We construct a 1D model Hamiltonian of spinless fermions for which the spinless analog of $\eta$-pairing states are quantum many-body scars of the model. These states are excited states and display subvolume entanglement entropy scaling; they form a tower of states that are equally spaced in energy (resulting in periodic oscillations in the Loschmidt echo and in the time evolution of observables for initial states prepared in a superposition of them) and are atypical in the sense that they weakly break the eigenstate thermalization hypothesis, while the other excited states are thermal. We extend the approach by presenting models with a tower of scar states generated by multimers located at the edge of the Brillouin zone.

We study theoretically the quantum phase transition from a metal to a Wigner-Mott insulator at fractional commensurate filling on a two-leg ladder. We show that a continuous transition out of a symmetry-preserving Luttinger liquid metal is possible where the onset of insulating behavior is accompanied by the breaking of the lattice translation symmetry. At fillings $\nu =1/m$ per spin per unit cell, we find that the spin degrees of freedom also acquire a gap at the Wigner-Mott transition for odd integer $m$. In contrast for even integer $m$, the spin sector remains gapless and the resulting insulator is a ladder analog of the two-dimensional spinon surface state. In both cases, a charge neutral spinless mode remains gapless across the Wigner-Mott transition. We discuss physical properties of these transitions and comment on insights obtained for thinking about continuous Wigner-Mott transitions in two-dimensional systems which are being studied in moire materials.

Subgap states are responsible for the low-bias transport features of hybrid superconducting-semiconducting devices. Here we analyze the local and nonlocal differential conductance of Coulomb-blockaded multiterminal superconducting islands that host subgap states with different spatial structures. The emerging patterns of their transport spectroscopy are used to characterize the possible topological nature of these devices and offer the possibility of controlling their transport properties. We develop a next-to-leading order master equation to describe the multiterminal transport in superconductors with both strong Coulomb interactions and multiple subgap states, coupled with metallic leads. We show that the nonlocal differential conductance characterizes the spatial extension of the subgap states and signals the presence of degenerate bound states with a finite support on different parts of the device. Additionally, it displays sharp sign changes as a function of the induced charge of the superconductor, signaling energy crossings among its lowest excited states.

We study the interplay between disorder and light-matter coupling by considering a disordered one-dimensional chain of lossy dipoles coupled to a multimode optical cavity, through a microscopically derived Hamiltonian. Such a system, hosting polaritonic excitations, may be realized experimentally in a wide range of platforms under strong light-matter coupling. By analyzing both the eigenspectrum and the driven-dissipative transport properties of our system, we find that in the strong-coupling regime, increasing disorder leads almost uncoupled dark states to acquire a photonic part, allowing them to inherit polaritonic long-range transport characteristics. Crucially, we show that this disorder-enhanced transport mechanism is increasingly noticeable when the considered dipoles are lossier.

Metafluids, the version of metamaterials with fluid background, are generally characterized by two parameters: the effective mass density and bulk modulus. However, we recently theoretically demonstrated that a metafluid, with built-in quadrupolar resonances, can counterintuitively accommodate a third parameter, the effective shearlike modulus. In this letter, we go further to experimentally implement this metafluid, realized as a square lattice array of hollow steel cylinders in water. The effective parameters are extracted by matching the measured dispersion curves with the effective medium theory. By virtue of the emergent parameter, the metafluid can intrinsically support surface waves at the interface with water, which updates the knowledge that surface waves cannot exist at the interface of two fluids. Our work has potential in expanding the applications of metafluids.

The Hall effect that occurs when current flows through a CoFeB/MgO/NM ($\mathrm{NM}=\mathrm{Pt}$,Ta) tunnel junction is investigated. It is shown that the transverse voltage in NM electrodes is nonlinear on a DC voltage applied to the tunnel junction. It has both linear (odd) and quadratic (even) parts with respect to electric field. The linear part contains well-known contributions of the anomalous Hall effect in the ferromagnetic electrode, inverse spin-hall effect in NM, and others. The quadratic part is a phenomenon caused by the spin-orbit scattering of electrons in an external electric field induced by a voltage applied to the barrier. This field reaches values of ${10}^9$ V/m, which is close to internal atomic fields. The magnitude of both effects decreases as the thickness of the NM electrode is increased due to shunting effects.

