We investigate the electronic properties of type-II superconducting Nb(110) in an external magnetic field. Scanning tunneling spectroscopy reveals a complex vortex shape which develops from circular via coffee bean shaped to elliptical when decreasing the energy from the edge of the superconducting gap to the Fermi level. This anisotropy is traced back to the local density of states of Caroli–de Gennes–Matricon states which exhibits a direction-dependent splitting. Oxidizing the Nb(110) surface triggers the transition from the clean to the dirty limit, attenuates the vortex bound states, and leads to an isotropic appearance of the vortices. Density functional theory shows that the Nb(110) Fermi surface is stadium shaped near the $\overline{\mathrm{\Gamma }}$ point. Calculations within the Bogoliubov–de Gennes theory using these Fermi contours consistently reproduce the experimental results.

Classical reversible cellular automata (CAs), which describe the discrete-time dynamics of classical degrees of freedom in a finite state space, can exhibit exact, nonthermal quantum eigenstates despite being classically chaotic. We show that every classical CA defines a family of generically nonintegrable, periodically driven (Floquet) quantum dynamics with exact, nonthermal eigenstates. These Floquet dynamics are nonergodic in the sense that certain product states on a periodic classical orbit fail to thermalize, while generic initial states thermalize as expected in a quantum chaotic system. We demonstrate that some signatures of these effects can be probed in quantum simulators based on Rydberg atoms in the blockade regime. These results establish classical CAs as parent models for a class of quantum chaotic systems with rare nonthermal eigenstates.

In systems with time-reversal symmetry, the orbital magnetization is zero in equilibrium. Recently, it has been proposed that the orbital magnetization can be induced by an electric current in a helical crystal structure in the same manner as that in a classical solenoid. In this paper, we extend this theory and study the current-induced orbital magnetization in a broader class of systems without inversion symmetry. First, we consider polar metals which have no inversion symmetry. We find that the current-induced orbital magnetization appears in a direction perpendicular to the electric current even without spin-orbit coupling. Using the perturbation method, we physically clarify how the current-induced orbital magnetization appears in polar metals. As an example, we calculate the current-induced orbital magnetization in SnP and find that it might be sufficiently large for measurement. Next, we consider a two-dimensional system without inversion symmetry. We establish a method to calculate the current-induced orbital magnetization in the in-plane direction by using real-space coordinates in the thickness direction. By applying this theory to surfaces and interfaces of insulators, we find that an electric current along surfaces and interfaces induces an orbital magnetization perpendicular to the electric current.

The interaction of electrons with a flux of ballistic phonons leads to excitation of many angular harmonics of an electron distribution function. We show that this property dramatically modifies the magnetothermoelectric phenomena in two-dimensional electron systems with boundaries. By considering classical magnetotransport of electrons in a narrow channel with partly diffusive boundary scattering, we show that the phonon flux excites a pattern of current stripes with alternating directions of propagation along the channel. The Nernst voltage due to phonon drag appears already in the classical transport regime and can be comparable with the Seebeck voltage, while the latter acquires a dependence on the magnetic field. The temperature dependence of these voltages shows an unusual behavior determined by relaxation of higher-order harmonics of the distribution function via electron-electron scattering. Our experimental studies of mesoscopic samples based on high-quality GaAs quantum wells confirm the main properties of the thermoelectric response suggested by the theory.

Time-dependent driving influences the quantum and thermodynamic fluctuations of a system, changing the familiar physical picture of electronic noise which is an important source of information about the microscopic mechanism of quantum transport. Giving access to all cumulants of the current, the full counting statistics (FCS) is the powerful theoretical method to study fluctuations in nonequilibrium quantum systems. In this paper, we propose the application of FCS to consider periodic driven junctions. The combination of Floquet theory for time dynamics and nonequilibrium counting-field Green's functions enables the practical formulation of FCS for the system. The counting-field Green's functions are used to compute the moment generating function, allowing for the calculation of the time-averaged cumulants of the electronic current. The theory is illustrated using different transport scenarios in model systems.

We compute the jerk current tensor of GaAs, Si, and ferroelectric single-layer GeS, GeSe, SnS, and SnSe. We find peak values of the order of ${10}^{14}\mathrm{mA}/{\mathrm{V}}^3{\mathrm{s}}^2$ in GaAs and Si within the visible energy spectrum and an order of magnitude larger in single-layer GeS, GeSe, SnSe, and SnS. We show that the detailed knowledge of this tensor and its large value in single-layer GeS, GeSe, SnSe, and SnS make it possible to predict the magnitude and angle of rotation of polarization of intense terahertz pulses generated in photoconductive switches and point to alternative functionalities of these devices.

