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Intercalation of magnetic atoms into the van der Waals gaps of layered transition metal dichalcogenides offers an excellent platform to produce exotic physical properties. Here, we report a detailed study of magnetic and electrical transport properties of Co$_{0.28}$TaS$_2$. The temperature dependent resistivity measurements display anomalous upturn below 11 K, which persists in presence of magnetic field even up to 14 T. In the low temperature region, the resistivity upturn exhibits a unique $T^{1/2}$ scaling behavior, which remains unchanged when an external magnetic field is applied. The $T^{1/2}$ dependence of resistivity upturn is the hallmark of non-Fermi liquid state in orbital two-channel Kondo effect(2CK). This anomalous resistivity upturn in Co$_{0.28}$TaS$_2$ can be attributed to the orbital two-channel Kondo mechanism., Comment: 7 pages, 5 figures

We introduce a one-dimensional correlated-hopping model of spinless fermions in which a particle can hop between two neighboring sites only if the sites to the left and right of those two sites have different particle numbers. Using a bond-to-site mapping, this model involving four-site terms can be mapped to an assisted pair-flipping model involving only three-site terms. This model shows strong Hilbert space fragmentation (HSF). We define irreducible strings (IS) to label the different fragments, determine the number of fragments, and the sizes of fragments corresponding to some special IS. In some classes of fragments, the Hamiltonian can be diagonalized completely, and in others it can be seen to have a structure characteristic of models which are not fully integrable. In the largest fragment in our model, the number of states grows exponentially with the system size, but the ratio of this number to the total Hilbert space size tends to zero exponentially in the thermodynamic limit. Within this fragment, we provide numerical evidence that only a weak version of the eigenstate thermalization hypothesis (ETH) remains valid; we call this subspace-restricted ETH. To understand the out-of-equilibrium dynamics of the model, we study the infinite-temperature time-dependent autocorrelation functions starting from a random initial state; we find that these exhibit a different behavior near the boundary compared to the bulk. Finally we propose an experimental setup to realize our correlated-hopping model., Comment: 22 pages, 17 figures; added discussion of typical and atypical fragments, ETH properties of additional typical fragments, and zero energy states; added some references

The transfer and storage of quantum information in a hybrid quantum system, consisting of an ensemble of atoms or spins interacting with a cavity, is adversely affected by the inhomogeneity of the spins, which negates the coherent exchange of excitations between the physical components. Using a full quantum treatment based on variational renormalization group, we show how quantum information encoded in the states of a parametrically driven hybrid system is strongly protected against any decoherence that may arise due to the inhomogeneity in the spin-ensemble., Comment: 7 pages, 3 figures

While there is compelling evidence for the existence of magnetic monopoles in spin ice, the direct observation of a point-like source of magnetic field in these systems remains an open challenge. One promising approach is electron holography, which combines atomic-scale resolution with extreme sensitivity to magnetic vector potentials, through the Aharonov-Bohm effect. Here we explore what holography can teach us about magnetic monopoles in spin ice, through experiments on artificial spin ice, and numerical simulations of pyrochlore spin ice. In the case of artificial spin ice, we show that holograms can be used to measure local magnetic charge. For pyrochlore spin ice, we demonstrate that holographic experiments are capable of resolving both magnetic monopoles and their dynamics, including the emergence of electric fields associated with fluctuations of closed loops of spins. These results establish that the observation of both magnetic monopoles and emergent electric fields in pyrochlore spin ice is a realistic possibility in an electron microscope with sufficiently--high phase resolution., Comment: 9 pages, 5 figures in main paper. 11 pages, 11 figures in supplemental V2: Updated citations and further details in supplemental

A scale for magnetic field resilience of a superconductor is set by the paramagnetic limit. Comparing the condensation energy of the Bardeen-Cooper-Schrieffer (BCS) singlet ground state with the paramagnetically polarised state suggests that for an applied field ${\mu_0}H > 1.8~T_c$ (in SI), singlet pairing is not energetically favourable. Materials exceeding or approaching this limit are interesting from fundamental and technological perspectives. This may be a potential indicator of triplet superconductivity, Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing and other mechanisms involving topological aspects of surface states, and also allow Cooper pair injection at high magnetic fields. We have analysed the microscopic composition of such a material arising from an unexpected source. A microjet of an organo-metallic gas, $\rm {W[(CO)_6]}$ can be decomposed by gallium ion-beam, leaving behind a track of complex residue of gallium, tungsten and carbon with remarkable superconducting properties, like an upper critical field, $H_{c2} > 10~{\rm T} $, above its paramagnetic limit. We carried out Atomic probe tomography to establish the formation of nano-crystalline tungsten carbide (WC) in the tracks and the absence of free tungsten. Supporting calculations show for Ga distributed on the surface of WC, its s,p-orbitals enhance the density of states near the Fermi energy. The observed variation of $H_{c2}(T)$ does not show features typical of enhancement of critical field due to granularity. Our observations may be significant in the context of some recent theoretical calculation of the band structure of WC and experimental observation of superconductivity in WC-metal interface., Comment: 6 pages, 3 figures, 59 References

The BBM is a promising candidate to study spin-one systems and to design quantum simulators based on its underlying Hamiltonian. The variety of different phases contains amongst other valuable and exotic phases the Haldane phase. We study the Kibble-Zurek physics of linear quenches into the Haldane phase. We outline ideal quench protocols to minimize defects in the final state while exploiting different linear quench protocols via the uniaxial or interaction term. Furthermore, we look at the fate of the string order when quenching from a topologically non-trivial phase to a trivial phase. Our studies show this depends significantly on the path chosen for quenching; for example, we discover quenches from \Neel{} to Haldane phase which reach a string order greater than their ground state counterparts for the initial or final state at intermediate quench times., Comment: 13 pages, 11 figures

