We study the electronic band structure of twisted double trilayer graphene. This system consists of two regularly stacked graphene trilayers rotated by a given angle. We consider two different arrangements for the trilayer units following their stackings: ABA-ABA and ABC-ABC. First-principles calculations at an angle of $13.1^{\circ }$ show that these two systems are semiconductors with narrow gaps, which result from a reduced symmetry due to the presence of the second trilayer. Next, we use these results to build a tight-binding model to study lower twist angles, which are not accessible to first-principles methods. In both cases, we find that, as the angle decreases, the magnitude of the gap decreases and eventually closes. At the same time, the low-energy bands develop into flat bands. The corresponding magic angle is greater than the values found in twisted bilayer graphene and twisted double bilayer graphene, thus supporting a hypothesis that it should increase as a function of the number of stacked layers in the rotating unit. We also discuss the spatial separation of the electronic states and their hybrization as a function of the twist angle, as well as the behavior of the systems under an external electric field. We find patterns that are reminiscent of the behaviors found in gated ABA and ABC trilayers, such as tunable overlaps or band gaps, respectively.

The electronic specific heat of Kondo insulators in a magnetic field is studied for the half-filled Kondo lattice model on a simple cubic lattice using low-temperature theory in Kumar representation. The calculated specific heat is found to show quantum oscillations, which appear soon after the inversion transition and become prominent with decreasing Kondo coupling. Interestingly, it is noted that the field derivative of specific heat closely resembles the magnetic quantum oscillations, and exhibits more pronounced oscillations at finite temperatures than the magnetization itself. An empirical Lifshitz-Kosevich fit with two frequencies given by the theory describes these quantum oscillations reasonably well, where the frequencies correspond to the extremal areas on the surface of the charge gap, a remnant of the Fermi surface in the insulating case.

The Kohlrausch(-Williams-Watts) law of stretched exponential relaxation has been observed for over a century and a half in diverse complex classical systems. Here we show that this law describes relaxation quite generically in closed (executing Schrödinger dynamics), interacting disordered many-body systems, using interaction range and disorder strength as primary tuning parameters. This we observe for both time-independent and periodically driven (Floquet) systems. Finite-size analysis indicates the persistence of this nonthermal relaxation regime in the thermodynamic limit thus defining a distinct dynamical regime. This regime exhibits a peak in the time scale of the long-time relaxation (following a transient), upon crossing over from weak to strong disorder. We provide a simple picture of this behavior, which naturally accounts for its generic occurrence. Formation of spin-glass — one of the possible mechanisms for stretched relaxation appears incidental to the occurrence of Kohlrausch law in our context. Finally, we provide a simple non-Hermitian Hamiltonian formulation for the dynamics of a single spin embedded in the disordered chain. This provides an analytical formula that captures not only the Kohlrausch relaxation of the disorder averaged autocorrelation but also captures the largely diverse dynamics of an arbitrary target spin in the system. Our work hence also provides a concrete quantification of the “prethermal slowness” in many-body disordered system.

We present an optimization principle for the Harper-Hofstadter model that naturally yields the critical value $\lambda =2$ for the Harper parameter. We provide proofs for this principle and its corollaries. We demonstrate that it can be applied to a continuum model, where it can be used to find the physical parameters for criticality.

Regularization aims to cure the singularities in field theory by modifying observables and making them finite; for example, lattice discretization is a traditional regularization scheme in which the lattice constant $a$ provides a hard ultraviolet cutoff. Here, we offer an alternative approach to regularize the continuous $(1+1)$-dimensional space-time, which is dubbed the “noncommutative circle.” This method combines two key ingredients: continuous torus geometry and Landau level projection in the quantum Hall physics. Based on this method, we study the critical phenomena of quantum phase transitions belonging to the Ising and Potts universality classes, and we systematically identify the low-energy eigenstates corresponding to Virasoro primary and quasiprimary operators and organize the remaining low-energy eigenstates into conformal towers.

