We construct $n$ levels of nested, self-similar winnerless competition dynamics of which we explicitly work out the first three levels in the framework of generalized Lotka-Volterra equations. We choose microscopic rules such that the competition in the form of rock-paper-scissors is played between metapopulations, populations, and individuals at the same time. The trajectory of individual activities moves through a hierarchically structured heteroclinic network in a desired way. The hierarchy in structure is able to induce a separation of timescales that translates into nested spirals if the heteroclinic networks are coupled via diffusion on a spatial grid. For sufficiently strong diffusion the dynamics of interacting heteroclinic networks gets synchronized between the sites, which amounts to a large dimensional reduction of phase space. Possible applications lie in ecology and in brain dynamics. Our model reproduces in particular chunking dynamics with slow oscillations modulating fast oscillations modulating faster ones as observed in brain dynamics.

For two-dimensional topological insulators, the integer and intrinsic (without external magnetic field) quantum Hall effect is described by the gauge anomalous ($2+1$)-dimensional [($2+1$)-d] Chern-Simons (CS) response for the background gauge potential of the electromagnetic U(1) field. The Hall conductance is given by the quantized prefactor of the CS term, which is a momentum-space topological invariant. Here, we show that three-dimensional crystalline topological insulators with no other symmetries are described by a topological ($3+1$)-dimensional [($3+1$)-d] mixed CS term. In addition to the electromagnetic U(1) gauge field, this term contains elasticity tetrad fields $E_{\mu }^a(\mathbf{r},t)={\partial }_{\mu }{X}^a(\mathbf{r},t)$ which are gradients of crystalline U(1) phase fields $X^a(\mathbf{r},t)$ and describe the deformations of the crystal. For a crystal in three spatial dimensions $a=1,2,3$ and the mixed axial-gravitational response contains three parameters protected by crystalline symmetries: the weak momentum-space topological invariants. The response of the Hall conductance to the deformations of the crystal is quantized in terms of these invariants. In the presence of dislocations, the anomalous ($3+1$)-d CS term describes the Callan-Harvey anomaly inflow mechanism. The response can be extended to all odd spatial dimensions. The elasticity tetrads, being the gradients of the lattice U(1) fields, have canonical dimension of inverse length. Similarly, if such tetrad fields enter general relativity, the metric becomes dimensionful, but the physical parameters, such as Newton's constant, the cosmological constant, and masses of particles, become dimensionless.

We consider a simple, physically and biologically motivated model of transient subdiffusion having different exponents in the mean squared displacement at short and long times. For this purpose, the sum of two independent stable processes (with different indexes) as subordinators is used. Based on their infinitely divisible properties, the probability density function of particle displacements and the Fokker-Planck-type equation are obtained. Manifesting different origins of inhomogeneities (traps) in the system, the subordinators' indexes affect the asymptotic behavior of the mean squared displacement for a particle walking in the environment. Links to the Jonscher universal relaxation law and the Prabhakar-type memory functions are given.

Domains of finite topological charge density can exist in chiral materials and chiral matter. Spatial and temporal variation of the average topological charge density, represented by the $\theta$ field, induces anomalous currents that are responsible for the chiral magnetic effect, the anomalous Hall effect, and other phenomena that are intimately related to the chiral anomaly. We consider domains with constant average topological charge density. We argue that even though the Maxwell equations in the bulk are not altered, the chiral anomaly manifests itself by the way of the boundary conditions. This is illustrated by several examples. The first example deals with the refraction of plane electromagnetic waves on a surface of a constant-$\theta$ domain. We derive the modified Fresnel equations and discuss the effect of the chiral anomaly on the amplitude and polarization of the reflected and transmitted waves. In particular, we argue that the Brewster's angle is sensitive to the value of $\theta$. In the second example we compute the spectrum of the transition radiation at high frequencies and show that it is enhanced at finite $\theta$.

