Strongly Correlated Electrons · Cross-listed from cond-mat.quant-gas
Temperature-induced effective topology in many-body ultracold atomic quantum systems
Nitya Cuzzuol, Michele Miotto, Arianna Montorsi et al. (+2 more)
Ultracold atomic
quantum systems offer an unprecedentedly powerful platform for exploring interacting
symmetry-protected topological phases. Here, we show that their characteristic control over temperature provides a resource for engineering effective topological regimes with no zero-temperature counterpart. Employing finite-temperature
matrix-product-state calculations, we investigate experimentally accessible
Hamiltonians - the interacting bosonic Su-Schrieffer-Heeger and
spin-1 XXZ chains - that host a topological phase at zero temperature, as well as a fermionic dipolar ladder model whose ground state exhibits no topological order. By tracking complementary topological markers, we identify an intriguing mechanism rooted in the structure of the zero-temperature phase diagrams: in finite-size systems, excitation gaps with different magnitudes define an intermediate-temperature window where the correlations associated with the lower gap are suppressed, while those protected by the larger gap persist. This enables the emergence of effective finite-temperature regimes exhibiting topological features that are either absent or qualitatively different from those at zero temperature. Our results establish a novel route toward exploring effective topological phases in ultracold atomic
quantum systems.
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All authors Nitya Cuzzuol, Michele Miotto, Arianna Montorsi, Giacomo Valtolina, Luca Barbiero
Strongly Correlated Electrons
Emergent Electronic Bond-Order Wave in a Quasi-One-Dimensional Chain
Honghao Wang, Tristan R. Cao, Pedro Schlottmann et al. (+1 more)
Collective order is notoriously difficult to stabilize in one dimension, where strong fluctuations suppress
symmetry-breaking states. Here we report the emergence of an electronic bond-order wave (BOW) in the quasi-one-dimensional (1D) material Ba9Rh8O24, in which structural bonds become active electronic degrees of freedom that overcome 1D fluctuations to establish long-range order. Single-
crystal X-ray diffraction uncovers a striking inversion of inequivalent Rh-Rh bonds across a transition TA = 180 K, where short and long bonds interchange their identities rather than undergoing conventional Peierls dimerization. This bond inversion coincides with a heat-capacity anomaly and a profound reorganization of the dielectric response with strong suppression of dielectric loss upon cooling. The BOW exhibits strongly nonlinear, frequency-dependent I-V characteristics, clockwise hysteresis, and nonvolatile memristive switching. These findings uncover an unprecedented transformation from a dynamic bond
liquid to a rigid yet electrically reconfigurable BOW, establishing bond-centered electronic order as a new organizing principle for 1D
quantum matter.
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All authors Honghao Wang, Tristan R. Cao, Pedro Schlottmann, Gang Cao
Strongly Correlated Electrons
Tuning Charge Density Wave transitions through lattice strain in NbSe3
Antoine Gallo Frantz, Aleksander Sinchenko, Luc Ortega et al. (+7 more)
The Charge Density Wave (CDW) state is a perfect example of a combined structural and electronic state, both characterized by a periodic
lattice distortion and an electronic modulation of condensed electrons, resulting from electron-
phonon coupling. They are thus prone to be tuned by
lattice strain. NbSe3 is a prototypical example of CDW states, with a chain-like structure displaying two CDWs at 145K and 59K, with wavevectors along and inclined with respect to the chain axis b. Here, we report on the
evolution of the
lattice structure and CDW properties in the quasi-one-dimensional charge-density-wave system NbSe3 under tensile stresses applied along and perpendicular to the chains axis b by a combination of X-ray diffraction and transport measurements. We find that the
lattice structure show exotic Poissons coefficients and strongly anisotropic Youngs moduli while the
evolution of the electrical resistance demonstrates shifts of both charge-density-wave critical temperatures that are strongly correlated with the
lattice parameters. The two CDW transitions display different behaviours under applied stresses, and suggest that a modification of the band
curvature leads to the observed transport signatures.
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All authors Antoine Gallo Frantz, Aleksander Sinchenko, Luc Ortega, Pavel Grigoriev, Vladislav Kochev, Pierre Godard, Pierre Olivier Renault, Dominique Thiaudiere, David Le Bolloch, Vincent Jacques
Strongly Correlated Electrons · Cross-listed from math-ph
Fermionic quantum cellular automata in 2d are trivial
Jeffrey Kwan, David M. Long and Jeongwan Haah
Fermionic
quantum cellular automata (QCA) are automorphisms of local fermionic operator
algebras ($\mathbb Z_2$-graded superalgebras) that have bounded spread: they map local operators to nearby operators. We prove that every 2-dimensional fermionic QCA on a locally finite-dimensional
algebra is a composition of local automorphisms and a fermionic shift. This is implied by our result that every locally finite-dimensional fermionic invertible subalgebra in a one-dimensional
lattice is Brauer trivial, i.e., it is stably bounded-spread isomorphic to a tensor product fermionic
algebra.
