We study the quantum Newman-Moore model, or quantum triangular plaquette model (qTPM), in the presence of a longitudinal field (qTPMz). We present evidence that indicates that the ground state phase diagram of the qTPMz includes various frustrated phases breaking translational symmetries, dependent on the specific sequence of system sizes used to take the large-size limit. This phase diagram includes the known first-order phase transition of the qTPM, but also additional first-order transitions due to the frustrated phases. Using the average longitudinal magnetization as an order parameter, we analyze the magnetization plateaus that characterize the ground state phases, describe their degeneracies, and obtain the qTPMz phase diagram using classical transfer matrix and quantum matrix product state techniques. We identify a region of the parameter space, which can be effectively described by a Rydberg blockade model on the triangular lattice. At the same time, it can be reformulated as an effective lattice gauge theory but also a model of quantum trimers. In this same region, we provide a variational ground state wave function similar to a resonating valence bond solid state, which accurately describes the ground state wave function of the system. Lastly, we fail to find indications of a phase with ${\mathbb{Z}}_2$ topological order connecting the quantum paramagnetic and classical frustrated phases.

The square cupola antiferromagnet $\mathrm{Pb}\left(\mathrm{TiO}\right){\mathrm{Cu}}_4{\left({\mathrm{PO}}_4\right)}_4$ exhibits the intriguing magnetoelectric responses arising from the consecutive change in the magnetic quadrupolar-type configuration of magnetic moments under external magnetic fields higher than 15 T. To clarify the high-field magnetic structures in $\mathrm{Pb}\left(\mathrm{TiO}\right){\mathrm{Cu}}_4{\left({\mathrm{PO}}_4\right)}_4$, an NMR measurement was performed in pulsed fields up to 32.2 T significantly extending the field range accessible by superconducting magnets. The double-peak structure of NMR spectra emerging above 29 T applied along the [001] direction evidences the successive magnetic transitions. The field dependence of NMR spectra was analyzed on the basis of cluster mean-field theory, which allows us to propose possible magnetic structures for the high-field magnetic states.

We investigate the influence of in-plane tensile strain on the magnetic ground state and spin-orbit torque (SOT)-driven magnetization processes in $\mathrm{M}{\mathrm{n}}_3\mathrm{Sn}$ thin films using atomistic spin modeling. Our study reveals that strain acts as a critical tuning parameter, inducing a transition from the $E_{1g}\left(A_x\right)$ to the $E_{1g}\left(A_y\right)$ magnetic structure beyond a threshold strain corresponding to a reduction of the exchange interaction $\left|\delta \mathrm{J}\right|\approx 2\%$. This transition is significant as the $E_{1g}\left(A_y\right)$ state is expected to support a large anomalous Hall effect, enabling strain-controlled topological transport properties. Additionally, tensile strain breaks the symmetry between antiferromagnetic sublattices, leading to a piezomagnetically induced net magnetization that increases linearly with strain and is oriented perpendicular to the film plane. Under SOT excitation, $\mathrm{M}{\mathrm{n}}_3\mathrm{Sn}$ under strain exhibits sharp, deterministic switching of the cluster octupole moment with a reduced threshold current density, highlighting enhanced SOT efficiency. In contrast, the strain-free system shows intermediate chiral spin rotations during the switching of the octupole moment. Dynamic simulations further reveal current-density-dependent distinct precession modes, including a transient optical mode within a narrow current density range and ultrafast precessions reaching terahertz frequencies. These findings demonstrate the potential of strain engineering to tailor magnetic ground states and achieve low-energy, high-speed magnetization control in noncollinear antiferromagnets. The resulting functionalities offer promising avenues for scalable spintronic devices operating at terahertz frequencies.

The Heisenberg antiferromagnet on the maple-leaf lattice has recently gathered a great deal of attention. Competition between three nonequivalent bond interactions results in various ground-state quantum phases, with the exact dimer-product singlet ground state being among them. The thermodynamic properties of this model are much less understood. We used high-temperature expansion up to the 18th order to study the thermodynamics of the $S=1/2$ Heisenberg model on the uniform maple-leaf lattice with the ground state exhibiting a six-sublattice ${120}^{\circ }$ long-range magnetic order. Padé approximants allow us to get reliable results up to the temperatures of about $T\approx 0.4$. To study thermodynamics for arbitrary temperatures, we made the interpolation using the entropy method. Based on the analysis of close Padé approximants, we find ground-state energy $e_0=-0.53064...-0.53023$ in good agreement with numerical results. The specific heat $c\left(T\right)$ has a typical maximum at rather low temperatures $T\approx 0.379$ and the uniform susceptibility $\chi \left(T\right)$ at $T\approx 0.49$. We also estimate the value of $\chi \left(T\right)$ at zero temperature ${\chi }_0\approx 0.05...0.06$. The ground-state order manifests itself in the divergence of the so-called generalized Wilson ratio.

