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Seminarios y Eventos

Seminars and Events

Joint Seminar Series ICMM+IFIMAC Condensed Matter @Cantoblanco

ICMM Coordinators: Elsa Prada, Mara Jos Caldern, Ramn Aguado, Sigmund Kohler

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24 de junio de 2021, 12:00 h. Sala de Seminarios, 182

Scattering and thermalization: wave-particle duality hits quantum thermodynamics

Juan MR Parrondo
Universidad Complutense de Madrid

An interesting class of open quantum systems is defined by the so-called repeated interaction scheme, where the system interacts sequentially with small and fresh subsystems or units coming from the reservoir. The interaction is unitary and relatively easy to analyze. However, it must be switched on and off, and this action introduces or extracts energy in many cases of interest, performing work and preventing thermalization. As a consequence, the repeated interaction scheme cannot be used to model thermostats in quantum thermodynamics.

We overcome this problem by considering collisional reservoirs where the units are particles that collide with the system. The whole setup is autonomous and, if the units are in thermal equilibrium, the work to switch on and off the interaction becomes heat, and thermalization is recovered in most cases. However, to induce well-defined collisions, one needs to bombard the system with wave packets of finite width, and, surprisingly, this finite width can keep and even generate coherences in the system in some situations. These results prompt a fundamental question for quantum thermodynamics: what comes out by effusion from a container with a quantum gas in thermal equilibrium: waves or particles?

17 de junio de 2021, 12:00 h. online

NanoSQUID magnetometry of multishaped individual nanoparticles

Mara Jos Martnez-Prez
INMA-CSIC, Universidad de Zaragoza, Spain

Performing magnetization studies on individual nanoparticles is a highly demanding task, especially when measurements need to be carried out under large sweeping magnetic fields or variable temperature. Yet, characterization under varying ambient conditions is paramount in order to fully understand the magnetic behavior of these objects, e.g., the formation of non-uniform states, the mechanisms leading to magnetization reversal, thermal stability or damping processes. This, in turn, is necessary for the integration of magnetic nanoparticles and nanowires into useful devices, e.g., spin-valves, racetrack memories or magnetic tip probes. I will show that YBa2Cu3O7 nano Superconducting Quantum Interference Devices (YBCO nanoSQUIDs) are particularly well suited for this task. I will present measurements of individual nanoparticles of soft magnetic materials with different shapes (nanodots, nanodiscs and nanowires) performed under sweeping magnetic fields (up to ~ 500 mT) and variable temperature (1.4 - 80 K). Measurements underscore the intrinsic differences between samples owing to their shape and the presence (or absence) of magnetocrystalline anisotropy. This also serves to distinguish the mechanisms leading to magnetization reversal mediated by, i.e., nucleation/propagation of domain walls or nucleation/annihilation of magnetic vortices, shedding light on the nature and magnitude of the energy barriers separating different magnetic states, nucleation/annihilation fields and switching times.

10 de junio de 2021, 12:00 h. online

Quasinormal modes, Purcell factors and corrected Fermis golden rule for spontaneous emission in absorptive and amplifying media

Stephen Hughes
Queens University, Canada

Coupled loss and gain resonators can exhibit parity-time symmetry and exceptional points, and find rich applications in sensing, lasing, and quantum optics. This talk first presents an intuitive and powerful quasinormal mode theory for coupled loss and gain resonators, including a quantitatively accurate coupled mode theory [1]. As an application of the theory, we demonstrate extremely rich spectral lineshapes and Purcell factors for coupled loss-gain microdisk cavities. We then point out a fundamental flaw in currently adopted theories of spontaneous emission in such media and present a corrected Fermi s golden rule, one that requires a fully quantum mechanical description [2].

