Strongly correlated electron systems

Noncollinear magnetic structure in U₂Pd₂In at high magnetic fields

We report an unexpected magnetic-field-driven magnetic structure in the 5f-electron Shastry-Sutherland system U2Pd2In. This phase develops at low temperatures from a noncollinear antiferromagnetic ground state above the critical field of 25.8 T applied along the a-axis. All U moments have a net magnetic moment in the direction of the applied field, described by a ferromagnetic propagation vector q_F = (0 0 0) and an antiferromagnetic component described by a propagation vector q_AF = (0 0.30 1/2) due to a modulation in the direction perpendicular to the applied field. This noncollinear magnetic structure is due to a complex competition between the single-ion anisotropy, the Dzyaloshinskii-Moryia interaction, and the external magnetic field.

K Prokeš, M Bartkowiak, DI Gorbunov, O Prokhnenko, O Rivin, P Smeibidl, Phys. Rev. Research 2 (2020) 013137

see also the associated Highlight Report

Stabilization of three-dimensional charge order in YBa₂Cu₃O_6+x via epitaxial growth

Incommensurate charge order (CO) has been identified as the leading competitor of high-temperature superconductivity in all major families of layered copper oxides, but the perplexing variety of CO states in different cuprates has confounded investigations of its impact on the transport and thermodynamic properties. The three-dimensional (3D) CO observed in YBa₂Cu₃O_6+x in high magnetic fields is of particular interest, because quantum transport measurements have revealed detailed information about the corresponding Fermi surface. Here we use resonant X-ray scattering to demonstrate 3D-CO in underdoped YBa₂Cu₃O_6+x films grown epitaxially on SrTiO₃ in the absence of magnetic fields. The resonance profiles indicate that Cu sites in the charge-reservoir layers participate in the CO state, and thus efficiently transmit CO correlations between adjacent CuO₂ bilayer units. The results offer fresh perspectives for experiments elucidating the influence of 3D-CO on the electronic properties of cuprates without the need to apply high magnetic fields.

M Bluschke, A Frano, E Schierle, D Putzky, F Ghorbani, R Ortiz, H Suzuki, G Christiani, G Logvenov, E Weschke, RJ Birgeneau, ED da Silva Neto, M Minola, S Blanco-Canosa, B Keimer, Nature Commun. 9 (2018) 2978 

Magnetic structure of $U{\left({}_{0.92}{}_{0.08}\right)}_2{\mathrm{Si}}_2$ in static magnetic fields up to 24 T

Neutron diffraction in high magnetic fields reveals a field-induced magnetic phase in a single crystal of $U{\left({\mathrm{Ru}}_{0.92}{\mathrm{Rh}}_{0.08}\right)}^{}{\mathrm{2Si}}_2$. Our neutron study, combined with high-field magnetization, shows that the magnetic phase above the first metamagnetic transition at ${\mu }_0{H}_{c1}=21.6$ T has an uncompensated commensurate antiferromagnetic structure with a propagation vector $Q_2=\left(\frac{}{}\mathrm{2/3,\; 0,}0\right)$ possessing two single-$Q$ domains. U moments of $1.45\left(9\right){\mu }_B$ directed along the $c$ axis are arranged in an up-up-down sequence propagating along the $a$ axis, in agreement with bulk measurements. The U magnetic form factor at high fields is consistent with both the $U^{3+}$ and $U^{4+}$ types. The low-field short-range order that emerges from pure ${\mathrm{URu}}_2{\mathrm{Si}}_2$ due to Rh doping is initially strengthened by the field but disappears in the field-induced phase. The tetragonal symmetry is preserved across the transition, but the $a$-axis lattice parameter increases already at low fields. Our results are in agreement with an itinerant electron model with $5f$ states forming bands pinned in the vicinity of the Fermi surface that is significantly reconstructed by the applied magnetic field.

K Prokeš, M Bartkowiak, O Rivin, O Prokhnenko, T Förster, S Gerischer, R Wahle, Y.-K. Huang, J. A. Mydosh, Phys. Rev B 96(R) (2017) 121117

K. Prokeš, T. Förster, Y.-K. Huang, J. A. Mydosh Phys. Rev. B 99 (2019) 045104, Open Access Version

Transfer of Magnetic Order and Anisotropy through Epitaxial Integration of 3d and 4f Spin Systems

Resonant x-ray scattering at the Dy M₅ and Ni L₃ absorption edges was used to probe the temperature and magnetic field dependence of magnetic order in epitaxial LaNiO₃ − DyScO₃ superlattices. For superlattices with 2 unit cell thick LaNiO₃ layers, a commensurate spiral state develops in the Ni spin system below 100 K. Upon cooling below T_ind = 18 K, Dy-Ni exchange interactions across the LaNiO₃ − DyScO₃ interfaces induce collinear magnetic order of interfacial Dy moments as well as a reorientation of the Ni spins to a direction dictated by the strong magnetocrystalline anisotropy of Dy. This transition is reversible by an external magnetic field of 3 T. Tailored exchange interactions between rare-earth and transition-metal ions thus open up new perspectives for the manipulation of spin structures in metal-oxide heterostructures and devices.

M Bluschke, A Frano, E Schierle, M Minola, M Hepting, G Christiani, G Logvenov, E Weschke, E Benckiser, B Keimer, Phys. Rev. Lett. 118 (2017) 207203

Doping dependent charge order correlations in electron-doped cuprates

Whereas charge order has been shown to be present in almost all known classes of hole-doped cuprate superconductors, evidence for this phenomenon in the case of electron doping was lacking. This gap in our understanding has now been closed by the observation of charge order in two electron-doped cuprate families, La_2-xCe_xCuO₄ (LCCO) and Nd_2-xCe_xCuO₄ (NCCO). The Figure displays a phase diagram that includes the region of charge order (data points), very much resembling the case of the hole-doped cuprates. These apparent similarities suggest a common origin for this type of instability in the Cu-O planes. Differences do however exist, application of an external magnetic field was not found to yield the substantial enhancement of charge order in electron doped cuprates in contrast to the enhancement typically found for hole-doped cuprates.

E. H. da Silva Neto, B. Yu, M. Minola, R. Sutarto,  E. Schierle, F. Boschini, M. Zonno, M. Bluschke, J. Higgins, Y. Li, G. Yu, E. Weschke, F. He, M. Le Tacon, R. L. Greene, M. Greven, G. A. Sawatzky, B. Keimer, A. Damascelli, Sci. Adv. 2 (2016) e1600782

Long-range charge-density-wave proximity effect at cuprate/manganate interfaces

We used resonant X-ray scattering in zero magnetic field to show that interfaces with the metallic ferromagnet La_2/3Ca_1/3MnO₃ greatly enhance CDW formation in the optimally doped high-temperature superconductor YBa₂Cu₃O_6+x (x~1), and that this effect persists over several tens of nanometres. The wavevector of the incommensurate CDW serves as an internal calibration standard of the charge carrier concentration, which allows us to rule out any significant influence of oxygen non-stoichiometry, and to attribute the observed phenomenon to a genuine electronic proximity effect. Long-range proximity effects induced by heterointerfaces thus offer a powerful method to stabilize the charge-density-wave state in the cuprates and, more generally, to manipulate the interplay between different collective phenomena in metal oxides.

A Frano, S Blanco-Canosa, E Schierle, Y Lu, M Wu, M Bluschke, M Minola, G Christiani, HU Habermeier, G Logvenov, Y Wang, PA van Aken, E Benckiser, E Weschke, M Le Tacon, B Keimer, Nat. Mater. 15 (2016) 831

See also the associated highlight report