We study the electronic transport of heterojunctions made of chiral topological superconductors (TSCs) with integer $N$ chiral Majorana fermion modes and quantum Hall insulators (QHIs) with integer Chern number $C$. In the weak disorder regime, we show the two-terminal conductance ${\sigma }_{12}$ of a QHI-TSC-QHI junction for most $N>1$ is nonquantized but obeys a certain distribution determined by $C$ and $N$, which is induced by random $\mathrm{SO}\left(N\right)$ rotations of chiral Majorana fermion modes during propagation along the TSC edges. Oppositely, in the strong disorder regime, ${\sigma }_{12}$ tends to a quantized value. This provides a unique electrical signature for chiral TSC with $N>1$, which is significantly different from the extensively studied $N=1$ case. We conclude with a brief discussion on the fractionally quantized thermal conductances of the junction.

The magnetic properties over a wide range of temperatures in diluted magnetic semiconductors (DMSs) are discussed in the framework of the Kondo lattice model with magnetic impurity disorder. In the approach of dynamical mean-field theory, a set of self-consistent equations has been derived to specify single-particle Green functions. Analytical expressions of the static magnetic susceptibility and the $B_{1g}$ channel Raman response are then delivered. Inspecting for signatures of an itinerant carrier density of states and magnetization, we have identified a stable ferromagnetic (FM) state at low temperature. With increasing temperature, thermal fluctuations diminish the ordered state and the system favors a paramagnetic (PM) phase. Tracking and tracing different model parameters, the FM-PM transition phase diagram has been constructed. Spin fluctuations in the PM state have been pointed out in the behaviors of the self-energies, the static magnetic susceptibility, and the Raman scattering. Analyzing the properties of the $B_{1g}$ channel Raman response, we have attributed a formation of magnetic polarons in the PM state. The magnetic polaron scenario in a wide range of temperatures has been then intensively discussed. For the first time, both the static magnetic susceptibility and the $B_{1g}$ Raman response have been combined together to discuss the magnetic properties in DMSs compactly based on the dynamical mean-field approach.

The shape of the Fermi surface of topological nodal-ring semimetals at low carrier concentrations is characterized by the ring radius $b/\hslash v_F$. This peculiar topological property may not have a clear signature in measurable physical quantities. We demonstrate an accurate and definitive method to determine the radius of topological nodal-ring semimetals. Under a magnetic field along the ring axis, the axial magneto-optical response (${\sigma }_{zz}$) has a giant peak. The position of this ultrastrong response is at the frequency of exactly $2b$ and is independent of the strength of the magnetic field. The amplitude of the peak response is many times stronger than that of any other inter-Landau level transitions if the magnetic energy is greater than $b$ and is similar strength if $b$ is greater than the magnetic energy. The origin of the ultrastrong response is that the axial magnetic transition is governed by selection rules completely different to those governing ${\sigma }_{xx}$ where the giant response is absent [R. Y. Chen et al., Phys. Rev. Lett. 115, 176404 (2015)]. The present work provides a method to accurately determine parameters of the topological properties of semimetals.

We study the localization-driven correlated states among two isolated dirty interacting helical edges as realized at the boundaries of two-dimensional ${\mathbb{Z}}_2$ topological insulators. We show that an interplay of time-reversal symmetric disorder and strong interedge interactions generically drives the entire system to a gapless localized state, preempting all other intraedge instabilities. For weaker interactions, an antisymmetric interlocked fluid, causing a negative perfect drag, can emerge from dirty edges with different densities. We also find that the interlocked fluid states of helical edges are stable against the leading intraedge perturbation down to zero temperature. The corresponding experimental signatures including zero-temperature and finite-temperature transport are discussed.

The fractional quantum Hall effect (FQHE) observed at half filling of the second Landau level is believed to be caused by a pairing of composite fermions captured by the Moore-Read Pfaffian wave function. The generating Hamiltonian for the Moore-Read Pfaffian is a purely three-body model that breaks particle-hole symmetry and lacks other properties, such as dominate two-body repulsive interactions, expected from a physical model of the FQHE. We use exact diagonalization to study the low-energy states of a more physical two-body generator model derived from the three-body model. We find that the two-body model exhibits the essential features expected from the Moore-Read Pfaffian: pairing, non-Abelian anyon excitations, and a neutral fermion mode. The model also satisfies constraints expected for a physical model of the FQHE at half-filling because it is short range, spatially decaying, particle-hole symmetric, and supports a roton mode with a robust spectral gap in the thermodynamic limit. Hence, this two-body model offers a bridge between artificial three-body generator models for paired states and the physical Coulomb interaction and can be used to further explore properties of non-Abelian physics in the FQHE.