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Strongly Correlated Electrons
Finite-Temperature Flat-Band Ferromagnetism in the Kagome Hubbard Model
Alon Strugatsky, Jonas B. Profe and Roser Valentí
Kagome metals exhibit a rich interplay of
topology, electronic correlations, and
lattice dynamics. Recent discoveries of Kagome materials with a flat band near the Fermi level have revealed a variety of correlated electronic phases. However, elucidating their microscopic origin remains challenging, as realistic descriptions require accounting for multiple orbitals and competing interactions on an equal footing. To disentangle correlation effects from material-specific details and identify the essential physics of the flat-band regime, we study the single-orbital Kagome-Hubbard model at flat-band fillings using dynamical mean-field theory. We find strong signatures of flat-band ferromagnetism, consistent with exact and mean-field ground-state results. Moreover, we uncover an unconventional quasi-ordered phase in which a partially filled
spin-polarized flat band pinned at the Fermi level gives rise to persistent local
spin fluctuations down to zero temperature, in striking contrast to the classical behavior expected for a conventional ferromagnet. Our results demonstrate that these anomalous fluctuations are an intrinsic consequence of the flat-band degeneracy and establish a minimal framework for understanding correlation effects in flat-band Kagome systems.
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Strongly Correlated Electrons
Two-magnon response from light scattering in altermagnets
Shuyi Li, Lexu Zhao and Chunjing Jia
Altermagnetism is a recently established class of
magnetic order that combines fully compensated moments with momentum-dependent
spin splitting, yet identifying its spectroscopic fingerprints remains an open challenge. In this work, we investigate finite-momentum two-
magnon excitations in a two-dimensional $d$-wave altermagnet by calculating the two-
magnon light scattering intensity in different polarization channels. Using linear
spin-wave theory and further incorporating the leading $1/S$
quantum corrections, we demonstrate that the characteristic
magnon splitting of altermagnets shifts the upper edge of the two-
magnon continuum and the corresponding spectral features to higher energy at $\boldsymbol{X}=(\pi,0)$ relative to the conventional antiferromagnet, by an amount linear in the exchange anisotropy $|\delta J_2|$, while leaving the response at the Brillouin-zone center unchanged. Although
magnon-
magnon interactions strongly redistribute spectral weight toward lower energies, the energy scale associated with the high-energy momentum-selective reconstruction remains robust. The interactions additionally generate a pronounced low-energy two-peak structure that has no counterpart within linear
spin-wave theory. At $\boldsymbol{K}=(\pi/2,\pi/2)$, we show that the interacting two-
magnon resonance is twofold degenerate in the conventional antiferromagnetic phase, while a finite altermagnetic exchange anisotropy lifts this degeneracy, producing two peaks whose separation is linear in $|\delta J_2|$. The characteristic energy scales underlying both features are intrinsic to the two-
magnon sector rather than to a specific scattering operator. These findings highlight the potential of finite-momentum two-
magnon spectroscopy for identifying altermagnetic order in insulating magnets and motivate momentum-resolved resonant inelastic x-ray scattering studies of candidate altermagnetic materials.
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Strongly Correlated Electrons
Green's Functions from Sample-based Krylov Quantum Diagonalization: An Impurity Solver for Dynamical Mean-Field Theory
Jay Patel, Chakradhar Rangi and Ka-Ming Tam
We generalize the sample-based Krylov
quantum diagonalization (SKQD) method from ground-state calculations to the evaluation of single-particle Green's functions. By constructing and sampling
unitary Krylov subspaces in the N +/- 1 particle-number sectors and evaluating all sector-connecting overlaps classically, the approach reconstructs the Green's function via a Lanczos continued fraction while retaining the shallow-
circuit, ancilla-free character of SKQD. The
quantum device is required only to prepare and sample short-time evolutions. Applied to the particle-hole-symmetric single-impurity Anderson model in chain geometry, with the discrete bath representation used in dynamical mean-field theory (DMFT), the method recovers the spectral function using a relatively small fraction of the full
Hilbert space. Across a range of interaction strengths that spans the metal-
insulator transition, the main spectral features are reproduced. These results suggest that SKQD-based Green's-function calculations may allow DMFT impurity solvers with a larger number of bath sites on near-term
quantum hardware than is currently practical.
