We numerically investigate the localization transition in a one-dimensional system subjected to a composite potential consisting of periodic and quasiperiodic components. For the rational wave vector $\alpha =1/2$, the periodic component reduces to a staggered potential, which has been reported to induce the reentrant localization transition. In addition to $\alpha =1/2$, we find that other rational wave vectors can also lead to the reentrant phenomenon. To investigate the underlying mechanisms of the reentrant localization transition, we vary the parameters of the composite potential and find that the reentrant localization transition is sensitive to the phase factor of the periodic component. By further studying the structure of the periodic component, we confirm that this sensitivity arises from the periodic phase factor modulating the mirror symmetry. Finally, we map out a global phase diagram and reveal that the reentrant localization transition originates from a paradoxical effect: Increasing the amplitude of the periodic component enhances localization but simultaneously strengthens the mirror symmetry, which favors the formation of extended states. Our numerical analysis suggests that the interplay between these competing factors drives the reentrant localization transition.

We successfully synthesized $\left[{\mathrm{Cu}}_2{\left(\mathrm{AcO}\right)}_4{(p-Py-V-p-\mathrm{F})}_2\right]·4{\mathrm{CHCl}}_3$, a verdazyl-based complex with a paddlewheel structure comprising two Cu atoms, which induces strong antiferromagnetic (AF) exchange interactions between Cu spins, generating a nonmagnetic singlet state at low temperatures. Two primary exchange interactions between radical spins generate a spin-1/2 AF two-leg ladder. In addition, two possible positional configurations of the F atom in the complex create four different overlap patterns of molecular orbitals, introducing bond randomness in the spin ladder. The observed experimental behaviors, such as the Curie tail in the magnetic susceptibility and the gapless gradual increase in the magnetization curve, are attributed to a broad distribution of excitation energies and a few orphan spins in the random-singlet (RS) state that are stabilized by bond randomness. The low-temperature specific heat exhibits a temperature dependence with $\propto 1/{\left|\ln T\right|}^3$, demonstrating the formation of the RS state in unfrustrated systems. We also consider the effect of restricted patterns of exchange interactions and one-dimensional nature of the system on the RS state.

This study establishes a fundamental connection between the dissipation and polarization of spin waves, which are often treated as independent phenomena. Through theoretical analysis and numerical validation, we demonstrate that within the linearized spin-wave regime, a spin-wave mode's dissipation rate, defined as the ratio of linewidth to the resonance frequency, exceeds Gilbert damping by a factor given by its spatially averaged polarization. This average is governed by a non-positive-definite weight, whose magnitude depends on the magnon density of the local excitation, while its sign is dictated by the local polarization handedness. Remarkably, this universal connection applies across diverse magnetic interactions and textures, offering crucial insights into spin-wave dynamics and dissipation.

Ergodicity has been one of the fundamental concepts underpinning our understanding of thermalization in isolated systems since the first developments in classical statistical mechanics. Recently, a similar notion has been introduced for quantum systems, termed complete Hilbert space ergodicity (CHSE), in which the evolving quantum state explores all of the available Hilbert space. This contrasts with the eigenstate thermalization hypothesis (ETH), in which thermalization is formulated via the properties of matrix elements of local operators in the energy eigenbasis. In this work we explore how ETH-violation mechanisms, including quantum many-body scars and Hilbert space fragmentation, can affect complete Hilbert space ergodicity. We find that the presence of these mechanisms leads to CHSE in decoupled subspaces, a phenomenon we call Hilbert subspace ergodicity, and which represents a protocol for constructing $t$-designs in subspaces.

Magnetic tunnel junctions (MTJs) based on ferromagnetic (FM) metal electrodes exhibit a tunneling magnetoresistance (TMR) effect, which can be well understood using a model of two spin-conduction channels and spin conservation in the tunneling process. Recently, TMR has been predicted and observed in antiferromagnetic (AFM) tunnel junctions (AFMTJs) based on noncollinear AFM electrodes, promising for high-speed and high-density spintronic applications. These findings challenge the conventional mechanism of TMR due to generally no spin conservation in noncollinear AFM metals. Here, we explore spin-polarized tunneling in an $\mathrm{M}{\mathrm{n}}_3\mathrm{GaN}/\mathrm{SrTi}{\mathrm{O}}_3/\mathrm{SrRu}{\mathrm{O}}_3$ (001) MTJ, where the reference layer is a noncollinear AFM $\mathrm{M}{\mathrm{n}}_3\mathrm{GaN}$ electrode and the free layer is a collinear FM $\mathrm{SrRu}{\mathrm{O}}_3$ electrode. Based on quantum-transport calculations, we predict that the rotation of FM magnetization of $\mathrm{SrRu}{\mathrm{O}}_3$ leads to the angular-dependent TMR being largely controlled by the matching of the average momentum-dependent spin polarization of the two electrodes. These results demonstrate that despite broken spin conservation in the tunneling process, the momentum-dependent spin polarization of the electrodes is a valuable quantity which can be used for elucidating TMR in MTJs with noncollinear AFM electrodes.

