Spin-orbit Coupling, Correlations, and Topology

© Simon Wegener

News & Events


  • Independence Grant Awards 2019

    Congratulations to
    Dr. Jens Brede, Dr. Oliver Breunig, Dr. Christian Dickel,
    Dr. Jeison Fischer, Dr. Boris Senkovskiy and Dr. Shilong Wu,
    six promising young researchers who have been awarded a CRC1238 Independence Grant.


    This grant will allow them to become more independent and help their own career by supporting their travel and own project's costs.

  • Exotic behaviour of electrons observed

    A group of physicists at the Institute of Physics II have, for the first time, seen a particularly exotic electron behaviour in real space. Electrons usually move almost freely through three-dimensional space. However, when they are forced to move in only one dimension – i.e. along a chain of atoms – the electrons’ properties seem to split up. They normally have both a ‘spin’ – a quantum mechanical angular momentum – and a charge. In one dimension however, they stop behaving like normal electrons due to their strong interaction with each other. Instead, they divide into two types of quasi-particle that carry either the spin or the charge only. Until now, this phenomenon could only be shown indirectly by physicists’ experiments. Recently, an international team lead by Professor Dr Thomas Michely has created one-dimensional wires, in which they could locally observe this rare behaviour of trapped electrons for the first time, using a scanning tunnelling microscope. With this new find the limits of the Tomonaga-Luttinger Liquid theory – which explains this strange phenomenon – can be tested with new precision.


    Physical Review X

    Pro Physik

    Science Daily

    Phys. Org

    press release



  • Classic double-slit experiment in a new light

    Young’s double-slit experiment is the prototype for any interference phenomenon based on elastic scattering. The discovery of a double-slit-type interference pattern in resonant inelastic x-ray scattering (RIXS) on Ba3CeIr2O9 confirms a prediction dating from 1994 and establishes a new versatile tool to measure the symmetry of excited states in the same way as elastic scattering does for the ground state. The two-beam interference of dimers is the simplest and most transparent example for such interference effects. In Ba3CeIr2O9, it reveals clear fingerprints of a dimerized valence bond solid with singlets built from spin-orbit-entangled j=1/2 pseudospins instead of simple spins, as reported in Science Advances.


    Science Advances

    Welt der Physik

    Physics World

    press release

  • CRC1238 Invited Speakers at the APS March Meeting 2020

    Three CRC1238 members, Ciarán Hickey (Postdoctoral fellow), Thomas Lorenz (Principal Investigator), and Daniel Khomskii (Mercator Fellow) will be giving invited talks at the upcoming  APS March Meeting, taking place in Boston from March 4th to 8th, 2019. The talks will cover Kitaev spin liquids, field-driven phase transitions in spin chain materials, and the formation of molecular clusters in 4d and 5d compounds.


© Simon Wegener



Control and Dynamics of Quantum Materials

Spin orbit coupling, correlations, and topology

Advances in materials science are one of the strongest drivers of technological innovations and thereby shape our daily life, though often in an unseen way. Powerful examples from recent years include the advent of novel memory technologies building on magnetoresistance read/write heads, ferroelectric, and phase-change memories. The discovery of fascinating materials like graphene has led to a worldwide surge of research initiatives for innovative applications of these and other novel two dimensional materials. Spin-orbit coupled materials such as the recently discovered topological insulators from a new class of solids that have a strong potential for novel functionalities.


Material-based technological innovations are more often than not initiated on the basic-science level through discoveries of new concepts, phenomena, and principles governing the physical properties of quantum materials. Research on quantum materials is a rapidly developing and internationally highly competitive interdisciplinary field. At the forefront of this field, new materials are being investigated in which relativistic spin-orbit effects and non-trivial topologies are at center stage. At the same time, materials with strong electronic correlations exhibit a wealth of non-trivial quantum ordering phenomena including superconductivity, magnetism, and other exotic orders. Precisely at the intersection of these research fields, our collaborative research center aims at exploring, understanding, developing, and utilizing quantum materials to gain deliberate control of the physical properties of these materials and to understand their dynamics, explore driven states of matter, and enable new functionalities.


