The induced magnetic moments in the V 3d electronic states of interface atomic layers in a Fe(6ML)/V(7ML) superlattice was investigated by x-ray resonant magnetic scattering. The first V atomic layer next to Fe was found to be strongly antiferromagnetically polarized relatively to Fe and the magnetic moments of the next few atomic layers in the interior V region decay exponentially with increasing distance from the interface, while the magnetic moments of the Fe atomic layers largely remain bulk-like. The induced V moments decay more rapidly as observed by x-ray magnetic scattering than in standard x-ray magnetic circular dichroism. The theoretical description of the induced magnetic atomic layer profile in V was found to strongly rely on the interface roughness within the superlattice period. These results provide new insight into interface magnetism by taking advantage of the enhanced depth sensitivity to the magnetic profile over a certain resonant energy bandwidth in the vicinity of the Bragg angles.
In ferromagnetic thin films, the Curie temperature variation with the thickness is always considered as continuous when the thickness is varied from $n$ to $n+1$ atomic planes. We show that it is not the case for Fe in Fe/Ir superlattices. For an integer number of atomic planes, a unique magnetic transition is observed by susceptibility measurements, whereas two magnetic transitions are observed for fractional numbers of planes. This behavior is attributed to successive transitions of areas with $n$ and $n+1$ atomic planes, for which the $T_c$'s are not the same. Indeed, the magnetic correlati…
We explore computationally the formation of tri-layer superlattices as an alternative approach for combining ferroelectricity with magnetism to form magnetoelectric multiferroics. We find that the contribution to the superlattice polarization from tri-layering is small compared to typical polarizations in conventionalferroelectrics, and the switchable ferroelectric component is negligible. In contrast, we show that epitaxial strain and ``negative pressure'' can yield large, switchable polarizations that are compatible with the coexistence of magnetism, even in materials with no active ferroele…
(LaNiO3)n/(LaMnO3)2 superlattices were grown using ozone-assisted molecular beam epitaxy, where LaNiO3 is a paramagnetic metal and LaMnO3 is an antiferromagnetic insulator. The superlattices exhibit excellent crystallinity and interfacial roughness of less than 1 unit cell. X-ray spectroscopy and dichroism measurements indicate that electrons are transferred from the LaMnO3 to the LaNiO3, inducing magnetism in LaNiO3. Magnetotransport measurements reveal a transition from metallic to insulating behavior as the LaNiO3 layer thickness is reduced from 5 unit cells to 2 unit cells and suggest a mo…
The emergence of magnetic reconstructions at the interfaces of oxide heterostructures are often explained via subtle modifications in the electronic densities, exchange couplings, or strain. Here an additional possible route for induced magnetism is studied in the context of the (LaNiO$_3$)$_n$/(LaMnO$_3$)$_n$ superlattices using a hybrid tight-binding model. In the LaNiO$_3$ region, the induced magnetizations decouple from the intensity of charge leakage from Mn to Ni, but originate from the spin-filtered quantum confinement present in these nanostructures. In general, the induced magnetizati…
We study the magnetic structure of the (LaMnO$_3$)$_{2n}$/(SrMnO$_3$)$_n$ superlattices from density-functional calculations. In agreement with the experiments, we find that the magnetism changes with the layer thickness `n'. The reason for the different magnetic structures is shown to be the varying potential barrier across the interface, which controls the leakage of the Mn-e$_g$ electrons from the LMO side to the SMO side. This in turn affects the interfacial magnetism via the carrier-mediated Zener double exchange. For n=1 superlattice, the Mn-e$_g$ electrons are more or less spread over t…
Two-dimensional electron gas due to semiconductor interfaces can have high mobility and exhibits superconductivity, magnetism, and other exotic properties that are unexpected in constituent bulk materials. We study crystal structures, electronic states, and magnetism of short-period (BTO)$_m$/(GTO)$_2$ ($m$=2 and 4) superlattices consisting of ferroelectric BaTiO$_3$ (BTO) and ferrimagnetic insulating polar GdTiO$_3$ (GTO) by first principles calculations. Our investigation shows that the middle Ti-O monolayer in the GTO layer becomes metallic because the ferroelectricity in the insulating BTO…
Using polarized neutron reflectometry (PNR) we measured the neutron spin dependent reflectivity from four LaAlO3/SrTiO3 superlattices. This experiment implies that the upper limit for the magnetization induced by an 11 T magnetic field at 1.7 K is 2 emu/cm3. SQUID magnetometry of the superlattices sporadically finds an enhanced moment, possibly due to experimental artifacts. These observations set important restrictions on theories which imply a strongly enhanced magnetism at the interface between LaAlO3 and SrTiO3.
