We perform systematic analyses of single and multifrequency driving protocols on a Rashba nanowire with superconducting correlations induced by proximity effects. The results for the single-mode drive reveal interesting frequency dependencies of the Majorana modes, in the sense that the parameters corresponding to the trivial and the topological limits of the undriven (static) case host Majorana zero modes, respectively, at low and high frequencies. Further, emergence of long-range interactions are noted that give rise to multiple gap-closing scenarios, where the latter implies occurrence of multiple Majorana modes. On the other hand, the multifrequency driving protocol, subgrouped into commensurate and incommensurate ratios of the frequencies, demonstrates intriguing consequences. The commensurate case yields dynamical control over the stability of the edge modes, whereas more intricate driving protocols, such as those with larger frequency ratios, are studies as well and they are found to harm the Majoranas by pushing them into the bulk. Finally, the incommensurate case yields independent Majorana modes occurring at low-symmetry points in the Brillouin zone. While the single and the commensurate multifrequency driving protocols admit the usage of symmetric time frames for the computation of the topological invariants, the incommensurate case relies on the framework of many-mode Floquet theory, where the topological properties are ascertained via calculating the Berry phase. We present band structure and phase diagrams to substantiate all our results. The robustness and concurrent existence of these unique Majorana modes, even amid a very dense energy spectrum along with a lack of global time periodicity, hold promise for future applications in the field of quantum computation.

In this work we consider superconductor-semiconductor hybrids containing both trivial and Majorana zero modes and explore their signatures in the Majorana polarization. In particular, we consider trivial zero-energy states due to confinement and disorder, which seem to be very likely experimental scenarios. We show that the Majorana polarization is able to characterize the topological phase transition as well as the emergence of Majorana zero modes even when trivial zero-energy states proliferate. Notably, the Majorana polarization inherits direct information about spatial correlations which are then the key for distinguishing Majorana and trivial zero modes. We demonstrate the utility of the Majorana polarization in normal-superconductor junctions and superconductor-normal-superconductor Josephson junctions. Our results support the interpretation of the Majorana polarization as a real-space topological indicator.

We characterize the superconducting diode effect (SDE) in two-dimensional diffusive structures with Rashba spin-orbit coupling using the quasiclassical formalism. We consider both homogeneous superconductors and Josephson junctions. In the first case, the diode effect monotonically increases as the magnetic field is increased and the temperature is reduced, in contrast to the nonmonotonic behavior found in clean structures. In Josephson junctions, SDE dramatically increases and changes its sign close to the $0\text{−}\pi$ transition of the junction, which occurs at specific junction lengths and strengths of the magnetic field. We show that the SDE is strongly suppressed in narrow junctions. Our results are relevant for understanding recent experiments that measure SDE in mesoscopic nanostructures, where significant disorder is unavoidable.

We have grown single crystals of ${\mathrm{PrMgAl}}_{11}{\mathrm{O}}_{19}$, an ideal triangular-lattice antiferromagnet, and performed magnetic susceptibility, specific heat, and thermal conductivity measurements at low temperatures. The main results are as follows: (i) The temperature-dependent susceptibility shows a negligible in-plane response, and the isothermal magnetization curves confirm the easy axis along the $c$ axis. (ii) The specific heat measurements reveal the absence of long-range magnetic order down to 60 mK, and the power-law temperature dependence indicates the existence of the gapless magnetic excitations in the system. (iii) The ultralow-temperature thermal conductivity exhibits negligibly small residual term (${\kappa }_0/T$) and strong spin-phonon scattering effect, suggesting that the spin excitations are also involved. Our results further demonstrate that ${\mathrm{PrMgAl}}_{11}{\mathrm{O}}_{19}$ is a rare quantum spin liquid candidate with Ising-like anisotropy.

Motivated by the possibility of finding a bosonic quantum spin liquid in the integer spin-$S$ Heisenberg-Kitaev model on the honeycomb lattice, we derive a Schwinger boson mean-field theory involving both singlet and triplet pairing channels which includes hopping and pairing operators on equal footing. The mixed construction introduced here is justified by the good comparison with exact diagonalization energies of the $S\le 3/2$ Heisenberg-Kitaev model and the perfect match with the Luttinger-Tisza semiclassical energies obtained at large $S$. We find various competing gapped quantum spin liquids close to the Kitaev point. A comparison of their spin excitation spectrum with the dynamical structure factor obtained from exact diagonalizations allows us to identify the physical spin liquid Ansatz of the model. In particular, we identify a chiral quantum spin liquid state whose spin excitation spectrum follows closely the exact diagonalization data and survives up to large spin $S\lesssim 2$. We propose this state as a promising quantum spin liquid candidate for the integer spin-$S$ antiferromagnetic Kitaev model which may be realized in $S=1$ Kitaev materials ${\mathrm{A}}_3{\mathrm{Ni}}_2{\mathrm{XO}}_6$ and ${\mathrm{KNiAsO}}_4$.

