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Université de Fribourg

Influence of La and Mn vacancies on the electronic and magnetic properties of LaMnO₃ thin films grown by pulsed laser deposition

Marozau, Ivan ; Das, Proloy T. ; Döbeli, Max ; Storey, James G. ; Uribe-Laverde, Miguel A. ; Das, Saikat ; Wang, Chennan ; Rössle, Matthias ; Bernhard, Christian

In: Physical Review B, 2014, vol. 89, no. 17, p. 174422

With pulsed laser deposition, we have grown c axis oriented thin films of the nominal composition LaMnO3 (LMO) on LSAT(001) substrates. We find that, depending on the oxygen background pressure during growth, the LMO films contain sizeable amounts of La and/or Mn vacancies that strongly influence their electronic and magnetic properties. Specifically, we show that the Mn/La ratio can be...

Université de Fribourg

Optical probe of ferroelectric order in bulk and thin-film perovskite titanates

Rössle, Matthias ; Wang, Chen Nan ; Maršík, Premysl ; Yazdi-Rizi, M. ; Kim, Kyung Wan ; Dubroka, Adam ; Marozau, Ivan ; Schneider, C. W. ; Humlíček, J. ; Baeriswyl, Dionys ; Bernhard, Christian

In: Physical Review B, 2013, vol. 88, no. 10, p. 104110

We have measured the temperature dependence of the direct band gap Eg in SrTiO₃ and BaTiO₃ and related materials with quantum-paraelectric and ferroelectric properties using optical spectroscopy. We show that Eg exhibits an anomalous temperature dependence with pronounced changes in the vicinity of the ferroelectric transition that can be...

Université de Fribourg

Electric-Field-Induced Polar Order and Localization of the Confined Electrons in LaAlO₃/SrTiO₃ Heterostructures

Rössle, Matthias ; Kim, Kyung Wan ; Dubroka, Adam ; Maršík, Premysl ; Wang, Chen Nan ; Jany, R. ; Richter, C. ; Mannhart, J. ; Schneider, C. W. ; Frano, A. ; Wochner, P. ; Lu, Y. ; Keimer, B. ; Shukla, D. K. ; Strempfer, J. ; Bernhard, Christian

In: Physical Review Letters, 2013, vol. 110, no. 13, p. 136805

With ellipsometry, x-ray diffraction, and resistance measurements we investigated the electric-field effect on the confined electrons at the LaAlO₃/SrTiO₃ interface. We obtained evidence that the localization of the electrons at negative gate voltage is induced, or at least enhanced, by a polar phase transition in SrTiO₃ which strongly reduces the lattice polarizability and the subsequent...

Université de Fribourg

Macroscopic phase segregation in superconducting K0.73Fe1.67Se₂ as seen by muon spin rotation and infrared spectroscopy

Wang, Chen Nan ; Maršik, Premysl ; Schuster, Roman ; Dubroka, Adam ; Rössle, Matthias ; Niedermayer, Ch. ; Varma, G. D. ; Wang, A. F. ; Chen, X. H. ; Wolf, T. ; Bernhard, Christian

In: Physical Review B - Condensed matter and materials physics, 2012, vol. 85, no. 21, p. 214503

Using muon spin rotation and infrared spectroscopy, we investigated the recently discovered superconductor K0.73Fe1.67Se₂ with Tc≈32 K. We show that the combined data can be consistently described in terms of a macroscopically phase-segregated state with a matrix of ∼88% volume fraction that is insulating and strongly magnetic and inclusions with an ∼12%...

Université de Fribourg

Evidence of a Precursor Superconducting Phase at Temperatures as High as 180 K in RBa₂Cu₃O7-δ (R=Y,Gd,Eu) Superconducting Crystals from Infrared Spectroscopy

Dubroka, Adam ; Rössle, Matthias ; Kim, Kyung Wan ; Malik, Vivek Kumar ; Munzar, Dominik ; Basov, D. N. ; Schafgans, A. A. ; Moon, S. J. ; Lin, C. T. ; Haug, D. ; Hinkov, V. ; Keimer, B. ; Wolf, Th. ; Storey, J. G. ; Tallon, Jeffery L. ; Bernhard, Christian

In: Physical Review Letters, 2011, vol. 106, no. 4, p. 047006

We show that a multilayer analysis of the infrared c-axis response of RBa₂Cu₃O7-δ (R=Y,Gd,Eu) provides important new information about the anomalous normal-state properties of underdoped cuprate high temperature superconductors. In addition to competing correlations which give rise to a pseudogap that depletes the low-energy electronic states below...