Our research deals with materials-oriented experimental condensed matter research with particular emphasis on quantum materials and nanoscale systems. Besides fundamental physics and materials syntheses we are also involved in application oriented research which ranges from electronics to biomedical applications.

"Quantum materials"  

In Quantum Materials a possible potential for technological applications emerges from their complex, quantum mechanical electronic properties. The complex electronic properties of " Quantum Materials" may result from the interplay and unusual ordering phenomena of electronic spin , orbital and charge degrees of freedom and can be observed in the context of topologically protected spin or charge states

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The above mentioned physical material's properties manifest in a number of material classes: in certain families of transition-metal oxides, in molecular solids and in a range of intermetallic materials. What sets these systems apart is that their valence and conduction electrons typically retain to some extent their atomic character, resulting in a rich interplay of localized and delocalized electronic degrees of freedom. This renders these materials both practically and conceptually very different from simple metals and semiconductors with well-understood itinerant quasi-particles. Often the quantum mechanical interplay between the localized and delocalized electronic degrees of freedom leads to anomalous charge transport properties, for instance due to the presence of metal-insulator transitions, and exceptional types of ordering phenomena, such as unconventional forms of superconductivity and quantum magnetism. Functionalities that arise from this are for instance large magnetocaloric effects, high temperature superconductivity, magnetism with very strong anisotropy and colossal/giant magnetoresistance.      

The plethora of spectacular and surprising phenomena that can occur in Quantum Materials poses one of the greatest set of challenges for cutting-edge experimental and theoretical condensed matter physics. As a rule material-specific predictions for the occurrence of many of these phenomena are very difficult, even if some of the presently booming research topics in this field, for instance the investigation of magnetic skyrmions and new topological states of matter, have emerged from a strong theoretical research effort and remain being strongly pushed by it.

“Nanometer-scale Quantum Materials”

When the dimensions of materials are restricted to the nanometer length-scale, new electronic properties emerge. This is related to the fact that any macroscopic object, when scaled down to a nanometer-scale, starts exhibiting distinct quantum mechanical properties. However, at the nanoscale also entirely new physical properties may emerge, for instance at surfaces and interfaces of topological insulators (TIs) where the spin of surface electrons is locked to their momentum, a property that is interesting in the context of spintronics.

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The technological ability to engineer and shape materials at the nanoscale opens up a very well-defined road to control the materials properties and functionality in a systematic manner. It requires the synthesis, modelling and structuring of nanosystems, which is pursued in the context of a broad span of nanoparticles, ranging from endohedral fullerenes, carbon-based buckytubes to intermetallic or oxide nanoparticles. This combined approach is also the basis for the design of interfaces and heterostructures of superconducting materials, magnetic systems and molecular solids. In these heterostructures charge transfer effects at or across interfaces are decisive for the properties and functionality. An advantage of such interfaces is that they can be modified and engineered to a much greater extent than bulk Quantum Materials.

Building on the traditional strength in the field of Quantum Materials, and in order to strengthen in particular this research area and its potential for device applications, in 2013 the Center for Transport and Devices of Emergent Materials (CTD) has been founded together with the TU Dresden.

Unique methodology: search, synthesis, analysis, and application potential of new materials

Our research teams search for new materials with the outlined unusual electronic properties and study their fundamental physical properties using a broad range of experimental techniques. Customized high resolution methodology is developed according to the specific scientific questions and phenomena, and finally, based on the experimental results, the chemistry, the morphology and the intrinsic physical properties of the materials are optimized with respect to technical applications. Some of the methodological developments of our institute push the limits of current condensed matter research. Such set-ups as well as the special infrastructure for materials synthesis are made available to cooperation partners at universities (crystal growth laboratory), worldwide users (ARPES measurement stations at the Berlin Synchrotron BESSY), or to industry partners (laboratory for spectroelectrochemistry).

Application-driven research activities

Based on our scientific expertise, our methodological experience, and based on our dedicated knowledge of specific materials classes, we also perform application-driven research in close cooperation with various industry partners. In many of these activities key challenges of the modern industrial and information society are addressed. For example, there are projects in cancer research based on our knowledge of molecular nanostructures.

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Additionally, our specific methodology and expertise for spectroelectrochemistry, magnetic materials, and oxide nanomaterials is used in industry projects concerning energy and/or mobility. The activities on novel magnetic materials are also motivated by the urgent issues of resources and sustainability. Moreover, the industry-oriented research of our institute includes since many years the topic "Surface Acoustic Waves (SAW)" dealing with innovative micro-acoustic components and devices as well as the associated high-tech materials and technologies. The IFW-driven "SAWLab Saxony - Competence Center for Acoustoelectronic Phenomena, Technologies and Devices" aims to bundle our profound SAW knowledge with experience and demands of several small and medium-sized Saxon high-tech companies fostering the close cooperation of our institute with the regional industry.

