Project

Strongly-correlated electron systems; High-pressure physics; Heavy-fermion materials; One-dimensional spin systems; Quantum phase transitions; Nuclear magnetic resonance

Lead
Lay summary
Investigating quantumcriticality via nuclear magnetic resonance (NMR) Close to the absolute zero oftemperature, materials exhibit properties that are dominated by quantumeffects. In this regime, transitions between different states of matter drivenby quantum rather than by thermal fluctuations are possible. Studies of theso-called quantum phase transitions (QPTs), that connect competing groundstates across a quantum critical point, provide new insights into problems relatedto strong interactions and entanglement in condensed matter. The presence of aQCP is also felt at non-zero temperatures, where it is supposed to control thephysics of systems such as high-temperature and other exotic superconductors,transition metal oxides, metamagnetic materials, etc. Our project aims to addressthe behaviour of materials close to a quantum critical point, with a particularemphasis on the dynamics of the corresponding elementary excitations. In ourexperimental approach we employ mainly NMR methods, complemented by suitableother experimental techniques. The unique possibility of performing NMRexperiments on materials under the extreme conditions that are required toaccess the quantum critical regime (including ultra-low temperatures, highpressure and high magnetic fields), makes NMR one of the most favourableexperimental tools for exploring quantum criticality.

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Last update: 21.02.2013

Active participation

Communication	Title	Media	Place	Year

Number	Title	Start	Funding scheme

The omnipresent thermal agitation excludes macroscopic quantum phenomena from our everyday experience. Close to the absolute zero, though, quantum coherence is preserved and transitions between different states of matter driven by quantum rather than thermal fluctuations are possible. Quantum phase transitions (QPTs), which connect competing ground states, provide new insights into long-standing problems related to, i.e., strong correlation and entanglement in condensed matter. Consequences of a quantum critical point, extended to finite temperatures, are believed to underlie the physics of systems such as high-temperature superconductors, heavy-fermion compounds, transition metal oxides, or metamagnetic materials.The aim of the present project is to address, mainly through magnetic resonance techniques, but also by other complementary experimental methods, the behaviour of materials close to a quantum critical point, with a particular regard to the dynamics of their elementary excitations.The unique possibility of performing NMR experiments in the extreme environment required to access the quantum critical regime (including ultra-low temperature, high pressure and high magnetic fields), make NMR one of the best experimental tools to explore quantum criticality. The present project is characterized by the following key features:Focus and Novelty: Our research will concentrate mainly on NMR/NQR investigations of strongly correlated electron systems in the proximity of a quantum critical transition. The often difficult study of the dynamics of quantum criticality (due to limitations of the experimental tools) will represent the distinguishing trait of the current project.Feasibility and Timing: Although we plan to investigate matter in challenging conditions, the current project is firmly grounded on previous experience and relies on well mastered experimental techniques. The wide scope of the research would require a 3-year period and will involve two PhD students.Teamwork: The proposed research will rely on existing and new collaborations involving material scientists, condensed matter theorists and international collaborators. This type of approach is particularly rewarding in investigating complex condensed matter.Impact and Perspective: Our experiments, to be carried out on different systems, will provide new insights into the respective low-temperature domains, possibly allowing us to extrapolate the common features of the various quantum phase diagram. Ultimately, our contribution would help to understand how competing orders interact in strongly correlated electronic systems.