The vortex dynamics in the spin-triplet superconductor ${\mathrm{UTe}}_2$ are studied by measuring the dc electrical resistivity with currents along the $a$ axis under magnetic fields along the $b$ axis. Surprisingly, we have discovered an island region of low critical current deep inside the superconducting (SC) state, well below the SC upper critical field, attributed to a weakening of vortex pinning. Notably, this region coincides with the recently proposed intermediate-field SC state. We discuss the possibility of nonsingular vortices in the intermediate state, where the SC order parameter does not vanish entirely in the vortex cores due to the mixing of multiple SC components.

We investigate an idealized continuum model of a twisted homotrilayer transition metal dichalcogenides with negligible next-nearest-layer couplings. We systematically analyze band structure and topology of various stacking configurations in a twist angle range from $1^{\circ }$ to $4^{\circ }$. This allows us to uncover a plethora of topological transitions as well as various angle regimes with flat bands, some of them topologically nontrivial, which are of growing interest for the realization of exotic strongly correlated phases. Additionally, we uncover surprising properties, such as that for certain stacking configurations, some layers effectively decouple from other layers. In this case, the only remnant of coupling between layers is a layer-dependent energy shift.

We study the current driven by an applied voltage as a function of time through the Sachdev-Ye-Kitaev model when coupled to two normal or superconducting reservoirs. For normal leads, in the strong coupling limit and for small bias, the current through the Sachdev-Ye-Kitaev model, described by a quartic interaction term, reaches monotonically the stationarity, in contrast to the case of a disordered quadratic interaction where the current has a peak before reaching the stationary phase. For superconducting leads the currents have oscillations whose frequencies are determined by the gap and the voltage, and are suppressed in the strong coupling limit. Moreover, due to different short time scales between the normal and the oscillating part of the superconducting current, a peak appears before reaching the stationarity.

Slow light effect plays a crucial role in both optical physics and devices. Herein, we explore the possibility to achieve ultraslow light effect based on the quasibound states in the continuum (quasi-BICs) in a compound grating waveguide structure. Driven by the unique resonant property of the quasi-BIC, the group velocity of light can be intensively slowed down to the order of ${10}^{-4}c$. Interestingly, we disclose that the group velocity of light and geometric perturbation parameters conforms to double-logarithm linear relationship. Our findings not only offer unique insight for the relation between slow light effect and BIC, but also provide a feasible route to achieving ultraslow light effect.

The dynamics of interacting quantum many-body systems has two seemingly disparate but fundamental facets. The first is the dynamics of real-space local observables, and if and how they thermalize. The second is to interpret the dynamics of the many-body state as that of a fictitious particle on the underlying Hilbert-space graph. In this work, we derive an explicit relation between these two aspects of the dynamics. We show that the temporal decay of the autocorrelation in a disordered quantum spin chain is explicitly encoded in how the return probability on Hilbert space approaches its late-time saturation. As such, the latter has the same functional form in time as the decay of autocorrelations but with renormalized parameters. Our analytical treatment is rooted in an understanding of the morphology of the time-evolving state on the Hilbert-space graph, and corroborated by exact numerical results.

We provide a quantitative and controlled analysis of the phase diagram of the Yukawa-Sachdev-Ye-Kitaev model on a lattice, in the normal and superconducting states. We analyze the entire crossover from Bardeen-Cooper-Schrieffer (BCS)/weak coupling to Eliashberg/strong coupling superconductivity, as a function of fermion-boson interaction strength and hopping parameter. Cooper pairs of sharp Fermi-liquid quasiparticles at weak coupling evolve into pairing of fully incoherent fermions in the non-Fermi liquid regime. The crossovers leave observable traces in the critical temperature, the zero-temperature and zero-energy gap, the entropy, and the phase stiffness.

The ability to apply and tune large magnetic fields locally is a crucial requirement for several devices, most notably for the detection and generation of Majorana fermions. Such a functionality can be achieved in superconductor (S)/ferromagnet (F) bilayers, where superconductivity is strengthened on top of domain walls due to local lowering of the proximity-induced effective exchange fields. By using niobium and ferromagnetic insulating (GdN) bilayers, and through detailed magnetotransport measurements, we demonstrate the phenomena of switching in and out of the domain wall superconducting phase in S/F bilayers by purely paramagnetic tuning of induced exchange fields. In the thinnest of niobium layers, we estimate that this tunability can be as high as 1.3 T with the application of in-plane external fields of a few milliteslas.

