Showing 1–50 of 127 results for author: Zou, L

Chirality-selective topological magnon phase transition induced by interplay of anisotropic exchange interactions in honeycomb ferromagnet

Authors: Jin-Yu Ni, Xia-Ming Zheng, Peng-Tao Wei, Da-Yong Liu, Liang-Jian Zou

Abstract: A variety of distinct anisotropic exchange interactions commonly exist in one magnetic material due to complex crystal, magnetic and orbital symmetries. Here we investigate the effects of multiple anisotropic exchange interactions on topological magnon in a honeycomb ferromagnet, and find a chirality-selective topological magnon phase transition induced by a complicated interplay of Dzyaloshinsky-… ▽ More A variety of distinct anisotropic exchange interactions commonly exist in one magnetic material due to complex crystal, magnetic and orbital symmetries. Here we investigate the effects of multiple anisotropic exchange interactions on topological magnon in a honeycomb ferromagnet, and find a chirality-selective topological magnon phase transition induced by a complicated interplay of Dzyaloshinsky-Moriya interaction (DMI) and pseudo-dipolar interaction (PDI), accompanied by the bulk gap close and reopen with chiral inversion. Moreover, this novel topological phase transition involves band inversion at high symmetry points $K$ and $K'$, which can be regarded as a pseudo-orbital reversal, i.e. magnon valley degree of freedom, implying a new manipulation corresponding to a sign change of the magnon thermal Hall conductivity. Indeed, it can be realized in 4$d$ or 5$d$ correlated materials with both spin-orbit coupling and orbital localized states, such as iridates and ruthenates, etc. This novel regulation may have potential applications on magnon devices and topological magnonics. △ Less

Submitted 25 December, 2025; originally announced December 2025.

Comments: 20 pages, 8 figures

Journal ref: J. Phys.: Condens. Matter 36, 255801 (2024)

Multiple topological phases of magnons induced by Dzyaloshinskii-Moriya and pseudodipolar anisotropic exchange interactions in Kagome ferromagnets

Authors: Jin-Yu Ni, Xia-Ming Zheng, Peng-Tao Wei, Da-Yong Liu, Liang-Jian Zou

Abstract: Kagome magnets naturally hosting Dirac points and flat bands exhibit novel topological phases, enabling rich interplays between interactions and topologies. The discovery of two-dimensional (2D) magnets generally coexisting with different types of magnetic interactions poses a challenge for topological magnonic manipulation. Here we investigate the topological magnon phases of 2D Kagome ferromagne… ▽ More Kagome magnets naturally hosting Dirac points and flat bands exhibit novel topological phases, enabling rich interplays between interactions and topologies. The discovery of two-dimensional (2D) magnets generally coexisting with different types of magnetic interactions poses a challenge for topological magnonic manipulation. Here we investigate the topological magnon phases of 2D Kagome ferromagnet with multiple magnetic anisotropic interactions, i.e. Dzyaloshinskii-Moriya interaction (DMI) and pseudo-dipolar interaction (PDI). It is found that the different sole magnetic anisotropic interactions introduce completely distinct topological phase diagrams and topological states. The multiple topological magnon phases with high Chern number emerge due to the distinct anisotropic interactions. Moreover, the interplay of the multiple anisotropic DMI and PDI interactions involved with Dirac and flat bands controls a variety of topological phase transitions, implying greater manipulation potential. In addition, the sign reversal of thermal Hall and Nernst conductivities induced by temperature is found in particular topological phase regions, namely topological origin, relating to the energy gap and Berry curvature (Chern number) in the vicinity of magnetic phase transition from the thermal fluctuations, providing a possible explanation for the experimental puzzles. All these results demonstrate that the novel topological magnonic properties in Kagome magnet with multiple magnetic anisotropic interactions can realize a potential platform for magnonic devices and quantum computing. △ Less

Submitted 23 December, 2025; originally announced December 2025.

Comments: 33 pages, 13 figures

Journal ref: Phys. Rev. B 112, 184431 (2025)

Universal quasi-degenerate orbital origin of two-dome phases in iron pnictide superconductors

Authors: Da-Yong Liu, Zhe Sun, Feng Lu, Wei-Hua Wang, Liang-Jian Zou

Abstract: A series of experiments revealed that novel bipartite magnetic and superconducting (SC) phases widely exist in the phase diagrams of iron pnictides and chalcogenides. Nevertheless, the origin of the two-dome magnetic and SC phases in iron-based compounds remains unclear. Here we theoretically investigated the electronic structures, magnetic and SC properties of three representative iron-based syst… ▽ More A series of experiments revealed that novel bipartite magnetic and superconducting (SC) phases widely exist in the phase diagrams of iron pnictides and chalcogenides. Nevertheless, the origin of the two-dome magnetic and SC phases in iron-based compounds remains unclear. Here we theoretically investigated the electronic structures, magnetic and SC properties of three representative iron-based systems, i.e. LaFeAsO$_{1-x}$H$_{x}$, LaFeAs$_{1-x}$P$_{x}$O and KFe$_{2}$As$_{2}$. We propose a unified quasi-degenerate orbital mechanism for the emergence of the two-dome parent magnetic/structural phase and the subsequent two-dome SC phase. It is found that the degenerate in-plane anisotropic $d_{xz/yz}$ orbitals dominate the first magnetic/structural and SC phases, while in-plane isotropic orbitals $d_{xy}$ or $d_{3z^{2}-r^{2}}$ with quasi-degeneracy originating from quasi-symmetry drive the emergence of the second magnetic/SC dome phase. Moreover, a matching rule of spin and orbital modes for SC pairing state is proposed in multi-orbital iron-based systems. These results imply an orbital-driven mechanism as well as an orbital-selective scenario, and shed light on the understanding of the multi-dome magnetic and SC phases in multi-orbital systems. △ Less

Submitted 23 December, 2025; originally announced December 2025.

Comments: 36 pages, 16 figures; this article supersedes arXiv: 1701.02500

Journal ref: Phys. Rev. B 112, 014505 (2025)

Unveiling the Phase Diagram and Nonlinear Optical Responses of a Twisted Kitaev Chain

Authors: Ya-Min Quan, Shi-Qing Jia, Xiang-Long Yu, Hai-Qing Lin, Liang-Jian Zou

Abstract: Detecting Kitaev interactions in real materials remains challenge, as conventional experimental techniques often have difficulty distinguishing fractionalized excitations from other normal contributions. Terahertz two-dimensional coherent spectroscopy (2DCS) offers a novel approach for probing many-body phenomena, such as exotic excitations in quantum magnets. Motivated by recent experiments on Co… ▽ More Detecting Kitaev interactions in real materials remains challenge, as conventional experimental techniques often have difficulty distinguishing fractionalized excitations from other normal contributions. Terahertz two-dimensional coherent spectroscopy (2DCS) offers a novel approach for probing many-body phenomena, such as exotic excitations in quantum magnets. Motivated by recent experiments on CoNb$_2$O$_6$ and the development of the terahertz spectroscopy in Kitaev quantum spin liquid, we proposed a twisted Kitaev model for CoNb$_2$O$_6$ and determined the precise twist angle according to experimental specific-heat phase diagram. With this calibrated model, we found that non-rephasing diagonal and rephasing anti-diagonal signals appear in the 2DCS nonlinear response. The $x$ and $y$ components of the spin superexchange interactions split the rephasing signals into a grid of discrete peaks. We further demonstrate that the diagonal and the discrete rephasing signals primarily originate from two-spinon and four-spinon excitation processes based on numerical projection method. These findings indicate that even weak Kitaev interactions in quantum materials can be effectively detected via two-dimensional coherent spectroscopy . △ Less

Submitted 23 December, 2025; originally announced December 2025.

Evolution of correlated electronic states of La2NiO4 under hydrostatic pressure

Authors: Shu-Hong Tang, Han-Yu Wang, Da-Yong Liu, Feng Lu, Wei-Hua Wang, H. -Q. Lin, Liang-Jian Zou

Abstract: We elucidate the electronic structure and quantum many-body instabilities of the monolayer nickelate La2NiO4 under hydrostatic pressure using a combination of density functional theory, dynamical mean-field theory (DFT+DMFT), and random phase approximation (RPA). Our DFT+DMFT calculations reveal non-Fermi-liquid behavior and coherence loss near the Fermi level at low pressures, driven by strong el… ▽ More We elucidate the electronic structure and quantum many-body instabilities of the monolayer nickelate La2NiO4 under hydrostatic pressure using a combination of density functional theory, dynamical mean-field theory (DFT+DMFT), and random phase approximation (RPA). Our DFT+DMFT calculations reveal non-Fermi-liquid behavior and coherence loss near the Fermi level at low pressures, driven by strong electron correlations within the Ni-e_g orbital manifold, which is analogous to the low-energy electronic properties observed in La3Ni2O7. However, multi-orbital spin susceptibility analysis demonstrates an exceptionally suppressed critical Stoner parameter U_c (about 0.4~0.7 eV), indicating robust magnetic order that dominates the ground state and precludes superconductivity in the pristine system. Below U_c, superconducting instabilities exhibit a pressure-driven symmetry transition: the d_(x2-y2)-wave pairing prevails at ambient and low pressure, while the s+g-wave symmetry occurs above 75 GPa. This transition is attributed to pressure-induced self-doping effect. The high-angular-momentum g-wave component incurs significant energetic penalties, rendering high-Tc superconductivity unlikely. We conclude that the absence of superconductivity in La2NiO4 arises from its robust intrinsic magnetism and the unfavorable pairing symmetry under pressure, suggesting that alternative routes-such as chemical doping or epitaxial strain-are necessary to suppress magnetism and unlock superconducting states. △ Less

Submitted 19 November, 2025; originally announced November 2025.

Comments: 15 pages, 6 figures

Topological Valley Transport in Bilayer Graphene Induced by Interlayer Sliding

Authors: Jie Pan, Huanhuan Wang, Lin Zou, Xiaoyu Wang, Lihao Zhang, Xueyan Dong, Haibo Xie, Yi Ding, Yuze Zhang, Takashi Taniguchi, Kenji Watanabe, Shuxi Wang, Zhe Wang

Abstract: Interlayer sliding, together with twist angle, is a crucial parameter that defines the atomic registry and thus determines the properties of two-dimensional (2D) material homobilayers. Here, we theoretically demonstrate that controlled interlayer sliding in bilayer graphene induces Berry curvature reversals, leading to topological states confined within a one-dimensional moiré channel. We experime… ▽ More Interlayer sliding, together with twist angle, is a crucial parameter that defines the atomic registry and thus determines the properties of two-dimensional (2D) material homobilayers. Here, we theoretically demonstrate that controlled interlayer sliding in bilayer graphene induces Berry curvature reversals, leading to topological states confined within a one-dimensional moiré channel. We experimentally realize interlayer sliding by bending the bilayer graphene geometry across a nanoridge. Systematic electronic transport measurements reveal topological valley transport when the Fermi energy resides within the band gap, consistent with theoretical predictions of eight topological channels. Our findings establish interlayer sliding as a powerful tool for tuning the electronic properties of bilayer graphene and underscore its potential for broad application across 2D material systems. △ Less

Submitted 15 November, 2025; originally announced November 2025.

