In this work we investigate collective excitations at the boundary of a recently constructed 4D q... more In this work we investigate collective excitations at the boundary of a recently constructed 4D quantum Hall state. Local bosonic operators for creating these collective excitations can be constructed explicitly. Massless relativistic wave equations with helicity $S$ can be derived exactly for these operators from their Heisenberg equation of motion. For the S=1 and S=2 cases these equations reduce to the free Maxwell and linearized Einstein equation respectively. These collective excitations can be interpreted as hydrodynamical modes at the boundary of the 4D QHE droplet. Outstanding issues are critically discussed.
We use bulk magnetic susceptibility, electronic specific heat, and neutron scattering to study st... more We use bulk magnetic susceptibility, electronic specific heat, and neutron scattering to study structural and magnetic phase transitions in Fe$_{1+y}$Se% $_x$Te$_{1-x}$. Fe$_{1.068}$Te exhibits a first order phase transition near 67 K with a tetragonal to monoclinic structural transition and simultaneously develops a collinear antiferromagnetic (AF) order responsible for the entropy change across the transition. Systematic studies of FeSe$%_{1-x}$Te$_x$ system reveal that the AF structure and lattice distortion in these materials are different from those of FeAs-based pnictides. These results call into question the conclusions of present density functional calculations, where FeSe$_{1-x}$Te$_x$ and FeAs-based pnictides are expected to have similar Fermi surfaces and therefore the same spin-density-wave AF order.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
We construct a generalization of the quantum Hall effect, where particles move in four dimensiona... more We construct a generalization of the quantum Hall effect, where particles move in four dimensional space under a SU(2) gauge field. This system has a macroscopic number of degenerate single particle states. At appropriate integer or fractional filling fractions the system forms an incompressible quantum liquid. Gapped elementary excitations in the bulk interior and gapless elementary excitations at the boundary are investigated.
We construct a generalization of the quantum Hall effect where particles move in an eight dimensi... more We construct a generalization of the quantum Hall effect where particles move in an eight dimensional space under an SO(8) gauge field. The underlying mathematics of this particle liquid is that of the last normed division algebra, the octonions. Two fundamentally different liquids with distinct configurations spaces can be constructed, depending on whether the particles carry spinor or vector SO(8) quantum numbers. One of the liquids lives on a 20 dimensional manifold of with an internal component of SO(7) holonomy, whereas the second liquid lives on a 14 dimensional manifold with an internal component of $G_2$ holonomy.
We study the pairing symmetry of a two orbital $J_1-J_2$ model for FeAs layers in oxypnictides. W... more We study the pairing symmetry of a two orbital $J_1-J_2$ model for FeAs layers in oxypnictides. We vary the doping and the value of $J_1$ and $J_2$ to compare all possible pairing symmetries in a mean-field calculation. We show that the mixture of an intra-orbital unconventional $s_{x^2y^2}\sim \cos(k_x)\cos(k_y)$ pairing symmetry and a $d_{x^2-y^2}\sim \cos(k_x)-\cos(k_y)$ pairing symmetry is favored in a large part of $J_1-J_2$ phase diagram. A pure $ s_{x^2y^2}$ pairing state is favored for $J_2>>J_1$. The signs of the $d_{x^2-y^2}$ order parameters in two different orbitals are opposite. While a small $d_{xy}\sim \sin(k_x)\sin(k_y)$ inter-orbital pairing order coexists in the above phases, the intra-orbital $d_{xy}$ pairing symmetry is not favored even for large values of $J_2$.
The experimental consequences of different order parameters in iron-based superconductors are the... more The experimental consequences of different order parameters in iron-based superconductors are theoretically analyzed. We consider both nodeless and nodal order parameters, with an emphasis on the $\cos(k_x)\cdot \cos(k_y)$ nodeless order parameter recently derived by two of us. We analyze the effect of this order parameter on the spectral function, density of states, tunneling differential conductance, penetration depth, and the NMR spin relaxation time. This extended s-wave symmetry has line-zeroes in between the electron and hole pockets, but they do not intersect the two Fermi surfaces for moderate doping, and the superconductor is fully gapped. However, this suggests several quantitative tests: the exponential decay of the penetration depth weakens and the density of states reveals a smaller gap upon electron or hole doping. Moreover, the $\cos(k_x) \cdot \cos(k_y)$ superconducting gap is largest on the smallest (hole) Fermi surface. For the $1/T_1$ NMR spin relaxation rate, the inter-band contribution is consistent with the current experimental results, including a (non-universal) $T^{3}$ behavior and the absence of a coherence peak. However, the intra-band contribution is considerably larger than the inter-band contributions and still exhibits a small enhancement in the NMR spin relaxation rate right below $T_c$ in the clean limit.
