. W. Moll
Max Planck Institute for the Structure and Dynamics of Matter

Materials that can host different states of electronic order form a recurring theme in physics and
materials science, and they are of particular interest if they are coupled strongly. A famous
example are ferroelectrics, in which electric polarization and magnetism not only coexist but are
strongly linked. This both unveils a rich physics of correlated states, and also opens unexpected
application avenues as the coupling promises to manipulate one state by a stimulus that primarily
acts on another – say switching magnetism using electric fields.
Recently, materials based on the structural motif of the Kagome web have attracted significant
attention for their tendency to host such strongly coupled phases. In particular, the centro-
symmetric layered Kagome metal (K,Cs)V3Sb5 have entered the focus of experimental and
theoretical research. They host a charge-density-wave type transition at elevated temperatures
~100K, followed by a superconducting transition at 3K (exact values depend on composition).
Yet there is another type of electronic order which thus far eludes exact microscopic
identification. A series of experimental probes detects the onset of anomalous behavior around
T’~30-40K, including thermal Hall, µSR, NMR, magnetic torque, Kerr rotation. The anomalous
low-temperature state carries the characteristics of a chiral, nematic and time-reversal-symmetry
breaking fluid (all of which are under most active debate currently).
Yet what crystallizes out of the current state of experimental data is a highly entangled system
which is extraordinarily responsive to external perturbations. This materials main strength is
equally its weakness, the unusual degree of coupling between states can hinder its systematic
investigation. However, it is already clear that it provides a platform to explore strongly coupled
correlated phases, and as a result it displays a thus-far unknown electromagnetic response, a
diode in which the forward direction can be switched by the application of a magnetic field. I
will review the current state of the field, and discuss ongoing projects in my department.

[1] C. Guo et al., Nature 611, 461-466 (2022)
[2] X. Huang et al., PRB 106, 064510 (2022)

Venue

Retreat Meeting 2023
2023-10-09 - 2023-10-10 | Kloster Irsee, Klosterring 4, Irsee, 87660, Germany
The first project retreat meeting of TRR360 – ConQuMat takes place at Kloster Irrsee. There, all project members get together to introduce their research plans and subprojects as well as get to know each other.