Comments: 19 pages

Journal ref: Phys. Rev. Lett. 135, 126603(2025)

Universal decay of (conditional) mutual information in gapped pure- and mixed-state quantum matter

Authors: Jinmin Yi, Kangle Li, Chuan Liu, Zixuan Li, Liujun Zou

Abstract: For spin and fermionic systems in any spatial dimension, we establish that the superpolynomial decay behavior of mutual information and conditional mutual information is a universal property of gapped pure- and mixed-state phases, i.e., all systems in such a phase possess this property if one system in this phase possesses this property. We further demonstrate that the (conditional) mutual informa… ▽ More For spin and fermionic systems in any spatial dimension, we establish that the superpolynomial decay behavior of mutual information and conditional mutual information is a universal property of gapped pure- and mixed-state phases, i.e., all systems in such a phase possess this property if one system in this phase possesses this property. We further demonstrate that the (conditional) mutual information indeed decays superpolynomially in a large class of phases, including chiral phases. As a byproduct, we sharpen the notion of mixed-state phases. △ Less

Submitted 4 November, 2025; v1 submitted 26 October, 2025; originally announced October 2025.

Comments: 7+17 pages, 3+3 figures

A ferroelectric junction transistor memory made from switchable van der Waals p-n heterojunctions

Authors: Baoyu Wang, Lingrui Zou, Tao Wang, Lijun Xu, Zexin Dong, Xin He, Shangui Lan, Yinchang Ma, Meng Tang, Maolin Chen, Chen Liu, Zhengdong Luo, Lijie Zhang, Zhenhua Wu, Yan Liu, Genquan Han, Bin Yu, Xixiang Zhang, Fei Xue, Kai Chang

Abstract: Van der Waals (vdW) p-n heterojunctions are important building blocks for advanced electronics and optoelectronics, in which high-quality heterojunctions essentially determine device performances or functionalities. Creating tunable depletion regions with substantially suppressed leakage currents presents huge challenges, but is crucial for heterojunction applications. Here, by using band-aligned… ▽ More Van der Waals (vdW) p-n heterojunctions are important building blocks for advanced electronics and optoelectronics, in which high-quality heterojunctions essentially determine device performances or functionalities. Creating tunable depletion regions with substantially suppressed leakage currents presents huge challenges, but is crucial for heterojunction applications. Here, by using band-aligned p-type SnSe and n-type ferroelectric α-In2Se3 as a model, we report near-ideal multifunctional vdW p-n heterojunctions with small reverse leakage currents (0.1 pA) and a desired diode ideality factor (1.95). We realize ferroelectric-tuned band alignment with a giant barrier modulation of 900 meV. Based on such tunable heterojunctions, we propose and demonstrate a fundamental different memory device termed ferroelectric junction field-effect transistor memory, which shows large memory windows (1.8 V), ultrafast speed (100 ns), high operation temperature (393 K), and low cycle-to-cycle variation (2 %). Additionally, the reliable synaptic characteristics of these memory devices promise low-power neuromorphic computing. Our work provides a new device platform with switchable memory heterojunctions, applicable to high performance brain-inspired electronics and optoelectronics. △ Less

Submitted 26 November, 2025; v1 submitted 12 October, 2025; originally announced October 2025.

Twisted locality-preserving automorphisms, anomaly index, and generalized Lieb-Schultz-Mattis theorems with anti-unitary symmetries

Authors: Ruizhi Liu, Jinmin Yi, Liujun Zou

Abstract: Symmetries and their anomalies are powerful tools to understand quantum matter. In this work, for quantum spin chains, we define twisted locality-preserving automorphisms and their Gross-Nesme-Vogts-Werner indices, which provide a unified framework to describe both unitary and anti-unitary symmetries, on-site and non-on-site symmetries, and internal and translation symmetries. For a symmetry $G$ w… ▽ More Symmetries and their anomalies are powerful tools to understand quantum matter. In this work, for quantum spin chains, we define twisted locality-preserving automorphisms and their Gross-Nesme-Vogts-Werner indices, which provide a unified framework to describe both unitary and anti-unitary symmetries, on-site and non-on-site symmetries, and internal and translation symmetries. For a symmetry $G$ with actions given by twisted locality-preserving automorphisms, we give a microscopic definition of its anomaly index, which is an element in $H^3_\varphi(G; U(1))$, where the subscript $\varphi$ means that anti-unitary elements of $G$ act on $U(1)$ by complex conjugation. We show that an anomalous symmetry leads to multiple Lieb-Schultz-Matttis-type theorems. In particular, any state with an anomalous symmetry must either have long-range correlation or violate the entanglement area law. Based on this theorem, we further deduce that any state with an anomalous symmetry must have long-range entanglement, and any Hamiltonian that has an anomalous symmetry cannot have a unique gapped symmetric ground state, as long as the interactions in the Hamiltonian decay fast enough as the range of the interaction increases. For Hamiltonians with only two-spin interactions, the last theorem holds if the interactions decay faster than $1/r^2$, where $r$ is the distance between the two interacting spins. We demonstrate these general theorems in various concrete examples. △ Less

Submitted 7 October, 2025; originally announced October 2025.

Comments: 24 pages + appendices + references

Non-Abelian Gauge Theory of Spin Triplet Superconductivity and Spin Triplet Magnon Spintronics

Authors: Franklin H. Cho, Y. M. Cho, Pengming Zhang, Li-Ping Zou

Abstract: We present an SU(2)xU(1) genralization of the Ginzburg-Landau theory for the spin triplet ferromagnetic superconductivity which could also describe the physics of the spin triplet magnon spintronics, where the SU(2) gauge interaction of the magnon plays an important role. The theory is made of the massive photon, massless neutral magnon, massive non-Abelian magnon, and the Higgs scalar field which… ▽ More We present an SU(2)xU(1) genralization of the Ginzburg-Landau theory for the spin triplet ferromagnetic superconductivity which could also describe the physics of the spin triplet magnon spintronics, where the SU(2) gauge interaction of the magnon plays an important role. The theory is made of the massive photon, massless neutral magnon, massive non-Abelian magnon, and the Higgs scalar field which represents the density of the Copper pair. It has the following characteristic features, the long range magnetic interaction mediated by the massless magnon, two types of conserved supercurrents (the ordinary charge current and the spin current of the magnons), and the non-Abelian Meissner effect generated by the spin current. Moreover, it has non-Abelian topological objects, the quantized non-Abelian magnonic vortex and non-Abelian magnonic monopole, as well as the ordinary Abrikosov vortex. The theory is characterized by three scales. In addition to the correlation length fixed by the mass of the Higgs field it has two different mass scales, the one fixed by the mass of the photon and the other fixed by the mass of the off-diagonal magnon. We compare the theory with the non-Abelian gauge theory of the spin doublet ferromagnetic superconductivity which could also be interpreted as an effective theory of the electron spintronics. We discuss the physical implications of the non-Abelian gauge theories in condensed matter physics. △ Less

Submitted 17 December, 2025; v1 submitted 16 September, 2025; originally announced September 2025.

Magnetic, charge and orbital properties of parent and Sr-doped La$_2$NiO$_4$ and its pressure evolutions

Authors: Han-Yu Wang, Shu-Hong Tang, Xiao-Teng Huang, Ya-Min Quan, XianLong Wang, Yan-Ling Li, Da-Yong Liu, H. -Q. Lin, Zhi Zeng, Liang-Jian Zou

Abstract: Recent discovery of unconventional superconductivity on multilayer nickelates under high pressure have stimulated great interest. The magnetic and charge configurations in the normal phase of multilayer nickelates which closely relate to the spin-charge fluctuations remain under strongly debated. In this work, we focus the normal-state magnetic, charge and orbital configurations and its evolutions… ▽ More Recent discovery of unconventional superconductivity on multilayer nickelates under high pressure have stimulated great interest. The magnetic and charge configurations in the normal phase of multilayer nickelates which closely relate to the spin-charge fluctuations remain under strongly debated. In this work, we focus the normal-state magnetic, charge and orbital configurations and its evolutions with hydrostatic pressure and Sr-doping concentration of monolayer nickelate La$_2$NiO$_4$. We reveal that in the ambient pressure tetragonal La2NiO4 displays Neel-type antiferromagnetic order in planer Ni spins with negligible interlayer magnetic coupling; with the increase of pressure, La2NiO4 evolves from insulate into metallic state with the critical pressure about P = 50 GPa; with the substitution of La by Sr, the magnetic ground state evolves from G-type, A-type, to double spin striped antiferromagnetic states, as well as weak charge and orbital orders, at x=1; These results can greatly promote our understanding of the magnetic properties of Ruddlesden-Popper nickelates, and shed the light of the pairing mechanism of unconventional nickelate superconductors. △ Less

Submitted 3 July, 2025; originally announced July 2025.

Comments: 7 pages, 4 figures

Structured Random Binding: a minimal model of protein-protein interactions

Authors: Ling-Nan Zou

Abstract: We describe Structured Random Binding (SRB), a minimal model of protein-protein interactions rooted in the statistical physics of disordered systems. In this model, nonspecific binding is a generic consequence of the interaction between random proteins, exhibiting a phase transition from a high temperature state where nonspecific complexes are transient and lack well-defined interaction interfaces… ▽ More We describe Structured Random Binding (SRB), a minimal model of protein-protein interactions rooted in the statistical physics of disordered systems. In this model, nonspecific binding is a generic consequence of the interaction between random proteins, exhibiting a phase transition from a high temperature state where nonspecific complexes are transient and lack well-defined interaction interfaces, to a low temperature state where the complex structure is frozen and a definite interaction interface is present. Numerically, weakly-bound nonspecific complexes can evolve into tightly-bound, highly specific complexes, but only if the structural correlation length along the peptide backbone is short; moreover, evolved tightly-bound homodimers favor the same interface structure that is predominant in real protein homodimers. △ Less

Submitted 26 March, 2025; originally announced March 2025.

Symmetry-enforced minimal entanglement and correlation in quantum spin chains

Authors: Kangle Li, Liujun Zou

Abstract: The interplay between symmetry, entanglement and correlation is an interesting and important topic in quantum many-body physics. Within the framework of matrix product states, in this paper we study the minimal entanglement and correlation enforced by the $SO(3)$ spin rotation symmetry and lattice translation symmetry in a quantum spin-$J$ chain, with $J$ a positive integer. When neither symmetry… ▽ More The interplay between symmetry, entanglement and correlation is an interesting and important topic in quantum many-body physics. Within the framework of matrix product states, in this paper we study the minimal entanglement and correlation enforced by the $SO(3)$ spin rotation symmetry and lattice translation symmetry in a quantum spin-$J$ chain, with $J$ a positive integer. When neither symmetry is spontaneously broken, for a sufficiently long segment in a sufficiently large closed chain, we find that the minimal Rényi-$α$ entropy compatible with these symmetries is $\min\{ -\frac{2}{α-1}\ln(\frac{1}{2^α}({1+\frac{1}{(2J+1)^{α-1}}})), 2\ln(J+1) \}$, for any $α\in\mathbb{R}^+$. In an infinitely long open chain with such symmetries, for any $α\in\mathbb{R}^+$ the minimal Rényi-$α$ entropy of half of the system is $\min\{ -\frac{1}{α-1}\ln(\frac{1}{2^α}({1+\frac{1}{(2J+1)^{α-1}}})), \ln(J+1) \}$. When $α\rightarrow 1$, these lower bounds give the symmetry-enforced minimal von Neumann entropies in these setups. Moreover, we show that no state in a quantum spin-$J$ chain with these symmetries can have a vanishing correlation length. Interestingly, the states with the minimal entanglement may not be a state with the minimal correlation length. △ Less

Submitted 18 July, 2025; v1 submitted 30 December, 2024; originally announced December 2024.

