$\beta$-delayed one-proton emissions of ${}^{22}\mathrm{Si}$, the lightest nucleus with an isospin projection ${\mathrm{T}}_z=-3$, are studied with a silicon array surrounded by high-purity germanium detectors. Properties of $\beta$-decay branches and the reduced transition probabilities for the transitions to the low-lying states of ${}^{22}\mathrm{Al}$ are determined. Compared to the mirror $\beta$ decay of ${}^{22}\mathrm{O}$, the largest value of mirror asymmetry in low-lying states by far, with $\delta =209(96)$, is found in the transition to the first $1^{+}$ excited state. Shell-model calculation with isospin-nonconserving forces, including the $T=1$, $J=2$, 3 interaction related to the $s_{1/2}$ orbit that introduces explicitly the isospin-symmetry breaking force and describes the loosely bound nature of the wave functions of the $s_{1/2}$ orbit, can reproduce the observed data well and consistently explain the observation that a large $\delta$ value occurs for the first but not for the second $1^{+}$ excited state of ${}^{22}\mathrm{Al}$. Our results, while supporting the proton-halo structure in ${}^{22}\mathrm{Al}$, might provide another means to identify halo nuclei.

From fireflies to cardiac cells, synchronization governs important aspects of nature, and the Kuramoto model is the staple for research in this area. We show that generalizing the model to oscillators of dimensions higher than 2 and introducing a positive feedback mechanism between the coupling and the global order parameter leads to a rich and novel scenario: the synchronization transition is explosive at all even dimensions, whilst it is mediated by a time-dependent, rhythmic, state at all odd dimensions. Such a latter circumstance, in particular, differs from all other time-dependent states observed so far in the model. We provide the analytic description of this novel state, which is fully corroborated by numerical calculations. Our results can, therefore, help untangle secrets of observed time-dependent swarming and flocking dynamics that unfold in three dimensions, and where this novel state could thus provide a fresh perspective for as yet not understood formations.

While the breakdown of the perturbation expansion for the many-electron problem has several formal consequences, here we unveil its physical effect: flipping the sign of the effective electronic interaction in specific scattering channels. By decomposing local and uniform susceptibilities of the Hubbard model via their spectral representations, we prove how entering the nonperturbative regime causes an enhancement of the charge response, ultimately responsible for the phase-separation instabilities close to the Mott metal-insulator transition. Our analysis opens a new route for understanding phase transitions in the nonperturbative regime and clarifies why attractive effects emerging from a strong repulsion can induce phase separations but not $s$-wave pairing or charge-density wave instabilities.

We investigate spin-charge conversion phenomena in hybrid structures of topological insulator thin films and magnetic insulators. We find an anisotropic inverse spin-galvanic effect that yields a highly tunable spin-orbit torque. Concentrating on the quasiballistic limit, we also predict a giant anisotropic magnetoresistance at low dopings. These effects, which have no counterparts in thick topological insulators, depend on the simultaneous presence of the hybridization between the surface states and the in-plane magnetization. Both the inverse spin-galvanic effect and anisotropic magnetoresistance exhibit a strong dependence on the magnetization and the Fermi level position and can be used for spintronics and spin-orbit-torque-based applications at the nanoscale.

We study electronic contribution to the Raman scattering signals of two-, three- and four-layer graphene with layers at one of the interfaces twisted by a small angle with respect to each other. We find that the Raman spectra of these systems feature two peaks produced by van Hove singularities in moiré minibands of twistronic graphene, one related to direct hybridization of the Dirac states, and the other resulting from band folding caused by moiré superlattice. The positions of both peaks strongly depend on the twist angle, so that their detection can be used for noninvasive characterization of the twist, even in hBN-encapsulated structures.

We study a 2D system of trion polaritons at the quantum level and demonstrate that for monolayer semiconductors they can exhibit a strongly nonlinear optical response. The effect is due to the composite nature of trion-based excitations resulting in their nontrivial quantum statistical properties, and enhanced phase space filling effects. We present the full quantum theory to describe the statistics of trion polaritons, and demonstrate that the associated nonlinearity persists at the level of few quanta, where two qualitatively different regimes of photon antibunching are present for weak and strong single photon-trion coupling. We find that single photon emission from trion polaritons becomes experimentally feasible in state-of-the-art transition metal dichalcogenide setups. This can foster the development of quantum polaritonics using 2D monolayers as a material platform.

The development of bright free-electron lasers (FEL) has revolutionized our ability to create and study matter in the high-energy-density (HED) regime. Current diagnostic techniques have been successful in yielding information on fundamental thermodynamic plasma properties, but provide only limited or indirect information on the detailed quantum structure of these systems, and on how it is affected by ionization dynamics. Here we show how the valence electronic structure of solid-density nickel, heated to temperatures of around 10 of eV on femtosecond timescales, can be probed by single-shot resonant inelastic x-ray scattering (RIXS) at the Linac Coherent Light Source FEL. The RIXS spectrum provides a wealth of information on the HED system that goes well beyond what can be extracted from x-ray absorption or emission spectroscopy alone, and is particularly well suited to time-resolved studies of electronic-structure dynamics.

We theoretically predict and experimentally demonstrate a nonthermal pathway to optically enhance superexchange interaction energies in a material based on exciting ligand-to-metal charge-transfer transitions, which introduces lower-order virtual hopping contributions that are absent in the ground state. We demonstrate this effect in the layered ferromagnetic insulator ${\mathrm{CrSiTe}}_3$ by exciting Te-to-Cr charge-transfer transitions using ultrashort laser pulses and detecting coherent phonon oscillations that are impulsively generated by superexchange enhancement via magneto-elastic coupling. This mechanism kicks in below the temperature scale where short-range in-plane spin correlations begin to develop and disappears when the excitation energy is tuned away from the charge-transfer resonance, consistent with our predictions.