We use a two-orbital double-exchange model including Jahn-Teller lattice distortions, superexchange interactions, and long-range Coulomb (LRC) interactions to investigate the origin of magnetically disordered interfaces between ferromagnetic metallic (FM) and antiferromagnetic insulating (AFI) manganites in FM/AFI superlattices. The induced magnetic moment in the AFI layer varies non-monotonically with increasing AFI layer width as seen in the experiment. We provide a framework for understanding this non-monotonic behavior which has a one-to-one correspondence with the magnetization of the FM …
Interfaces between correlated complex oxides are promising avenues to realize new forms of magnetism that arise as a result of charge transfer, proximity effects and locally broken symmetries. We report upon the discovery of a non-collinear magnetic structure in superlattices of the ferromagnetic metallic oxide La2/3Sr1/3MnO3 (LSMO) and the correlated metal LaNiO3 (LNO). The exchange interaction between LSMO layers is mediated by the intervening LNO, such that the angle between the magnetization of neighboring LSMO layers varies in an oscillatory manner with the thickness of the LNO layer. The…
Charge dipole moment and spin moment rarely coexist in single-phase bulk materials except in some multiferroics. Despite the progress in the past decade, for most multiferroics their magnetoelectric performance remains poor due to the intrinsic exclusion between charge dipole and spin moment. As an alternative approach, the oxide heterostructures may evade the intrinsic limits in bulk materials and provide more attractive potential to realize the magnetoelectric functions. Here we perform a first-principles study on LaAlO$_3$/PbTiO$_3$ superlattices. Although neither of the components is magne…
Resonant tunnelling is a quantum mechanical process that has long been attracting both scientific and technological attention owing to its intriguing underlying physics and unique applications for high-speed electronics. The materials system exhibiting resonant tunnelling, however, has been largely limited to the conventional semiconductors, partially due to their excellent crystalline quality. Here we show that a deliberately designed transition metal oxide superlattice exhibits a resonant tunnelling behaviour with a clear negative differential resistance. The tunnelling occurred through an a…
LaCoO$_3$ provides a poignant example of a transition metal oxide where the cobalt cations display multiple spin states and spin transitions and which continues to garner substantial attention. In this work, we describe first principles studies, based on DFT+$U$ theory, of superlattices containing LaCoO$_3$, specifically (LaCoO$_3$)$_n$+(LaTiO$_3$)$_n$ for $n=1,2$. The superlattices show strong electron transfer from Ti to Co resulting in Co$^{2+}$, significant structural distortions and a robust orbital polarization of Co$^{2+}$. We predict high-spin Co$^{2+}$ and a checkerboard or G-type ant…
We investigate theoretically the resonant splitting of ballistic conductance peaks in magnetic superlattices. It is found that, for magnetic superlattices with periodically arranged $n$ identical magnetic-barriers, there exists a general $(n-1)$-fold resonant peak splitting rule for ballistic conductance, which is the analogy of the $(n-1)$-fold resonant splitting for transmission in $n$-barrier electric superlattices (R. Tsu and L. Esaki, Appl. Phys. Lett. {\bf 22}, 562 (1973)).
Scanning and transmission electron microscopy reveal that SiOx/Si layers can roll-up into microtubes and radial superlattices on a Si substrate. These hybrid objects are thermally stable up to 850 C and emit light in the visible spectral range at room temperature. For tubes disengaged from the substrate surface, optically resonant emission with mode spacings inversely proportional to the tube diameter are observed and agree excellently with those obtained from Finite-Different-Time-Domain simulations. The resonant modes we record are strictly polarized along the tube axis.
