Exploring Quantum Matter Using Advanced Instrumentation
LIN researchers use their internationally recognized expertise in the design of advanced neutron instrumentation as well as in sample environment to tackle outstanding scientific challenges in quantum matter research. Here we are particularly interested in understanding how tuning of the underlying microscopic interactions via external control parameters (pressure, field, strain, crystal chemistry) may be used to understand and optimize material properties.
Below a few exemplary projects are summarized.
Magnetic Quantum Phase Transitions in Correlated Metals
Strongly correlated metals near magnetic quantum phase transitions are well-established hunting grounds for novel quantum matter states. Because the conduction electrons carry both charge and spin degrees of freedom the abundance of magnetic quantum fluctuations originating at quantum phase transitions entail strong electronic correlations with new characteristic energy scales, as well as the formation of novel states of matter, where unconventional superconductivity may be the most prominent example. The outstanding challenge is that the underlying characteristic energy scales that drive new quantum matter states are tiny compared to typical electronic energy scales in solids, and are, in turn, notoriously difficult to measure.
Exploiting recent advances in the resolution of neutron spectroscopy methods now allow us to take a fresh look to obtain detailed insights in strongly correlated quantum states. Notably, the novel Modulated IntEnsity by Zero Effort (MIEZE) technique implemented at the neutron spectrometer RESEDA in Munich, ultra-high energy resolution of a few neV can be achieved even when studying magnetic materials. For example, we have used MIEZE to reveal that the spin fluctuations in UGe2 exhibit a dual nature arising from the interplay of localized and itinerant electronic degrees of freedom is consistent with spin-triplet superconductivity proposed for this material.
The spin fluctuation spectrum of the putative spin-triplet superconductor UGe 2 as revealed by Modulated Intensity with Zero Effort (MIEZE) with ultrahigh energy resolution is shown. The spin fluctuations are purely longitudinal and exhibit a dual nature arising from localized 5f electrons that are hybridized with the conduction electrons. Local spin fluctuations are perfectly described by the Ising universality class in three dimensions, whereas itinerant spin fluctuations occur over length scales comparable to the superconducting coherence length, showing that MIEZE is able to spectroscopically disentangle the complex low-energy behavior characteristic of quantum materials.