We revisit the ground state of the Hubbard model on two-legged ladders in this paper. We perform density matrix renormalization group (DMRG) calculations on large system sizes with large numbers of kept states and perform extrapolation of DMRG results with truncation errors in the converged region. We find that the superconducting correlation exponent $K_{sc}$ extracted from the pair-pair correlation is very sensitive to the position of the reference bond, reflecting a huge boundary effect on it. By systematically removing the effects from boundary conditions, finite sizes, and truncation errors in DMRG, we obtain more accurate values of $K_{sc}$ and $K_{\rho }$ with DMRG. With these exponents, we confirm that the two-legged Hubbard model is in the Luther-Emery liquid phase with $K_{sc}·K_{\rho }=1$ from tiny doping near half filling to $1/8$ hole doping. When the doping is increased to $\delta ⪆1/6$, the behaviors of charge, pairing, and spin correlations do not change qualitatively, but the relationship $K_{sc}·K_{\rho }=1$ is likely to be violated. With the further increase of the doping to $\delta =1/3$, the quasi-long-ranged charge correlation turns into a true long-ranged charge order, and the spin gap is closed, while the pair-pair correlation still decays algebraically. Our work provides a standard way to analyze the correlation functions when studying systems with open boundary conditions.

Quantum inverse problem is defined as how to determine a local Hamiltonian from a single eigenstate. This question is valid not only in Hermitian system but also in non-Hermitian system. So far, most attempts are limited to Hermitian systems, while the possible non-Hermitian solution remains outstanding. In this work, we generalize the quantum covariance matrix method to the cases that are applicable to non-Hermitian systems, through which we are able to explicitly reconstruct the non-Hermitian parent Hamiltonian from an arbitrary pair of biorthogonal eigenstates. As concrete examples, we successfully apply our approach in spin chain with Lee-Yang singularity and a non-Hermitian interacting fermion model. Some generalization and further application of our approach are also discussed. Our work provides a systematical and efficient way to construct non-Hermitian Hamiltonian from a single pair of biorthogonal eigenstates and shed light on future exploration on non-Hermitian physics.

We study the coupling between topological bands and two distinct magnetic sublattices in ${\mathrm{EuMn}}_{1-x}{\mathrm{Zn}}_x{\mathrm{Sb}}_2$ $(0\le x\le 1)$ using a combination of magnetotransport measurements and density functional theory (DFT) calculations. Hall measurements reveal a low carrier concentration with high mobility across all samples, allowing the observation of quantum oscillation in the range of $0\le x\le 0.8$ at a relatively low magnetic field. Upon analyzing the quantum oscillation data, the fast Fourier transform spectra for $0\le x\le 0.8$ exhibit a relatively weak Zn doping dependency but a significant temperature dependency. This weak Zn doping dependency suggests that the magnetotransport properties of ${\mathrm{EuMn}}_{1-x}{\mathrm{Zn}}_x{\mathrm{Sb}}_2$ are dominated by quasi-two-dimensional small Fermi pockets originating from the Sb zigzag chains, which remain largely unaffected by varying Mn content. The significant temperature-dependent phase of the oscillation indicates that the topological state is tunable by the magnetism of Eu. Our observations suggest that the topological bands arising from Sb zigzag chains are sensitive to adjacent Eu magnetism but are relatively insensitive to more distant Mn atoms. Our experimental results are in good agreement with the DFT calculations, which show that Zn doping introduces only minor electron-type carriers at the Fermi level without substantially altering the Dirac bands. Our study will be helpful for understanding the mechanism of coupling between spatially separated magnetism and topological bands, offering insights that could be valuable for the design of materials with magnetism-tunable topological electronic structures.

We consider coupling of acoustic phonons to pseudospins consisting of electronic spins locked to orbital angular momentum states. We show that a Berry phase term arises from projection onto the time-dependent lowest-energy manifold. We examine consequences on the phonon modes, particularly mode splitting, induced chirality, and Berry curvatures under an external magnetic field which Zeeman couples to the pseudospin.