Sufficiently strong inter-site interactions in extended-Hubbard and XXZ spin models result in dynamically-bound clusters at neighboring sites. We show that the dynamics of these clusters in two-dimensional lattices is remarkably different and richer than that of repulsively-bound on-site clusters in gases without inter-site interactions. Whereas on-site pairs move in the same lattice as individual particles, nearest-neighbor dimers perform an interacting quantum walk in a different lattice geometry, leading to a peculiar dynamics characterized by more than one time scale. The latter is general for any lattice geometry, but it is especially relevant in triangular and diamond lattices, where dimers move resonantly in an effective kagome and Lieb lattice, respectively. As a result, dimers experience partial quasi-localization due to an effective flat band, and may move slower than longer clusters. This surprising link between anomalously slow quantum walk dynamics in these models and flat-band physics may be readily observed in experiments with lanthanide atoms., Comment: 5 pages + Supplementary Material

We report the anisotropic magnetic properties of the ternary compound ErAl$_2$Ge$_2$. Single crystals of this compound were grown by high temperature solution growth technique,using Al:Ge eutectic composition as flux. From the powder x-ray diffraction we confirmed that ErAl$_2$Ge$_2$ crystallizes in the trigonal CaAl$_2$Si$_2$-type crystal structure. The anisotropic magnetic properties of a single crystal were investigated by measuring the magnetic susceptibility, magnetization, heat capacity and electrical resistivity. A bulk magnetic ordering occurs around 4 K inferred from the magnetic susceptibility and the heat capacity. The magnetization measured along the $ab$-plane increases more rapidly than along the $c$-axis suggesting the basal $ab$-plane as the easy plane of magnetization. The magnetic susceptibility, magnetization and the $4f$-derived part of the heat capacity in the paramagnetic regime analysed based on the point charge model of the crystalline electric field (CEF) indicate a relatively low CEF energy level splitting., Comment: 6 pages, 6 figures

We propose a scheme for controlling the movement of dimers, trimers, and other multimers in optical lattices by modulating the lattice potential. In deep optical lattices the propagation of deeply bound atomic clusters is slowed down by the high energy cost of virtual intermediate states. Adapting the well-known method of lattice modulation spectroscopy, the movement of the clusters can be made resonant by utilizing sequences of bound-bound transitions. Using the scheme, the mobility of each specific cluster can be selectively controlled by tuning the modulation frequency. We formulate a simple and intuitive model and confirm the validity of the model by numerical simulations of dimers and trimers in a one-dimensional optical lattice., Comment: 9 Pages

One-dimensional polar gases in deep optical lattices present a severely constrained dynamics due to the interplay between dipolar interactions, energy conservation, and finite bandwidth. The appearance of dynamically-bound nearest-neighbor dimers enhances the role of the $1/r^3$ dipolar tail, resulting, in the absence of external disorder, in quasi-localization via dimer clustering for very low densities and moderate dipole strengths. Furthermore, even weak dipoles allow for the formation of self-bound superfluid lattice droplets with a finite doping of mobile, but confined, holons. Our results, which can be extrapolated to other power-law interactions, are directly relevant for current and future lattice experiments with magnetic atoms and polar molecules., Comment: 5 + 2 Pages

It is well known that the notions of spatial locality are often lost in quantum systems with long-range interactions, as exhibited by the emergence of phases with exotic long-range order and faster propagation of quantum correlations. We demonstrate here that such induced ``quasinonlocal" effects do not necessarily translate to growth of global entanglement in the quantum system. By investigating the ground and quenched states of the variable-range, spin-1/2 Heisenberg Hamiltonian, we observe that the genuine multiparty entanglement in the system can either increase or counterintuitively diminish with a growing range of interactions. The behavior is reflective of the underlying phase structure of the quantum system and provides key insights for generation of multipartite entanglement in experimental atomic, molecular, and optical physics where such variable-range interactions have been implemented., Comment: 9 pages, 5 figures, close to the published version

Polycrystalline samples of Ce(Cu$_{1-x}$Co$_x$)$_2$Ge$_2$ were investigated by means of electrical resistivity $\rho$($T$), magnetic susceptibility $\chi$($T$), specific heat $C$$_p$($T$) and thermo electric power $S$($T$) measurements. The long-range antiferromagnetic (AFM) order, which set in at $T$$_N$ = 4.1 K in CeCu$_2$Ge$_2$, is suppressed by non-iso-electronic cobalt (Co) doping at a critical value of the concentration $x$$_c$ = 0.6, accompanied by non-Fermi liquid (NFL) behavior inferred from the power law dependence of heat capacity and susceptibility i.e. $C$($T$)/$T$ and $\chi$($T$) $\propto$ $T$$^{-1+\lambda}$ down to 0.4 K, along with a clear deviation from $T$$^2$ behavior of the electrical resistivity. However, we have not seen any superconducting phase in the quantum critical regime down to 0.4 K., Comment: 8 pages, 11 figures

We study the effect of impurities on the two types of spin-dimers in the hybrid chain/ladder spin 1/2 quantum magnet Sr$_{14}$Cu$_{24}$O$_{41}$. Four different impurities were used, namely, the non-magnetic Zn (0.0025 and 0.01 per Cu) and Al (0.0025 and 0.01 per Cu), and magnetic Ni (0.0025 and 0.01 per Cu) and Co (0.01, 0.03, 0.05 and 0.1 per Cu). These impurities were doped in high-quality single-crystals synthesized by the floating zone method. The magnetic susceptibility of pristine Sr$_{14}$Cu$_{24}$O$_{41}$ is analyzed rigorously to confirm that at low temperatures (T $<$ 5 K), the "free" spins in the chains undergo a long-distance dimerization as proposed in a recent study [Sahling et al. Nature Phys., \textbf{11}, 255 (2015)]. The effect of impurity on these dimers is analyzed by measuring the specific heat down to T = 0.06 K. We found that even at the lower impurity concentration, the long-distance dimers are significantly severed, but the quantum entangled spin dimerized state of the chains persists. On the other hand, the other type of spin dimers that forms at relatively higher temperatures via an intervening Zhang-Rice singlet are found to be practically unaffected at the lower impurity concentration; but at 1\% doping, even these are found to be considerably severed. The effect of Co impurity turned out to be most unusual displaying a strongly anisotropic response, and with a dimerization gap that suppresses faster along the chain/ladder direction than perpendicular to it as a function of increasing Co concentration.