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Strongly Correlated Electrons · Cross-listed from cond-mat.quant-gas
Few-body bound states in the anyon-Hubbard model
Isaac Tesfaye, Christina Mascherbauer, Joyce Kwan et al. (+6 more)
Quantum statistics in low-dimensional systems predicts anyonic particles with fractional exchange statistics which are neither that of
bosons nor
fermions. While anyons are typically found in two dimensions as excitations of topologically-ordered states of matter, anyon-like exchange statistics has also been discussed in one dimension, for instance, in the context of the anyon-Hubbard model (AHM), the physics of which has recently been observed in experiment [Kwan et al., arXiv:2306.01737; Dhar et al., arXiv:2412.21131; and Bakkali-Hassani et al., arXiv:2602.20421]. The AHM can be formulated in terms of
bosons featuring density-dependent Peierls phases, described by a statistical phase angle $\theta$, which controls asymmetric transport and the formation of dynamically bound pairs at finite momentum. Here, we show theoretically that the AHM also hosts exact two-body bound states in the continuum (BICs) for arbitrary $\theta\neq 0$, and genuine three- and four-body bound states. Unlike conventional bound states stabilized by attractive (or repulsive) interactions, which are energetically localized with a large effective mass, these clusters here are bound by a purely kinematic mechanism endowing them with fast chiral transport properties. We provide a simple variational approximation to the three-body bound states and explain their binding mechanism. Moreover, we show that the signatures of three-body bound states in the AHM can be directly probed experimentally from the expansion dynamics starting from three localized particles.
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All authors Isaac Tesfaye, Christina Mascherbauer, Joyce Kwan, Perrin Segura, Yanfei Li, Markus Greiner, Luis Santos, André Eckardt, Brice Bakkali-Hassani
Strongly Correlated Electrons · Cross-listed from cond-mat.mes-hall
Topological Impurity Bands
Arnab Seth and Itamar Kimchi
The effects of disorder on topological phases of matter are typically either preservation of
topology or its destruction. For example, the
quantum Hall effect's quantization and chiral edge mode remain robust until a strong-disorder percolation transition exits the topological phase. Disorder can also enlarge a preexisting topological phase, yielding a topological Anderson
insulator (TAI). However, the reliance of TAI and other theoretical treatments on perturbatively averaging out long-wavelength randomness suggests that additional effects might appear when the disorder involves localized defects. Here we show that a finite density of randomly distributed defects can generate various new topological phase transitions. This route to disorder-induced
topology can be viewed as the formation of topological impurity bands (TIB) and is applicable even if the initial clean model is a trivial band
insulator. The theory relies on an orbital-dependent vorticity of impurity bound states, which we derive analytically near a generic Dirac cone phase transition as well as using the Chern
insulator lattice models of Qi-Wu-Zhang and Haldane. Their numerically computed phase diagrams at 3% defect density show robust topological transitions in distinct TIB and TAI regimes, suggesting a local route to topological phases.
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Strongly Correlated Electrons
On spectral properties of Generalized Kadanoff–Baym Ansatz
Miroslav Hopjan
The Generalized Kadanoff–Baym Ansatz with mean-field propagators is increasingly used to simulate non-
equilibrium quantum fermionic and bosonic systems. Compared with the full Kadanoff–Baym equations, its mean-field propagators substantially reduce computational cost, enabling simulations with computational effort that scales linearly with propagation time. However, the time-diagonal structure of the Generalized Kadanoff–Baym Ansatz obscures spectral properties within the collision integral of the transport equation. Here, we recover and investigate these hidden spectral properties using the extended Generalized Kadanoff–Baym Ansatz. For a Hubbard cluster, we compare ground-state spectral functions obtained with the extended Generalized Kadanoff–Baym Ansatz against those from standard Kadanoff–Baym equations. At moderate interaction strengths, the spectral functions show good agreement. At large interaction strengths, however, significant deviations emerge, and the spectral function obtained with the extended Generalized Kadanoff–Baym Ansatz becomes negative. These results demonstrate that, despite its computational advantages, the Generalized Kadanoff–Baym Ansatz has important limitations in strongly interacting regimes and may produce unphysical spectral properties when interactions become sufficiently large.