Thermal management challenges arise from interfacial thermal resistance as modern semiconductors are miniatured to nanoscale. Authors of previous studies have found that graded mass distribution in the interface can maximumly enhance the interfacial thermal conductance (ITC) of crystalline interface; however, whether this strategy is effective for amorphous interface is less explored. In this paper, a graded mass distribution in the amorphous interface between crystalline Si and crystalline Ge is optimized to increase ITC by the extended atomistic Green's function method. The results show that atomic mass of 26 amu for one type of atomic mass and 24 and 31 amu for two types of atomic mass in the amorphous interface can maximumly increase ITC. Therefore, the strategy of graded mass distribution is still effective when only considering the atoms in the amorphous interface. In addition, applying the value of the smaller atomic mass of the two contacts to the amorphous interface can largely enhance interface thermal conductance, which is only 0.9% smaller than the maximum value. Further analyses show that atomic mass of 26 amu can increase the phonon modal transmission at large frequency $(>2\mathrm{THz})$ for most phonons, and the phonon spectral transmissions are almost the same at low frequency $(<2\mathrm{THz})$ for different distributions of atomic mass in the amorphous interface in this paper. The findings in this paper are expected to be valuable for optimizing ITC of amorphous interfaces for semiconductor devices.

This paper focuses on investigating high-order harmonic generation (HHG) in graphene quantum dots (GQDs) under intense near-infrared laser fields. To model the GQD and its interaction with the laser field, we utilize a mean-field approach. Our analysis of the HHG power spectrum reveals fine structures and a noticeable enhancement in cutoff harmonics due to the long-range correlations. We also demonstrate the essential role of Coulomb interaction in determining of harmonic intensities and cutoff position. Unlike atomic HHG, where the cutoff energy is proportional to the pump wave intensity, in GQDs the cutoff energy scales with the square root of the field strength amplitude. A detailed time-frequency analysis of the entire range of the HHG spectrum is presented using a wavelet transform. The analysis reveals intricate details of the spectral and temporal fine structures of HHG, offering insights into the various HHG mechanisms in GQDs.

Using the crystalline lattice to manipulate magnetic ordering represents an intriguing direction of future research, particularly when attempting to modify the rather robust magnetization of an antiferromagnet (AFM). Here, we study how magnetization can be all-optically rotated in the canted AFM iron borate, utilizing mid- to far-infrared ultrashort light pulses. We discover that this excitation gives rise to a peculiar pattern of metastable magnetic domains with a tunable symmetry, which can be qualitatively understood by considering how light-induced radial strain interacts with the Néel vector. Our results reveal how optically induced strain can be used to spatially modify the magnetic order parameter of an AFM, which could have important applications in future AFM-based data-storage technologies.

We report terahertz spectroscopic measurements of quantum spin dynamics in the spin-1/2 honeycomb magnet ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$ as a function of applied magnetic field with different terahertz polarizations. Distinct field dependencies of the resolved spin dynamics are identified in three regimes, which are separated by two critical fields at $B_{c1}\approx 7$ and $B_{c2}\approx 10$ T. A polarization-selective continuum is observed in the intermediate phase, featuring spin fluctuations of a proximate quantum spin liquid.

We study the effect of quantum geometry on the many-body ground state of one-dimensional interacting bosonic systems. We find that the Drude weight is given by the sum of the kinetic energy and a term proportional to the many-body quantum metric of the ground state. Notably, the many-body quantum metric determines the upper bound of the Drude weight. We validate our results on the Creutz ladder, a flat-band model, using exact diagonalization at half and unit densities. Our work sheds light on the importance of the many-body quantum geometry in one-dimensional interacting bosonic systems.