Comments: 17 pages + appendices + references

Journal ref: SciPost Phys. 19, 020 (2025)

Inducing Berry Curvature Dipole in Multilayer Graphene through Inhomogeneous Interlayer Sliding

Authors: Jie Pan, Huanhuan Wang, Lin Zou, Haibo Xie, Yi Ding, Yuze Zhang, Aiping Fang, Zhe Wang

Abstract: Breaking lattice symmetry is crucial for generating a nonzero Berry curvature. While manipulating twisting angles between adjacent layers has successfully broken lattice symmetry through strain field and generated nonzero Berry curvature, interlayer sliding in principle offers a promising alternative route. However, realizing uniform interlayer sliding faces experimental challenges due to its ener… ▽ More Breaking lattice symmetry is crucial for generating a nonzero Berry curvature. While manipulating twisting angles between adjacent layers has successfully broken lattice symmetry through strain field and generated nonzero Berry curvature, interlayer sliding in principle offers a promising alternative route. However, realizing uniform interlayer sliding faces experimental challenges due to its energetic instability. In this work, we introduce an experimentally feasible method, using a corrugated substrate to induce an inhomogeneous but energetically more stable interlayer sliding in multilayer graphene. Our simulations demonstrate that inhomogeneous interlayer sliding produces a sizable Berry curvature dipole, which can be further tuned by varying the interlayer sliding distances and potential differences. The resulting Berry curvature dipole magnitude is remarkably up to 100 times greater than the maximum displacement involved in the inhomogeneous sliding. Our results highlight inhomogeneous interlayer sliding as a viable and effective method to induce a significant Berry curvature dipole in graphene systems and propose the experimentally feasible way to realize it. △ Less

Submitted 17 December, 2024; originally announced December 2024.

Comments: 9 pages, 7 figures

Journal ref: Physical Review B, 110, 235418 (2024)

Persistent Homology for Structural Characterization in Disordered Systems

Authors: An Wang, Li Zou

Abstract: We propose a unified framework based on persistent homology (PH) to characterize both local and global structures in disordered systems. It can simultaneously generate local and global descriptors using the same algorithm and data structure, and has shown to be highly effective and interpretable in predicting particle rearrangements and classifying global phases. We also demonstrated that using a… ▽ More We propose a unified framework based on persistent homology (PH) to characterize both local and global structures in disordered systems. It can simultaneously generate local and global descriptors using the same algorithm and data structure, and has shown to be highly effective and interpretable in predicting particle rearrangements and classifying global phases. We also demonstrated that using a single variable enables a linear SVM to achieve nearly perfect three-phase classification. Inspired by this discovery, we define a non-parametric metric, the Separation Index (SI), which not only achieves this classification without sacrificing significant performance but also establishes a connection between particle environments and the global phase structure. Our methods provide an effective framework for understanding and analyzing the properties of disordered materials, with broad potential applications in materials science and even wider studies of complex systems. △ Less

Submitted 31 October, 2025; v1 submitted 21 November, 2024; originally announced November 2024.

Comments: 24 pages, 19 figures

MSC Class: 55N31; 62R40 ACM Class: I.3.5

Journal ref: Phys. Rev. E 111, 045306 (2025)

Entanglement area law and Lieb-Schultz-Mattis theorem in long-range interacting systems, and symmetry-enforced long-range entanglement

Authors: Ruizhi Liu, Jinmin Yi, Shiyu Zhou, Liujun Zou

Abstract: We establish multiple interrelated, fundamental results in quantum many-body systems that can have long-range interactions. For a sufficiently long quantum spin chain, we first show that if the multi-spin interactions in the Hamiltonian decay fast enough as their ranges increase and the Hamiltonian is gapped, then the ground states satisfy the entanglement area law, even if there is a ground state… ▽ More We establish multiple interrelated, fundamental results in quantum many-body systems that can have long-range interactions. For a sufficiently long quantum spin chain, we first show that if the multi-spin interactions in the Hamiltonian decay fast enough as their ranges increase and the Hamiltonian is gapped, then the ground states satisfy the entanglement area law, even if there is a ground state degeneracy due to a spontaneously broken discrete symmetry. This area law also holds for certain excited states. Second, if such a long-range interacting Hamiltonian has an anomalous symmetry, then the Lieb-Schultz-Mattis theorem applies, i.e., the Hamiltonian cannot have a unique gapped symmetric ground state. If the Hamiltonian contains only 2-spin interactions, these results hold when the interactions decay faster than $1/r^2$, with $r$ the distance between the two interacting spins. Third, we show that pure states with an anomalous symmetry, which may not be a ground state of any natural Hamiltonian, must be long-range entangled. The symmetries we consider include on-site internal symmetries combined with lattice translation symmetries, and they can also extend to purely internal but non-on-site symmetries. Moreover, these internal symmetries can be discrete or continuous. We explore the applications of these results through various examples. △ Less

Submitted 4 December, 2025; v1 submitted 23 May, 2024; originally announced May 2024.

Comments: This is a much improved version with significantly more results and deeper understanding. The paper contains a 10-page main text and various appendices

Journal ref: Phys. Rev. B 112, 214408 (2025)

Anomalous Phonon in Charge-Density-Wave Phase of Kagome Metal CsV3Sb5

Authors: Han-Yu Wang, Xiao-Cheng Bai, Wen-Feng Wu, Zhi Zeng, Da-Yong Liu, Liang-Jian Zou

Abstract: CsV3Sb5, a notable compound within the kagome family, is renowned for its topological and superconducting properties, as well as its detection of local magnetic field and anomalous Hall effect in experiments. However, the origin of this local magnetic field is still veiled. In this study, we employ the first-principles calculations to investigate the atomic vibration in both the pristine and the c… ▽ More CsV3Sb5, a notable compound within the kagome family, is renowned for its topological and superconducting properties, as well as its detection of local magnetic field and anomalous Hall effect in experiments. However, the origin of this local magnetic field is still veiled. In this study, we employ the first-principles calculations to investigate the atomic vibration in both the pristine and the charge-density-wave phases of CsV$_3$Sb$_5$. Our analysis reveals the presence of ``anomalous phonons" in these structures, these phonon induce the circular vibration of atoms, contributing to the phonon magnetic moments and subsequently to the observed the local magnetic fields. Additionally, we observe that lattice distortion in the charge-density-wave phase amplifies these circular vibrations, resulting in a stronger local magnetic field, particularly from the vanadium atoms. This investigation not only reveals the potential relation between lattice distortion and atomic polarization but also offers a novel idea to understand the origin of local magnetic moment in CsV3Sb5. △ Less

Submitted 28 April, 2024; originally announced April 2024.

Comments: 6 pages, 5 figures

Magnetism measurements of two-dimensional van der Waals antiferromagnet CrPS4 using dynamic cantilever magnetometry

Authors: Qi Li, Weili Zhen, Ning Wang, Meng Shi, Yang Yu, Senyang Pan, Lin Deng, Jiaqiang Cai, Kang Wang, Lvkuan Zou, Zhongming Zeng, Jinglei Zhang

Abstract: Recent experimental and theoretical work has focused on two-dimensional van der Waals (2D vdW) magnets due to their potential applications in sensing and spintronics devises. In measurements of these emerging materials, conventional magnetometry often encounters challenges in characterizing the magnetic properties of small-sized vdW materials, especially for antiferromagnets with nearly compensate… ▽ More Recent experimental and theoretical work has focused on two-dimensional van der Waals (2D vdW) magnets due to their potential applications in sensing and spintronics devises. In measurements of these emerging materials, conventional magnetometry often encounters challenges in characterizing the magnetic properties of small-sized vdW materials, especially for antiferromagnets with nearly compensated magnetic moments. Here, we investigate the magnetism of 2D antiferromagnet CrPS4 with a thickness of 8nm by using dynamic cantilever magnetometry (DCM). Through a combination of DCM experiment and the calculation based on a Stoner--Wohlfarth-type model, we unravel the magnetization states in 2D CrPS4 antiferromagnet. In the case of H parallel with c, a two-stage phase transition is observed. For H perpendicular to c, a hump in the effective magnetic restoring force is noted, which implies the presence of spin reorientation as temperature increases. These results demonstrate the benefits of DCM for studying magnetism of 2D magnets. △ Less

Submitted 12 October, 2024; v1 submitted 12 April, 2024; originally announced April 2024.

Pressure-tuning topological phase transitions in Kagome superconductor CsTi$_3$Bi$_5$

Authors: Wenfeng Wu, Xiaocheng Bai, Xianlong Wang, Dayong Liu, Zhi Zeng, Liangjian Zou

Abstract: Recently, the Kagome metal CsTi$_3$Bi$_5$ has exhibited several novel quantum properties similar to CsV$_3$Sb$_5$, such as nontrivial topology, double-dome superconductivity, and flat band features. However, CsTi$_3$Bi$_5$ lacks the charge-density wave (CDW) present in CsV$_3$Sb$_5$, making the study of its emergence of double-dome superconductivity a focus of research. In this work, we have ident… ▽ More Recently, the Kagome metal CsTi$_3$Bi$_5$ has exhibited several novel quantum properties similar to CsV$_3$Sb$_5$, such as nontrivial topology, double-dome superconductivity, and flat band features. However, CsTi$_3$Bi$_5$ lacks the charge-density wave (CDW) present in CsV$_3$Sb$_5$, making the study of its emergence of double-dome superconductivity a focus of research. In this work, we have identified an order parameter, the three-band Z$_2$ topological index, that can describe the superconducting phase diagram of CsTi$_3$Bi$_5$ under pressure. Its evolution with pressure follows the expected behavior for superconductivity. Furthermore, the results of the Fermi surface under pressure reveal the potential presence of a Lifshitz transition in the vicinity of the vanishing point of the superconducting temperature change with pressure in CsTi$_3$Bi$_5$. These results indicate that the superconducting behavior of CsTi$_3$Bi$_5$ under pressure is caused by changes in the electronic structure leading to alterations in the topological properties, provide new insights and approaches for understanding the superconducting phenomenon in Kagome metals. △ Less

Submitted 24 March, 2024; originally announced March 2024.