We present the nonequilibrium implementation of the two-particle self-consistent (TPSC) approach, which has been shown to provide a reliable equilibrium description of interacting lattice systems in the weak- and intermediate-correlation regime. This method captures the effects of local and nonlocal correlations in two- and higher-dimensional systems and satisfies the Mermin-Wagner theorem. We demonstrate the versatility of nonequilibrium TPSC with calculations of the time-dependent spin and charge response functions and the evolution of effective temperatures extracted from different correlation functions, after interaction ramps in the two-dimensional Hubbard model.

Viscous fluid in an ultrahigh-mobility two-dimensional electron gas (2DEG) in GaAs/AlGaAs quantum wells is systematically studied through measurements of negative magnetoresistance (NMR) and photoresistance under microwave radiation, and the data are analyzed according to recent theoretical work [P. S. Alekseev, Phys. Rev. Lett. 117, 166601 (2016)]. Size-dependent and temperature dependent NMR are found to conform to the theoretical predictions. The size dependence of microwave induced resistance oscillations and that of the second harmonic peak indicate that 2DEG in a moderate magnetic field should be regarded as viscous fluid as well. Size-dependent radiation heating effect is found by using NMR as electron thermometry. Our results suggest that the hydrodynamic effects must be considered in order to understand semiclassical electronic transport in a clean 2DEG.

Recent studies on quantum transport in metals have revealed that a gauge field acting on the electron wavefunction yields a peculiar Hall or Nernst effect. When topologically nontrivial spin textures are present, a gauge field appears in real space and affects the electron transport. However, the understanding of the Nernst effect emerging from a real-space gauge field (topological Nernst effect) remains qualitative, and moreover, the influence of thermal fluctuations has been elusive. Here, we report a pronounced temperature-dependent topological Nernst effect in the metastable skyrmion lattice in MnSi. Our density functional theory, assuming a temperature-independent gauge field, is successful in an order-of-magnitude estimate of the Nernst signal, whereas the experimental values decrease more significantly with increasing temperature. A similar tendency is observed for the topological Hall effect, thus indicating that pronounced suppression of the real-space gauge field is crucial for the quantitative understanding of the quantum transport induced by topological spin textures at finite temperatures.

We discuss quantum dynamics in the transverse field Ising model in two spatial dimensions. We show that, up to a prethermal timescale, which we quantify, the Hilbert space “shatters” into dynamically disconnected subsectors. We identify this shattering as originating from the interplay of a $\text{U}\left(1\right)$ conservation law and a one-form ${\mathbb{Z}}_2$ constraint. We show that the number of dynamically disconnected sectors is exponential in system volume, and includes a subspace exponential in system volume within which the dynamics is exactly localized, even in the absence of quenched disorder. Depending on the emergent sector in which we work, the shattering can be weak (such that typical initial conditions thermalize with respect to their emergent symmetry sector), or strong (such that typical initial conditions exhibit localized dynamics). We present analytical and numerical evidence that a first-order-like “freezing transition” between weak and strong shattering occurs as a function of the symmetry sector, in a nonstandard thermodynamic limit. We further numerically show that on the “weak” (melted) side of the transition domain wall dynamics follows ordinary diffusion.

