Mixed triplet and singlet pairing in multicomponent fermion systems with dipolar interactions (2009)
The symmetry properties of the Cooper pairing problem for multi-component ultra-cold dipolar molecular systems are investigated. The dipolar anisotropy provides a natural and robust mechanism for...
Quasiparticle Interference on the Surface of the Topological Insulator Bi$_2$Te$_3$ (2009)
Lee, Wei-Cheng, Wu, Congjun, Arovas, Daniel P., Zhang, Shou-Cheng
The quasiparticle interference of the spectroscopic imaging scanning tunneling microscopy has been investigated for the surface states of the large gap topological insulator Bi$_2$Te$_3$ through the...
Frustrated Cooper pairing and the $f$-wave supersolidity (2009)
Hung, Hsiang-hsuan, Lee, Wei-Cheng, Wu, Congjun
Geometric frustration in quantum magnetism refers to that magnetic interactions on different bonds cannot be simultaneously minimized. The usual Cooper pairing systems favor the uniform distribution...
Anisotropic Fermi liquid theory of fermionic polar molecules (2009)
Chan, Ching-Kit, Wu, Congjun, Lee, Wei-cheng, Sarma, S. Das
We study the Fermi liquid properties of the anisotropic cold atomic dipolar Fermi gases. Due to the explicit anisotropy of the dipolar interaction, Fermi surfaces exhibit distortions of the...
Unlike charge and spin, the orbital degree of freedom of electrons in transition metal oxides is difficult to detect. We present the theoretical study of a new detection method in metallic orbitally...
$F$-wave pairing of cold atoms in optical lattices (2009)
Lee, Wei-Cheng, Wu, Congjun, Sarma, S. Das
The tremendous development of cold atom physics has opened up a whole new opportunity to study novel states of matter which are not easily accessible in solid state systems. Here we propose to...
Nematic electron states enhanced by orbital band hybridization (2009)
We study the Fermi surface instability of the Pomeranchuk type in orbital band systems. Band hybridization significantly enhances the Landau interactions in non-s-wave channels and results in...
Kondo effect in the helical edge liquid of the quantum spin Hall state (2009)
Maciejko, Joseph, Liu, Chaoxing, Oreg, Yuval, Qi, Xiao-Liang, Wu, Congjun, Zhang, Shou-Cheng
Following the recent observation of the quantum spin Hall (QSH) effect in HgTe quantum wells, an important issue is to understand the effect of impurities on transport in the QSH regime. Using linear...
Unconventional Bose-Einstein Condensations Beyond the "No-node" Theorem (2009)
Feynman's "no-node" theorem states that the conventional many-body ground-state wavefunctions of bosons in the coordinate representation is positive-definite. This implies that time-reversal symmetry...
A $\Gamma$-matrix generalization of the Kitaev model (2008)
Wu, Congjun, Arovas, Daniel, Hung, Hsiang-Hsuan
We extend the Kitaev model defined for the Pauli-matrices to the Clifford algebra of $\Gamma$-matrices, taking the $4 \times 4$ representation as an example. On a decorated square lattice, the ground...
Time-reversal symmetry breaking pairing state in FeAs based superconductors (2008)
Lee, Wei-Cheng, Zhang, Shou-Cheng, Wu, Congjun
We investigate the competition between the extended $s_{\pm}$-wave and $d_{x^2-y^2}$-wave pairing order parameters in the iron-based superconductors. Because of the frustrating pairing interactions...
Exciton condensation with spontaneous time-reversal symmetry breaking (2008)
Wu, Congjun, Shem, Ian Mondragon
According to Feynman's argument, many-body ground state wavefunctions of usual Bose-Einstein condensation (BEC) are positive-definite, thus time-reversal symmetry cannot be spontaneously broken. We...
Orbital analogue of quantum anomalous Hall effect in $p$-band systems (2008)
We investigate the topological insulating states of the $p$-band systems in optical lattices induced by the onsite orbital angular momentum polarization, which exhibit gapless edge modes in the...
Proposed realization of itinerant ferromagnetism in optical lattices (2008)
Zhang, Shizhong, Hung, Hsiang-hsuan, Wu, Congjun
We propose to realize the itinerant ferromagnetism of two-component cold fermionic atoms in the $p$-orbital bands in optical lattices. The band flatness in the two-dimensional honeycomb lattice...
Incommensurate superfluidity of bosons in a double-well optical lattice (2008)
Stojanovic, Vladimir M., Wu, Congjun, Liu, W. Vincent, Sarma, S. Das
We study bosons in the first excited Bloch band of a double-well optical lattice, recently realized at NIST. By calculating the relevant parameters from a realistic nonseparable lattice potential, we...
Band touching from real space topology in frustrated hopping models (2008)
Bergman, Doron L., Wu, Congjun, Balents, Leon
We study ``frustrated'' hopping models, in which at least one energy band, at the maximum or minimum of the spectrum, is dispersionless. The states of the flat band(s) can be represented in a basis...