Metasurface spectrometers beyond resolution-sensitivity constraints

Authors: Feng Tang, Jingjun Wu, Tom Albrow-Owen, Hanxiao Cui, Fujia Chen, Yaqi Shi, Lan Zou, Jun Chen, Xuhan Guo, Yijun Sun, Jikui Luo, Bingfeng Ju, Jing Huang, Shuangli Liu, Bo Li, Liming Yang, Eric Anthony Munro, Wanguo Zheng, Hannah J. Joyce, Hongsheng Chen, Lufeng Che, Shurong Dong, Tawfique Hasan, Xin Ye, Yihao Yang , et al. (1 additional authors not shown)

Abstract: Optical spectroscopy plays an essential role across scientific research and industry for non-contact materials analysis1-3, increasingly through in-situ or portable platforms4-6. However, when considering low-light-level applications, conventional spectrometer designs necessitate a compromise between their resolution and sensitivity7,8, especially as device and detector dimensions are scaled down.… ▽ More Optical spectroscopy plays an essential role across scientific research and industry for non-contact materials analysis1-3, increasingly through in-situ or portable platforms4-6. However, when considering low-light-level applications, conventional spectrometer designs necessitate a compromise between their resolution and sensitivity7,8, especially as device and detector dimensions are scaled down. Here, we report on a miniaturizable spectrometer platform where light throughput onto the detector is instead enhanced as the resolution is increased. This planar, CMOS-compatible platform is based around metasurface encoders designed to exhibit photonic bound states in the continuum9, where operational range can be altered or extended simply through adjusting geometric parameters. This system can enhance photon collection efficiency by up to two orders of magnitude versus conventional designs; we demonstrate this sensitivity advantage through ultra-low-intensity fluorescent and astrophotonic spectroscopy. This work represents a step forward for the practical utility of spectrometers, affording a route to integrated, chip-based devices that maintain high resolution and SNR without requiring prohibitively long integration times. △ Less

Submitted 1 March, 2024; v1 submitted 29 February, 2024; originally announced February 2024.

Symmetries and anomalies of Kitaev spin-$S$ models: Identifying symmetry-enforced exotic quantum matter

Authors: Ruizhi Liu, Ho Tat Lam, Han Ma, Liujun Zou

Abstract: We analyze the internal symmetries and their anomalies in the Kitaev spin-$S$ models. Importantly, these models have a lattice version of a $\mathbb{Z}_2$ 1-form symmetry, denoted by $\mathbb{Z}_2^{[1]}$. There is also an ordinary 0-form $\mathbb{Z}_2^{(x)}\times\mathbb{Z}_2^{(y)}\times\mathbb{Z}_2^T$ symmetry, where $\mathbb{Z}_2^{(x)}\times\mathbb{Z}_2^{(y)}$ are $π$ spin rotations around two or… ▽ More We analyze the internal symmetries and their anomalies in the Kitaev spin-$S$ models. Importantly, these models have a lattice version of a $\mathbb{Z}_2$ 1-form symmetry, denoted by $\mathbb{Z}_2^{[1]}$. There is also an ordinary 0-form $\mathbb{Z}_2^{(x)}\times\mathbb{Z}_2^{(y)}\times\mathbb{Z}_2^T$ symmetry, where $\mathbb{Z}_2^{(x)}\times\mathbb{Z}_2^{(y)}$ are $π$ spin rotations around two orthogonal axes, and $\mathbb{Z}_2^T$ is the time reversal symmetry. The anomalies associated with the full $\mathbb{Z}_2^{(x)}\times\mathbb{Z}_2^{(y)}\times\mathbb{Z}_2^T\times\mathbb{Z}_2^{[1]}$ symmetry are classified by $\mathbb{Z}_2^{17}$. We find that for $S\in\mathbb{Z}$ the model is anomaly-free, while for $S\in\mathbb{Z}+\frac{1}{2}$ there is an anomaly purely associated with the 1-form symmetry, but there is no anomaly purely associated with the ordinary symmetry or mixed anomaly between the 0-form and 1-form symmetries. The consequences of these symmetries and anomalies apply to not only the Kitaev spin-$S$ models, but also any of their perturbed versions, assuming that the perturbations are local and respect the symmetries. If these local perturbations are weak, generically these consequences still apply even if the perturbations break the 1-form symmetry. A notable consequence is that there should generically be a deconfined fermionic excitation carrying no fractional quantum number under the $\mathbb{Z}_2^{(x)}\times\mathbb{Z}_2^{(y)}\times\mathbb{Z}_2^T$ symmetry if $S\in\mathbb{Z}+\frac{1}{2}$, which implies symmetry-enforced exotic quantum matter. We also discuss the consequences for $S\in\mathbb{Z}$. △ Less

Submitted 15 April, 2024; v1 submitted 25 October, 2023; originally announced October 2023.

Comments: published version

Report number: MIT-CTP/5638

Journal ref: SciPost Phys. 16, 100 (2024)

Classification of symmetry-enriched topological quantum spin liquids

Authors: Weicheng Ye, Liujun Zou

Abstract: We present a systematic framework to classify symmetry-enriched topological quantum spin liquids in two spatial dimensions. This framework can deal with all topological quantum spin liquids, which may be either Abelian or non-Abelian, chiral or non-chiral. It can systematically treat a general symmetry, which may include both lattice symmetry and internal symmetry, may contain anti-unitary symmetr… ▽ More We present a systematic framework to classify symmetry-enriched topological quantum spin liquids in two spatial dimensions. This framework can deal with all topological quantum spin liquids, which may be either Abelian or non-Abelian, chiral or non-chiral. It can systematically treat a general symmetry, which may include both lattice symmetry and internal symmetry, may contain anti-unitary symmetry, and may permute anyons. The framework applies to all types of lattices, and can systematically distinguish different lattice systems with the same symmetry group using their Lieb-Schultz-Mattis anomalies. We apply this framework to classify $U(1)_{2N}$ chiral states and non-Abelian Ising$^{(ν)}$ states enriched by a $p6\times SO(3)$ or $p4\times SO(3)$ symmetry, and $\mathbb{Z}_N$ topological orders and $U(1)_{2N}\times U(1)_{-2N}$ topological orders enriched by a $p6m\times SO(3)\times\mathbb{Z}_2^T$, $p4m\times SO(3)\times\mathbb{Z}_2^T$, $p6m\times\mathbb{Z}_2^T$ or $p4m\times\mathbb{Z}_2^T$ symmetry, where $p6$, $p4$, $p6m$ and $p4m$ are lattice symmetries, while $SO(3)$ and $\mathbb{Z}_2^T$ are spin rotation and time reversal symmetries, respectively. In particular, we identify symmetry-enriched topological quantum spin liquids that are not easily captured by the usual parton-mean-field approach, including examples with the familiar $\mathbb{Z}_2$ topological order. △ Less

Submitted 26 September, 2024; v1 submitted 26 September, 2023; originally announced September 2023.

Comments: Minor modification, nearly identical to the published version in PRX, Reference Fixed

Journal ref: Phys. Rev. X 14, 021053 (2024)

Electronic instability in pressured black phosphorus under strong magnetic field

Authors: Zhong-Yi Wang, Da-Yong Liu, Liang-Jian Zou

Abstract: In this paper we have systematically studied the electronic instability of pressured black phosphorous (BP) under strong magnetic field. We first present an effective model Hamiltonian for pressured BP near the Lifshitz point. We show that when the magnetic field exceeds a certain critical value, the nodal-line semimetal (NLSM) state of BP with a small band overlap re-enters semiconductive phase b… ▽ More In this paper we have systematically studied the electronic instability of pressured black phosphorous (BP) under strong magnetic field. We first present an effective model Hamiltonian for pressured BP near the Lifshitz point. We show that when the magnetic field exceeds a certain critical value, the nodal-line semimetal (NLSM) state of BP with a small band overlap re-enters semiconductive phase by re-opening a small gap. This results in a narrow-band semiconductor with a partially flat valence band edge. We show that above this critical magnetic field, two possible instabilities, i.e., charge density wave (CDW) phase or excitonic insulator (EI) phase, are predicted as the ground state for high and low doping concentrations, respectively. By comparing our results with the experiment, we suggest the field-induced instability observed in recent experiment as EI. Furthermore, we propose that the semimetallic BP under pressure with small band overlaps may provide a good platform to study the magneto-exciton insulators. Our findings bring the first insight into the electronic instability of topological NLSM in the quantum limit. △ Less

Submitted 14 May, 2023; originally announced May 2023.

Comments: 15 pages,6 figures

Possible high-temperature magnetically topological material Mn$_{3}$Bi$_{2}$Te$_{6}$

Authors: Wen-Feng Wu, Han-Yu Wang, Wei-Hua Wang, Da-Yong Liu, Xiang-Long Yu, Zhi Zeng, Liang-Jian Zou

Abstract: The Mn-Bi-Te family displaying magnetism and non-trivial topological properties has received extensive attention. Here, we predict that the antiferromagnetic structure of Mn$_{3}$Bi$_{2}$Te$_{6}$ with three MnTe layers is energetically stable and the magnetic coupling strength of Mn-Mn is enhanced four times compared with that in the single MnTe layer of MnBi$_{2}$Te$_{4}$. The predicted Néel tran… ▽ More The Mn-Bi-Te family displaying magnetism and non-trivial topological properties has received extensive attention. Here, we predict that the antiferromagnetic structure of Mn$_{3}$Bi$_{2}$Te$_{6}$ with three MnTe layers is energetically stable and the magnetic coupling strength of Mn-Mn is enhanced four times compared with that in the single MnTe layer of MnBi$_{2}$Te$_{4}$. The predicted Néel transition point is higher than 77 K, the liquid-nitrogen temperature. The topological properties show that with the variation of the MnTe layer from a single layer to three layers, the system transforms from a nontrivial topological phase to a trivial topological phase. Interestingly, the ferromagnetic state of Mn$_{3}$Bi$_{2}$Te$_{6}$ is a topological semimetal and it exhibits a topological transition from trivial to nontrivial induced by the magnetic transition. Our results enrich the Mn-Bi-Te family system, offer a new platform for studying topological phase transitions, and pave a new way to improve the working temperature of magnetically topological devices. △ Less

Submitted 8 April, 2023; originally announced April 2023.

Finite size effects on hinge states in three-dimensional second-order topological insulators

Authors: Penglei Wang, Yong-Lian Zou, Juntao Song

Abstract: We investigate the finite size effects of a three-dimensional second-order topological insulator with fourfold rotational symmetry and time-reversal symmetry. Starting from the effective Hamiltonian of the three-dimensional second-order topological insulator, we derive the effective Hamiltonian of four two-dimensional surface states with gaps derived by perturbative methods. Then, the sign alterna… ▽ More We investigate the finite size effects of a three-dimensional second-order topological insulator with fourfold rotational symmetry and time-reversal symmetry. Starting from the effective Hamiltonian of the three-dimensional second-order topological insulator, we derive the effective Hamiltonian of four two-dimensional surface states with gaps derived by perturbative methods. Then, the sign alternation of the mass term of the effective Hamiltonian on the adjacent surface leads to the hinge state. In addition, we obtain the effective Hamiltonian and its wave function of one-dimensional gapless hinge states with semi-infinite boundary conditions based on the effective Hamiltonian of two-dimensional surface states. In particular, we find that the hinge states on the two sides of the same surface can couple to produce a finite energy gap. △ Less

Submitted 24 December, 2022; originally announced December 2022.

