We analyze the tensor network loop cluster expansion, introduced by G. Park et al. [Phys. Rev. B 112, 174310 (2025)] as a systematic correction to belief propagation, in the context of general quantum many-body problems. We provide numerical examples of the accuracy and practical applicability of the approach for the computation of ground-state observables for high bond dimension tensor networks, in two and three dimensions, with open and periodic boundary conditions, and for spin and fermion problems. We find that the contraction error converges approximately exponentially with cluster size, enabling accurate local observable and energy estimates for many systems where standard contraction methods are otherwise impractical.

We propose a ground-state entanglement probe for gapped, two-dimensional quantum many-body systems that involves taking powers of reduced density matrices in a particular geometric configuration. This quantity, which we denote by ${\omega }_{\alpha ,\beta }$, is parameterized by two positive real numbers, $\alpha \text{and}\beta$, and can be seen as a “Rényi-like” generalization of the modular commutator—another entanglement probe proposed as a way to compute the chiral central charge from a bulk wave function. We obtain analytic expressions for ${\omega }_{\alpha ,\beta }$ for gapped ground states of noninteracting-fermion Hamiltonians as well as ground states of string-net models. In both cases, we find that ${\omega }_{\alpha ,\beta }$ takes a universal value related to the chiral central charge. For integer values of $\alpha$ and $\beta$, our quantity ${\omega }_{\alpha ,\beta }$ can be expressed as an expectation value of permutation operators acting on an appropriate replica system, providing a natural route to measuring ${\omega }_{\alpha ,\beta }$ in numerical simulations and experiments.

Pressure-induced changes in the magnetic and superconducting properties of a spin-triplet superconductor candidate ${\mathrm{UTe}}_2$ have attracted considerable interest, underscoring the need for microscopic theoretical insight. In this paper, we investigate magnetic fluctuations and their anisotropy at ambient pressure and under pressure using density functional theory (DFT) combined with the random phase approximation (RPA). For each pressure, we perform $\mathrm{DFT}+U$ calculations for several values of the Coulomb interaction $U$, construct a 72-orbital periodic Anderson model, and calculate magnetic susceptibilities with use of the RPA. For $U=2\mathrm{eV}$, the Fermi surface has a quasi-two-dimensional shape, antiferromagnetic fluctuations develop with the wave vector along the ${\mathit{a}}^{*}$ axis, and the magnetic anisotropy follows ${\chi }^b>{\chi }^a>{\chi }^c$. The antiferromagnetic fluctuations are suppressed under pressure because of a reduced density of states at the Fermi level, while the magnetic anisotropy is weakened. In contrast, for $U=1\mathrm{eV}$, where the Fermi surface is more three dimensional, antiferromagnetic fluctuations with ${\mathit{Q}}_2=0.22{\mathit{b}}^{*}$ appear, accompanied by anisotropy ${\chi }^a>{\chi }^c>{\chi }^b$, consistent with experiments. Under pressure, antiferromagnetic fluctuations around ${\mathit{Q}}_2$ are enhanced, the magnetic wave vector tilts slightly toward the ${\mathit{a}}^{*}$ direction due to Fermi-surface distortion, and the magnetic anisotropy is suppressed. These results demonstrate that the pressure evolution of magnetism in ${\mathrm{UTe}}_2$ is governed by the momentum-space distribution of U $5f$ states and the density of states at the Fermi level, providing a microscopic basis for understanding the magnetic and superconducting properties of ${\mathrm{UTe}}_2$.