Orbital ordering and frustration of $p$-band Mott-insulators (2008)
We investigate the general structure of orbital exchange physics in Mott-insulating states of $p$-orbital systems in optical lattices. Orbital orders occur in both the triangular and Kagome lattices....
Resonating plaquette phases in large spin cold atom systems (2008)
Large spin cold atom systems can exhibit novel magnetic properties which do not appear in usual spin-1/2 systems. We investigate the SU(4) resonating plaquette state in the three dimensional cubic...
The $p_{x,y}$-orbital counterpart of graphene: cold atoms in the honeycomb optical lattice (2007)
We study the ground state properties of the interacting spinless fermions in the $p_{x,y}$-orbital bands in the two dimensional honeycomb optical lattice, which exhibit different novel features from...
Hu, Jiangping, Wu, Congjun, Dai, Xi
We propose a new type of Josephson junction formed by two superconductors close to the superconductor-Mott-insulator transition, one of which is doped with holes and the other is doped with...
Flat bands and Wigner crystallization in the honeycomb optical lattice (2007)
Wu, Congjun, Bergman, Doron, Balents, Leon, Sarma, S. Das
We study the ground states of cold atoms in the tight-binding bands built from p-orbitals on a two dimensional honeycomb optical lattice. The band structure includes two completely flat bands. Exact...
Current carrying ground state in a bilayer model of strongly correlated systems (2007)
Capponi, Sylvain, Wu, Congjun, Zhang, Shou-Cheng
Strongly interacting systems have been conjectured to spontaneously develop current carrying ground states under certain conditions. We demonstrate the existence of a commensurate staggered...
Fermi liquid instabilities in the spin channel (2006)
Wu, Congjun, Sun, Kai, Fradkin, Eduardo, Zhang, Shou-Cheng
We study the Fermi surface instabilities of the Pomeranchuk type in the spin triplet channel with high orbital partial waves ($F_{l}^a ~(l>0)$). The ordered phases are classified into two classes,...
Hidden symmetry and quantum phases in spin-3/2 cold atomic systems (2006)
Optical traps and lattices provide a new opportunity to study strongly correlated high spin systems with cold atoms. In this article, we review the recent progress on the hidden symmetry properties...
Band Collapse and the Quantum Hall Effect in Graphene (2006)
Bernevig, B. Andrei, Hughes, Taylor L., Chen, Han-Dong, Wu, Congjun, Zhang, Shou-Cheng
The recent Quantum Hall experiments in graphene have confirmed the theoretically well-understood picture of the quantum Hall (QH) conductance in fermion systems with continuum Dirac spectrum. In this...
Prediction of quantum stripe ordering in optical lattices (2006)
Wu, Congjun, Liu, W. Vincent, Moore, Joel, Sarma, Sankar Das
We predict the robust existence of a novel quantum orbital stripe order in the $p$-band Bose-Hubbard model of two-dimensional triangular optical lattices with cold bosonic atoms. An orbital angular...
One-dimensional spin pyrochlore lattice: exact ground state and elementary excitations (2006)
Chen, Shu, Wang, Yupeng, Ning, W. Q., Wu, Congjun, Lin, H. Q.
We study the antiferromagnetic spin exchange models with $S=1/2$ and S=1 on a one-dimensional tetrahedron chain by both analytical and numerical approaches. The system is shown to be effectively...
Atomic matter of non-zero momentum Bose-Einstein condensation and orbital current order (2006)
The paradigm of Bose-Einstein condensation has been associated with zero momentum to which a macroscopic fraction of bosons condense. Here we propose a new quantum state where bosonic alkali-metal...
Quintet pairing and non-Abelian vortex string in spin-3/2 cold atomic systems (2005)
Wu, Congjun, Hu, Jiangping, Zhang, Shou-Cheng
We study the s-wave quintet Cooper pairing phase ($S_{tot}=2$) in spin-3/2 cold atomic systems and identify various novel features which do not appear in the spin-1/2 counterpart. A single quantum...
We study the quantum dynamics of superfluids of bosons hybridized with Cooper pairs near Feshbach resonances and the influence of fermion-boson conversion on Mott states. We derive a set of equations...
The Helical Liquid and the Edge of Quantum Spin Hall Systems (2005)
Wu, Congjun, Bernevig, B. Andrei, Zhang, Shou-Cheng
The edge states of the recently proposed quantum spin Hall systems constitute a new symmetry class of one-dimensional liquids dubbed the ``helical liquid'', where the spin orientation is determined...
Exact spontaneous plaquette ground states for high-spin ladder models (2005)
Chen, Shu, Wu, Congjun, Zhang, Shou-Cheng, Wang, Yupeng
We study the exchange physics in high spin Mott insulating systems with $S=3/2$ which is realizable in ultracold atomic systems. The high symmetry of SO(5) or SU(4) therein renders stronger quantum...
