Quartet condensation of fermions

GERD RÖPKE, Alexander Schnell, Peter Schuck +1 more

Four-particle correlations in fermion systems at finite temperatures are investigated with special attention to the formation of a condensate. Instead of the instability of the normal state with respect to the onset of pairing described by the Gorkov equation, a new equation is obtained which describes the onset of ``quartetting.'' Applying to symmetric nuclear matter, below a critical density, the four-particle condensation ( $\ensuremath{\alpha}$-like quartetting) is found to be favored over deuteron condensation (triplet pairing). This pairing-quartetting competition is expected to be a general feature of interacting fermion systems, such as the exciton-biexciton system in excited semiconductors. Possible experimental consequences are pointed out.

Hidekazu Kamei, Kazumasa Miyake

Possibility of a quartet superfluidity in fermionic systems is studied as a new aspect of atomic gas at ultra low temperatures. The four-fold degeneracy of hyperfine state and moderate coupling is indispensable for the quartet superfluidity to occur. Possible superconductivity with quartet condensation in electron systems is discussed.

M. Ya. Amusia, Konstantin G. Popov, Vasily R. Shaginyan +1 more

Aseem Talukdar

Condensation of Cooper pairs and Cooper quartets in fermionic systems with multiple internal degrees of freedom is studied.In this thesis work, I work on two major projects.On the first project I discuss Cooper pair condensation and while on the second I discuss Cooper quartet condensation.Due to the restrictions imposed by Pauli's principle, no two identical fermions can occupy a single quantum state.Therefore for electronic systems with two internal states, the maximum number of electrons that could be bound together is two.However; for a fermionic system having more than two internal states, it is possible that the bound state structure could be quite different.On my thesis I focus on systems that have four internal states.On one hand it is possible that the system will still undergo some types of pairing condensation, but there is also a possibility that the fermions will form a more complex structure where four fermions are bound together which we call a quartet.Physical systems where fermions can have four internal states include a system of spin-3 2 fermionic atoms and a two band electronic system.I look at possible two and four particle bound state structures in such systems.

M. Ya. Amusia, Vasily R. Shaginyan