The Kitaev candidate material ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$ is proposed to be proximate to a quantum spin liquid state but a suitable spin model and the nature of its ground states are still under debate. Our high-frequency/high-field electron spin resonance spectroscopy studies of ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$ single crystals under in-plane and out-of-plane magnetic fields elucidate the ground state by investigating its low-energy spin wave excitations. Several excitation modes are observed in the low-field phase and in the phases induced by $B\parallel a^{*}$. In addition, the spectra exhibit a frequency-independent feature at the phase boundary connected to the putative quantum phase transition. For magnetic fields applied along the $c$ axis, the observation of three distinct spin wave modes in the antiferromagnetic (AFM) ground state reveals a previously unresolved splitting of the zero-field excitation gap into $\mathrm{\Delta }=211\mathrm{GHz}$ and ${\mathrm{\Delta }}_2=237\mathrm{GHz}$. The softening of one of these modes evidences a field-induced phase transition at $B_{\mathrm{c}1}=4.7\mathrm{T}$, which is corroborated by a clear anomaly in the isothermal magnetization. Spin wave calculations based on the extended Heisenberg-Kitaev model exclude a zigzag ground state of the AFM phase. A triple-$\mathbf{q}$ spin configuration correctly predicts two spin wave modes but fails to reproduce the softening mode. Our analysis shows that the triple-$\mathbf{q}$ ground state model of ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$ is incomplete and suggests the relevance of interlayer interactions.

The evolution of the role of lattice vibrations in the formation of the pseudogap state in strongly correlated electron systems has been investigated concerning changes in the electron-phonon coupling parameters and the concentration of doped charge carriers. We apply the polaronic version of the generalized tight-binding method to analyze the band structure of a realistic multiband two-dimensional model that incorporates the electron-lattice contributions of both Holstein and Peierls types. It has been demonstrated that the emergence of polaronic effects begins with the modulation of spectral function intensity. However, within a specific region of the phase diagram, a significant transformation of the electron band structure and pseudogap state occurs. It results from coherent polaron excitations that create a partially flat band near the Fermi level. This process leads to a change in the topology of the Fermi surface and the emergence of corresponding features in the density of states.

Nonlocal Coulomb interactions play a crucial role in stabilizing distinct electronic phases in kagome materials. In this work, we systematically investigate the effects of on-site ($U$) and intersite ($V$) Coulomb interactions on the electronic structure and stability of charge-density-wave (CDW) phases in the kagome metal ${\mathrm{KV}}_3{\mathrm{Sb}}_5$ using density functional theory ($\text{DFT}+U+V$) calculations. We demonstrate that $V$ promotes the formation and stability of CDW phases, whereas $U$ suppresses these phases, highlighting a fundamental competition between local and nonlocal Coulomb interactions. By directly comparing our theoretical results with angle-resolved photoemission spectroscopy (ARPES) data, we identify realistic values of $U$ and $V$ that accurately describe the electronic band structure of ${\mathrm{KV}}_3{\mathrm{Sb}}_5$. Our findings establish a detailed $U\text{−}V$ phase diagram for ${\mathrm{KV}}_3{\mathrm{Sb}}_5$, offering valuable insights into the correlated electronic states in kagome metals and serving as a foundation for future explorations of correlation-driven phenomena in related materials.

Utilizing the framework of matrix product states, we investigate gauging as a method for exploring quantum phases of matter. Specifically, we describe how symmetry-protected topological (SPT) phases and spontaneous symmetry breaking (SSB) phases in one-dimensional spin systems behave under twisted gauging, a generalization of the well-known gauging procedure for globally symmetric states. Compared to previous order parameter-based approaches, our analysis is not limited to the case of maximally noncommutative (MNC) phases, and we use our findings to propose a generalization of the Kennedy-Tasaki transformation to the non-MNC setting. A key result of our work is that gauging produces configurations characterized by a combination of MNC order and symmetry breaking, when applied to non-MNC SPT phases. More generally, we conjecture a precise correspondence between SSB and non-MNC SPT phases, possibly enabling the detection of such phases using local and string order parameters.