We report the observation of weak magnetism in superlattices of LaAlO3/SrTiO3 using beta-detected nuclear magnetic resonance. The spin lattice relaxation rate of 8 Li in superlattices with a spacer layers of 8 and 6 unit cells of LaAlO3 exhibits a strong peak near ~35 K, whereas no such peak is observed in a superlattice with spacer layer thickness of 3 unit cells. We attribute the observed temperature dependence to slowing down of weakly coupled electronic moments at the LaAlO3/SrTiO3 interface. These results show that the magnetism at the interface depends strongly on the thickness of the sp…
We study coherent electron dynamics in a biassed undriven ideal semiconductor superlattice coupled to the continuum, near energy level anticrossings. In particular, we examine the dependence of wavepacket dynamical characteristics on electric field detuning, and investigate mixed regimes involving a superposition of energy level anticrossings showing both Rabi oscillations and resonant tunnelling. In earlier work [Phys. Rev. B 75 165421 (2007)], Rabi and Zener resonances were shown to have a common origin, and a criteria for the occurrence of either was proposed. The present results allow a be…
We show that resonant electron transport in semiconductor superlattices with an applied electric and tilted magnetic field can, surprisingly, become more pronounced as the lattice and conduction electron temperature increases from 4.2 K to room temperature and beyond. It has previously been demonstrated that at certain critical field parameters, the semiclassical trajectories of electrons in the lowest miniband of the superlattice change abruptly from fully localised to completely unbounded. The unbounded electron orbits propagate through intricate web patterns, known as stochastic webs, in ph…
We show that very large paramagnetic moments are created in ultrathin Pd layers through indirect interlayer exchange coupling. Pd $L$-edge x-ray magnetic circular dichroism measurements show Pd moments in [Pd(2.5nm)/Cu(3nm)/Ni$_{81}$Fe$_{19}$(5nm)/Cu(3nm)]$_{20}$ superlattices which are ferromagnetically aligned with the applied field and nearly 3% the size of Pd moments created in directly exchange coupled [Pd(2.5nm)/Ni$_{81}$Fe$_{19}$(5nm)]$_{20}$ superlattices. The induced moment is two orders of magnitude larger than that expected from RKKY exchange acting on the bulk paramagnetic suscepti…
Exchange interactions and finite-temperature magnetism in (111)-oriented (LaMnO$_3$)$_{2n}$|(SrMnO$_3$)$_n$ superlattices
Institute of Physics, Nicolaus Copernicus University（尼古拉·哥白尼大学物理研究所）；School of Physics, Engineering and Technology, University of York（约克大学物理、工程与技术学院）；Department of Physics and Institute of Quantum Convergence and Technology, Kangwon National University（江原国立大学物理系及量子融合技术研究所）；Department of Energy Technology, Korea Institute of Energy Technology (KENTECH)（韩国能源技术研究院能源技术部）；Department of Physics and Astronomy, Uppsala University（乌普萨拉大学物理与天文系）
The problem of localization of the resonant impurity states is discussed for an illustrative example of Titanium doped Lead Telluride. Electronic structure of PbTe:Ti is studied using first principles methods, densities of states and Bloch spectral functions are analyzed. We show that Ti creates resonant states in the conduction band of PbTe, however, spectral functions of the system strongly suggest localization of these states and show poor hybridization with PbTe electronic structure. The contrast between results presented here and previously reported spectral functions for PbTe:Tl correlat…
Twisted graphene bilayers provide a versatile platform to engineer metamaterials with novel emergent properties by exploiting the resulting geometric moiré superlattice. Such superlattices are known to host bulk valley currents at tiny angles ($α\approx 0.3 ^\circ$) and flat bands at magic angles ($α\approx 1^\circ$). We show that tuning the twist angle to $α^*\approx 0.8^\circ$ generates flat bands away from charge neutrality with a triangular superlattice periodicity. When doped with $\pm 6$ electrons per moiré cell, these bands are half-filled and electronic interactions produce a symmetry-…
Polar compensation can play an important role in the determination of interfacial electronic and magnetic properties in oxide heterostructures. Using x-ray absorption spectroscopy, x-ray magnetic circular dichroism, bulk magnetometry, and transport measurements, we find that interfacial charge redistribution via polar compensation is essential for explaining the evolution of interfacial ferromagnetism in LaNiO$_3$/CaMnO$_3$ superlattices as a function of LaNiO$_3$ layer thickness. In insulating superlattices (4 unit cells or less of LaNiO$_3$), magnetism is dominated by Ni-Mn superexchange, wh…
