We investigate the classical chiral Ashkin-Teller model on a square lattice with the corner transfer matrix renormalization group algorithm. We show that the melting of the period-4 phase in the presence of a chiral perturbation takes different forms depending on the coefficient of the four-spin term in the Ashkin-Teller model. Close to the clock limit of two decoupled Ising models, the system undergoes a two-step commensurate-incommensurate transition as soon as the chirality is introduced, with an intermediate critical floating phase bounded by a Kosterlitz-Thouless transition at high temperature and a Pokrovsky-Talapov transition at low temperature. By contrast, close to the four-states Potts model, we argue for the existence of a unique commensurate-incommensurate transition that belongs to the chiral universality class, and for the presence of a Lifshitz point where the ordered, disordered, and floating phases meet. Finally, we map the whole phase diagram, which turns out to be in qualitative agreement with the 40-year-old prediction by Huse and Fisher.

Controlling the spread of correlations in quantum many-body systems is a key challenge at the heart of quantum science and technology. Correlations are usually destroyed by dissipation arising from coupling between a system and its environment. Here, we show that dissipation can instead be used to engineer a wide variety of spatiotemporal correlation profiles in an easily tunable manner. We describe how dissipation with any translationally invariant spatial profile can be realized in cold atoms trapped in an optical cavity. A uniform external field and the choice of spatial profile can be used to design when and how dissipation creates or destroys correlations. We demonstrate this control by generating entanglement preferentially sensitive to a desired spatial component of a magnetic field. We thus establish nonlocal dissipation as a route toward engineering the far-from-equilibrium dynamics of quantum information, with potential applications in quantum metrology, state preparation, and transport.

We show that corner Majorana zero modes in a two-dimensional $p+id$ topological superconductor can be controlled by the manipulation of the parent $p$-wave superconducting order. Assuming that the $p$-wave superconducting order is in either a chiral or helical phase, we find that when a $d_{x^2-y^2}$ wave superconducting order is induced, the system exhibits quite different behavior depending on the nature of the parent $p$-wave phase. In particular, we find that while in the helical phase, a localized Majorana mode appears at each of the four corners, in the chiral phase, it is localized along only two of the four edges. We furthermore demonstrate that the Majoranas can be directly controlled by the form of the edges, as we explicitly show in the case of circular edges. We argue that the application of strain may provide additional means of fine-tuning the Majorana zero modes in the system; in particular, it can partially gap them out. Our findings may be relevant for probing the topology in two-dimensional mixed-pairing superconductors.

Topological insulator (TI) nanowires in proximity to conventional superconductors have been proposed as a tunable platform to realize topological superconductivity and Majorana zero modes. The tuning is done using an axial magnetic flux $\varphi$ which allows transforming the system from trivial at $\varphi =0$ to topologically nontrivial when half a magnetic flux quantum ${\varphi }_0/2$ threads the cross-section of the wire. Here, we explore the expected topological transition in TI-wire-based Josephson junctions as a function of magnetic flux by probing the $4\pi$-periodic fraction of the supercurrent, which is considered an indicator of topological superconductivity. Our data suggest that this $4\pi$-periodic supercurrent is at lower magnetic field largely of trivial origin but that, at magnetic fields above $\sim {\varphi }_0/4$, topological $4\pi$-periodic supercurrents take over.

