We demonstrate how potential impurities are a very powerful tool for determining the pairing symmetry in graphene, proximity coupled to a spin-singlet superconductor. All $d$-wave states are characterized by subgap resonances, with spatial patterns clearly distinguishing between nodal and chiral $d$-wave symmetry, while $s$-wave states have no subgap resonances. We also find strong supergap impurity resonances associated with the normal state Dirac point. Subgap and supergap resonances only interact at very low doping levels, then causing suppression of the supergap resonances.

We investigate quantum phase transitions and quantum coherence in a quantum compass chain under an alternating transverse magnetic field. The model can be analytically solved by the Jordan-Wigner transformation and this solution shows that it is equivalent to a two-component one-dimensional (1D) Fermi gas on a lattice. We explore mutual effects of the staggered magnetic interaction and multisite interactions on the energy spectra and analyze the ground-state phase diagram. We use quantum coherence measures to identify the quantum phase transitions. Our results show that $l_1$ norm of coherence fails to detect faithfully the quantum critical points separating a gapped phase from a gapless phase, which can be pinpointed exactly by relative entropy of coherence. Jensen-Shannon divergence is somewhat obscure at exception points. We also propose an experimental realization of such a 1D system using superconducting quantum circuits.

We consider the transport properties of a single-electron transistor consisting of a diffusive normal-metal island and superconducting electrodes. We show that the interplay of a dissipative impedance of the gate electrode, a weak magnetic field, and a charging energy of the island causes a suppression of the critical supercurrent of the transistor. When the device is voltage biased, pumping of single electrons can be achieved by a periodic modulation of the gate voltage. We derive the analytic expressions for the error rates and show that they are suppressed by the applied magnetic field.

Monobismuthides of lutetium and yttrium are shown as representatives of materials which exhibit extreme magnetoresistance and magnetic-field-induced resistivity plateaus. At low temperatures and in magnetic fields of 9 T, the magnetoresistance attains orders of magnitude of ${10}^4\%$ and ${10}^3\%$, on YBi and LuBi, respectively. Our thorough examination of electron-transport properties of both compounds shows that observed features are the consequence of nearly perfect carrier compensation rather than of possible nontrivial topology of electronic states. The field-induced plateau of electrical resistivity can be explained with Kohler scaling. An anisotropic multiband model of electronic transport describes very well the magnetic field dependence of electrical resistivity and Hall resistivity. Data obtained from the Shubnikov–de Haas oscillation analysis also confirm that the Fermi surface of each compound contains almost equal amounts of holes and electrons. First-principle calculations of electronic band structure are in a very good agreement with the experimental data.

We present the magnetoresistance (MR) and Hall resistivity of layered ternary ${\mathrm{Nb}}_3\mathrm{Si}{\mathrm{Te}}_6$ thin flakes with magnetic field up to 33 T. The flakes show strong angle-dependent MR properties and unsaturated quasilinear dependence accompanied with Shubnikov–de Haas (SdH) oscillations. Hall resistivity study demonstrates that the hole carriers dominate the transport properties in the whole temperature range. The angle-dependent SdH oscillations reveal a two-dimensional Fermi surface of ${\mathrm{Nb}}_3\mathrm{Si}{\mathrm{Te}}_6$. Furthermore, by analysis of SdH oscillations, we observed a nontrivial $\pi$-Berry phase in the SdH oscillations which suggests the nontrivial topological nature of ${\mathrm{Nb}}_3\mathrm{Si}{\mathrm{Te}}_6$.