Two-dimensional moire superlattices have recently emerged as a fertile ground for creating novel electronic phases of matter with unprecedented control. Despite intensive efforts, theoretical investigation of correlated moire systems has been challenged by the large number of atoms in a superlattice unit cell and the inherent difficulty of treating electron correlation. The physics of correlated moire systems is governed by low-energy electrons in a coarse-grained long-wavelength potential, unlike the singular Coulomb potential of atomically-spaced ions in natural solids. Motivated by the sepa…
Oxide superlattices and microstructures hold the promise for creating a new class of devices with unprecedented functionalities. Density-functional studies of the recently fabricated superlattices of lattice-matched perovskite titanates (SrTiO3)n/(LaTiO3)m reveal a classic wedge-shaped potential originating from the Coulomb potential of a charged sheet of La atoms. The potential in turn confines the electrons in the vicinity of the sheet, leading to an Airy-function localization of the electron states. Magnetism is suppressed for structures with a single LaTiO3 monolayer, while the bulk antife…
It is demonstrated that the effect of coexistence of bulk and surface polaritons within the same frequency band and wavevector space can be achieved in a magnetic-semiconductor superlattice providing a conscious choice of characteristic resonant frequencies and material fractions of the structure's underlying components as well as geometry of the external static magnetic field. The study is based on the effective medium theory which is involved to calculate dispersion characteristics of the long-wavelength electromagnetic modes of ordinary and extraordinary bulk polaritons and hybrid EH and HE…
Perovskite oxide heterostructures offer an important path forward for stabilizing and controlling low-dimensional magnetism. One of the guiding design principles for these materials systems is octahedral connectivity. In superlattices composed of perovskites with different crystal symmetries, variation of the relative ratio of the constituent layers as well as the individual layer thicknesses gives rise to non-equilibrium crystal symmetries that, in turn, lead to unprecedented control of interfacial ferromagnetism. We have found that in superlattices of CaMnO$_3$ (CMO) and LaNiO$_3$ (LNO), int…
We discuss peculiarities of bulk and surface polaritons propagating in a composite magnetic-semiconductor superlattice influenced by an external static magnetic field. Three particular configurations of magnetization, namely the Voigt, polar and Faraday geometries are considered. In the long-wavelength limit, involving the effective medium theory, the proposed superlattice is described as an anisotropic uniform medium defined by the tensors of effective permittivity and effective permeability. The study is carried out in the frequency band where the characteristic resonant frequencies of the u…
In this paper we study the possible relation between the electronic and magnetic structure of the TiO2/LaAlO3 interface and the unexpected magnetism found in undoped TiO2 films grown on LaAlO$_3$. We concentrate on the role played by structural relaxation and interfacial oxygen vacancies. LaAlO3 has a layered structure along the (001) direction with alternating LaO and AlO2 planes, with nominal charges of +1 and -1, respectively. As a consequence of that, an oxygen deficient TiO2 film with anatase structure will grow preferently on the AlO2 surface layer. We have therefore performed ab-initio …
We review both the fundamental aspects and the applications of functional magneto-optic and opto-magnetic metamaterials displaying collective and coupling effects on the nanoscale, where the concepts of optics and magnetism merge to produce unconventional phenomena. The use of magnetic materials instead of the usual noble metals allows for an additional degree of freedom for the control of electromagnetic field properties, as well as it allows light to interact with the spins of the electrons and to actively manipulate the magnetic properties of such nanomaterials. In this context, we explore …