A fundamental issue in the renormalization-group (RG) theory of critical phenomena concerns the allowed values of critical exponents that are consistent with the continuous nature of a phase transition. Here, we conjecture a lower bound for the length-scale exponent $\nu$, which should hold for the large class of continuous transitions associated with $d$-dimensional Landau–Ginzburg–Wilson (LGW) ${\mathrm{\Phi }}^4$ theories with a multicomponent scalar field $\mathit{\phi }$ and a unique $\mathit{\phi }·\mathit{\phi }$ quadratic term (including some extensions with fermionic and gauge fields), describing many universality classes of critical phenomena. If ${\mathrm{\Delta }}_{\phi }=(d-2+\eta )/2$ is the dimension of the order-parameter field $\mathit{\phi }$, and ${\mathrm{\Delta }}_{\varepsilon }=d-1/\nu$ is the RG dimension of the energy operator $\varepsilon$, which can be identified with $[\mathit{\phi }·\mathit{\phi }]$ (the squared field with a proper subtraction of the mixing with the identity), we conjecture the inequality ${\mathrm{\Delta }}_{\varepsilon }\ge 2{\mathrm{\Delta }}_{\phi }$, which implies $\nu \ge {(2-\eta )}^{-1}$ and $\gamma =(2-\eta )\nu \ge 1$. These inequalities are supported by general arguments for ferromagnetic lattice models, by $\epsilon$-expansion results for generic LGW ${\mathrm{\Phi }}^4$ theories close to four dimensions, by exact relations for two-dimensional minimal conformal field theories, and are consistent with all further known (numerical, perturbative, and exact) results for LGW ${\mathrm{\Phi }}^4$ theories. In particular, since unitarity requires $\eta \ge 0$, the above inequality implies $\nu \ge 1/2$ for unitary theories. This lower bound is more restrictive than $\nu >1/d$, derived by noting that $\nu =1/d$ characterizes the singular finite-size behavior at first-order transitions.

We present a fully atomistic approach to exciton-phonon coupling in semiconductor quantum dots that bridges microscopic electronic-structure calculations with non-Markovian open-quantum-system dynamics. On the example of an InAsP quantum dot embedded in an InP matrix, we compute single-particle states using an ab initio-parametrized tight-binding model, then obtain correlated many-body wave functions of neutral excitons, biexcitons, and charged trions via the configuration-interaction method. Using these correlated states, we compute the exciton-phonon coupling matrix elements. The resulting phonon spectral densities for different excitonic complexes are compared with the widely used analytical super-Ohmic form and reveal deviations at higher energies originating from the realistic dot geometry and atomistic wave functions, whereas configuration mixing is found to play only a minor role. Furthermore, we extract radiative lifetimes comparable to values experimentally measured. As a direct application, we simulate the emission brightness of a pulsed-driven quantum dot and demonstrate that the atomistically derived spectral density substantially broadens the region of efficient off-resonant excitation compared to the analytical model. The presented framework provides a nearly parameter-free route to simulate the non-Markovian open quantum dynamics in semiconductor quantum dots.

We calculate the edge current and its fluctuations, i.e., noise, in a two-dimensional topological superconductor using the $T$-matrix and the Green's function techniques. We show that the current is zero for nonchiral edge states and nonzero for chiral edge states, while the edge noise is nonzero whatever the chirality of the edge states. By applying our results to toy models with chiral edge states, we find that the noise is closely related to the Chern number. The edge noise is nonzero only when the Chern number is nonzero, and the bulk noise exhibits a peak each time the Chern number varies, meaning that there are strong current fluctuations when a topological phase transition occurs. Our results suggest that the bulk noise could be seen as a topological susceptibility. In the extended Qi-Wu-Zhang model, where an edge state is present even though the Chern number is zero, the edge noise no longer follows the same behavior as it does in the nonzero Chern number model. Instead, it is related to other topological invariants, such as the Zak phase.

Twisting magnetic van der Waals materials provides a compelling approach to generate emergent spin textures through moiré engineering. In this study, we show that a twisted bilayer formed by two antiferromagnetic MnSe monolayers exhibits sublayer-resolved $i$-wave altermagnetic spin splitting. Combining first-principles calculations with a symmetry-constrained continuum theory, we reveal that this spin splitting originates from the rotational misalignment between two hexagonal warping parabolic band dispersions of the monolayer, coupled with sublayer-dependent moiré potentials arising from interfacial charge redistribution. While both AA- and ${\mathrm{AA}}^R$-twisted configurations display similar patterns of altermagnetic splitting, the underlying symmetry mechanisms are fundamentally distinct. In AA-twisted configuration, the effect is driven by locally inversion symmetric moiré potentials in the two layers, whereas in ${\mathrm{AA}}^R$-twisted configuration, it is dictated by a global in-plane $C_2$ symmetry that enforces opposite moiré potential phase relations between the magnetic sublayers. Additionally, we observe that altermagnetic splitting diminishes with decreasing twist angle, indicating a weakening of the rotational misalignment between the warping dispersions and a reduction in moiré momentum scale. Our results establish twisted MnSe as a representative system for layered antiferromagnets with spin-layer coupling and anisotropic warping band edge, offering a versatile platform for engineering twist-induced altermagnetic phases.