Magnetically frustrated platforms have resurged in spintronics as optimal candidates for hosting three-dimensional topological spin textures (e.g., Shankar skyrmions and $4\pi$-vortices) as well as topological defects (e.g., magnetic disclinations). These topological excitations are encoded in the noncollinear order emerging at the mesoscale from the measurement of the spin-spin correlation, and have not been observed experimentally so far due to the absence of probes coupling directly to this exotic rotation-matrix order parameter. In this work we examine the spin-transfer and topological Hall physics of metallic frustrated magnets and show that SO(3) solitons and magnetic disclinations mediate previously unidentified contributions to the corresponding effects, with no analog in collinear magnetism. In particular, we present a minimal low-energy long-wavelength theory of the Yang-Mills type for the itinerant carriers and also discuss the emergent electrodynamics mediated by the topological solitons/defects arising in the noncoplanar magnetic background. We also considered the effect of symmetry reduction (with respect to the case of full rotational symmetry) on both spin-transfer and topological Hall responses of the magnetic conductor. Furthermore, we discuss experimental setups for the detection of the aforesaid Hall currents. Our findings open new avenues for the detection of topological solitons/defects in magnetic systems with order-parameter manifolds beyond the conventional $S^2$ paradigm.

We report the nonreciprocal excitation of propagating forward volume exchange spin waves in yttrium iron garnet (YIG) thin film with perpendicular anisotropy by bringing the in-plane magnetization of ${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$ (CoFeB) nanowires to resonance. All-electric spin-wave spectroscopy is used to measure propagating spin waves in YIG subjected to out-of-plane external magnetic fields. The nonreciprocity can be reconfigured by inverting the in-plane magnetization of the CoFeB nanowires. The exchange spin waves achieved in the experiments have wavelengths down to about 150 nm and fast group velocities of up to 1.6 km/s, which can be accounted for with the dipole-exchange spin-wave dispersion of the forward volume mode. Micromagnetic simulations reproduce these experimental features, verifying that the key physics behind this nonreciprocity is the intrinsically chiral dynamic stray fields generated by the resonating CoFeB magnetization. Our results provide key insights into advanced and high-frequency magnonic devices.

Although most studies of strongly correlated systems away from equilibrium have focused on clean systems, it is well known that disorder may significantly modify observed properties in various nontrivial ways. The nonequilibrium interplay of interaction and disorder in these systems thus requires further investigation. In the present paper, we use the recently developed nonequilibrium $\text{DMFT}+\text{CPA}$ embedding scheme, that combines both the dynamical mean field theory (DMFT) and the coherent potential approximation (CPA) nonequilibrium extensions, to characterize the relaxation and the thermalization of a disordered interacting system described by the Anderson-Hubbard model under an interaction quench. The system, initially in equilibrium at a given temperature, has the interaction abruptly switched from zero to a finite value at a given time. To investigate the role of disorder, we use our effective medium approach to calculate, for different values of the final interaction and of the disorder strength, the distribution functions as the system evolves in time. This allows us to determine the effective temperature after the quench and to analyze the effects of disorder on the thermalization for various interaction strengths. We find that, for moderate interactions after the interaction quench, disorder can tune the final temperature of the system across a broad range of values with increased disorder strength leading to lower effective temperature.

$1T$-phase $\mathrm{Cr}{\mathrm{Te}}_2$ $\left(1T\text{−}\mathrm{Cr}{\mathrm{Te}}_2\right)$ has received considerable interest recently due to its high Curie temperature $\left(T_C\right)$, which is desirable for practical spintronics applications. However, various magnetic behaviors of $1T\text{−}\mathrm{Cr}{\mathrm{Te}}_2$ have been reported in recent experimental and theoretical studies when its thickness reduces to ultrathin limit. In this work, the magnetic diagram of monolayer (ML) $1T\text{−}\mathrm{Cr}{\mathrm{Te}}_2$ with respect to in-plane biaxial strain and on-site Coulomb repulsion $U$ is obtained based on first-principles calculations. Our results indicate that the magnetic order of ML $1T\text{−}\mathrm{Cr}{\mathrm{Te}}_2$ can vary among ferromagnets and antiferromagnets with strain and electronic correlation. We show that the large exchange anisotropy and higher-order biquadratic interactions are crucial to accurately describe the spin energies in ML $1T\text{−}\mathrm{Cr}{\mathrm{Te}}_2$. The perplexing dependencies of the magnetocrystalline anisotropy on strain and $U$ are then well explained. Our work not only gives insight into the fundamental understanding of the unusual magnetic properties of ML $1T\text{−}\mathrm{Cr}{\mathrm{Te}}_2$, which is helpful to understand the diverse observations on the magnetic order in $\mathrm{Cr}{\mathrm{Te}}_2$, but also sheds light on engineering their performance for spintronic devices.