We consider unconventional magnets with proximity-induced superconductivity and investigate the emergence of superconducting correlations by carrying out a full classification of allowed Cooper pair symmetries. In particular, we focus on $d$-wave altermagnets and $p$-wave magnets under the influence of spin-singlet and spin-triplet superconductivity induced by proximity effect. Under generic conditions, we find that unconventional magnets not only drive a spin-singlet to spin-triplet conversion but also they transfer their parity symmetry that induces superconducting correlations with higher angular momentum. For instance, a conventional spin-singlet $s$-wave superconductor with $d$-wave altermagnetism is able to host odd-frequency mixed spin-triplet $d$-wave superconducting pair amplitudes, while when combining with $p$-wave magnetism the emerging superconducting pairing acquires an even-frequency mixed spin-triplet $p$-wave symmetry. We further demonstrate that unconventional magnetism produces even more exotic superconducting correlations in spin-singlet $d$-wave superconductors, where odd-frequency mixed spin-triplet $g$-wave and even-frequency mixed spin-triplet $f$-wave pair symmetries are possible in altermagnets and $p$-wave magnets, respectively. We also discuss how these ideas generalize to spin-triplet $p$-wave superconductors and show how our results can be applied to unconventional magnets with higher angular momentum, such as with $f$-, $g$-, and $i$-wave symmetries. Our results can help us understand the emergent superconducting correlations due to the interplay of unconventional magnetism and superconductivity.

Making use of first-principles calculations, we analyze the effect of quantum ionic fluctuations and lattice anharmonicity on the crystal structure and superconductivity of $I\overline{4}3m {\mathrm{CH}}_4\text{−}{\mathrm{H}}_3\mathrm{S}$, one of the lowest enthalpy structures in the C-S-H system, in the 150–300 GPa pressure range within the stochastic self-consistent harmonic approximation. We predict a correction to the crystal structure, which is formed by an ${\mathrm{H}}_3\mathrm{S}$ lattice and ${\mathrm{CH}}_4$ molecules, the phonon spectra, and the pressure-dependent superconducting critical temperatures, which have been estimated in previous calculations without considering ionic fluctuations on the crystal structure and assuming the harmonic approximation for the lattice dynamics. Our results show that quantum ionic fluctuations have an impact on the distance between H atoms and S atoms in the ${\mathrm{H}}_3\mathrm{S}$ host lattice, pushing it towards more symmetric bonds, while the methane molecules are barely affected. According to our anharmonic phonon spectra, this structure is dynamically stable above 150 GPa, which is 30 GPa lower than the pressure at which the harmonic approximation predicts the emergence of an instability. As a consequence of the strong anharmonic enhancement of the phonon frequencies, the electron-phonon coupling constant is suppressed by 46% at 200 GPa, and even more at lower pressures. As a result, the superconducting critical temperature is overestimated by around 50 K at 200 GPa, such that it falls below 150 K in the whole pressure range studied. Our results underline that ternary hydrides are subject to strong anharmonic effects on their structural, vibrational, and superconducting properties.

We utilize the topological holographic framework to characterize and gain insights into the nature of quantum critical points and gapless phases in fermionic quantum systems. Topological holography is a general framework that describes the generalized global symmetry and the symmetry charges of a local quantum system in terms of a slab of a topological order, termed as the symmetry topological field theory (SymTFT), in one higher dimension. In this work, we consider a generalization of the topological holographic picture for (1+1)$d$ fermionic quantum phases of matter. We discuss how spin structures are encoded in the SymTFT, and we establish the connection between the formal fermionization formula in quantum field theory and the choice of fermionic gapped boundary conditions of the SymTFT. We demonstrate the identification and the characterization of the fermionic gapped phases and phase transitions through detailed analysis of various examples, including the fermionic systems with ${\mathbb{Z}}_2^F, {\mathbb{Z}}_2\times {\mathbb{Z}}_2^F, {\mathbb{Z}}_4^F$, and the fermionic version of the noninvertible $\text{Rep}\left(S_3\right)$ symmetry. Our work uncovers many exotic fermionic gapped phases, quantum critical points, and gapless phases. These include gapped phases with fermionic noninvertible $\text{Rep}\left(S_3\right)$ symmetry, two kinds of fermionic symmetry-enriched quantum critical points, a fermionic gapless symmetry-protected topological phase, and a fermionic gapless spontaneous symmetry-breaking phase that breaks the fermionic noninvertible symmetry.