Nonequilibrium manipulation of quantum materials via electromagnetic dressing provides an on-demand route to tailoring electronic band structures through Floquet engineering. Time- and angle-resolved photoemission spectroscopy offers a direct means to probe these light-dressed electronic states. In such photoemission experiments, electromagnetic dressing can also occur for quasifree electrons outside the material, giving rise to so-called Volkov states. In certain cases, most notably in metallic systems, strong surface screening reduces the penetration of the driving electromagnetic field into the solid, resulting in Volkov contributions that dominate over Floquet ones. This underscores the importance of carefully accounting for the material's dielectric response when analyzing the origin of light-induced band replicas using time- and angle-resolved photoemission spectroscopy. In this work, we systematically investigate the influence of materials' dielectric properties on Floquet-Volkov dressing of semiconductors, focusing on bulk layered van der Waals materials GeS, SnS, and $2\mathrm{H}\text{−}{\mathrm{WSe}}_2$. First, by combining a simple model based on Fresnel equations with an electron-scattering description of Volkov amplitudes, we use polarization-dependent Volkov sideband intensities to extract a lower bound for the real part of the materials' dielectric function. The extracted values typically lie between the reported dielectric constants for monolayer and bulk crystals. Furthermore, we demonstrate that increasing the pump fluence of the infrared pump laser enables the generation of high-order Volkov sidebands, which exhibit clear signatures of nonlinear light-matter interactions in their temporal dynamics, polarization dependence, and angular distributions. Finally, we show that for our experimental geometry, the quasitransparent nature of semiconductors in the below-band-gap driving regime allows the optical pump to propagate within the sample and undergo multiple total internal reflections. This process produces a series of temporally delayed Volkov replicas in pump-probe measurements via electromagnetic dressing of photoelectrons by the evanescent field associated with total internal reflections. Together, these systematic studies uncover several previously unexplored aspects of Floquet-Volkov dressing in solids, highlighting the central role of dielectric screening of the driving field.

Two-dimensional (2D) semiconductors possessing strong spin-orbit coupling (SOC) and nontrivial topological features are central to the development of energy-efficient spintronics. While Weyl physics is extensively studied in semimetals, its realization in atomically thin semiconductors remains limited. Using first-principles calculations, we identify layered ${\mathrm{SnP}}_2{\mathrm{Se}}_6$ as a versatile topological semiconductor platform. In its monolayer form, the intrinsic structural chirality gives rise to a coexistence of Ising-type and Weyl-like (the properties of this material cannot be fully characterized as those of Dirac or Weyl materials) SOC. The latter is characterized by radial hedgehoglike spin textures—a signature of unique manifestation of Weyl-type SOC in a 2D chiral lattice within a 2D semiconductor—resulting in a significant intrinsic spin Hall conductivity (SHC) of up to 10.2 (ℏ/e) S/cm. In multilayer ${\mathrm{SnP}}_2{\mathrm{Se}}_6$, symmetry evolution facilitates a distinct regime where Weyl-like and Rashba spin textures coexist. This transition preserves substantial spin-charge conversion efficiency while introducing chirality-switchable components to the SHC tensor, providing a layer-dependent degree of freedom for spin manipulation. The interplay between strong SOC, topological band features, and structural chirality establishes ${\mathrm{SnP}}_2{\mathrm{Se}}_6$ as a platform for thickness-engineered spintronic devices.

