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Integration of ferroelectric materials into novel technological applications requires low coercive field materials, and consequently, design strategies to reduce the ferroelectric switching barriers. In this first principles study, we show that biaxial strain, which has a strong effect on the ferroelectric ground states, can also be used to tune the switching barrier of hybrid improper ferroelectric Ruddlesden–Popper oxides. We identify the region of the strain-tolerance factor phase diagram where this intrinsic barrier is suppressed, and show that it can be explained in relation to strain-induced phase transitions to nonpolar phases.

Broken time-reversal symmetry in the absence of spin order indicates the presence of unusual phases such as orbital magnetism and loop currents 1 , 2 , 3 – 4 . The recently discovered kagome superconductors AV 3 Sb 5 (where A is K, Rb or Cs) 5 , 6 display an exotic charge-density-wave (CDW) state and have emerged as a strong candidate for materials hosting a loop current phase. The idea that the CDW breaks time-reversal symmetry 7 , 8 , 9 , 10 , 11 , 12 , 13 – 14 is, however, being intensely debated due to conflicting experimental data 15 , 16 – 17 . Here we use laser-coupled scanning tunnelling microscopy to study RbV 3 Sb 5 . By applying linearly polarized light along high-symmetry directions, we show that the relative intensities of the CDW peaks can be reversibly switched, implying a substantial electro-striction response, indicative of strong nonlinear electron–phonon coupling. A similar CDW intensity switching is observed with perpendicular magnetic fields, which implies an unusual piezo-magnetic response that, in turn, requires time-reversal symmetry breaking. We show that the simplest CDW that satisfies these constraints is an out-of-phase combination of bond charge order and loop currents that we dub a congruent CDW flux phase. Our laser scanning tunnelling microscopy data open the door to the possibility of dynamic optical control of complex quantum phenomenon in correlated materials. The charge-density-wave state in RbV 3 Sb 5 can be optically manipulated by applying linearly polarized light along high-symmetry directions, which demonstrates the potential of light as a control knob to manipulate complex quantum phenomena in correlated materials.

The Sabatier principle and the scaling relations have been widely used to search for and screen new catalysts in the field of catalysis. However, these powerful tools can also serve as limitations of catalyst control and breakthrough. To overcome this challenge, this work proposes an efficient method of studying catalyst control by support polarization from first-principles. The results demonstrate that the properties of catalysts are determined by support polarization, irrespective of the magnitude of spontaneous polarization of support. The approach enables elucidating the scaling relations between binding energies at various polarization values of support. Moreover, we observe the breakdown of scaling relations for the surface controlled by support polarization. By studying the surface electronic structure and decomposing the induced charge into contributions from different atoms and orbitals, we identify the inherent structural property of the interface that leads to the breaking of the scaling relations. Specifically, the displacements of the underlying oxide support impose its symmetry on the catalyst, causing the scaling relations between different adsorption sites to break. Can support polarisation introduce an extra degree of freedom in catalyst scaling relations? This research considers a computational approach for studying catalysts on polar supports and identifies the origin of broken scaling relations.

Few materials have been identified as high-performance transparent conductors in the visible regime (400–700 nm). Even fewer conductors are known to be transparent in ultraviolet (UV) spectrum, especially at wavelengths below 320 nm. Doped wide-bandgap semiconductors employed currently as UV transparent conductors have insufficient electrical conductivities, posing a significant challenge for achieving low resistance electrodes. Here, we propose SrNbO 3 as an alternative transparent conductor material with excellent performance not only in the visible, but also in the UV spectrum. The high transparency to UV light originates from energetic isolation of the conduction band, which shifts the absorption edge into the UV regime. The standard figure of merit measured for SrNbO 3 in the UV spectral range of 260–320 nm is on par with indium tin oxide in the visible, making SrNbO 3 an ideal electrode material in high-performance UV light emitting diodes relevant in sanitation application, food packaging, UV photochemotherapy, and biomolecule sensing. Optically transparent electrodes with high electrical conductance are essential for the implementation of optoelectronics, but current technology performs poorly in the ultraviolet regime. Here, SrNbO 3 is proposed as an alternative material due to its high figure of merit in the ultraviolet range.

