A variety of experimental observations in monolayer transition metal dichalcogenide superconductors with Ising spin-orbit coupling suggest the presence of an unconventional superconducting pairing mechanism. Some of these experiments include observation of Leggett modes and a nodal superconducting gap in STM experiments, a large in-plane upper critical field compared to the Pauli limit, and the observation of a twofold gap anisotropy in magnetoresistance measurements. Here, we propose a superconducting pairing mechanism mediated by spin and charge fluctuations and identify the dominant superconducting instability relevant to monolayer ${\mathrm{TaS}}_2$. We then explore the effect of an additional electron-phonon pairing contribution, and compare our results with recent experimental findings. In particular, our theory stabilizes a superconducting ground state with nodal-like density of states that agrees with STM experiments. The theory obtains a large in-plane upper critical field due to a combination of Ising spin-orbit coupling and even-odd parity mixing in the superconducting state. Further, we find that an in-plane magnetic field splits the degeneracy of the superconducting ground state, and the resulting twofold symmetric superconducting order parameter could explain the gap anisotropy observed in magnetoresistance experiments. Overall, the proposed theoretical pairing model can reconcile diverse experimental observations and remains consistent with observations on other dichalcogenide superconductors such as monolayer ${\mathrm{NbSe}}_2$.

We investigate the numerical behavior of the Eliashberg equations for phonon-mediated superconductivity, incorporating normal-state self-energy calculations within the consistent $G{W}_0$ approximation. We account for the full wave-number and frequency dependencies of both the screened Coulomb interaction and phonon-mediated attraction. We present results for the prototypical uniform electron gas system with model Einstein phonons at temperatures of a few kelvin. At extremely low temperatures, we efficiently execute the required convolutions of Green's functions and interactions in Matsubara frequency and wave number using intermediate representation and Fourier convolution techniques. In particular, we elucidate the interplay between electron-phonon $\omega$-mass and $k$-mass renormalizations of the electronic self-energy in determining the normal-state effective mass, spectral weight, and the superconducting transition temperature. The electron density regimes where the plasmon effect enhances or suppresses the phonon-mediated superconductivity on top of the static Coulomb effect are revealed. We compare our comprehensive Eliashberg calculation results with those from density functional theory for superconductors, where the functionals have been constructed with reference to Eliashberg theory. Our model, methods, and results provide a valuable benchmark for first-principles superconducting calculations that treat screened Coulomb interaction effects non-empirically.

A supercurrent is well recognized as being of prime importance within mean-field theory, but remains largely unexplored in strongly correlated electron systems (SCES) and the quantum critical region. To clarify the impact of the supercurrent on magnetism and superconductivity near an antiferromagnetic quantum critical point, we study the two-dimensional Hubbard model based on a fluctuation exchange approximation for a current-carrying superconducting state. We show a supercurrent-induced antiferromagnetism and emergence of spin-triplet Cooper pairs. The former results from Bogoliubov Fermi surfaces, suppression in the superconducting gap, and strong correlation effects beyond the mean-field theory. Our results suggest that the supercurrent can bring out rich phenomena of superconductivity in SCES.

We investigate pressure-induced changes in the structure, lattice dynamics, mechanical properties, and bonding of the strongly anisotropic, monoclinic $P{2}_1$ phase of $\mathrm{Mg}{\left({\mathrm{IO}}_3\right)}_2$ via the density functional theory with a global hybrid density functional approximation. Infrared and Raman spectra are simulated, which highlight a peculiar pressure-induced phonon softening of certain bands assigned to I-O stretching modes. As pressure increases, a redistribution of the electron density around the iodine atoms is observed leading to the elongation and weakening of the three I-O interactions within $\left[{\mathrm{IO}}_3\right]$ structural units, with a corresponding pressure-induced expansion of the a and c lattice vectors, which translates into a negative linear compressibility of the material in the ac plane. This is accompanied by the shortening and strengthening of the interaction of iodine atoms with their three second-neighboring oxygen atoms, with a corresponding compression of the b lattice vector along which they are mainly oriented. Quasiharmonic lattice dynamical calculations reveal a negative thermal expansion in the ac plane. The strength of various interatomic interactions, as well as their evolution with pressure, is assessed in terms of local mode adiabatic force constants obtained through a new periodic implementation of the local vibrational mode theory. We complement and corroborate the analysis with a topological description of the electron density through the quantum theory of atoms in molecules.

