Yoji Ohashi

BCS-BEC crossover in a gas of Fermi atoms with a Feshbach resonance

We discuss the BCS-BEC crossover in a degenerate Fermi gas of two hyperfine states interacting close to a Feshbach resonance. We show that, by including fluctuation contributions to the free energy similar to that considered by Nozières and Schmitt-Rink, the character of the superfluid phase transition continuously changes from the BCS-type to the BEC-type, as the threshold of the quasimolecular band is lowered. In the BEC regime, the superfluid phase transition is interpreted in terms of molecules associated with both the Feshbach resonance and Cooper pairing.

Theory of unconventional spin density wave: A possible mechanism of the micromagnetism in U-based heavy fermion compounds

We propose a novel spin density wave (SDW) state as a possible mechanism of the anomalous antiferromagnetism, so-called the micromagnetism, in URu_2Si_2 below 17.5[K]. In this new SDW, the electron-hole pair amplitude changes its sign in the momentum space as in the case of the unconventional superconductivity. It is shown that this state can be realized in an extended Hubbard model within the mean field theory. We also examine some characteristic properties of this SDW to compare with the experimental results. All these properties well explain the unsolved problem of the micromagnetism.

Single-particle properties and pseudogap effects in the BCS-BEC crossover regime of an ultracold Fermi gas above Tc

We investigate strong-coupling effects on normal-state properties of an ultracold Fermi gas. Within the framework of

Superfluidity and collective modes in a uniform gas of Fermi atoms with a Feshbach resonance

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BCS-BEC crossover in a gas of fermi atoms with a p-wave feshbach resonance

-matrix approximation in terms of pairing fluctuations, we calculate the single-particle density of states (DOS), as well as the spectral weight, over the entire BCS\char21{}Bose-Einstein condensate (BEC) crossover region above the superfluid phase-transition temperature

Resonance state localized around nonmagnetic impurity with unitarity scattering in two-dimensional d-wave superconductor

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Pairing and Depairing Effects of Antiferromagnetic Spin Fluctuations in High-Tc Superconductivity

. Starting from the weak-coupling BCS regime, we show that the so-called pseudogap develops in DOS above

Unusual Proximity Effect of d-Wave Superconductivity

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Superfluid density of states and pseudogap phenomenon in the BCS-BEC crossover regime of a superfluid Fermi gas

, which becomes remarkable in the crossover region. The pseudogap structure continuously changes into a fully gapped one in the strong-coupling BEC regime, where the gap energy is directly related to the binding energy of tightly bound molecules. We determine the pseudogap temperature

Superfluid density and condensate fraction in the BCS-BEC crossover regime at finite temperatures

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