Saving energy one byte at a time by Can Onur Avci (ICMAB-CSIC)
European Researchers’ Night
Friday, 30/09/2022, 7:30 pm at CosmoCaixa Auditorium for the Late Show: Research on Stage
Tag: 2022
Talk at the International Workshop on Oxide Electronics (WOE28)
Gervasi Herranz delivers a talk at the International Workshop on Oxide Electronics (https://iwoe28.events.yale.edu/), Portland, Maine, USA: The talk is entitled “Light-matter interactions modulated by electron-lattice coupling in transition metal oxides” and is held on Wednesday 5 October 2022 (1oh15am).
Pep Fontcuberta delivers an Invited Lecture at SPIN 2022
Pep Fontcuberta delivers an Invited Lecture on ” Electron-phonon and spin-orbit couplings in early-transition metal in conducting oxides” at SPIN 2022 (Bariloche, Argentina))
Pep Fontcuberta delivers a Lecture at Magnetism and Magnetic Materials Conferences MMM 2022
Pep Fontcuberta delivers a Lecture on “Direct exchange-interactions boost magnetic frustration and a large zero-point entropy in the novel MnTa2N4 diamond-lattice spinel” at Magnetism and Magnetic Materials Conferences MMM 2022 (MInnesota , USA)
Pep Fontcuberta at Nit de la Recerca 2022
Pep Fontcuberta participa a la Nit de la Recerca 2022 ( Dijous 29 de Setembre 2022) amb una xerrada sobre:
“La Màgia de la LLum i la Conversió Fotovoltaica”
Dr. Kyle Shen at MULFOX
Dr. Kyle Shen, director of Laboratory of Atomic & Solid State Physics, Cornell University, arrives to MULFOX-ICMAB for a Sabatical stay of 12 months.
Gervasi Herranz delivers a talk at the International Workshop on Oxide Electronics
Gervasi Herranz delivers a talk at the International Workshop on Oxide Electronics (https://iwoe28.events.yale.edu/), Portland, Maine, USA: The talk is entitled “Light-matter interactions modulated by electron-lattice coupling in transition metal oxides” and is held on Wednesday 5 October 2022 (1oh15am).
Congratulations Dr. Tingfeng Song, new graduate!
The PhD Committee that evaluated the Thesis was formed by José Francisco Rivadulla Fernández, Universidad Santiago de Compostela (President), Eric Langenberg Pérez, Universitat de Barcelona (Secretary) and Uwe Schroeder, Namlab, Germany (Vocal).
Doctor Tingfeng Song’s PhD thesis was part of the PhD Programme in Materials Science from the Universitat Autònoma de Barcelona (UAB).
Alejandro Sánchez Miñarro delivers a talk at “QUOROM 7 conference”
Alejandro Sánchez Miñarro delivers the talk “Light-matter interactions and spin-orbit coupling in solids” at the QUOROM 7 conference. The seminar is online and is held on September 15th (11h15am).
Electrical characterization and extraction of activation energies of the defect states in the LaAlO3/SrTiO3 heterostructure
Yoann Lechaux, Yu Chen; Albert Minj, Florencio Sánchez, Gervasi Herranz, Laurence Méchin, Bruno Guillet
In this work, we study the electronic properties of defects in the LaAlO3/SrTiO3 heterostructure, which is known to host a high mobility two-dimensional electron gas (2DEG) at the interface. This 2DEG also shows photoconductance, which could be related to defects that act as deep center trapping and releasing carriers by interaction with light. This phenomenon has raised an interest for the identification of deep energy levels in the LaAlO3/SrTiO3 heterostructure. We have studied the defect state properties using electrical characterization such as capacitance–voltage (C–V), current–voltage (I–V) measurements, and deep-level transient Fourier spectroscopy (DLTFS). From C–V and I–V analyses, a hysteresis was observed indicating an effect of mobile charges in the LaAlO3. Using DLTFS, we identify three defect states located at around 0.17 eV below conduction band and at 0.23 and 0.26 eV above the valence band. These defect states were attributed to defects in SrTiO3 such as strontium vacancies or titanium vacancies. We identify a fourth defect state having an energy of about 0.69 eV below the conduction band that could be related to oxygen vacancies in LaAlO3 or in SrTiO3. In addition, the observation of an effect of the electric field with DLTFS indicated that oxygen vacancies might be involved in Fowler–Nordheim or trap-assisted tunneling through the LaAlO3 layer.