The Lieb-Schultz-Mattis (LSM) theorem implies that gapped phases of matter must satisfy nontrivial conditions on their low-energy properties when a combination of lattice translation and $U\left(1\right)$ symmetry are imposed. We describe a framework to characterize the action of symmetry on fractons and other subdimensional fractional excitations, and use this together with the LSM theorem to establish that X-cube fracton order can occur only at integer or half-odd-integer filling. Using explicit parton constructions, we demonstrate that “odd” versions of X-cube fracton order can occur in systems at half-odd-integer filling, generalizing the notion of odd $Z_2$ gauge theory to the fracton setting. At half-odd-integer filling, exiting the X-cube phase by condensing fractional quasiparticles leads to symmetry breaking, thereby allowing us to identify a class of conventionally ordered phases proximate to phases with fracton order. We leverage a dual description of one of these ordered phases to show that its topological defects naturally have restricted mobility. Condensing pairs of these defects then leads to a fracton phase, whose excitations inherit these mobility restrictions.

We investigate the response of three-dimensional Luttinger semimetals to localized charge and spin impurities as a function of doping. The strong spin-orbit coupling of these materials strongly influences the Friedel oscillations and RKKY interactions. This can be seen at short distances with an $1/r^4$ divergence of the responses and anisotropic behavior. Certain of the spin-orbital signatures are robust to temperature, even if the charge and spin oscillations are smeared out, and give an unusual diamagnetic Pauli susceptibility. We compare our results to the experimental literature on the bismuth-based half-Heuslers such as YPtBi and on the pyrochlore iridate ${\mathrm{Pr}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$.

Magnetic Compton scattering, x-ray magnetic circular dichroism spectroscopy, and bulk magnetometry measurements are performed on a set of medium- (NiFeCo and NiFeCoCr) and high-entropy (NiFeCoCrPd and NiFeCoCrMn) Cantor-Wu alloys. The bulk spin momentum densities determined by magnetic Compton scattering are remarkably isotropic, and this is a consequence of the smearing of the electronic structure by disorder scattering of the electron quasiparticles. Nonzero x-ray magnetic circular dichroism signals are observed for every element in every alloy indicating differences in the populations of the majority and minority spin states implying finite magnetic moments. When Cr is included in the solid solution, the Cr spin moment is unambiguously antiparallel to the total magnetic moment, while a vanishingly small magnetic moment is observed for Mn, despite calculations indicating a large moment. Some significant discrepancies are observed between the experimental bulk and surface magnetic moments. Despite the lack of quantitative agreement, the element-specific surface magnetic moments seem to be qualitatively reasonable.

We have probed directly the temperature and magnetic field dependence of pinned uncompensated magnetization at the interface of antiferromagnetic ${\mathrm{FeF}}_2$ with Cu, using ${\mathrm{FeF}}_2\text{−}\mathrm{Cu}\text{−}\mathrm{Co}$ spin valves. Electrons polarized by the Co layer are scattered by the pinned uncompensated moments at the ${\mathrm{FeF}}_2\text{−}\mathrm{Cu}$ interface giving rise to giant magnetoresistance. We determined the direction and magnitude of the pinned uncompensated magnetization at different magnetic fields and temperatures using the angular dependencies of resistance. The strong ${\mathrm{FeF}}_2$ anisotropy pins the uncompensated magnetization along the easy axis independent of the cooling field orientation. Most interestingly, magnetic fields as high as 90 kOe cannot break the pinning at the ${\mathrm{FeF}}_2\text{−}\mathrm{Cu}$ interface. This proves that the pinned interfacial magnetization is strongly coupled to the antiferromagnetic order inside the bulk ${\mathrm{FeF}}_2$ layer. Studies as a function of ${\mathrm{FeF}}_2$ crystalline orientation show that uncompensated spins are only detected in a spin valve with (110) crystal orientation, but not in valves containing ${\mathrm{FeF}}_2\left(100\right)$ and ${\mathrm{FeF}}_2\left(001\right)$. This observation is in agreement with symmetry-related considerations which predict the equilibrium boundary magnetization for the ${\mathrm{FeF}}_2\left(110\right)$ layer.

