The Critical Properties of One—Dimensional Extended Hubbard Model

In the framework of nonperturbative quantum field theory, the critical phenomena of one-dimensionalextended Hubbard model (EHM) at half-filling are discussed from weak to intermediate interactions. After the EHMbeing mapped into two decoupled sine-Gordon models, the ground state phase diagram of the system is derived in anexplicit way. It is confirmed that the coexisting phases appear in different interaction regimes which cannot be foundby conventional theoretical methods. The diagram shows that there are seven different phase regions in the groundstate, which seems not to be the same as previous discussions, especially the boundary between the phase separationand condensed phase regions. The phase transition properties of the model between various phase regions are studied indetail.

The c—Axis Infrared Conductivity of a dx^2—y^2— Wave Superconductor with the Hopping Assisted by the Spin Fluctuations

A theory of the c-axis infrared conductivity of a dx2-y2-wave superconductor due to the competition between the interlayer direct hopping and the hopping assisted by the spin fluctuations has been developed. The prediction of our theory captures the main feature of the experiment. Thus we argue that the anomalous behavior of the c-axis infrared conductivity of the underdoped cuprates in superconducting state may be properly understood within the theory.

A Ship Deperming Coil System Using High Temperature Superconducting Cable Technology Refrigeration--

The purpose of ship deperming is to reduce its permanent magnetism to avoid the threat of magnetic sea-mines which appeared first in battlefields in World War II and stored by many navies and unanimous groups since then. Magnetic fields for deperming are mostly generated by electric current through conductor cable and the intensity of such fields decreases with the distance from the cable. In order to impose sufficient field to the ship, the deperming cable is tightly wrapped around the hull of the ship. A cable with superconducting material as the conductor is expected to pass high electric current because of its zero-electric resistivity and has potential to make deperming coil system more separated from the ship hull. In the previous study, we designed superconducting coil system set flat on the seabed for ship deperming by calculating magnetic field generated by the coil based on the characteristic of HTS （high temperature superconducting） tape seen in published papers. This time we have kept our design to utilize HTS tape conductors that are existing and readily available in the open market. In addition, the limitations of the manufacturing potential and capacity of the HTS tape conductor industry have been taken into account for the design. Then we designed the refrigerating system which is to keep the superconducting property of the cable materials.

Phase diagrams on composition-spread Fe_(y)Te_(1-x)Se_(x) films

Fe_(y)Te_(1-x)Se_(x),an archetypical iron-based high-temperature superconductor with a simple structure but rich physical properties,has attracted lots of attention because the two end compositions,Se content x=0 and 1,exhibit antiferromagnetism and nematicity,respectively,making it an ideal candidate for studying their interactions with superconductivity.However,what is clearly lacking to date is a complete phase diagram of Fe_(y)Te_(1-x)Se_(x)as functions of its chemical compositions since phase separation usually occurs from x~0.6 to 0.9 in bulk crystals.Moreover,fine control of its composition is experimentally challenging because both Te and Se are volatile elements.Here we establish a complete phase diagram of Fe_(y)Te_(1-x)Se_(x),achieved by high-throughput film synthesis and characterization techniques.An advanced combinatorial synthesis process enables us to fabricate an epitaxial composition-spread Fe_(y)Te_(1-x)Se_(x)film encompassing the entire Se content x from 0 to 1 on a single piece of CaFsubstrate.The micro-region composition analysis and X-ray diffraction show a successful continuous tuning of chemical compositions and lattice parameters,respectively.The micro-scale pattern technique allows the mapping of electrical transport properties as a function of relative Se content with an unprecedented resolution of0.0074.Combining with the spin patterns in literature,we build a detailed phase diagram that can unify the electronic and magnetic properties of Fe_(y)Te_(1-x)Se_(x).Our composition-spread Fe_(y)Te_(1-x)Se_(x) films,overcoming the challenges of phase separation and precise control of chemical compositions,provide an ideal platform for studying the relationship between superconductivity and magnetism.

Relationship between the parent charge transfer gap and maximum transition temperature in cuprates

One of the biggest puzzles concerning the cup- rate high temperature superconductors is what determines the maximum transition temperature （Tc,max）, which varies from less than 30 to above 130 K in different compounds. Despite this dramatic variation, a robust trend is that within each family, the double-layer compound always has higher Tc,max than the single-layer counterpart. Here we use scanning tunneling microscopy to investigate the electronic structure of four cuprate parent compounds belonging to two different families. We find that within each family, the double layer compound has a much smaller charge transfer gap size （ACT）, indicating a clear anticorrelation between AcT and Tc,max. These results suggest that the charge transfer gap plays a key role in the superconducting physics of cuprates, which shed important new light on the high To mechanism from doped Mott insulator perspective.

A possible new family of unconventional high temperature superconductors

We suggest a new family of Co[Ni-based materials that may host unconventional high temperature superconductivity （high-To）. These materials carry layered square lattices with each layer being formed by vertex-shared transition metal tetrahedra cation-anion complexes. The electronic physics in these materials is determined by the two dimensional layer and is fully attributed to the three near degenerated t2g d-orbitals close to a d7 filling configuration in the d-shell of CoJNi atoms. The electronic structure meets the necessary criteria for unconventional high Tc materials proposed recently by us to unify the two known high-Tc families, cuprates and iron-based superconductors. We predict that they host superconducting states with a d-wave pairing symmetry with Tc potentially higher than those of iron-based superconductors. These materials, if realized, can be a fertile new ground to study strongly correlated electronic Physics and provide decisive evidence for superconducting pairing mechanism.