Despite their highly anisotropic complex-oxidic nature, certain delafossite compounds ( e.g ., PdCoO 2 , PtCoO 2 ) are the most conductive oxides known, for reasons that remain poorly understood. Their room-temperature conductivity can exceed that of Au, while their low-temperature electronic mean-free-paths reach an astonishing 20 μm. It is widely accepted that these materials must be ultrapure to achieve this, although the methods for their growth (which produce only small crystals) are not typically capable of such. Here, we report a different approach to PdCoO 2 crystal growth, using chemical vapor transport methods to achieve order-of-magnitude gains in size, the highest structural qualities yet reported, and record residual resistivity ratios ( > 440). Nevertheless, detailed mass spectrometry measurements on these materials reveal that they are not ultrapure in a general sense, typically harboring 100s-of-parts-per-million impurity levels. Through quantitative crystal-chemical analyses, we resolve this apparent dichotomy, showing that the vast majority of impurities are forced to reside in the Co-O octahedral layers, leaving the conductive Pd sheets highly pure (∼1 ppm impurity concentrations). These purities are shown to be in quantitative agreement with measured residual resistivities. We thus conclude that a sublattice purification mechanism is essential to the ultrahigh low-temperature conductivity and mean-free-path of metallic delafossites. Certain delafossite materials are the most conductive oxides known, for poorly understood reasons. This work elucidates this finding by uncovering a sublattice purification mechanism that enables ultrapure conductive planes even in impure crystals.

Symmetry plays an important role in determining the physical properties in condensed matter physics, as the symmetry operations of any physical property must include the symmetry operations of the point group of the crystal. As a consequence, crystallographic polarity and chirality are expected to have an impact on the Cooper pairing in a superconductor. While superconductivity with crystallographic polarity and chirality have both been found in a few crystalline phases separately; however, their coexistence and material realizations have not been studied. Here, by utilizing transport, Raman scattering, and transmission electron microscopy, we unveil a unique realization of superconductivity in single-crystalline Mo 3 Al 2 C (superconducting T c =8 K) with a polar charge-density-wave phase and well-defined crystallographic chirality. We show that the intriguing charge density wave order leads to a noncentrosymmetric-nonpolar to polar transition below T *=155K via breaking both the translational and rotational symmetries. Superconductivity emerges in this polar and chiral crystal structure below T c =8 K. Our results establish that Mo 3 Al 2 C is a superconductor with crystallographic polarity and chirality simultaneously, and motivate future studies of unconventional superconductivity in this category. The coexistence of crystallographic polarity and chirality is rare in a superconductor. Here, the authors establish that Mo 3 Al 2 C is a superconductor with crystallographic polarity and chirality simultaneously.

Advancements in materials synthesis have been key to unveil the quantum nature of electronic properties in solids by providing experimental reference points for a correct theoretical description. Here, we report hidden transport phenomena emerging in the ultraclean limit of the archetypical correlated electron system SrVO 3 . The low temperature, low magnetic field transport was found to be dominated by anisotropic scattering, whereas, at high temperature, we find a yet undiscovered phase that exhibits clear deviations from the expected Landau Fermi liquid, which is reminiscent of strange-metal physics in materials on the verge of a Mott transition. Further, the high sample purity enabled accessing the high magnetic field transport regime at low temperature, which revealed an anomalously high Hall coefficient. Taken with the strong anisotropic scattering, this presents a more complex picture of SrVO 3 that deviates from a simple Landau Fermi liquid. These hidden transport anomalies observed in the ultraclean limit prompt a theoretical reexamination of this canonical correlated electron system beyond the Landau Fermi liquid paradigm, and more generally serves as an experimental basis to refine theoretical methods to capture such nontrivial experimental consequences emerging in correlated electron systems. A correlated material SrVO 3 has been considered to be a Fermi liquid, however previous studies have been limited to disordered samples. Here the authors study transport in ultraclean films of SrVO 3 , finding deviations from the Fermi liquid picture.