The magnetic topological materials have attracted much attention recently for their potential realization of various novel quantum states. However, the onset of magnetization in these materials usually occurs at low temperatures, impeding further applications. Here, by means of high pressure, we have significantly increased the magnetic transition temperature in an antiferromagnetic axion insulator candidate $\mathrm{Eu}{\mathrm{In}}_2{\mathrm{As}}_2$. Both crystal and magnetic structures remain the same with pressure up to 17 GPa. The Néel temperature can be monotonously increased from 16 K (ambient pressure) to 65 K (14.7 GPa). This is mainly attributed to the enhancement of intralayer ferromagnetic exchange coupling by pressure. With increasing pressure up to 17 GPa, a crystalline-to-amorphous phase transition occurs, which impedes further enhancement of the Néel temperature. Our results show that high pressure is an effective pathway to greatly enhance the magnetic transition temperature in topological materials. It is helpful for the realization of novel quantum states at elevated temperatures.

The principal Hugoniot, sound velocity, and Grüneisen parameter of polystyrene were measured at conditions relevant to shocks in inertial confinement fusion implosions, from 100 to 1000 GPa. The sound velocity is in good agreement with quantum molecular dynamics calculations and all tabular equation of state models at pressures below 200 GPa. Above 200 GPa, the experimental results agree with two of the examined tables, but do not agree with the most recent table developed for design of inertial confinement fusion (ICF) experiments. The Grüneisen parameter increases with density below $\sim 3.1\mathrm{g}/{\mathrm{cm}}^3$ and approaches the asymptotic value for an ideal gas after complete dissociation. This behavior is in good agreement with quantum molecular dynamics results and previous work but is not represented by any of the tabular models. The discrepancy between tabular models and experimental measurement of the sound velocity and Grüneisen parameter is sufficient to impact simulations of ICF experiments.

Previous experimental evidence showed that silane ($\mathrm{Si}{\mathrm{H}}_4$) becomes a superconductive phase at a critical temperature ($T_{\mathrm{c}}$) of 17 K above 96 GPa, although this observation was not supported by later experiments due to the fact that $\mathrm{Si}{\mathrm{H}}_4$ was measured to decompose into amorphous silicon and solid hydrogen at $\sim 60–90\mathrm{GPa}$ and then recrystallized into a nonmetallic phase up to $\sim 130\mathrm{GPa}$. Given lithium has a short atomic radius and low electronegativity, it could be incorporated into the binary hydrides and act as an electron donor by doping electrons into the lattice of parent binary hydrides, enabling the modification of crystal structures and superconductivity for the resulting ternary hydride system. In this work, therefore, we attempted to chemically tune crystal structures and improve the superconductivity of the Si-H system via lithium incorporation, by performing structure searching simulations on the Li-Si-H system at a wide pressure range of 50–350 GPa. As a result, four stable stoichiometries of $\mathrm{LiSi}{\mathrm{H}}_5, \mathrm{LiSi}{\mathrm{H}}_6, \mathrm{LiS}{\mathrm{i}}_2{\mathrm{H}}_9$, and $\mathrm{L}{\mathrm{i}}_2\mathrm{Si}{\mathrm{H}}_6$, as well as two metastable stoichiometries of $\mathrm{LiSi}{\mathrm{H}}_4$ and $\mathrm{LiSi}{\mathrm{H}}_8$, were uncovered under high pressures. Among these predicted stoichiometries, $\mathrm{LiS}{\mathrm{i}}_2{\mathrm{H}}_9$ and $\mathrm{LiSi}{\mathrm{H}}_8$ are predicted to become good phonon-mediated superconductors with estimated $T_{\mathrm{c}}$ of 54 and 77 K at 172 and 250 GPa, respectively. These results highlight the role of lithium incorporation in chemically tuning crystal structures, which induce the significant change of electronic properties for a Si-H system from nonmetallicity or poor metallicity to high-$T_{\mathrm{c}}$ superconductivity, shedding light on the exploration and discovery of high-$T_{\mathrm{c}}$ superconductivity in a variety of ternary hydrogen-rich compounds associated with lithium incorporation.

The Fe sublattice in the compound ${\mathrm{ZrFe}}_4{\mathrm{Si}}_2$ features geometrical frustration and quasi-one-dimensionality. We therefore investigated the magnetic behavior in ${\mathrm{ZrFe}}_4{\mathrm{Si}}_2$ and its evolution upon substituting Ge for Si and under the application of hydrostatic pressure using structural, magnetic, thermodynamic, and electrical-transport probes. Magnetic measurements reveal that ${\mathrm{ZrFe}}_4{\mathrm{Si}}_2$ holds paramagnetic Fe moments with an effective moment ${\mu }_{\mathrm{eff}}=2.18{\mu }_B$. At low temperatures the compound shows a weak short-range magnetic order below 6 K. Our studies demonstrate that substituting Ge for Si increases the unit-cell volume and stabilizes the short-range order into a long-range spin-density wave type magnetic order. On the other hand, hydrostatic pressure studies using electrical-resistivity measurements on ${\mathrm{ZrFe}}_4{\left({\mathrm{Si}}_{0.88}{\mathrm{Ge}}_{0.12}\right)}_2$ indicate a continuous suppression of the magnetic ordering upon increasing pressure. Therefore, our combined chemical substitution and hydrostatic pressure studies suggest the existence of a lattice-volume-controlled quantum critical point in ${\mathrm{ZrFe}}_4{\mathrm{Si}}_2$.

