Electronic nematicity has been found in a wide range of strongly correlated electron materials, resulting in the electronic states having-4.5pcPlease note that the spelling of the following author ...name(s) in the manuscript differs from the spelling provided in the article metadata: Izidor Benedičič. The spelling provided in the manuscript has been retained; please confirm. a symmetry that is lower than that of the crystal that hosts them. One of the most astonishing examples is Sr3Ru2O7, in which a small in-plane component of a magnetic field induces significant resistivity anisotropy. The direction of this anisotropy follows the direction of the in-plane field. The microscopic origin of this field-induced nematicity has been a long-standing puzzle, with recent experiments suggesting a field-induced spin density wave driving the anisotropy. Here, we report spectroscopic imaging of a field-controlled anisotropy of the electronic structure at the surface of Sr3Ru2O7. We track the electronic structure as a function of the direction of the field, revealing a continuous change with the angle. This continuous evolution suggests a mechanism based on spin–orbit coupling resulting in compass-like control of the electronic bands. The anisotropy of the electronic structure persists to temperatures about an order of magnitude higher compared to the bulk, demonstrating novel routes to stabilize such phases over a wider temperature range.
2D and layered electronic materials characterized by a kagome lattice, whose valence band structure includes two Dirac bands and one flat band, can host a wide range of tunable topological and ...strongly correlated electronic phases. While strong electron correlations have been observed in inorganic kagome crystals, they remain elusive in organic systems, which benefit from versatile synthesis protocols via molecular self‐assembly and metal‐ligand coordination. Here, direct experimental evidence of local magnetic moments resulting from strong electron–electron Coulomb interactions in a 2D metal–organic framework (MOF) is reported. The latter consists of di‐cyano‐anthracene (DCA) molecules arranged in a kagome structure via coordination with copper (Cu) atoms on a silver surface Ag(111). Temperature‐dependent scanning tunneling spectroscopy reveals magnetic moments spatially confined to DCA and Cu sites of the MOF, and Kondo screened by the Ag(111) conduction electrons. By density functional theory and mean‐field Hubbard modeling, it is shown that these magnetic moments are the direct consequence of strong Coulomb interactions between electrons within the kagome MOF. The findings pave the way for nanoelectronics and spintronics technologies based on controllable correlated electron phases in 2D organic materials.
Materials with a 2D kagome crystal structure yield potential for a wide range of tunable topological and correlated electron phases. The emergence of local magnetic moments resulting from strong electron‐electron Coulomb interactions in a 2D kagome metal–organic framework is demonstrated. These findings pave the way for tunable electron correlations—and hence controllable electronic and magnetic quantum phases—in 2D organic materials.
We give a summary of recent progress in the field of electronic structure calculations for materials with strong electronic Coulomb correlations. The discussion focuses on developments beyond the by ...now well established combination of density functional and dynamical mean field theory dubbed 'LDA + DMFT'. It is organized around the description of dynamical screening effects in the solid. Indeed, screening in the solid gives rise to dynamical local Coulomb interactions U(ω) (Aryasetiawan et al 2004 Phys. Rev. B 70 195104), and this frequency dependence leads to effects that cannot be neglected in a truly first principles description. We review the recently introduced extension of LDA + DMFT to dynamical local Coulomb interactions 'LDA + U(ω) + DMFT' (Casula et al 2012 Phys. Rev. B 85 035115, Werner et al 2012 Nature Phys. 1745-2481). A reliable description of dynamical screening effects is also a central ingredient of the 'GW + DMFT' scheme (Biermann et al 2003 Phys. Rev. Lett. 90 086402), a combination of many-body perturbation theory in Hedin's GW approximation and dynamical mean field theory. Recently, the first GW + DMFT calculations including dynamical screening effects for real materials have been achieved, with applications to SrV O3 (Tomczak et al 2012 Europhys. Lett. 100 67001, Tomczak et al Phys. Rev. B submitted (available electronically as arXiv:1312.7546)) and adatom systems on surfaces (Hansmann et al 2013 Phys. Rev. Lett. 110 166401). We review these and comment on further perspectives in the field. This review is an attempt to put elements of the original works into the broad perspective of the development of truly first principles techniques for correlated electron materials.
