My thesis presents a resonant inelastic and elastic X-ray scattering (RIXS/REXS) study on epi-taxial YBa2Cu3O7/Nd1-x(Ca1-ySry)xMnO3 heterostructures (NYN). It shows that the Cu-charge density wave (CDW) can be strongly manipulated by controlling the hole doping and tolerance factor of Nd1-x(Ca1-ySry)xMnO3, i.e. by changing x and y.
At x=0.35 we observe a quasi-2D Cu-CDW order with dx2-y2 orbital character that resembles the one that is commonly found in underdoped bulk YBCO. The strength of the corresponding Bragg peak at Q||0.3 r.l.u. gets strongly enhanced as the tolerance factor of the manganite lay-ers1 is decreased and its CE-type antiferromagnetic and charge/orbital ordered (COO) is rein-forced. Eventually, it becomes even stronger than in bulk YBCO.
For NYN multilayers with x=0.5 we discovered a new kind of Cu-based charge order with a strong Bragg peak at Q||=0.1 r.l.u. and an unusually large correlation length of about 40 nm 3. This Cu-based charge order seems to be of a dz2 type, instead of the usual dx2-y2 type, and persists well above 170K. Its origin is presently not understood, but seems to be rooted in the particular prop-erties of this cuprate/manganite interface. Additional, X-ray absorption spectroscopy (XAS) data reveal indeed that a significant charge transfer and orbital reconstruction occurs at this interface that may exhibit a modulation along the lateral direction.
Finally, we studied how the Cu-CDW order at x=0.35 is affected by a large magnetic field up to 6.9 Tesla. Unlike the COO of the manganite layers, which is strongly suppressed by such a large magnetic field, we find that the Cu-CDW exhibits an anomalous enhancement above 6T 2. Addi-tional magneto-transport measurements indicate that this enhancement of the Cu-CDW is ac-companied by a crossover in the dynamical properties of the domain boundaries of the Mn-COO, which become more mobile and flexible above 6 Tesla. Our findings thus point towards an indi-rect coupling mechanism between the Cu-CDW and Mn-COO that involves the domain bounda-ries of the Mn-COO2.
While further studies are required to fully understand this interfacial coupling mechanism(s), the possibility of tuning the Cu-CDW holds great prospects for studying its relationship with high temperature superconductivity and hopefully, for future quantum devices.
 E. Perret et al., Coupled Cu and Mn charge and orbital orders in YBa2Cu3O7/Nd0.65(Ca1-ySry)0.35MnO3 multi-layers, Communications Physics, 1, Article number: 45 (2018); DOI: 10.1038/s42005-018-0046-z.
 R. Gaina et al., Magnetic-field dependence of the copper charge density wave order in a YBa2Cu3O7/ Nd0.65(Ca0.7Sr0.3)0.35MnO3 superlattice, manuscript under submission
|Where?||PER 08 2.73
Chemin du Musée 3
|speaker||Roxana Capu Gaina
présentation publique de thèse de Doctorat
|Contact||Département de physique