Electronic nematicity is an intriguing phenomenon found in unconventional superconductors and its mechanism invokes intense studies. The precise measurement of the director and amplitude of electronic nematicity by electric transport demands a full mapping of the longitudinal and transverse resistivity, $\rho$ and ${\rho }_T$, along different directions. Fabricating Hall bars along every possible in-plane direction would be so labor intensive and vulnerable to sample to sample variations that it becomes impractical. Instead, here we make the local current density $\mathit{J}$ continuously rotate in plane by independently controlling its in-plane components along two orthogonal axes and measure $\rho$ and ${\rho }_T$ as a function of the azimuth angle $\varphi$ between $\mathit{J}$ and the crystallographic $\left[100\right]$ direction. Clear substantial angular oscillations in $\rho \left(\varphi \right)$ and ${\rho }_T\left(\varphi \right)$ were observed from the optimally doped ${\mathrm{La}}_{1.84}{\mathrm{Sr}}_{0.16}\mathrm{Cu}{\mathrm{O}}_4$ film, in stark contrast to those of the control gold film. This angle-resolved resistivity method demonstrates unprecedented precision in determining the director and amplitude of electronic nematicity and is applicable to anisotropic transport due to mechanisms other than electronic nematicity as well. This method paves the way for the studies of the nematic domains and fluctuations of the nematic order in films and bulk crystals.

We study the (001) surface state of a recently proposed $E_g$ symmetry interorbital-odd spin-triplet $s$-wave superconducting (SC) state in ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$. We confirm that this pair potential is transformed into a chiral $d$-wave pair potential and a pseudo-Zeeman field in the band basis for a low-energy range. Because of the chiral $d$-wave pair potential, the surface states appear near zero energy in the momentum range enclosed by the nodal lines of the chiral $d$-wave pair potential for each band at the (001) surface. Nevertheless, the pseudo-Zeeman field gives band splitting of the surface states, and its splitting energy is much smaller than the SC energy gap. The local density of states (LDOS) at the (001) surface of the SC state has a pronounced peak structure at zero energy because of the surface states near zero energy when the order of the resolution is lower than the splitting energy. This peak structure is robust against perturbations, such as an orbital Rashba coupling or an $E_u$ SC pair potential at the surface.

Antiferromagnets have recently been propelled to the forefront of spintronics by their high potential for revolutionizing memory technologies. For this, understanding the formation and driving mechanisms of the domain structure is paramount. In this work, we investigate the domain structure in a thin-film canted antiferromagnet $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$. We find that the internal destressing fields driving the formation of domains do not follow the crystal symmetry of $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$, but fluctuate due to substrate clamping. This leads to an overall isotropic distribution of the Néel order with locally varying effective anisotropy in antiferromagnetic thin films. Furthermore, we show that the weak ferromagnetic nature of $\alpha \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ leads to a qualitatively different dependence on the magnetic field compared to collinear antiferromagnets such as NiO. The insights gained from our work serve as a foundation for further studies of electrical and optical manipulation of the domain structure of antiferromagnetic thin films.

The interpretation of how superconductivity disappears in cuprates at large hole doping has been controversial. To address this issue, we present an experimental study of single-crystal and thin film samples of ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ (LSCO) with $x\ge 0.25$. In particular, measurements of bulk susceptibility on LSCO crystals with $x=0.25$ indicate an onset of diamagnetism at $T_{c1}=38.5$ K, with a sharp transition to a phase with full bulk shielding at $T_{c2}=18$ K, independent of field direction. Strikingly, the in-plane resistivity only goes to zero at $T_{c2}$. Inelastic neutron scattering on $x=0.25$ crystals confirms the presence of low-energy incommensurate magnetic excitations with reduced strength compared to lower doping levels. The ratio of the spin gap to $T_{c2}$ is anomalously large. Our results are consistent with a theoretical prediction for strongly overdoped cuprates by Spivak, Oreto, and Kivelson, in which superconductivity initially develops within disconnected self-organized grains characterized by a reduced hole concentration, with bulk superconductivity occurring only after superconductivity is induced by proximity effect in the surrounding medium of higher hole concentration. Beyond the superconducting-to-metal transition, local differential conductance measurements on an LSCO thin film suggest that regions with pairing correlations survive, but are too dilute to support superconducting order. Future experiments will be needed to test the degree to which these results apply to overdoped cuprates in general.