The trigonal structure of EuMn$_{2}$As$_{2}$ is an anomaly in the tetragonal 122-type pnictide family. We report detailed investigation of the underlying magnetic correlations in single crystal EuMn$_{2}$As$_{2}$ using high resolution elastic neutron scattering measurements. The system undergoes through two successive antiferromagnetic transitions at $T$ = 135 K and 14.4 K, respectively. Numerical modeling of the experimental data reveals the long range antiferromagnetic correlation of Mn-ions in the $a-b$ plane below $T_N1$ = 135 K. Mn spins are aligned closer to the diagonal axis of the unit cell. The lower temperature transition, below $T_N2$ = 14.4 K, is found to arise due to the long range antiferromagnetic correlation of Eu spins that are rotated by $\theta$ = 55 degree from the $c$-axis of the unit cell., Comment: 5 pages, 4 figures

We report on the single crystal growth and anisotropic physical properties of CeAgAs$_2$. The compound crystallizes as on ordered variant of the HfCuSi$_2$-type crystal structure and adopts the orthorhombic space group $Pmca$~(\#57) with two symmetry inequivalent cerium atomic positions in the unit cell. The orthorhombic crystal structure of our single crystal was confirmed from the powder x-ray diffraction and from electron diffraction patterns obtained from the transmission electron microscope. The anisotropic physical properties have been investigated on a good quality single crystal by measuring the magnetic susceptibility, isothermal magnetization, electrical transport and heat capacity. The magnetic susceptibility and magnetization measurements revealed that this compound orders antiferromagnetically with two closely spaced magnetic transitions at $T_{\rm N1} = 6$~K and $T_{\rm N2} = 4.9$~K. Magnetization studies have revealed a large magnetocrystalline anisotropy due to the crystalline electric field (CEF) with an easy axis of magnetization along the [010] direction. The magnetic susceptibility measured along the [001] direction exhibited a broad hump in the temperature range 50 to 250~K, while typical Curie-Weiss behaviour was observed along the other two orthogonal directions. The electrical resistivity and the heat capacity measurements revealed that CeAgAs$_2$ is a Kondo lattice system with a magnetic ground state.

We devise a method based on the tensor-network formalism to calculate genuine multisite entanglement in ground states of infinite spin chains containing spin-1/2 or spin-1 quantum particles. The ground state is obtained by employing an infinite time-evolving block decimation method acting upon an initial matrix product state for the infinite spin system. We explicitly show how such infinite matrix product states with translational invariance provide a natural framework to derive the generalized geometric measure, a computable measure of genuine multisite entanglement, in the thermodynamic limit of quantum many-body systems with both spin-1/2 and higher-spin particles., Comment: 8 pages, 3 figures, close to the published version

Mesoscopic spin ensembles coupled to a cavity offer the exciting prospect of observing complex nonclassical phenomena that pool the microscopic features from a few spins with those of macroscopic spin ensembles. Here, we demonstrate how the collective interactions in an ensemble of as many as hundred spins can be harnessed to obtain a periodic pulse train of nonclassical light. To unravel the full quantum dynamics and photon statistics, we develop a time-adaptive variational renormalization group method that accurately captures the underlying Lindbladian dynamics of the mesoscopic spin-cavity system., Comment: 15 pages, 4 figures, REVTeX 4.1. Accepted version; includes Supplemental Material

Using a fully ab-initio methodology, we demonstrate how the lattice vibrations couple with neutral excitons in monolayer WSe2 and contribute to the non-radiative excitonic lifetime. We show that only by treating the electron-electron and electron-phonon interactions at the same time it is possible to obtain an unprecedented agreement of the zero and finite-temperature optical gaps and absorption spectra with the experimental results. The bare energies were calculated by solving the Kohn-Sham equations, whereas G$_{0}$W$_{0}$ many body perturbation theory was used to extract the excited state energies. A coupled electron-hole Bethe-Salpeter equation was solved incorporating the polaronic energies to show that it is the in-plane torsional acoustic phonon branch that contributes mostly to the A and B exciton build-up. We find that the three A, B and C excitonic peaks exhibit different behaviour with temperature, displaying different non-radiative linewidths. There is no considerable transition in the strength of the excitons with temperature but A-exciton exhibits darker nature in comparison to C-exciton. Further, all the excitonic peaks redshifts as temperature rises. Renormalization of the bare electronic energies by phonon interactions and the anharmonic lattice thermal expansion causes a decreasing band-gap with increasing temperature. The zero point energy renormalization (31 meV) is found to be entirely due to the polaronic interaction with negligible contribution from lattice anharmonicites. These findings may find a profound impact on electronic and optoelectronic device technologies based on these monolayers., Comment: 11 pages, 7 figures

We consider a one-dimensional two component extended Fermi-Hubbard model with nearest neighbor interactions and mass imbalance between the two species. We study the stability of trimers, various observables for detecting them, and expansion dynamics. We generalize the definition of the trimer gap to include the formation of different types of clusters originating from nearest neighbor interactions. Expansion dynamics reveal rapidly propagating trimers, with speeds exceeding doublon propagation in strongly interacting regime. We present a simple model for understanding this unique feature of the movement of the trimers, and we discuss the potential for experimental realization., Comment: 10 pages, 10 figures

An interesting aspect of antiferromagnetic quantum spin ladders, with complete dimer coverings, is that the wave function can be recursively generated by estimating the number of coverings in the valence bond basis, which follow the fabled Fibonacci sequence. In this work, we derive generalized forms of this sequence for multi-legged and doped quantum spin ladders, which allow the corresponding dimer-covered state to be recursively generated. We show that these sequences allow for estimation of physically and information-theoretically relevant quantities in large spin lattices without resorting to complex numerical methods. We apply the formalism to calculate the valence bond entanglement entropy, which is an important figure of merit for studying cooperative phenomena in quantum spin systems with SU(2) symmetry. We show that introduction of doping may mitigate, within the quarters of entanglement entropy, the dichotomy between odd- and even- legged quantum spin ladders., Comment: 13 pages, 9 figures, close to the published version