Topological magnons in one-dimensional ferromagnetic Su-Schrieffer-Heeger model with anisotropic interaction

Authors: Peng-Tao Wei, Jin-Yu Ni, Xia-Ming Zheng, Da-Yong Liu, Liang-Jian Zou

Abstract: Topological magnons in a one-dimensional (1D) ferromagnetic (FM) Su-Schrieffer-Heeger (SSH) model with anisotropic exchange interactions are investigated. Apart from the inter-cellular isotropic Heisenberg interaction, the intercellular anisotropic exchange interactions, i.e. Dzyaloshinskii-Moriya interaction (DMI) and pseudo-dipolar interaction (PDI), also can induce the emergence of the non-triv… ▽ More Topological magnons in a one-dimensional (1D) ferromagnetic (FM) Su-Schrieffer-Heeger (SSH) model with anisotropic exchange interactions are investigated. Apart from the inter-cellular isotropic Heisenberg interaction, the intercellular anisotropic exchange interactions, i.e. Dzyaloshinskii-Moriya interaction (DMI) and pseudo-dipolar interaction (PDI), also can induce the emergence of the non-trivial phase with two degenerate in-gap edge states separately localized at the two ends of the 1D chain, while the intracellular interactions instead unfavors the topological phase. The interplay among them has synergistic effects on the topological phase transition, very different from that in the two-dimensional (2D) ferromagnet. These results demonstrate that the 1D magnons possess rich topological phase diagrams distinctly different from the electronic version of the SSH model and even the 2D magnons. Due to the lower dimensional structural characteristics of this 1D topological magnonic system, the magnonic crystals can be constructed from bottom to top, which has important potential applications in the design of novel magnonic devices. △ Less

Submitted 27 October, 2022; originally announced October 2022.

Comments: 22 pages, 11 figures

Journal ref: J. Phys.: Condens. Matter 34, 495801 (2022)

Anomaly of $(2+1)$-Dimensional Symmetry-Enriched Topological Order from $(3+1)$-Dimensional Topological Quantum Field Theory

Authors: Weicheng Ye, Liujun Zou

Abstract: Symmetry acting on a (2+1)$D$ topological order can be anomalous in the sense that they possess an obstruction to being realized as a purely (2+1)$D$ on-site symmetry. In this paper, we develop a (3+1)$D$ topological quantum field theory to calculate the anomaly indicators of a (2+1)$D$ topological order with a general symmetry group $G$, which may be discrete or continuous, Abelian or non-Abelian… ▽ More Symmetry acting on a (2+1)$D$ topological order can be anomalous in the sense that they possess an obstruction to being realized as a purely (2+1)$D$ on-site symmetry. In this paper, we develop a (3+1)$D$ topological quantum field theory to calculate the anomaly indicators of a (2+1)$D$ topological order with a general symmetry group $G$, which may be discrete or continuous, Abelian or non-Abelian, contain anti-unitary elements or not, and permute anyons or not. These anomaly indicators are partition functions of the (3+1)$D$ topological quantum field theory on a specific manifold equipped with some $G$-bundle, and they are expressed using the data characterizing the topological order and the symmetry actions. Our framework is applied to derive the anomaly indicators for various symmetry groups, including $\mathbb{Z}_2\times\mathbb{Z}_2$, $\mathbb{Z}_2^T\times\mathbb{Z}_2^T$, $SO(N)$, $O(N)^T$, $SO(N)\times \mathbb{Z}_2^T$, etc, where $\mathbb{Z}_2$ and $\mathbb{Z}_2^T$ denote a unitary and anti-unitary order-2 group, respectively, and $O(N)^T$ denotes a symmetry group $O(N)$ such that elements in $O(N)$ with determinant $-1$ are anti-unitary. In particular, we demonstrate that some anomaly of $O(N)^T$ and $SO(N)\times \mathbb{Z}_2^T$ exhibit symmetry-enforced gaplessness, i.e., they cannot be realized by any symmetry-enriched topological order. As a byproduct, for $SO(N)$ symmetric topological orders, we derive their $SO(N)$ Hall conductance. △ Less

Submitted 30 May, 2023; v1 submitted 5 October, 2022; originally announced October 2022.

Comments: Recipe of calculating the partition function involving continuous symmetries added, together with extra examples

Journal ref: SciPost Phys. 15, 004 (2023)

Entanglement-enabled symmetry-breaking orders

Authors: Cheng-Ju Lin, Liujun Zou

Abstract: A spontaneous symmetry-breaking order is conventionally described by a tensor-product wave-function of some few-body clusters. We discuss a type of symmetry-breaking orders, dubbed entanglement-enabled symmetry-breaking orders, which cannot be realized by any tensor-product state. Given a symmetry breaking pattern, we propose a criterion to diagnose if the symmetry-breaking order is entanglement-e… ▽ More A spontaneous symmetry-breaking order is conventionally described by a tensor-product wave-function of some few-body clusters. We discuss a type of symmetry-breaking orders, dubbed entanglement-enabled symmetry-breaking orders, which cannot be realized by any tensor-product state. Given a symmetry breaking pattern, we propose a criterion to diagnose if the symmetry-breaking order is entanglement-enabled, by examining the compatibility between the symmetries and the tensor-product description. For concreteness, we present an infinite family of exactly solvable gapped models on one-dimensional lattices with nearest-neighbor interactions, whose ground states exhibit entanglement-enabled symmetry-breaking orders from a discrete symmetry breaking. In addition, these ground states have gapless edge modes protected by the unbroken symmetries. We also propose a construction to realize entanglement-enabled symmetry-breaking orders with spontaneously broken continuous symmetries. Under the unbroken symmetries, some of our examples can be viewed as symmetry-protected topological states that are beyond the conventional classifications. △ Less

Submitted 23 March, 2024; v1 submitted 18 July, 2022; originally announced July 2022.

Comments: Published version

Journal ref: SciPost Phys. Core 7, 010 (2024)

Renormalization-group Perspective on Gravitational Critical Collapse

Authors: Huan Yang, Liujun Zou

Abstract: In this work, we propose extremal black holes (BH) as critical points of a new class of gravitational collapses. The conjecture is made by observing the Continuous Self Similarity (CSS) and Discrete Self Similarity (DSS) behaviours of perturbations of an extremal black hole spacetime and compare them to similar properties of Choptuik-type critical solutions. By performing analytical perturbation s… ▽ More In this work, we propose extremal black holes (BH) as critical points of a new class of gravitational collapses. The conjecture is made by observing the Continuous Self Similarity (CSS) and Discrete Self Similarity (DSS) behaviours of perturbations of an extremal black hole spacetime and compare them to similar properties of Choptuik-type critical solutions. By performing analytical perturbation studies on extremal black holes, we explicitly show that the DSS solution found here can be interpreted as renormalization group (RG) limit cycles, and the transition between CSS and DSS regimes occurs as the stable and unstable fixed points collide and move to the complex plane. We argue that the DSS solutions found in spherically symmetric gravitational collapses can be similarly interpreted. We identify various phenomena in non-gravitational systems with RG limit cycles, including DSS correlation function, DSS scaling laws in correlation length and order parameters, which are observed in gravitational critical collapses. We also discuss a version of gravitational Efimov effect. △ Less

Submitted 18 May, 2024; v1 submitted 9 July, 2022; originally announced July 2022.

Comments: 10 pages, 1 figure

Journal ref: Phys. Rev. D 109, 104034 (2024)

Designing wake-up free ferroelectric capacitors based on the $\mathrm{HfO_2/ZrO_2}$ superlattice structure

Authors: Na Bai, Kan-Hao Xue, Jinhai Huang, Jun-Hui Yuan, Wenlin Wang, Ge-Qi Mao, Lanqing Zou, Shengxin Yang, Hong Lu, Huajun Sun, Xiangshui Miao

Abstract: The wake-up phenomenon widely exists in hafnia-based ferroelectric capacitors, which causes device parameter variation over time. Crystallization at higher temperatures have been reported to be effective in eliminating wake-up, but high temperature may yield the monoclinic phase or generate high concentration oxygen vacancies. In this work, a unidirectional annealing method is proposed for the cry… ▽ More The wake-up phenomenon widely exists in hafnia-based ferroelectric capacitors, which causes device parameter variation over time. Crystallization at higher temperatures have been reported to be effective in eliminating wake-up, but high temperature may yield the monoclinic phase or generate high concentration oxygen vacancies. In this work, a unidirectional annealing method is proposed for the crystallization of $\mathrm{Hf_{0.5}Zr_{0.5}O_2}$ (HZO) superlattice ferroelectrics, which involves heating from the $\mathrm{Pt/ZrO_2}$ interface side. Nanoscale $\mathrm{ZrO_2}$ is selected to resist the formation of monoclinic phase, and the chemically inert Pt electrode can avoid the continuous generation of oxygen vacancies during annealing. It is demonstrated that $\mathrm{600^oC}$ annealing only leads to a moderate content of monoclinic phase in HZO, and the TiN/HZO/Pt capacitor exhibits wake-up free nature and a $2P_\mathrm{r}$ value of 27.4 $μ\mathrm{C/cm^2}$. On the other hand, heating from the $\mathrm{TiN/HfO_2}$ side, or using $\mathrm{500^oC}$ annealing temperature, both yield ferroelectric devices that require a wake-up process. The special configuration of $\mathrm{Pt/ZrO_2}$ is verified by comparative studies with several other superlattice structures and HZO solid-state solutions. It is discovered that heating from the $\mathrm{Pt/HfO_2}$ side at $\mathrm{600^oC}$ leads to high leakage current and a memristor behavior. The mechanisms of ferroelectric phase stabilization and memristor formation have been discussed. The unidirectional heating method can also be useful for other hafnia-based ferroelectric devices. △ Less

Submitted 29 June, 2022; originally announced June 2022.

Comments: 16 pages, 7 figures

Journal ref: Advanced Electronic Materials 9, 2200737 (2023)

Ferromagnetism in layered metallic Fe1/4TaS2 in the presence of conventional and Dirac carriers

Authors: Jin-Hua Wang, Ya-Min Quan, Da-Yong Liu, Liang-Jian Zou

Abstract: In this paper we present the microscopic origin of the ferromagnetism of Fe0.25TaS2 and its finite-temperature magnetic properties. We first obtain the band structures of Fe0.25TaS2 by the first-principles calculations and find that both conventional and Dirac carriers coexist in metallic Fe0.25TaS2. Accordingly, considering the spin-orbit coupling of Fe 3d ion, we derive an effective RKKY-type Ha… ▽ More In this paper we present the microscopic origin of the ferromagnetism of Fe0.25TaS2 and its finite-temperature magnetic properties. We first obtain the band structures of Fe0.25TaS2 by the first-principles calculations and find that both conventional and Dirac carriers coexist in metallic Fe0.25TaS2. Accordingly, considering the spin-orbit coupling of Fe 3d ion, we derive an effective RKKY-type Hamiltonian between Fe spins in the presence of both the conventional parabolic-dispersion and the Dirac linear-dispersion carriers, which contains a Heisenberg-like, an Ising-like and an XY-like term. In addition, we obtain the ferromagnetic Curie temperature Tc by using the cluster self-consistent field method. Our results could address not only the high ferromagnetic Curie temperature, but also the large magnetic anisotropy in FexTaS2. △ Less

Submitted 8 March, 2022; originally announced March 2022.