In this work, we report an excitation of chaos and a nontrivial magnetization switching via transient chaos in a three-terminal spin-torque oscillator (STO). The driving force of the chaos is a voltage-controlled magnetic anisotropy (VCMA) effect generated by a feedback signal from the STO since the feedback effect is known to be effective in exciting chaos in a dynamical system. Solving the Landau-Lifshitz-Gilbert equation numerically and applying temporal and statistical analyses to its solution, the existence of the chaos driven by the feedback VCMA effect is identified. Simultaneously, however, transient chaos is also observed, where the magnetization initially shows chaotic behavior but finally switches its direction. This transient dynamics from chaos to magnetization switching was unexpected because the sign of the feedback VCMA effect was chosen so that the switching current increases and, as a result, the situation rather favors the condition for sustaining chaos. It is implied that this switching happens when narrowing a stable region of the magnetic potential energy by the feedback effect and magnetization precession pointing to a saddle point coincidentally occur simultaneously.

Quantum resonance in the paradigmatic kicked rotor system is a purely quantum effect that ignores the state of underlying classical chaos. In this work, it is shown that quantum resonance leads to superlinear entanglement production. In $N$ interacting kicked rotors set to be at quantum resonance, entanglement growth is superlinear until a crossover timescale $t^{*}$, beyond which growth slows down to a logarithmic form with superimposed oscillations. By mapping positional interaction to momentum space and analytically assessing the linear entropy, we unravel the mechanism driving these two distinct growth profiles. The analytical result obtained for the linear entropy agrees with the corresponding numerical simulations performed for two and three interacting kicked rotors. The late time entanglement oscillation is sensitive to changes in scaled Planck's constant with a high-quality factor suitable for high-precision measurements. These results are amenable to an experimental realization on atom optics setups.

We explore the universal signatures of quantum phase transitions that can be extracted with the density matrix renormalization group (DMRG) algorithm applied to quantum chains with a gradient. We present high-quality data collapses for the order parameter and for the entanglement entropy for three minimal models: transverse-field Ising, three-state Potts, and Ashkin-Teller. Furthermore, we show that scan-DMRG successfully captures the universal critical scaling when applied across the magnetic Wess-Zumino-Witten and nonmagnetic Ising transitions in the frustrated Haldane chain. In addition, we report a universal scaling of the lowest excitation energy as a function of a gradient rate. Finally, we argue that the scan-DMRG approach has significantly lower computational cost compare to the conventional DMRG protocols to study quantum phase transitions.

In this paper, we revisit the effect of flat bands on the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction by using a coordinate transformation that detangles flat-band states from dispersive ones. Under this transformation, original flat-band systems containing magnetic impurities are mapped onto a generalized Fano-Anderson model, where flat-band states act as Fano defects. From this perspective, several features of exact RKKY couplings calculated numerically can be understood easily. As an illustrative example, we analyze a dimerized diamond chain model, which can exhibit either gapped or gapless spectra depending on the ratio of hopping integrals. We find that anomalous decay in the RKKY couplings arises exclusively in the gapless case and with specific magnetic coupling configurations. Furthermore, the conventional wisdom regarding the signs of RKKY interactions breaks down under certain conditions. These subtleties arising from flat bands find explanation within our present approach. Our investigation offers deeper insights into how flat bands influence carrier-mediated exchange interactions, with implications extending to broader contexts.

The $j=3/2$ fermions in cubic crystals or cold atomic gases can form Cooper pairs in both singlet ($J=0$) and unconventional quintet ($J=2$) $s$-wave states. Our study utilizes analytical field theory to examine fluctuations in these states within the framework of the Luttinger-Kohn model. We investigate how collective modes evolve with varying spin-orbit coupling (SOC) strength. In the singlet state, quintet Bardasis-Schrieffer modes soften at a finite wave vector, hinting at Fulde-Ferrell-Larkin-Ovchinnikov physics. In the quintet state, we identify additional gapless and gapped modes originating from the partially broken symmetry due to SOC. Our results can be readily detected using current experimental techniques.