We report an infrared spectroscopy study of the antiferromagnetic (AFM) insulator ${\mathrm{EuZn}}_2{\mathrm{As}}_2$ over a broad frequency range, spanning temperatures both above and below the AFM transition $T_{\mathrm{N}}\simeq 20$ K. The optical response reveals an insulating behavior, featuring two prominent infrared-active phonon modes at around 95 and 190 ${\mathrm{cm}}^{-1}$, and two subtle absorption peaks at around 130 ($\alpha$ peak) and 2 700 ${\mathrm{cm}}^{-1}$ ($\beta$ peak), along with a strong absorption edge rising around 9000 ${\mathrm{cm}}^{-1}$ ($\gamma$ peak). Significantly, the temperature-dependent changes in these peaks show noticeable anomalies across the AFM transition, particularly the emergence of the $\alpha$ peak and an unusual redshift of the $\gamma$ peak, suggesting a strong interaction between the charge excitations and the AFM order. Band-structure calculations reveal that these anomalies arise from magnetization-induced band renormalizations, including shifts and foldings. Additionally, both phonon modes feature asymmetric Fano line shapes at low temperatures, with the 95 ${\mathrm{cm}}^{-1}$ phonon mode exhibiting strong coupling to the fluctuations of Eu spins. These findings highlight a complex interplay of spin, charge, and lattice degrees of freedom in ${\mathrm{EuZn}}_2{\mathrm{As}}_2$.

The spin Coulomb drag effect, arising from the exchange of momentum between electrons of opposite spins, plays a crucial role in the spin transport of interacting electron systems and can be characterized by the exchange-correlation (XC) kernel in the spin channel $K_{\mathrm{XC}}^{-}(q,\omega )$. Using the state-of-the-art variational diagrammatic Monte Carlo approach, we compute the Matsubara-frequency-resolved spin XC kernel $K_{\mathrm{XC}}^{-}(q,i{\omega }_n)$ for the three-dimensional uniform electron gas at sufficiently low temperatures with high precision. In the long-wavelength limit, we identified a singular behavior of the form $A\left(i{\omega }_n\right)/q^2$, confirming the theoretically predicted ultranonlocal behavior associated with spin Coulomb drag. Analysis of this structure in the low-frequency region enables precise determination of two crucial parameters characterizing the spin Coulomb drag effect: the spin mass enhancement factor and spin diffusion relaxation time. We observe a significant trend of increasing enhancement of the spin mass factor with decreasing electron density, and we provide clear evidence for the suppression of spin diffusion at low temperatures. These quantitative findings advance our understanding of Coulomb interaction effects on spin transport and provide essential parameters for time-dependent density functional theory and spintronics applications.

We show that the recently proposed Lebeda-Aschebrock-Kümmel (LAK) meta-generalized gradient approximation, the accuracy of which was previously established for atomization energies, bond lengths, and band gaps, also captures weak interactions near equilibrium without a dispersion correction. We discuss how this is achieved. Furthermore, we show that among the semilocal cost pure functionals, LAK is the one that reaches the highest accuracy for the large GMTKN55 database for general thermochemistry and kinetics. Next, we explain the design strategy of enhancement factor engineering. Its key idea is to complement exact constraints with construction principles. Finally, we discuss areas of research in which the use of LAK may offer advantages over existing functionals.

Although the QAH state with dissipationless chiral edge current has been observed in magnetic topological insulators (TIs) experimentally, the extremely low operation temperature calls for the search of TI systems with larger topological nontrivial band gap. Based on density-functional theory calculations, we find that ${\mathrm{Cr}}_2{\mathrm{O}}_3$(0001) substrate can be a promising substrate for the two-dimensional honeycomb stanene. When stanene is coupled to the ${\mathrm{Cr}}_2{\mathrm{O}}_3$(0001) substrate which shows ferromagnetism on the surface, ferromagnetism is induced in stanene by proximity effect. With the spin-orbit coupling (SOC) effect considered, a band gap as large as 130 meV can be obtained, and the nontrivial topological features of the obtained insulating states are confirmed by a nonzero Chern number ($\mathcal{C}=1)$ and one chiral edge state. Our results show that the ${\mathrm{Cr}}_2{\mathrm{O}}_3$(0001) substrate is an ideal substrate to realize the QAH effect in stanene at room temperature.