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Strongly Correlated Electrons · Cross-listed from quant-ph
Modular commutator as a robust topological invariant and approximate Markovianity
Tai Hsuan Yang
The modular commutator provides a bulk, local, single-wave-function probe of the chiral central charge $c_-$ for gapped ground states. Its invariance under deformations was previously established under a local
quantum Markov condition—namely, the conditional mutual information $I(A:C|B)$ is zero for all tripartitions of a disk into three consecutive strips A, B, and C \cite{Modular-commutator-Gapped}. However, the local
quantum Markov condition also forces the probe to vanish, leaving open whether modular commutator remains robust in physically relevant states where the Markov property holds only approximately. In this paper, we resolve this tension for finite-dimensional
Hilbert spaces: the approximate local
quantum Markov property implies the change of the modular commutator under
topology-preserving deformations vanishes asymptotically. We next prove trace-norm continuity of the modular commutator. Combining deformation invariance with trace-norm continuity, we establish that the modular commutator remains asymptotically invariant within gapped
quantum phases connected by quasi-local
unitary paths that preserve the approximate local
quantum Markov condition. Conversely, by analyzing finite-time dynamics generated by modular
Hamiltonians, we derive a quantitative lower bound on the conditional mutual information required for a non-zero modular commutator: $I(A:C|B)$ across such strip tripartitions cannot decay faster than exponentially with the width of B given that the state satisfies
entanglement area law, extending the exact no-go
theorem of \cite{strict-J-2024} to a quantitative finite bound . Finally, we demonstrate that those conclusions apply equally to the Hall conductance
estimator \cite{FanSahayVishwanath2023}.
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Strongly Correlated Electrons
Real-time Dyson expansion for the nonequilibrium $GW$ approximation: Correlated spectra and dependence on the reference propagator
Erik Schroedter, Jan-Philip Joost, Michael Bonitz et al. (+1 more)
Electronic spectra provide direct insight into the excitations and correlations of condensed matter systems. Their description requires electron correlations beyond mean field. In
equilibrium, the $GW$ approximation has become the method of choice for many materials. Extending this approximation to nonequilibrium, however, is challenging. Full two-time $GW$ simulations within the nonequilibrium Green's functions approach scale at least cubically with propagation time, whereas improved scaling schemes such as time-local (adiabatic) approximations or the generalized Kadanoff–Baym ansatz usually retain only mean-field character in the spectra. The recently introduced real-time Dyson expansion recovers dynamical correlations in the spectrum at time-linear cost, but has so far been restricted to the second-order Born approximation with mean-field reference propagators. Here we formulate and implement the RT-DE for the nonequilibrium $GW$ self-energy with reference propagators of general form whose off-diagonal
evolution is time local. In particular, we assess Hartree–Fock propagators, propagators with statically screened exchange with nonequilibrium screening, and a correlated propagator based on the Hartree–Fock GKBA.
Benchmarks against exact diagonalization for a driven two-band
lattice model with long-range interactions show that the mean-field and statically screened references yield the most accurate spectra, including satellite structures absent at mean-field level, whereas the GKBA-based approach best captures scattering-induced occupation dynamics, but artificially broadens and splits spectral peaks. When applied to large systems that are beyond the reach of exact methods, the scheme resolves the excitonic replica of the valence band and satellites identified as
exciton shake-up, as well as their reshaping with increasing excitation density.
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All authors Erik Schroedter, Jan-Philip Joost, Michael Bonitz, Vojtech Vlcek
Strongly Correlated Electrons
Positive Temperature Coefficient of Anisotropy due to $d^6L$ Groundstate in $\epsilon$-Fe$_2$O$_3$
Rachel Nickel, Kurt Kummer and Johan van Lierop
Positive anisotropy temperature coefficients ($dK/dT>0$) usually arise from hybridization between
magnetic 3d states and strongly
spin-orbit-coupled (SOC) subsystems. Yet $\epsilon$-Fe$_2$O$_3$ shows $dK/dT>0$ (125-200~K) without an obvious SOC partner. We study pure and Cr-doped (with weakened Fe-O hybridization) $\epsilon$-Fe$_2$O$_3$ across the transition from low temperature incommensurate to high-anisotropy
magnetic phases. We identify a $d^6L$ groundstate in $\epsilon$-Fe$_2$O$_3$ while reduced hybridization yields $d^6 + d^6L^2$ in the Cr-doped system, highlighting metal-ligand hybridization as a route to tune
magnetic, electronic and orbitronic properties.
