We investigate a Zeeman-split quantum dot (QD) containing a single spin $1/2$ weakly coupled to a helical Luttinger liquid (HLL) within a generalized master equation approach. The HLL induces a tunable magnetization direction on the QD controlled by an applied bias voltage when the quantization axes of the QD and the HLL are noncollinear. The backscattering conductance (BSC) in the HLL is finite and shows a resonance feature when the bias voltage equals the Zeeman energy in magnitude. The observed BSC asymmetry in bias voltage directly reflects the quantization axis of the HLL spin.

We show that in the presence of ferromagnetic electronic reservoirs and spin-dependent tunnel couplings, molecular vibrations in nonmagnetic single molecular transistors induce an effective intramolecular exchange magnetic field. It generates a finite spin accumulation and precession for the electrons confined on the molecular bridge and occurs under (non)equilibrium conditions. The effective exchange magnetic field is calculated here to lowest order in the tunnel coupling for a nonequilibrium transport setup. Coulomb interaction between electrons is taken into account as well as a finite electron-phonon coupling. We show that for realistic physical parameters, an effective spin-phonon coupling emerges. It is induced by quantum many-body interactions, which are either of electron-phonon or Coulomb type. We investigate the precession and accumulation of the confined spins as function of bias and gate voltages as well as their dependence on the angle enclosed by the magnetizations between the left and right reservoir.

We calculate the tunneling density of states (TDOS) in a dissipationless three-wire junction of interacting spin-1/2 electrons, and find an anomalous enhancement of the TDOS in the zero-bias limit, even for repulsive interactions for several bosonic fixed points. This enhancement is physically related to the reflection of holes from the junction for incident electrons, and it occurs only in the vicinity of the junction ($x<v_{\min }/2\omega$, where $v_{\min }$ is the minimum of the velocity of charge or spin excitations and $\omega$ is the bias frequency), crossing over to the bulk value, which is always suppressed at larger distances. The TDOS exponent can be directly probed in an STM experiment by measuring the differential tunneling conductance as a function of either the bias voltage or temperature as done in C. Blumenstein et al., Nat. Phys. 7, 776 (2011).

We study the light scattering by plasmonic and dielectric symmetric trimers to investigate the existence of polarization-independent Fano resonances. Plasmonic hybridization theory is revealed to hide simple physics, and we instead provide a simplified model for hybridization to derive a plasmonic trimer's eigenmodes analytically. This approach is demonstrated to accurately recreate full wave simulations of plasmonic trimers and their Fano resonances. We are subsequently able to deduce the grounds for modal interference in plasmonic trimers and the related formation of Fano resonances. However, by generalizing our simplified hybridization approach, we are also able to investigate the eigenmodes of all-dielectric trimers. We show that bianisotropic coupling channels between high-index dielectric nanoparticles are able to increase the capacity for Fano resonances, even at normal incidence. We finally provide the first experimental measurements of sharp, polarization-independent Fano resonances from a symmetric all-dielectric trimer, with very good agreement with the predicted response from our simplified hybridization theory.

The isolated one-dimensional Heisenberg model with static random magnetic fields has become paradigmatic for the analysis of many-body localization. Here, we study the dynamics of this system initially prepared in a highly-excited nonstationary state. Our focus is on the probability for finding the initial state later in time, the so-called survival probability. Two distinct behaviors are identified before equilibration. At short times, the decay is very fast and equivalent to that of clean systems. It subsequently slows down and develops a power-law behavior with an exponent that coincides with the multifractal dimension of the eigenstates.

We use the recently developed typical medium dynamical cluster (TMDCA) approach [Ekuma et al., Phys. Rev. B 89, 081107 (2014)] to perform a detailed study of the Anderson localization transition in three dimensions for the box, Gaussian, Lorentzian, and binary disorder distributions, and benchmark them with exact numerical results. Utilizing the nonlocal hybridization function and the momentum resolved typical spectra to characterize the localization transition in three dimensions, we demonstrate the importance of both spatial correlations and a typical environment for the proper characterization of the localization transition in all the disorder distributions studied. As a function of increasing cluster size, the TMDCA systematically recovers the re-entrance behavior of the mobility edge for disorder distributions with finite variance, obtaining the correct critical disorder strengths, and shows that the order parameter critical exponent for the Anderson localization transition is universal. The TMDCA is computationally efficient, requiring only a small cluster to obtain qualitative and quantitative data in good agreement with numerical exact results at a fraction of the computational cost. Our results demonstrate that the TMDCA provides a consistent and systematic description of the Anderson localization transition.

