Motivated by recently reported magnetic-field-induced topological phases in ultracold atoms and correlated Moiré materials, we investigate topological phase transitions in a minimal model consisting of interacting spinless fermions described by the Hofstadter model with Coulomb interaction on a square lattice. For interacting lattice Hamiltonians in the presence of a commensurate magnetic flux it has been demonstrated that the quantized Hall conductivity is constrained by a Lieb-Schultz-Mattis (LSM) type theorem due to magnetic translation symmetry. In this work, we revisit the validity of the theorem for such models and establish that a topological phase transition from a topological to a trivial insulating phase can be realized but must be accompanied by spontaneous magnetic translation symmetry breaking caused by charge ordering of the spinless fermions. To support our findings, the topological phase diagram for varying interaction strength is mapped out numerically with exact diagonalization for different flux quantum ratios and band fillings using symmetry indicators. We discuss our results in the context of the LSM-type theorem.

Fluxons in a superconducting loop can be coherently coupled by quantum phase slips occurring at a weak link such as a Josephson junction. If Cooper pair tunneling at the junction occurs through a resonant level, then $2\pi$ quantum phase slips are suppressed, and fluxons are predominantly coupled by $4\pi$ quantum phase slips. We analyze this scenario by computing the coupling between fluxons as the level is brought into resonance with the superconducting condensate. The results indicate that the $4\pi$-dominated regime can be observed directly in the transition spectrum for circuit parameters typical of a fluxonium qubit. We also show that if the inductive energy of the loop is much smaller than the plasma frequency of the junction, then the low-energy Hamiltonian of the circuit is dual to that of a topological superconducting island. These findings can inform experiments on bifluxon qubits as well as the design of novel types of protected qubits.

Network structures by semiconductor nanowires hold great promise for advanced quantum devices, especially for applications in topological quantum computing. In this paper, we created networks of PbTe nanowires arranged in loop configurations. Using shadow-wall epitaxy, we defined superconducting quantum interference devices (SQUIDs) using the superconductor Pb. These SQUIDs exhibit oscillations in supercurrent upon the scanning of a magnetic field. Most of the oscillations can be fitted assuming a sinusoidal current-phase relation for each Josephson junction. Under certain conditions, the oscillations are found to be skewed, suggesting a possible deviation from a sinusoidal behavior. Our results highlight the potential of PbTe nanowires for building complex quantum devices in the form of networks.

Recently, higher-order four-phonon scattering has been revealed significant in the phonon thermal transport in crystalline materials with wide phononic band gap or with horizontal mirror symmetry. In this work, by utilizing first-principles calculations combined with phonon Boltzmann transport theory, we explore the four-phonon scattering and its effect on the lattice thermal conductivity ${\kappa }_L$ of two-dimensional (2D) semiconductor SnC—that possesses both wide phononic gap and mirror symmetry. Our calculations show that four-phonon scattering significantly reduces the intrinsic ${\kappa }_L$ of SnC from 43 to 19 W/(m K) at room temperature, by $54\%$. This reduction is found to come mainly from the out-of-plane, flexural acoustic (ZA) phonons, whose lifetimes are dominated by four-phonon scattering over three-phonon scattering due to the mirror symmetry-induced selection rules. Moreover, we predict based on four-phonon theory that applying $2\%$ tensile strain increases the ${\kappa }_L$ of SnC by a factor of five at room temperature. Through analyzing the modal contribution to ${\kappa }_L$, we attribute this huge improvement of ${\kappa }_L$ primarily to the in-plane transverse acoustic (TA) phonons, whose scattering rates are extremely sensitive to strain. This fundamentally originates from the quadratic ZA phonon dispersion, which is linearized by the tensile strain in the long-wavelength limit, resulting in severe suppression of three-phonon and four-phonon processes involving ZA modes. Specifically, the linearized ZA branch causes the three-phonon scattering rate of TA modes to decrease rapidly from the original constant in the long-wavelength limit, and the corresponding four-phonon counterparts also decrease significantly. These findings highlight the importance of strain in modulating phonon-phonon scattering and thermal transport in 2D planar materials.