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Strongly Correlated Electrons
Examining Convergence of Cluster Perturbation Theory and Cluster Coupled Cluster for J1-J2 Heisenberg Spin Lattices
Jeffrey Keyes and Carlos Jimenez-Hoyos
In previous work, it was shown that using the cluster mean field(cMF) wavefunction as the zeroth order wavefunction for perturbation theory and coupled cluster produces a reasonable approximation for the J 1-J 2 Heisenberg model in the thermodynamic limit(TDL). However, this work was limited to cPT4 and cCCSD. The central claim of cMF is that it takes strongly correlated systems and makes them weakly correlated so that PT weakly correlated methods can be used. To confirm that this claim is true, it is important to show that the PT and CC series converge. In this paper, we extend the previous calculations to cPT7 and cCCSDTQ5 where we show that the energy is converging. We also discuss how to perform cluster based calculations efficiently in the thermodynamic limit, which is crucial for these more expensive calculations.
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Strongly Correlated Electrons
$g$-wave altermagnetic order parameter in hematite
Tianren Wang, Yuehong Li, Yu Feng et al. (+11 more)
Altermagnets combine the vanishing net magnetization of antiferromagnets with momentum-dependent
spin splitting.
Magnon band splitting provides a direct probe of altermagnetic order and may enable chirality-selective
magnon transport, yet the momentum-space
symmetry of this splitting has not been determined quantitatively. Here we use inelastic
neutron scattering to map the momentum dependence of altermagnetic
magnon splitting in hematite ($\alpha$-Fe$_2$O$_3$). The splitting vanishes along nodal directions and reaches maxima off the nodes, revealing the $g$-wave
symmetry of the altermagnetic order parameter. These results agree with linear
spin-wave theory calculations based on the altermagnetic model, which further identify the nondegenerate branches as
magnons of opposite chirality and trace the splitting to
symmetry-inequivalent long-range exchange interactions. Our results provide the first quantitative determination of the momentum-space
symmetry of altermagnetic chiral
magnons. These findings, together with hematite's high
magnetic ordering temperature and low
magnon damping, establish it as a promising platform for low-dissipation,
symmetry-selective magnonic applications.
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All authors Tianren Wang, Yuehong Li, Yu Feng, Andong Liu, Yuetong Wu, Qian Zhao, Yujie Yan, Wei Luo, Xin Tong, Yi Lu, Yao Shen, Stefano Agrestini, Jaewon Choi, Qisi Wang
Strongly Correlated Electrons · Cross-listed from cond-mat.mtrl-sci
Polymorph Engineering of the Layered Rare-Earth Magnet GdAlGe
Dmitry V. Averyanov, Ivan S. Sokolov, Alexander N. Taldenkov et al. (+7 more)
The recent advances in research on layered magnets have established them as invaluable materials for spintronic applications and precursors to 2D magnets. The problem is that the number of such materials available for experimentation is still low. To tackle the problem, one may employ phase engineering; in particular, the interplay between the phase stability and dimensionality provides great opportunities for design of layered magnets. Here, this interrelation is harnessed to produce epitaxial films of an overlooked layered polymorph of GdAlGe. The compound is formed by alternating triangular Gd and honeycomb AlGe
lattices. It is stable in ultrathin films, up to 5 monolayers. In thicker films, an additional unwanted phase emerges. The structural quality of the ultrathin films is witnessed by electron and X-ray diffraction as well as electron microscopy. Magnetization measurements detect an anisotropic ferromagnetic state. The GdAlGe magnetism is corroborated by a study of electron transport revealing the anomalous Hall effect and negative magnetoresistance. The material is naturally integrated with Ge, a technological
semiconductor, which should facilitate applications. The present study can serve as a blueprint for design of layered magnets via polymorph engineering.
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All authors Dmitry V. Averyanov, Ivan S. Sokolov, Alexander N. Taldenkov, Oleg E. Parfenov, Alexey N. Mihalyuk, Ivan A. Yakovlev, Igor A. Karateev, Oleg A. Kondratev, Andrey M. Tokmachev, Vyacheslav G. Storchak
Strongly Correlated Electrons
Magnetic phases of Kondo lattice materials Ce$_5$RhGe$_2$ and Ce$_5$IrGe$_2$
Jiawen Zhang, Yanan Zhang, Mingyi Wang et al. (+5 more)
Single
crystals of Ce$_5$RhGe$_2$ and Ce$_5$IrGe$_2$ have been systematically investigated by electrical resistivity, specific heat, and magnetization measurements. Together with Ce$_5$CoGe$_2$, all three compounds crystallize in the orthorhombic Pnma structure, with the
lattice parameters increasing monotonically from Co to Rh to Ir, consistent with the effect of negative chemical pressure. Magnetization measurements along the three principal crystallographic axes identify the a axis as the easy magnetization direction throughout the series. Ce$_5$RhGe$_2$ exhibits ferromagnetic ordering with a Curie temperature of approximately 11.5 K and shows
magnetic behavior closely resembling that of Ce$_5$CoGe$_2$. In contrast, Ce$_5$IrGe$_2$ undergoes two successive
magnetic transitions at $T_{\rm M1}=12.7$ K and $T_{\rm M2}=11.8$ K, and there are multiple metamagnetic transitions under
magnetic fields, giving rise to magnetization plateaus at fractions of the saturation magnetization $M_{\rm s}$ of approximately $M_{\rm s}/5$ and $M_{\rm s}/3$. The low-field metamagnetic transition along the easy axis shifts to lower field with decreasing temperature, and eventually a pronounced hysteresis loop is observed about zero-field, establishing that Ce$_5$IrGe$_2$ exhibits a ferrimagnetic ground state at the lowest measured temperatures.