In recent years, density functional theory (DFT) for material design and discovery has gained significant interest. Traditional approximations with the DFT, like the local density approximation (LDA), tend to underestimate band gaps. On the other hand, the Heyd-Scuseria-Ernzerhof (HSE) method provides better accuracy for band gaps but at a high computational cost. In 2008, Ferreira et al. introduced the DFT-1/2 method, which improves band gap predictions at a computational cost similar to LDA. This method adjusts the valence band energy levels by applying Self-Interaction Correction at the local potential level. The extent of this correction is determined by a parameter called 'cutoff,' which must be self-consistently calculated. Although DFT-1/2 is computationally efficient, it requires extra effort in parameter tuning. Moreover, it may not accurately predict band gaps for certain materials, such as narrow-gap semiconductors. Variations like DFT-1/4 or shDFT-1/2 have been developed to address this issue, providing more accurate band gaps for these materials but reducing accuracy for others. Therefore, choosing the optimal method is essential and material-dependent. To overcome these empirical challenges, we introduce a novel parameter-free approach in the framework of DFT-1/2 (parameter-free DFT-1/2). Unlike the original DFT-1/2, which requires an additional self-consistent field (SCF) loop to determine the cutoff radius that maximizes the band gap, our proposed method calculates the cutoff radius directly from the crystal structure, thus eliminating the need for the extra SCF loop. We validated the performance of parameter-free DFT-1/2 by calculating key electronic properties such as band gaps, effective masses, ionization energies, and electron affinities. We also assessed defect levels in the charge transition states of a silicon point defect in silicon carbide (SiC) for the first time. The results demonstrate that parameter-free DFT-1/2 can reproduce spin density with accuracy comparable to HSE and that parameter-free DFT-1/2 is also effective for predicting charge transition levels in defects.

We study the transport properties of a quantum dot contacted to two superconducting reservoirs by means of the Keldysh field theory approach, showing how this technique allows us to straightforwardly recover previous results, resulting extremely effective in dealing with the quantum transport problem. In particular, we determine the direct current occurring at equilibrium and the electric and thermoelectric currents triggered when the system is driven out of equilibrium by a voltage or a temperature bias, also for a normal-quantum dot-superconductor junction. The main result of the work is the derivation of the full expression for the thermoelectric current in a superconductor-quantum dot-superconductor junction for any values of the temperature difference between the superconducting leads. We show that in the linear response regime, in addition to the Josephson current, a weakly phase-dependent thermoelectric contribution occurs, provided that electron-hole symmetry is broken. Far from linearity, instead, other contributions arise which lead to thermoelectric effects, dominant at weak coupling, also in the presence of particle-hole symmetry.

In two-dimensional ultrathin materials, lower dielectric screening enables stronger exciton binding, which plays a crucial role for large excitonic radiative lifetimes. In this work, we have investigated a polar monolayer of $\mathrm{Hf}{}_3{\mathrm{ZrS}}_8$ from the perspective of many-body perturbation theory and the Bethe-Salpeter equation (BSE) to determine the corresponding excited state properties, particularly the excitonic radiative lifetime. We have envisaged the impact of external biaxial compressive and tensile strain on the excitonic lifetime, optical absorption, and excitonic wave function in the monolayer, based on the $GW$-BSE formalism, while including relativistic spin-orbit coupling effect. The polar monolayer possesses strong binding energy of the first bright exciton within the quasiparticle band-gap range, while the excitonic radiative lifetime is determined in picoseconds. The optical band gap increases and decreases with tensile and compressive strain, respectively. We have obtained an excitonic radiative lifetime approximately three times larger than the pristine one under biaxial compressive strain. Our finding reveals that the $\mathrm{Hf}{}_3{\mathrm{ZrS}}_8$ monolayer under the influence of biaxial strain could be useful for miniaturized optoelectronic and photonic devices.

The search for Kitaev quantum spin liquids (Kitaev-QSLs) in real materials has mainly focused on $4d$- and $5d$-electron honeycomb systems. A recent experimental study on the $4f^5$ honeycomb iodide ${\text{SmI}}_3$ reported the absence of long-range magnetic order down to $0.1\text{K}$, suggesting a possible Kitaev-QSL phase. Motivated by the interplay between the complex exchange processes inherent to the $4f^5$ multielectron configuration and the strong spin-orbit coupling (SOC) of the iodine ligands, we systematically investigate the effective exchange interactions in ${\text{SmI}}_3$ using the strong coupling expansion method. Our findings reveal that bond-dependent SOCs (bond-SOCs), extracted from relativistic density functional theory calculations, significantly enhance the antiferromagnetic (AFM) Kitaev interaction, driving the system close to the AFM Kitaev point. A microscopic analysis based on the Slater-Koster approach further indicates that the strong SOC of the iodine ligands (ligand-SOC) is the origin of bond-SOCs and plays a pivotal role in mediating the superexchange processes. Additionally, we identify a spin-flop transition induced by the bond-SOCs, where the enhanced AFM Kitaev interactions shift the AFM order from the out-of-plane $[1,1,1]$ direction to an in-plane orientation, breaking the $C_3$ rotational symmetry. Linear spin-wave theory further predicts the emergence of gapless modes following the spin-flop transition, indicating enhanced fluctuations and increased instability near the AFM Kitaev point. Our results highlight the crucial role of strong ligand-SOC in stabilizing the dominant AFM Kitaev interactions in ${\text{SmI}}_3$ and provide valuable insights for discovering unique $f$-electron Kitaev-QSL candidates.

