MPSD Seminar

18880 1559038731

Electrical control of quantum spins

Magnetic fields are challenging to localise to short length scales because their sources are electrical currents. Conversely, electric fields can be applied using electrostatic gates on scales limited only by lithography. This has important consequences for the design of spin-based information technologies: while the Zeeman interaction with a magnetic field provides a convenient tool for manipulating spins, it is difficult to achieve local control of individual spins on the length scale anticipated for useful quantum technologies. This motivates the study of electric field control of spin Hamiltonians [1]. Mn2+ defects in ZnO exhibit extremely long spin coherence times and a small axial zero-field splitting. Their environment is inversion-symmetry-broken, and the zero-field splitting shows a linear dependence on an externally-applied electric field. This control over the spin Hamiltonian offers a route to controlling the phase of superpositions of spin states using d.c. electric field pulses, and to driving spin transitions using microwave electric fields [2]. Experiments on Mn defects in ZnO provide insights into how to achieve manipulation of individual spins on surfaces using a scanning tunnelling microscope. A high-frequency voltage applied to the tip can drive electron spin resonance in Fe atoms on MgO surfaces via modulation of the crystal field experienced by the Fe atom [3]. It has been proposed theoretically that frustrated exchange-coupled molecular clusters might offer sensitivity to externally-applied electric fields [4]. Experiments on an antiferromagnetically-coupled Cu3 compound reveal a small linear electric field effect. A comparable sensitivity is exhibited by the heterometallic S = 1 antiferromagnetic ring Cr7Mn, but no effect is found for the S = 1/2 Cr7Ni [5]. [mehr]

MPSD Seminar

18182 1553856301

Many-body dynamics in pump and probe experiments: From light amplification to terahertz STM

I will discuss new theoretical approaches for analyzing pump and probe experiments in solid state systems. The focus will be on combining theoretical techniques from condensed matter physics and quantum optics. Several examples will be discussed, including light amplification in photo-excited superconductors and insulators, ultrafast molecular dynamics in terahertz-STM experiments. [mehr]

MPSD Seminar

15742 1539615484

Elisa Palacino Gonzalez - Molecular Photodynamics of Open Quantum Systems. Simulation of Nonlinear Optical Spectroscopies using Nonperturbative Approaches

The theoretical description of nonlinear optical spectroscopy has traditionally been laid in the framework of perturbation theory. Within this formalism, an intuitive approach to the understanding of the dynamics of a molecular system excited by several external laser pulses is based on the concept of nonlinear response functions. However, as the system complexity increases or nontrivial dynamic effects have to be taken into account (nonadiabatic interstate couplings, bath-induced relaxation) the perturbative approach becomes computationally expensive. To tackle this scenario nonperturbative approaches based on the numerically exact solution of quantum equations of motions have been developed. [mehr]

MPSD Seminar

15741 1539608230

Michael Bonitz - Femtosecond electron dynamics in strongly correlated finite systems

[mehr]

MPSD Seminar

14290 1528280544

Workshop on Open Access Publishing

How can you publish via Open Access journals and boost your citations? What are GOLD and GREEN Open Access? Which science journals have Open Access or reduced fee agreements with the Max Planck Society? These and many other questions will be answered at this two-hour workshop. Open to all. To register, please mail jenny.witt@mpsd.mpg.de. [mehr]

Disputation

14161 1526643739

Atomically resolved dynamics of correlated quantum systems

[mehr]

MPSD Seminar

13735 1523627150

A New Room Temperature Multiferroic in the Bi-Fe-O System

Multiferroic materials, which exhibiting simultaneously two or more coupled ferroic orders, are attracting extensive research interest mainly due to their promising device applications in low power electronics and the exotic physics involved. Despite the fact that an increasing number of multiferroics have been identified through two decades of diligent and creative studies, their low transition temperature or small magnetoelectric coupling strength has hindered direct device applications. Searching for materials with room-temperature ferroelectricity, a large enough magnetization and coupling between these two is still the Holy Grail for fundamental condensed matter research. In this talk, I will report a novel room temperature multiferroic in the Bi-Fe-O system. The material is comprised of a hitherto-unexplored, hexagonal crystalline structure with Bi2O3 layers separated by γ-Fe2O3 blocks, which blends the excellent ferroelectric and ferrimagnetic performances of BiFeO3 and γ-Fe2O3 together to form an exotic multiferroic material with ferroelectric and ferrimagnetic transition temperature of above 760 K and 600 K, respectively. A combination of experimental and theoretical studies reveals that the polar state stems from the two dissimilar Bi sites and extends further into oxygen ions with the exquisitely modulated structure. This finding identifies a novel strategy for the realization of high-temperature multiferroicity and paves the pathway for the realization of practical room temperature magnetoelectric devices. [mehr]

MPSD Seminar

MPSD Seminar

13446 1522938563

Liquid-Phase Electron Microscopy of Cells and Nanomaterials in Liquid

Transmission electron microscopy (TEM) has traditionally been associated with the study of thin solid samples in vacuum. With the availability of reliable thin membranes of silicon nitride, TEM of liquid specimens has become accessible with nanoscale resolution in the past decade [1]. The usage of scanning transmission electron microscopy (STEM) presents a novel concept to study membrane proteins within whole mammalian cells in their native liquid environment [2]. The cells in liquid are placed in a microfluidic chamber enclosing the sample in the vacuum of the electron microscope, and are then imaged with STEM. It is not always necessary to enclose the cells in the microfluidic chamber. For many studies, it is sufficient to obtain information from the thin outer regions of the cells, and those can be imaged with high resolution using environmental scanning electron microscopy (ESEM) with STEM detector [3]. A third option is to cover a liquid specimen under a thin membrane of graphene providing the thinnest possible layer [4]. Liquid STEM was used to explore the formation of HER2 homodimers at the single-molecule level in intact SKBR3 breast cancer cells in liquid state [3]. HER2 is a membrane protein and plays an important role in breast cancer aggressiveness and progression. Data analysis based on calculating the pair correlation function from individual HER2 positions revealed remarkable differences its functional state between rare- and bulk cancer cells with relevance for studying the role of cancer cell heterogeneity in drug response. We discovered a small sub-populations of cancer cells with a different response to a prescription drug [5]. Liquid STEM was also used to explore the behavior of nanoparticles in liquid in time-lapse experiments. It was discovered that nanoparticle movement in close proximity of the supporting silicon nitride membrane was three orders of magnitude slower than what was expected on the basis of Brownian motion for a bulk liquid [6], pointing to the existence of a layer of highly ordered liquid at the membrane. References [1] de Jonge, N. and Ross, F.M. Nat. Nanotechnol., 6, 695-704 (2011) [2] de Jonge, N., et al. Proc. Natl. Acad. Sci., 106, 2159-2164 (2009) [3] Peckys, D.B., et al. Sci. Adv., 1, e1500165 (2015) [4] Dahmke, I.N., et al. ACS Nano, 11, 11108-11117 (2017) [5] Peckys, D.B., et al. Mol. Biol. Cell, 28, 3193-3202 (2017) [6] Verch, A., et al. Langmuir, 31, 6956–6964 (2015) [mehr]

MPSD Seminar

13505 1522938489

Sub-optical-cycle control of light and matter

[mehr]

MPSD Seminar

13503 1522937711

Slow-Electrons Interacting with Light and Matter

[mehr]

MPSD Seminar

12449 1515660508

Takashi Oka - Applied Floquet engineering

[mehr]

MPSD Seminar

12436 1515576330

Mitsuharo Uemoto - TDDFT+Maxwell multiscale method for lightpropagation calculation in semiconducting media

[mehr]

 
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