The family of materials ${\left(\mathrm{EDO}\text{−}\mathrm{TTF}\right)}_2\mathrm{X}{\mathrm{F}}_6$ represents quasi-one-dimensional quarter filled systems exhibiting insulator-to-metal (I-M) phase transition at thermal equilibrium. ${\left(\mathrm{EDO}\text{−}\mathrm{TTF}\right)}_2\mathrm{P}{\mathrm{F}}_6$ is known to undergo a photoinduced I-M conversion with cooperative response to light excitation. Here we use femtosecond pump-probe experiments to study the photoresponse of ${\left(\mathrm{EDO}\text{−}\mathrm{TTF}\right)}_2\mathrm{Sb}{\mathrm{F}}_6$ made of a larger counteranion $\mathrm{Sb}{\mathrm{F}}_6$ compared to the well studied ${\left(\mathrm{EDO}\text{−}\mathrm{TTF}\right)}_2\mathrm{P}{\mathrm{F}}_6$. In the early stage of the photoinduced process, we reveal a multicomponent coherent oscillating feature. The evolution of this feature with excitation density and temperature points to the local nature of the photoswitching in ${\left(\mathrm{EDO}\text{−}\mathrm{TTF}\right)}_2\mathrm{Sb}{\mathrm{F}}_6$. At longer time scale, we did not detect the features associated with the transformation to the M phase, albeit observed in the $\mathrm{P}{\mathrm{F}}_6$ derivative. We propose a scenario whereby the bigger size of the counteranion in ${\left(\mathrm{EDO}\text{−}\mathrm{TTF}\right)}_2\mathrm{Sb}{\mathrm{F}}_6$ hinders the establishment of this transformation at macroscopic scale.

We report structural, magnetic, transport, and thermal properties of single-crystal $\mathrm{C}{\mathrm{a}}_2\mathrm{R}{\mathrm{u}}_{1-x}\mathrm{I}{\mathrm{r}}_x{\mathrm{O}}_4(0\le x\le 0.65)$. $\mathrm{C}{\mathrm{a}}_2\mathrm{Ru}{\mathrm{O}}_4$ is a structurally driven Mott insulator with a metal-insulator transition at $T_{\mathrm{MI}}=357\mathrm{K}$, which is well separated from antiferromagnetic order at $T_N=110\mathrm{K}$. Substitution of a $5d$ element, Ir, for Ru enhances spin-orbit coupling and locking between the structural distortions and magnetic moment canting. Ir doping intensifies the distortion or rotation of $\mathrm{Ru}/\mathrm{Ir}{\mathrm{O}}_6$ octahedra and induces weak ferromagnetic behavior along the $c$ axis. In particular, Ir doping suppresses $T_N$ but concurrently causes an additional magnetic ordering $T_{N2}$ at a higher temperature up to 210 K for $x=0.65$. The effect of Ir doping sharply contrasts with that of $3d$-element doping such as Cr, Mn, and Fe, which suppresses $T_N$ and induces unusual negative volume thermal expansion. The stark difference between $3d$- and $5d$-element doping underlines a strong magnetoelastic coupling inherent in the Ir-rich oxides.

We investigate theoretically how the proximity effect in superconductor/ferromagnet hybrid structures with intrinsic spin-orbit coupling manifests in two measurable quantities, namely, the density of states and critical temperature. To describe a general scenario, we allow for both Rashba- and Dresselhaus-type spin-orbit coupling. Our results are obtained via the quasiclassical theory of superconductivity, extended to include spin-orbit coupling in the Usadel equation and in the Kupriyanov-Lukichev boundary conditions. Unlike previous works, we have derived a Riccati parametrization of the Usadel equation with spin-orbit coupling which allows us to address the full proximity regime and not only the linearized weak proximity regime. First, we consider the density of states in both SF bilayers and SFS trilayers, where the spectroscopic features in the latter case are sensitive to the phase difference between the two superconductors. We find that the presence of spin-orbit coupling leaves clear spectroscopic fingerprints in the density of states due to its role in creating spin-triplet Cooper pairs. Unlike SF and SFS structures without spin-orbit coupling, the density of states in the present case depends strongly on the direction of magnetization. Moreover, we show that the spin-orbit coupling can stabilize spin-singlet superconductivity even in the presence of a strong exchange field $h\gg \mathrm{\Delta }$. This leads to the possibility of a magnetically tunable minigap: changing the direction of the exchange field opens and closes the minigap. We also determine how the critical temperature $T_c$ of an SF bilayer is affected by spin-orbit coupling and, interestingly, demonstrate that one can achieve a spin-valve effect with a single ferromagnet. We find that $T_c$ displays highly nonmonotonic behavior both as a function of the magnetization direction as well as the type and direction of the spin-orbit coupling, offering a new way to exert control over the superconductivity of proximity structures.