Lattice matched GaAs/AlGaAs epitaxial structures with quantum dots are studied at $T=4.2$ K under static uniaxial stress applied either along the [001] or [110] crystal directions. We conduct simultaneous measurements of the spectral shifts in the photoluminescence of the bulk GaAs substrate, which relate to strain via deformation potentials $a$ and $b$, and the quadrupolar shifts in the optically detected nuclear magnetic resonance spectra of the quantum dots, which relate to the same strain via the gradient-elastic tensor $S_{ijkl}$. Measurements in two uniaxial stress configurations are used to derive the ratio $b/a=0.242\pm 0.008$ in good agreement with previous studies on GaAs. Based on the previously estimated value of $a\approx -8.8$ eV we derive the product of the nuclear quadrupolar moment $Q$ and the $S$-tensor diagonal component in GaAs to be $Q{S}_{11}\approx +0.758\times {10}^{-6}$ V for ${}^{75}\mathrm{As}$ and $Q{S}_{11}\approx -0.377\times {10}^{-6}$ V for ${}^{69}\mathrm{Ga}$ nuclei. In our experiments the signs of $S_{11}$ are directly measurable, which was not possible in the earlier nuclear acoustic resonance studies. Our $Q{S}_{11}$ values are a factor of $\sim 1.4$ smaller than those derived from the nuclear acoustic resonance experiments [Phys. Rev. B 10, 4244 (1974)]. The gradient-elastic tensor values measured in this work can be applied in structural analysis of strained III-V semiconductor nanostructures via accurate modeling of their magnetic resonance spectra.

We study the formation of magnetic states in localized impurities embedded into two-dimensional semiconductors. By considering various energy configurations, we illustrate the interplay of the gap and the bands in the system magnetization. Finally, we consider finite-temperature effects to show how increasing $T$ can lead to formation and destruction of magnetization.

We present a hierarchical quantum master equation (HQME) approach which provides a numerically exact description of nonequilibrium charge transport in nanosystems with electronic-vibrational coupling. In contrast to previous work [C. Schinabeck et al., Phys. Rev. B 94, 201407 (2016)], the active vibrational degrees of freedom are treated in the reservoir subspace and are integrated out. This facilitates applications to systems with very high excitation levels, for example, due to current-induced heating, while properties of the vibrational degrees of freedom, such as the excitation level and other moments of the vibrational distribution function, are still accessible. The method is applied to a model of a nanosystem, which comprises a single electronic level that is coupled to fermionic leads and a vibrational degree of freedom. Converged results are obtained in a broad spectrum of parameters, ranging from the nonadiabatic to the adiabatic transport regime. We specifically investigate the phenomenon of vibrational instability, that is, the increase of current-induced vibrational excitation for decreasing electronic-vibrational coupling. The HQME approach allows us to analyze the influence of level broadening due to molecule-lead coupling as well as broadening of the Fermi distribution caused by temperature. Results obtained for the first two moments suggest that the vibrational excitation is always described by a geometric distribution in the weak electronic-vibrational coupling limit.

We present an exactly solvable model of a spin-triplet $f$-wave topological superconductor on the honeycomb lattice in the presence of the Hubbard interaction for arbitrary interaction strength. First, we show that the Kane-Mele model with corresponding spin-triplet $f$-wave superconducting pairings becomes a full-gap topological superconductor possessing time-reversal symmetry. We then introduce the Hubbard interaction. The exactly solvable condition is found to be the emergence of perfect flat bands at zero energy. They generate infinitely many conserved quantities. It is intriguing that the Hubbard interaction spontaneously breaks the time-reversal symmetry. As a result, the system turns into a trivial superconductor. We demonstrate this topological property based on the topological number and by analyzing the edge state in nanoribbon geometry.

The magnetic properties of rare earth compounds are usually well captured by assuming a fully localized $f$ shell and only considering the Hund's rule ground state multiplet split by a crystal electric field (CEF). Currently, the standard technique for probing CEF excitations in lanthanides is inelastic neutron scattering. Here we show that with the recent leap in energy resolution, resonant inelastic soft x-ray scattering (RIXS) has become an attractive alternative for looking at CEF excitations. This has been used for studying the CEF scheme in ${\mathrm{CeRh}}_2{\mathrm{Si}}_2$, a system that has been investigated intensely for more than two decades now but for which no consensus has been reached yet as to its CEF scheme. Using high energy resolution of about 30 meV as well as polarization analysis in the scattered beam, both features that have become available only very recently in RIXS, allowed us to find a unique CEF description for ${\mathrm{CeRh}}_2{\mathrm{Si}}_2$. The result agrees well with previous inelastic neutron scattering and magnetic susceptibility studies. Due to its strong resonant character, RIXS is applicable to very small samples, presents very high cross sections for all lanthanides, and further benefits from the very weak coupling to phonon excitations. The foreseeable further progress in energy resolution will make this technique increasingly attractive for the investigation of the CEF scheme in lanthanides.