Although rich phenomena have been microscopically observed in magic-angle twisted bilayer graphene, layer-resolved excitations within the flat bands, which provide a direct understanding of the coupling between the two layers with subtle interlayer interactions, have not been directly observed. Such observations are fundamentally limited in electronic systems due to the lack of minimally invasive probes between the two adjacent graphene layers. Here, with phononic twisted bilayer graphene (PTBG) as an analog to the electronic system, we directly measure the excitations within and in between each adjacent layer, enabling in situ layer-resolved flat-band excitations observations. Paired with theoretical modeling, the layer-resolved measurement directly demonstrates the interlayer coupling effect in magic-angle twisted PTBG, presenting its significance. Meanwhile, in large-angle twisted PTBG, the low-energy states are only mildly affected by the moiré effect and can be approximated by those from two decoupled Dirac cones from the individual phononic layers. This work extends twistronics to artificial crystals, opening new approaches to investigate moiré physics.

The magnetoelectric antiferromagnet ${\mathrm{Co}}_3{\mathrm{O}}_4$ has recently been reported as a promising platform for isothermal electric manipulation of antiferromagnetic states. Here, we report a detailed study on magnetization, heat capacity, dielectric properties, and electric polarization in single crystals of ${\mathrm{Co}}_3{\mathrm{O}}_4$. Magnetization and heat capacity measurements affirm the occurrence of a Néel-type collinear antiferromagnetic ordering below its Néel temperature $T_{\mathrm{N}}$ = 30 K, where the direction of the Néel vector can be rotated by weak fields. This magnetic ordering breaks the spatial inversion and time reversal symmetries and permits a strong linear magnetoelectric effect, leading to the emergence of field-induced electric polarization below $T_{\mathrm{N}}$, and is also manifested in a magnetic field-induced sharp $\lambda$-like peak in the dielectric constant at $T_{\mathrm{N}}$. Notably, the corresponding magnetocapacitance reaches a maximum value as high as 110% close to $T_{\mathrm{N}}$. This magnetocapacitance exhibits a quadratic dependence on the strength of the applied magnetic field, which is discussed within the framework of a phenomenological Landau theory.

We report a study of the ${\mathrm{La}}_{1-x}{\mathrm{Ce}}_x\mathrm{FeSiH}$ solid solution $(0\le x\le 1)$, a family of intermetallic hydrides of ZrCuSiAs-type structure, with space group $P4/nmm$. For low cerium concentrations $x\le 0.20$, we observe the presence of superconductivity, which originates from the correlated $3d$ electrons of iron. The superconducting regime is progressively suppressed by the cerium substitution. For moderate cerium concentration $0.07\le x\le 0.50$, we observe evidence of the single-ion Kondo effect and no magnetic phase transition down to 2 K. For $0.07\le x\le 0.20$, the single-ion Kondo effect coexists with a superconducting ground state at low temperatures. From $x>0.50$, we observe signatures of Kondo coherence and a heavy Fermi liquid regime at low temperature. Finally, at high cerium concentration $x\ge 0.85$, we observe signatures of magnetic ordering at low temperatures. We discuss our results by introducing temperature scales related to superconductivity, the Kondo effect, and magnetic order, which permits building a rich phase diagram temperature versus cerium content $x$. This shows that using the cerium concentration $x$ as a unique control parameter, we can explore the Kondo entanglement between correlated $3d$ and $4f$ electrons, which suggests an unusual change between the superconducting state related to the $3d$ electrons and the Kondo coherent state involving both $3d$ and $4f$ electrons.

Liouvillian skin effects, manifested as the localization of Liouvillian eigenstates around the boundary, are distinctive features of non-Hermitian systems and are particularly notable for their impact on system dynamics. Despite their significance, Liouvillian skin effects have not been sufficiently explored in electron systems. In this work, we demonstrate that a two-dimensional electron system on a substrate exhibits $\mathbb{Z}$ and ${\mathbb{Z}}_2$ Liouvillian skin effects due to the interplay among energy dissipations, spin-orbit coupling, and a transverse magnetic field. In addition, our analysis of the temperature dependence reveals that these Liouvillian skin effects become pronounced below the energy scale of band splitting induced by the spin-orbit coupling and the magnetic field. While our $\mathbb{Z}$ Liouvillian skin effect leads to charge accumulation under quench dynamics, its relaxation time is independent of the system size, in contrast to that of previously reported Liouvillian skin effects. This difference is attributed to the scale-free behavior of the localization length, which is analogous to non-Hermitian critical skin effects.

We present a quantum Monte Carlo-based approach to detect and compute the most dominant correlations for many-body systems without prior knowledge. It is based on the measurement and analysis of the correlation density matrix between two (small) subsystems embedded in the full (large) sample. In order to benchmark this procedure, we investigate zero-temperature quantum phase transitions in one- and two-dimensional quantum Ising model as well as the two-dimensional bilayer Heisenberg antiferromagnet. The method paves the way for a systematic identification of unknown or exotic order parameters in unexplored phases on large systems accessible to quantum Monte Carlo methods.