The thermal conductivity above room temperature is investigated for LaCoO
3
-based materials showing spin-state and insulator-metal crossovers. A positive temperature coefficient (PTC) of the thermal ...conductivity is observed during the insulator-metal crossover around 500 K. Our analysis indicates that the phononic thermal transport is also enhanced in addition to the electronic contribution as the insulator-metal crossover takes place. The enhancement of the phononic component is ascribed to the reduction of the incoherent local lattice distortion coupled with the spin/orbital state of each Co
3+
ion, which is induced by the enhanced spin-state fluctuation between low and excited spin-states. Moreover, fine tunability for the PTC of the thermal conductivity is demonstrated via doping hole-type carriers into LaCoO
3
. The observed enhancement ratio of the thermal conductivity κ
T
(773 K) / κ
T
(323 K) = 2.6 in La
0.95
Sr
0.05
CoO
3
is the largest value among oxide materials which exhibit a PTC of their thermal conductivity above room temperature. The thermal rectification ratio is estimated to reach 61% for a hypothetical thermal diode consisting of La
0.95
Sr
0.05
CoO
3
and LaGaO
3
, the latter of which is a typical band insulator. These results indicate that utilizing spin-state and orbital degrees of freedom in strongly correlated materials is a useful strategy for tuning thermal transport properties, especially for designing thermal diodes.
In the most studied family of organic superconductors κ-(BEDT-TTF)2X, the BEDT-TTF molecules that make up the conducting planes are coupled as dimers. For some anions X, an antiferromagnetic ...insulator is found at low temperatures adjacent to superconductivity. With an average of one hole carrier per dimer, the BEDT-TTF band is effectively 12-filled. Numerous theories have suggested that fluctuations of the magnetic order can drive superconducting pairing in these models, even as direct calculations of superconducting pairing in monomer 12-filled band models find no superconductivity. Here, we present accurate zero-temperature Density Matrix Renormalization Group (DMRG) calculations of a dimerized lattice with one hole per dimer. While we do find an antiferromagnetic state in our results, we find no evidence for superconducting pairing. This further demonstrates that magnetic fluctuations in the effective 12-filled band approach do not drive superconductivity in these and related materials.
► We have optimized the grating optics for VLS type RIXS spectrometers. ► Cu L3 RIXS can efficiently probe magnetic fluctuations in quasi-one dimensional cuprates. ► RIXS is sensitive to spin–orbital ...separation in one-dimensional cuprates. ► RIXS is capable to give information on interface states in oxide heterostructures. ► Mapping of electron–hole pair excitations with RIXS probes the unoccupied band structure.
The experimental development of the resonant inelastic X-ray scattering (RIXS) technique in the soft X-ray energy range has been tremendous during the last years. The ADRESS beamline at the Paul Scherrer Institut in Switzerland and its RIXS spectrometer SAXES has boosted the scientific capabilities with soft X-ray RIXS. Increased resolving power above 10,000 and the possibility to rotate the spectrometer to different scattering geometries allows analyzing the collective behavior of charge, orbital and spin excitations by assessing their momentum dependence. Focus of most projects at this facility lies in the investigation of low- and medium-energy excitations in correlated electron materials. In addition ADRESS has also been used for RIXS investigations on molecules in the liquid and gaseous phase. This review reports on the recent extension of the optics of the SAXES RIXS spectrometer with an additional grating optimized for the spectral range from ca. 400 to 700eV. Furthermore, the scientific opportunities emerging from ADRESS are highlighted in RIXS studies on quasi one-dimensional cuprates, oxide heterostructures and a weakly correlated broad band material.