The Hund-metal route to strong correlations continues to attract large interest in the condensed-matter community. The question arose to what extent it applies to the infinite-layer nickelates and, as a related question, to two-orbital systems in general. Here, we provide a low-energy perspective on this topic through a dynamical mean-field study using the numerical renormalization group (NRG) as a real-frequency impurity solver. We find that the RG flow from high to low energy is a uniquely adequate tool to reveal two-stage Kondo screening (2SKS), a fascinating mechanism for Hund physics. Further, we show that 2SKS takes place in a quarter-filled two-orbital system, but can be easily suppressed by a sufficiently large crystal-field splitting. We apply these insights to ${\mathrm{LaNiO}}_2$ using a recently proposed two-orbital model and show that it is indeed the crystal-field splitting that suppresses multiorbital phenomena in this scenario. Our general findings open the way for further explorations of 2SKS, and we propose a way of potentially inducing low-energy Hund physics in ${\mathrm{LaNiO}}_2$ by counteracting the crystal field.

The recent experimental observation of a potentially fractional quantum spin Hall (FQSH) state in the twisted ${\mathrm{MoTe}}_2$ system has sparked theoretical explorations at total filling ${\nu }_T=1$ of a pair of $C=\pm 1$ Chern bands from the two spins (locked to valley). One intriguing candidate is a vortex spin liquid (VSL), which can be viewed as an exciton version of composite Fermi liquid (CFL). The VSL insulator is incompressible in the charge channel, while compressible in the spin channel. Here, we investigate fully gapped descendants of the VSL phase at the total filling ${\nu }_T={\nu }_{\uparrow }+{\nu }_{\downarrow }=1$. At zero magnetization, a non-Abelian state with both FQSH and thermal Hall effect emerges from weak $p+ip$ pairing of the neutral Fermi surface, hosting 12 anyons (up to addition of physical electron) including two independent Ising anyons separately carrying charge and spin. Strong pairing leads to a ${\mathrm{Z}}_4$ topological order with only FQSH effect. At nonzero magnetization $m=2S_z$, there is a Jain sequence of magnetic plateaus with $m=\frac{1}{p},p\in Z$, exhibiting both half FQSH effect and spin fractional quantum Hall effect (SFQH). Our study highlights the VSL's potential as a parent state to organize numerous FQSH insulators with nontrivial intervalley correlations at ${\nu }_T=1$. The quantized FQSH behavior remains robust even in the presence of ferromagnetism, thanks to the spin-charge separation nature inherent in the parent VSL phase. Future experimental investigations are crucial to validate or rule out spontaneous magnetization and time-reversal symmetry breaking.

Two-dimensional (2D) MXenes have made great achievements as electrodes and functional protective layers for alkali and alkaline earth metal ion batteries. However, their application in rechargeable anion batteries is lethally limited by the electrostatic repulsion between anions and surface terminal groups. Here, first-principles calculations were employed to investigate the effects and mechanism of MXenes surface terminal groups (OH, C, O, N, and P) on the storage of chloride anion and the electrochemical performance of their corresponding battery. $\mathrm{C}{\mathrm{l}}^{-}$ can be successfully stored on the surface of N-terminated MXenes ($\mathrm{T}{\mathrm{i}}_3{\mathrm{C}}_2{\mathrm{N}}_2$) because a covalent bond can be formed between N and Cl. At the same time, $\mathrm{T}{\mathrm{i}}_3{\mathrm{C}}_2{\mathrm{N}}_2$ has a satisfactory theoretical capacity and open-circuit voltage of $1095\mathrm{mAh}{\mathrm{g}}^{-1}$ and 1.11 V, respectively, and meets the stringent requirements for rapid ion migration (1.15 eV) and high energy density ($1215\mathrm{Wh}{\mathrm{g}}^{-1}$) for cathode materials in anion batteries. Moreover, the N-terminal functional group of MXenes exhibits excellent performance on all halogen anion batteries. Even when the metallic element Ti is replaced with other metallic elements, these N-terminated MXenes show superior ability to store anions. Therefore, the N-terminal group is expected to bring spring to the application of MXenes in halogen anion batteries.