[1] Juanjuan Ren, Sebastian Franke, Stephen Hughes, Quasinormal modes and Purcell factors of coupled loss and gain resonators near an exceptional point, e-print: arXiv:2101.07633 (2021)

[2] Sebastian Franke, Juanjuan Ren, Marten Richter, Andreas Knorr, Stephen Hughes, Fermis golden rule for spontaneous emission in absorptive and amplifying media, e-print: arXiv:2102.13015 (2021); Phys Rev Lett, in-press

03 de junio de 2021, 12:00 h. online

Hybrid nanowires, dots and bound states - elements for quantum devices

Jesper Nygard
Niels Bohr Institute, University of Copenhagen

Recent years superconductor-semiconductor hybrid materials have been established as an essential platform for quantum devices, notably used in the search for Majorana zero modes and other bound states that may serve as qubits. In this talk we will look beneath the surface of these nanowire devices and discuss recent advances in materials science and nanofabrication. In particular we will see how in-situ fabrication and new superconductors have been implemented, expanding the available parameter space for hybrid quantum devices.

T. Kanne et al., Epitaxial Pb on InAs nanowires for quantum devices, Nature Nanotechnology (2021)

D. Carrad et al., Shadow Epitaxy for In Situ Growth of Generic Semiconductor/Superconductor Hybrids, Advanced Materials (2020)

T. Kanne et al., Double nanowires for hybrid quantum devices, arXiv:2103.13938

27 de mayo de 2021, 12:00 h. online

Electronic structure of the superconducting layered nickelates

Victor Pardo
Universidade de Santiago de Compostela, Spain

For years, various systems have been considered cuprate analogues and superconductivity has been pursued profusely in some of them. Finally, in 2020 superconductivity was found in infinite-layered nickelates[1], that share some important structural and electronic-structure features with superconducting cuprates.

Infinite-layer nickelates are nominally Ni+: d9 systems, but they are metallic and are largely self-doped (the actual filling of the d band is less than 9 electrons). Our calculations[2] show that doping with Sr modifies the self-doping effect, leading to a situation more similar to that in the cuprates. E.g. Ni2+ dopants are non-magnetic, just like the Zhang-Rice singlets in the cuprates.

Although LaNiO2 or NdNiO2 are non-magnetic metals, an antiferromagnetic insulating phase exists in the phase diagram of the superconducting cuprates when the dimensionality of the system is reduced. This can be done in various ways, as our ab initio calculations show[3].

Infinite-layer nickelates are part of a more general family of layered nickelates with formula Rn+1NinO2n+2, that span different doping regimes of the Ni d band (increasing as n increases). The confinement of the NiO2 layers introduces some differences in terms of the peculiar occupation of the Ni dz2 orbitals and also changing the magnetic properties[4,5].

It has been found[6] that Pr4Ni3O8 presents a large orbital polarization of the d manifold, resembling the electronic structure of the cuprates. Electron-doping this system[7] would recover the electronic structure of the parent phase of the cuprates, showing a promising way to search for superconductivity within this series.

[1] Danfeng Li et al., Nature 572, 624 (2019).

[2] J. Krishna et al., Phys. Rev. B 102, 224506 (2020).

[3] V. Pardo, A.S. Botana, arxiv/2012.02711 (2020).

[4] V. Pardo, W.E. Pickett, Phys. Rev. Lett. 105, 266402 (2010).

[5] A.S. Botana, V. Pardo et al., Phys. Rev. B 94, 081105 (2016).

[6] J. Zhang, A.S. Botana et al., Nature Physics 13, 864 (2017).

[7] A.S. Botana, V. Pardo, M.R. Norman, Phys. Rev. Materials 1, 021801(R) (2017).

20 de mayo de 2021, 12:00 h. online

Beyond Topological Quantum Chemistry

Maia G. Vergniory
MPI CPfS (Germany) and DIPC (Spain)

Topological quantum chemistry (TQC) framework has provided a complete description of the universal properties of all possible atomic band insulators in all space groups considering the crystalline unitary symmetries. It links the chemical and symmetry structure of a given material with its topological properties. While this formalism filled the gap between the mathematical classification and the practical diagnosis of topological materials, an obvious limitation is that it only applies to weakly interacting systems. It is an open question to which extent this formalism can be generalized to correlated systems that can exhibit symmetry protected topological Mott insulators of magnetic topological phases. In this talk I will first introduce TQC and its application and then I will address this question by first, extending the formalism to magnetic materials and then combining cluster perturbation theory and topological Hamiltonians within TQC. This simple formalism will be applied to calculate to the phase diagram of a representative model. The results are compared to numerically exact calculations from density matrix renormalization group and variational Monte Carlo simulations together with many-body topological invariants.

