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Jia-Wei Mei

Publications and source records attributed to Jia-Wei Mei.

70 records · Page 4Linked to original sources
arXiv2015

Fractionalized spin-wave continuum in spin liquid states on the kagome lattice

Motivated by spin-wave continuum (SWC) observed in recent neutron scattering experiments in Herbertsmithite, we use Gutzwiller-projected wave functions to study dynamic spin structure factor $S(\mathbf{q},ω)$ of spin liquid states on the kagome lattice. Spin-1 excited states in spin liquids are represented by Gutzwiller-projected two-spinon excited wave functions. We investigate three different spin liquid candidates, spinon Fermi-surface spin liquid (FSL), Dirac spin liquid (DSL) and random-flux spin liquid (RSL). FSL and RSL have low energy peaks in $S(\mathbf{q},ω)$ at $K$ points in the extended magnetic Brillouin zone, in contrast to experiments where low energy peaks are found at $M$ points. There is no obviuos contradiction between DSL and neutron scattering measurements. Besides a fractionalized spin (i.e. spin-1/2), spinons in DSL carry a fractionalized crystal momentum which is potentially detectable in SWC in the neutron scattering measurements.

cond-mat.str-el↗
arXiv2015

Classification and Monte Carlo study of symmetric $Z_{2}$ spin liquids on the triangular lattice

We study different ways of symmetry fractionalization in $Z_{2}$ spin liquids on the triangular lattice. Our classification can be used to identify the symmetry fractionalization in the $Z_{2}$ spin liquid reported in recent density-matrix-renormalization-group simulations for $J_{1}-J_{2}$ spin model on the triangular lattice. We find 64 types of symmetry enriched $Z_{2}$ spin liquid states on triangular lattice. Besides 8 states constructed in Schwinger-boson parton wavefunctions, 12 more states can be realized in Abrikosov-fermion parton construction. Within a larger gauge group than SU(2), the rest 44 states are also found in a spin-3/2 system. Among 20 types of Abrikosov-fermion Gutzwillerprojected wavefunctions, No.B5 state is a promising candidate for the $Z_{2}$ spin liquid for $J_{1}-J_{2}$ spin model on the triangular lattice. No.B5 lies close to Dirac spin liquid (DSL). However, variational Monte Carlo simulation find that DSL has a good variational energy and $J_{1}-J_{2}$ spin model cannot open a gap for spinons on top of DSL to stabilize No.B5 state.

cond-mat.str-el↗
arXiv2015

Selective doping Barlowite for quantum spin liquid: a first-principles study

Barlowite $Cu_4(OH)_6FBr$ is a newly found mineral containing $Cu^{2+}$ kagome planes. Despite similarities in many aspects to Herbertsmithite $Cu_3Zn(OH)_6Cl_2$, the well-known quantum spin liquid (QSL) candidate, intrinsic Barlowite turns out not to be a QSL, possibly due to the presence of $Cu^{2+}$ ions in between kagome planes that induce interkagome magnetic interaction [PRL, 113, 227203 (2014)]. Using first-principles calculation, we systematically study the feasibility of selective substitution of the interkagome Cu ions with isovalent nonmagnetic ions. Unlike previous speculation of using larger dopants, such as $Cd^{2+}$ and $Ca^{2+}$, we identify the most ideal stoichiometric doping elements to be Mg and Zn in forming $Cu_3Mg(OH)_6FBr$ and $Cu_3Zn(OH)_6FBr$ with the highest site selectivity and smallest lattice distortion. The equilibirium anti-site disorder in Mg/Zn- doped Barlowite is estimated to be one order of magnitude lower than that in Herbertsmithite. The single-electron band structure and orbital component analysis show that the proposed selective doping effectively mitigates the difference between Barlowite and Herbertsmithite.

cond-mat.mtrl-sci↗
arXiv2015

Reconstructed Fermi surface and quantum oscillation of doped resonating valence bond state with incommensurate charge order in underdoped cuprates

Recent experiments have revealed incommensurate charge density wave (CDW) in the pseudogap regime in underdoped cuprates, e.g. YBa$_2$Cu$_3$O$_{6+δ}$ and HgBa$_2$CuO$_{4+δ}$. However, its relationship with the pseudogap is still controversial. In this work, we take a phenomenological synthesis of the doped resonating valence bond (RVB) state and the CDW order. Starting from the Yang-Rice-Zhang Green's function ansatz for the doped RVB state [Phys. Rev. B {\bf 73}, 174501 (2006)], in which the Fermi surface is partially truncated into four nodal hole-like Fermi pockets by the antinodal RVB gap, we show that the CDW order at the wavevectors connecting the tips of the Fermi arcs (the hotspots) induces Fermi surface reconstruction, giving rise to an electron-like Fermi pocket ($α$ orbit) and a new hole-like Fermi pocket ($β$ orbit). The $α$ orbit is formed by joining the Fermi arcs at the hotspots and it dominates the quantum oscillation Fourier spectrum, while the $β$ orbit is formed by joining the outer patches of the original hole pockets, which has vanishingly small spectral weight. The areas enclosed by these orbits are extracted from the density of states oscillation in magnetic field and quantitatively agree with the experiments.