We simulate the motion of a commensurate vortex lattice in a periodic lattice of artificial circular pinning sites having different diameters, pinning strengths, and spacings using the time-dependent Ginzburg-Landau formalism. Above some critical DC current density $J_{\mathrm{c}}$, the vortices depin, and the resulting steady-state motion then induces an oscillatory electric field $E\left(t\right)$ with a defect “hopping” frequency $f_0$, which depends on the applied current density and the pinning landscape characteristics. The frequency generated can be locked to an applied AC current density over some range of frequencies, which depends on the amplitude of the DC as well as the AC current densities. Both synchronous and asynchronous collective hopping behaviors are studied as a function of the supercell size of the simulated system and the (asymptotic) synchronization threshold current densities determined.

The intricate interplay between charge motion and magnetic order in geometrically frustrated lattices is central for the properties of many two-dimensional quantum materials. The triangular lattice antiferromagnet is a canonical example of a frustrated system, and here we analyze the dynamics of a hole in such a lattice focusing on observables that have become accessible in a new generation of experiments. Using the $t-J$ model, we solve the problem exactly within linear spin wave theory in the limit of strong magnetic interactions, showing that the ground state is described by a coherent state of spin waves. The derivation highlights the crucial role played by the interaction between a static hole and the neighboring spins, which originates in the geometric frustration and has often been omitted in earlier works. Furthermore, we show that the nonequilibrium dynamics after a hole has abruptly been inserted at a lattice site is given by a coherent state with time-dependent oscillatory coefficients. Physically, this describes a burst of magnetic frustration propagating through only two-thirds of the lattice sites, since a destructive interference of spin waves leaves spins parallel to that removed by the hole unperturbed. After the wave has propagated through the lattice, the magnetization relaxes to that of the ground state. We then use our analytical solution to benchmark the widely used self-consistent Born approximation (SCBA) in the limit of strong magnetic interactions, showing that it is very accurate also for a triangular lattice. The magnetic polaron spectrum is analyzed for general magnetic interactions using the SCBA, and we compare our results with those for a square lattice.

We present general design principles for engineering and discovering periodic systems with flat bands. Our paradigm exploits spin-orbit assisted orbital frustration on a lattice to produce band structures that contain multiplets of narrowly dispersing bands whose bandwidth is smaller than all other energy scales of the problem including the band gap surrounding the flat bands. We present a series of models in one dimension and two dimensions on various lattices with different intracellular spin-orbit like potentials that hybridize the degrees of freedom in the unit cell. As an alternative to machine learning based exhaustive searches, these design principles and models can be used to search for flat-band systems in a variety of physical settings and can be used to investigate the role of weakly dispersing highly orbitally frustrated degrees of freedom in systems where the interactions dominate over the kinetic energy scales of the system.

The optical nonlinearity of Dirac fermions in two and three dimensions show unique properties determined by analytic expressions in the independent particle approximation, which promotes their host materials as potential candidates for providing optical nonlinear functionalities. In this work we theoretically study the third-order optical nonlinearity for one-dimensional Dirac fermions and obtain analytical expressions for third-order optical conductivities at general light frequencies. The conductivity includes many resonant peaks induced by the resonant optical transitions associated with intraband motion as well as one-, two-, and three-photon interband processes. The conductivities for field-induced second harmonic generation and third harmonic generation are discussed in detail. To connect with real materials, we choose armchair graphene nanoribbons, which host one-dimensional Dirac fermions for its low energy electronic excitation, and our analytical expressions are applied to get the third-order conductivity for harmonic generations with different ribbon width. By comparing with numerical results evaluated from a full band structure in a tight binding model, the analytic and numerical results agree pretty well for photon energy below 2.5 eV.

We demonstrate a rare nonsymmorphic crystalline symmetry-protected nodal-line semimetallic phase in ${\text{SrIrO}}_3$ by acquiring a spatial dependence of the terahertz spectral structure. An extremely low momentum-relaxation scattering rate of $\sim 8.32 {\text{cm}}^{-1}$ emerging from high-mobility Dirac electrons, diversity in the carrier dynamics controlled by the orientation and symmetry of epitaxial thin films, and a group theory analysis corroborate the formation of this phase. The presence of Dirac electrons only along selected crystal orientations of this three-dimensional semimetal uniquely interrelates the symmetry-enforced band crossings, a template that can explore the prevalence of this superior topological phase in complex systems.