We report on experimental observation of next-nearest-neighbor coupling between ballistically expanding spinor exciton-polariton condensates in a planar semiconductor microcavity. All-optical control over the coupling strength between neighboring condensates is demonstrated through distance-periodic pseudospin screening of their ballistic particle outflow due to the inherent splitting of the planar cavity transverse-electric and transverse-magnetic modes. By screening the nearest-neighbor coupling we overcome the conventional spatial coupling hierarchy between condensates. This offers a promising route toward creating unconventional nonplanar many-body Hamiltonians using networks of ballistically expanding spinor exciton-polariton condensates.

Measurements performed on quantum systems are too specific. Unlike their classical counterparts, quantum measurements can be invasive and destroy the state of interest. Besides, quantumness limits the accuracy of measurements performed on quantum systems. Uncertainty relations define the universal accuracy limit of the quantum measurements. Relatively recently, it was discovered that quantum correlations and quantum memory might reduce the uncertainty of quantum measurements. In this paper, we study two different types of measurements performed on the topological system. Namely, we discuss measurements performed on the spin operators and measurements performed on the canonical pair of operators: momentum and coordinate. We quantify the spin operator's measurements through the entropic measures of uncertainty and exploit the concept of quantum memory. In contrast, for the momentum and coordinate operators, we exploit the improved uncertainty relations. We discover that quantum memory reduces the uncertainties of spin measurements. On the other hand, we prove that the uncertainties in the measurements of the coordinate and momentum operators depend on the value of the momentum and are substantially enhanced at small distances between itinerant and localized electrons (the large-momentum limit). We note that the topological nature of the system leads to the spin-momentum locking. The momentum of the electron depends on the spin, and vice versa. Therefore we suggest an indirect measurement scheme for the momentum and coordinate operators through the spin operator. Due to the factor of quantum memory, such indirect measurements in topological insulators have smaller uncertainties than direct measurements.

Zero thermal expansion (ZTE) is a rare phenomenon of great importance in the field of materials design. $A{\mathrm{Zr}}_2{\left(\mathrm{P}{\mathrm{O}}_4\right)}_3$ $(A=\mathrm{Na},\mathrm{K},\mathrm{Rb},\mathrm{Cs})$ exhibit near-zero thermal expansion. In this work, we perform first principles calculations in $A{\mathrm{Zr}}_2{\left(\mathrm{P}{\mathrm{O}}_4\right)}_3$ $(A=\mathrm{Na},\mathrm{K},\mathrm{Rb},\mathrm{Cs})$ and ${\mathrm{Zr}}_2{\left(\mathrm{P}{\mathrm{O}}_4\right)}_3$ compounds to elucidate the effects of $A$ cations on the thermal expansion behavior. Structural and vibrational analysis shows that the near-zero thermal expansion is strongly related to the dynamics of the “lantern” units of ${[\mathrm{Zr}}_2{\left(\mathrm{P}{\mathrm{O}}_4\right)}_3$], where the ${\mathrm{ZrO}}_6$ and ${\mathrm{PO}}_4$ polyhedra are rigid. The calculated Grüneisen parameters reveal that different $A$-site alkali metal atoms heavily affect the phonon modes of $A$ atoms and the rotation of ${\mathrm{ZrO}}_6$ and ${\mathrm{PO}}_4$ polyhedra, as well as the acoustic phonon modes, thus resulting in a different thermal expansion behavior of $A{\mathrm{Zr}}_2{\left(\mathrm{P}{\mathrm{O}}_4\right)}_3$ $(A=\mathrm{Na},\mathrm{K},\mathrm{Rb},\mathrm{Cs})$. The absence of $A$ atoms in ${\mathrm{Zr}}_2{\left(\mathrm{P}{\mathrm{O}}_4\right)}_3$ facilitates the structural flexibility and therefore the occurrence of a stronger negative thermal expansion. This work provides insights into the modulation of thermal expansion of these ${\mathrm{NaZr}}_2{\left(\mathrm{P}{\mathrm{O}}_4\right)}_3$-type compounds.