cond-mat.supr-con↗
arXiv2014

$U(1)\times U(1)$ Symmetry Protected Topological Order in Gutzwiller Wave Functions

Gutzwiller projection is a way to construct many-body wave functions that could carry topological order or symmetry protected topological (SPT) order. However, an important issue is to determine whether or not a given Gutzwiller-projected wave functions (GWF) carries a non-trivial SPT order, and which SPT order is carried by the wavefunction. In this paper, we numerically study the SPT order in a spin $S = 1$ GWF on the Kagome lattice. Using the standard Monte Carlo method, we directly confirm that the GWF has (1) gapped bulk with short-range correlations, (2) a trivial topological order via nondegenerate ground state, and zero topological entanglement entropy, (3) a non-trivial $U(1)\times U(1)$ SPT order via the Hall conductances of the protecting $U(1)\times U(1)$ symmetry, and (4) symmetry protected gapless boundary. This represents numerical evidence of continuous symmetry protected topological order in two-dimensional bosonic lattice systems.

cond-mat.str-el↗
arXiv2014

Modular matrices from universal wave function overlaps in Gutzwiller-projected parton wave functions

We implement the universal wave function overlap (UWFO) method to extract modular $S$ and $T$ matrices for topological orders in Gutzwiller-projected parton wave functions (GPWFs). The modular $S$ and $T$ matrices generate a projective representation of $SL(2,\mathbb{Z})$ on the degenerate-ground-state Hilbert space on a torus and may fully characterize the 2+1D topological orders, i.e. the quasi-particle statistics and chiral central charge (up to $E_8$ bosonic quantum Hall states). We used the variational Monte Carlo method to computed the $S$ and $T$ matrices of the chiral spin liquid (CSL) constructed by the GPWF on the square lattice, and confirm that the CSL carries the same topological order as the $ν=\frac{1}{2}$ bosonic Laughlin state. We find that the non-universal exponents in UWFO can be small and direct numerical computation is able to be applied on relatively large systems. We also discuss the UWFO method for GPWFs on other Bravais lattices in two and three dimensions by using the Monte Carlo method. UWFO may be a powerful method to calculate the topological order in GPWFs.

cond-mat.str-el↗
arXiv2014

Design local spin models for Gutzwiller-projected parton wave functions

We introduce a method to design a local spin Hamiltonian to realize a Gutzwiller-projected parton wave functions (GPWF) as its ground state. For example, the Dirac spin liquid (DSL) state is quite close to the true ground state of the spin-1/2 Heisenberg model on kagome lattice. We examine what kind of perturbations we should add in order to drive the DSL to more stable chiral spin liquid (CSL), valence bond solid (VBS) or Gutzwiller-projected spin Hall (GSH) states. We compute the two-body reduced-density-matrices (2-RDM) of GPWFs for those target states, and compare them to the 2-RDM of the DSL. This allows us to design local spin models with only two-body interactions that may realize those interesting target states. Our results agree very well with recent numerical calculations for CSL on kagome lattice. We also study spin-1 systems on kagome lattice, and design local spin models that may realize CSL, VBS and symmetry-protected topological (SPT) states. Our work establishes a directional guide for further numerical simulations.

cond-mat.str-el↗
arXiv2013

Origin of the unusual strong suppression of low frequency antiferromagnetic fluctuations in underdoped HgBa$_2$CuO$_{4+δ}$

Generally strong charge and magnetic inhomogeneities are observed in NQR/NMR experiments on underdoped cuprates. It is not the case for the underdoped HgBa$_2$CuO$_{4+δ}$, the most symmetric and highest T$_c$ single layer cuprate, whose magnetic inhomogeneity is strongly suppressed. Also neutron scattering experiments reveal a unique pair of weakly dispersive magnetic modes in this material. We propose that these special properties stem from the symmetric positioning of the O-dopants between adjacent CuO$_2$ layers that lead to a strong superexchange interaction between a pair of hole spins. In this Letter we present a theoretical model, which gives a consistent explanation to the anomalous magnetic properties of this material.

cond-mat.supr-con↗
arXiv2013

Different roles of Zn$^{2+}$ and Li$^{+}$ impurities in the CuO$_2$ plane in undoped cuprate compounds