Hexagonal transition metal dichalcogenides (TMDCs) represent a famous material family with rich structural phases and elemental compositions, whose diverse electronic properties, like magnetism, topological property, and superconductivity (SC), spark promising applications in the interdisciplinary field of “XX-tronics”. Here we found tetragonal TMDCs with distorted Lieb ($d\mathrm{Lieb}$) lattice present similar electronic properties as hexagonal TMDCs, by demonstrating the stability of transition metal diselenides ($d\mathrm{Lieb}-M{\mathrm{Se}}_2$) and ditellurides ($d\mathrm{Lieb}-M{\mathrm{Te}}_2$) with semiconductivity, half-metallicity, magnetic metallicity, topological electronic states, or phonon-mediated SC. Specifically, $d\mathrm{Lieb}-\mathrm{TiS}{\mathrm{e}}_2$ and $d\mathrm{Lieb}-\mathrm{TiT}{\mathrm{e}}_2$ are semiconductors, whereas partial occupation of localized $d_{z^2}$ states induces Stoner magnetism in $d\mathrm{Lieb}-M{\mathrm{Se}}_2$ ($M=\mathrm{Nb}$, V, Cr) with half-metallicity and in $d\mathrm{Lieb}-\mathrm{MnS}{\mathrm{e}}_2$ with metallicity. Notably, as the only TMDC monolayer with the magnetism stemming from Nb atom, $d\mathrm{Lieb}-\mathrm{NbS}{\mathrm{e}}_2$ monolayer was found exhibiting exotic chiral topological edge states. The Stoner magnetism will be suppressed in $d\mathrm{Lieb}-\mathrm{FeS}{\mathrm{e}}_2$ monolayer with fully occupied $d_{z^2}$ states, which could enable phonon-mediated SC with a transition temperature $T_{\mathrm{C}}\sim 4$ Kelvin. Together with our previously proposed disulfides $d\mathrm{Lieb}-M{\mathrm{S}}_2$, this work provides an overview table for tetragonal TMDCs with diverse electronic properties, which appear as promising alternatives for hexagonal TMDCs in the application of “XX-tronics”.

The approach of solving the Boltzmann transport equation (BTE) is widely used to evaluate the thermal conductivity and screen low thermal conductivity materials for thermoelectric applications, where phonon transport is approximated as particlelike propagation. Phonon transport through a wavelike tunneling channel, as described by the Wigner transport equation (WTE), will have a notable effect in some two-dimensional (2D) materials due to the parabolic out-of-plane acoustic modes and lower phonon energy, which is usually neglected, inducing an underestimation of thermal conductivity. Here, we investigate the phonon transport of four representative 2D structures by the WTE approach. Both the low-symmetry unit cell with heavy atoms and the strong anharmonicity will lead to a higher contribution from the tunneling channel. The total lattice thermal conductivity of low-symmetry KAgSe is only 0.34 ${\mathrm{W}\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ at 800 K, of which 26% is contributed by the wavelike tunneling. The strong lattice anharmonicity of 2D InSe with lone-pair electrons induces wide phonon linewidths for both acoustic and optical phonon modes, suppressing the conductivity through particlelike propagation channel. The coherence conductivity through wavelike tunneling accounts for 58% of the total one at 800 K. Our work helps to gain a better understanding of the dual-channel phonon transport in complex 2D structures. The strong anharmonic acoustic modes are crucial to achieve ultralow lattice thermal conductivity.

We provide a theoretical demonstration of controllable nonrelativistic spin splitting in both electronic and magnonic bands via targeted structural distortions tied to specific phonon modes. Using ${\mathrm{MnF}}_2$ as a model system, we identify a $d$-wave magnon band splitting between magnon modes of specific handedness, directly correlated with the nonrelativistic spin splitting observed in the electronic structure. Crucially, we show that structural distortions associated with the ${\mathrm{A}}_{2u}$ and ${\mathrm{A}}_{1g}$ phonon modes (8.52 and 9.74 THz) modulate these splittings without altering the antiferromagnetic order. The effect originates from changes in the nonmagnetic ligand environment, highlighting the key role of lattice degrees of freedom in governing spin dynamics. Our findings establish a novel route for structure-mediated control of spin splitting, opening possibilities for tunable magnonic and spintronic functionalities in antiferromagnetic materials.