We introduce equations of motion for a parity-violating fermionic mean-field theory (PV-FMFT): a numerically efficient fermionic mean-field theory based on parity-violating fermionic Gaussian states (PV-FGS). This work provides explicit equations of motion for studying the real- and imaginary-time evolution of spin-1/2 Hamiltonians with arbitrary geometries and interactions. We extend previous formulations of parity-preserving fermionic mean-field theory (PP-FMFT) by including fermionic displacement operators in the variational Ansatz. Unlike PP-FMFT, PV-FMFT can be applied to general spin-1/2 Hamiltonians, describe quenches from arbitrary initial spin-1/2 product states, and compute local and nonlocal observables in a straightforward manner at the same modest computational cost as PP-FMFT—scaling as $O\left(N^3\right)$ in the worst case for a system of $N$ spins or fermionic modes. We demonstrate that PV-FMFT can exactly capture the imaginary- and real-time dynamics of noninteracting spin-1/2 Hamiltonians. We then study the postquench dynamics of the one- and two-dimensional Ising model in the presence of longitudinal and transversal fields with PV-FMFT and compute the single site magnetization and correlation functions, and compare them against results from other state-of-the-art numerical approaches. In two-dimensional spin systems, we show that the employed spin-to-fermion mapping can break rotational symmetry within the PV-FMFT description, and we discuss the resulting consequences for the calculated correlation functions. Our work introduces PV-FMFT as a benchmark for other numerical techniques and quantum simulators, and it outlines both its capabilities and its limitations.

Increasing the valley splitting in Si-based heterostructures is critical for improving the performance of semiconductor qubits. This paper establishes that the two low-energy conduction band valleys are not independent parabolic bands. Instead, they originate from the X point of the Brillouin zone, where they are interconnected by a degeneracy protected by the nonsymmorphic symmetry of the diamond lattice. This semi-Dirac-node degeneracy gives rise to the ${\mathrm{\Delta }}_1$ and ${\mathrm{\Delta }}_{2^{\prime }}$ bands, which constitute the valley degrees of freedom. By explicitly computing the two-component Bloch functions $X_1^{\pm }$, using the wave vector group at the X point, we determine the transformation properties of the object $(X_1^{+},X_1^{-})$. We demonstrate that these properties are fundamentally different from those of a spinor. Consequently, we introduce the term “valleyor” to emphasize this fundamental distinction. The transformation properties of valleyors induce corresponding transformations of the Pauli matrices ${\tau }_1,{\tau }_2$ and ${\tau }_3$ in the valley space. Determining these transformations allows us to classify possible external perturbations that couple to each valley Pauli matrix, thereby identifying candidates for valley-magnetic fields, $\vec{\mathcal{B}}$. These fields are defined by a Zeeman-like coupling $\vec{\mathcal{B}}·\vec{\tau }$ to the valley degree of freedom. In this way, we identify scenarios where an applied magnetic field $\vec{B}$ can leverage other background fields, such as strain, to generate a valley-magnetic field $\vec{\mathcal{B}}$. This analysis suggests that beyond the well-known mechanism of potential scattering from Ge impurities, there exist additional channels—mediated by combinations of magnetic and strain-induced vector potentials—to control the valley degree of freedom.

Propagation of short pulses through ${\mathrm{Cu}}_2\mathrm{O}$ crystal containing Rydberg excitons is studied with the use of the density matrix formalism and the finite difference time domain method. Effects of the so-called Rydberg blockade are studied extensively, exploring not only a reduction of absorption (bleaching) but also power-dependent changes of dispersive properties of the medium. The role of an exciton lifetime and coherent population oscillations in the dynamics of the system are investigated. A pump-probe setup with two pulses is also studied, showing a good agreement with recent experimental results. Calculations are performed for Rydberg states, both for low $n<10$ and high $n\sim 20$ principal quantum numbers.