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All authors Jiawen Zhang, Yanan Zhang, Mingyi Wang, Ye Chen, Yu Liu, Yongjun Zhang, Michael Smidman, Huiqiu Yuan
Strongly Correlated Electrons
Schwinger boson perturbation theory for spin-$S$ Kitaev-Heisenberg magnets: phase diagram and dynamical response near Kitaev spin liquids
Daiki Sasamoto and Joji Nasu
We develop a Schwinger
boson perturbative framework for the
spin-$S$ Kitaev-Heisenberg model. The
spin-
liquid saddle point of the pure Kitaev model is used as the unperturbed state, and
magnetic instabilities and dynamical
spin correlations are evaluated around this saddle point. We decompose the
Hamiltonian exactly into two parts by exploiting the Klein duality intrinsic to the Kitaev-Heisenberg model. We perform the random-phase approximation by taking the part invariant under the duality transformation as the unperturbed term and treating the remaining term, which changes sign under it, as the perturbation. We determine the phase boundaries separating the
quantum spin-
liquid regimes from the adjacent magnetically ordered phases for $S=1/2$, $1$, $3/2$, and $2$. The
spin-
liquid regions shrink rapidly with increasing $S$ and become very narrow at $S=2$. We also compute the
spin dynamics of the
spin-$S$ Kitaev-Heisenberg model, focusing on $S=1$, and find that the dressed dynamical
spin structure factor retains a broad two-spinon continuum at finite energies, while the low-energy spectral weight softens at the ordering wave vectors of the adjacent
magnetic phases. Our framework thus enables thermodynamic-limit calculations of
spin dynamics near
magnetic instabilities.
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Strongly Correlated Electrons
High-resolution angle-resolved photoemission spectroscopy with tunable magnetic field
Jairo Obando-Guevara, Huu-Thong Le, Emiliano Corcino Aracena et al. (+7 more)
The control and perturbation of
quantum phenomena with
magnetic fields is an indispensable tool in materials research. Recently, in-situ field tuning was implemented into angle-resolved photoemission spectroscopy (magneto-ARPES), which provides direct momentum and energy-resolved information of the field-dependent electronic structure. However, aberrations of the electron trajectories were shown to be substantial, leading to significant spectral distortions and broadening even in small fields. Here we show that the electronic structure can be recovered from magneto-ARPES spectra with high accuracy while maintaining high momentum resolution even when strong trajectory aberrations are present. We studied Bi$_2$Se$_3$ in a dipole field of a coil using a
laser-based ARPES system. The electronic structure was reconstructed in post-processing using detailed electron trajectory simulations. We identify two-dimensional (2D) momentum mapping, a micron beam spot size, and precise numerical field simulations as critical technical requirements for high-resolution magneto-ARPES. We show how circular dichroism can provide additional information about the coupling of the
magnetic field to the
spin. The experimental achievements and the scaling laws from our simulations provide a road map towards magneto-ARPES in larger fields.
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All authors Jairo Obando-Guevara, Huu-Thong Le, Emiliano Corcino Aracena, Sayan Singha, Kyungchan Lee, Yingdong Guan, Zhiqiang Mao, Dezhe Jin, Chaoxing Liu, Heike Pfau
Strongly Correlated Electrons
Theory of Kondo hybridization wave in Kondo lattice
Yin Zhong
Recent scanning tunneling microscopy experiments have discovered emergent spatially modulated Kondo hybridization wave (KHW) order in the heavy
fermion superconductor UTe$_2$ and the artificial Kondo
lattice system 1T/1H-TaS$_2$, challenging the conventional paradigm of spatially uniform Kondo hybridization in heavy
fermion physics. Here, we develop a microscopic theory for KHW order based on the canonical square-
lattice Kondo
lattice model within the large-$N$ fermionic mean-field approximation. We systematically identify stable modulated KHW phases and establish their ground-state phase diagram. The prominent $\boldsymbol{Q}=(0,\pi)$ KHW phase yields uniaxial stripe modulation of the Kondo hybridization gap, which faithfully reproduces the spatial modulation pattern observed in UTe$_2$. Moreover, its inherent unit-
cell-doubling modulation precisely accounts for the spectroscopic features measured in 1T/1H-TaS$_2$. We further predict a characteristic in-plane conductivity anisotropy that serves as a definitive transport fingerprint to discriminate KHW states with distinct ordering wavevectors. Our work provides a microscopic foundation for the newly observed KHW order and establishes a unified theoretical framework for understanding emergent modulated hybridization phenomena in heavy
fermion materials.
