Manifestation of quantum fluctuations in strongly correlated systems

Dai S. Hirashima, 平島 大

Nayana Shah

O. Topic, M. Scherer, Grebremedh Gebreyesus +6 more

Bose-Einstein condensates of atoms with non-zero spin are known to constitute an ideal system to investigate fundamental properties of magnetic superfluids. More recently it was realized that they also provide the fascinating opportunity to investigate the macroscopic amplification of quantum and classical fluctuations. This is strikingly manifested in a sample initially prepared in the m F = 0 state, where spin-changing collisions triggered by quantum fluctuations may lead to the creation of correlated pairs in m F = ±1. We show that the pair creation efficiency is strongly influenced by the interplay between the external trapping potential and the Zeeman effect. It thus reflects the confinement-induced magnetic field dependence of elementary spin excitations of the condensate. Remarkably, pair production in our experiments is therefore characterized by a multi-resonant dependence on the magnetic field. Pair creation at these resonances acts as strong parametric matter-wave amplifier. Depending on the resonance condition, this amplification can be extremely sensitive or insensitive to the presence of seed atoms. We show that pair creation at a resonance which is insensitive to the presence of seed atoms is triggered purely by quantum fluctuations and thus the system acts as a matter-wave amplifier for the vacuum state.

Jae-Hyeon Eom, Sung‐Ho Suck Salk

The U(1) holon-pair boson theory of Lee and Salk [Phys. Rev. B 64, 052501 (2001)] is applied to investigate the quantum scaling behavior of optical conductivity in the two-dimensional systems of strongly correlated electrons. We examine the role of both the gauge field fluctuations and spin pair excitations on the $\ensuremath{\omega}∕T$ scaling behavior of the optical conductivity. It is shown that the gauge field fluctuations but not the spin pair excitations are responsible for the scaling behavior in the low-frequency region $\ensuremath{\omega}∕T⪡1$. The importance for the contribution of the nodal spinons to the Drude peak is discussed. It is shown that the $\ensuremath{\omega}∕T$ scaling behavior is manifest in the low-frequency region at low hole concentrations close to a critical concentration at which superconductivity arises at $T=0\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

Pavel V. Shevchenko

Jae-Hyeon Eom, Sung-Sik Lee, Ki‐Seok Kim +1 more

The U(1) holon-pair boson theory of Lee and Salk(Phys. Rev. B 64, 052501 (2001)) is applied to investigate the quantum scaling behavior of optical conductivity in the two dimensional systems of strongly correlated electrons. We examine the role of both the gauge field fluctuations and spin pair excitations on the w/T scaling behavior of the optical conductivity. It is shown that the gauge field fluctuations but not the spin pair excitations are responsible for the scaling behavior in the low frequency region w/T <<1. Importance for the contribution of the nodal spinons to the Drude peak is discussed. It is shown that the w/T scaling behavior is manifest in the low frequency region at low hole concentrations close to a critical concentration at which superconductivity arises at T=0K.