The properties of a two-dimensional electron gas (2DEG) in a semiconductor host with two valleys related by an underlying $C_4$ rotational symmetry are studied using Hartree-Fock and various other many-body approaches. A familiar artifact of the HF approach is a degeneracy between the valley-polarized—“Ising nematic”—and spin-polarized—ferromagnetic—phases, which is inconsistent with recent variational Monte Carlo (VMC) results. Correlation effects, computed either within the random phase approximation (RPA) or the T-matrix approximation, enhance the valley susceptibility relative to the spin susceptibility. Extrapolating the results to finite interaction strength, we find a direct first-order transition from a symmetry-unbroken state to a spin-unpolarized Ising nematic fluid with full valley polarization, in qualitative agreement with VMC. The RPA results are also reminiscent of experiments on the corresponding 2DEG in AlAs heterostructures.

Low-temperature luminescence spectra reveal the presence of two independent populations of GaN excitons within a GaN/AlGaN/$\mathrm{GaN}/{\mathrm{Al}}_2{\mathrm{O}}_3$ heterostructure in which a thick ($1.5\mu \mathrm{m}$) AlGaN layer separates a thin (150 nm) top GaN layer and a thick ($3.5\mu \mathrm{m}$) bottom GaN layer grown on sapphire. The presence of these two spectrally distinct families of excitons in each GaN layer of the heterostructure is demonstrated using three different experimental methods: (i) low-power $\mu$ photoluminescence ($\mu \mathrm{PL}$) using laser excitation sources with wavelengths above and below the AlGaN band gap, (ii) $\mu \mathrm{PL}$ as a function of optically injected free carrier density, and (iii) measurements of $\mu$ reflectivity ($\mu \mathrm{R}$), followed by quantitative numerical simulation to determine the physical parameters of each exciton population. One major impact of the built-in electric field is the reduction of the excitonic lifetime in the GaN surface layer, which transitions from less than 10 ps in the presence of the built-in electric field to the bulk lifetime (90 ps) when the field is screened. This increase in the excitonic lifetime is related to the modification of the band structure in the presence of optically injected free carriers. The effect of these lifetime variations on the luminescence spectra is analyzed. Lastly, we provide an estimate of the Mott density in GaN as $n_{\mathrm{Mott}}=4\times {10}^{17}{\mathrm{cm}}^{-3}$ at 130 K, consistent with values reported in the literature and accounting for the free carrier density required to screen the electric field.

We investigate the impact of the quantized mechanical motion of optically trapped atoms, arranged in proximity to a one-dimensional waveguide, on the propagation of polariton modes. Our study identifies a regime of resonant phonon-assisted mixing between lower and upper polaritons, resulting in a pronounced polaron effect. This effect is characterized by the formation of new band gaps and the appearance of weakly dispersive states within the original polariton band gap. The polaron spectrum, which can be directly probed via resonant elastic scattering, provides novel opportunities for quantum optical applications. These findings open avenues for enhanced control in state-of-the-art waveguide quantum electrodynamics experiments with cold atoms.

We report the discovery of an ultrastable antiferromagnetic two-dimensional (2D) ${\mathrm{CrF}}_3$ phase that is energetically more favorable than the traditionally assumed hexagonal structure. Using first-principles calculations combined with evolutionary structure searches, we identify a new low-energy rectangular configuration of ${\mathrm{CrF}}_3$, which exhibits remarkable anisotropic properties. Mechanically, this phase features zero in-plane Poisson's ratio, a rare negative out-of-plane Poisson's ratio, and quasi-one-dimensional (quasi-1D) mechanical behavior, characterized by minimal coupling between orthogonal directions. Electronically, ${\mathrm{CrF}}_3$ demonstrates quasi-1D transport properties with two independent conduction bands near the Fermi level, which are selectively tunable by applying uniaxial strain. The calculated band gap is 3.05 eV, and it can be continuously modulated under strain, providing a controllable means to engineer its electronic properties. The material also displays out-of-plane antiferromagnetic ordering with a magnetic anisotropy energy of 0.098 meV/Cr atom and an estimated Néel temperature of 24 K. In addition, we investigate the thermal conductivity of monolayer rectangular ${\mathrm{CrF}}_3$ (r-${\mathrm{CrF}}_3$), revealing significant anisotropy in its heat transport properties. The thermal conductivity along the $y$-axis is approximately 60.5 W/mK at 300 K, much higher than along the $x$-axis, where it is only 13.2 W/mK. The thermal anisotropic factor is computed to be 4.58, highlighting the material's strong directional heat transport capabilities. This factor surpasses that of other 2D materials such as black phosphorene, ${\mathrm{WTe}}_2$, and arsenene, indicating the potential of r-${\mathrm{CrF}}_3$ for advanced directional heat management applications. This makes the rectangular ${\mathrm{CrF}}_3$ phase a promising candidate for applications in spintronics, strain-engineered nanoelectronics, mechanical metamaterials, and thermal management technologies.