The near-field energy transfer between dielectric nanoparticles by considering the full coupling between all the thermal electric fields is studied theoretically for the case of a dimer and a trimer. We show that coupled modes between nanoparticles open channels through which energy may be transferred, increasing the power exchanged more than one order of magnitude as compared with existing models. We discuss how the contribution from coupled modes changes as parameters of the system are varied for the case of a two- and three-particle system. It is done by developing a spectral representation formalism for the near field, where fluctuating multipolar moments are fully incorporated, allowing identification of the contribution of energy transfer of each coupled mode. This information can be used to understand and control the energy flux among nanoparticles.

We consider a recent proposal for a physical realization of the Sachdev-Ye-Kitaev (SYK) model in the zeroth-Landau-level sector of an irregularly shaped graphene flake. We study in detail charge transport signatures of the unique non-Fermi-liquid state of such a quantum dot coupled to noninteracting leads. The properties of this setup depend essentially on the ratio $p$ between the number of transverse modes in the lead $M$ and the number of the fermion degrees of freedom $N$ on the SYK dot. This ratio can be tuned via the magnetic field applied to the dot. Our proposed setup gives access to the nontrivial conformal-invariant regime associated with the SYK model as well as a more conventional Fermi-liquid regime via tuning the field. The dimensionless linear-response conductance acquires distinct $\sqrt{p}$ and $1/\sqrt{p}$ dependencies for the two phases, respectively, in the low-temperature limit, with a universal jump at the transition. We find that corrections scale linearly and quadratically in either temperature or frequency on the two sides of the transition. In the weak-tunneling regime, we find differential conductance proportional to the inverse square root of the applied voltage bias $U$. This dependence is replaced by a conventional Ohmic behavior with constant conductance proportional to $1/\sqrt{T}$ for bias energy $eU$ smaller than temperature scale $k_{B}T$. We also describe the out-of-equilibrium current-bias characteristics and discuss various crossovers between the limiting behaviors mentioned above.

We investigate the ferromagnetic resonance modes of the magnetic vortex states on ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ ellipses using broadband ferromagnetic resonance measurements and micromagnetic simulations. Experiments show a rich structure of modes in the resonance absorption spectra, with absorption peak amplitudes dependent on the direction of the probing radio-frequency field. The evolution of the resonant modes is observed to be symmetric around zero field, due to the reversibility of the vortex core motion. The simulated absorption spectra reproduce the main features of the experimental results. A detailed analysis of the resonant modes at zero field shows that the observed absorption profiles result from the overlap of resonant modes which have an increasing complexity with the frequency. Besides, the simplest resonant modes are not those that exhibit the larger absorption amplitudes. Furthermore, the observed frequency splitting of some of the oscillation modes with the external field is correlated to the symmetry breaking during the vortex motion.

Experimental evidence suggests that FeSe is close to a magnetic instability, and recent scanning tunneling microscopy (STM) measurements on FeSe multilayer films have revealed stripe order locally pinned near defect sites. Motivated by these findings, we perform a theoretical study of locally induced magnetic order near nonmagnetic impurities in a model relevant for FeSe. We find that relatively weak repulsive impurities indeed are capable of generating short-range magnetism, and we explain the driving mechanism for the local order by resonant $e_g$-orbital impurity states. In addition, we investigate the importance of orbital-selective self-energy effects relevant for Hund's metals, and show how the structure of the induced magnetization cloud gets modified by orbital selectivity. Finally, we make a concrete connection to STM measurements of iron-based superconductors by symmetry arguments of the induced magnetic order, and the basic properties of the Fe Wannier functions relevant for tunneling spectroscopy.

We have fabricated superconductor-normal metal side junctions with different barrier transparencies out of ${\mathrm{PdTe}}_2$ crystalline flakes and measured the differential conductance spectra. Modeling our measurements using a modified Blonder, Tinkham, and Klapwijk (BTK) formalism confirms that the superconductivity is mostly comprised of the conventional $s$-wave symmetry. We have found that for junctions with very low barrier transparencies, the junctions can enter a thermal regime, where the critical current becomes important. Adding this to the BTK model allows us to accurately fit the experimental data, from which we conclude that the superconductivity in the $a-b$ plane of ${\mathrm{PdTe}}_2$ is dominated by conventional $s$-wave pairing.