Comments: 13 pages, 4 figures

Journal ref: Chinese Physics Letters 37, 017101 (2020)

Effective minimal model and unconventional spin-singlet pairing in Kagome superconductor CsV3Sb5

Authors: Xiao-Cheng Bai, Wen-Feng Wu, Han-Yu Wang, Ya-Min Quan, Xian-Long Wang, Zhi Zeng, Liang-Jian Zou

Abstract: Recently synthesized Kagome compounds AV$_3$Sb$_5$ attract great attention due to the unusual coexistence of the topology, charge density wave and superconductivity. In this {\it Letter}, based on the band structures for CsV$_3$Sb$_5$ in pristine phase, we fit an effective 6-band model for the low-energy processes; utilizing the random phase approximation (RPA) on the effective minimal model, we o… ▽ More Recently synthesized Kagome compounds AV$_3$Sb$_5$ attract great attention due to the unusual coexistence of the topology, charge density wave and superconductivity. In this {\it Letter}, based on the band structures for CsV$_3$Sb$_5$ in pristine phase, we fit an effective 6-band model for the low-energy processes; utilizing the random phase approximation (RPA) on the effective minimal model, we obtain the momentum-resolved static spin susceptibility attributing the spin-fluctuation pairing mechanism, we find that the superconducting pairing strengths increase with the lift of the Coulomb correlation, and the superconductive pairing symmetry is singlet, the gap functions are antisymmetric with respect to the x-axis and the y-axis in the intermediate to strong Coulomb correlated regime,indicating the unconventional superconductivity in Kagome compounds AV$_3$Sb$_5$. △ Less

Submitted 15 February, 2022; v1 submitted 24 January, 2022; originally announced January 2022.

Comments: 6 pages, 6 figures

Transport in the emergent Bose liquid: Bad metal, strange metal, and weak insulator, all in one system

Authors: Tao Zeng, Anthony Hegg, Long Zou, Shengtao Jiang, Wei Ku

Abstract: Non-saturating high-temperature resistivity ("bad metal"), T-linear low-temperature resistivity ("strange metal"), and a crossover to activation-free growth of the resistivity in the low-temperature limit ("weak insulator") are among the most exotic behaviors widely observed in many strongly correlated materials for decades that defy the standard Fermi liquid description of solids. Here we investi… ▽ More Non-saturating high-temperature resistivity ("bad metal"), T-linear low-temperature resistivity ("strange metal"), and a crossover to activation-free growth of the resistivity in the low-temperature limit ("weak insulator") are among the most exotic behaviors widely observed in many strongly correlated materials for decades that defy the standard Fermi liquid description of solids. Here we investigate these puzzling behaviors by computing temperature-dependent optical conductivity of an emergent Bose liquid and find that it reproduces all the unexplained features of the experiments, including a featureless continuum and a well-known mid-infrared peak. Amazingly and with physically intuitive mechanisms, the corresponding doping- and temperature-dependent resistivity displays the bad metal and strange metal simultaneously and sometimes weak insulating behaviors as well. The unification of all these non-Fermi liquid behaviors in a single model suggests that a new quantum state of matter, namely the emergent Bose liquid, will guide the development of the next generation of solid state physics. △ Less

Submitted 10 December, 2021; originally announced December 2021.

Topological characterization of Lieb-Schultz-Mattis constraints and applications to symmetry-enriched quantum criticality

Authors: Weicheng Ye, Meng Guo, Yin-Chen He, Chong Wang, Liujun Zou

Abstract: Lieb-Schultz-Mattis (LSM) theorems provide powerful constraints on the emergibility problem, i.e. whether a quantum phase or phase transition can emerge in a many-body system. We derive the topological partition functions that characterize the LSM constraints in spin systems with $G_s\times G_{int}$ symmetry, where $G_s$ is an arbitrary space group in one or two spatial dimensions, and $G_{int}$ i… ▽ More Lieb-Schultz-Mattis (LSM) theorems provide powerful constraints on the emergibility problem, i.e. whether a quantum phase or phase transition can emerge in a many-body system. We derive the topological partition functions that characterize the LSM constraints in spin systems with $G_s\times G_{int}$ symmetry, where $G_s$ is an arbitrary space group in one or two spatial dimensions, and $G_{int}$ is any internal symmetry whose projective representations are classified by $\mathbb{Z}_2^k$ with $k$ an integer. We then apply these results to study the emergibility of a class of exotic quantum critical states, including the well-known deconfined quantum critical point (DQCP), $U(1)$ Dirac spin liquid (DSL), and the recently proposed non-Lagrangian Stiefel liquid. These states can emerge as a consequence of the competition between a magnetic state and a non-magnetic state. We identify all possible realizations of these states on systems with $SO(3)\times \mathbb{Z}_2^T$ internal symmetry and either $p6m$ or $p4m$ lattice symmetry. Many interesting examples are discovered, including a DQCP adjacent to a ferromagnet, stable DSLs on square and honeycomb lattices, and a class of quantum critical spin-quadrupolar liquids of which the most relevant spinful fluctuations carry spin-$2$. In particular, there is a realization of spin-quadrupolar DSL that is beyond the usual parton construction. We further use our formalism to analyze the stability of these states under symmetry-breaking perturbations, such as spin-orbit coupling. As a concrete example, we find that a DSL can be stable in a recently proposed candidate material, NaYbO$_2$. △ Less

Submitted 4 October, 2022; v1 submitted 23 November, 2021; originally announced November 2021.

Comments: 23 pages of main text + appendices + ancillary files

Journal ref: SciPost Phys. 13, 066 (2022)

Edge physics at the deconfined transition between a quantum spin Hall insulator and a superconductor

Authors: Ruochen Ma, Liujun Zou, Chong Wang

Abstract: We study the edge physics of the deconfined quantum phase transition (DQCP) between a spontaneous quantum spin Hall (QSH) insulator and a spin-singlet superconductor (SC). Although the bulk of this transition is in the same universality class as the paradigmatic deconfined Neel to valence-bond-solid transition, the boundary physics has a richer structure due to proximity to a quantum spin Hall sta… ▽ More We study the edge physics of the deconfined quantum phase transition (DQCP) between a spontaneous quantum spin Hall (QSH) insulator and a spin-singlet superconductor (SC). Although the bulk of this transition is in the same universality class as the paradigmatic deconfined Neel to valence-bond-solid transition, the boundary physics has a richer structure due to proximity to a quantum spin Hall state. We use the parton trick to write down an effective field theory for the QSH-SC transition in the presence of a boundary. We calculate various edge properties in an $N\to\infty$ limit. We show that the boundary Luttinger liquid in the QSH state survives at the phase transition, but only as "fractional" degrees of freedom that carry charge but not spin. The physical fermion remains gapless on the edge at the critical point, with a universal jump in the fermion scaling dimension as the system approaches the transition from the QSH side. The critical point could be viewed as a gapless analogue of the quantum spin Hall state but with the full $SU(2)$ spin rotation symmetry, which cannot be realized if the bulk is gapped. △ Less

Submitted 16 June, 2022; v1 submitted 15 October, 2021; originally announced October 2021.

Comments: 9 pages + references

Journal ref: SciPost Phys. 12, 196 (2022)

Band crossover and magnetic phase diagram of high-Tc superconducting compound Ba2CuO4-δ

Authors: Xiao-Cheng Bai, Ya-Min Quan, H. Q. Lin, Liang-Jian Zou

Abstract: We present the influences of electronic and magnetic correlations and doping evolution on the groundstate properties of recently discovered superconductor Ba$_{2}$CuO$_{4-δ}$ by utilizing the Kotliar-Ruckenstein slave boson method. Starting with an effective two-orbital Hubbard model (Scalapino {\it et al.} Phys. Rev. {\bf B 99}, 224515 (2019)), we demonstrate that with increasing doping concentra… ▽ More We present the influences of electronic and magnetic correlations and doping evolution on the groundstate properties of recently discovered superconductor Ba$_{2}$CuO$_{4-δ}$ by utilizing the Kotliar-Ruckenstein slave boson method. Starting with an effective two-orbital Hubbard model (Scalapino {\it et al.} Phys. Rev. {\bf B 99}, 224515 (2019)), we demonstrate that with increasing doping concentration, the paramagnetic (PM) system evolves from two-band character to single-band ones around the electron filling n=2.5, with the band nature of the $d_{3z^{2}-r^{2}}$ and $d_{x^{2}-y^{2}}$ orbitals to the $d_{x^{2}-y^{2}}$ orbital, slightly affected when the electronic correlation U varies from 2 to 4 eV. Considering the magnetic correlations, the system displays one antiferromagnetically metallic (AFM) phase in $2<n<2.16$ and a PM phase in $n>2.16$ at U=2 eV, or two AFM phases in $2<n<2.57$ and $2.76<n<3$, and a PM phase in $2.57<n<2.76$ respectively, at U=4 eV. Our results show that near realistic superconducting state around n=2.6 the intermediate correlated Ba$_{2}$CuO$_{3,2}$ should be single band character, and the s-wave superconducting pairing strength becomes significant when U$>$2 eV, and crosses over to d-wave when U$>$2.2 eV. △ Less

Submitted 7 September, 2021; originally announced September 2021.

Comments: 9 pages, 10 figures

Ultraviolet-Infrared Mixing in Marginal Fermi Liquids

Authors: Weicheng Ye, Sung-Sik Lee, Liujun Zou

Abstract: When Fermi surfaces (FSs) are subject to long-range interactions that are marginal in the renormalization-group sense, Landau Fermi liquids are destroyed, but only barely. With the interaction further screened by particle-hole excitations through one-loop quantum corrections, it has been believed that these marginal Fermi liquids (MFLs) are described by weakly coupled field theories at low energie… ▽ More When Fermi surfaces (FSs) are subject to long-range interactions that are marginal in the renormalization-group sense, Landau Fermi liquids are destroyed, but only barely. With the interaction further screened by particle-hole excitations through one-loop quantum corrections, it has been believed that these marginal Fermi liquids (MFLs) are described by weakly coupled field theories at low energies. In this Letter, we point out a possibility in which higher-loop processes qualitatively change the picture through UV-IR mixing, in which the size of the FS enters as a relevant scale. The UV-IR mixing effect enhances the coupling at low energies, such that the basin of attraction for the weakly coupled fixed point of a $(2+1)$-dimensional MFL shrinks to a measure-zero set in the low-energy limit. This UV-IR mixing is caused by gapless virtual Cooper pairs that spread over the entire FS through marginal long-range interactions. Our finding signals a possible breakdown of the patch description for the MFL and questions the validity of using the MFL as the base theory in a controlled scheme for non-Fermi liquids that arise from relevant long-range interactions. △ Less

Submitted 15 March, 2022; v1 submitted 31 August, 2021; originally announced September 2021.

