arXiv subjects

Jiangping Hu

Publications and source records attributed to Jiangping Hu.

At least 217 records · Page 12Linked to original sources

arXiv2014

Robust antiferromagnetism preventing superconductivity in pressurized Ba0.61K0.39Mn2Bi2

Here, we report that K-doped BaMn2Bi2 shows no experimental evidence of superconductivity down to 1.5 K under pressures up to 35.6 GPa, however, a tetragonal to an orthorhombic phase transition is observed at pressure of 20 GPa. Theoretical calculations for the tetragonal and orthorhombic phases, on basis of our high-pressure XRD data, find that the AFM order is robust in both of the phases in pressurized Ba0.61K0.39Mn2Bi2. Our experimental and theoretical results suggest that the K-doped BaMn2Bi2 belongs to a strong Hunds AFM metal with a hybridization of localized spin electrons and itinerant electrons, and that its robust AFM order essentially prevents the emergence of superconductivity.

cond-mat.supr-con↗

arXiv2014

Pairing Symmetry in Layered BiS$_2$ Compounds Driven by Electron-Electron Correlation

We investigate the pairing symmetry of layered BiS$_2$ compounds by assuming that electron-electron correlation is still important so that the pairing is rather short range. We find that the extended s-wave pairing symmetry always wins over d-wave when the pairing is confined between two short range sites up to next nearest neighbors. The pairing strength is peaked around the doping level x=0.5, which is consistent with experimental observation. The extended s-wave pairing symmetry is very robust against spin-orbital coupling because it is mainly determined by the structure of Fermi surfaces. Moreover, the extended s-wave pairing can be distinguished from conventional s-wave pairing by measuring and comparing superconducting gaps of different Fermi surfaces.

cond-mat.supr-con↗

arXiv2014

Functional Renormalization Group Analysis of $η$-Pairing in Iron-based Superconductors

Using functional renormalization group (FRG) approach, we analyze the $η$ pairing in a five d-orbital model for iron-pncitides. We find that the $η$ pairing between two hole pockets is a leading instability at low energy when the two hole pockets are close to a nesting condition. The result suggests that the system can spontaneously enter into a superconducting state with both normal pairing and $η$ paring and the $η$ pairing is driven by the inter-orbital antiferromagnetic exchange coupling while the normal pairing is driven by the intra-orbital antiferromagnetic ones. An effective model at low energy is proposed to account for the $η$ pairing instability.

cond-mat.supr-con↗

arXiv2014

Topological Phases in the Single-Layer FeSe

A distinct electronic structure was observed in the single-layer FeSe which shows surprising high temperature superconductivity over 65k. Here we demonstrate that the electronic structure can be explained by the strain effect due to substrates. More importantly, we find that this electronic structure can be tuned into robust topological phases from a topologically trivial metallic phase by the spin-orbital interaction and couplings to substrates. The topological phase is robust against any perturbations that preserve the time-reversal symmetry. Our studies suggest that topological phases and topologically related properties such as Majorana Fermions can be realized in iron-based high T$_{c}$ superconductors.

cond-mat.supr-con↗

arXiv2014

The effect of As-Chain layers in CaFeAs$_2$

The new discovered iron-based superconductors have chain-like As layers. These layers generate an additional 3-dimensional hole pocket and cone-like electron pockets. The former is attributed to the Ca $d$ and As1 $p_z$ orbitals and the latter are attributed to the anisotropic Dirac cone, contributed by As1 $p_x$ and $p_y$ orbitals. We find that large gaps on these pockets open in the collinear antiferromagnetic ground state of CaFeAs$_2$, suggesting that the chain-like As layers are strongly coupled to FeAs layers. Moreover due to the low symmetry crystal induced by the As layers, the bands attributed to FeAs layers in $k_y=π$ plane are two-fold degenerate but in $k_x=π$ plane are lifted. This degeneracy is protected by a hidden symmetry $\hatΥ=\hat{T}\hat{R}_y$. Ignoring the electron cones, the materials can be well described by a six-band model, including five Fe $d$ and As1 $p_z$ orbitals. We suggest that these new features may help us to identify the sign change and pairing symmetry in iron based superconductors.

cond-mat.supr-con↗

arXiv2014

Odd parity pairing and nodeless anti-phase $s^\pm$ in Iron-Based Superconductors

We discuss the sign change of superconducting order parameters in both real and reciprocal spaces when the odd parity spin singlet pairing proposed recently in\cite{huoddparity} is allowed. We show that in this case an nodeless anti-phase $s^\pm$ can be generated. In a 2-Fe Brilliouin zone (BZ), sign change exists between two hole pockets and between two electron pockets. In a 1-Fe BZ which includes two 2-Fe BZs, the sign change is between two 2-Fe BZs, which leads to a d-wave type sign distribution on the electron pockets, namely, an anti-phase $s^\pm$ state with no symmetry protected gapless node on the electron pockets. This sign change character consistently explains experimental results related to sign change properties measured on both iron-pnictides and iron-chalcogenides.