Sulfur vacancies in ${\mathrm{MoS}}_2$ on Au(111) have been shown to be negatively charged as reflected by a Kondo resonance. Here, we use scanning tunneling microscopy to show that these vacancies serve as anchoring sites for thiol-based molecules $\left({\mathrm{CF}}_3\text{−}3\mathrm{P}\text{−}\mathrm{SH}\right)$ with two distinct reaction products, one of them showing a Kondo resonance. Based on comparisons with density-functional theory (DFT) calculations, including a random structure search and computation of energies and electronic properties at a hybrid exchange-correlation functional level, we conclude that both anchored molecules are charge neutral. We propose that one of them is an anchored intact ${\mathrm{CF}}_3\text{−}3\mathrm{P}\text{−}\mathrm{SH}$ molecule while the other one is the result of catalytically activated dehydrogenation to ${\mathrm{CF}}_3\text{−}3\mathrm{P}\text{−}\mathrm{S}$ with subsequent anchoring. Our investigations highlight a perspective of functionalizing defects with thiol-terminated molecules that can be equipped with additional functional groups, such as charge donor or acceptor moieties, switching units, or magnetic centers.

The selective confinement of light holes (LHs) in a tensile-strained germanium (Ge) quantum well is studied by mapping the electronic structure of ${\mathrm{Ge}}_{1-x}{\mathrm{Sn}}_x/\mathrm{Ge}/{\mathrm{Ge}}_{1-x}{\mathrm{Sn}}_x$ heterostructures as a function of Sn content, residual strain, and Ge well thickness. It is shown that above $12\text{at.}\%$ Sn and below $0.4\%$ residual compressive strain in the barriers, the tensile strain in Ge becomes sufficiently large to yield a valence band edge with LH-like character, thus forming a quasi two-dimensional LH gas in Ge. The LH ground state has a larger in-plane effective mass than that of heavy holes (HHs) in ${\mathrm{Si}}_{1-y}{\mathrm{Ge}}_y/\mathrm{Ge}/{\mathrm{Si}}_{1-y}{\mathrm{Ge}}_y$ quantum wells. Moreover, LHs in optimal ${\mathrm{Ge}}_{1-x}{\mathrm{Sn}}_x/\mathrm{Ge}/{\mathrm{Ge}}_{1-x}{\mathrm{Sn}}_x$ heterostructures are found to exhibit a strong $g$-tensor anisotropy, with the in-plane component one order of magnitude larger than that of HHs in typical planar systems. Two of three structure-inversion-asymmetry Rashba parameters, both of which are critical in electric-dipole-spin-resonance experiments, are effectively 10 times the size of the cubic Rashba parameter in HH quantum wells. In the regime of LH selective confinement, every layer of the heterostructure is of direct bandgap, which can be relevant for efficient optical photon-spin qubit interfaces. This work discusses the broad landscape of the characteristics of LH spin confined in Ge to guide the design and implementation of LH spin-based devices.

Information theoretic measures have helped to sharpen our understanding of many-body quantum states. As perhaps the most well-known example, the entanglement entropy (or more generally, the bipartite mutual information) has become a powerful tool for characterizing the dynamical growth of quantum correlations. By contrast, although computable, the bipartite mutual information (MI) is almost never explored in classical many particle systems; this owes in part to the fact that computing the MI requires keeping track of the evolution of the full probability distribution, a feat which is rarely done (or thought to be needed) in classical many-body simulations. Here, we utilize the MI to analyze the spreading of information in 1D elementary cellular automata (CA). Broadly speaking, we find that the behavior of the MI in these dynamical systems exhibits a few different types of scaling that roughly correspond to known CA universality classes. Of particular note is that we observe a set of automata for which the MI converges parametrically slowly to its thermodynamic value. We develop a microscopic understanding of this behavior by analyzing a two-species model of annihilating particles moving in opposite directions. Our work suggests the possibility that information theoretic tools such as the MI might enable a more fine-grained characterization of classical many-body states and dynamics.

Dynamical formation of doublons or on-site repulsively bound pairs of particles on a lattice is a highly nontrivial phenomenon. In this work, we show the signatures of doublon formation in a quantum computer by simulating the continuous time quantum walk in the framework of the one-dimensional extended Fermi-Hubbard model. By considering two up-component and one down-component particles initially created at the three neighboring sites at the middle of the lattice and allowing intra- (inter-)component nearest-neighbor (on-site) interactions, we show the formation of a stable on-site doublon in the quantum walk. The probability of such doublon formation is more (less) if the hopping strength of the down particle is weaker (stronger) compared to the up particle. On the contrary, for an initial doublon along with a free up particle, the stability of the doublon is more prominent than the doublon dissociation in the dynamics irrespective of the hopping asymmetry between the two components. We first numerically obtain the signatures of the stable doublon formation in the dynamics and then observe them using noisy intermediate-scale quantum (NISQ) devices.