[1] M.G. Vergniory et al., A complete catalogue of High Quality Topological Materials , Nature 566, 480-485 (2019); [2] B. Bradlyn et al., Topological quantum chemistry, Nature 547 (7663), 298-305 (2017); [3] Mikel Iraola et al., arXiv preprint arXiv:2101.04135 [4] Dominik Lessnich et al. arXiv preprint arXiv:2103.02624

13 de mayo de 2021, 12:00 h. online

Majorana bound states in topological insulators without a vortex

Jelena Klinovaja
University of Basel, Switzerland

In my talk, I will discuss topological phases in a three-dimensional topological insulator (TI) wire with a non-uniform chemical potential induced by gating across the cross-section [1]. This inhomogeneity in chemical potential lifts the degeneracy between two one-dimensional surface state subbands. A magnetic field applied along the wire, due to orbital effects, breaks time-reversal symmetry and lifts the Kramers degeneracy at zero-momentum. If placed in proximity to an s-wave superconductor, the system can be brought into a topological phase at relatively weak magnetic fields. Majorana bound states (MBSs), localized at the ends of the TI wire, emerge and are present for an exceptionally large region of parameter space in realistic systems. Unlike in previous proposals, these MBSs occur without the requirement of a vortex in the superconducting pairing potential, which represents a significant simplification for experiments. Our results open a pathway to the realisation of MBSs in present day TI wire devices. In the second part of my talk, I will switch from non-interacting systems, in which one neglects effects of strong electron-electron interactions, to interacting systems and, thus, to exotic fractional phases. In particular, I will focus on second-order TIs [2-5] and discuss two-dimensional fractional second-order topological superconductors, hosting zero-energy parafermion corner states.

[1] H. F. Legg, D. Loss, and J. Klinovaja, arXiv:2103.13412

[2] Y. Volpez, D. Loss, and J. Klinovaja, Phys. Rev. Lett. 122,126402 (2019).

[3] C.-H. Hsu, P. Stano, J. Klinovaja, and D. Loss, Phys. Rev. Lett. 121,196801 (2018).

[4] K. Laubscher, D. Loss, and J. Klinovaja, Phys. Rev. Research 1, 032017(R) (2019).

[5] K. Laubscher, D. Loss, and J. Klinovaja, Phys. Rev. Research 2, 013330 (2020).

06 de mayo de 2021, 12:00 h. online

Catching the quantum butterfly: Thermalization and information scrambling on a 53-qubit quantum processor

Xiao Mi
Google Research, Santa Barbara

Over the past decade, rapid progress in quantum engineering has allowed full fabrication and control of superconducting quantum processors with over 50 qubits and full planar connectivity, as exemplified by Googles Sycamore processor. Using random circuits carefully designed to randomly explore the immense Hilbert space with 10^16 dimensions, a bit-string sampling task that proves difficult for classical computation has been recently demonstrated on Sycamore. In this presentation, I will first detail the formulation and execution of the original quantum supremacy experiment. I will then describe current works being done in our group, with a particular emphasis on the efforts to discover useful quantum computing applications in the Noisy Intermediate-Scale Quantum (NISQ) era. As an example, I will present preliminary experimental results on using Sycamore to study the physics of information scrambling and thermalization in quantum circuits that are challenging to analyze or simulate classically.

29 de abril de 2021, 12:00 h. online

Topological Quantum Error Correction: From Theoretical Concepts to Experiments

Markus Mller
RWTH Aachen University and Forschungszentrum Jlich, Germany

To date, the construction of a fault-tolerant quantum computer remains a fundamental scientific and technological challenge, due the influence of unavoidable noise which affects the fragile quantum states. In our talk, we first introduce basic concepts of quantum error correction and topological quantum codes, which allow one to protect quantum information during storage and processing. We then present strategies to detect and fight various sources of errors, including the loss of qubits [1], and present new intriguing theoretical connections between quantum error correction and classical statistical mechanics models and percolation theory [2]. In the final part, I will discuss recent theory work from our group and experimental progress towards fault-tolerant quantum error correction with trapped ions [3,4].