We study the far-from-equilibrium dynamics of isolated two-dimensional Heisenberg antiferromagnets. We consider spin-spiral initial conditions which imprint a position-dependent staggered magnetization (or Neel order) in the two-dimensional lattice. Remarkably, we find a long-lived prethermal regime characterized by self-similar behavior of staggered magnetization fluctuations, although the system has no long-range order at finite energy and the staggered magnetization does not couple to conserved charges. By exploiting the separation of length scales introduced by the initial conditions, we derive an analytical model that allows us to compute the spatial-temporal scaling exponents and power-law distribution of the staggered magnetization fluctuations, and find excellent agreement with numerical simulations using phase-space methods. The scaling exponents are insensitive to details of the initial condition, in particular, no fine tuning of energy is required to trigger the self-similar scaling regime. Compared with recent results on far-from-equilibrium universality on the Heisenberg ferromagnet, we find quantitatively distinct spatial-temporal scaling exponents, therefore suggesting that the Heisenberg model can host different universal regimes depending on the initial conditions. Our predictions are relevant to ultracold-atom simulators of Heisenberg magnets and driven antiferromagnetic insulators.

The TiSiCO-family monolayers have recently been attracting significant attention due to their unique valley-layer coupling (VLC). In this work, we present a minimal, four-band tight-binding (TB) model to capture the low-energy physics of the TiSiCO-family monolayers $Z_{2}Y{\mathrm{CO}}_2$ $(Z=\text{Ti}, \mathrm{Zr}, \mathrm{Hf}; Y=\text{Si}, \mathrm{Ge})$ with strong VLC. These monolayers comprise two $Z$ atom layers separated by approximately 4 Å in the out-of-plane direction. Around each valley $(X \mathrm{or} X^{\prime })$, the conduction and valence bands are mainly dominated by the $A_1\left\{d_{z^2(x^2-y^2)}\right\}$ and $B_2\left\{d_{yz}\right\}$ orbitals of the top $Z$ atoms, and the $A_1\left\{d_{z^2(x^2-y^2)}\right\}$ and $B_1\left\{d_{xz}\right\}$ orbitals of the bottom $Z$ atoms. Using these four states as a basis, we construct a symmetry-allowed TB model. Through parameter fitting from first-principles calculations, the four-band TB model not only reproduces the electronic band structure, but also captures the strong VLC, high-order topology, and valley-contrasting linear dichroism of the monolayers. Furthermore, the TB model reveals that these monolayers may exhibit various intriguing topological phases under electric fields and biaxial strains. Hence, the TB model established here can serve as the starting point for future research exploring the physics related to VLC and the $Z_{2}Y{\mathrm{CO}}_2$ monolayers.

We present a temperature-extrapolation technique for self-consistent many-body methods, which provides a causal starting point for converging to a solution at a target temperature. The technique employs the Carathéodory formalism for interpolating causal matrix-valued functions and is applicable to various many-body methods, including dynamical mean-field theory, its cluster extensions, and self-consistent perturbative methods such as the self-consistent GW approximation. We show results that demonstrate that this technique can efficiently simulate heating and cooling hysteresis at a first-order phase transition, as well as accelerate convergence.

We study a system composed of two quantum dots connected in series between two leads at different temperatures, in the limit of large intratomic repulsion. Using the noncrossing approximation, we calculate the spectral densities at both dots ${\rho }_i\left(\omega \right)$, the thermal and thermoelectric responses, thermopower, and figure of merit in different regimes. The interatomic repulsion leads to finite heat transport even if the hopping between the dots $t=0$. The thermopower can be very large compared to single-dot systems in several regimes. The changes in sign of the thermoelectric current can be understood from the position and magnitude of the Kondo and charge-transfer peaks in ${\rho }_i\left(\omega \right)$. The figure of merit can reach values near 0.7. The violation of the Wiedemann-Franz law is much more significant than in previously studied nanoscopic systems. An analysis of the widths of ${\rho }_i\left(\omega \right)$ indicates that the dots are at effective temperatures $T_i$ intermediate between those of the two leads, which tend to be the same for large $t$.