Investigating the phase relations of the system $\left\{\mathrm{Th},\mathrm{U}\right\}$-Pt-B at $900{}^{\circ }\mathrm{C}$ the formation of two compounds has been observed: cubic ${\mathrm{ThPt}}_3\mathrm{B}$ with $Pm\overline{3}m$ structure as a representative of the perovskites, and tetragonal ${\mathrm{UPt}}_3\mathrm{B}$ with $P4mm$ structure being isotypic to the noncentrosymmetric structure of ${\mathrm{CePt}}_3\mathrm{B}$. The crystal structures of the two compounds are defined by combined x-ray diffraction and transmission electron microscopy. Characterization of physical properties for ${\mathrm{ThPt}}_3\mathrm{B}$ reveals a superconducting transition at 0.75 K and an upper critical field at $T=0$ exceeding 0.4 T. For nonsuperconducting ${\mathrm{UPt}}_3\mathrm{B}$ a metallic resistivity behavior was found in the entire temperature range; at very low temperatures spin fluctuations become evident and the resistivity $\rho \left(T\right)$ follows non-Fermi liquid characteristics, $\rho ={\rho }_0+A{T}^n$ with $n=1.6$. Density functional theory (DFT) calculations were performed for both compounds for both types of structures. They predict that the experimentally claimed cubic structure of ${\mathrm{ThPt}}_3\mathrm{B}$ is thermodynamically not stable in comparison to a tetragonal phase, with a very large enthalpy difference of 25 kJ/mol, which cannot be explained by the formation energy of B vacancies. However, the presence of random boron vacancies possibly stabilizes the cubic structure via a local strain compensation mechanism during the growth of the crystal. For ${\mathrm{UPt}}_3\mathrm{B}$ the DFT results agree well with the experimental findings.

We study low-energy effective-field theories for non-Fermi liquids with Fermi surfaces of general dimensions and codimensions. When the dimension of the Fermi surface is greater than one, low-energy particle-hole excitations remain strongly coupled with each other across the entire Fermi surface. In this case, even the observables that are local in the momentum space (such as the Green's functions) become dependent on the size of the Fermi surface in singular ways, resulting in a ultraviolet/infrared (UV/IR) mixing. By tuning the dimension and codimension of the Fermi surface independently, we find perturbative non-Fermi-liquid fixed points controlled by both UV/IR mixing and interactions.

The infinite projected entangled pair states (iPEPS) algorithm [J. Jordan et al., Phys. Rev. Lett. 101, 250602 (2008)] has become a useful tool in the calculation of ground-state properties of two-dimensional quantum lattice systems in the thermodynamic limit. Despite its many successful implementations, the method has some limitations in its present formulation which hinder its application to some highly entangled systems. The purpose of this paper is to unravel some of these issues, in turn enhancing the stability and efficiency of iPEPS methods. For this, we first introduce the fast full update scheme, where effective environment and iPEPS tensors are both simultaneously updated (or evolved) throughout time. As we shall show, this implies two crucial advantages: (i) dramatic computational savings and (ii) improved overall stability. In addition, we extend the application of the local gauge fixing, successfully implemented for finite-size PEPS [M. Lubasch et al., Phys. Rev. B 90, 064425 (2014)], to the iPEPS algorithm. We see that the gauge fixing not only further improves the stability of the method but also accelerates the convergence of the alternating least-squares sweeping in the (either “full” or “fast full”) tensor update scheme. The improvement in terms of computational cost and stability of the resulting “improved” iPEPS algorithm is benchmarked by studying the ground-state properties of the quantum Heisenberg and transverse-field Ising models on an infinite square lattice.