We report on ground state phases of a doped one-dimensional Hubbard model, which for large onsite interactions is governed by the $t$-$J$ Hamiltonian, where the extant entanglement is immutable under perturbative or sudden changes of system parameters, a phenomenon termed as adiabatic freezing. We observe that in the metallic Luttinger liquid phase of the model bipartite entanglement decays polynomially and is adiabatically frozen, in contrast to the variable, exponential decay in the phase-separation and superconducting spin-gap phases. Significantly, at low fixed electron densities, the spin-gap phase shows remarkable affinity to doped resonating valence bond gas, with multipartite entanglement frozen across all parameter space. We note that entanglement, in general, is sensitive to external perturbation, as observed in several systems, and hitherto, no such invariance or freezing behavior has been reported., Comment: 7 pages, 4 figures, close to the published version

The magnetocrystalline anisotropy exhibited in PrPd$_2$Ge$_2$ single crystal has been investigated by measuring the magnetization, magnetic susceptibility, electrical resistivity and heat capacity. PrPd$_2$Ge$_2$ crystallizes in the well known ThCr$_2$Si$_2$\--type tetragonal structure. The antiferromagnetic ordering is confirmed as 5.1~K with the [001]-axis as the easy axis of magnetization. A superzone gap formation is observed from the electrical resistivity measurement when the current is passed along the [001] direction. The crystal electric field (CEF) analysis on the magnetic susceptibility, magnetization and the heat capacity measurements confirms a doublet ground state with a relatively low over all CEF level splitting. The CEF level spacings and the Zeeman splitting at high fields become comparable and lead to metamagnetic transition at 34~T due to the CEF level crossing.

Phase transition in quantum many-body systems inevitably causes changes in certain physical properties which then serve as potential indicators of critical phenomena. Besides the traditional order parameters, characterization of quantum entanglement has proven to be a computationally efficient and successful method for detection of phase boundaries, especially in one-dimensional models. Here we determine the rich phase diagram of the ground states of a quantum spin-1/2 XXZ ladder by analyzing the variation of bipartite and multipartite entanglements. Our study characterizes the different ground state phases and notes the correspondence with known results, while highlighting the finer details that emerge from the behavior of ground state entanglement. Analysis of entanglement in the ground state provides a clearer picture of the complex ground state phase diagram of the system using only a moderate-size model., Comment: 12 pages, 10 figures, REVTeX 4.1

Monogamy is an intrinsic feature of quantum correlations that gives rise to several interesting quantum characteristics which are not amenable to classical explanations. The monogamy property imposes physical restrictions on unconditional sharability of quantum correlations between the different parts of a multipartite quantum system, and thus has a direct bearing on the cooperative properties of states of multiparty systems, including large many-body systems. On the contrary, a certain party can be maximally classical correlated with an arbitrary number of parties in a multiparty system. In recent years, the monogamy property of quantum correlations has been applied to understand several key aspects of quantum physics, including distribution of quantum resources, security in quantum communication, critical phenomena, and quantum biology. In this chapter, we look at some of the salient developments and applications in quantum physics that have been closely associated with the monogamy of quantum discord, and "discord-like" quantum correlation measures., Comment: 21 pages, 6 figures

Single crystals of the new compound CeCu0.18Al0.24Si1.58 have been grown by high-temperature solution growth method using a eutectic Al-Si mixture as flux. This compound is derived from the binary CeSi2 (tetragonal ThSi2-type, Pearson symbol tI12, space group I41/amd) obtained by partial substitution of Si by Cu and Al atoms but showing full occupation of the Si crystal site (8e). While CeSi2 is a well-known valence-fluctuating paramagnetic compound, the CeCu0.18Al0.24Si1.58 phase orders ferromagnetically at TC = 9.3 K. At low temperatures the easy-axis of magnetization is along the a-axis, which re-orients itself along the c-axis above 30 K. The presence of hysteresis in the magnetization curve, negative temperature coefficient of resistivity at high temperatures, reduced jump in the heat capacity and a relatively lower entropy released up to the ordering temperature, and enhanced Sommerfeld coefficient (~100 mJ/mol K2) show that CeCu0.18Al0.24Si1.58 is a Kondo lattice ferromagnetic, moderate heavy fermion compound. Analysis of the high temperature heat capacity data in the paramagnetic region lets us infer that the crystal electric field split doublet levels are located at 178 and 357 K, respectively, and Kondo temperature (8.4 K) is of the order of TC in CeCu0.18Al0.24Si1.58.

We report the existence of Griffiths phase (GP) and its influence on critical phenomena in layered Sr$_2$IrO$_4$ ferromagnet (T$_C$ = 221.5 K). The power law behavior of inverse magentic susceptibility, 1/$\chi$(T) with exponent $\lambda = 0.18(2)$ confirm the GP in the regime T$_C$ $<$ T $\leq$ T$_G$ = 279.0(5) K. Moreover, the detailed critical analysis via modified Arrott plot method exhibits unrealistic critical exponents $\beta$ = 0.77(1), $\gamma$ = 1.59(2) and $\delta = 3.06(4)$, in corroboration with magneto-caloric study. The abnormal exponent values have been viewed in context of ferromagnetic-Griffiths phase transition. The GP has been further analyzed using Bray model, which yields a reliable value of $\beta$ = 0.19(2), belonging to the two-dimensional (2D) XYh$_4$ universality class with strong anisotropy present in Sr$_2$IrO$_4$. The present study proposes Bray model as a possible tool to investigate the critical behavior for Griffiths ferromagnets in place of conventional Arrott plot analysis. The possible origins of GP and its correlation with insulating nature of Sr$_2$IrO$_4$ have been discussed.