cond-mat.supr-con↗

arXiv2013

Event-based Bipartite Consensus on Signed Networks

In this paper, a bipartite consensus problem for a multi-agent system is formulated firstly. Then an event-based interaction rule is proposed for the multi-agent system with antagonistic interactions. The bipartite consensus stability is analyzed on the basis of spectral properties of the signed Laplacian matrix associated with multi-agent networks. Some simulation results are presented to illustrate the bipartite consensus with the proposed interaction rule.

nlin.AO↗

arXiv2013

Loop Current and Orbital Magnetism in Pyrite-Type $Ir_{3}Ch_{8}$ ($Ch=Se,Te$)

We study the parent compound of the pyrite-type $Ir_{x}Ch_{2}$ iridium chalcogenide superconductors, $Ir_{0.75}Ch_{2}$ (or $Ir_{3}Ch_{8}$). While the lattice structure of the material is rather complicated, we show that the electron physics near the Fermi surface (FS) can be described by a three-band tight-binding model. We find that the material possesses a loop current ground state which is responsible for the highly anisotropic strong diamagnetism observed in experiments. The fluctuations of this loop current state can be a possible pairing mechanism for superconductivity.

cond-mat.supr-con↗

arXiv2013

Quantum Hall Effects in Monolayer-Bilayer Graphene Planar Junctions

The Hall resistance of a homogeneous electron system is well known to be anti-symmetric with respect to the magnetic field and the sign of charge carriers. We have observed that such symmetries no longer hold in planar hybrid structures consisting of partly single layer graphene (SLG) and partly bilayer graphene (BLG) in the quantum Hall (QH) regime. In particular, the Hall resistance (R12xy) across the SLG and BLG interface is observed to exhibit quantized plateaus that switch between those characteristic of SLG QH states and BLG QH states when either the sign of the charge carriers (controlled by a back gate) or the direction of the magnetic field is reversed. Simultaneously reversing both the carrier type and the magnetic field gives rise to the same quantized Hall resistances. The observed SLG-BLG interface QH states, with characteristic asymmetries with respect to the signs of carriers and magnetic field, are determined only by the chirality of the QH edge states and can be explained by a Landauer-Büttiker analysis applied to such graphene hybrid structures involving two regions of different Landau level (LL) structures.

cond-mat.mes-hall↗

arXiv2013

Spin excitation anisotropy as a probe of orbital ordering in the paramagnetic tetragonal phase of superconducting BaFe1.904Ni0.096As2

We use polarized neutron scattering to demonstrate that in-plane spin excitations in electron doped superconducting BaFe1.904Ni0.096As2 (Tc=19.8 K) change from isotropic to anisotropic in the tetragonal phase well above the antiferromagnetic (AF) ordering and tetragonal-to-orthorhombic lattice distortion temperatures (Tn=Ts=33 K) without an uniaxial pressure. While the anisotropic spin excitations are not sensitive to the AF order and tetragonal-to-orthorhombic lattice distortion, superconductivity induces further anisotropy for spin excitations along the [1,1,0] and [1,-1,0] directions. These results indicate that the spin excitation anisotropy is a probe of the electronic anisotropy or orbital ordering in the tetragonal phase of iron pnictides.

cond-mat.supr-con↗

arXiv2013

Chiral f-wave Topological Superuid in Triangular Optical Lattices

We demonstrate that an exotically chiral f-wave topological superfluid can be induced in coldfermionic-atom triangular optical lattices through the laser-field-generated effective non-Abelian gauge field, controllable Zeeman fields and s-wave Feshbach resonance. We find that the chiral f-wave topological superfluid is characterized by three gapless Majorana edge states located on the boundary of the system. More interestingly, these Majorana edge states degenerate into one Majorana fermion bound to each vortex in the superfluid. Our proposal enlarges topological superfluid family and specifies a unique experimentally controllable system to study the Majorana fermion physics.

cond-mat.quant-gas↗

arXiv2013

Iron-Based Superconductors as Parity Odd Superconductors

Parity is a fundamental quantum number to classify a state of matter. Materials rarely possess ground states with odd parity. We show that the superconducting state in iron-based superconductors is classified as an odd parity s-wave spin-singlet pairing state in a single trilayer FeAs/Se, the building block of the materials. In a low energy effective model constructed on the Fe square bipartite lattice, the superconducting order parameter in this state is a combination of a s-wave normal pairing between two sublattices and a s-wave $η$-pairing within the sublattices. Parity conservation was violated in proposed superconducting states in the past. The state has a fingerprint with a real space sign inversion between the top and bottom As/Se layers. The results demonstrate iron-based superconductors being a new quantum state of matter and suggest that the measurement of the odd parity can establish fundamental principles related to high temperature superconducting mechanism.