Alejandro Sánchez Miñarro delivers a talk at “XXXVIII Reunión Bienal de la Real Sociedad Española de Física”
Alejandro Sánchez Miñarro delivers the talk “Spin-orbit mixed states in an electromagnetic field” at the Symposium “S15 Nuevas fronteras y retos en magnetismo (CEMAG-IEEE Magnetics)” of the XXXVIII Reunión Bienal de la Real Sociedad Española de Física Murcia, 11 -15 July 2022
MnTa2N4: A Ternary Nitride Spinel with a Strong Magnetic Frustration
Rafael Trócoli, Carlos Frontera, Judith Oró-Solé, Clemens Ritter, Pere Alemany, Enric Canadell, M. Rosa Palacín, Josep Fontcuberta, and Amparo Fuertes
Chem. Mater. 2022, 34, 13, 6098–6107 (2022); DOI:doi.org/10.1021/acs.chemmater.2c01240
Abstract
Magnetic frustration results from competing magnetic interactions and leads to unusual ground states, ranging from non-collinear magnetic orders to spin liquids (SLs), opening the path to new physics and emerging properties. We report the engineered magnetic interaction design and synthesis of the new ternary nitride MnTa2N4 with a normal spinel structure, where the magnetic cations Mn2+ occupy exclusively the tetrahedral sites forming a diamond lattice.
Although the magnetic interactions are strongly antiferromagnetic (θCW ≈ −140 K), a long-range magnetic order is not established, but a smooth magnetic anomaly is observed at T* ≈ 5.1 K, fingerprinting a large magnetic frustration. A short-range helicoidal magnetic order emerges at low temperatures. The ordered moment is ≈70% of the expected magnetic moment of Mn2+ ions and a large part (≈28%) of the spin entropy remains at 400 mK, signaling the coexistence of a helicoidal order with spin-glass-like or SL textures. First-principles calculations unveil an unexpected large direct Mn–Mn exchange interaction that balances the superexchange and accounts for the magnetic frustration. These findings open new avenues toward the design of quantum materials.
Dynamic control of octahedral rotation in perovskites by defect engineering
Jiahui Jia, Xu He, Arsalan Akhtar, Gervasi Herranz, and Miguel Pruneda
Phys. Rev. B 105, 224112 (2022); DOI:doi.org/10.1103/PhysRevB.105.224112
Abstract
Engineering oxygen octahedra rotation patterns in ABO3 perovskites is a powerful route to design functional materials. Here we propose a strategy that exploits point defects that create local electric dipoles and couple to the oxygen sublattice, enabling direct actuation on the rotational degrees of freedom. This approach, which relies on substituting an A site with a smaller ion, paves a way to couple dynamically octahedra rotations to external electric fields.
A common antisite defect, AlLa, in rhombohedral LaAlO3 is taken as a prototype to validate the idea, with atomistic density functional theory calculations supported with an effective lattice model to simulate the dynamics of switching of the local rotational degrees of freedom to long distances. Our simulations provide an insight of the main parameters that govern the operation of the proposed mechanism, and allow to define guidelines for screening other systems where this approach could be used for tuning the properties of the host material.
Bulk photovoltaic effect modulated by ferroelectric polarization back-switching
Yunwei Sheng, Ignasi Fina, Marin Gospodinov, and Josep Fontcuberta
Appl. Phys. Lett. 120, 242901 (2022); DOI:doi.org/10.1063/5.0094837
Abstract
Short-circuit photocurrent due to bulk photovoltaic effect displays an oscillatory dependence on the polarization state of light. Here, we explore how the ferroelectric polarization direction in h-LuMnO3 crystals affects the oscillating short-circuit photocurrent. It is shown that after prepoling the crystal at saturation, at remanence, the direction and amplitude of photocurrent oscillations are no longer dictated by prepoling voltage but are largely modulated by polarization back-switching, here ruled by the imprint field.