Quantum networks are an integral component in performing efficient computation and communication tasks that are not accessible using classical systems. A key aspect in designing an effective and scalable quantum network is generating entanglement between its nodes, which is robust against defects in the network. We consider an isotropic quantum network of spin-1/2 particles with a finite fraction of defects, where the corresponding wave function of the network is rotationally invariant under the action of local unitaries, and we show that any reduced density matrix also remains unaltered under the local actions. By using quantum information-theoretic concepts like strong subadditivity of von Neumann entropy and approximate quantum telecloning, we prove analytically that in the presence of defects, caused by loss of a finite fraction of spins, the network sustains genuine multisite entanglement, and at the same time may exhibit finite moderate-range bipartite entanglement, in contrast to the network with no defects., Comment: 8 pages, 5 figures

Titanium dioxide (TiO$_2$) has rich physical properties with potential implications in both fundamental physics and new applications. Up-to-date, the main focus of applied research is to tune its optical properties, which is usually done via doping and/or nano-engineering. However, understanding the role of $d$-electrons in materials and possible functionalization of $d$-electron properties are still major challenges. Herewith, within a combination of an innovative experimental technique, high energy optical conductivity, and of the state-of-the-art {\it ab initio} electronic structure calculations, we report an emerging, novel resonant exciton in the deep ultraviolet region of the optical response. The resonant exciton evolves upon low concentration Ta-substitution in anatase TiO$_{2}$ films. It is surprisingly robust and related to strong electron-electron and electron-hole interactions. The $d$- and $f$- orbitals localization, due to Ta-substitution, plays an unexpected role, activating strong electronic correlations and dominating the optical response under photoexcitation. Our results shed light on a new optical phenomenon in anatase TiO$_{2}$ films and on the possibility of tuning electronic properties by Ta substitution.

We present here a neutron diffraction study, both in zero field and as a function of magnetic field, of the magnetic structure of the tetragonal intermetallic \eun\ on a single crystalline sample. This material is known to undergo a cascade of transitions, first at 13.2\,K towards an incommensurate modulated magnetic structure, then at 10.5\,K to an equal moment, yet undetermined, antiferromagnetic structure. We show here that the low temperature phase presents a spiral moment arrangement with wave-vector {\bf k} = ($\frac{1}{4},\delta,0)$. For a magnetic field applied along the tetragonal {\bf c}-axis, the square root of the scattering intensity of a chosen reflection matches very well the complex metamagnetic behavior of the magnetization along {\bf c} measured previously. For the magnetic field applied along the {\bf b}-axis, two magnetic transitions are observed below the transition to a fully polarized state.

We formulate an analytical recursive method to generate the wave function of doped short-range resonating valence bond (RVB) states as a tool to efficiently estimate multisite entanglement as well as other physical quantities in doped quantum spin ladders. We prove that doped RVB ladder states are always genuine multipartite entangled. Importantly, our results show that within specific doping concentration and model parameter regimes, the doped RVB state essentially characterizes the trends of genuine multiparty entanglement in the exact ground states of the Hubbard model with large onsite interactions, in the limit which yields the $t$-$J$ Hamiltonian., Comment: 11 pages, 6 figures, RevTex 4-1, accepted in Phys. Rev. B

We have investigated the underlying magnetism in newly discovered single crystal Kondo lattices CeXAl4Si2, where X = Rh, Ir. We show that the compound undergoes an incommensurate-to-commensurate magnetic transition at Tc = 9.19 K (10.75 K in Ir). The spin correlation in the incommensurate phase is described by a spin density wave configuration of Ce-ions, which locks-in to the long-range antiferromagnetic order at T = Tc. The qualitative analysis of the experimental data suggests the role of the Fermi surface nesting, instead of the lattice distortion causing the Umklapp correction or the soliton propagation, as the primary mechanism behind this phenomenon., Comment: 5 pages, 4 figures

We have grown the single crystal of PrRhAl$_4$Si$_2$, which crystallizes in the tetragonal crystal structure. From the low temperature physical property measurements like, magnetic susceptibility, magnetization, heat capacity and electrical resistivity, we found that this compound does not show any magnetic ordering down to 70~mK. Our crystal field calculations on the magnetic susceptibility and specific heat measurements reveal that the 9-fold degenerate $(2J+1)$ levels of Pr atom in PrRhAl$_4$Si$_2$, splits into 7 levels, with a singlet ground state and a well separated excited doublet state at 123~K, with a overall level splitting energy of 320~K., Comment: 5 figures

EuRhAl4Si2, crystallizes in tetragonal crystal structure and orders antiferromagnetically at ~12 K. The isothermal magnetization along the two principle directions is highly anisotropic despite Eu2+ being an S-state ion. The variation of entropy change, which is a measure of MCE, with field and temperature, calculated from the isothermal magnetization data taken at various temperatures along the principal crystallographic directions present interesting behavior in EuRhAl4Si2. In the magnetically ordered state the entropy change is non-monotonic below spin flip fields; however, in the paramagnetic region, it is negative irrespective of the strength of applied magnetic field. For H || [001] the maximum entropy change at 7 T is -21 J/Kg K around TN, which is large and comparable to the largest known values in this temperature range. The variation of the MCE with field strongly depends upon the direction of the applied magnetic field. Magnetic phase diagram of EuRhAl4Si2 derived from M(H) data is also constructed., Comment: 11 pages, 6 figures, 20th International Conference on Magnetism (ICM 2015)

We investigate finite-size scaling of genuine multisite entanglement in the ground state of quantum spin-1/2 Heisenberg ladders. We obtain the ground states of odd- and even-legged Heisenberg ladder Hamiltonians and compute genuine multisite entanglement, the generalized geometric measure (GGM), which shows that for even rungs, GGM increases for odd-legged ladder while it decreases for even ones. Interestingly, the ground state obtained by short-range dimer coverings, under the resonating valence bond (RVB) ansatz, encapsulates the qualitative features of GGM for both the ladders. We find that while the GGMs for higher legged odd- and even-ladders converge to a single value in the asymptotic limit of a large number of rungs, the finite-size scaling exponents of the same tend to diverge. The scaling exponent of GGM obtained by employing density matrix recursion method is therefore a reliable quantity in distinguishing the odd-even dichotomy in Heisenberg ladders, even when the corresponding multisite entanglements merge., Comment: 12 pages, 4 figures. This is an author-created, un-copyedited version of an article accepted for publication in New J. Phys