Comments: 4.5 pages + references + supplemental material

Journal ref: Phys. Rev. Lett. 128, 106402 (2022)

Orbital driven two-dome superconducting phases in multiorbital superconductors

Authors: Jing Liu, Qing-Wei Wang, Liang-Jian Zou

Abstract: We theoretically study the superconductivity in multiorbital superconductors based on a three-orbital tight-banding model. With appropriate values of the nearest-neighbour exchange $J_{1}^{αβ}$ and the next-nearest-neighbour exchange $J_{2}^{αβ}$, we find a two-dome structure in the $T_{c}-n$ phase diagram: one dome in the doping range $n<3.9$ where the superconducting (SC) state is mainly… ▽ More We theoretically study the superconductivity in multiorbital superconductors based on a three-orbital tight-banding model. With appropriate values of the nearest-neighbour exchange $J_{1}^{αβ}$ and the next-nearest-neighbour exchange $J_{2}^{αβ}$, we find a two-dome structure in the $T_{c}-n$ phase diagram: one dome in the doping range $n<3.9$ where the superconducting (SC) state is mainly $s_{x^{2} y^{2}}$ component contributed by inter-orbital pairing, the other dome in the doping range $3.9<n<4.46$ where the SC state is mainly $s_{x^{2} y^{2}}+s_{x^{2}+y^{2}}$ components contributed by intra-orbital pairing. We find that the competition between different orbital pairing leads to two-dome SC phase diagrams in multiorbital superconductors, and different matrix elements of $J_{1}$ and $J_{2}$ considerably affect the boundary of two SC domes. △ Less

Submitted 26 April, 2021; originally announced April 2021.

Comments: 16 pages, 6 figures

Journal ref: Physics Letters A391 (2021) 127118

Topological quantum phase transitions of anisotropic AFM Kitaev model driven by magnetic field

Authors: Shi-Qing Jia, Ya-Min Quan, Hai-Qing Lin, Liang-Jian Zou

Abstract: We investigate the quantum spin liquid (QSL) ground state of anisotropic Kitaev model with antiferromagnetic (AFM) coupling under the $[001]$ magnetic field with the finite-temperature Lanczos method (FTLM). In this anisotropic AFM Kitaev model with $K_{X}=K_{Y}$, $K_{X}+K_{Y}+K_{Z}=-3K$, and $K_{Z}<-K$, with magnetic field increasing, the gapped QSL experiences a transition to a gapless QSL at… ▽ More We investigate the quantum spin liquid (QSL) ground state of anisotropic Kitaev model with antiferromagnetic (AFM) coupling under the $[001]$ magnetic field with the finite-temperature Lanczos method (FTLM). In this anisotropic AFM Kitaev model with $K_{X}=K_{Y}$, $K_{X}+K_{Y}+K_{Z}=-3K$, and $K_{Z}<-K$, with magnetic field increasing, the gapped QSL experiences a transition to a gapless QSL at $h_{c1}=gμ_{B}H_{z1}/K$, to another gapless QSL with $C_{6}$ rotational symmetry at $h_{c2}$, and to a new $U(1)$ gapless QSL between $h_{c3}$ and $h_{c4}$, respectively. These indicate that magnetic field could first turn the anisotropic gapped or gapless QSL back into the isotropic $C_{6}$ gapless one and then make it to undergo the similar evolution as the isotropic case. Moreover, the critical magnetic fields $h_{c1}$, $h_{c2}$, $h_{c3}$, and $h_{c4}$ come up monotonically with the increasing Kitaev coupling; this suggests that the magnetic field can be applied to the modulation of the anisotropic Kitaev materials. △ Less

Submitted 31 October, 2021; v1 submitted 26 April, 2021; originally announced April 2021.

Comments: 10 pages, 11 figures, add figures of the variation of Chern number with magnetic field

Reaction-diffusion dynamics in a Fibonacci chain: Interplay between classical and quantum behavior

Authors: Cheng-Ju Lin, Liujun Zou

Abstract: We study the reaction-diffusion dynamics of Fibonacci anyons in a one dimensional lattice. Due to their non-Abelian nature, besides the position degree of freedom (DOF), these anyons also have a nonlocal internal DOF, which can be characterized by a fusion tree. We first consider a pure-reaction dynamics associated with the internal DOF, which is of intrinsically quantum origin, with either an "al… ▽ More We study the reaction-diffusion dynamics of Fibonacci anyons in a one dimensional lattice. Due to their non-Abelian nature, besides the position degree of freedom (DOF), these anyons also have a nonlocal internal DOF, which can be characterized by a fusion tree. We first consider a pure-reaction dynamics associated with the internal DOF, which is of intrinsically quantum origin, with either an "all-$τ$" or "completely random" initial fusion tree. These two fusion trees are unstable and likely stable steady states for the internal DOF, respectively. We obtain the decay rate of the anyon number for these two cases exactly. Still using these two initial fusion trees, we study the full reaction-diffusion dynamics, and find an interesting interplay between classical and quantum behaviors: These two fusion trees are still respectively unstable and likely stable steady states of the internal DOF, while the dynamics of the position DOF can be mapped to a hybrid classical $A+A\rightarrow 0$ and $A+A\rightarrow A$ reaction-diffuson dynamics, with the relative reaction rates of these two classical dynamics determined by the state of the nonlocal internal DOF. In particular, the anyon density at late times are given by $ρ(t)=\frac{c}{\sqrt{8π}}(Dt)^{-Δ}$, where $D$ is a non-universal diffusion constant, $Δ=1/2$ is superuniversal, and $c$ is universal and can be obtained exactly in terms of the fusion tree structure. Specifically, $c=\frac{2\varphi}{\varphi+1}$ and $c=\frac{2(4\varphi+3)}{5(\varphi+1)}$ for the all-$τ$ and completely random configuration respectively, where $\varphi=\frac{\sqrt{5}+1}{2}$ is the golden ratio. We also study the two-point correlation functions. △ Less

Submitted 20 May, 2021; v1 submitted 25 March, 2021; originally announced March 2021.

Comments: A table of contents is provided

Journal ref: Phys. Rev. B 103, 174305 (2021)

Electron Tunneling Spectroscopy of the Anisotropic Kitaev Quantum Spin Liquid Sandwiched with Superconductors

Authors: Shi-Qing Jia, Ya-Min Quan, Hai-Qing Lin, Liang-Jian Zou

Abstract: We present the electron tunneling transport and spectroscopic characters of a superconducting {\it Josephson} junction with a barrier of single anisotropic Kitaev quantum spin liquid (QSL) layer. We find that the dynamical spin correlation features are well reflected in the direct-current differential conductance $dI^{c}/dV$ of the single-particle tunneling, including the unique spin gap and dress… ▽ More We present the electron tunneling transport and spectroscopic characters of a superconducting {\it Josephson} junction with a barrier of single anisotropic Kitaev quantum spin liquid (QSL) layer. We find that the dynamical spin correlation features are well reflected in the direct-current differential conductance $dI^{c}/dV$ of the single-particle tunneling, including the unique spin gap and dressed itinerant Majorana dispersive band, in addition to an energy shift $2Δ$ of two-lead superconducting gaps. From the spectral characters, we identify different topological quantum phases of the anisotropic Kitaev QSL. We also present the zero-voltage {\it Josephson} current $I^{s}$ which displays residual features of the anisotropic Kitaev QSL. These results pave a new way to measure the dynamical spinon or Majorana fermion spectroscopy of the Kitaev and other spin liquid materials. △ Less

Submitted 8 March, 2022; v1 submitted 1 March, 2021; originally announced March 2021.

Comments: 10 pages, 7 figures

Stiefel Liquids: Possible Non-Lagrangian Quantum Criticality from Intertwined Orders

Authors: Liujun Zou, Yin-Chen He, Chong Wang

Abstract: We propose a new type of quantum liquids, dubbed Stiefel liquids, based on $2+1$ dimensional nonlinear sigma models on target space $SO(N)/SO(4)$, supplemented with Wess-Zumino-Witten terms. We argue that the Stiefel liquids form a class of critical quantum liquids with extraordinary properties, such as large emergent symmetries, a cascade structure, and nontrivial quantum anomalies. We show that… ▽ More We propose a new type of quantum liquids, dubbed Stiefel liquids, based on $2+1$ dimensional nonlinear sigma models on target space $SO(N)/SO(4)$, supplemented with Wess-Zumino-Witten terms. We argue that the Stiefel liquids form a class of critical quantum liquids with extraordinary properties, such as large emergent symmetries, a cascade structure, and nontrivial quantum anomalies. We show that the well known deconfined quantum critical point and $U(1)$ Dirac spin liquid are unified as two special examples of Stiefel liquids, with $N=5$ and $N=6$, respectively. Furthermore, we conjecture that Stiefel liquids with $N>6$ are non-Lagrangian, in the sense that under renormalization group they flow to infrared (conformally invariant) fixed points that cannot be described by any renormalizable continuum Lagrangian. Such non-Lagrangian states are beyond the paradigm of parton gauge mean-field theory familiar in the study of exotic quantum liquids in condensed matter physics. The intrinsic absence of (conventional or parton-like) mean-field construction also means that, within the traditional approaches, it will be difficult to decide whether a non-Lagrangian state can actually emerge from a specific UV system (such as a lattice spin system). For this purpose we hypothesize that a quantum state is emergible from a lattice system if its quantum anomalies match with the constraints from the (generalized) Lieb-Schultz-Mattis theorems. Based on this hypothesis, we find that some of the non-Lagrangian Stiefel liquids can indeed be realized in frustrated quantum spin systems, for example, on triangular or Kagome lattice, through the intertwinement between non-coplanar magnetic orders and valence-bond-solid orders. △ Less

Submitted 25 August, 2021; v1 submitted 19 January, 2021; originally announced January 2021.

Comments: A summary of results can be found on pages 4-6

Journal ref: Phys. Rev. X 11, 031043 (2021)

RKKY interaction of magnetic impurities in node-line semimetals

Authors: Zhong-Yi Wang, Da-Yong Liu, Liang-Jian Zou

Abstract: Motivated by the recent upsurge in research of three-dimensional topological semimetals (SMs), we theoretically study the RKKY interaction between magnetic impurities in node-line SMs with and without the chirality and obtain the analytical expressions. We find that unique toroidal Fermi surface (FS) in nodal-line SMs, distinctly different from the spheroid FS in the SMs with the point nodes, has… ▽ More Motivated by the recent upsurge in research of three-dimensional topological semimetals (SMs), we theoretically study the RKKY interaction between magnetic impurities in node-line SMs with and without the chirality and obtain the analytical expressions. We find that unique toroidal Fermi surface (FS) in nodal-line SMs, distinctly different from the spheroid FS in the SMs with the point nodes, has significant influences on the RKKY interaction, leading to strong anisotropic oscillation and unique decay features. In the direction perpendicular to node-line plane, as usual, there is only one oscillation period related to the Fermi energy. In contrast, in the node-line plane, the RKKY interaction form a beating pattern and oscillates more rapidly with two distinct periods: one is coming from the Fermi energy and the other is from the radius of node-line. More importantly, inside nodal-line SMs bulk, the decay rate of RKKY interaction manifests a typical two-dimensional feature for impurities aligned along the direction perpendicular to nodal-line plane. Furthermore, the magnetic interactions in nodal-line SMs with linear and quadratic dispersions in the nodal-line plane are compared. We also discuss the possible application of the present theory on realistic NLSM ZrSiSe. Our results shed the light for application of magnetically doped node-line SMs in spintronics. △ Less

Submitted 8 November, 2020; originally announced November 2020.