The self-consistent Born approximation quantitatively fails to capture disorder effects in semimetals. We present an alternative, simple-to-use nonperturbative approach to calculate the disorder-induced self-energy. It requires a sufficient broadening of the quasiparticle pole and the solution of a differential equation on the imaginary frequency axis. We demonstrate the performance of our method for various paradigmatic semimetal Hamiltonians and compare our results to exact numerical reference data. For intermediate and strong disorder, our approach yields quantitatively correct momentum-resolved results. It is thus complementary to existing renormalization group treatments of weak disorder in semimetals.

Employing an exact diagonalization Monte Carlo solution of the first-principles-derived model Hamiltonian of a number of $A_{2}B{B}^{\prime }{\mathrm{O}}_6$ double-perovskite compounds, containing a $3d$ transition metal at the $B$ site and a $4d$ or $5d$ transition metal ion at the $B^{\prime }$ site, we investigate the effect of $B/B^{\prime }$ cation disorder on their magnetic properties. Our exhaustive study reveals that the influence of cation disorder on both the magnetic transition temperature and magnetization depends strongly on the underlying exchange mechanism with a distinct difference between the double exchange mechanism and a combined double exchange and superexchange mechanism. We further find that the nature of the disorder has a remarkable effect. While the uncorrelated or random disorder has a severely detrimental effect, especially for magnetism having a superexchange contribution, correlated disorder with a high degree of short-range order retains the magnetic properties of the fully cation-ordered compounds to a large extent. Our findings shed light on the puzzling report of magnetic order in fully cation-disordered CrRu oxides.

We show that a single-fermion quantum dot acquires odd-frequency Gor'kov anomalous averages in proximity to strongly correlated Majorana zero modes, described by the Sachdev-Ye-Kitaev (SYK) model. Despite the presence of finite anomalous pairing, the superconducting gap vanishes for the intermediate coupling strength between the quantum dot and Majoranas. The increase of the coupling leads to smooth suppression of the original quasiparticles. This effect might be used as a characterization tool for recently proposed tabletop realizations of the SYK model.

We have studied electronic properties of ${\mathrm{BaV}}_{10}{\mathrm{O}}_{15}$ in the intermediate-temperature phase as well as in the high-temperature metallic phase by using hard x-ray photoemission spectroscopy (HAXPES). The V $2p$ HAXPES show a shift in the high-temperature phase between 300 and 245 K which is similar to the shift of spectral weight near the Fermi edge. The binding energy of the O $1\mathit{s}$ HAXPES peak does not change except a slight shift of the lower binding energy edge in the opposite direction between 300 and 180 K across the transition to the intermediate-temperature phase. This behavior is in sharp contrast to the transition to the low-temperature insulating phase where V $2p$ and O $1s$ HAXPES show dramatic shifts in the same direction. This indicates that the charge-orbital change in the intermediate-temperature phase is driven by the correlated V $3d$ electrons and is electronic. The ${\mathrm{V}}^{2.5+}\text{−}{\mathrm{V}}^{2.5+}$ bond ordering is related to the metallic contribution and gradually decreases with cooling from 300 K. The valence-band HAXPES show the metallic features of the pseudogap behavior near the Fermi edge in and above the intermediate-temperature phase due to ${\mathrm{V}}^{2.5+}\text{−}{\mathrm{V}}^{3+}$ charge fluctuation. The magnitude of the pseudogap increases from 300 to 180 K in parallel with the gradual breaking of the ${\mathrm{V}}^{2.5+}\text{−}{\mathrm{V}}^{2.5+}$ bond and formation of trimers.