[1] R. Stricker, et al., Nature 585, 207 (2020)

[2] D. Vodola, et al., Phys. Rev. Lett. 121, 060501 (2018)

[3] P. Parrado-Rodrguez et al., arXiv:2012.11366 (2020)

[4] A. Bermudez et al., Physical Review X 7, 041061 (2017)

22 de abril de 2021, 12:00 h. online

Molecule-based magnetic heterostructures for spintronics and quantum computing

Enrique Burzur
Universidad Autnoma de Madrid

Magnetic molecules are versatile building blocks for quantum computing and molecular spintronics. The molecular spin can encode quantum information in Qbits or even perform logic operations as Qgates with unmatched reproducibility and scalability[1]. In spintronics, that same molecular spin could generate spin currents in molecular-based spin filters, switches or spin valves among other applications[2]. However, the positioning of individual molecules into nanoscale devices, together with the typically insulating character of most molecule-based magnetic materials, challenges their implementation in nanoelectronics.

Here I will show how we overcome these limitations by creating heterostructures that combine magnetic molecules with one-dimensional single-walled carbon nanotubes (SWCNT). SWCNTs can act as electrical and mechanical backbones that protect and sense the molecular spin. Besides, they can be used as vessels to deterministically place the molecules in devices. In particular, I will show the encapsulation of spin cross-over (SCO) molecules within the SWCNT and their placement between nanoscale electrodes [3]. The host SWCNT conductance is modified by the spin state of the guest encapsulated molecules. In turn, the confinement experienced by the molecules is translated into the appearance of a large thermal hysteresis in the SCO molecules. Besides, I will show the mechanical bond of magnetic porphyrin macrocycles embracing SWCNTs [4]. I will show how we place these hybrids in superconducting resonators and how, in the future, this configuration may allow to reach a strong spin-photon coupling at the single molecule level.

[1] Leuenberger and Loss, Nature 410, 789 (2001), E. Moreno-Pineda et al., Chem Soc. Rev. 47, 501(2018)

[2] Pal et al., Nat. Commun. 10, 1 (2019)

[3] Villalva et al., Nat. Commun. 2021. DOI: 10.1038/s41467-021-21791-3

[4] de Juan-Fernndez et al., Chem Sci 9, 6779 (2018)

15 de abril de 2021, 12:00 h. online

Andreev bound states: detection and the road towards quantum technologies

Attila Geresdi
Chalmers University

Andreev bound states are the basis of the microscopic picture of the Josephson effect, describing the coupling of two superconductors via a weak link by the formation of localized, single quasiparticle states decoupled from the continuum above the superconducting gap. With the recent improvement of superconductor-semiconductor nanoscale hybrid devices, the readout and manipulation of quasiparticles occupying the Andreev levels became experimentally feasible. In this talk, I will discuss the experimental settings for the measurement of individual Andreev levels in this system. Then, I will provide an overview of the quantum manipulation of the quasiparticle charge and spin, and finally showcase our ongoing efforts towards scalable quantum technologies with Andreev levels.

08 de abril de 2021, 12:00 h. online

Epitaxial growth of 2D materials: Insights from scanning tunneling microscopy

Manuela Garnica
IMDEA Nanociencia

The success of graphene has spurred tremendous expectations and research efforts in the development of novel 2D materials with outstanding properties. A large variety of electronic structures, including band gaps and collective ground states, can be found in the direct analogs of graphene such as its insulating counterpart the hexagonal boron nitride (h-BN) or monolayers of transition-metal dichalcogenides, e.g. MoTe2.

In this talk, I will explore the epitaxial growth of 2D materials and hybrid structures on carefully chosen substrates. The quality of the resulting layers, their physical properties and their interaction with substrates will be examined by high-resolution scanning probe microscopy and first-principle calculations.

25 de marzo de 2021, 12:00 h. online

Scaling silicon-based quantum computers using CMOS technology

Fernando Gonzlez-Zalba
Quantum Motion Technologies

The spins of isolated electrons in silicon are one of the most promising solid-state systems on which to implement quantum information processing. With the recent demonstrations of long coherence times, high-fidelity spin readout, and one- and two-qubit gates, the basic requirements to build a quantum computer have been fulfilled. Now, scaling the technology to a number of qubits sufficiently large to perform computationally relevant calculations is one of the major objectives and several proposals for large scale integration have been put forward.