We extend to quenched-disordered systems the variational scheme for real-space renormalization group calculations that we recently introduced for homogeneous spin Hamiltonians. When disorder is present our approach gives access to the flow of the renormalized Hamiltonian distribution, from which one can compute the critical exponents if the correlations of the renormalized couplings retain finite range. Key to the variational approach is the bias potential found by minimizing a convex functional in statistical mechanics. This potential reduces dramatically the Monte Carlo relaxation time in large disordered systems. We demonstrate the method with applications to the two-dimensional dilute Ising model, the random transverse field quantum Ising chain, and the random field Ising in two- and three-dimensional lattices.

We determine a previously unknown universal quantity, the location of the Yang-Lee edge singularity for the $\mathrm{O}(N)$ theories in a wide range of $N$ and various dimensions. At large $N$, we reproduce the $N\to \infty$ analytical result on the location of the singularity and, additionally, we obtain the mean-field result for the location in $d=4$ dimensions. In order to capture the nonperturbative physics for arbitrary $N$, $d$ and complex-valued external fields, we use the functional renormalization group approach.

The transverse-momentum-dependent (TMD) soft function is a key ingredient in QCD factorization of Drell-Yan and other processes with relatively small transverse momentum. We present a lattice QCD study of this function at moderately large rapidity on a $2+1$ flavor CLS dynamic ensemble with $a=0.098\mathrm{fm}$. We extract the rapidity-independent (or intrinsic) part of the soft function through a large-momentum-transfer pseudoscalar meson form factor and its quasi-TMD wave function using leading-order factorization in large-momentum effective theory. We also investigate the rapidity-dependent part of the soft function—the Collins-Soper evolution kernel—based on the large-momentum evolution of the quasi-TMD wave function.

We propose a new Monte Carlo method called the pinhole trace algorithm for ab initio calculations of the thermodynamics of nuclear systems. For typical simulations of interest, the computational speedup relative to conventional grand-canonical ensemble calculations can be as large as a factor of one thousand. Using a leading-order effective interaction that reproduces the properties of many atomic nuclei and neutron matter to a few percent accuracy, we determine the location of the critical point and the liquid-vapor coexistence line for symmetric nuclear matter with equal numbers of protons and neutrons. We also present the first ab initio study of the density and temperature dependence of nuclear clustering.

The (pseudo)spin degrees of freedom greatly enriches the physics of cold atoms. This is particularly so for systems with high spins (i.e., spin quantum number larger than $1/2$). For example, one can construct not only the rank-1 spin vector, but also the rank-2 spin tensor in high spin systems. Here we propose a simple scheme to couple the spin tensor and the center-of-mass orbital angular momentum in a spin-1 cold atom system and show that this leads to a new quantum phase of the matter: the spin-nematic vortex state that features vorticity in an SU(2) spin-nematic tensor subspace. Under proper conditions, such states are characterized by quantized topological numbers. Our work opens up new avenues of research in topological quantum matter with high spins.

The concept of swapping the two most important spin interactions—exchange and spin-orbit coupling—is proposed based on two-dimensional multilayer van der Waals heterostructures. Specifically, we show by performing realistic ab initio simulations, that a single device consisting of a bilayer graphene sandwiched by a 2D ferromagnet ${\mathrm{Cr}}_2{\mathrm{Ge}}_2{\mathrm{Te}}_6$ (CGT) and a monolayer ${\mathrm{WS}}_2$, is able not only to generate, but also to swap the two interactions. The highly efficient swapping is enabled by the interplay of gate-dependent layer polarization in bilayer graphene and short-range spin-orbit and exchange proximity effects affecting only the layers in contact with the sandwiching materials. We call these structures ex-so-tic, for supplying either exchange (ex) or spin-orbit (so) coupling in a single device, by gating. Such bifunctional devices demonstrate the potential of van der Waals spintronics engineering using 2D crystal multilayers.

We study the Sachdev-Ye-Kitaev (${\mathrm{SYK}}_4$) model with a weak ${\mathrm{SYK}}_2$ term of magnitude $\mathrm{\Gamma }$ beyond the simplest perturbative limit considered previously. For intermediate values of the perturbation strength, $J/N\ll \mathrm{\Gamma }\ll J/\sqrt{N}$, fluctuations of the Schwarzian mode are suppressed, and the ${\mathrm{SYK}}_4$ mean-field solution remains valid beyond the timescale $t_0\sim N/J$ up to $t_{*}\sim J/{\mathrm{\Gamma }}^2$. The out-of-time-order correlation function displays at short time intervals exponential growth with maximal Lyapunov exponent $2\pi T$, but its prefactor scales as $T$ at low temperatures $T\le \mathrm{\Gamma }$.

It is suggested that networks of Majorana-Cooper pair boxes connected by metallic nanowires can simulate various exotic states of matter. In this simulation Majorana-Cooper boxes play the role of effective spins $S=1/2$ and the metallic connections generate the Kondo screening and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. Depending on what prevails—whether it is the Kondo effect or the RKKY exchange, one will have either a Kondo lattice or an effective spin model. The list of exotic states includes the famous hexagonal Kitaev model, a generalization of this model for a Kondo lattice, and various spin models with three-spin interactions. Special emphasis is made on the discussion of the Kondo lattice scenario.