In this work we investigate collective excitations at the boundary of a recently constructed 4D q... more In this work we investigate collective excitations at the boundary of a recently constructed 4D quantum Hall state. Local bosonic operators for creating these collective excitations can be constructed explicitly. Massless relativistic wave equations with helicity $S$ can be derived exactly for these operators from their Heisenberg equation of motion. For the S=1 and S=2 cases these equations reduce to the free Maxwell and linearized Einstein equation respectively. These collective excitations can be interpreted as hydrodynamical modes at the boundary of the 4D QHE droplet. Outstanding issues are critically discussed.
We use bulk magnetic susceptibility, electronic specific heat, and neutron scattering to study st... more We use bulk magnetic susceptibility, electronic specific heat, and neutron scattering to study structural and magnetic phase transitions in Fe$_{1+y}$Se% $_x$Te$_{1-x}$. Fe$_{1.068}$Te exhibits a first order phase transition near 67 K with a tetragonal to monoclinic structural transition and simultaneously develops a collinear antiferromagnetic (AF) order responsible for the entropy change across the transition. Systematic studies of FeSe$%_{1-x}$Te$_x$ system reveal that the AF structure and lattice distortion in these materials are different from those of FeAs-based pnictides. These results call into question the conclusions of present density functional calculations, where FeSe$_{1-x}$Te$_x$ and FeAs-based pnictides are expected to have similar Fermi surfaces and therefore the same spin-density-wave AF order.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
We construct a generalization of the quantum Hall effect, where particles move in four dimensiona... more We construct a generalization of the quantum Hall effect, where particles move in four dimensional space under a SU(2) gauge field. This system has a macroscopic number of degenerate single particle states. At appropriate integer or fractional filling fractions the system forms an incompressible quantum liquid. Gapped elementary excitations in the bulk interior and gapless elementary excitations at the boundary are investigated.
We construct a generalization of the quantum Hall effect where particles move in an eight dimensi... more We construct a generalization of the quantum Hall effect where particles move in an eight dimensional space under an SO(8) gauge field. The underlying mathematics of this particle liquid is that of the last normed division algebra, the octonions. Two fundamentally different liquids with distinct configurations spaces can be constructed, depending on whether the particles carry spinor or vector SO(8) quantum numbers. One of the liquids lives on a 20 dimensional manifold of with an internal component of SO(7) holonomy, whereas the second liquid lives on a 14 dimensional manifold with an internal component of $G_2$ holonomy.
We study the pairing symmetry of a two orbital $J_1-J_2$ model for FeAs layers in oxypnictides. W... more We study the pairing symmetry of a two orbital $J_1-J_2$ model for FeAs layers in oxypnictides. We vary the doping and the value of $J_1$ and $J_2$ to compare all possible pairing symmetries in a mean-field calculation. We show that the mixture of an intra-orbital unconventional $s_{x^2y^2}\sim \cos(k_x)\cos(k_y)$ pairing symmetry and a $d_{x^2-y^2}\sim \cos(k_x)-\cos(k_y)$ pairing symmetry is favored in a large part of $J_1-J_2$ phase diagram. A pure $ s_{x^2y^2}$ pairing state is favored for $J_2>>J_1$. The signs of the $d_{x^2-y^2}$ order parameters in two different orbitals are opposite. While a small $d_{xy}\sim \sin(k_x)\sin(k_y)$ inter-orbital pairing order coexists in the above phases, the intra-orbital $d_{xy}$ pairing symmetry is not favored even for large values of $J_2$.
The experimental consequences of different order parameters in iron-based superconductors are the... more The experimental consequences of different order parameters in iron-based superconductors are theoretically analyzed. We consider both nodeless and nodal order parameters, with an emphasis on the $\cos(k_x)\cdot \cos(k_y)$ nodeless order parameter recently derived by two of us. We analyze the effect of this order parameter on the spectral function, density of states, tunneling differential conductance, penetration depth, and the NMR spin relaxation time. This extended s-wave symmetry has line-zeroes in between the electron and hole pockets, but they do not intersect the two Fermi surfaces for moderate doping, and the superconductor is fully gapped. However, this suggests several quantitative tests: the exponential decay of the penetration depth weakens and the density of states reveals a smaller gap upon electron or hole doping. Moreover, the $\cos(k_x) \cdot \cos(k_y)$ superconducting gap is largest on the smallest (hole) Fermi surface. For the $1/T_1$ NMR spin relaxation rate, the inter-band contribution is consistent with the current experimental results, including a (non-universal) $T^{3}$ behavior and the absence of a coherence peak. However, the intra-band contribution is considerably larger than the inter-band contributions and still exhibits a small enhancement in the NMR spin relaxation rate right below $T_c$ in the clean limit.
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Papers by Jiangping Hu