Lack of inversion symmetry in metals breaks SU(2) symmetry, which results in spin-splitting of the electronic states at the Fermi level due to various types of spin-orbit coupling (SOC) such as Dresselhaus, Rashba, or Ising (also called valley-Zeeman). This splitting is known to enable both incoherent spin-flip excitations and coherent chiral-spin modes. Another effect of breaking of SU(2) is the introduction of a direct spin-photon interaction. We use this concept to formulate a theory of inelastic scattering of photons from the charge carriers of such a system [electronic Raman scattering (eRS)]. As a result of broken SU(2), we show that the eRS probe, unlike the conventional theory of Raman scattering, couples to spin excitations even without tuning the laser to an internal resonance. We show that the spin-dependent excitations induced by photon scattering are sensitive to the polarization geometries as well as to the spin structure of the Hilbert space of the low-energy states. As a concrete realization, we examine doped/gated graphene on substrates with strong SOC with various compositions of Rashba and valley-Zeeman SOC and compare their spectra with those for a model 2D electron gas (2DEG). The spectra are shown to have a resonant feature in select polarization geometries near the SOC-splitting energy and, importantly, are shown to be different in the two systems. The signal in graphene systems is shown to be stronger than that in a 2DEG by orders of magnitude due to the large Dirac velocity. We also outline how the line shapes from the spectra can be used to infer various components of SOC in the system.

Open-shell nanographenes offer a controlled setting to study correlated magnetism emerging from $\pi$-electron systems. Here, we study non-bipartite Fermi-Hubbard ladders describing oligo(indenoindene) molecules. These feature a gapped, weakly dispersing manifold of quasizero modes in their single-particle spectra, and we show that their low-energy properties can be effectively mapped onto an interacting set of spin-1/2 degrees of freedom. Using density matrix renormalization group simulations of the full Fermi-Hubbard model, we obtain their excitation spectra, entanglement profiles, and spin-spin correlations. We then construct optimized delocalized fermionic modes that act as emergent spins and demonstrate that their interactions are well described by a frustrated $J_1–J_2$ Heisenberg chain. This effective description clarifies how spin degrees of freedom arise and interact in non-bipartite nanographene ladders, providing a compact and accurate representation of their correlated behavior.

Asymptotic behavior of generic Tomonaga-Luttinger liquid in the vicinity of phase-separated regions is known to produce an instability where well-known relativistic conformal field theory (CFT) techniques fail. In this paper, we introduce an analytic paradigm that provides a continuum description of this important issue. We show that there is an emergent Carrollian symmetry when phase separation is reached, and techniques of Carroll CFT, as opposed to its relativistic relative, are central to the understanding of the physics. We work with the analogous spinless fermionic system in this region and capture the transition across this phase separation. Our numerical results corroborate the density-density correlations intrinsically computed using Carroll CFT. We further test the framework in a number of lattice systems, namely the spinless and spinfull fermionic models with distinct microscopic content, and find the same scaling at the transition. We discuss the scope of the framework and broader perspective.

We use high-dimensional bosonization to derive an effective field theory that describes the Pomeranchuck transition in isotropic two-dimensional Fermi liquids. We find that the transition is triggered by the softening of an eigenmode that leads to spontaneous Fermi surface distortion. The resultant theory in terms of this critical mode has dynamical critical exponent $z=2$ and the upper critical dimension is $d_c=4-z=2$. As a result the system is at the upper critical dimension in 2D, resulting in a Gaussian fixed point with a marginally irrelevant quartic perturbation.

We investigate localization transitions in a one-dimensional non-Hermitian quasiperiodic chain with period-2 mosaic modulation and nonreciprocal hopping. We show that tuning the degree of non-Hermiticity can induce a rich reentrant localization behavior: As the hopping asymmetry increases, reentrant localization successively emerges, disappears, resurges, and ultimately vanishes. By mapping the non-Hermitian Hamiltonian to a Hermitian reference chain via an imaginary gauge transformation and performing a transfer-matrix analysis, we introduce an effective Lyapunov exponent ${\gamma }_{\mathrm{eff}}={\gamma }_{\mathrm{qp}}-\alpha$, where ${\gamma }_{\mathrm{qp}}$ denotes the Lyapunov exponent of the Hermitian chain and $\alpha$ characterizes the hopping asymmetry. The interplay between ${\gamma }_{\mathrm{qp}}$ and $\alpha$ reveals that reentrant localization and its resurgence arise from the competition between quasiperiodic disorder and non-Hermiticity. Numerical analyses of participation ratios, single-particle spectra, and spectral winding numbers corroborate these findings.