The reduced dielectric screening in atomically thin semiconductors leads to remarkably strong electron interactions. As a result, bound electron-hole pairs (excitons) and charged excitons (trions), which have binding energies in the hundreds and tens of meV, respectively, typically dominate the optical properties of these materials. However, the long-range nature of the interactions between charges represents a significant challenge to the exact calculation of binding energies of complexes larger than the exciton. Here, we demonstrate that the trion binding energy can be efficiently calculated directly from the three-body Schrödinger equation in momentum space. Key to this result is a highly accurate way of treating the pole of the electronic interactions at small momentum exchange (i.e., large separation between charges) via the Landé subtraction method. Our results are in excellent agreement with quantum Monte Carlo calculations, while yielding a substantially larger ratio of the trion to exciton binding energies than obtained in recent variational calculations. Our numerical approach may be extended to a host of different few-body problems in 2D semiconductors and even potentially to the description of exciton polarons.

We present a thorough investigation of nonstabilizerness—a fundamental quantum resource that quantifies state complexity within the framework of quantum computing—in a one-dimensional U(1) lattice gauge theory including matter fields. We show how nonstabilizerness is always extensive with volume, and has no direct relation to the presence of critical points. However, its derivatives typically display discontinuities across the latter: This indicates that nonstabilizerness is strongly sensitive to criticality, but in a manner that is very different from entanglement (which, typically, is maximal at the critical point). Our results indicate that error-corrected simulations of lattice gauge theories close to the continuum limit have similar computational costs to those at finite correlation length and provide rigorous lower bounds for quantum resources of such quantum computations.

The Janus VSBrI monolayer, identified by first-principles calculations, emerges as a promising semiconducting material with desirable ferromagnetic and ferroelectric properties. Its in-plane magnetic anisotropic energy is up to $460\mu \mathrm{eV}$/V, which is larger than many other known two-dimensional materials. The energy variations among different magnetic states show a strong correlate with polarization. Interestingly, the stability of the ferroelectric phase can be further enhanced by the application of biaxial tensile strain. The Janus VSBrI monolayer exhibits a notable out-of-plane piezoelectric response ($d_{32}=1.60$ pm/V) due to its disrupted out-of-plane symmetry, a characteristic uncommon in Janus monolayers. These intriguing properties make the Janus VSBrI monolayer highly desirable for practical applications in piezoelectronic devices, and a promising candidate for multifunctional spintronic devices.

Quantum coherence, a fundamental resource in quantum computing and quantum information, often competes with localization effects that affect quantum states in disordered systems. In this work, we prove exact trade-off relations between quantum coherence and a measure of localization and many-body localization, namely, the inverse participation ratio (IPR). We prove that for a pure quantum state, the $l_1$ norm of quantum coherence and the relative entropy of coherence satisfy complementarity relations with IPR. For a mixed state, IPR and the $l_2$ norm of quantum coherence as well as relative entropy of coherence satisfy trade-off inequalities. We further explore the applicability of these general relations between quantum coherence and measure of localization in the context of delocalization to many-body localization transition in a disordered interacting quantum many-body system and demonstrate that quantum coherence is also an ideal characterization of the delocalization to many-body localization transition. Our numerical analysis shows that though the full system loses coherence in the many-body localization phase, coherence of a subsystem can increase with the combined effect of disorder and interactions. We believe that these trade-off relations can help in better understanding of how coherence can be preserved or lost in realistic many-body quantum systems, which is vital for developing robust quantum technologies and uncovering new phases of quantum matter.