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Strongly Correlated Electrons
Hong-Hao Song and Gang v. Chen
We show that zero-energy gapless Weyl-line
phonons of the Kane-Lubensky's type can arise in the three-dimensional Maxwell
lattice frustrated Mott
insulators through the magnetopological mechanics. In a pyrochlore antiferromagnet with the
spin-
lattice coupling, a
magnetic field selects the
spin state whose
lattice distortion generates a $P4_3 32$ topological
lattice. More crucially, the
spin-
lattice coupling and the
spin configuration cause the bending of the neighbouring bonds, and converts the system into the topological Maxwell
lattice. Remarkably, the resulting system is found to host the bulk zero-frequency Weyl-line
phonons protected topologically, and these gapless
phonons are not Goldstone modes. Unlike the conventional ${C_{\rm ph}\sim T^3}$ for the Goldstone
phonons, these one-dimensional zero-mode
manifolds yield a characteristic low-temperature
phonon specific heat ${C_{\rm ph}\sim T^2}$. Our results could find applications in the Cr-based spinel systems, and moreover, we establish a low-energy platform where an extensive number of topological zero-frequency
phonons can strongly couple to other degrees of freedom, opening a route to exotic
phonon-mediated phenomena.
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Strongly Correlated Electrons · Cross-listed from cond-mat.quant-gas
Large-Chern-number flat bands, anomalous Dirac cones, and unconventional superfluidity in square-lattice systems with SU(N) non-Abelian gauge fields
Wentao Zhong and Zhongbo Yan
We study topological band structures and superfluid phases in two-dimensional square-
lattice systems with homogeneous SU($N$) non-Abelian gauge fields. Starting from an SU(4) gauge-field model related to the Hofstadter model with flux $\alpha=1/4$, we show that the lowest and highest bands are isolated Chern bands that carry Chern numbers $C=-4$ and give rise to four chiral edge modes in a strip geometry. Remarkably, although the two middle bands touch and form $16$ gapless Dirac cones, their combined Chern number is $C=8$. We then generalize the construction to SU($N$) systems and reveal an even–odd structure of the band
topology: when $N$ is odd, all bands are isolated and carry nonzero Chern numbers; when $N$ is even, the two middle bands touch at $N^{2}$ Dirac points, while all other bands remain isolated and topologically nontrivial. We find that the uppermost and lowermost bands become increasingly flat and their Berry
curvature becomes more uniform as $N$ increases, providing a promising platform for realizing fractional Chern insulating phases. We further examine the
spin-$3/2$ SU(4) model with on-site attractive Hubbard interactions, exploring its superfluid phases at partial filling. We find that the non-Abelian gauge field breaks the hidden SO(5) degeneracy of the quintet pairing and selects distinct nematic superfluid states. For fillings in the middle-band regime, the resulting spectrum can host topologically protected Bogoliubov Fermi surfaces. Our results provide a starting point for exploring both topological band physics and unconventional superfluidity in synthetic SU($N$) cold-atom systems.
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Strongly Correlated Electrons
Successive Phase Transitions from a Composite Fermion Liquid to a Fractional Quantum Hall State at {\nu}=3/2 Driven by In-Plane Magnetic Field
Xinghao Wang, L. N. Pfeiffer, A. Gupta et al. (+3 more)
We report an even-denominator fractional
quantum Hall state at {\nu} = 3/2 induced entirely by in-plane
magnetic field B_|| in an ultra-high-mobility GaAs
quantum well. As B_|| increases, the system undergoes two successive transitions: from a composite
fermion liquid to a soft-gap FQH state (B_||~12.2 T), then via a topological phase transition to a hard-gap robust FQH state (B_||~14.7 T), accompanied by a daughter state at {\nu} = 19/13. We present systematic data, and discuss a possible scenario in interpreting these findings. Our work demonstrates that topological order may be engineered through k-space Fermi contour splitting under an in-plane
magnetic field.