We study the Hilbert space fragmentation (HSF) in hardcore Bose and Fermi Hubbard models in the framework of the restricted spectrum generating algebra (RSGA). We present a family of hardcore Bose-Hubbard models with repulsive density-density interactions on a generalized Lieb lattice. We show that this system possesses the RSGA structure in the large interaction strength limit, exhibiting quantum HSF. It allows us to construct a set of exact condensate eigenstates, possessing off-diagonal long-range order. Based on numerical simulations conducted on several representative lattices, we demonstrate the existence of weak fragmentations when the constraints are not exact. As applications, we also studied the connection between HSF and RSGA in modified fermionic Hubbard models, where the $\eta$-pairing states are shown to be energy towers, acting as quantum scars.

Motivated by the recent Ge hole spin qubit experiments, we construct and study a two-leg spin ladder from a quantum dot array with spin-orbit couplings (SOCs), aiming to uncover the many-body phase diagrams and provide concrete guidance for the Ge hole spin qubit experiments. The spin ladder is described by an unprecedented, complex spin Hamiltonian, which contains antiferromagnetic Heisenberg exchange, Dzyaloshinskii–Moriya (DM), and anisotropic exchange interactions. We analyze the spin ladder Hamiltonian in two complementary situations, the strong rung coupling limit and the weak rung coupling limit. In the strong rung coupling limit, we systematically construct effective spin-$1/2$ chain models, connecting the well-studied one-dimensional spin models and providing a recipe for Hamiltonian engineering. It is worth emphasizing that effective DM interactions can be completely turned off while the microscopic DM interactions are generically inevitable. More intriguingly, the staggered DM interactions, which allow for the field-induced gap pertinent to the sine-Gordon model, can also be realized in the effective spin chain model, opening up a route for studying the sine-Gordon model in spin qubits. In the weak rung coupling limit, we employ Abelian bosonization and Luther-Emery fermionization, uncovering a multitude of phases. Several commensurate-incommensurate transitions are driven by both the longitudinal magnetic field and the DM interactions in the legs (chains). Remarkably, the low-energy phase diagrams show strong dependence in the DM interaction, providing a concrete way to identify the strength of SOC in the experiments. We further demonstrate that different phases can be reached by tuning the magnetic field, both in amplitude and direction, paving the way for the efficient manipulation of the quantum many-body states in spin qubit experiments. Our work bridges quantum many-body theory and spin qubit device physics, establishing spin ladders made of spin-orbit-coupled quantum dots as a promising platform for engineering exotic spin models, constructing quantum many-body states, and paving the way for quantum computations and emulations.

Transport and magnetotransport properties of the single-atom-thick ${\mathrm{EuPb}}_3$ kagome compound on Si(111) were explored in situ using the linear four-point-probe technique within a temperature range from 2.5 to 40 K and at the magnetic field varied from $-6$ to $+6\mathrm{T}$. Our results revealed that ${\mathrm{EuPb}}_3$ displays the occurrence of the magnetic critical temperature of 5 K and two successive magnetoresistance jumps at the magnetic fields of 0.2 T and approximately 1.0 T, both exhibiting considerable hysteresis. Our density functional theory analysis suggests that the ground-state magnetic configuration of the single-atomic-layer metallic ${\mathrm{EuPb}}_3$ is possibly striped antiferromagnetic, with Eu magnetic moments aligned perpendicular to the surface. The occurrence of the magnetic hysteresis at the field-induced transitions is a signature of the first-order transitions and magnetocrystalline anisotropy in the ${\mathrm{EuPb}}_3/\mathrm{Si}\left(111\right)$ system.

The graphyne family represents a versatile class of carbon-based materials, encompassing both semiconductors and semimetals with promising potential for technological applications. In this work, we analyze the influence of structural changes on the mechanical, electronic, and optical properties of sulfur-doped graphyne (S-GY), a recently synthesized carbon-based material composed of five-membered rings connected by acetylenic linkers. The S-GY monolayer is an indirect band-gap semiconductor with a gap of $\sim 1.3\mathrm{e}\mathrm{V}$. Furthermore, sulfur incorporation along with the resulting structural modifications breaks the electron-hole symmetry typically observed in pristine graphyne phases. Its thermodynamic stability is confirmed by phonon dispersion and ab initio molecular dynamics simulations, while the elastic response reveals pronounced anisotropy. The optical absorption spectrum indicates the presence of bound excitons, with a binding energy of $460\mathrm{m}\mathrm{e}\mathrm{V}$ for the ground-state exciton, while the estimated maximum power-conversion efficiency of $\sim 22\%$ highlights S-GY as a promising alkynyl carbon material for next-generation photovoltaic technologies.