Magnetic spiral structures can exhibit ferroelectric moments as recently demonstrated in various multiferroic materials. In such cases the helicity of the magnetic spiral is directly correlated with the direction of the ferroelectric moment and measurement of the helicity of magnetic structures is of current interest. Soft x-ray resonant diffraction is particularly advantageous because it combines element selectivity with a large magnetic cross-section. We calculate the polarization dependence of the resonant magnetic x-ray cross-section (electric dipole transition) for the basal plane magneti…
Emergence of unconventional magnetic order in strain-engineered RuO2/TiO2 superlattices
University of Minnesota−Twin Cities（明尼苏达大学双城分校）；University of Minnesota（明尼苏达大学）；Sungkyunkwan University（成均馆大学）；Massachusetts Institute of Technology（麻省理工学院）；National Institute of Standards and Technology（美国国家标准与技术研究院）；Oak Ridge National Laboratory（橡树岭国家实验室）
We explore manganite interface magnetism in epitaxially grown La0.7Sr0.3MnO3(LSMO)/SrTiO3 ultrathin superlattices (SL) along (110) orientation. we show that robust ferromagnetism persists down to four monolayers LSMO(MLs) (~1.1 nm in thickness), of which 50% Mn is at the interface state. Above eight MLs, the magnetic moment is nearly saturated to the theoretical value of 3.7u_B, with an estimated interface moment of 3.2u_B. In comparison to (100)-oriented SLs which were previously shown to have a spin canted ground state, (110)-oriented SLs exhibit stronger low-dimensional ferromagnetism and b…
Atomic defects have a significant impact in the low-energy properties of graphene systems. By means of first-principles calculations and tight-binding models we provide evidence that chemical impurities modify both the normal and the superconducting states of twisted bilayer graphene. A single hydrogen atom attached to the bilayer surface yields a triple-point crossing, whereas self-doping and three-fold symmetry-breaking are created by a vacant site. Both types of defects lead to time-reversal symmetry-breaking and the creation of local magnetic moments. Hydrogen-induced magnetism is found to…
The epitaxial stabilization of a single layer or superlattice structures composed of complex oxide materials on polar (111) surfaces is severely burdened by reconstructions at the interface, that commonly arise to neutralize the polarity. We report on the synthesis of high quality LaNiO$_3$/mLaAlO$_3$ pseudo cubic (111) superlattices on polar (111)-oriented LaAlO$_3$, the proposed complex oxide candidate for a topological insulating behavior. Comprehensive X-Ray diffraction measurements, RHEED, and element specific resonant X-ray absorption spectroscopy affirm their high structural and chemica…
Fe-doped III-V ferromagnetic semiconductors (FMSs) such as (In,Fe)As, (Ga,Fe)Sb, (In,Fe)Sb, and (Al,Fe)Sb are promising materials for spintronic device applications because of the availability of both n- and p-type materials and the high Curie temperatures. On the other hand, (Ga,Fe)As, which has the same zinc-blende crystal structure as the Fe-doped III-V FMSs, shows paramagnetism. The origin of the different magnetic properties in the Fe-doped III-V semiconductors remains to be elucidated. To address this issue, we use resonant photoemission spectroscopy (RPES) and x-ray magnetic circular di…
A series of (ZnO)m(CoO)n digital alloys and superlattices grown by atomic layer deposition has been investigated by a range of experimental methods. The data provide evidences that the Co interdiffusion in the digital alloy structures is sufficient to produce truly random Zn1-xCoxO mixed crystals with x up to 40%. Conversely, in the superlattice structures the interdiffusion is not strong enough to homogenize the Co content along the growth direction results in the formation of (Zn,Co)O films with spatially modulated Co concentrations. All structures deposited at 160\circC show magnetic proper…
We use synchrotron x-ray diffraction and electrical transport under pressure to probe both the magnetism and the structure of single crystal NiS2 across its Mott-Hubbard transition. In the insulator, the low-temperature antiferromagnetic order results from superexchange among correlated electrons and couples to a (1/2, 1/2, 1/2) superlattice distortion. Applying pressure suppresses the insulating state, but enhances the magnetism as the superexchange increases with decreasing lattice constant. By comparing our results under pressure to previous studies of doped crystals we show that this depen…
