Friedemann group

• Dr. Sven Friedemann

  Theme Lead for Quantum & Soft Matter and Associate Professor

Research Interests & Activities

My research group studies superconductors and quantum materials at high pressures. We use pressures up to 2 million atmospheres to tune the behaviour of materials and to access novel states of matter. We monitor electronic transport, magnetic, and thermodynamic properties to study the quantum behaviour of electrons in a wide range of materials. Our research contributes to finding novel superconductors and quantum materials with the potential to contribute to a wide range of applications from energy via sensing to computing.

Record superconductivity in hydrogen materials at high pressures

Record superconductivity has been discovered in hydrogen compounds at high pressures over the last years. I have set up one of the few groups around the world capable to conduct experiments of the superconducting state at these high pressures. We have discovered high-temperature superconductivity in the clathrate hydride La₄H₂₃ with a T_c of 95 K at 97 GPa [1] , provided critical evidence for the diffusive nature of hydrogen in lanthanum hydrides at extreme pressures [2], and demonstrated clean-limit superconductivity in H₃S with a T_c of almost 200 K at 155 GPa [3].  Our studies contribute to the global effort to find superconductors with higher Tc and at lower pressures.

Unconventional superconductivity in charge ordered Materials

My team has discovered evidence for unconventional superconductivity in TiSe2 [4]. This material is prototypical for charge order [5] which we suppress with high pressures. Interestingly, we find that superconductivity only emerges when electrons with different momenta are present indicating inter-band superconductivity likely with an unconventional mechanism for the formation of pairs of electrons from these two states. The peak in superconductivity is present when charge order is just suppressed to zero temperature indicating that the fluctuations of the charge order mediate the superconductivity. This insight contributes to the understanding of unconventional superconductivity in a range of materials.

Current researchers and PhD students