Traditional van der Waals spin valves, usually comprising of a nonmagnetic monolayer sandwiched between two ferromagnetic monolayers, present a significant challenge for precise synthesis in contemporary experimental techniques. Can spin valves be implemented with a monolayer compound instead of a van der Waals multilayer heterostructure? Here, we propose a room-temperature ${\mathrm{HfCr}}_2{\mathrm{N}}_4$ monolayer spin valve based on density functional theory and Boltzmann transport theory. The ${\mathrm{HfCr}}_2{\mathrm{N}}_4$ monolayer is a ferromagnetic half-metal with a high Curie temperature above room temperature. The transition from half-metal to semiconductor can be achieved by manipulating the relative orientation of magnetizations of the Cr atomic layers. Interestingly, the biaxial strain applied in the $xy$ plane is an effective strategy to switch the magnetic configurations. The magnetic ground state of the ${\mathrm{HfCr}}_2{\mathrm{N}}_4$ monolayer converts to the antiferromagnetic configuration under $-4\%$ strain. Remarkably, the ${\mathrm{HfCr}}_2{\mathrm{N}}_4$ monolayer exhibits a substantial room-temperature magnetoresistance ratio of $572\%$, attributed to variations in band gaps and carrier mobilities. Our findings pave the way for designing future room-temperature monolayer spin valve devices.

We present the non-Hermitian many-body localization (MBL) induced by imaginary disorder. By numerically calculating the entanglement entropy and complex level spacing, we identify a clear thermal-MBL transition: the entanglement entropy from the volume law to area law and the level spacing from the repulsive distribution to the uncorrelated Poisson distribution. In the complex energy plane, there exists a mobility loop separating different phases, which is similar to the mobility edge for the Hermitian MBL. Surprisingly, we find that the confluence of imaginary disorder and the localization length provides tunneling channels for dynamically jumping of the particles from the initial to the final state in both the real and Hilbert spaces. Our work provides an example of non-Hermitian many-body phases induced by imaginary disorder, which offers new possibilities for studying strongly correlated non-Hermitian physics.

We investigate the magnetic and transport properties of ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3\left(\mathrm{LSMO}\right)/{\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ (PCMO) like ferromagnetic/antiferromagnetic superlattices (for electron densities $n=1-x$ = 0.5 and 0.55) in three dimensions using a two orbitals double exchange model incorporating the Jahn-Teller lattice distortions, superexchange interactions and long-range Coulomb interactions. In our Monte Carlo simulations, we primarily focus on periodic arrangement of $w_L$ planes of ferromagnetic LSMO and $w_P$ planes of antiferromagnetic PCMO manganites, and set $w_L+w_P=10$. The induced ferromagnetic correlations in the parent antiferromagnetic PCMO layer decrease monotonically with increasing the antiferromagnetic layer width $w_P$ at high temperatures (below the ferromagnetic $T_C$ of LSMO layer, but just above the charge ordering temperature of PCMO layer) for both half-doping and off-half-doping scenarios. As we decrease the temperature further, the induced ferromagnetic moments in PCMO layer disappear or decrease considerably at half-doping because of the onset of charge ordering in antiferromagnetic PCMO layer. Overall, the magnetization in PCMO layer decreases at low temperatures and the metal-insulator transition temperature of the LSMO/PCMO superlattices increases with increase in the PCMO layer width $w_P$, similar to the experiments. On the other hand, at off-half-doping ($n=0.55$), the induced ferromagnetic moment survives even at low temperatures, caused by the weakened charge ordering in PCMO layer, and interestingly, varies nonmonotonically with the PCMO layer width, in agreement with experiments. The nonmonotonic trend of the conductivity of the superlattice with increase in the PCMO layer width $w_P$ shows a one-to-one correspondence between the conductivity of the superlattice and the induced ferromagnetic moments in PCMO layer. We highlight the key role of induced ferromagnetic moments in PCMO layer in analyzing the magnetotransport properties of the LSMO/PCMO superlattices.

Plutonium is a highly oxidizable metal, and the study of Pu oxide has always been an active field. In this study, the low-oxidation state of plutonium monoxide (PuO) was investigated using density functional theory combined with dynamical mean field theory (DFT + DMFT). The study reveals that in PuO, four of the Pu $5f$ electrons occupy the $j=5/2$ configuration and display itinerant behavior, whereas approximately 0.688 electrons occupy the localized $j=7/2$ configuration. This explains why there are no magnetic moments in PuO. Temperature does not induce transitions between the localized and itinerant electrons in PuO, suggesting that the $5f$ electrons predominantly exhibit itinerant characteristics. With increasing temperature, the correlation of the $f$ electrons in PuO decreases, and the hybridization between the $5f$ electrons and valence electrons of oxygen is extremely weak, with minimal involvement in bonding. Additionally, the transport capability of PuO increases with temperature. Moreover, within the temperature range studied, PuO can exist as a stable binary phase. In addition, this paper obtained the Debye temperature and linear coefficient of heat capacity for PuO through the harmonic approximation, and these results can serve as references for future experimental and theoretical studies on PuO.