Classical spin liquids (CSL) lack long-range magnetic order and are characterized by an extensive ground-state degeneracy. We propose a classification scheme of CSLs based on the structure of the flat bands of their Hamiltonians. Depending on absence or presence of the gap from the flat band, the CSL are classified as algebraic or fragile topological, respectively. Each category is further classified: the algebraic case by the nature of the emergent Gauss's law at the gap-closing point(s), and the fragile topological case by the homotopy of the eigenvector winding around the Brillouin zone. Previously identified models of CSLs fit snugly into our scheme, on a landscape where algebraic CSLs are located at transitions between fragile topological ones. It also allows us to present new families of models illustrating this landscape, which hosts both fragile topological and algebraic CSLs, as well as transitions between them.

Nonlinear optics has regained attention in recent years, especially in the context of optospintronics and topological materials. Nonlinear responses involved in various degrees of freedom manifest their intricacy more pronounced than linear responses. However, for a certain class of nonlinear responses, a connection can be established with linear-response coefficients, enabling the exploration of diverse nonlinear-response functionality in terms of the linear-response counterpart. Our study quantum mechanically elucidates the relation between such nonlinear and linear responses we call the Pitaevskii relation and identifies the condition for the relation to hold. Following the obtained general formulation, we systematically identify the Pitaevskii relations such as the inverse magnetoelectric effect and inverse natural optical activity unique to systems manifesting the space-inversion-symmetry breaking. These results provide a systematic understanding of intricate nonlinear responses and may offer further implications to ultrafast spintronics.

We explore the possibility to control the superconducting transition temperature at optimal hole doping $T_c^{\mathrm{opt}}$ in cuprates by tuning the chemical formula (CF). $T_c^{\mathrm{opt}}$ can be theoretically predicted from the parameters of the ab initio low-energy effective Hamiltonian with one antibonding (AB) $\mathrm{Cu}3d_{x^2-y^2}/\mathrm{O}2p_{\sigma }$ orbital per Cu atom in the ${\mathrm{CuO}}_2$ plane, notably the nearest-neighbor hopping amplitude $|t_1|$ and the ratio $u=U/|t_1|$, where $U$ is the onsite effective Coulomb repulsion. However, the CF dependence of $|t_1|$ and $u$ is a highly nontrivial question. In this paper, we propose the universal dependence of $|t_1|$ and $u$ on the CF and structural features in hole doped cuprates with a single ${\mathrm{CuO}}_2$ layer sandwiched between block layers. To do so, we perform extensive ab initio calculations of $|t_1|$ and $u$ and analyze the results by employing a machine-learning method called hierarchical dependence extraction (HDE). The main results are (a) $|t_1|$ has a main-order dependence on the radii $R_{\mathrm{X}}$ and $R_{\mathrm{A}}$ of the apical anion X and cation A in the block layer. ($|t_1|$ increases when $R_{\mathrm{X}}$ or $R_{\mathrm{A}}$ decreases.) (b) $u$ has a main-order dependence on the ionic charge $Z_{\mathrm{X}}$ of X and the hole doping $\delta$ of the AB orbital. ($u$ decreases when $|Z_{\mathrm{X}}|$ increases or $\delta$ increases.) We elucidate and discuss the microscopic mechanism of items (a) and (b). We demonstrate the predictive power of the HDE by showing the consistency between items (a) and (b) and results from previous works. The present results provide a basis for optimizing superconducting properties in cuprates and possibly akin materials. Also, the HDE method offers a general platform to identify dependencies between physical quantities.

Recently, the discovery of superconductivity in Ruddlesden-Popper (RP) ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$ under pressure has further expanded the realm of nickelate-based superconductor family. In this paper, we perform a first-principles study of ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$ for both the $P{2}_1/a$ phase at ambient pressure and $I4/mmm$ phase at high pressure, with $U=0$, 3.5 eV. Our results confirm the characteristic upward shift of a $\mathrm{Ni}\text{−}{d}_{z^2}$ bonding band under pressure. Moreover, our analysis of electronic spectrum and orbital occupancy unveil the dynamic mechanism of electronic reconstructions under pressure, embedded in a critical dual effect. Based on our results, we further propose a trilayer two-orbital model by performing Wannier downfolding on $\mathrm{Ni}\text{−}{e}_g$ orbitals. Our model reveals four Fermi surface sheets with $\alpha ,\beta ,{\beta }^{\prime },\gamma$ pockets, bearing resemblance to that of bilayer ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$. According to the model, our calculated spin susceptibility under random phase approximation shows that the $d_{x^2-y^2}$ orbital is also important for the magnetic fluctuation in the RP series. Finally, a high energy 16-orbital model with direct $dp,pp$ hoppings is proposed, which implies that ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$ also lies in the charge-transfer picture within the Zaanen-Sawatzky-Allen scheme. Our exposition of electronic reconstructions and multiorbital models shed light on theoretical electronic correlation study and experimental exploration of lower pressure superconductors in the RP series.