We show that a superlattice potential can be employed to engineer topology in massive Dirac fermions in systems such as bilayer graphene, moiré graphene-boron nitride, and transition-metal dichalcogenide (TMD) monolayers and bilayers. We use symmetry analysis to analyze band inversions to determine the Chern number $\mathcal{C}$ for the valence band as a function of tunable potential parameters for a class of $C_4$ and $C_3$ symmetric potentials. We present a method to engineer Chern number $\mathcal{C}=2$ for the valence band and show that the applied potential at minimum must have a scalar together with a nonscalar periodic part. We discover that certain forms of the superlattice potential, which may be difficult to realize in naturally occurring moiré patterns, allow for the possibility of nontrivial topological transitions. These forms may be achievable using an external superlattice potential that can be created using contemporary experimental techniques. Our paper paves the way to realize the quantum spin Hall effect (QSHE), quantum anomalous Hall effect (QAHE), and even exotic non-Abelian anyons in the fractional quantum Hall effect (FQHE).

Chiral metasurfaces, with appealing properties for studying light-matter interactions at the nanoscale, have emerged as a promising platform for the realization of chiral optical responses, thereby showing advantages in chirality-related applications. The conventional approaches primarily concentrate on circular dichroism and the high $Q$ factor of the chiral resonances, while little attention has been paid to the aspects of flexibility and controllability in the modulation of optical chirality, further inhibiting the implementation of tunable and multifunctional chiral metadevices. Here, we employ a planar chiral silicon metasurface governed by bound states in the continuum (BICs) to unravel steerable chiral optical responses. In particular, the BIC-based intrinsic and extrinsic planar chiralities can be precisely steered by breaking the in-plane symmetry and the illumination symmetry, respectively. Moreover, a hybrid $\mathrm{Si}\text{−}{\mathrm{VO}}_2$ metasurface, manifested by the chiral coupled-mode theory, showcases the feasibility of actively tuning the dissipative loss while maintaining chiral quasi-BICs, then yielding desired loss-steered optical chirality. Our results provide alternative insights into tunable optical chirality and pave the way for advancements in chiroptical applications.

We consider thermo-optic bistability induced by a high-quality defect mode in the square array of dielectric rods. It is demonstrated that the scattering problem with an account of the variation of the dielectric constant by heating can be solved with the $T$-matrix method by introducing an explicit dependence of the permittivity of the defect rod on temperature. We found that the bistability occurs at low intensities of the incident $\text{wave}\approx 0.01\mathrm{mW}/\mu {\mathrm{m}}^2$ in a square array of $7\times 7$ silicon rods with a defect rod in the middle.

Bound state in the continuum (BIC) in all-dielectric metasurfaces can strongly enhance light-matter interactions in mid-infrared range, owing to their extreme field confinement with low optical losses. The excitation of BIC thus bear potential for vibrational strong coupling (VSC) with molecules, which has rarely been studied so far. Here, we combine poly (methyl methacrylate) (PMMA) molecules with a simple all-dielectric metasurface, demonstrating the VSC between symmetry-protected BIC modes and PMMA molecular vibrations with a flexible tuning of the coupling strength. We demonstrate the strong dependence of the coupling strength on the $Q$ factor of the quasi-BIC (QBIC) mode and achieve a large Rabi splitting up to 4.45 meV (67 ${\text{cm}}^{-1}$), which is the maximum value reported so far in BIC-based dielectric nanostructures. A full-quantum model is utilized to fully describe the coupling dynamics of the strongly interacting system, revealing the ultrafast energy transfer between the QBIC and variational state with long coherence time. The proposed hybrid system provides a promising platform both for the fundamental study on light-matter interactions and for potential applications in high-compact nanophotonic devices in mid-infrared frequencies.