Recently, important developments in the field of nanodevice engineering have shown that qubits can be manufactured in a similar fashion to field-effect transistors (FET), creating an opportunity to leverage the scaling capabilities of the semiconductor industry to address the challenge. Quantum computing with silicon transistors fully profits from the most established industrial technology to fabricate large scale integrated circuits while facilitating the integration with conventional electronics for fast data processing of the binary outputs of the quantum processor.
In this talk, I will present a series of results on CMOS transistors at milikelvin temperatures that show this technology could provide a platform on to which implement electron-spin qubits. I will specially concentrate on our efforts to develop a qubit specific measurement technique that is accurate and scalable while being compatible with the industrial fabrication processes. With that, I will show the first measurements of an electron spin in a silicon industry-fabricated device and finally, I will present results on how digital and quantum devices can be combined with this technique to time-multiplex the readout of several qubits.

11 de marzo de 2021, 12:00 h. online

Quantum thermoelectrics: using interference, entanglement and non-equilibriumness

Rafael Snchez
Departamento de Fsica Terica de la Materia Condensada, Universidad Autnoma de

Electrons in a conductor react not only to voltage but also to temperature gradients. In their motion, they carry electric charge as well as energy. This makes it possible to think of devices that are absorb excess heat from their environment and convert it into useful power. This can be done in three terminal devices: Two terminals support the charge current with the third one serving as the heat source, enabling the separation of charge and heat flows. Mesoscopic (nanoscale) systems are good candidates for this, because of their high degree of tunability and rich variety of different effects that allow for the mechanism of heat to power conversion: Coulomb interactions [1], resonant tunneling [2], entanglement [3], quantum interference, or the absence of thermalization [4]. I will review recent proposals and experimental implementations of three terminal energy harvesters.

[1] R. Snchez, M. Bttiker, Phys. Rev. B 87, 075312 (2011); H.
Thierschmann et al., Nature Nanotech. 10, 854 (2015); B. Roche et al., Nature Comm. 6, 6738 (2015).
[2] A. N. Jordan, B. Sothmann, R. Snchez and M. Bttiker, Phys. Rev. B 87, 075312 (2013); G. Jaliel et al., Phys. Rev. Let. 123, 117701 (2019).
[3] R. Snchez,P. Burset, and A. L. Yeyati, Phys. Rev. B 98, 241414 (2018).
[4] R. Snchez, J. Splettstoesser and R. S. Whitney, Phys. Rev. Lett. 123, 216801 (2019)

04 de marzo de 2021, 12:00 h. online

Colloidal design: building molecules and materials at the micro- and nanometer scale

Peter Schall
Institute of Physics University of Amsterdam, Netherlands

Recent breakthroughs in the synthesis and design of colloidal building blocks allow the assembly of complex structures with unprecedented control over their architecture. In particular, patchy particles exhibiting highly directional interactions enable the assembly of colloidal molecules, and colloidal graphene, analogues of the atomic compounds at the colloidal scale. Such assembly control promises fascinating applications in the design of new functional materials at micrometer and nanometer length scales. In this talk, I will show how the combination of patchy particles and solvent-mediated interactions enables new control in the directional bonding that can be explored to build colloidal molecules and investigate their assembly kinetics and reactions. Using tetramer particles, we assemble colloidal analogs of well-known sp3-hybridized carbon compounds such as (cyclo)butane, butyne, cyclopentane, and cyclohexane, and investigate their transition states. Adsorbed at an attractive substrate, these particles assemble into two-dimensional materials such as graphene. This control applied to the nanoscale can assemble quantum dots, leading to new electronic states useful for active films in optoelectronic devices. These results demonstrate the opportunities for applications and exciting new science that can be explored with these novel colloidal architectures.

25 de febrero de 2021, 12:00 h. online

Evolution in uses of Antimony: from ancient Egyptian queen make-up to new 2D-materials

Flix Zamora
Departmento de Qumica Inorgnica, Institute for Advanced Research in Chemical Sciences (IAdChem), and Condensed Matter Physics Center (IFIMAC), Universidad Autnoma de Madrid.