We study the role of electron correlations in the presumed type-II Weyl semimetallic candidate $\gamma \text{−}{\mathrm{MoTe}}_2$ by employing density functional theory (DFT) where the on-site Coulomb repulsion (Hubbard $U)$ for the Mo $4d$ states is included within the DFT+$U$ scheme. We show that pure DFT calculations fail to describe important features of the light-polarization dependence of the angular resolved photoemission intensity which can be accounted for by including the role of the Hubbard $U$. At the same time, while pure DFT calculations cannot explain the angular dependence of the Fermi surface as revealed by quantum oscillation experiments (a fact which had raised doubt about the presence of the Weyl physics in $\gamma \text{−}{\mathrm{MoTe}}_2)$, inclusion of such on-site Coulomb repulsion can. We find that while the number of Weyl points (WPs) and their position in the Brillouin zone change as a function of $U$, a pair of such WPs very close to the Fermi level survive the inclusion of these important corrections. Our calculations suggest that the Fermi surface of $\gamma \text{−}{\mathrm{MoTe}}_2$ is in the vicinity of a correlations-induced Lifshitz transition, which can be probed experimentally and its interplay with the Weyl physics might be intriguing.

While the thermoelectric and photoconduction effects are crucial in pristine and low-doped graphene, the bolometric effect is known to dominate the photoresponse in biased graphene. Here, we present a detailed microscopic investigation of the photoresponse due to the bolometric effect in graphene. Based on the semiconductor Bloch equations, we investigate the time- and momentum-resolved carrier dynamics in graphene in the presence of a constant electric field under optical excitation. The magnitude of the bolometric effect is determined by the optically induced increase of temperature times the conductivity change. Investigating both factors independently, we reveal that the importance of the bolometric effect in the high-doping regime can be mostly ascribed to the latter showing a parabolic dependence on the doping.

We investigate the impact of optically induced Förster coupling in van der Waals heterostructures consisting of graphene and a monolayer transition-metal dichalcogenide (TMD). In particular, we predict the corresponding dephasing rates and a fast energy transfer between the TMD layer and graphene being in the picosecond range. Exemplary we find a transition rate of thermalized excitons of about 4 ${\mathrm{ps}}^{-1}$ in a ${\mathrm{MoSe}}_2$-graphene stack at room temperature. This time scale is in good agreement with the recently measured exciton lifetime in this heterostructure.

The energy charging of a quantum battery is analyzed in an open quantum setting, where the interaction between the battery element and the external power source is mediated by an ancilla system (the quantum charger) that acts as a controllable switch. Different implementations are analyzed putting emphasis on the interplay between coherent energy pumping mechanisms and thermalization.

We have used rotational anisotropic polarized Raman spectroscopy to study the symmetries, the temperature, and the doping dependence of the charge ordered state in metallic ${\left(\mathrm{S}{\mathrm{r}}_{1\text{−}x}\mathrm{L}{\mathrm{a}}_x\right)}_3\mathrm{I}{\mathrm{r}}_2{\mathrm{O}}_7$. Despite the fact that the Raman probe size is greater than the charge ordering length, we establish that the charge ordering breaks the fourfold rotational symmetry of the underlying tetragonal crystal lattice into twofold, as well as the translational symmetry, and forms short-range domains with ${90}^{\circ }$ rotated charge order wave vectors, as soon as the charge order sets in below $T_{\mathrm{CO}}=\sim 200\mathrm{K}$ and across the doping-induced insulator metal transition. We observe that this charge order mode frequency remains nearly constant over a wide temperature range and up to the highest doping level. These features above are highly reminiscent of the ubiquitous unidirectional charge order in underdoped high-$T_{\mathrm{C}}$ copper-oxide-based superconductors (cuprates). We further resolve that the charge order damping rate diverges when approaching $T_{\mathrm{CO}}$ from below and increases significantly as increasing the La-doping level, which resembles the behaviors for a disorder-interrupted ordered phase and has not been observed for the charge order in cuprates.

We propose a definition of a ${\mathbb{Z}}_2$ topological invariant for magnon spin Hall systems which are the bosonic analog of two-dimensional topological insulators in class AII. The existence of “Kramers pairs” in these systems is guaranteed by pseudo-time-reversal symmetry which is the same as time-reversal symmetry up to some unitary transformation. The ${\mathbb{Z}}_2$ index of each Kramers pair of bands is expressed in terms of the bosonic counterparts of the Berry connection and curvature. We construct explicit examples of magnon spin Hall systems and demonstrate that our ${\mathbb{Z}}_2$ index precisely characterizes the presence or absence of helical edge states. The proposed ${\mathbb{Z}}_2$ index and the formalism developed can be applied not only to magnonic systems but also to other noninteracting bosonic systems.