We propose a protocol based only on local conductance measurements for distinguishing trivial from topological phases in realistic three-terminal superconducting nanowires coupled to normal leads, capable of hosting Majorana zero modes (MZMs). By using Green's functions and the scattering matrix approach, we calculate the conductance matrix and the local density of states (LDOS) as functions of the asymmetry in the couplings to the left $\left({\mathrm{\Gamma }}_L\right)$ and right $\left({\mathrm{\Gamma }}_R\right)$ leads. In the trivial phase, we find that the zero-bias local conductances are distinctively affected by variations in ${\mathrm{\Gamma }}_R$ (for fixed ${\mathrm{\Gamma }}_L$): while $G_{LL}$ is mostly constant, $G_{RR}$ decays exponentially as ${\mathrm{\Gamma }}_R$ is decreased. In the topological phase, surprisingly, $G_{LL}$ and $G_{RR}$ are both suppressed with $G_{LL}\sim G_{RR}$. This nonlocal suppression of $G_{LL}$ with ${\mathrm{\Gamma }}_R$ scales with the MZM hybridization energy ${\varepsilon }_m$ and arises from the emergence of a dip in the LDOS near zero energy at the left end of the wire, which affects the local Andreev reflection. We further exploit this nonlocality of the local Andreev processes and the gate-controlled suppression of the LDOS by proposing a Majorana-based transistor. Our results hold for zero and low electron temperatures $T<20\mathrm{mK}$. For $T=30,40\mathrm{mK}$, $G_{LL}$ and $G_{RR}$ become less correlated. As an additional nonlocal fingerprint of the topological phase at higher $T^{\prime }\mathrm{s}$, we predict modulations in our asymmetric conductance deviation $\delta G_{LL}^{\mathrm{asym}}=G_{LL}^{{\mathrm{\Gamma }}_R={\mathrm{\Gamma }}_L}-G_{LL}^{{\mathrm{\Gamma }}_R\ll {\mathrm{\Gamma }}_L}$ that remains commensurate with the Majorana oscillations in ${\varepsilon }_m$ over the range $30<T<150\mathrm{mK}$.

Local counterdiabatic driving (CD) provides a feasible approach for realizing approximate adiabatic or reversible processes like quantum state preparation using only local controls and without demanding excessively long protocol times. However, in many instances getting high accuracy of such CD protocols requires engineering very complicated new controls or pulse sequences. In this work, we describe a systematic method for altering the adiabatic path by adding extra local controls along which performance of local CD protocols is enhanced, both close to and far from the adiabatic limit. We also identify an iterative procedure to improve the performance of local counterdiabatic driving further without any knowledge of the quantum wave function. We then show that these methods provides dramatic improvement in the preparation of nontrivial Greenberger-Horne-Zeilinger ground states of several different spin systems with both short-range and long-range interactions.

We explore the contributions of adiabatic and nonadiabatic spin-transfer torques (STT) of a spin-polarized current to the thermally activated creep motion of domain walls in a thin (Ga,Mn)(As,P) film with perpendicular anisotropy. The nonadiabatic STT is found to compensate linearly an external magnetic field, with a slope compatible with a steady domain-wall internal structure. Close to the compensation, the adiabatic contribution is strongly enhanced and may both increase or reduce domain-wall velocity, which we associate to variations of creep pinning energy barrier with domain-wall internal structure. Far from compensation, the effects of adiabatic STT become negligible and so field and current driven domain-wall motion presents common universal behaviors described by the quenched Edwards Wilkinson universality class.

Both the Haldane spin chain and a topologically dimerized chain feature topologically protected edge states that are expected to be robust against some kind of noise. To elucidate whether it might be feasible to create such edge states in dimerized chains in a controlled manner in solid states environments, e.g., as spin chains on surfaces, as has already been successfully achieved with the Haldane chain, we investigate their robustness with respect to long-range coupling, anisotropies, and finite chain length. The theoretical investigation is based on an alternating Heisenberg spin chain with spin-$1/2$, which is investigated using exact diagonalization. We find that dimerized chains and Haldane chains have robustness against long-range coupling and anisotropies. In particular, dimerized spin chains are significantly more robust than Haldane chains.