We explore the Mott transition in orthorhombic diamond lattices relevant to $\left(\mathrm{ET}\right){\mathrm{Ag}}_4{\left(\mathrm{CN}\right)}_5$ molecular compounds. The noninteracting phases include nodal line, Dirac and/or Weyl semimetals depending on the strength of spin-orbit coupling, and the degree of dimerization of the lattice. Based on an extension of slave-rotor mean-field theory which accounts for magnetic order, we find a transition from a semimetal to a paramagnetic Mott insulator at a critical onsite Coulomb repulsion $U_c$, which becomes Néel ordered at a larger $U_{\mathrm{cm}}>U_c$. The resulting intermediate Mott phase is a $\text{U}\left(1\right)$ quantum spin liquid (QSL) consisting on spinons preserving the nodal structure of the nearby semimetallic phases. While the QSL can be regarded a nodal-line Mott insulator (NLMI) in the absence of spin-orbit interaction (SOI), it behaves as a Dirac Mott insulator for nonzero SOI. An analysis of the Green's function in the NLMI shows how the zeros follow the spinon nodal-line bands carrying the topology while the poles describe the Hubbard bands. Our results are relevant to recent observations in $\left(\mathrm{ET}\right){\mathrm{Ag}}_4{\left(\mathrm{CN}\right)}_5$ molecular compounds in which the ambient pressure Néel ordered Mott insulator is gradually suppressed until semimetallic behavior arises at larger pressures.

We theoretically predict a multiwrapped parity-time ($\mathcal{PT}$)-symmetric topological insulator characterized by winding numbers $W=1$ and $W=2$ driven by the nonreciprocal spin-orbit coupling (SOC) in one-dimensional systems. The nonreciprocal SOC triggers a $\mathcal{PT}$-symmetry phase transition, resulting in the emergence of exceptional points. We find that the broken $\mathcal{PT}$ symmetry forbids the $W=1$ topological phase due to the coalescence of the bands. In contrast, the $\mathcal{PT}$-symmetric phase hosts both the single- and double-wrapped topological insulator phases. For the $\mathcal{PT}$-symmetric topological insulator, we can realize complete spin polarization by tuning the nonreciprocal SOC equipped with the bulk-boundary correspondence. The most significant spin polarization can be observed in exceptional points. The nonreciprocal SOC may lead us to unveil novel phases of matter by combining topological and non-Hermitian principles.

Anisotropic magnetic molecules can be employed to manipulate charge transport in molecular nanojunctions. Charge transport through a molecular orbital connected to two leads and exchange-coupled with a precessing anisotropic molecular spin in a constant magnetic field is studied here. The magnetic field and the uniaxial magnetic anisotropy parameter of the molecular spin modulate the total precession frequency. The precessing molecular magnetization drives inelastic tunneling processes between electronic quasienergy levels. The dc-bias voltages allow to unveil the quasienergy levels, Larmor frequency, and the anisotropy parameter, through characteristics of charge-transport measurements involving features such as steps, peaks, and dips. Quantum interference effects between states connected with spin-flip events are reflected in the shot noise as peak-dip (dip-peak) features, resembling Fano-like resonance profiles, and are controlled by the anisotropy parameter and Larmor frequency. Under zero bias, the increase of the anisotropy parameter enables the decrease of the precession frequency or alters the precession direction, and shot noise is reduced. Furthermore, it is possible to adjust the anisotropy parameter to suppress the precession frequency, leading to the suppression of shot noise. The results show that in the given setup, the charge current and shot noise can be controlled by the magnetic anisotropy parameter of the molecular spin.