The rare earths are known to have intriguing changes of the valence, depending on the chemical surrounding or geometry. Here, we aim at predicting the transition of valence when passing from the atomic divalent limit to the bulk trivalent limit. This transition is analyzed by addressing clusters of various size for selected rare-earth elements, i.e., Sm, Tb, and Tm, via a theoretical treatment that combines density functional theory with atomic multiplet theory. Our results show that Tm clusters change from pure divalent to pure trivalent at a size of six atoms, while Tb clusters are already divalent for two atoms and stay so until eight atoms and the bulk limit. Instead, Sm clusters are respectively purely divalent up to eight atoms. For larger Sm clusters, a transition to a trivalent configuration is expected and likely accompanied by a regime of mixed valence. The valence of all rare-earth clusters, as a function of size, is predicted from the interpolation of our calculated results. These predictions are argued to be best investigated by spectroscopic measurements. To ease experimental analysis, we provide theoretical spectra, based on dynamical mean-field theory in the Hubbard I approximation.

Photoemission studies of FeSe monolayer films on ${\text{SrTiO}}_3$ substrate have shown electronic structures that deviate from pristine FeSe, consistent with heavy electron doping. With the help of first-principles calculations we studied the effect of excess Fe and Se atoms on the monolayer and oxygen vacancies in the substrate in order to understand the reported Fermi surface in this system. We find that both excess Fe and Se atoms prefer the same adsorption site above the bottom Se atoms on the monolayer. The adsorbed Fe is strongly magnetic and contributes electrons to the monolayer, while excess Se hybridizes with the monolayer $\text{Fe-}d$ states and partially opens a gap just above the Fermi energy. We also find that the two-dimensional electron gas generated by the oxygen vacancies is partly transferred to the monolayer and can potentially suppress the hole pockets around the $\mathrm{\Gamma }$ point. Thus, both O vacancies in the ${\text{SrTiO}}_3$ substrate and excess Fe over the monolayer can provide high levels of electron doping.

Small polaron optical properties are studied comprehensively in thin film samples of the narrow bandwidth manganite $\mathrm{P}{\mathrm{r}}_{1-x}\mathrm{C}{\mathrm{a}}_x\mathrm{Mn}{\mathrm{O}}_3$ by optical absorption spectroscopy as a function of doping and temperature. A broad near infrared double-peak absorption band in the optical conductivity spectras is observed and interpreted in the framework of photon-assisted small polaron intersite hopping and on-site Jahn-Teller excitation. Application of quasiclassical small polaron theory to both transitions allows an approximate determination of polaron specific parameters like the polaron binding energy, the characteristic phonon energy, as well as the Jahn-Teller splitting energy as a function of temperature and doping. Based on electronic structure calculations, we consider the impact of the hybridization of $\mathrm{O}2p$ and Mn $3d$ electronic states on the Jahn-Teller splitting and the polaron properties. The interplay between hopping and Jahn-Teller excitations is discussed in the alternative pictures of mixed valence $\mathrm{M}{\mathrm{n}}^{3+}/\mathrm{M}{\mathrm{n}}^{4+}$ sites (Jahn-Teller polaron) and equivalent $\mathrm{M}{\mathrm{n}}^{\left(3+x\right)+}$ sites (Zener polaron). We give a careful evaluation of the estimated polaron parameters and discuss the limitations of small polaron quasiclassical theory for application to narrow bandwidth manganites.

We study the effect of a magnetic field on the current-phase relation of a topological Josephson junction formed by connecting two superconductors through the helical edge states of a quantum spin-Hall insulator. We predict that the Zeeman effect along the spin quantization axis of the helical edges results in an anomalous Josephson relation that allows for a supercurrent to flow in the absence of superconducting phase bias. We relate the associated field-tunable phase shift ${\varphi }_0$ in the Josephson relation of such a ${\varphi }_0$ junction to the existence of a so-called helical superconductivity, which may result from the interplay of the Zeeman effect and spin-orbit coupling. We analyze the dependence of the magneto-supercurrent on the junction length and discuss its observability in suitably designed hybrid structures subject to an in-plane magnetic field.

We study the multicritical behavior for the semimetal-insulator transitions on graphene's honeycomb lattice using the Gross-Neveu-Yukawa effective theory with two order parameters: the SO(3) (Heisenberg) order parameter describes the antiferromagnetic transition, and the ${\mathbb{Z}}_2$ (Ising) order parameter describes the transition to a staggered density state. Their coupling induces multicritical behavior which determines the structure of the phase diagram close to the multicritical point. Depending on the number of fermion flavors $N_f$ and working in the perturbative regime in the vicinity of three (spatial) dimensions, we observe first-order or continuous phase transitions at the multicritical point. For the graphene case of $N_f=2$ and within our low-order approximation, the phase diagram displays a tetracritical structure.