Giant Shubnikov-de Haas oscillations (SdHO) with V-shaped minima are experimentally studied in a high-mobility two-dimensional electron gas based on GaAs/AlGaAs heterostructures. A phenomenological model with two parameters (transport momentum relaxation time ${\tau }_{\text{tr}}$ and quantum scattering time ${\tau }_q$) is developed, accurately describing experimentally measured magnetoresistance over an unexpectedly wide range of magnetic fields (up to $3.5\mathrm{T}$) and temperatures (2–15 K). The model combines: (i) a quasiclassical density of states with a magnetic-field-dependent Gaussian broadening of Landau levels, (ii) a momentum relaxation time scaling with the density of states, and (iii) oscillations of the Fermi level at a fixed electron density. This model reproduces V-shaped oscillation minima with zero-resistance points, a smooth background of positive magnetoresistance, and enables the extraction of ${\tau }_q$ and ${\tau }_{\text{tr}}$ even in microstructures where ballistic and viscous effects dominate at low fields. As expected, the temperature dependence reveals that ${\tau }_{\text{tr}}$ scales inversely with temperature because of acoustic phonon scattering, while ${\tau }_q$ remains temperature independent.

The dynamical structure factor of the transverse field Ising model (TFIM) shows universal power-law divergence at its quantum critical point, signatures of which have been arguably observed in inelastic neutron scattering studies of quantum spin chain materials, for example ${\mathrm{CoNb}}_2{\mathrm{O}}_6$. However, it has recently been suggested that its microscopic description is better captured in terms of a twisted Kitaev spin chain (TKSC) with bond-anisotropic couplings. Here, we present exact results for the dynamical structure factor of the TKSC across its quantum critical point, analyzing both the universal low-frequency response and the non-universal high-energy features. In addition, we explore extensions of the model including broken glide symmetry as well as the case of random, and incommensurate magnetic fields. Notably, in the latter case, the fermionic excitations exhibit a localization-delocalization transition, which is manifest in the dynamical response as a distinct signature at finite frequency. We discuss the relevance of these features for the observation of quantum critical response in experiments.

We analyze the leading vestigial instability due to the melting of a bidirectional pair-density-wave state in two dimensions. In a previous work by one of the authors, it was found that the interplay between pair-density-wave fluctuations with ordering momenta along the $x$ and $y$ directions can provide a strong attractive interaction for charge-$4e$ superconductivity in the $d$-wave channel. In this work, we go beyond the artificial large-$M$ mean-field theory previously adopted and compute the phase diagram by incorporating phase fluctuations of the pair-density-wave order parameters. By investigating the relevance of various topological defects, we show that the interaction in the $d$-wave channel, together with the strong anisotropy of phase fluctuations around the pair-density-wave ordering momenta favors a vestigial charge-$4e$ superconducting order at intermediate temperatures. By contrast, a competing charge-density-wave vestigial order does not develop, due to the suppression of its stiffness.

We study bulk photovoltaic effects in electron-phonon coupled systems. The conservation of current or gauge invariance, manifested as the Ward-Takahashi identity, plays an essential role in the analysis of the Feynman diagrams, and the leading order contribution to the phonon shift current is identified accordingly. The leading order contribution essentially arises from the electric polarization carried by optically excited phonons, where the shift current is generated as a result of a change of electric polarization in the steady state under the optical excitation of phonons.

We report the successful synthesis and comprehensive characterization of the kagome metal $\mathrm{C}{\mathrm{u}}_3{\mathrm{V}}_2\mathrm{S}{\mathrm{b}}_4$. This material exhibits a quadratic temperature dependence of resistivity over a broad temperature range, indicative of strong electron-electron interactions, as confirmed by the fact that specific heat measurements with the Kadowaki-Woods ratio lie between those of transition metal and heavy fermion systems. Magnetoresistance measurements reveal a linear magnetic field dependence at low temperatures, while Hall effect measurements display nonlinear behavior describable with a semiclassical two-band model. The angle-dependent magnetoresistance further reveals twofold symmetry. These results collectively suggest an evolution of the band structure within the temperature range of 50–80 K. Magnetic susceptibility measurements indicate paramagnetic behavior with evidence of short-range magnetic correlations emerging near 25 K. Our findings broaden the material landscape of kagome metals and provide a promising platform for exploring correlated electron states and topological quantum phenomena in novel quantum materials.