Lee-Yang zeros are points in the complex plane of an external control parameter at which the partition function vanishes for a many-body system of finite size. In the thermodynamic limit, the Lee-Yang zeros approach the critical value on the real axis, where a phase transition occurs. Partition function zeros have for many years been considered a purely theoretical concept; however, the situation is changing now as Lee-Yang zeros have been determined in several recent experiments. Motivated by these developments, we here devise a direct pathway from measurements of partition function zeros to the determination of critical points and universal critical exponents of continuous phase transitions. To illustrate the feasibility of our approach, we extract the critical exponents of the Ising model in two and three dimensions from the fluctuations of the total energy and the magnetization in lattices of finite size. Importantly, the critical exponents can be determined even if the system is away from the phase transition. Moreover, in contrast to standard methods based on Binder cumulants, it is not necessary to drive the system across the phase transition. As such, our method provides an intriguing perspective for investigations of phase transitions that may be hard to reach experimentally, for instance at very low temperatures or at very high pressures.

We report on spectroscopic and time-domain measurements on a fixed-frequency concentric transmon qubit in an applied in-plane magnetic field to explore its limits of magnetic field compatibility. We demonstrate quantum coherence of the qubit up to field values of $B=40\text{mT}$, even without an optimized chip design or material combination of the qubit. The dephasing rate ${\mathrm{\Gamma }}_{\phi }$ is shown to be unaffected by the magnetic field in a broad range of the qubit transition frequency. For the evolution of the qubit transition frequency, we find the unintended second junction created in the shadow angle evaporation process to be non-negligible and deduce an analytic formula for the field-dependent qubit energies. We discuss the relevant field-dependent loss channels, which cannot be distinguished by our measurements, inviting further theoretical and experimental investigation. Using well-known and well-studied standard components of the superconducting quantum architecture, we are able to reach a field regime relevant for quantum sensing and hybrid applications of magnetic spins and spin systems.

Most of the non-Abelian string vortices studied so far are characterized by two-dimensional $\mathbb{CP}\left(N\right)$ models with various degrees of supersymmetry on their worldsheet. We generalize this construction to “composite” non-Abelian strings supporting the Grassmann $\mathcal{G}(L,M)$ models (here $L+M=N$). The generalization is straightforward and provides, among other results, a simple and transparent way for counting the number of vacua in $\mathcal{N}=(2,2)$ Grassmannian model.

The notion of stringy naturalness—that an observable ${\mathcal{O}}_2$ is more natural than ${\mathcal{O}}_1$ if more (phenomenologically acceptable) vacua solutions lead to ${\mathcal{O}}_2$ rather than ${\mathcal{O}}_1$—is examined within the context of the Standard model (SM) and various supersymmetric models (SUSY) extensions: Constrained minimal supersymmetric standard model (CMSSM)/minimal supergravity model (mSUGRA), high-scale SUSY, and radiatively driven natural SUSY (RNS). Rather general arguments from string theory suggest a (possibly mild) statistical draw towards vacua with large soft SUSY breaking terms. These vacua must be tempered by an anthropic veto of nonstandard vacua or vacua with too large a value of the weak scale $m_{\mathrm{weak}}$. We argue that the SM, the CMSSM and various high-scale SUSY models are all expected to be relatively rare occurrences within the string theory landscape of vacua. In contrast, models with TeV-scale soft terms but with $m_{\mathrm{weak}}\sim 100\mathrm{GeV}$ and consequent light higgsinos (SUSY with radiatively driven naturalness) should be much more common on the landscape. These latter models have a statistical preference for $m_h\simeq 125\mathrm{GeV}$ and strongly interacting sparticles beyond current LHC reach. Thus, while conventional naturalness favors sparticles close to the weak scale, stringy naturalness favors sparticles so heavy that electroweak symmetry is barely broken and one is living dangerously close to vacua with charge-or-color breaking minima, no electroweak breaking or pocket universe weak-scale values too far from our measured value. Expectations for how landscape SUSY would manifest itself at collider and dark matter search experiments are then modified compared to usual notions.

We theoretically study the effect of a magnetic field on quasicrystalline superconductors, by modeling them as an attractive Hubbard model on a Penrose-tiling structure. We find that at low temperatures and under a high magnetic field there appears an exotic superconducting state with the order parameter changing its sign in real space. We discuss the state in comparison with the Fulde-Ferrell-Larkin-Ovchinnikov state proposed many years ago for periodic systems, clarifying commonalities and differences. It is remarkable that, even in the absence of periodicity, the electronic system finds a way to keep a coherent superconducting state with a spatially sign-changing order parameter compatible with the underlying quasiperiodic structure.

