Crossover from a pseudogap state to a superconducting state

On the basis of our calculation we deduce that the particular electronic structure of cuprate superconductors confines Cooper pairs to be firstly formed in the antinodal region which is far from the Fermi surface, and these pairs are incoherent and result in the pseudogap state. With the change of doping or temperature, some pairs are formed in the nodal region which locates the Fermi surface, and these pairs are coherent and lead to superconductivity. Thus the coexistence of the pseudogap and the superconducting gap is explained when the two kinds of gaps are not all on the Fermi surface. It is also shown that the symmetry of the pseudogap and the superconducting gap are determined by the electronic structure, and non-s wave symmetry gap favors the high-temperature superconductivity. Why the high-temperature superconductivity occurs in the metal region near the Mott metal-insulator transition is also explained.Comment: 7 pages, 2 figure

Political connections with corrupt government bureaucrats and corporate M&A decisions: A natural experiment from the anti-corruption cases in China

Using 29 recent high level anti-corruption cases in China as a natural experiment, we examine the patterns in merger and acquisition (M&A) decisions and performance in Chinese non-state owned enterprises (non-SOEs) before and after the exogenous severing of political connections. We identify a set of listed related non-SOEs whose managers bribed or had connections, through past working and educational experience, with corrupt bureaucrats from 2005 to 2011. We document that, after the arrest of corrupt bureaucrats, corruption related non-SOEs lose their competitive advantages in the M&A market. We observe a significant reduction in the likelihood of conducting M&As and the ability to access local and state-owned targets for these firms. They pay a higher takeover premium and consequently have worse post-M&A performance. Our results are robust when we exclude bribing firms, and firms whose related corrupt bureaucrats are arrested within a year before the announcement of the M&A. Furthermore, the influence of anti-corruption events varies across regions that have different levels of corruption index and industries with different levels of government support and competition. Overall, our study provides direct evidence to the question of why firms seek to establish connections with government officials through bribery or personal connections, and we reveal the benefits and costs of such connections

Family control and corporate cash holdings: Evidence from China

This study examines the effect of family control on the cash holding policy in China. We find that family firms with excess control rights tend to have high cash holdings that are tunneled rather than being invested or paid to shareholders. We further show that the incentive for controlling families to hold cash and for tunneling is exacerbated by the agency conflict between controlling and minority shareholders, i.e., it is weakened after the Chinese Non-tradable share (NTS) reform and strengthened by the presence of multiple large shareholders who probably play no monitoring role in Chinese family firms. Furthermore, family firms' incentive to hold cash for tunneling is influenced by the unique characteristics of Chinese firms in the following ways: the incentive is stronger when the family founder has one child and face family succession problem, and when the founder has political connections and directly involves in firm's management; while it is weakened by family founder's social interpersonal trust with other entrepreneurs through their membership of Chambers of Commerce. Overall, we argue that family firms in China tend to hold high levels of cash for tunneling, which harms firm value, while the severe controlling-minority shareholder agency conflicts and unique Chinese family characteristics only make this situation worse

Superconducting correlations in ultra-small metallic grains

To describe the crossover from the bulk BCS superconductivity to a fluctuation-dominated regime in ultrasmall metallic grains, new order parameters and correlation functions, such as ``parity gap'' and ``pair-mixing correlation function'', have been recently introduced. In this paper, we discuss the small-grain behaviour of the Penrose-Onsager-Yang off-diagonal long-range order (ODLRO) parameter in a pseudo-spin representation. Relations between the ODLRO parameter and those mentioned above are established through analytical and numerical calculations.Comment: 7 pages, 1 figur

The roles of deformation and orientation in heavy-ion collisions induced by light deformed nuclei at intermediate energy

The reaction dynamics of axisymmetric deformed $^{24}$Mg + $^{24}$Mg collisions have been investigated systematically by an isospin-dependent quantum molecular dynamics (IDQMD) model. It is found that different deformations and orientations result in apparently different properties of reaction dynamics. We revealed that some observables such as nuclear stopping power ($R$), multiplicity of fragments, and elliptic flow are very sensitive to the initial deformations and orientations. There exists an eccentricity scaling of elliptic flow in central body-body collisions with different deformations. In addition, the tip-tip and body-body configurations turn out to be two extreme cases in central reaction dynamical process.Comment: 5 pages, 7 figures, to appear in Physical Review C (Rapid Communication

Isoscaling in the Lattice Gas Model

The isoscaling behavior is investigated using the isotopic/isobaric yields from the equilibrated thermal source which is prepared by the lattice gas model for lighter systems with A = 36. The isoscaling parameters $\alpha$ and -$\beta$ are observed to drop with temperature. The difference of neutron and proton chemical potential shows a turning point around 5 MeV where the liquid gas phase transition occurs in the model. The relative free neutron or proton density shows a nearly linear relation with the N/Z (neutron to proton ratio) of system and the isospin fractionation is observed.Comment: 5 figures, 5 pages; the final version to appear in Phys Rev