We report the magnetic properties of two Eu based compounds, single crystalline EuIrGe$_3$ and EuRhGe$_3$, inferred from magnetisation, electrical transport, heat capacity and $^{151}$Eu M\"{o}ssbauer spectroscopy. These previously known compounds crystallise in the non-centrosymmetric, tetragonal, $I4mm$, BaNiSn$_3$-type structure. Single crystals of EuIrGe$_3$ and EuRhGe$_3$ were grown using high temperature solution growth method using In as flux. EuIrGe$_3$ exhibits two magnetic orderings at $T_{\rm N1}$ = 12.4 K, and $T_{\rm N2}$ = 7.3 K. On the other hand EuRhGe$_3$ presents a single magnetic transition with a $T_{\rm N}$ = 12 K. $^{151}$Eu M\"{o}ssbauer spectra present evidence for a cascade of transitions from paramagnetic to incommensurate amplitude modulated followed by an equal moment antiferromagnetic phase at lower temperatures in EuIrGe$_3$, the transitions having a substantial first order character. On the other hand the $^{151}$Eu M\"{o}ssbauer spectra at 4.2 and 9 K in EuRhGe$_3$ present evidence of a single magnetic transition. In both compounds a superzone gap is observed for the current density $J\parallel$ [001], which enhances with transverse magnetic field. The magnetisation measured up to 14 T shows the occurrence of field induced transitions, which are well documented in the magnetotransport data as well. The magnetic phase diagram constructed from these data is complex, revealing the presence of many phases in the $H-T$ phase space.

We consider a process to create quasi long-range quantum discord between the non-interacting end spins of a quantum spin chain, with the end spins weakly coupled to the bulk of the chain. The process is not only capable of creating long-range quantum correlation but the latter remains frozen, when certain weak end-couplings are adiabatically varied below certain thresholds. We term this phenomenon as adiabatic freezing of quantum correlation. We observe that the freezing is robust to moderate thermal fluctuations and is intrinsically related to the cooperative properties of the quantum spin chain. In particular, we find that the energy gap of the system remains frozen for these adiabatic variations, and moreover, considering the end spins as probes, we show that the interval of freezing can detect the anisotropy transition in quantum XY spin chains. Importantly, the adiabatic freezing of long-range quantum correlations can be simulated with contemporary experimental techniques., Comment: Main text (6 pages, 6 figures) and Supplemental material (4 pages, 4 figures), REVTeX 4-1

We report on the physical properties of single crystalline EuRhSi$_3$ and polycrystalline EuIrSi$_3$, inferred from magnetisation, electrical transport, heat capacity and $^{151}$Eu M\"ossbauer spectroscopy. These previously known compounds crystallise in the tetragonal BaNiSn$_3$-type structure. The single crystal magnetisation in EuRhSi$_3$ has a strongly anisotropic behaviour at 2 K with a spin-flop field of 13 T, and we present a model of these magnetic properties which allows the exchange constants to be determined. In both compounds, specific heat shows the presence of a cascade of two close transitions near 50 K, and the $^{151}$Eu M\"ossbauer spectra demonstrate that the intermediate phase has an incommensurate amplitude modulated structure. We find anomalously large values, with respect to other members of the series, for the RKKY N\'eel temperature, for the spin-flop field (13 T), for the spin-wave gap ($\simeq$ 20-25 K) inferred from both resistivity and specific heat data, for the spin-disorder resistivity in EuRhSi$_3$ ($\simeq 35$ $\mu$Ohm.cm) and for the saturated hyperfine field (52 T). We show that all these quantities depend on the electronic density of states at the Fermi level, implying that the latter must be strongly enhanced in these two materials. EuIrSi$_3$ exhibits a giant magnetoresistance ratio, with values exceeding 600 % at 2 K in a field of 14 T., Comment: 6 pages, 8 figures

We report the synthesis and the magnetic properties of single crystalline CeRhAl$_4$Si$_2$ and CeIrAl$_4$Si$_2$ and their non magnetic La-analogs. The single crystals of these quaternary compounds were grown using Al-Si binary eutectic as flux. The anisotropic magnetic properties of the cerium compounds were explored in detail by means of magnetic susceptibility, isothermal magnetization, electrical resistivity, magnetoresistivity and heat capacity measurements. Both CeRhAl$_4$Si$_2$ and CeIrAl$_4$Si$_2$ undergo two antiferromagnetic transitions, first from the paramagnetic to an antiferromagnetic state at $T_{\rm N1}$~=~12.6~K and 15.5~K, followed by a second transition at lower temperatures $T_{\rm N2}$~=~9.4~K and 13.8~K, respectively. The paramagnetic susceptibility is highly anisotropic and its temperature dependence in the magnetically ordered state suggests the $c$-axis to be the relatively easy axis of magnetization. Concomitantly, isothermal magnetization at 2~K along the $c$-axis shows a sharp spin-flop transition accompanied by a sizeable hysteresis, while it varies nearly linearly with field along the [100] direction up to the highest field 14~T, of our measurement. The electrical resistivity provides evidence of the Kondo interaction in both compounds, inferred from its $-lnT$ behavior in the paramagnetic region. The heat capacity data confirm the bulk nature of the two magnetic transitions in each compound, and further confirm the presence of Kondo interaction by a reduced value of the entropy associated with the magnetic ordering. From the heat capacity data below 1~K, the coefficient of the linear term in the electronic heat capacity, $\gamma$, is inferred to be 195.6 and 49.4~mJ/mol K$^2$ in CeRhAl$_4$Si$_2$ and CeIrAl$_4$Si$_2$, respectively classifying these materials as moderate heavy fermion compounds., Comment: 16 pages, 11 Figures

A detailed defect energy level map was investigated for heterostructures of 26 unit cells of LaAlO3 on SrTiO3 prepared at a low oxygen partial pressure of 10-6 mbar. The origin is attributed to the presence of dominating oxygen defects in SrTiO3 substrate. Using femtosecond laser spectroscopy, the transient absorption and relaxation times for various transitions were determined. An ultrafast relaxation process of 2-3 picosecond from the conduction band to the closest defect level and a slower process of 70-92 picosecond from conduction band to intra-band defect level were observed. The results are discussed on the basis of propose defect-band diagram., Comment: 11 pages, 4 figures