Wu, Congjun, Zaanen, Jan, Zhang, Shou-Cheng
We study the effects of spin-orbit coupling in the $d$-density wave (DDW) phase. In the low-temperature orthorhombic phase of La$_{2-x}$Ba$_x$CuO$_4$, we find that spin-orbit coupling induces a...
Applications of the symmetry principle in condensed matter and cold atomic systems / (2005)
Wu, Congjun., Zhang, Shou-Cheng Advisor
Submitted to the Department of Physics.
Competing orders in one dimensional spin 3/2 fermionic systems (2004)
Novel competing orders are found in spin 3/2 cold atomic systems in one-dimensional optical traps and lattices. In particular, the quartetting phase, a four-fermion counterpart of Cooper pairing,...
Wu, Congjun, Zhang, Shou-Cheng
Quantum Monte-Carlo (QMC) simulations involving fermions have the notorious sign problem. Some well-known exceptions of the auxiliary field QMC algorithm rely on the factorizibility of the fermion...
Current Carrying Ground State in a Bi-layer Model (2004)
Capponi, Sylvain, Wu, Congjun, Zhang, Shou-Cheng
Strongly interacting systems have been conjectured to spontaneously develop current carrying ground states under certain conditions. We conclusively demonstrate the existence of a commensurate...
Dynamic generation of spin orbit coupling (2003)
Wu, Congjun, Zhang, Shou-Cheng
Spin-orbit coupling plays an important role in determining the properties of solids, and is crucial for spintronics device applications. Conventional spin-orbit coupling arises microscopically from...
Quantitative Test of SO(5) Symmetry in the Vortex State of $Nd_{1.85}Ce_{0.15}CuO_4$ (2003)
Chen, Han-Dong, Wu, Congjun, Zhang, Shou-Cheng
By numerically solving models with competing superconducting and antiferromagnetic orders, we study the magnetic field dependence of the antiferromagnetic moment in both the weak and strong field...
Spin Current in Spin-Orbit Coupling Systems (2003)
Hu, Jiangping, Bernevig, Bogdan A., Wu, Congjun
We present a simple and pedagogical derivation of the spin current as the linear response to an external electric field for both Rashba and Luttinger spin-orbital coupling Hamiltonians. Except for...
Non-abelian Berry's phase and Chern numbers in higher spin pairing condensates (2003)
Chern, Chyh-Hong, Chen, Han-Dong, Wu, Congjun, Hu, Jiang-Ping, Zhang, Shou-Cheng
We show that the non-Abelian Berry phase emerges naturally in the s-wave and spin quintet pairing channel of spin-3/2 fermions. The topological structure of this pairing condensate is characterized...
Exact SO(5) Symmetry in spin 3/2 fermionic system (2003)
Wu, Congjun, Hu, Jiang-ping, Zhang, Shou-cheng
The spin 3/2 fermion models with contact interactions have a {\it generic} SO(5) symmetry without any fine-tuning of parameters. Its physical consequences are discussed in both the continuum and...
Vortex configurations of bosons in an optical lattice (2002)
Wu, Congjun, Chen, Han-dong, Hu, Jiang-ping, Zhang, Shou-Cheng
The single vortex problem in a strongly correlated bosonic system is investigated self-consistently within the mean-field theory of the Bose-Hubbard model. Near the superfluid-Mott transition, the...
Competing Orders in Coupled Luttinger Liquids (2002)
Wu, Congjun, Liu, W. Vincent, Fradkin, Eduardo
We consider the problem of two coupled Luttinger liquids both at half filling and at low doping levels, to investigate the problem of competing orders in quasi-one-dimensional strongly correlated...
Thermodynamic properties of the d-density wave order in cuprates (2002)
We solve a popular effective Hamiltonian of competing $d$-density wave and d-wave superconductivity orders self-consistently at the mean-field level for a wide range of doping and temperature. The...
Wu, Congjun, Xiang, Tao, Su, Zhao-Bin
The c-axis tunneling matrix of high-Tc superconductors is shown to depend strongly on the in-plane momentum of electrons and vanish along the four nodal lines of the d(x^2-y^2)-wave energy gap. This...
Electronic and Structural Properties of C$_{36}$ Molecule (2000)
Yu, Xiaoqing, Wu, Congjun, Wang, Chui-lin, Su, Zhao-Bin
The extended SSH model and Bogoliubov-de Gennes(BdeG) formalism are applied to investigate the electronic properties and stable lattice configurations of C$_{36}$. We focus the problem on the...
Schwinger boson mean field theory of the Heisenberg Ferrimagnetic Spin Chain (1999)
Wu, Congjun, Chen, Bin, Dai, Xi, Yu, Yue, Su, Zhao-Bin
The Schwinger boson mean field theory is applied to the quantum ferrimagnetic Heisenberg chain. There is a ferrimagnetic long range order in the ground state. We observe two branches of the low lying...