Comments: 17 pages, 3 figures

Journal ref: J. Magn. Magn. Mater. 553, 169164 (2022)

Abelian and Non-Abelian Monopole Configuration in Condensed Matters

Authors: Yunkyu Bang, Y. M. Cho, Tieyan Si, Li-Ping Zou

Abstract: We discuss the Abelian and non-Abelian monopoles which could exist in condensed matters. We show how the Dirac monopole can be regularized by the charge screening, and argue that the Dirac monopole of mass of hundred meVs could exist in dielectric condensed matters. Moreover, we generalize this result to non-Abelian condensed matters to show the existence of the non-Abelian monopole configuration… ▽ More We discuss the Abelian and non-Abelian monopoles which could exist in condensed matters. We show how the Dirac monopole can be regularized by the charge screening, and argue that the Dirac monopole of mass of hundred meVs could exist in dielectric condensed matters. Moreover, we generalize this result to non-Abelian condensed matters to show the existence of the non-Abelian monopole configuration in two-gap condensed matters, and present explicit monopole solutions. △ Less

Submitted 11 October, 2020; originally announced October 2020.

Spin-crossover induced ferromagnetism and layer stacking-order change in pressurized 2D antiferromagnet MnPS$_3$

Authors: Hanxing Zhang, Caoping Ni, Jie Zhang, Liangjian Zou, Zhi Zeng, Xianlong Wang

Abstract: High-pressure properties of MnPS$_3$ are investigated by using the hybrid functional, we report a spin-crossover pressure of 35 GPa consisting with experimental observation (30 GPa), less than half of existing report (63 GPa) using the Hubbard U correction. Interestingly, a spin-crossover induced antiferromagnetism-to-ferromagnetism transition combined with stacking-order change from monoclinic to… ▽ More High-pressure properties of MnPS$_3$ are investigated by using the hybrid functional, we report a spin-crossover pressure of 35 GPa consisting with experimental observation (30 GPa), less than half of existing report (63 GPa) using the Hubbard U correction. Interestingly, a spin-crossover induced antiferromagnetism-to-ferromagnetism transition combined with stacking-order change from monoclinic to rhombohedral are founded, and the ferromagnetism origins from the partially occupied $t_{2g}$ orbitals. Different from previous understanding, the Mott metal-insulator transition of MnPS$_3$ does not occur simultaneously with the spin-crossover but in pressurized low-spin phase. △ Less

Submitted 15 August, 2020; originally announced August 2020.

Comments: 20 pages, 6 figures and 1 table

Topologically different spin disorder phases of the J1-J2 Heisenberg model on the honeycomb lattice

Authors: Jing Liu, Ya-Min Quan, H. Q. Lin, Liang-Jian Zou

Abstract: Searching for spin liquids on the honeycomb J1-J2 Heisenberg model has been attracting great attention in the past decade. In this Paper we investigate the topological properties of the J1-J2 Heisenberg model by introducing nearest-neighbour and next-nearest-neighbour bond parameters. We find that there exist two topologically different phases in the spin disordered regime 0.2<J2/J1<0.5: for J2/J1… ▽ More Searching for spin liquids on the honeycomb J1-J2 Heisenberg model has been attracting great attention in the past decade. In this Paper we investigate the topological properties of the J1-J2 Heisenberg model by introducing nearest-neighbour and next-nearest-neighbour bond parameters. We find that there exist two topologically different phases in the spin disordered regime 0.2<J2/J1<0.5: for J2/J1<0.32, the system is a zero-flux spin liquid which is topological trivial and gapless; for J2/J1>0.32, it is a pi-flux chiral spin liquid, which is topological nontrivial and gapped. These results suggest that there exist two topologically different spin disorder phases in honeycomb J1-J2 Heisenberg model. △ Less

Submitted 8 June, 2020; originally announced June 2020.

Comments: 11 pages, 4 figures

Journal ref: Physica E: 120, 114037 (2020)

Electron Tunneling Transport and Magnetic Field Modulation through a Superconductor-Kitaev layer-Superconductor Junction

Authors: Shiqing Jia, Yamin Quan, Hai-Qing Lin, Liang-Jian Zou

Abstract: We present the electron tunneling transport and its magnetic field modulation of a superconducting (SC) Josephson junction with a barrier of single ferromagnetic (FM) Kitaev layer. We find that at H = 0, the Josephson current IS displays two peaks at K/Δ = 3.4 and 10, which stem from the resonant tunnelings between the SC gap boundaries and the spinon flat bands and between the SC gap edges and th… ▽ More We present the electron tunneling transport and its magnetic field modulation of a superconducting (SC) Josephson junction with a barrier of single ferromagnetic (FM) Kitaev layer. We find that at H = 0, the Josephson current IS displays two peaks at K/Δ = 3.4 and 10, which stem from the resonant tunnelings between the SC gap boundaries and the spinon flat bands and between the SC gap edges and the spinon dispersive bands, respectively. With the increasing magnetic field, IS gradually decreases and abruptly drops to a platform at the critical magnetic field hc = gμBHc/Δ = 0.03K/Δ, since the applied field suppresses the spinon density of states (DOS) once upon the Kitaev layer enters the polarized FM phase. These results pave a new way to measure the spinon or Majorana fermion DOS of the Kitaev and other spin liquid materials. △ Less

Submitted 4 June, 2020; originally announced June 2020.

Comments: 12 pages, 4 figures

Deconfined Metal-Insulator Transitions in Quantum Hall Bilayers

Authors: Liujun Zou, Debanjan Chowdhury

Abstract: We propose that quantum Hall bilayers in the presence of a periodic potential at the scale of the magnetic length can host examples of a Deconfined Metal-Insulator Transition (DMIT), where a Fermi liquid (FL) metal with a generic electronic Fermi surface evolves into a gapped insulator (or, an insulator with Goldstone modes) through a continuous quantum phase transition. The transition can be acce… ▽ More We propose that quantum Hall bilayers in the presence of a periodic potential at the scale of the magnetic length can host examples of a Deconfined Metal-Insulator Transition (DMIT), where a Fermi liquid (FL) metal with a generic electronic Fermi surface evolves into a gapped insulator (or, an insulator with Goldstone modes) through a continuous quantum phase transition. The transition can be accessed by tuning a single parameter, and its universal critical properties can be understood using a controlled framework. At the transition, the two layers are effectively decoupled, where each layer undergoes a continuous transition from a FL to a generalized composite Fermi liquid (gCFL). The thermodynamic and transport properties of the gCFL are similar to the usual CFL, while its spectral properties are qualitatively different. The FL-gCFL quantum critical point hosts a sharply defined Fermi surface without long-lived electronic quasiparticles. Immediately across the transition, the two layers of gCFL are unstable to forming an insulating phase. We discuss the topological properties of the insulator and various observable signatures associated with the DMIT. △ Less

Submitted 22 September, 2020; v1 submitted 29 April, 2020; originally announced April 2020.

Comments: 6 pages + appendices

Journal ref: Phys. Rev. Research 2, 032071 (2020)

Deconfined metallic quantum criticality: A $U(2)$ gauge-theoretic approach

Authors: Liujun Zou, Debanjan Chowdhury

Abstract: We discuss a new class of quantum phase transitions -- Deconfined Mott Transition (DMT) -- that describe a continuous transition between a Fermi liquid metal with a generic electronic Fermi surface and an electrical insulator without Fermi surfaces of emergent neutral excitations. We construct a unified $U(2)$ gauge theory to describe a variety of metallic and insulating phases, which include Ferm… ▽ More We discuss a new class of quantum phase transitions -- Deconfined Mott Transition (DMT) -- that describe a continuous transition between a Fermi liquid metal with a generic electronic Fermi surface and an electrical insulator without Fermi surfaces of emergent neutral excitations. We construct a unified $U(2)$ gauge theory to describe a variety of metallic and insulating phases, which include Fermi liquids, fractionalized Fermi liquids (FL*), conventional insulators and quantum spin liquids, as well as the quantum phase transitions between them. Using the DMT as a basic building block, we propose a distinct quantum phase transition -- Deconfined Metal-Metal Transition (DM$^2$T) -- that describes a continuous transition between two metallic phases, accompanied by a jump in the size of their electronic Fermi surfaces (also dubbed a 'Fermi transition'). We study these new classes of deconfined metallic quantum critical points using a renormalization group framework at the leading nontrivial order in a controlled expansion, and comment on the various interesting scenarios that can emerge going beyond this leading order calculation. We also study a $U(1)\times U(1)$ gauge theory that shares a number of similarities with the $U(2)$ gauge theory and sheds important light on many phenomena related to DMT, DM$^2$T and quantum spin liquids. △ Less

Submitted 17 June, 2020; v1 submitted 7 February, 2020; originally announced February 2020.

Comments: 16 pages + references + appendices

Journal ref: Phys. Rev. Research 2, 023344 (2020)

Electronic correlation-driven orbital polarization transitions in the orbital-selective Mott compound Ba$_2$CuO$_{4-δ}$

Authors: Yu Ni, Ya-Min Quan, Jingyi Liu, Yun Song, Liang-Jian Zou

Abstract: The electronic states near the Fermi level of recently discovered superconductor Ba$_2$CuO$_{4-δ}$ consist primarily of the Cu $d_{x^2-y^2}$ and $d_{3z^2-r^2}$ orbitals. We investigate the electronic correlation effect and the orbital polarization of an effective two-orbital Hubbard model mimicking the low-energy physics of Ba$_2$CuO$_{4-δ}$ in the hole-rich regime by utilizing the dynamical mean-… ▽ More The electronic states near the Fermi level of recently discovered superconductor Ba$_2$CuO$_{4-δ}$ consist primarily of the Cu $d_{x^2-y^2}$ and $d_{3z^2-r^2}$ orbitals. We investigate the electronic correlation effect and the orbital polarization of an effective two-orbital Hubbard model mimicking the low-energy physics of Ba$_2$CuO$_{4-δ}$ in the hole-rich regime by utilizing the dynamical mean-field theory with the Lanczos method as the impurity solver. We find that the hole-overdoped Ba$_2$CuO$_{4-δ}$ with $3d^8$ (Cu$^{3+}$) is in the orbital-selective Mott phase (OSMP) at half-filling, and the typical two-orbital feature remains in Ba$_2$CuO$_{4-δ}$ when the electron filling approaches $n_e\sim 2.5$, which closely approximates to the experimental hole doping for the emergence of the high-$T_c$ superconductivity. We also obtain that the orbital polarization is very stable in the OSMP, and the multiorbital correlation can drive orbital polarization transitions. These results indicate that in hole-overdoped Ba$_2$CuO$_{4-δ}$ the OSMP physics and orbital polarization, local magnetic moment, and spin or orbital fluctuations still exist. We propose that our present results are also applicable to Sr$_2$CuO$_{4-δ}$ and other two-orbital cuprates, demanding an unconventional multiorbital superconducting scenario in hole-overdoped high-$T_c$ cuprates. △ Less

Submitted 15 June, 2021; v1 submitted 22 December, 2019; originally announced December 2019.

Comments: 9 pages, 10 figures

Journal ref: Phys. Rev. B 103, 214510 (2021)