Recently, kirigami's high extensibility has been understood as a transition in the force-elongation curve. In this Rapid Communication, we consider a model, which modifies our previous model, to show a striking analogy between the present theory and the Landau theory of continuous thermodynamic transitions, if we regard a rotation angle and elongation of kirigami as the order parameter and the inverse temperature, respectively. The present study points out the importance of the distinction between the discontinuity and continuity of the high-extensibility transition in an elementary kirigami structure, and shows that the mechanical response of kirigami can be understood using the tools of statistical physics, which have been proved to be useful in many fields of physics.

Single-photon detectors have historically consisted of macroscopic-sized materials but recent experimental and theoretical progress suggests new approaches based on nanoscale and molecular electronics. Here, we present a theoretical study of photodetection in a system composed of a quantum electronic transport channel functionalized by a photon absorber. Notably, the photon field, absorption process, transduction mechanism, and measurement process are all treated as part of one fully coupled quantum system, with explicit interactions. Using nonequilibrium, time-dependent quantum transport simulations, we reveal the unique temporal signatures of the single-photon detection process, and show that the system can be described using optical Bloch equations, with a new nonlinearity as a consequence of time-dependent detuning caused by the back-action from the transport channel via the dynamical Stark effect. We compute the photodetector signal-to-noise ratio and demonstrate that single-photon detection at high count rate is possible for realistic parameters by exploiting a unique nonequilibrium control of back-action.

We address the interplay of electron-electron ($e-e$) and electron-phonon ($e$-ph) interactions in the Hubbard-Holstein model, using a two-component density functional theory. Exchange-correlation potentials constructed via dynamical mean field theory for a $D=\infty$ Bethe lattice and analytically for an isolated site give a new perspective on $e$-ph screening of the $e-e$ interactions and its effect on the charge- and spin-Kondo regimes. Comparisons to exact benchmarks show that the approach is suitable to describe transport properties and real-time dynamics in homogeneous and inhomogeneous lattice systems.

Recent advances in the surface treatments of niobium superconducting radio-frequency (SRF) cavities have led to substantially increased $Q$ factors and a maximum surface field. This poses theoretical challenges to identify the mechanisms responsible for such performance enhancements. We report theoretical results for the effects of inhomogeneous surface disorder on the superheating field—the surface magnetic field above which the Meissner state is globally unstable. We find that inhomogeneous disorder, such as that introduced by the infusion of nitrogen into the surface layers of niobium SRF cavities, can increase the superheating field above the maximum for superconductors in the clean limit or with homogeneously distributed disorder. Homogeneous disorder increases the penetration of the screening current, but also suppresses the maximum supercurrent. Inhomogeneous disorder in the form of an impurity diffusion layer biases this trade-off by increasing the penetration of the screening currents into cleaner regions with larger critical currents, thus limiting the suppression of the screening current to a thin dirty region close to the surface. Our results suggest that the impurity diffusion layers play a role in enhancing the maximum accelerating gradient of nitrogen-treated niobium SRF cavities.

Bundling and crosslinking of actin networks provide cells with tensile strength and mobility and play critical roles in diverse mechanical processes such as wounding healing and fertilization. One simple mechanism for bundling and crosslinking actin networks is using divalent counterions such as ${\mathrm{Mg}}^{2+}$ to form crossbridges between actin filaments. Counterion crossbridges can also be exploited in materials engineering to alter the mechanics of polyelectrolyte materials. As such, the mechanical properties that counterion crossbridges confer to actin networks needs to be explored. Here, we use optical tweezers microrheology to characterize the mechanical response of actin networks in the presence of varying concentrations of ${\mathrm{Mg}}^{2+}$. We couple mechanics to structure by using confocal microscopy to characterize the mobility and architecture of networks. We show that only modest bundling and network rearrangement is required to induce dramatic increases in the elasticity and stiffness of the networks. We further show that bundles are resilient to nonlinear forcing and exhibit surprisingly minimal dissipation above a critical counterion concentration. Finally, we demonstrate that while crosslinking of network fibers plays an important role in linear regime mechanics, filament bundling dictates the nonlinear response.