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Junior group at BESSY

The junior research group is set up to strengthen the collaboration between the HZB and IFW in the field of photoemission spectroscopy of quantum materials by means of further improvement of experimental equipment at BESSY synchrotron. Nowadays the successful photoemission experiments require state-of-the-art combination of synchrotron beamline and end-station with the spectrometer. It should provide the high momentum and energy resolution, broad temperature range at which measurements are possible with the emphasis of the coldest side, as well as a high degree of the automatization. A special importance have the integration of all the components including the monochromator of the beamline, cryostat, electron energy analyzer and manipulator into a common system with flexible communication between all these components and comfortable user interface. With the help of such improved experimental equipment the group is supposed to demonstrate how the modern photoemission experiment can contribute to design and understanding of novel quantum functional materials.


Unraveling the Nature of Magnetism of the 5d4 Double Perovskite Ba2YIrO6

S. Fuchs, T. Dey, G. Aslan-Cansever, A. Maljuk, S. Wurmehl, B. Büchner, and V. Kataev

Complex iridium oxides have attracted a large amount of interest in the condensed matter community worldwide due to prediction of exotic magnetic behaviours emerging from the strong coupling of the spin and orbital momenta (SOC) of the 5d iridium ions. In this respect, the origin of magnetism of the pentavalent iridium double perovskite Ba2YIrO6 was controversially debated. On conventional grounds the strong SOC should render it nonmagnetic. However, the contradictory experimental reports on either strongly antiferromagnetic or just weakly paramagnetic behaviour of Ba2YIrO6 have triggered theoretical scenarios on the possible breakdown of the SOC in the pentavalent iridates. Our multifrequency electron spin resonance (ESR) experiments on Ba2YIrO6 have ultimately settled this dispute. We have shown that the entire magnetic response of Ba2YIrO6 is due to the presence of defect paramagnetic Ir4+ (5d5) and Ir6+ (5d3) sites, while the regular Ir5+ (5d4) sites remain nonmagnetic. Remarkably, the defect Ir6+ species, which give the major contribution to the total magnetic response, manifest magnetic correlations in the ESR spectra at low temperatures, highlighting the relevance of long-range magnetic interactions in 5d double perovskites proposed in recent theoretical models. In fact, they might be even responsible for the magnetic order of defect Ir-based spin centers in Ba2YIrO6 if their concentration exceeds a certain threshold value.

Physical Review Letter

Intrinsic Charge Dynamics in High-Tc AFeAs(O,F) Superconductors

A. Charnukha, D. Pröpper, N. D. Zhigadlo, M. Naito, M. Schmidt, Zhe Wang, J. Deisenhofer, A. Loidl, B. Keimer, A. V. Boris, and D. N. Basov

Among the high-temperature iron-based superconductors, AFeAs(O,F) (A - rare earth element) or 1111-type materials hold the record for the highest superconducting transition temperature observed in the bulk, up to 55K. And yet, these compounds are among the least studied. This state of affairs owes to the difficulties in both material growth and experimental investigation: the laborious high-pressure synthesis produces microscopic single crystals with a polar cleavage plane, tremendously complicating both conventional optical and electron spectroscopy. Here, we employ an array of state-of-the-art experimental techniques to shed first direct light onto the intrinsic bulk charge carrier dynamics in 1111-type superconductors. We find a remarkably strong itinerant response, which is drastically modified in the superconducting state and provides evidence for a nodeless superconducting energy gap in the strong-coupling limit. Furthermore, we discover a conspicuous collective mode in the THz spectral range, whose energy and width vary linearly with temperature, suggestive of the hydrodynamics of density-wave fluctuations in correlated bad metals. Our observations uncover that highest-Tc iron-based pnictides share key correlated-electron phenomenology with other unconventional superconductors.

Nature Physics

Direct observation of spin–orbit coupling in iron-based superconductors

S. V. Borisenko, D. V. Evtushinsky, Z.-H. Liu, I. Morozov, R. Kappenberger, S. Wurmehl, B. Büchner, A. N. Yaresko, T. K. Kim, M. Hoesch, T. Wolf & N. D. Zhigadlo

Spin–orbit coupling is a fundamental interaction in solids that can induce a broad range of unusual physical properties, from topologically non-trivial insulating states to unconventional pairing in superconductors. In iron-based superconductors its role has, so far, not been considered of primary importance, with models based on spin- or orbital fluctuations pairing being used most widely. Using angle-resolved photoemission spectroscopy, we directly observe a sizeable spin–orbit splitting in all the main members of the iron-based superconductors.