Self-organized electronically ordered phases are a recurring feature in correlated materials, resulting in, for example, fluctuating charge stripes whose role in high-TC superconductivity is under ...debate. However, the relevant cause-effect relations between real-space charge correlations and low-energy excitations remain hidden in time-averaged studies. Here we reveal ultrafast charge localization and lattice vibrational coupling as dynamic precursors of stripe formation in the model compound La(1.75)Sr(0.25)NiO4, using ultrafast and equilibrium mid-infrared spectroscopy. The opening of a pseudogap at a crossover temperature T* far above long-range stripe formation establishes the onset of electronic localization, which is accompanied by an enhanced Fano asymmetry of Ni-O stretch vibrations. Ultrafast excitation triggers a sub-picosecond dynamics exposing the synchronous modulation of electron-phonon coupling and charge localization. These results illuminate the role of localization in forming the pseudogap in nickelates, opening a path to understanding this mysterious phase in a broad class of complex oxides.
Electrical resistivity, specific heat, and magnetization measurements on the URu
Os
Si
system suggest a phase transition from the 'hidden order' phase to another unidentified phase that is likely to ...be a large moment antiferromagnetic phase. It is noteworthy that the hidden order/large moment antiferromagnetic phase boundary
is enhanced from 17.5 K at
= 0 to 50 K at
= 1. However, as
increases, the gap opening in the Fermi surface due to the hidden order phase transition, deduced from electrical resistivity and specific heat measurements, decreases. This study reveals that both Fe and Os isoelectronic substitutions for Ru in URu
Si
yield an enhancement of
. In contrast to the URu
Fe
Si
system, where the unit cell volume decreases with
, in the URu
Os
Si
system, the unit cell volume increases with
. Thus the enhancement of the hidden order/large moment antiferromagnetic transition temperature cannot be solely due to an increase in chemical pressure.
Significance Point-contact spectroscopy is a bulk spectroscopic probe that has been reliably used to map out bosonic and superconducting order parameter spectra via quasiparticle classical and ...Andreev scattering, respectively. We previously showed this technique to be exquisitely sensitive to an effective density of states specifically arising from non-Fermi liquid behavior, and in the case of the iron pnictides and chalcogenides, electronic nematicity manifesting as a zero bias conductance peak corresponds to an increased effective density of states at the Fermi level arising from orbital fluctuations. We developed a quantum mechanical theory to show how this technique reveals such effective density of states while being insensitive to gapless Fermi surface reconstructions and is therefore a valuable filter for detecting non-Fermi liquid behavior.
We developed a microscopic theory for the point-contact conductance between a metallic electrode and a strongly correlated material using the nonequilibrium Schwinger-Kadanoff-Baym-Keldysh formalism. We explicitly show that, in the classical limit, contact size shorter than the scattering length of the system, the microscopic model can be reduced to an effective model with transfer matrix elements that conserve in-plane momentum. We found that the conductance dI / dV is proportional to the effective density of states, that is, the integrated single-particle spectral function A ( ω = eV ) over the whole Brillouin zone. From this conclusion, we are able to establish the conditions under which a non-Fermi liquid metal exhibits a zero-bias peak in the conductance. This finding is discussed in the context of recent point-contact spectroscopy on the iron pnictides and chalcogenides, which has exhibited a zero-bias conductance peak.
The signature of correlated electron materials (CEMs) is the coupling between spin, charge, orbital and lattice resulting in exotic functionality. This complexity is directly responsible for their ...tunability. We demonstrate here that the broken symmetry, through cubic to orthorhombic distortion in the lattice structure in a prototype manganite single crystal, La₀.₆₉Ca₀.₃₁MnO₃, leads to an anisotropic magneto-elastic response to an external field, and consequently to remarkable magneto-transport behavior. An anomalous anisotropic magnetoresistance (AMR) effect occurs close to the metal-insulator transition (MIT) in the system, showing a direct correlation with the anisotropic field-tuned MIT in the system and can be understood by means of a simple phenomenological model. A small crystalline anisotropy stimulates a "colossal" AMR near the MIT phase boundary of the system, thus revealing the intimate interplay between magneto-and electroniccrystalline couplings.
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