Topological spintronics aims to exploit the spin-momentum locking in the helical surface states of topological insulators for spin-orbit torque devices. We address a fundamental question that still remains unresolved in this context: Does the topological surface state alone produce the largest values of spin-charge conversion efficiency or can the strongly spin-orbit coupled bulk states also contribute significantly? By studying the Fermi level dependence of spin pumping in topological insulator/ferrimagnetic insulator bilayers, we show that the spin Hall conductivity is constant when the Fermi level is tuned across the bulk band gap, consistent with a full bulk band calculation. The results suggest a different perspective, wherein “bulk-surface correspondence” allows spin-charge conversion to be simultaneously viewed either as coming from the full bulk band, or from spin-momentum locking of the surface state.

Although the crystal structures of pure metals are material dependent, we theoretically find that entropy-driven docosahedral local structures are the most frequent in their melts and glasses, independent of their crystal structures. In terms of the docosahedral short-range order, we explain why body-centered-cubic metals have higher glass-forming ability than face-centered-cubic ones.

We show that microwave-driven NV centers can function as robust mode switches by utilizing a special degeneracy called an exceptional point (EP). While previous theoretical and experimental work on EP-based mode switches applies only to pure states, we develop here a general theory for switching between mixed states, statistical ensembles of different pure states, resulting from the interaction with the environment. Our theory is general and applicable to all leading platforms for quantum information processing and quantum technologies. However, our numerical simulations use empirical parameters of NV centers. We provide guidelines for coping with the main challenges for experimental realization of this protocol: decoherence and mixed-state preparation.

Motivated by the recent surge of field-driven phenomena discussed for Kitaev materials, in particular the experimental observation of a finite thermal Hall effect and theoretical proposals for the emergence of additional spin liquid phases beyond the conventional Kitaev spin liquid, we develop a theoretical understanding of the thermal Hall effect in honeycomb Kitaev materials in magnetic fields. Our focus is on gapless U(1) spin liquids with a spinon Fermi surface, which have been shown to arise as field-induced phases. We demonstrate that in the presence of symmetry-allowed second-neighbor Dzyaloshinskii-Moriya interactions these spin liquids give rise to a finite, nonquantized, thermal Hall conductance in a magnetic field. The microscopic origin of this thermal Hall effect can be traced back to an interplay of Dzyaloshinskii-Moriya interaction and Zeeman coupling, which generates an internal U(1) gauge flux that twists the motion of the emergent spinons. We argue that such a nonquantized thermal Hall effect is a generic response in Kitaev models for a range of couplings.

Studying a single atomic ion confined in a time-dependent periodic anharmonic potential, we find large amplitude trajectories stable for millions of oscillation periods in the presence of stochastic laser cooling. Accounting for the complexity of the laser cooling process we calculate the details of the effective dynamics away from thermal equilibrium. The competition between energy gain from the time-dependent drive and damping leads to the stabilization of such stochastic limit cycles. Instead of converging to the global minimum of the averaged potential, the steady-state phase-space distribution develops multiple peaks in the regions of phase space where the frequency of the motion is close to a multiple of the periodic drive. Such distinct nonequilibrium behavior can be observed in realistic radio-frequency traps with laser-cooled ions, suggesting that Paul traps offer a well-controlled test bed for studying the transport and dynamics of microscopically driven systems.

We report intrinsic spin decay length of an antiferromagnetic insulator. We found that at an antiferromagnetic/ferromagnetic interface, a spin current generated by spin pumping is strongly suppressed by two-magnon scattering. By eliminating the two-magnon contribution, we discovered that the characteristic length of spin decay in polycrystalline NiO changes by two orders of magnitude through the paramagnetic to antiferromagnetic transition. The spin decay length in the antiferromagnetic state is around 100 nm, which is an order of magnitude longer than that previously believed. These results provide a crucial piece of information for the fundamental understanding of the physics of spin transport.