The ground-state magnetic structures of the ${\mathrm{Eu}}^{2+}$ spins in recently discovered $\mathrm{RbEu}{\left({\mathrm{Fe}}_{1-x}{\mathrm{Ni}}_x\right)}_4{\mathrm{As}}_4$ superconductors have been investigated by neutron powder diffraction measurements. It is found that as the superconductivity gets suppressed with the increase in Ni doping, the magnetic propagation vector of the Eu sublattice diminishes, corresponding to the decrease in the rotation angle between the moments in neighboring Eu layers. The ferromagnetic Eu layers are helically modulated along the $\mathit{c}$ axis with an incommensurate magnetic propagation vector in both the ferromagnetic superconductor $\mathrm{RbEu}{\left({\mathrm{Fe}}_{0.95}{\mathrm{Ni}}_{0.05}\right)}_4{\mathrm{As}}_4$ and the superconducting ferromagnet $\mathrm{RbEu}{\left({\mathrm{Fe}}_{0.93}{\mathrm{Ni}}_{0.07}\right)}_4{\mathrm{As}}_4$. Such a helical structure transforms into a purely collinear ferromagnetic structure for nonsuperconducting $\mathrm{RbEu}{\left({\mathrm{Fe}}_{0.91}{\mathrm{Ni}}_{0.09}\right)}_4{\mathrm{As}}_4$, with all the ${\mathrm{Eu}}^{2+}$ spins lying along the tetragonal (1 1 0) direction. The evolution from helical to collinear ferromagnetic order of the ${\mathrm{Eu}}^{2+}$ spins with increasing Ni doping is supported by first-principles calculations. The variation of the rotation angle between adjacent ${\mathrm{Eu}}^{2+}$ layers can be well explained by considering the change of magnetic exchange couplings mediated by the indirect Ruderman-Kittel-Kasuya-Yosida interaction.

Quantum multicritical points (QMCPs) emerge at the junction of two or more quantum phase transitions due to the interplay of disparate fluctuations, leading to novel universality classes. While quantum critical points have been well characterized, our understanding of QMCPs is much more limited, even though they might be less elusive to study experimentally than quantum critical points. Here, we characterize the QMCP of an interacting heterogeneous quantum system in two and three dimensions, the ferromagnetic random transverse-field Ising model (RTIM). The QMCP of the RTIM emerges due to both geometric and quantum fluctuations, studied here numerically by the strong disorder renormalization group method. The QMCP of the RTIM is found to exhibit ultraslow, activated dynamic scaling, governed by an infinite disorder fixed point. This ensures that the obtained multicritical exponents tend to the exact values at large scales, while also being universal—i.e., independent of the form of disorder—providing a solid theoretical basis for future experiments.

We study transport properties of a single electron transistor based on elastic nanotube. Assuming that an external compressive force is applied to the nanotube, we focus on the vicinity of the Euler buckling instability. We demonstrate that in this regime the transport through the transistor is extremely sensitive to elastic disorder. In particular, built-in curvature (random or regular) leads to the “elastic curvature blockade”: appearance of threshold bias voltage in the $I\text{−}V$ curve which can be larger than the Coulomb-blockade-induced one. In the case of a random curvature, an additional plateau in the dependence of the average current on a bias voltage appears.

Frustrated magnets with highly degenerate ground states are at the heart of hunting exotic states of matter. Recent studies in spin-orbit coupled honeycomb magnets have generated immense interest in bond-dependent interactions, appreciating a symmetric off-diagonal $\mathrm{\Gamma }$ interaction which exhibits a macroscopic degeneracy in the classical limit. Here, we study a generic spin model and discover a chiral-spin (CS) ordering with spontaneously broken time-reversal symmetry near the dominant $\mathrm{\Gamma }$ region. The CS phase is demonstrated to possess a staggered chirality relation in different sublattices, and it exhibits gapless excitations, as revealed by the vanishing energy gap and the finite central charge on cylinders. Although there is a vestige of a tiny peak in the corner of the second Brillouin zone, the magnetic order is likely to vanish as the system size increases. Finally, we also attempt to gain insight into the possible topological signature of the CS phase by calculating the dynamic structure factor and the modular $\mathcal{S}$ matrix.