Thus, the light polarization dependence of photocurrent is also ruled by the imprint field. The impact of these effects on the determination of the Glass coefficients of the material is discussed.
Voltage-driven strain-mediated modulation of exchange bias in Ir20Mn80/Fe80Ga20/Ta/⟨011⟩-oriented PMN-32PT heterostructures
E. Demirci, J. de Rojas, A. Quintana, I. Fina, E. Menéndez, and J. Sort
Appl. Phys. Lett. 121, 081904 (2022); DOI:doi.org/10.1063/5.0091231
Abstract
Manipulation of exchange bias with electric field is appealing to boost energy efficiency in spintronic devices. Here, this effect is shown at room temperature in Ir20Mn80/Fe80Ga20/Ta layers grown onto ⟨011⟩-oriented PMN-32PT single crystals. After magnetic field-cooling (FC) along the [01-1] and [100] in-plane directions of PMN-32PT and upon allowing the system to relax through consecutive hysteresis loops (training effect), the exchange bias field (HEB) is measured under the action of voltage (out-of-plane poling). Depending on the applied voltage (magnitude and sign), HEB can either increase or decrease with respect to its value at 0 V. The relative variations of HEB are 24% and 5.5% after FC along the [01-1] and [100] directions, respectively.
These results stem from strain-mediated magnetoelectric coupling. The applied electric field causes changes in the coercivity and the squareness ratio of the films, suggesting a reorientation of the effective magnetic easy axis in Fe80Ga20. However, larger HEB values are observed when the squareness ratio is lower. It is claimed that the effect of voltage is equivalent to an in-plane component of an applied magnetic field oriented perpendicular to the cooling field direction. Perpendicular in-plane magnetic fields have been shown to induce an increase in exchange bias in some ferromagnetic/antiferromagnetic systems due to partial recovery of the untrained antiferromagnetic state. Remarkably, here, this effect is directly induced with voltage, therefore enhancing energy efficiency.
Two-gap s±-wave superconductivity at an oxide interface
G. Singh, G. Venditti, G. Saiz, G. Herranz, F. Sánchez, A. Jouan, C. Feuillet-Palma, J. Lesueur, M. Grilli, S. Caprara, and N. Bergeal
Phys. Rev. B 105, 064512 (2022); DOI:doi.org/10.1103/PhysRevB.105.064512
Abstract
After half a century of debate, superconductivity in doped SrTiO3 has come to the fore again with the discovery of interfacial superconductivity in the LaAlO3/SrTiO3 heterostructures. While these interfaces share the interesting properties of bulk SrTiO3 , quantum confinement generates a complex band structure involving bands with different orbital symmetries whose occupancy is tunable by electrostating doping.
Multigap superconductivity has been predicted to emerge in LaAlO3/SrTiO3 at large doping, with a Bose-Einstein condensation character at the Lifshtiz transition. In this article, we report on the measurement of the upper critical magnetic field Hc2 of superconducting (110)-oriented LaAlO3/SrTiO3 heterostructures and evidence a two-gap superconducting regime at high doping. Our results are quantitatively explained by a theoretical model based on the formation of an unconventional s±-wave superconducting state with a repulsive coupling between the two condensates.