The nature of the magnetic order in (La2/3Sr1/3MnO3)9/(LaNiO3)3 superlattices is investigated using x-ray resonant magnetic reflectometry. We observe a new c-axis magnetic helix state in the (LaNiO3)3 layers that had never been reported in nickelates, and which mediates the ~130deg magnetic coupling between the ferromagnetic (La2/3Sr1/3MnO3)9 layers, illustrating the power of x-rays for discovering the magnetic state of complex oxide interfaces. Resonant inelastic x-ray scattering and x-ray absorption spectroscopy show that Ni-O ligand hole states from bulk LaNiO3 are mostly filled due to inte…
Emergent Noncollinearity and Near-Degenerate Magnetic Superlattices in AT6X6 Kagome Metals
Ames National Laboratory, U.S. Department of Energy, Iowa State University（艾姆斯国家实验室，美国能源部，爱荷华州立大学）；Department of Physics and Astronomy, Iowa State University（爱荷华州立大学物理与天文系）
An oxide heterostructure made of manganite bilayers and ferroelectric perovskites is predicted to lead to the full control of magnetism when switching the ferroelectric polarizations. By using asymmetric polar interfaces in the superlattices, more electrons occupy the Mn layer at the $n$-type interface side than at the $p$-type side. This charge disproportionation can be enhanced or suppressed by the ferroelectric polarization. Quantum model and density functional theory calculations reach the same conclusion: a ferromagnetic-ferrimagnetic phase transition with maximal change $>90%$ of the tot…
We use resonant soft x-ray scattering to study electronic reconstruction at the interface between the Mott insulator LaMnO3 and the "band" insulator SrMnO3. Superlattices of these two insulators were shown previously to have both ferromagnetism and metallic tendencies [Koida et al., Phys. Rev. B 66, 144418 (2002)]. By studying a judiciously chosen superlattice reflection we show that the interface density of states exhibits a pronounced peak at the Fermi level, similar to that predicted by Okamoto et al. [Phys. Rev. B 70, 241104(R) (2004)]. The intensity of this peak correlates with the conduc…
We report on evaluation of lattice thermal conductivity of GeTe/Sb$_{2}$Te$_{3}$ superlattice (SL) by using femtosecond coherent phonon spectroscopy at various lattice temperatures. The time-resolved transient reflectivity obtained in amorphous and crystalline GeTe/Sb$_{2}$Te$_{3}$ SL films exhibits the coherent $A_{1}$ optical modes at terahertz (THz) frequencies with picoseconds dephasing time. Based on the Debye theory, we calculate the lattice thermal conductivity, including scattering by grain boundary and point defect, umklapp process, and phonon resonant scattering. The results indicate…
Heterostructured material systems devoid of ferroic components are presumed not to display ordering associated with ferroelectricity. In heterostructures composed of transition metal oxides, however, the disruption introduced by an interface can affect the balance of the competing interactions among electronic spins, charges and orbitals. This has led to the emergence of properties absent in the original building blocks of a heterostructure, including metallicity, magnetism and superconductivity. Here we report the discovery of ferroelectricity in artificial tri-layer superlattices consisting …
Resonant interlayer coupling in NbSe$_2$-graphite epitaxial moir{é} superlattices
SUPA, School of Physics and Astronomy, University of St Andrews（圣安德鲁斯大学物理与天文学学院）；Department of Physics and Astronomy, University of Manchester（曼彻斯特大学物理与天文学系）；Max Planck Institute for Chemical Physics of Solids（马克斯·普朗克固体化学物理研究所）；Physics Study Program, Faculty of Science and Technology, Syarif Hidayatullah State Islamic University Jakarta（雅加达希达亚图拉伊斯兰国立大学科技理学院物理学专业）；Institute for Materials Research, Tohoku University（东北大学材料科学研究所）
Spin-orbit entangled pseudospins hold promise for a wide array of exotic magnetism ranging from a Heisenberg antiferromagnet to a Kitaev spin liquid depending on the lattice and bonding geometry, but many of the host materials suffer from lattice distortions and deviate from idealized models in part due to inherent strong pseudospin-lattice coupling. Here, we report on the synthesis of a magnetic superlattice comprising the single ($n$=1) and the double ($n$=2) layer members of the Ruddlesden-Popper series iridates Sr$_{n+1}$Ir$_{n}$O$_{3n+1}$ alternating along the $c$-axis, and provide a comp…