In the search for 2D semiconductor materials, our research group and others have recently pointed out that antimonene, i.e. single or few-layer antimony, can be an interesting option. This seminar will aim to provide a perspective revision of our results on antimonene. I will describe several preparation methods developed in our group to prepare this material, going from top-down procedures, such as micromechanical exfoliation, which allows the isolation of monoatomic layers, or liquid phase exfoliation, to bottom-up synthesis that provides a way to produce large quantities of high-quality few-layer antimonene. Some selected physical and chemical properties found for the isolated antimonene materials will be discussed. Finally, I will show the first results obtained in the exfoliation of 3D covalent crystals, alpha-germanium, which opens new avenues for the 2D-materials.

18 de febrero de 2021, 12:00 h. online

Unconventional superconductivity in two-dimensional Van der Waals materials

Miguel M. Ugeda
Donostia International Physics Center (DIPC), Paseo Manuel de Lardizbal 4, 20018 San Sebastin, Spain.

Van der Waals materials provide an ideal platform to explore superconductivity in the presence of strong electronic correlations, which are detrimental of the conventional phonon-mediated Cooper pairing in the BCS-Eliashberg theory and, simultaneously, promote magnetic fluctuations. Despite recent progress in understanding superconductivity in layered materials, the glue pairing mechanism remains largely unexplored in the single-layer limit, where electron-electron interactions are dramatically enhanced. In this talk, I will present experimental evidence of unconventional Cooper pairing mediated by magnetic excitations in monolayers of Se-based transition metal superconductors (NbSe2 and TaSe2), two model strongly correlated 2D materials. 2D TMD materials will reduce the enormous complexity associated with the investigation of unconventional superconductivity, and will rapidly allow us to expand our current limited knowledge of non-phononic Cooper pairing. They offer unprecedented simplicity for modelling as compared to the most studied bulky unconventional superconductors, i.e., cuprates, Fe-pnictides and heavy-fermion compounds. In two dimensions, TMD superconductors are even simpler to model than twisted bilayer graphene, where superconductivity is intrinsically linked to specific magic angles. From the experimental point of view, our work opens the tantalizing possibility to explore unconventional superconductivity in simple, scalable and widely accessible 2D materials.

11 de febrero de 2021, 12:00 h. online

From Andreev to Majorana bound states in hybrid superconductor semiconductor nanowires

Elsa Prada
Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC)

Electronic excitations above the ground state must overcome an energy gap in superconductors with spatially-homogeneous s-wave pairing. In contrast, inhomogeneous superconductors such as those with magnetic impurities or weak links, or heterojunctions containing normal metals or quantum dots, can host subgap electronic excitations that are generically known as Andreev bound states (ABSs). With the advent of topological superconductivity, a new kind of ABS with exotic qualities, known as Majorana bound state (MBS), has been discovered. In this talk, I will focus on hybrid superconductor-semiconductor nanowires as one of the most flexible and promising experimental platforms to study ABSs and MBSs. I'll discuss how the combined effect of spin-orbit coupling and Zeeman field in these wires triggers the transition from ABSs into MBSs. I'll show theoretical progress beyond minimal models in understanding experiments, including the possibility of a type of robust zero mode that may emerge without a band-topological transition, called quasi-MBS or non-topological MBS in the field. Finally, I'll discuss the role of spatial non-locality, a special property of MBS wavefunctions that, together with non-Abelian braiding, is the key to realizing topological quantum computation. This work has been recently published as a review in: Nature Reviews Physics 2, 575 (2020)

04 de febrero de 2021, 12:00 h. online

Quantum simulations of condensed matter systems with quantum technologies

Lucas Lamata
Universidad de Sevilla

In this talk I will review recent research on quantum simulations of condensed matter systems with quantum controllable platforms, including trapped ions and superconducting circuits. Among others, we will describe efficient quantum algorithms for simulating fermionic systems in two and three spatial dimensions, as well as proposals for the quantum simulation of the quantum Rabi and Dicke models with analog and digital-analog quantum simulators.

28 de enero de 2021, 12:00 h. online

Toroids, Active Nematics and Topological Defects

Alberto Fernandez-Nieves
Department of Condensed Matter Physics, University of Barcelona ICREA - Instituci Catalana de Recerca i Estudis Avanats, Barcelona

We will discuss recent results with active nematics confined to either toroidal space. We will first review how we make and stabilize non-spherical droplets and describe how curvature affects defect arrangement on tori. We will show that despite the intrinsic activity and out-of-equilibrium character of the system, there are still remnants of the expected curvature-induced defect unbinding predicted for nematics in their ground state. Activity, however, augments the behavior leading to unexpected defect distributions. We will then focus on defect orientation and show that on flat space, there is short-range orientational correlations without long-range orientational order.