We propose a realistic regime to detect the light-induced topological band gap in graphene via time-resolved angle-resolved photoelectron spectroscopy (trARPES), which can be achieved with current technology. The direct observation of Floquet-Bloch bands in graphene is limited by low-mobility, Fourier-broadening, laser-assisted photoemission (LAPE), probe-pulse energy-resolution bounds, space-charge effects, and more. We characterize a regime of low driving frequency and high amplitude of the circularly polarized light that induces an effective band gap at the Dirac point that exceeds the Floquet zone. This circumvents limitations due to energy resolutions and band broadening. The electron distribution across the Floquet replicas in this limit allows for distinguishing LAPE replicas from Floquet replicas. We derive our results from a dissipative master equation approach that gives access to two-point correlation functions and the electron distribution relevant for trARPES measurements.

The dynamic engineering of band structures for ultracold atoms in optical lattices represents an innovative approach to understanding and exploring the fundamental principles of topological matter. In particular, the folded Floquet spectrum determines the associated band topology via band inversion. We experimentally and theoretically study two-frequency phase modulation to asymmetrically hybridize the lowest two bands of a one-dimensional lattice. Using quasidegenerate perturbation theory in the extended Floquet space we derive an effective two-band model that quantitatively describes our setting. The energy gaps are experimentally probed via Landau-Zener transitions between Floquet-Bloch bands using an accelerated Bose-Einstein condensate. Separate and simultaneous control over the closing and reopening of these band gaps is demonstrated. We find good agreement between experiment and theory, establishing an analytic description for resonant Floquet-Bloch engineering that includes single- and multiphoton couplings, as well as interference effects between several commensurate drives.

We study black and white hole analogs in Weyl semimetals with inhomogeneous nodal tilts. We study how the presence of a microscopic lattice, giving rise to low-energy fermion doubler states at large momenta that are not present for elementary particles, affects the analogy between Weyl Hamiltonians and general relativity. Using a microscopic tight-binding lattice model, we find the doubler states to give rise to Hawking fragmentation and Hawking attenuation of wave packets by the analog event horizon. These phenomena depend on an analog Hawking temperature and can be measured in metamaterials and solids, as we confirm by numerical simulations.

We report a detailed study of electrical and thermal transport properties in $2\mathrm{H}\text{−}{\mathrm{M}}_x{\mathrm{TaS}}_2 (\mathrm{M}=\mathrm{Mn}, \mathrm{Co})$ magnets where M atoms are intercalated in the van der Waals gap. The intercalation induces ferromagnetism (FM) with an easy-plane anisotropy in $2\mathrm{H}\text{−}{\mathrm{Mn}}_x{\mathrm{TaS}}_2$, but FM with a strong uniaxial anisotropy in $2\mathrm{H}\text{−}{\mathrm{Co}}_{0.22}{\mathrm{TaS}}_2$, which finally evolves into a three-dimensional antiferromagnetism (AFM) in $2\mathrm{H}\text{−}{\mathrm{Co}}_{0.34}{\mathrm{TaS}}_2$. Temperature-dependent electrical resistivity shows metallic behavior for all samples. Thermopower is negative in the whole temperature range for $2\mathrm{H}\text{−}{\mathrm{Co}}_x{\mathrm{TaS}}_2$, whereas the sign changes from negative to positive with increasing Mn for $2\mathrm{H}\text{−}{\mathrm{Mn}}_x{\mathrm{TaS}}_2$. The diffusive thermoelectric response dominates in both high- and low-temperature ranges for all samples. A clear kink in electrical resistivity, a weak anomaly in thermal conductivity, as well as a slope change in thermopower were observed at the magnetic transitions for $2\mathrm{H}\text{−}{\mathrm{Mn}}_{0.28}{\mathrm{TaS}}_2$ ($T_{\text{c}}\approx$ 82 K) and $2\mathrm{H}\text{−}{\mathrm{Co}}_{0.34}{\mathrm{TaS}}_2$ ($T_{\text{N}}\approx$ 36 K), respectively, albeit weaker for lower $x$ crystals. Co-intercalation promoted FM to AFM transition is further confirmed by Hall resistivity; the sign change of the ordinary Hall coefficient indicates a multiband behavior in $2\mathrm{H}\text{−}{\mathrm{Co}}_x{\mathrm{TaS}}_2$.