Creating 1D or 2D extended defects in thin films that propagate throughout the film thickness enables engineering nanoscale materials with anisotropic properties governed by these defects. Performing defect engineering of thin films with location specificity facilitates new nanoscale device architectures that harness the unique properties of these anisotropic extended defects. Here we demonstrate that, by combining Ga focused ion-beam (FIB) exposure and subsequent heat treatment, it is possible to pattern nanoscale structural perturbations on the substrate surface that promote nucleation and propagation of extended defects in thin films epitaxially grown on these substrates. Using SrTiO 3 as a substrate for growing perovskite BaSnO 3 and SrSnO 3 thin films, we demonstrate engineering ultra-high densities of threading 1D dislocations and 2D Ruddlesden-Popper faults with nanometer-level location specificity limited only by the resolution of the patterning Ga ion-beam of the FIB. Given the versatility of this method, it can be applied to different substrates and films, serving as a flexible means of defect-driven material engineering. A method of nanometre-level patterning of high-density extended 1D and 2D defects in thin films of perovskite oxides is developed.

The nodal-line semiconductor Mn 3 Si 2 Te 6 is generating enormous excitment due to the recent discovery of a field-driven insulator-to-metal transition and associated colossal magnetoresistance as well as evidence for a new type of quantum state involving chiral orbital currents. Strikingly, these qualities persist even in the absence of traditional Jahn-Teller distortions and double-exchange mechanisms, raising questions about exactly how and why magnetoresistance occurs along with conjecture as to the likely signatures of loop currents. Here, we measured the infrared response of Mn 3 Si 2 Te 6 across the magnetic ordering and field-induced insulator-to-metal transitions in order to explore colossal magnetoresistance in the absence of Jahn-Teller and double-exchange interactions. Rather than a traditional metal with screened phonons, the field-driven insulator-to-metal transition leads to a weakly metallic state with localized carriers. Our spectral data are fit by a percolation model, providing evidence for electronic inhomogeneity and phase separation. Modeling also reveals a frequency-dependent threshold field for carriers contributing to colossal magnetoresistance which we discuss in terms of polaron formation, chiral orbital currents, and short-range spin fluctuations. These findings enhance the understanding of insulator-to-metal transitions in new settings and open the door to the design of unconventional colossal magnetoresistant materials. Field-driven insulator-to-metal transition and associated colossal magnetoresistance have been reported in the magnetic nodal-line semiconductor Mn 3 Si 2 Te 6 . Gu et al. measure infrared response across magnetic ordering and the transition, revealing a weakly metallic state instead of a traditional metallic state.

Kagome vanadates A V 3 Sb 5 display unusual low-temperature electronic properties including charge density waves (CDW), whose microscopic origin remains unsettled. Recently, CDW order has been discovered in a new material ScV 6 Sn 6 , providing an opportunity to explore whether the onset of CDW leads to unusual electronic properties. Here, we study this question using angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM). The ARPES measurements show minimal changes to the electronic structure after the onset of CDW. However, STM quasiparticle interference (QPI) measurements show strong dispersing features related to the CDW ordering vectors. A plausible explanation is the presence of a strong momentum-dependent scattering potential peaked at the CDW wavevector, associated with the existence of competing CDW instabilities. Our STM results further indicate that the bands most affected by the CDW are near vHS, analogous to the case of A V 3 Sb 5 despite very different CDW wavevectors. The authors use angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM) to study the charge density wave (CDW) in the kagome material ScV 6 Sn 6 . The ARPES data shows minimal changes to the electronic structure in the CDW state, while STM quasiparticle interference measurements imply a strong reconstruction of the electronic structure in the CDW state.