Nuclear spins of dopant atoms in semiconductors are promising candidates as quantum bits, due to the long lifetime of their quantum states. Conventionally, coherent control of nuclear spins is done using ac magnetic fields. Using the example of a phosphorus atom in silicon, we theoretically demonstrate that hyperfine interaction can enhance the speed of magnetic control: the electron on the donor amplifies the ac magnetic field felt by the nuclear spin. Based on that result, we show that hyperfine interaction also provides a means to control the nuclear spin efficiently using an ac electric field, in the presence of intrinsic or artificial spin-orbit interaction. This electric control scheme is especially efficient and noise resilient in a hybrid dot-donor system holding two electrons in the presence of an inhomogeneous magnetic field. The mechanisms proposed here could be used as building blocks in nuclear-spin-based electronic quantum information architectures.

We analyze and assign two low-intensity, double-resonant Raman bands at around 1950 ${\mathrm{cm}}^{-1}$ and 2450 ${\mathrm{cm}}^{-1}$ in carbon nanotube ensembles. We present Raman spectra of a high-pressure carbon monoxide sample for laser energies in the visible range. By using density functional theory plus zone folding, we simulate both combination modes for various excitation energies with respect to the chiral-index distribution of carbon nanotubes in the sample. For a comparison, double-resonant Raman spectra of single carbon nanotubes are also modeled within a symmetry-based nonorthogonal tight-binding approach, resulting in a different assignment of the 1950-${\mathrm{cm}}^{-1}$ band. Apparent discrepancies in the assignments are discussed in the article.

Two-dimensional artificial magnetic honeycomb lattice is predicted to manifest several magnetic phase transitions as a function of reducing temperature. We have performed the analysis of nonlinear susceptibility to explore the equilibrium nature of phase transition in artificial honeycomb lattice of ultrasmall connected permalloy (${\mathrm{Ni}}_{0.81}{\mathrm{Fe}}_{0.19}$) elements, typical length of $\simeq 12$ nm. The nonlinear susceptibility ${\chi }_{n1}$ is found to exhibit an unusual crossover character in both temperature and magnetic field. The higher order susceptibility ${\chi }_3$ changes from positive to negative as the system traverses through the spin solid phase transition at $T_s=29$ K. Additionally, the static critical exponents, used to test the scaling of ${\chi }_{n1}$, do not follow the conventional scaling relation. We conclude that the magnetic phase transition, especially to the low temperature spin solid order, is not conventional in nature at this length scale.

We study the crystal structure of Pd(100) ultrathin films, which show ferromagnetism induced by the quantum confinement effect, using in situ x-ray crystal truncation rod measurement and density functional calculation. The energy gain from the appearance of ferromagnetism in Pd results in flatter and uniform film growth of ferromagnetic Pd films compared with paramagnetic Pd. In addition, ferromagnetic Pd films expand the out-of-plane lattice constant to suppress the increase in kinetic energy of electrons accompanied by the occurrence of exchange splitting. Although the traditional theory of magnetism in metals indicates that the increase in density of states induces ferromagnetism (Stoner criterion), our present finding reveals a mechanism of modulation in the density of states via the appearance of ferromagnetism, i.e., the inverse mechanism of Stoner's theory.

We predict a large anomalous Nernst effect in the inverse Heusler compensated ferrimagnets ${\mathrm{Ti}}_2\mathrm{Mn}X$ ($X=\mathrm{Al}$, Ga, and In) with vanishing net magnetic moments. Though the net magnetic moment is zero, the Weyl points in these systems lead to a large anomalous Nernst conductivity (ANC) due to the lack of a global time-reversal symmetry operation that inverts the sign of the Berry curvature. In comparison to the noncollinear antiferromagnets ${\mathrm{Mn}}_3\mathrm{Sn}$ and ${\mathrm{Mn}}_3\mathrm{Ge}$, the high ANC stems almost entirely from the Weyl points in this class of compounds, and thus it is topologically protected. This work shows a large ANC with zero net magnetic moments in collinear systems, which is helpful for a comprehensive understanding of the thermoelectric effect in zero-moment magnetic materials and its further applications.