21 de enero de 2021, 12:00 h. online

Iron-based superconductors Materials, magnetism and tuning methods

Anna Bhmer
Ruhr-University Bochum

Iron-based superconductors represent a second class of high-temperature superconductors after the copper oxides. As they enter their second decade, the large variety of their chemical structures, modes of magnetic ordering and the methods available to tune their properties are all the more appreciated. As with many unconventional superconductors, their magnetic order needs to be suppressed for superconductivity to appear. I will present an overview of the magnetism in several of these iron-based materials and the methods to suppress, or tune, it. Magnetism is particularly strongly coupled to the crystal lattice, which makes structural tuning parameters interesting. I will also discuss some of the other surprising effects that arise from this close interaction of structure, magnetism and superconductivity. Comparing diverse materials and their properties helps us understand some of the common principles within this class of unconventional superconductors.

14 de enero de 2021, 12:00 h. online

Straintronics with 2D materials

Andrs Castellanos

Strain engineering is an interesting strategy to tune a materials electronic properties by subjecting its lattice to a mechanical deformation. Conventional straining approaches, used for 3D materials (including epitaxial growth on a substrate with a lattice parameter mis-match, the use of a dielectric capping layer or heavy ions implantation) are typically limited to strains lower than 2% in most cases due to the low maximum strains sustained by brittle bulk semiconducting materials. Bulk silicon, for example, can be strained only up to 1.5% before breaking. Moreover, these straining approaches induce static deformations of the semiconductor materials and therefore they are not suitable for tunable functional devices.2D materials can be literally stretched, folded, bent or even pierced. [1] This outstanding stretchability (and the possibility of using dynamically varying strain) of 2D materials promises to revolutionize the field of strain engineering and could lead to "straintronic" devices devices with electronic and optical properties that are engineered through the introduction of mechanical deformations.In this talk I will discuss our recent efforts to study strain engineering in 2D materials and to exploit it to fabricate strain tunable functional optoelectronic devices. [2-7].This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement n 755655, ERC-StG 2017 project 2D-TOPSENSE). ACG acknowledge funding from the EU Graphene Flagship funding (Grant Graphene Core 2, 785219).[1] Roldn et al. Journal of Physics: Condensed Matter (2015) 27 (31), 313201[2] A. Castellanos-Gomez, et al. Nano letters (2013) 13 (11), 5361-5366[3] J. Quereda, et al. Nano letters (2016) 16 (5), 2931-2937[4] J.O. Island, et al. Nanoscale (2016) 8 (5), 2589-2593[5] R. Schmidt et al. 2D Materials (2016) 3 (2), 021011[6] R. Frisenda, et al. npj 2D Materials and Applications (2017) 1 (1), 10[7] P. Gant, et al. Materials Today (2019)

17 de diciembre de 2020, 12:00 h. online

Mechanics of 2D materials

Cristina Gmez-Navarro
IFIMAC, Departamento de Fsica de la Materia Condensada, UAM

IFIMAC+ICMM Joint Seminar Series Condensed Matter @Cantoblanco -- Online event, for abstract and information see https://sites.google.com/view/ifimac-icmm-joint-seminars/home

10 de diciembre de 2020, 12:00 h. online

Twisted layers, narrow bands, and new phases in two dimensional materials

Francisco Guinea
IMDEA Nano & Donostia International Physics Center

IFIMAC+ICMM Joint Seminar Series Condensed Matter @Cantoblanco -- Online event, for abstract and information see https://sites.google.com/view/ifimac-icmm-joint-seminars/home

03 de diciembre de 2020, 12:00 h. online

Manipulating Light and Matter in van der Waals-bonded Semiconductors

Stephane Kena-Cohen
Polytechnique Montral

IFIMAC+ICMM Joint Seminar Series Condensed Matter @Cantoblanco -- Online event, see https://sites.google.com/view/ifimac-icmm-joint-seminars/home


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