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All authors Xinghao Wang, L. N. Pfeiffer, A. Gupta, K. W. Baldwin, K. W. West, Rui-Rui Du
Strongly Correlated Electrons
Observation of multipartite spin entanglement in a cuprate chain
S. F. R. TenHuisen, Z. Shen, V. Bhartiya et al. (+17 more)
Quantum materials are believed to host highly entangled states of matter, but probing and quantifying such
entanglement has long remained experimentally elusive. Here, we use resonant inelastic X-ray scattering (RIXS) as a probe of multipartite
spin entanglement. By projecting the RIXS cross section onto the appropriate
spin excitation channel, we show that the
Quantum Fisher Information can be extracted directly from the measured
spin fluctuation spectrum. We detect at least 7-partite
spin entanglement in the model one-dimensional cuprate Sr$_2$CuO$_3$, revealing one of the largest
entanglement depths yet reported in a solid. The observed
entanglement depth agrees with Hubbard-model expectations and persists to elevated temperatures. Our results establish RIXS as an experimental probe of many-body
spin entanglement and provide a platform for extensions to charge and orbital sectors and nonequilibrium settings.
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All authors S. F. R. TenHuisen, Z. Shen, V. Bhartiya, V. Menon, P. Sharma, H. Padma, Z. Guan, W. He, M. K. Lajer, J. Li, D. Banerjee, J. Pelliciari, I. A. Zaliznyak, G. D. Gu, M. D. Lukin, S. Johnston, M. P. M. Dean, V. Bisogni, Y. Wang, M. Mitrano
Strongly Correlated Electrons
Textures as a phase-transition probe for quantum spin chains
Heitor P. Casagrande, Isaac M. Carvalho, William J. Munro et al. (+1 more)
The idea of
quantum texture has been recently proposed and used as a tool for quantifying coherences and for
quantum gate identification. In this work we offer a study on its usage to
quantum phase transitions, demonstrating the rugosity metric as a simple tool for effective phase-transition probing. We establish the link between rugosity in the computational basis and the hierarchy of
spin correlators, and analyze rugosities defined in the global ground-state and in ground-states belonging to different magnetization sectors (to which we refer to as global vs
symmetry-resolved rugosities) to study the phase diagram of the Heisenberg XXZ model. We find distinct rugosity signatures at both transition points. In particular, a sharp feature appears at $\Delta=1$ already for small systems, revealing a pronounced sensitivity of the correlation hierarchy encoded by the texture to this point. Since the BKT transition coincides with the isotropic $SU(2)$ point of the XXZ model, this behavior may reflect a particular sensitivity of rugosity to the structure of the
spin-correlation hierarchy at isotropy.
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All authors Heitor P. Casagrande, Isaac M. Carvalho, William J. Munro, Krissia Zawadzki
Strongly Correlated Electrons
Selective coupling of high-order phonons in La2-xSrxCuO4
Ke-Jun Xu, Paulina Majchrzak, Nathan Giles-Donovan et al. (+14 more)
In
crystals and molecules with strong coupling between the charge carriers and atomic vibrations, high order harmonics of the vibrational excitations can be observed with intensity following the Franck-Condon envelope. Here, we uncover a new regime of electron-
phonon coupling in La2-xSrxCuO4 using resonant inelastic X-ray scattering. In the undoped compound, we find sharp peaks at approximately 85$\pm$5 meV, 180$\pm$7 meV, and 330$\pm$5 meV with no observable dispersion, and an absence of appreciable intensity from other modes observed in Raman spectroscopy in this energy range. The 180 meV and 330 meV excitations have energies approximately consistent with two-
phonon and four-
phonon in-plane Cu-O bond stretching mode, suggesting that the resonantly excited valence electrons strongly couple to this mode. These excitations exhibit significant doping dependence, eventually becoming unresolvable at 10% hole doping, where the low energy charge excitations are dominated by dispersive plasmons. The observation of selective coupling to even-ordered
phonons and stark contrast with the Raman spectra indicate anomalous electron-
phonon coupling beyond the Franck-Condon picture. One intriguing possibility is the existence of locally paired quasiparticles in insulating cuprates.
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All authors Ke-Jun Xu, Paulina Majchrzak, Nathan Giles-Donovan, Sangheon Kim, Jaewon Choi, Jun Okamoto, Ganesha Channagowdra, Hsiao-Yu Huang, Di-Jing Huang, Seiki Komiya, Takao Sasagawa, Shuichi Wakimoto, Wei-Sheng Lee, Zhi-Xun Shen, Thomas P. Devereaux, Dung-Hai Lee, Robert J. Birgeneau