We put forward that circularly polarized light is a versatile way to manipulate the quantum anomalous Hall effect (QAHE) in kagome noncollinear antiferromagnets. Employing model analysis and first-principles calculations, we investigate the origin of nontrivial insulator and nonvanishing anomalous Hall conductivity, where a topological phase transition from nontrivial semimetals to Chern insulators emerges accompanied by the breaking of mirror symmetry $\mathcal{M}$ and combined symmetry ${\mathcal{C}}_{6z}\mathcal{T}$. In particular, both the organic and inorganic material candidates, i.e., ${\mathrm{Cr}}_3{\text{(HAB)}}_2$ and ${\mathrm{Cr}}_3{\mathrm{Te}}_2$ monolayers, are proposed to realize the Floquet-engineered QAHE, confirmed via nonzero Chern numbers $\mathcal{C}=\pm 1$ and the emergence of one chiral edge state in the nanoribbons. Moreover, a tight-binding model is constructed to demonstrate the generality and feasibility of attaining Floquet-engineered QAHE in kagome noncollinear antiferromagnets. These findings hold substantial significance for the combination of QAHE, Floquet engineering, and noncollinear antiferromagnets with high possibility of innovative applications in topological spintronics.

Recently, ternary clathrate hydrides have become promising candidates for high-temperature superconductor. However, it is a formidable challenge to effectively hunt high-temperature superconductivity among multinary hydrides due to the expensive computational cost associated with large unit cells and huge stoichiometric choices. Here, we present an efficiently data-driven strategy, including generated clathrate frameworks, the quick estimation of stability for each framework, and superconducting critical temperature ($T_{\mathrm{c}}$) for each hydride structure, to accelerate the discovery of high-temperature superconducting hydrides. Our strategy was initialized with more than one million input structures via zeolite databases and our generated dataset. As a result, such a strategy hitherto uncovered 14 prototypical hydrogen frameworks for clathrate hydrides, which is 1.5 times greater than the number (9) of previously reported prototypes. Remarkably, 11 ternary clathrate structures were predicted to have $T_{\mathrm{c}}$'s above 250 K at 300 GPa. Further extensive global structure-searching simulations support that $\mathrm{L}{\mathrm{i}}_2\mathrm{Na}{\mathrm{H}}_{17}$ and $\mathrm{Th}{\mathrm{Y}}_2{\mathrm{H}}_{24}$ are thermodynamically stable at 220 and 150 GPa, respectively, with $T_{\mathrm{c}}$'s approaching room temperature of 297 and 303 K, which are promising for future synthesis. These results offer a platform to explore high-temperature superconductors via a great number of databases.

We investigate field-induced quantum phase transitions in a superconducting Ta thin film with a series of periodic hole arrays. While it is known that introducing a hole array can influence quantum phase transitions, this effect has not been systematically explored. Exploiting the effect of disorder in our platform, we discover remarkable suppression of the superconducting transition temperature and the Bose metallic state with increasing areal hole density. This systematic study on unique disorder indicates that the Bose metallic state can be reduced by the regulation of vortex motion.

We study the effects of flux creep on the linear AC response of the vortex lattice in single crystals ${\mathrm{Ca}}_3{\mathrm{Ir}}_4{\mathrm{Sn}}_{13}$ by measuring the Campbell penetration depth, ${\lambda }_{\mathrm{C}}(T,H,t)$. Thermal fluctuations release vortices from shallow pinning sites, only for them to become re-trapped by deeper potential wells, causing an initial increase of the effective Labusch parameter, which is proportional to the pinning well curvature. This effect cannot be detected in conventional magnetic relaxation measurements but is revealed by our observation of a nonmonotonic time evolution of ${\lambda }_{\mathrm{C}}(T,H,t)$, which directly probes the average curvature of the occupied pinning centers. The time evolution of ${\lambda }_{\mathrm{C}}(T,H,t)$ was measured at different temperatures in samples with different densities of pinning centers produced by electron irradiation. The curves can be collapsed together when plotted on a logarithmic time scale $t\to Tln(t/t_0)$ confirming that the time evolution is driven by flux creep. The ${\lambda }_{\mathrm{C}}(T,H,t)$ is hysteretic with a noticeable nonmonotonic relaxation in the presence of a vortex density gradient (after zero-field cooling), but is monotonic after field cooling, where the vortex density is uniform. This result quantitatively corroborates the novel picture of vortex creep based on the strong pinning theory.

