## Van der Waals-Zeeman Colloquium

**Thursday**, 22 Mar 2007, 16:00h

**Fermionic Quantum Criticality**

**Prof. dr. Jan Zaanen**

Instituut-Lorentz for Theoretical Physics, Univ. Leiden

Humanity is in a state of ignorance when dealing with quantum systems composed of infinite numbers of fermionic particles. It is the infamous Fermion sign problem disabling the technologies of field theory: all one knows to do is to declare the system to be an adiabatic continuation of the Fermi-gas, or either to be bound in bosons. Empirically we know, however, that also scale invariant Fermion systems exist: these are well documented in the heavy fermion context and I will forcefully make the case that this fermionic quantum criticality is the secret of high Tc superconductivity. Resting on Ceperley's constrained Fermion path integrals we have reasons to hope that the sign problem can be cracked at least on the phenomenological level: our discovery of the fractal nodal surface hidden behind Fermionic backflow and why this is good for BCS superconductivity.