Recent high-precision measurements employing different experimental techniques have unveiled an anomalous peak in the doping dependence of the London penetration depth which is accompanied by anomalies in the heat capacity in iron-pnictide superconductors at the optimal composition associated with the hidden antiferromagnetic quantum critical point. We argue that finite temperature effects can be a cause of observed features. Specifically we show that quantum critical magnetic fluctuations under superconducting dome can give rise to a nodal-like temperature dependence of both specific heat and magnetic penetration depth in a fully gapped superconductor. In the presence of line nodes in the superconducting gap fluctuations can lead to the significant renormalization of the relative slope of $T$-linear penetration depth which is steepest at the quantum critical point. The results we obtain are general and can be applied beyond the model we use.

The channel-decomposed functional renormalization group (FRG) approach, most recently presented in the variant of truncated-unity FRG (TUFRG), has so far been used for various two-dimensional model systems. Yet for many interesting material systems the third spatial dimension is of clear relevance. Therefore, FRG schemes working in three spatial dimensions (3D) are definitely on the wish list. Here we demonstrate that a 3D TUFRG scheme can be set up in a straightforward extension of previous two-dimensional codes and gives physically sensible results with affordable numerical effort, regarding both the qualitative and quantitative descriptions. The computed phase diagram of the three-dimensional Hubbard model at half filling or perfect nesting shows a phase transition to a $(\pi ,\pi ,\pi )$-ordered antiferromagnetic ground state for repulsive interactions at an energy scale that compares well with other numerical approaches in the literature. Furthermore, the method allowed us to detect a $d$-wave pairing and a concurring $(\pi ,\pi ,0)$ antiferromagnetic ground state in the hole-doped Hubbard model.

In this work we introduce the dual boson diagrammatic Monte Carlo technique for strongly interacting electronic systems. This method combines the strength of dynamical mean-filed theory for nonperturbative description of local correlations with the systematic account of nonlocal corrections in the dual boson theory by the diagrammatic Monte Carlo approach. It allows us to get a numerically exact solution of the dual boson theory at the two-particle local vertex level for the extended Hubbard model. We show that it can be efficiently applied to description of single-particle observables in a wide range of interaction strengths. We compare our exact results for the self-energy with the ladder dual boson approach and determine a physical regime, where the description of collective electronic effects requires more accurate consideration beyond the ladder approximation. Additionally, we find that the order-by-order analysis of the perturbative diagrammatic series for the single-particle Green's function allows to estimate the transition point to the charge density wave phase.

The chirality-induced spin selectivity (CISS), demonstrated in diverse chiral molecules by numerous experimental and theoretical groups, has been attracting extensive and ongoing interest in recent years. As the secondary structure of DNA, the charge transfer along DNA hairpins has been widely studied for more than two decades, finding that DNA hairpins exhibit spin-related effects as reported in recent experiments. Here, we propose a setup to demonstrate directly the CISS effect in DNA hairpins contacted by two nonmagnetic leads at both ends of the stem. Our results indicate that DNA hairpins present a pronounced CISS effect and the spin polarization could be enhanced by using conducting molecules as the loop. In particular, DNA hairpins exhibit several intriguing features. First, the local spin currents can flow circularly and assemble into a number of vortex clusters when the electron energy locates in the left/right electronic band of the stem. The chirality of vortex clusters in each band is the same and will be reversed by switching the electron energy from the left band to the right one, inducing the sign reversal of the spin polarization. Interestingly, the local spin currents can be greater than the corresponding spin component of the source-drain current. Second, both the conductance and the spin polarization can increase with molecular length as well as dephasing strength, contrary to the physical intuition that the transmission ability of molecular wires should be poorer when suffering from stronger scattering. Third, we unveil the optimal contact configuration of efficient electron transport and that of the CISS effect, which are distinct from each other and can be controlled by dephasing strength. The experimental realization of these results is discussed and the underlying physical mechanism is illustrated.