We develop a Ginzburg-Landau theory for commensurate pair density wave states in a hexagonal lattice system, relevant to the kagome superconductors ${\mathrm{AV}}_3{\mathrm{Sb}}_5$. Compared to previous theoretical frameworks, the commensurate wave vectors permit additional symmetric terms in the free energy, altering the system's ground state and its degeneracy. In particular, we analyze topological defects in the energetically favorable ${\psi }_{\text{kagome}}$ ground state and find that kinks on domain walls can carry $1/3$ topological charges. We further establish a correspondence between the superconducting fluctuations in these states and an effective $J_1-J_2$ frustrated XY model on the emergent kagome lattice. By employing a state-of-the-art numerical tensor network method, we rigorously solve this effective model at finite temperatures and confirm the existence of a vestigial phase characterized by $1/3$ vortex-antivortex pairs in low temperatures with the absence of phase coherence of Cooper pairs, which is dual to the charge-$6e$ condensed phase. Our theory provides a potential explanation for the vestigial charge-$6e$ magnetoresistance oscillations observed in recent experiments [J. Ge et al., Phys. Rev. X 14, 021025 (2024)].

We consider Josephson junctions formed by coupling two conventional superconductors via an unconventional magnet and investigate the formation of Andreev bound states, their impact on the Josephson effect, and the emergent superconducting correlations. In particular, we focus on unconventional magnets known as $d$-wave altermagnets and $p$-wave magnets. We find that the Andreev bound states in $d$-wave altermagnet and $p_y$-wave magnet Josephson junctions strongly depend on the transverse momentum, with a spin splitting and low-energy minima as a function of the superconducting phase difference $\phi$. In contrast, the Andreev bound states for $p_x$-wave magnets are insensitive to the transverse momentum. We then show that the Andreev bound states can be probed by the local density of states in the middle of the junction, which also reveals that $d_{x^2-y^2}$- and $p$-wave magnet junctions are prone to host zero energy peaks. While the zero-energy peak in $d_{x^2-y^2}$-wave altermagnet junctions tends to oscillate with the magnetic order, it remains robust in $p$-wave magnet junctions. We then discover that the Josephson current in $d$-wave altermagnet junctions is composed of higher harmonics of $\phi$, which originate a $\varphi$-Josephson junction behavior entirely controlled by the magnetic order in $d_{xy}$-wave altermagnets. In contrast, the Josephson current in Josephson junctions with $p$-wave magnets exhibits a conventional sinelike profile with a fast sign change at $\phi =\pi$ due to zero-energy Andreev bound states. We also demonstrate that the critical currents in $d$-wave altermagnet Josephson junctions exhibit an oscillatory decay with the increase of the magnetic order, while the oscillations are absent in $p$-wave magnet junctions albeit the currents exhibit a slow decay. Furthermore, we also demonstrate that the interplay of the Josephson effect and unconventional magnetic order of $d$-wave altermagnets and $p$-wave magnets originates from odd-frequency spin-triplet $s$-wave superconducting correlations that are otherwise absent. Our results can serve as a guide to pursue the new functionality of Josephson junctions based on unconventional magnets.

The optical properties of layered materials are dominated by intralayer excitons; especially for layered antiferromagnets the layer-to-layer charge hopping, and therefore interlayer excitons, are spin forbidden. An external magnetic field, however, can continuously drive the magnetic order towards layer-to-layer ferromagnetic, which opens spin-allowed charge-transfer channels between the layers. Here, we elaborate how their admixture changes the composition and nature of the excitons, leading to an extension over many layers, and causing a quadratic redshift with respect to the external magnetic field in CrSBr. We present a minimal four-band model to elucidate the interplay between the various interaction and coupling mechanisms which is able to reproduce the findings of our ab initio $GW$–Bethe-Salpeter equation calculations as a function of magnetic field. Our model is generally valid for any coupled layers with different spin directions and the insights help to systematically address excitons and to predict their optical signatures in such systems.