Our diverse team of principle investigators includes scientists from experimental and theoretical physics as well as crystallography, building and expanding on the excellent research infrastructure in Cologne embedded in the Excellence Initiative key profile area 'quantum matter and materials'. The Cologne team is augmented by excellent scientists with indispensable expertise from the University of Bonn and the Forschungszentrum Jülich. Guiding philosophies of our program are the ‘materials - physical properties - theory' cycle, which is one of the cornerstones of the success of condensed-matter physics at the University of Cologne, and a multifaceted approach arising from addressing scientific topics from a variety of different perspectives as defined in the focus areas of the program.


The CRC will consolidate and expand Cologne together with the associated groups from Bonn and Jülich as a leading international center within quantum condensed-matter physics. Our vision is to discover, understand, and control novel collective phenomena in quantum materials arising from the interplay of spin-orbit coupling, correlations, and topology.

© Simon Wegener


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Yoichi Ando

A04 /         /

topological materials,
materials synthesis,

transport measurements

Nicolae Atodiresei



first principles simulations,

molecular nanostructures,

hybrid interfaces, molecular

electronics and spintronics

Petra Becker-Bohatý



crystal chemistry,

structural crystallography,

crystal growth, crystal physics,

materials science

Stefan Blügel



theory of electronic properties of real solids, spintronics,

low-dimensional systems,

spin-orbit related phenomena



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Markus Braden

A02 /


strongly correlated electrons, magnetism, x-ray and neutron scattering, crystallography, sample synthesis

Ralf Bulla



theory of condensed matter,

quantum phase transitions,

quantum impurity physics,

renormalization group methods

Sebastian Diehl

C03 / C04


driven open quantum systems, topological order out of equilibrium, functional renormalization group techniques, Keldysh path integrals

Alexander Grüneis



2D materials: synthesis and

functionalization photoelectron spectroscopy

Raman spectroscopy


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Markus Grüninger

B02 / B03


exp. condensed matter physics, optical spectroscopy, strongly correlated  electron systems, spins and orbitals,

topological insulators

Joachim Hemberger



broadband dielectric and optical spectroscopy, frustrated magnetism,

ferroelectrics, multiferroics,

spin-ice, (quantum-)critical dynamics

Maria Hermanns



theory of condensed matter,

strongly correlated systems,

quantum spin liquids, entanglement, fractional quantum Hall effect

Corinna Kollath



correlated many body systems, non-equilibrium phenomena in quantum

systems, numerical many-body physics

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© Patrick Fouad

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Thomas Michely

A01 /


thin film growth kinetics and

epitaxy (oxides, metals, organics), epitaxial graphene and 2D-layers, scanning tunneling microscopy and spectroscopy

Thomas Lorenz

A02 /


thermodynamics and transport, crystal growth,
frustrated quantum spin systems, spin-state transitions, multiferroics


Achim Rosch

C02 / C04


condensed matter theory,

topological states, spin torques and skyrmions,

quantum phase transitions,

non-equilibrium and equilibration

Simon Trebst

C02 / C03


condensed matter theory,

correlated electron systems,

frustrated quantum magnets,

topological order, entanglement, numerical many-body physics


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Paul van Loosdrecht

B03 / B05


optically induced phenomena and non-equilibrium states of matter, steady state and time resolved advanced optical spectroscopy

Fan Yang



exp.condensed matter physics,
topological materials,
transport measurements,
nano-device fabrication

© Simon Wegener


Project Area A

Materials – preparation and characterization

A01 (Grüneis / Michely)

Spin-orbit coupling and many-body effects in novel 2D materials


A02 (Becker-Bohatý / Braden / Lorenz)

Crystal growth and design of materials


A04 (Ando / Yang)

Topological matter

Project Area B

Physical properties

© Simon Wegener

Participating institutes



Prof. Dr. Paul van Loosdrecht

II. Physikalisches Institut

Universität zu Köln

Zülpicher Str. 77

50937 Köln

Tel: +49 221 470 2707


Clara Berthet

II. Physikalisches Institut

Universität zu Köln

Zülpicher Str. 77

50937 Köln

Tel.: +49 221470 -2106 or -6998

Administrative coordinator

Dr. Thomas Koethe

II. Physikalisches Institut

Universität zu Köln

Zülpicher Str. 77

50937 Köln

Tel: +49 221 470 3659

Scientific coordinator



Road maps