-Hou Chung

Quantum Criticality in a Double-Quantum-Dot System

We discuss the realization of the quantum-critical non-Fermi-liquid state, originally discovered within the two-impurity Kondo model, in double-quantum-dot systems. Contrary to common belief, the corresponding fixed point is robust against particle-hole and various other asymmetries and is unstable only to charge transfer between the two dots. We propose an experimental setup where such charge transfer processes are suppressed, allowing a controlled approach to the quantum-critical state. We also discuss transport and scaling properties in the vicinity of the critical point.

Formation of an electronic nematic phase in interacting fermion systems

We study the formation of an electronic nematic phase characterized by a broken point-group symmetry in interacting fermion systems within the weak coupling theory. As a function of interaction strength and chemical potential, the phase transition between the isotropic Fermi liquid and nematic phase is first order at zero temperature and becomes second order at a finite temperature. The transition is present for all typical, including quasi-two-dimensional, electronic dispersions on the square lattice and takes place for arbitrarily small interaction when at van Hove filling, thus suppressing the Lifshitz transition. In connection with the formation of the nematic phase, we discuss the origin of the first-order transition and competition with other broken symmetry states.

Signatures of an electronic nematic phase at the isotropic-nematic phase transition

The electronic nematic phase occurs when the point-group symmetry of the lattice structure is broken, due to electron-electron interactions. We study a model for the nematic phase on a square lattice with emphasis on the phase transition between isotropic and nematic phases within mean-field theory. We find the transition to be first order, with dramatic changes in the Fermi-surface topology accompanying the transition. Furthermore, we study the conductivity tensor and Hall constant as probes of the nematic phase and its transition. The relevance of our findings to Hall resistivity experiments in the high-

Kondo effect in coupled quantum dots with RKKY interaction : Effects of finite temperature and magnetic field

{T}_{c}

Competing topological and Kondo insulator phases on a honeycomb lattice.

cuprates is discussed.

Planar pyrochlore antiferromagnet: A large-N analysis

We study transport through two quantum dots coupled by a Ruderman-Kittel-Kasuya-Yoshida interaction as a function of temperature and magnetic field. By applying the numerical renormalization group method, we obtain the transmission and the linear conductance. At zero temperature and magnetic field, we observe a quantum phase transition between the Kondo screened state and a local spin singlet as the RKKY interaction is tuned. Above the critical RKKY coupling, the Kondo peak is split. However, we find that both finite temperature and magnetic field restore the Kondo resonance. Our results agree well with recent transport experiments on gold grain quantum dots in the presence of magnetic impurities [H. B. Heersche et al., Phys. Rev. Lett. 96, 017205 (2006)].

Raman spectra of triplet superconductivity in Sr2RuO4

We investigate the competition between the spin-orbit interaction of itinerant electrons and their Kondo coupling with local moments densely distributed on the honeycomb lattice. We find that the model at half-filling displays a quantum phase transition between topological and Kondo insulators at a nonzero Kondo coupling. In the Kondo-screened case, tuning the electron concentration can lead to a new topological insulator phase. The results suggest that the heavy-fermion phase diagram contains a new regime with a competition among topological, Kondo-coherent and magnetic states, and that the regime may be especially relevant to Kondo lattice systems with 5d-conduction electrons. Finally, we discuss the implications of our results in the context of the recent experiments on SmB(6) implicating the surface states of a topological insulator, as well as the existing experiments on the phase transitions in SmB(6) under pressure and in CeNiSn under chemical pressure.

Competing Orders and Superconductivity in the Doped Mott Insulator on the Shastry-Sutherland Lattice

We study possible quantum phases of the Heisenberg antiferromagnet on the planar pyrochlore lattice, also known as the checkerboard lattice or the square lattice with crossings. It is assumed that the exchange coupling on the square-lattice-links is not necessarily the same as those along the crossing links. When all the couplings are the same, this model may be regarded as a two dimensional analog of the pyrochlore antiferromagnet. The large-N limit of the Sp(

Statistics of spinons in the spin-liquid phase of Cs2CuCl4

N

Quantum phase transitions in a resonant-level model with dissipation: Renormalization-group studies

) generalized model is considered and the phase diagram is obtained by analyzing the fluctuation effects about the