We present detailed investigations in single crystals of two recently reported quaternary intermetallic compounds EuRhAl$_4$Si$_2$ and EuIrAl$_4$Si$_2$ employing magnetization, electrical resistivity in zero and applied fields, heat capacity and $^{151}$Eu M\"{o}ssbauer spectroscopy measurements. The two compounds order antiferromagnetically at $T_{\rm N1}$ = 11.7 and 14.7\,K, respectively, each undergoing two magnetic transitions: the first from paramagnetic to incommensurate modulated antiferromagnetic, the second at lower temperature to a commensurate antiferromagnetic phase as confirmed by heat capacity and M\"{o}ssbauer spectra. The magnetic properties in the ordered state present a large anisotropy despite Eu$^{2+}$ being an $S$-state ion for which the single-ion anisotropy is expected to be weak. Two features in the magnetization measured along the $c$-axis are prominent. At 1.8\,K, a ferromagnetic-like jump occurs at very low field to a value one third of the saturation magnetization (1/3 M$_0$) followed by a wide plateau up to 2\,T for T = Rh and 4\,T for T = Ir. At this field value, a sharp hysteretic spin-flop transition occurs to a fully saturated state (M$_0$). Surprisingly, the magnetization does not return to origin when the field is reduced to zero in the return cycle, as expected in an antiferromagnet. Instead, a remnant magnetization 1/3 M$_0$ is observed and the magnetic loop around the origin shows hysteresis. This suggests that the zero field magnetic structure has a ferromagnetic component, and we present a model with up to third neighbor exchange and dipolar interaction which reproduces the magnetization curves and hints to an "up-up-down" magnetic structure in zero field., Comment: 9 Pages and 9 Figures

The magnetic state of the noncentrosymmetric antiferromagnet CeNiC$_2$ has been studied by magnetic susceptibility, heat capacity, muon spin relaxation ($\mu$SR) and inelastic neutron scattering (INS) measurements. CeNiC$_2$ exhibits three magnetic phase transitions at $T_{N_1}$ = 20 K, $T_{N_2}$ = 10 K and $T_{N_3}$ = 2.5 K. The presence of long range magnetic order below 20 K is confirmed by the observation of oscillations in the $\mu$SR spectra between 10 and 20 K and a sharp increase in the muon depolarization rate. INS studies reveal two well-defined crystal electric field (CEF) excitations around 8 and 30 meV. INS data have been analyzed using a CEF model and the wave functions were evaluated. We also calculated the direction and magnitude of the ground state moment using CEF wave functions and compare the results with that proposed from the neutron diffraction. Our CEF model correctly predicts that the moments order along the $b-$axis (or $y$-axis) and the observed magnetic moment is 0.687(5) $\mu_B$, which is higher than the moment observed from the neutron diffraction (0.25 $\mu_B$/Ce). We attribute the observed reduced moment due to the Kondo screening effect., Comment: 10 pages, 13 figures

Single crystal of PrSi was grown by Czochralski method in a tetra-arc furnace. Powder x-ray diffraction of the as grown crystal revealed that PrSi crystallizes in FeB$-$type structure with space group $Pnma$ (no. 62). PrSi undergoes a ferromagnetic transition at 52 K with [010] direction as the easy axis of magnetization. Heat capacity data confirm the bulk nature of the transition at 52 K and exhibit a huge anomaly at the transition. A sharp rise in the low temperature heat capacity has been observed (below 5 K) which is attributed to the $^{141}$Pr nuclear Schottky heat capacity arising from the hyperfine field of the Pr moment. The estimated Pr magnetic moment 2.88 $\mu_{\rm B}$/Pr from the hyperfine splitting is in agreement with the saturation magnetization value obtained from the magnetization data measured at 2 K. From the crystal electric field (CEF) analysis of the magnetic susceptibility, magnetization and the heat capacity data it is found that the degenerate $J = 4$ Hund's rule derived state of Pr$^{3+}$-ion splits into nine singlets with an overall splitting of 284 K, the first excited singlet state separated by just 9 K from the ground state. The magnetic ordering in PrGe appears to be due to the exchange generated admixture of low lying crystal field levels. Magnetocaloric effect (MCE) has been investigated from magnetization data along all the three principal crystallographic directions. Large magnetic entropy change, $-\Delta S_M = $22.2 J/kg K, and the relative cooling power, RCP = $460$ J/kg, characteristic of giant magneto caloric effect are achieved near the transition temperature ($T_{\rm C}$ = 52 K) for $H =$~70 kOe along $[010]$. Furthermore, the PrSi single crystal exhibits a giant MCE anisotropy., Comment: 10 pages, 11 figures

Single crystals of EuNiGe$_3$ crystallizing in the non-centrosymmetric BaNiSn$_3$-type structure have been grown using In flux, enabling us to explore the anisotropic magnetic properties which was not possible with previously reported polycrystalline samples. The EuNiGe$_3$ single crystalline sample is found to order antiferromagnetically at 13.2 K as revealed from the magnetic susceptibility, heat capacity and electrical resistivity data. The low temperature magnetization M(H) is distinctly different for field parallel to ${ab}$-plane and $c$-axis; the ${ab}$-plane magnetization varies nearly linearly with field before the occurrence of an induced ferromagnetic phase (spin-flip) at 6.2 Tesla; on the other hand M(H) along the $c$-axis is accompanied by two metamagnetic transitions followed by a spin-flip at 4.1 T. A model including anisotropic exchange and dipole-dipole interactions reproduces the main features of magnetization plots but falls short of full representation. (H,T) phase diagrams have been constructed for the field applied along the principal directions. From the $^{151}$Eu M\"{o}ssbauer spectra, we determine that the 13.2 K transition leads to an incommensurate antiferromagnetic intermediate phase followed by a transition near 10.5 K to a commensurate antiferromagnetic configuration., Comment: 10 pages, 15 Figures

