Unconventional states in quantum materials

Date

Jul 13, 2021

Time

10:55 AM - 11:40 AM

Speaker

Prof. Dr. Elena Hassinger

Affiliation

MPI CPfS Dresden

Language

en

Main Topic

Physik

Other Topics

Physik

Description

Abstract:

The discoveries of new materials with unexpected properties have always driven the advancement of technology. To give an example, liquid crystals were found in 1888, have been investigated since then and are now used in all LCD displays. Today, one group of materials where new phases occur are so-called quantum materials. In these, the appearance of unconventional states of matter is related with the fact that electrons interact strongly with each other. My group’s motivation for research is to understand this intriguing relation. In particular, we are interested in unconventional superconductivity and unconventional metallic states such as topological systems, heavy-Fermi and non-Fermi liquids. In my talk I will mainly focus on two groups of materials, namely topological semimetals and heavy fermion systems. In topological systems, the low energy excitations behave like relativistic particles and hence allow to investigate predictions from high energy physics. Our aim here is to find evidence for Weyl fermionic behavior in bulk experimental probes like low-temperature resistivity. In heavy fermion systems, superconductivity evolves out of unconventional ground states. In these materials we are interested in non-Fermi liquid behavior near quantum critical points and unconventional superconducting states.
My group’s expertise lies in high sensitivity - low temperature measurements and especially in the detection of quantum oscillations in metals. These oscillations are a direct consequence of the quantization of the electron orbits in a magnetic field. We measure thermodynamic and transport probes such as magnetic susceptibility, torque or resistivity. These techniques yield macroscopic information on the appearing phases. Additionally, quantum oscillations can be detected in those measurements if requirements of extremely pure materials, low temperatures, high magnetic fields and low noise levels are fulfilled. My group is one of the few in the world specialized in this quasiparticle spectroscopy that gives microscopic information on the energy eigenstates, scattering processes and the interactions between charge carriers in the metal.
In this talk I will present how we have been using these experimental techniques to answer the scientific questions mentioned above. Investigations of the topological Weyl semimetals TaAs, TaP, NbAs and NbP, have allowed to test if the chiral anomaly, a theoretical prediction from high-energy physics, induces a longitudinal magnetoresistance. This response should depend on the energy eigenstates of the electrons in these materials. Therefore, we have established the latter via quantum oscillations and hence were able to show that in TaAs and NbAs, electrons behave like Weyl fermions [1,2]. Additionally, our group has found evidence that an apparent negative longitudinal magnetoresistance can easily arise from an inhomogeneous current distribution caused by the extreme field-induced resistivity anisotropy typical for any compensated semimetal [1,3]. We succeeded revealing that when the current is flowing homogeneously, the magnetoresistance does not show clear signs of the chiral anomaly [4].
Unconventional superconductivity (SC) remains one of the most intriguing phenomena in condensed matter physics. We have recently discovered CeRh2As2, an outstanding unconventional superconductor [5]. This compound, which probably presents quadrupole order at around 0.4 K is locally non-centrosymmetric at the Ce-position while keeping an overall centrosymmetry. The superconducting state evolves below 0.26 K. Most peculiarly, it has two superconducting states as a function of magnetic field B||c and a critical field curve presenting a sharp kink at 4 T and increasing up to 14 T (see the figure). In my talk I will give details about this discovery and how it can be understood when considering that the local symmetry can give rise to spin-orbit interaction.

[1] F. Arnold et al., Nat. Commun. (2016)
[2] F. Arnold et al., Phys. Rev. Lett. (2016)
[3] R. D. dos Reis et al., New J. Phys. (2016)
[4] M. Naumann et al., Phys. Rev. Mat. (2020)
[5] S. Khim et al., submitted (2020)

Where: Zoom Meeting:

https://tu-dresden.zoom.us/j/85193786651?pwd=Q0V0KzR2emsyRnhvdzdLRDdTSnBaZz09 (https://tu-dresden.zoom.us/j/85193786651?pwd=Q0V0KzR2emsyRnhvdzdLRDdTSnBaZz09)
Meeting ID: 851 9378 6651
Passcode: reG3NboG#N

Links

• Webseite
• Termindetails auf den Webseiten der TU Dresden (https://tu-dresden.de)

Last modified: Jul 13, 2021, 12:10:15 AM