Spin-momentum locking is a unique intrinsic feature of strongly spin-orbit coupled materials and a key to their promise of applications in spintronics and quantum computation. Much of the existing work, in topological and nontopological pure materials, has been focused on the orthogonal locking in the vicinity of the $\mathrm{\Gamma }$ point where the directions of spin and momentum vectors are locked perpendicularly. With the orthogonal case, enforced by the symmetry in pure systems, mechanisms responsible for nonorthogonal spin-momentum locking (NOSML) have drawn little attention, although it has been reported on the topological surface of $\alpha$-Sn. Here, we demonstrate that the presence of the spin-orbit scattering from dilute spinless impurities can produce the NOSML state in the presence of a strong intrinsic spin-orbit coupling in the pristine material. We also observe an interesting coupling threshold for the NOSML state to occur. The relevant parameter in our analysis is the deflection angle from orthogonality which can be extracted experimentally from the spin-and-angle-resolved photoemission spectra. Our formalism is applicable to all strongly spin-orbit coupled systems with impurities and not limited to topological ones. The understanding of NOSML bears on spin-orbit dependent phenomena, including issues of spin-to-charge conversion and the interpretation of quasiparticle interference patterns as well as scanning-tunneling spectra in general spin-orbit coupled materials.

The Witten effect predicts that a magnetic monopole acquires a fractional electric charge inside topological insulators. In this work, we give a microscopic description of this phenomenon as well as an analogous two-dimensional system with a vortex. We solve the Dirac equation of electron field both analytically in a continuum and numerically on a lattice by adding the Wilson term and smearing the gauge field within a finite range to regularize the short-distance behavior of the system. Our results reveal that the Wilson term induces a strong positive mass shift, creating a domain-wall around the monopole or vortex. This small yet finite-sized domain wall localizes the chiral zero modes and ensures their stability through the Atiyah-Singer index theorem, whose cobordism invariance is crucial in explaining why the electric charge is fractional.

Low temperature, high resolution angle resolved photoemission experiments performed on bulk $1T\text{−}{\mathrm{TiSe}}_2$ samples display conspicuous band folding as the only prominent signature of the periodic lattice distortion. The presence of a bulk electronic gap supporting a charge density wave phase is not confirmed in light of the new data. These observations cast serious doubts on the common belief of an electronic instability as the likely origin for the observed structural transition in ${\mathrm{TiSe}}_2$.

This work is inspired by recent experiments on the formation of vortices in exciton-polariton condensates placed in rotating optical traps. We study theoretically the dynamics of the formation of such vortices and elucidate the fundamental role of the mode competition effect in determining the properties of stationary polariton states triggered by stimulated scattering of exciton-polaritons. The interplay between linear and nonlinear effects is shown to result in peculiar polariton dynamics. However, near the lasing threshold, the predominant contribution of the nonlinear effects is the saturation of the linear gain.

Andreev reflection occurs in a normal metal-superconductor junction, when an electron on the normal side can only be transmitted as a Cooper pair in the superconductor, with the reflection of a hole on the normal side. A similar phenomenon can occur in strongly correlated systems, in particular in the fractional quantum Hall effect (FQHE), as the system quasiparticles have a charge $e/m$ different from the electron charge. We study theoretically a setup involving two quantum point contacts (QPC) in the FQHE where Andreev reflection occurs, as charges $e/m$ impinging on the second QPC can only be transmitted as charges $e$, with the reflection of holes of charge $e(1-m)/m$. Using the bosonization formalism, and out-of-equilibrium Keldysh Green's function techniques, we provide a full analytical calculation of the current correlations at the outputs of the QPC, both at zero and finite temperature. The ratio between the auto- and cross-correlations of the output currents is a direct manifestation of Andreev reflection. Our results agree with recent experimental observations, and give precious information on the temperature dependence of this ratio.

We investigate the impact of charge transfer energy and band filling on the stability of the two-hole resonance relevant for Auger electron spectroscopy (AES) in transition-metal oxides. As a minimal model to study charge transfer effects in a transition metal (TM) and oxygen (OX) chain, we consider a one-dimensional chain with spinless fermions with an alternating motif of site-pairs with nearest-neighbor (NN) repulsion U and uncorrelated site-pairs, separated by a charge transfer gap $\mathrm{\Delta }$. We first show that while two holes added in a filled band of NN interacting fermions in one dimension can stabilize to a two-hole bound pair, the bound pair delocalizes with a $U$-dependent bandwidth. In contrast, we establish that the bandwidth of two holes added on a TM site pair in a filled band is dramatically suppressed, realizing a “local” two-hole resonance (L2HR) at the same TM site pair mimicking the AES phenomenology. Employing a memory-efficient exact numerical scheme and standard Lanczos-based diagonalization, we then study two-hole spectra for holes added at TM site pairs in partially filled bands. We analyze the multiple features that arise in the two-hole spectra at partial filling of the ground state. We uncover that in the strong-$U$ limit, there is a filling-dependent ${\mathrm{\Delta }}_{\mathrm{crit}}$ above which the L2HR remains stable for any band filling greater than 75%. In this regime, the energy location of the L2HR provides a direct estimate of the correlation strength at TM site pairs for partial filling and is reminiscent of the Cini-Sawatzky theory for the filled band case. At 75% band filling, an abrupt redistribution of two-hole spectral weight destroys the L2HR regardless of the $U$ or $\mathrm{\Delta }$ values. We discuss the relevance of these nonperturbative results, obtained with full lattice symmetry, for understanding the AES of partially filled bands in terms of the local two-hole spectrum.