We study the structural and magnetic properties of the MnBi inter-metallic compound. The LTP (Low Temperature Phase) MnBi compound is successfully synthesized in single step by vacuum encapsulation technique and rapid quenching from phase formation temperature. The phase purity and the magnetic moments of MnBi are highly dependent on heat treating schedule. The best phase purity and the magnetic moment are found for a sample heat treated at 310oC for 48h. Rietveld fitted X-ray diffraction (XRD) patterns revealed that the studied MnBi compound is crystallized in hexagonal P63/mmc space group with minute presence of unreacted Bi and Mn phases. The scanning electron microscopy (SEM) study is carried out to visualize the grains morphology and phase identification. The bulk MnBi powder showed appreciable magnetic moment of (62emu/g at 6Tesla) and maximum energy product (BHmax of 4.01MGOe at 6Tesla). The magnetic properties of synthesized MnBi show that it could be a potential candidate for rare earth free permanent magnets., Comment: 11 pages text and figures: comments/suggestions(awana@mail.nplindia.org)/ http://www.freewebs.com/vpsawana/

The anisotropic magnetic properties of the antiferromagnetic compound CePd$_2$Ge$_2$, crystallizing in the tetragonal crystal structure have been investigated in detail on a single crystal grown by Czochralski method. From the electrical transport, magnetization and heat capacity data, the N\'{e}el temperature is confirmed to be 5.1 K. Anisotropic behaviour of magnetization and resistivity is observed along the two principal crystallographic directions viz., [100] and [001]. The isothermal magnetization measured in the magnetically ordered state at 2 K exhibits a spin re-orientation at 13.5 T for field applied along [100] direction, whereas the magnetization was linear along the [001] direction attaining a value of 0.94 $\mu_{\rm B}$/Ce at 14 T. The reduced value of the magnetization is attributed to the crystalline electric field (CEF) effects. A sharp jump in the specific heat at the magnetic ordering temperature is observed. After subtracting the phononic contribution, the jump in the heat capacity amounts to 12.5 J/K mol which is the expected value for a spin ${1}{2}$ system. From the CEF analysis of the magnetization data the excited crystal field split energy levels were estimated to be at 120 K and 230 K respectively, which quantitatively explain the observed Schottky anomaly in the heat capacity. A magnetic phase diagram has been constructed based on the field dependence of magnetic susceptibility and the heat capacity data., Comment: 15 pages, 8 figures

We find that the dynamical phase transition (DPT) in nearest-neighbor bipartite entanglement of time-evolved states of the anisotropic infinite quantum XY spin chain, in a transverse time-dependent magnetic field, can be quantitatively characterized by the dynamics of an information-theoretic quantum correlation measure, namely, quantum work-deficit (QWD). We show that only those nonequilibrium states exhibit entanglement resurrection after death, on changing the field parameter during the DPT, for which the cumulative bipartite QWD is above a threshold. The results point to an interesting inter-relation between two quantum correlation measures that are conceptualized from different perspectives., Comment: 8 pages, 3 figures, elsarticle, final accepted version

We investigate the behavior of genuine multipartite entanglement of paradigmatic frustrated quantum spin systems. We consider six different spin models, whose frustration ranges from being very high to very low. We find that the highly frustrated quantum spin systems are near-maximally genuine multipartite entangled, while those with low frustration do not possess a similar definite behavior with regard to their genuine multipartite entanglement., Comment: 9 pages, 6 figures, RevTeX 4-1, added text and figure, results unchanged, published version

We consider a class of large superposed states, obtained from dimer coverings on spin-1/2 isotropic lattices, whose potential usefulness ranges from organic molecules to quantum computation. We show that they are genuinely multiparty entangled, irrespective of the geometry and dimension of the isotropic lattice. We then present an efficient method to characterize the genuine multisite entanglement in the case of isotropic square spin-1/2 lattices, with short-range dimer coverings. We use this iterative analytical method to calculate the multisite entanglement of finite-sized lattices, which through finite-size scaling, enables us to obtain the estimate of the multisite entanglement of the infinite square lattice. The method can be a useful tool to investigate other single- and multisite properties of such states., Comment: 5 + 1 pages, 1 + 1 figures, Supplemetal Material included, REVTeX 4.1, published version

The observation of a two dimensional electron gas (2DEG) (1, 2), superconductivity (3, 4), magnetic effects (5) and electronic phase separation (6-8) at the interfaces of insulating oxides, especially LaAlO3/SrTiO3, has further enhanced the potential of complex oxides for novel electronics. The occurrence of the 2DEG is strongly believed to be driven by the polarization discontinuity (9) at the interface between the two oxides. In this scenario, the crystal orientation plays an important role and no conductivity would be expected for e.g., the interface between LaAlO3 and (110)-oriented SrTiO3, which should not have a polarization discontinuity (10, 11). Here, we report the observation of unexpected conductivity at the LaAlO3/SrTiO3 interface prepared on (110)-oriented SrTiO3. The conductivity was further found to be strongly anisotropic, with the ratio of the conductance along the different directions parallel to the substrate surface showing a remarkable dependence on the oxygen pressure during deposition. The conductance and its anisotropy are discussed based on the atomic structure at the interface, as revealed by Scanning Transmission Electron Microscopy (STEM) and further supported by density functional theory (DFT) calculations., Comment: 17 pages, 5 figures

The interface between the polar LaAlO$_3$ and nonpolar SrTiO$_3$ layers has been shown to exhibit various electronic and magnetic phases such as two dimensional electron gas, superconductivity, magnetism and electronic phase separation. These rich phases are expected due to the strong interplay between charge, spin and orbital degree of freedom at the interface between these complex oxides, leading to the electronic reconstruction in this system. However, until now all of these new properties have been studied extensively based on the interfaces which involve a polar LaAlO$_3$ layer. To investigate the role of the A and B cationic sites of the ABO$_3$ polar layer, here we study various combinations of polar/nonpolar oxide (NdAlO$_3$/SrTiO$_3$, PrAlO$_3$/SrTiO$_3$ and NdGaO$_3$/SrTiO$_3$) interfaces which are similar in nature to LaAlO$_3$/SrTiO$_3$ interface. Our results show that all of these new interfaces can also produce 2DEG at their interfaces, supporting the idea that the electronic reconstruction is the driving mechanism for the creation of the 2DEG at these oxide interfaces. Furthermore, the electrical properties of these interfaces are shown to be strongly governed by the interface strain and strong correlation effects provided by the polar layers. Our observations may provide a novel approach to further tune the properties of the 2DEG at the selected polar/nonpolar oxide interfaces., Comment: 5 pages, 4 figures