Nature Communications

Nesting-driven multipolar order in CeB6 from photoemission tomography

A. Koitzsch, N. Heming, M. Knupfer, B. Büchner, P. Y. Portnichenko, A. V Dukhnenko, N. Y. Shitsevalova, V. B. Filipov, L. L. Lev, V. N. Strocov, J. Ollivier, D. S. Inosov        

Some heavy fermion materials show so-called hidden-order phases which are invisible to many characterization techniques and whose microscopic origin remained controversial for decades. Among such hidden-order compounds, CeB6 is of model character due to its simple electronic configuration and crystal structure. Apart from more conventional antiferromagnetism, it shows an elusive phase at low temperatures, which is commonly associated with multipolar order.

Physical Review Letter

Complex field-induced states in Linarite with a variety of high-order exotic SDWp states

B. Willenberg, M. Schäpers, A. U. B. Wolter, S.-L. Drechsler, M. Reehuis, J.-U. Hoffmann, B. Büchner, A. J. Studer, K. C. Rule, B. Ouladdiaf, S. Süllow, and S. Nishimoto

Angewandte Chemie Int. Ed. 2015

Synthesis and Structure of LaSc2N@Cs(hept)‐C80 with One Heptagon and Thirteen Pentagons

Y. Zhang, K. B. Ghiassi, Q. Deng, N. Samoylova, M. M. Olmstead, A. L. Balch, A. A. Popov

The synthesis and single-crystal X-ray structural characterization of the first endohedral metallofullerene to contain a heptagon in the carbon cage are reported. The carbon framework surrounding the planar LaSc2N unit in LaSc2N@Cs(hept)-C80 consists of one heptagon, 13 pentagons, and 28 hexagons. This cage is related to the most abundant Ih-C80 isomer by one Stone–Wales-like, heptagon/pentagon to hexagon/hexagon realignment. DFT computations predict that LaSc2N@Cs(hept)-C80 is more stable than LaSc2N@D5h-C80, and suggests that the low yield of the heptagon-containing endohedral fullerene may be caused by kinetic factors

Nature Communications

Orbital reconstruction in nonpolar tetravalent transition-metal oxide layers

N. A. Bogdanov, V. M. Katukuri, J. Romhányi, V. Yushankhai, V. Kataev, B. Büchner, J. van den Brink, and L. Hozoi

Sr2IrO4  is a prototypical spin-orbital Mott insulator which has attracted considerable interest in recent years. ESR experiments combined with ab initio quantum chemistry methods have enabled to untangle the 5d-shell electronic structure of Sr2IrO4, in particular an unexpected inversion of the ordering of the t2g orbital states.

Phys. Rev. Lett. 114

Mutual Independence of Critical Temperature and Superfluid Density under Pressure in Optimally Electron-Doped Superconducting LaFeAsO1−xFx

G. Prando, Th. Hartmann, W. Schottenhamel, Z. Guguchia, S. Sanna, F. Ahn, I. Nekrasov, C.G.F. Blum, A.U.B. Wolter, S. Wurmehl, R. Khasanov, I. Eremin and B. Büchner

ERC Consolidator Grant for
Dr. Christian Hess

Electronic Order, Magnetism, and Unconventional Superconductivity in Real-Space

ERC Consolidator Grant for
Dr. Alexey Popov

Surface-grafted metallofullerene molecular magnets with controllable alignment of magnetic moments

New Collaborative Research Center "Correlated Magnetism: From Frustration To Topology" (SFB 1143) with participation of scientists from the Institute for Solid State Research
(Press Release of TU Dresden)

Nature Materials

Orbital-driven Nematicity in FeSe

S-H. Baek, D. V. Efremov, J. M. Ok, J. S. Kim, J. van den Brink, and B. Büchner

Iron selenide is an appealingly clean system for understanding the origin of superconductivity in iron-based superconductors. A detailed NMR study shows that the nematic order preceding the superconducting phase is driven by orbital degree of freedom.

Physical Review Letters

Experimental Realization of a
Three-Dimensional Dirac

Using angle-resolved photoemission
spectroscopy, a 3D Dirac semimetal
phase has been observed in
Cadmium Arsenide for the first time.