Geometric representation lays the basis for understanding and flexible tuning of topological transitions in many physical systems. One example is the Poincaré sphere (PS), which facilitates the creation of various topological entities in light through continuous tuning spin or orbital angular momentum (OAM) states. Concurrently, how this approach can be utilized in condensed matter remains largely unexplored. In this work, we apply this geometric framework to a ferroelectric system through light-matter interaction and achieve a robust control on ferroelectric topologies. We show that: (1) PS engineering enables creation of dynamic polar antiskyrmions that are rarely found in ferroelectrics; (2) PS engineering acts as a tunable “knob”, allowing continuous control over transitions between topologically distinct skyrmion and antiskymion states; and (3) PS engineering can deterministically control the helicity of dynamical polar skyrmions and switch the chirality of polar vortices in an ultrafast manner. Our study thus opens new pathways for versatile manipulation of matter topologies through engineering structures of light.

High-pressure experiments allow us to induce and control chemical reactions or synthesize materials of unique properties. Furthermore, they are our primary means to replicate the conditions of geological processes and thus of studying, measuring, and understanding compositions and conditions in planetary interiors or asteroid impacts and subduction, etc. In all those experiments, time is a critical factor, as the compression rate or strain rate defines and alters the sample environment. Until recently, most experiments have been performed with either quasistatic strain rates, $\le {10}^{-3}{\mathrm{s}}^{-1}$, in diamond anvil cell and large volume press apparatus, or at very high strain rates, $\ge {10}^5{\mathrm{s}}^{-1}$, using gas gun, laser shock, and ramp compression. The work presented here focuses on intermediate compression rates applied to hcp Zn, using the dynamic diamond anvil cell. The evolution of the lattice parameters depends on the choice of the pressure transmitting medium. Nevertheless, at nonhydrostatic conditions we observe a significant change in the evolution of the lattice parameter when compressed at strain rates of $2\times {10}^{-2}{\mathrm{s}}^{-1}$ or $2.7\times {10}^2{\mathrm{s}}^{-1}$. At $2.7\times {10}^2{\mathrm{s}}^{-1}$, the c/a ratio does not correlate with the results of slow nonhydrostatic experiments, but its trend resembles closer with hydrostatic, quasistatic data. The deviation indicates that strain rates of $2.7\times {10}^2{\mathrm{s}}^{-1}$ interfere with the otherwise predominant deformation mechanism at quasistatic conditions.

The phenomenology of many-body localization (MBL) develops mainly from tackling the one-dimensional spin or fermion systems. The situation when interacting bosons get clustered in a random potential remains less explored. Using numerical quantum quenches with special emphasis on the integration of both symmetry and energy resolutions, we comprehensively study the dynamics of symmetry-resolved entanglement in a disordered Bose-Hubbard (dBH) model, concentrating on the two types of inhomogeneous initial states to target the lower- and higher-energy sections of its dynamical phase diagram. (i) Motivated by the recent experiment [A. Lukin et al., Science 364, 256 (2019)] which focused on the lower-energy dynamical behaviors of the dBH chain, we first show that at low energies, for a thermalizing state, although the second law of thermodynamics prohibits the decrease of the total entropy over time, for part of the channel-resolved entropies, a long-term entropic reduction may arise at weak disorder. (ii) A companion channel-resolved analysis at strong disorder further hints that the prior observed double-logarithmic growth of the number entropy might not directly indicate the breakdown of MBL in spin or fermion chains, providing a refreshing perspective on this major controversy in the community. (iii) From time-evolving the line-shape low-energy product state, we subsequently reveal an abrupt formation of a novel “entropy imbalance pattern” across the different symmetry channels. Intriguingly, this imbalance melts in the strong-disorder limit. We conjecture that the melting of the entropic pattern, together with the freezing of a concurrent particle-density wave, embodies a dual trait inherent to MBL. (iv) Conversely, the higher-energy section of the dynamical phase diagram is where the dBH model differs most significantly from the spin or fermion systems. This parametric space was not included in the previous literature. Specifically, we find a cluster MBL regime, unique to the Bose statistics, emerging from the higher-energy section. This cluster MBL regime, realizable even at weak disorder, does not appear to suffer from the finite-size drift and is distinguished by its absence of the hallmark of MBL—the unbounded growth of the entanglement entropy. Our theoretical predictions are, by and large, testable via the present experimental facilities.