A planar Mott insulator with easy plane Néel order can be mapped onto a Gutzwiller-projected spin Hall state. The in-plane substitution of Zn$^{2+}$ and Li$^{+}$ for Cu$^{2+}$ brings zero modes around the spin vacancy. The Gutzwiller projection precludes single particle excitations, however, preserves the zero modes which have a local spin moment for Zn$^{2+}$ and a local charged hole for Li$^{+}$, respectively. While the local spin moment for Zn$^{2+}$ is screened by the long-range spin correlations, the active charge degree of freedom for Li$^{+}$ impurity twists the spin background with long ranged disturbances. This proposal explains the very different roles of the Zn$^{2+}$ and Li$^{+}$ impurities on the magnetic perturbations in the CuO$_2$ plane in the undoped cuprate compounds.

cond-mat.str-el↗
arXiv2012

Flat Chern Band in a Two-Dimensional Organometallic Framework

By combining exotic band dispersion with nontrivial band topology, an interesting type of band structure, namely the flat chern band (FCB), has recently been proposed to spawn high-temperature fractional quantum hall states. Despite the proposal of several theoretical lattice models, however, it remains a doubt whether such a "romance of flatland" could exist in a real material. Here, we present a first-principles design of a two-dimensional (2D) Indium-Phenylene Organometallic Framework (IPOF) that realizes a nearly FCB right around the Fermi level by combining lattice geometry, spin-orbit coupling and ferromagnetism. An effective four-band model is constructed to reproduce the first-principles results. Our design in addition provides a general strategy to synthesize topologically nontrivial materials in virtue of organic chemistry and nanotechnology.

cond-mat.mtrl-sci↗
arXiv2012

Bilayer Twisted Hubbard Model for Sr3Ir2O7

We use the bilayer twisted Hubbard model to study the low energy electronic structure of Sr3Ir2O7. Sr3Ir2O7 is suggested as a Mott insulator and described by the bilayer twisted pseudospin-1/2 model. The bilayer twists in Sr3Ir2O7 bring the intrinsic anisotropy and the system is no longer SU(2) invariant. The anisotropy selects an easy c-axis collinear antiferromagnetic magnetic structure at low temperatures which breaks the discrete Ising symmetry. The transverse spin excitations are gapped and the longitudinal one is weakly dispersive. We implement the bond-operator mean field calculation to describe the magnetic properties of the bilayer twisted pseudospin-1/2 model in good agreement with experimental measurements in Sr3Ir2O7. The bilayer twisted Hubbard model is believed to be the good zeroth approximation for the low energy electronic structure of Sr3Ir2O7.

cond-mat.str-el↗
arXiv2012

Luttinger-volume violating Fermi liquid in the pseudogap phase of the cuprate superconductors

Based on the NMR measurements on Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+δ}$ (La-Bi2201) in strong magnetic fields, we identify the non-superconducting pseudogap phase in the cuprates as a Luttinger-volume violating Fermi liquid (LvvFL). This state is a zero temperature quantum liquid that does not break translational symmetry, and yet, the Fermi surface encloses a volume smaller than the large one given by the Luttinger theorem. The particle number enclosed by the small Fermi surface in the LvvFL equals the doping level $p$, not the total electron number $n_e=1-p$. Both the phase string theory and the dopon theory are introduced to describe the LvvFL. For the dopon theory, we can obtain a semi-quantitative agreement with the NMR experiments.

cond-mat.supr-con↗
arXiv2011

A Possible Fermi liquid in the lightly doped Kitaev spin liquid

In this paper, we study the lightly doped Kitaev spin liquid (DKSL) and find it to be a Fermi liquid state. The DKSL has a closed Fermi surface around the center of the Brillouin zone with the quantized volume determined by the Luttinger's theorem. It has well-defined quasiparticles near the Fermi surface and can be detected in the angle-resolved photoemission spectroscopy. The DKSL has the topological Kitaev spin liquid (KSL) as its neutral background. It violates the Wiedemann-Franz law and has a large Wilson ration. These results has the potential experimental test in the iridates upon doping.

cond-mat.str-el↗
arXiv2011

Chiral spin states in polarized kagome spin systems with spin-orbit coupling

We study quantum spin systems with a proper combination of geometric frustration, spin-orbit coupling and ferromagnetism. We argue that such a system is likely to be in a chiral spin state, a fractional quantum Hall (FQH) state for bosonic spin degrees of freedom. The energy scale of the bosonic FQH state is of the same order as the spin-orbit coupling and ferromagnetism --- overall much higher than the energy scale of FQH states in semiconductors.

cond-mat.str-el↗
arXiv2011

High temperature fractional quantum Hall states

We show that a suitable combination of geometric frustration, ferromagnetism and spin-orbit interactions can give rise to nearly flat bands with a large bandgap and non-zero Chern number. Partial filling of the flat band can give rise to fractional quantum Hall states at high temperatures (maybe even room temperature). While the identification of material candidates with suitable parameters remains open, our work indicates intriguing directions for exploration and synthesis.

cond-mat.str-el↗