Layered pnictide materials have provided a fruitful platform to study various emergent phenomena, including superconductivity, magnetism, charge density waves, etc. Here we report the observation of structural distortion and noncollinear magnetism in layered pnictide EuAg$_4$As$_2$ via transport, magnetization, single crystal X-ray and neutron diffraction data. EuAg$_4$As$_2$ single crystal shows a structural distortion at 120 K, where two sets of superlattice peaks with the propagation vectors of $q_1=\pm$(0, 0.25, 0.5) and $q_2=\pm$(0.25, 0, 1) emerge. Between 9 K to 15 K, the hexagonal Eu$^…
We report the observation of multiple phonon satellite features in ultra thin superlattices of form $n$SrIrO$_3$/$m$SrTiO$_3$ using resonant inelastic x-ray scattering. As the values of $n$ and $m$ vary the energy loss spectra show a systematic evolution in the relative intensity of the phonon satellites. Using a closed-form solution for the cross section, we extract the variation in the electron-phonon coupling strength as a function of $n$ and $m$. Combined with the negligible carrier doping into the SrTiO$_3$ layers, these results indicate that tuning of the electron-phonon coupling can be …
Ho2Ir3Si5 belongs to the family of three-dimensional (3D) R2Ir3Si5 (R = Lu, Er and Ho) compounds that exhibit a colossal first-order charge density wave (CDW) transition where there is a strong orthorhombic-to-triclinic distortion of the lattice accompanied by superlattice reflections. The analysis by single-crystal X-ray diffraction (SXRD) has revealed that the Ir-Ir zigzag chains along c are responsible for the CDW in all three compounds. The replacement of the rare earth element from non-magnetic Lu to magnetic Er or Ho lowers TCDW, where TCDWLu = 200 K, TCDWEr = 150 K and TCDWHo = 90 K. Ou…
At interfaces between oxide materials, lattice and electronic reconstructions always play important roles in exotic phenomena. In this study, the density functional theory and maximally localized Wannier functions are employed to investigate the (LaTiO$_3$)$_n$/(LaVO$_3$)$_n$ magnetic superlattices. The electron transfer from Ti$^{3+}$ to V$^{3+}$ is predicted, which violates the intuitive band alignment based on the electronic structures of LaTiO$_3$ and LaVO$_3$. Such unconventional charge transfer quenches the magnetism of LaTiO$_3$ layer mostly and leads to metal-insulator transition in th…
The number of atomic layers confined in a two-dimensional structure is crucial for the electronic and magnetic properties. Single-layer and bilayer $J_{\rm eff} = 1/2$ square lattices are well-known examples where the presence of the extra layer turns the XY-anisotropy to the $c$-axis anisotropy. We report on experimental realization of a hybrid SrIrO$_3$/SrTiO$_3$ superlattice that integrates monolayer and bilayer square lattices in one layered structure. By synchrotron x-ray diffraction, resonant x-ray magnetic scattering, magnetization, and resistivity measurements, we found that the hybrid…
We study theoretically the interplay between magnetism and topology in three-dimensional HgTe/MnTe superlattices stacked along the (001) axis. Our results show the evolution of the magnetic topological phases with respect to the magnetic configurations. An axion insulator phase is observed for the antiferromagnetic order with the out-of-plane Néel vector direction below a critical thickness of MnTe, which is the ground state amongst all magnetic configurations. Defining $T$ as the time-reversal symmetry, this axion insulator phase is protected by a magnetic two-fold rotational symmetry $C_2{\c…
In layered manganites with orbital and charge orderings, the degeneracy of the Mn $4p$ orbitals as well as the $3d$ ones is lifted by the effects of the $4p$ bands and the local Coulomb interactions. We formulate the atomic scattering factor for the resonant x-ray scattering in the memory function method by taking into account these effects on an equal footing. It is shown that the polarization dependences of the scattering intensities at the orbital and charge superlattice reflections observed in LaSr$_{2}$Mn$_2$O$_7$ are caused by the local and itinerant characters of $4p$ electrons, respect…
We investigate the interactions between two identical magnetic impurities substituted into a graphene superlattice. Using a first-principles approach, we calculate the electronic and magnetic properties for transition-metal substituted graphene systems with varying spatial separation. These calculations are compared for three different magnetic impurities, manganese, chromium, and vanadium. We determine the electronic band structure, density of states, and Millikan populations (magnetic moment) for each atom, as well as calculate the exchange parameter between the two magnetic atoms as a funct…