The Bloch theorem is a general theorem restricting the persistent current associated with a conserved U(1) charge in a ground state or in a thermal equilibrium. It gives an upper bound of the magnitude of the current density, which is inversely proportional to the system size. In a recent paper, Else and Senthil applied the argument for the Bloch theorem to a generalized Gibbs ensemble, assuming the presence of an additional conserved charge, and predicted a nonzero current density in the nonthermal steady state [Else and Senthil, Phys. Rev. B 104, 205132 (2021)]. In this paper, we provide a complementary derivation based on the canonical ensemble, given that the additional charge is strictly conserved within the system by itself. Furthermore, using the example where the additional conserved charge is the momentum operator, we discuss that the persistent current tends to vanish when the system is in contact with an external momentum reservoir in the comoving frame of the reservoir.

We report on transport experiments through high-mobility gate-tunable undoped InSb quantum wells (QWs). Due to the elimination of any Si modulation doping, the gate-defined two-dimensional electron gases in the QWs display a significantly increased mobility of $260000\mathrm{c}{\mathrm{m}}^2/\mathrm{Vs}$ at a rather low density of $2.4\times {10}^{11}\mathrm{c}{\mathrm{m}}^{\text{–}2}$. Using magnetotransport experiments, we characterize spin-orbit interactions by measuring weak antilocalization. Furthermore, by measuring Shubnikov–de Haas oscillations in tilted magnetic fields, we find that the $g$ factor agrees with $\mathbf{k}·\mathbf{p}$ theory calculations at low magnetic fields but grows with spin polarization and carrier density at high magnetic fields. Additionally, signatures of Ising quantum Hall ferromagnetism are found at filling factor $\nu =2$ for tilt angles where the Landau level energy equals the Zeeman energy. Despite the high mobility, the undoped InSb QWs exhibit no fractional quantum Hall effect up to magnetic fields of 25 T.

The outlook of protected quantum computing spurred enormous progress in the search for topological materials, sustaining a continued race to find the most experimentally feasible platform. Here we show that one of the simplest quantum circuits, the Cooper-pair transistor, exhibits a nontrivial Chern number which has not yet been discussed, in spite of the exhaustive existing literature. Surprisingly, the resulting quantized current response is robust with respect to a large number of external perturbations, most notably low-frequency charge noise and quasiparticle poisoning. Moreover, the fact that the higher bands experience crossings with higher topological charges leads to all the bands having the same Chern number, such that there is no restriction to stay close to the ground state. Remaining small perturbations are investigated based on a generic master equation approach. Finally, we discuss a feasible protocol to measure the quantized current.

We present a reformulation of the functional renormalization group (fRG) for many-electron systems, which relies on the recently introduced single-boson exchange (SBE) representation of the parquet equations [F. Krien, A. Valli, and M. Capone, Phys. Rev. B 100, 155149 (2019)]. The latter exploits a diagrammatic decomposition, which classifies the contributions to the full scattering amplitude in terms of their reducibility with respect to cutting one interaction line, naturally distinguishing the processes mediated by the exchange of a single boson in the different channels. We apply this idea to the fRG by splitting the one-loop fRG flow equations for the vertex function into SBE contributions and a residual four-point fermionic vertex. Similarly as in the case of parquet solvers, recasting the fRG algorithm in the SBE representation offers both computational and interpretative advantages: The SBE decomposition not only significantly reduces the numerical effort of treating the high-frequency asymptotics of the flowing vertices, but it also allows for a clear physical identification of the collective degrees of freedom at play. We illustrate the advantages of an SBE formulation of fRG-based schemes, by computing through the merger of dynamical mean-field theory and fRG the susceptibilities and the Yukawa couplings of the two-dimensional Hubbard model from weak to strong coupling, for which we also present an intuitive physical explanation of the results. The SBE formulation of the one-loop flow equations paves a promising route for future multiboson and multiloop extensions of fRG-based algorithms.