Enhanced electroresistance endurance of capped Hf0.5Zr0.5O2 ultrathin epitaxial tunnel barriers
Xiao Long, Huan Tan, Saúl Estandía, Jaume Gazquez, Florencio Sánchez, Ignasi Fina and Josep Fontcuberta
APL Materials 10, 031114 (2022); DOI:doi.org/10.1063/5.0076865
Abstract
Electroresistance in ultrathin Hf0.5Zr0.5O2 (HZO) films is pivotal toward the implementation of hafnia-based ferroelectrics in electronics. Here, we show that the electroresistance yield and endurance of large capacitors (∼314 µm2) of epitaxial HZO films only 2.2 nm thick grown on SrTiO3 or GdScO3 can be improved using 1 nm SrTiO3 capping layers. It is argued that the main role of the capping layer is to minimize charge transport along grain boundaries, and, thus, a similar strategy can be explored in polycrystalline films
Electroresistance in ultrathin Hf0.5Zr0.5O2 (HZO) films is pivotal toward the implementation of hafnia-based ferroelectrics in electronics. Here, we show that the electroresistance yield and endurance of large capacitors (∼314 µm2) of epitaxial HZO films only 2.2 nm thick grown on SrTiO3 or GdScO3 can be improved using 1 nm SrTiO3 capping layers. It is argued that the main role of the capping layer is to minimize charge transport along grain boundaries, and, thus, a similar strategy can be explored in polycrystalline films
Impact of non-ferroelectric phases on switching dynamics in epitaxial ferroelectric Hf0.5Zr0.5O2 films
Tingfeng Song, Florencio Sánchez, and Ignasi Fina
APL Materials 10, 031108 (2022); DOI:doi.org/10.1063/5.0083661
Abstract
Determining the switching speed and mechanisms in ferroelectric HfO2 is essential for applications. Switching dynamics in orthorhombic epitaxial ferroelectric Hf0.5Zr0.5O2 films with either significant or negligible presence of monoclinic paraelectric phase is characterized.
Switching spectroscopy reveals that the polarization dynamics in pure orthorhombic ferroelectric phase films can be modeled by the Kolmogorov–Avrami–Ishibashi mechanism with large characteristic time (≈1 µs), which is shortened in fatigued junctions. The long switching time indicates that non-archetypical switching mechanisms occur and that ionic motion or other extrinsic contributions might be at play. Films containing a higher amount of paraelectric monoclinic phase show a shorter switching time of 69 ns, even in pristine state, for applied electric field parallel to the imprint field, enabling synaptic-like activity using fast electric stimuli. Thus, the presence of defects or paraelectric phase is found to improve the switching speed, contrary to what one can expect a priori.
Josep Fontcuberta Key note Lecture at “Materials for Oxide Electronics”
Josep Fontcuberta delivers an opening “Key note Lecture” at the kick-off workshop “Materials for Oxide Electronics” at IKZ-Berlin (Leibniz-Institut für Kristallzüchtung on 10th February 2022 (https://www.ikz-berlin.de/en/about-us/events/)
Improved polarization and endurance in ferroelectric Hf0.5Zr0.5O2 films on SrTiO3(110)
Tingfeng Song, Huan Tan, Saúl Estandía, Jaume Gàzquez, Martí Gich, Nico Dix, Ignasi Fina and Florencio Sánchez
Nanoscale, 2022,14, 2337-2343 (2022); DOI:10.1039/D1NR06983G
Abstract
The metastable orthorhombic phase of Hf0.5Zr0.5O2 (HZO) can be stabilized in thin films on La0.67Sr0.33MnO3 (LSMO) buffered (001)-oriented SrTiO3 (STO) by intriguing epitaxy that results in (111)-HZO oriented growth and robust ferroelectric properties. Here, we show that the orthorhombic phase can also be epitaxially stabilized on LSMO/STO(110), presenting the same out-of-plane (111) orientation but a different distribution of the in-plane crystalline domains.
The remanent polarization of HZO films with a thickness of less than 7 nm on LSMO/STO(110) is 33 μC cm−3, which corresponds to a 50% improvement over equivalent films on LSMO/STO(001). Furthermore, HZO on LSMO/STO(110) presents higher endurance, switchable polarization is still observed up to 4 × 1010 cycles, and retention of more than 10 years. These results demonstrate that tuning the epitaxial growth of ferroelectric HfO2, here using STO(110) substrates, allows the improvement of functional properties of relevance for memory applications.
Tingfeng Song
Working on ferroelectric thin films under the supervision of Dr. Florencio Sánchez. Starting on 15/11/2018
Yunwei Sheng
Yunwei Sheng joint our team and initiate their PhD work on October 1st, 2018. Welcome !
Hello, I am Yunwei Sheng, from China University of Geosciences. Now I have joined the group of Multifunctional Oxides and Complex Structures to do my PhD work on ferroelectric films.
See you around!