• 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 2019

  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.

COLLABORATIVE RESEARCH CENTER 1238

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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© 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

B01 (Lorenz / Ando)

Transport and thermodynamics

 

B02 (Grüninger / Hemberger)

From mHz to PHz: Broadband dielectric and optical spectroscopy
of quantum matter

 

B03 (van Loosdrecht / Grüninger)

Inelastic photon scattering in spin-orbit-coupled matter

 

B04 (Braden)

Dynamics and correlations studied by neutron scattering

 

B05 (van Loosdrecht)

Optically driven matter

 

B06 (Michely / Ando)

Scanning tunneling spectroscopy

C01 (Atodiresei / Blügel)

Structure inversion-asymmetric  matter and spin-orbit
phenomena from ab-initio

 

C02 (Rosch / Trebst)

Spin-orbit driven topological and correlated states and
Dirac matter

 

C03 (Trebst / Diehl / Bulla)

Thermodynamics of fractionalization in spin-orbit entangled
matter

 

C04 (Diehl / Rosch)

Dynamics of topological and correlated states of matter

 

C05 (Kollath)

Driven quantum matter

Theory

© Simon Wegener

Directions

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Road maps

 

funded by: