Our group focuses on complex transition metal compounds with partially filled d- or f-shells. Such materials show a plethora of unusual and fascinating phenomena, such as high-temperature superconductivity, colossal magnetoresistance, multiferroic ordering phenomena, low-dimensional quantum magnetism or quantum phase transitions. All these effects arise from many-body physics of interacting electrons, which cause fluctuations and/or complex ordering phenomena of the spin, charge, lattice or orbital degrees of freedom. The understanding of the interplay of these degrees of freedom is of fundamental importance and goes far beyond the material-specific questions. The continuous search of new phenomena and systematic studies of proper model systems in order to identify the underlying microscopic mechanisms are of fundmental interest for modern solid-state physics.

Our in-house experimental techniques include crystal growth and characterization, measurements of different thermodynamic and magnetic properties as well as the study of electric and thermal transport properties. Depending on the experimental demands, these measurements can be performed in a temperature range from about 20 mK up to 1000K and in external magnetic fields up to 17 Tesla.

One focus of our current research work is the study of low-dimensional spin systems, whereby on the one hand the focus is on magnetic field-induced quantum phase transitions and on the other hand the influence of magnetic frustration [1-4]. Other focal points are the investigation of thermal and electrical transport properties [5, 6, 7] and the study of magnetic, structural and / or (ferro-) electrical ordering phenomena [7, 8, 9]. More literature about our work can be found here.

Bachelor or Master Thesis

All topics above are open for bachelor and master students to conduct part of our research within a thesis project. Depending on your personal interests, either more technical aspects (e.g. setting up new measurement environments) or more theoretical and analytical interpretation of experimental data may become the focus of the work. In case of interest on our research, please do not hesistate to contact us for a meeting.  Thomas Lorenz

[1] see e.g.: S. Sachdev and B. Keimer. Quantum criticality Phys. Today 64, 29 (2011)

[2] Zhe Wang, T. Lorenz, D.I. Gorbunov, P.T. Cong, Y. Kohama, S. Niesen, O. Breunig, J. Engelmayer, A. Herman, Jianda Wu, K. Kindo, J. Wosnitza, S. Zherlitsyn, A. Loidl; Quantum Criticality of an Ising-like Spin-1/2 Antiferromagnetic Chain in a Transverse Magnetic Field; Phys. Rev. Lett., 120, 207205, 2018

[3] Oliver Breunig, Markus Garst, Andreas Klümper, Jens Rohrkamp, Mark M. Turnbull, Thomas Lorenz; Quantum criticality in the spin-1/2 Heisenberg chain system copper pyrazine dinitrate; Sci Adv, 3, eaao3773, 2017

[4] O. Breunig, M. Garst, E. Sela, B. Buldmann, P. Becker, L. Bohaty, R. Müller, T. Lorenz; The spin-1/2 XXZ chain system Cs₂CoCl₄ in a transverse magnetic field; Phys. Rev. Lett., 111, 187202, 2013

[5] T. Lorenz; Spin-ice materials and magnetic monopoles; Lecture notes of the 48th IFF Juelich Spring School 2017

[6] G. Kolland, O. Breunig, M. Valldor, M. Hiertz, J. Frielingsdorf and T. Lorenz. Thermal conductivity and specific heat of the spin-ice compound Dy₂Ti₂O₇: Experimental evidence for monopole heat transport Phys. Rev. B 86, 060402(R) (2012)

[7] Johannes Engelmayer, Xiao Lin, Christoph P. Grams, Raphael German, Tobias Fröhlich, Joachim Hemberger, Kamran Behnia, Thomas Lorenz; Charge transport in oxygen-deficient EuTiO₃: The emerging picture of dilute metallicity in quantum-paraelectric perovskite oxides; Phys. Rev. Materials, 3, 051401(R), 2019,

[8] S. Kunkemöller, D. Brüning, A. Stunault, A.A. Nugroho, T. Lorenz, M. Braden; Magnetic shape-memory effect in SrRuO₃; Phys. Rev. B, 96, 220406(R), 2017

[9] Carl Rischau, Xiao Lin, Christoph Grams, Dennis Finck, Steffen Harms, Johannes Engelmayer, Thomas Lorenz, Yann Gallais, Benoit Fauqué, Joachim Hemberger, Kamran Behnia; A ferroelectric quantum phase transition inside the superconducting dome of Sr_1-xCa_xTiO_3-δ; Nature Physics, 13, 643, 2017