We study the ground-state phase diagram of the half-filled extended Haldane-Hubbard model on the honeycomb lattice with sublattice-dependent on-site repulsion ($U_{\text{A/B}}$) using the exact diagonalization (ED) and mean-field (MF) methods. The resulting phase diagram shows that there is a topologically nontrivial phase with the Chern number $C=1$, emerging via the development of the imbalance between $U_{\text{A}}$ and $U_{\text{B}}$. In this phase, the antiferromagnetic correlations are observed in the ED calculation, in line with the finite antiferromagnetic order obtained by the MF method. The spontaneous symmetry breaking of SU(2) spin rotation in the phase is also identified in the MF level. Distinct from previous studies in which the exotic $C=1$ phase relies on the interplay between sublattice-dependent potentials and electronic interactions, our paper presents an alternative way by solely tuning the on-site interactions.

The difference in the thermal vibration of oxygen in the cubic perovskites $\mathrm{PbTi}{\mathrm{O}}_3$ and $\mathrm{SrTi}{\mathrm{O}}_3$ was explored by associating it with their phase transitions at low temperatures. The thermal vibration factor for oxygen in cubic $\mathrm{PbTi}{\mathrm{O}}_3$ was estimated by employing an indirect approach that combines experimental Ti $L_{2,3}$-edge electron energy-loss spectroscopy and crystal field multiplet calculations incorporating atomic vibrations. The results uncovered relatively isotropic vibration behavior in $\mathrm{PbTi}{\mathrm{O}}_3$ and strong anisotropy in $\mathrm{SrTi}{\mathrm{O}}_3$, despite their identical lattice parameters at different temperatures. Specifically, similar vibration factors along the Ti-O bond were estimated for both materials, whereas the amplitude of oxygen vibration in the $A$-O plane for $\mathrm{PbTi}{\mathrm{O}}_3$ was significantly smaller than that for $\mathrm{SrTi}{\mathrm{O}}_3$. This larger oxygen vibration in the $A$-O plane of $\mathrm{SrTi}{\mathrm{O}}_3$ can be attributed to the existence of the rotational phonon mode, contributing to a $\mathrm{Ti}{\mathrm{O}}_6$ octahedron rotational phase transition at low temperature due to softening of the $R_{25}$ mode. Therefore, the smaller vibration amplitude for oxygen in $\mathrm{PbTi}{\mathrm{O}}_3$ could possibly be attributed to the intrinsic small rotational phonon mode, leading to a zone-center displacement-type phase transition induced by a softened ${\mathrm{\Gamma }}_{15}$ mode. Further, the charge density map obtained by density functional theory calculation proposes a broader valence electron distribution for $\mathrm{P}{\mathrm{b}}^{2+}$ compared to $\mathrm{S}{\mathrm{r}}^{2+}$ and greater electron repulsion between Pb and O, potentially contributing to smaller oxygen vibration in the Pb-O plane of $\mathrm{PbTi}{\mathrm{O}}_3$. This research provides valuable insights into the role of vibrational behavior in phase transition mechanisms, and offers the potential to predict the phase transition types for perovskites in the high-temperature cubic paraelectric phase.

Exciton binding energies are fundamental to understanding excitonic materials, especially those with the potential for ground-state exciton condensation. However, these energies are typically defined with significant limitations in their consideration of electron correlation. Here we present a variational theory for computing exciton binding energies in ground-state exciton condensates in which we define the binding as the energy difference between fully correlated many-electron systems with $M$ and $M-1$ excitons, respectively. The $(M-1)$ system is obtained by adding a constraint to the ground-state energy minimization that removes an exciton while allowing all other electronic degrees of freedom to relax. We perform the energy minimizations with variational calculations of the two-electron reduced density matrix (2-RDM) in which the additional constraint is treated along with the $N$-representability conditions—necessary constraints for the 2-RDM to represent an $N$-electron system—by semidefinite programming. We demonstrate the theory first in the Lipkin model and then in several stacked organic and inorganic systems that exhibit the beginnings of exciton condensation. We find that in the Lipkin model the traditional exciton binding model overbinds relative to the constrained approach. This has significant implications for theoretical characterizations of exciton condensates which rely on exciton binding energy to make predictions regarding condensate stability and critical temperatures. This correlated approach to defining and computing exciton binding energies may therefore have important applications for understanding the relationship between binding and condensation, especially for the BCS-BEC crossover.