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Phase transitions are driven by the tendency of systems to minimize their energy with respect to extrinsic parameters (pressure, magnetic field etc.). Very often phase transitions occur at finite temperatures, where the thermal fluctuations become smaller than a characteristic energy, in which case the energy is lowered via a symmetry change (“broken symmetry”) and the nature of the material changes, for example from liquid to solid as water freezes. We are interested in phase transitions that take place at T=0, known as quantum critical transitions, given that quantum and not thermal fluctuations are now at play. These often occur in a special class of metals known as heavy fermions. We are focusing on the Yb-based heavy fermion compounds, and their properties in the vicinity of the quantum critical point (QCP). Spin fluctuations modify the electron states near a QCP, leading to the breakdown of the Fermi Liquid (FL) theory. We aim at understanding how different control parameters (chemical doping, magnetic field, pressure) affect the non- Fermi liquid (NFL) state.
Sc3.1In: NFL behavior close to a QCP
Quantum phase transitions occur at absolute zero temperature and, in contrast to classical phase transitions, are driven by quantum rather than thermal fluctuations. Such transitions have been studied in a large number of magnetic compounds. Only a small number of itinerant moment systems have been known to exhibit quantum critical points (QCPs), with the majority of quantum critical systems being those with local-moment magnetism.
Sc3In is one of only two known itinerant ferromagnets without local moments. We recently showed that the magnetic state is described by non-mean-field crtical exponents, while doping with Lu drove the system to a quantum critical point (QCP) through a non-Fermi liquid (NFL) state.
YbRh3Si7 - Heavy Fermion Ferromagnet
We discovered a new Yb heavy fermion YbRh3Si7, with a ferromagnetic ground state. Measurements are currently underway to characterize the properties of this new Yb heavy fermion.