cond-mat.supr-con↗

arXiv2013

Mechanism for Odd Parity Superconductivity in Iron-Based Superconductors

Under the assumption that superconducting pairing is driven by local d-p hybridization, we show that the superconducting state in iron-based superconductors is classified as an odd parity s-wave spin-singlet pairing state in a single trilayer FeAs/Se, the building block of the materials. In a low energy effective model with only d-orbitals in an iron square bipartite lattice, the superconducting order parameter in this state is a combination of a s-wave normal pairing between two sublattices and a s-wave $η$-pairing within the sublattices. Parity conservation was violated in proposed superconducting states in the past. The results demonstrate iron-based superconductors being a new quantum state of matter and suggest that a measurement of odd parity can establish fundamental principles related to high temperature superconducting mechanism.

cond-mat.supr-con↗

arXiv2013

Quantum Monte Carlo Study of Pairing Symmetry and Correlation in Iron-based Superconductors

We perform a systematic quantum Monte Carlo study of the pairing correlation in the $S_4$ symmetric microscopic model for iron-based superconductors. It is found that the pairing with an extensive s-wave symmetry robustly dominates over other pairings at low temperature in reasonable parameter region. The pairing susceptibility, the effective pairing interaction and the $(π,0)$antiferromagnetic correlation strongly increase as the on-site Coulomb interaction increases, indicating the importance of the effect of electron-electron correlation. Our non-biased numerical results provide a unified understanding of superconducting mechanism in iron-pnictides and iron-chalcogenides and demonstrate that the superconductivity is driven by strong electron-electron correlation effects.

cond-mat.str-el↗

arXiv2013

Superconductivity and Strong Non-Fermi-Liquid Behavior in Single-Crystal Ir3Te8

We observe superconductivity below a critical temperature TC = 1.8 K in single-crystal Ir3Te8, which also exhibits normal-state diamagnetism and a linear temperature dependence of electrical resistivity for a wide temperature interval, 20 K < T < 700 K. Single-crystal Ir3Te8 also undergoes a structural phase transition at TS = 350 K from a cubic (above TS) to a rhombohedral lattice below TS. Our first-principles electronic structure calculations reveal two bands crossing the Fermi level; despite the three-dimensional lattice, one band is quasi-two-dimensional, and is responsible for the observed diamagnetism and structure transition. The strong non-Fermi-liquid behavior characterized by the observed linearity in resistivity in such a nonmagnetic state suggests novel physics in this newly discovered superconductor.

cond-mat.supr-con↗

arXiv2012

Magnetic ordering and multiferroicity in MnI$_2$

Density-functional calculations are carried out to investigate incommensurate magnetic structures and ferroelectric polarization in newly discovered multiferroic material MnI$_2$. The exchange interactions among local moments on Mn are parameterized by mapping the mean-field Heisenberg model on to total energy difference of several magnetic ordering states. The experimentally observed noncollinear magnetic states are well reproduced by using this model and exchange interaction parameters. The direction of polarization experimentally measured is also consistent with the result derived from the symmetry analysis of the magnetically ordered state. In particular, we find that the inter-plane magnetic exchange coupling is pivotal to the emergence of the spiral magnetic structure. This noncollinear magnetic structure, combined with spin-orbit coupling mainly from I ions, is responsible for the appearance of ferroelectric polarization.

cond-mat.str-el↗

arXiv2012

Magnetism and its microscopic origin in iron-based high-temperature superconductors

High-temperature superconductivity in the iron-based materials emerges from, or sometimes coexists with, their metallic or insulating parent compound states. This is surprising since these undoped states display dramatically different antiferromagnetic (AF) spin arrangements and N$\rm \acute{e}$el temperatures. Although there is general consensus that magnetic interactions are important for superconductivity, much is still unknown concerning the microscopic origin of the magnetic states. In this review, progress in this area is summarized, focusing on recent experimental and theoretical results and discussing their microscopic implications. It is concluded that the parent compounds are in a state that is more complex than implied by a simple Fermi surface nesting scenario, and a dual description including both itinerant and localized degrees of freedom is needed to properly describe these fascinating materials.

cond-mat.supr-con↗

arXiv2012

A Short Review of the $S_4$ Symmetric Microscopic Model for Iron-Based High Temperature Superconductors

We briefly review the recently constructed two orbital microscopic model for iron-based superconductors based on $S_4$ symmetry (PRX 2 021009(2012)). With this faithful representation of the kinematics of the tri-layer FeAs or FeSe structure, the model provides answers and physical pictures to fundamental questions related to the robustness of superconductivity and pairing symmetry, unifies different families of iron-based superconductors, casts new insight into the connections to the other high $T_c$ superconductors, cuprates, and reveals why an s-wave pairing can be stabilized by repulsive interactions. Further progresses include that the model provides a clean understanding of band reconstruction observed in magnetically ordered states, which is a strong support to the kinematics of the $S_4$ model, and captures the essential low energy physics of iron-based superconductors based on numerical results from unbiased quantum Monte Carlo simulation.

cond-mat.supr-con↗