Photoexcitation spectroscopy of cold molecules in the Cryogenic Storage Ring “CSR”
The Cryogenic Storage Ring (CSR) [1] located at Max-Planck-Institut für Kernphysik in Heidelberg,Germany is an ideal experimental setup to perform collision studies of photons and cold electrons as well neutrals with the stored molecular ions of kinetic energies between 20-300 keV. The circumference of the ring is 35 m and being fully electrostatic, it has no mass limit for stored ions. The cryogenic temperature of about 6 K offers unique storage capabilities in extremely high vacuum conditions of below 140 rest-gas particles per cm3 and almost vanishing blackbody radiation. An electron cooler(ecool) is installed in one straight section of the CSR which uses a photocathode to produce cold electrons. These cold electrons can further reduce the momentum spread of the stored ion beam upon interaction. A tunable optical parametric oscillator (OPO) laser system in the same section allows photon interaction studies from the ultraviolet (225 nm) to the infrared (2600 nm) regime. The CSR is equipped with two independent ion source platforms, which can deliver ions up to an energy of 60 and 300 keV per charge state, respectively. The low energy platform can be used to produce neutral beams by photodetachment of the negative ions. Whereas the 300 kV platform presently contains a metal ion sputter source, a Penning source and an electron cyclotron resonance source; extension by a laser vaporization and an electrospray ionization ion source is in progress. The entire facility enables to perform photodissociation, electron-ion recombination, and ion-atom interaction studies with ro-vibrationally cooled stored positive and negative ions as well as clusters and highly charged ions. Further experiments aim to study decay rates of metastable ions and radiative lifetimes. The first experimental results,machine characteristics as well as future experimental possibilities of this unique infrastructure will be discussed [2, 3].
References
R. von Hahn, et al., Rev. Sci. Instrum.87, 063115 (2016).
A. O’ Connor, et al., Phys. Rev. Lett.116, 113002 (2016).
C. Meyer, et al., Phys. Rev. Lett.119, 023202 (2017).
12/01/2018 at 11:00 am
Dr. Deepak Kar, University of Witwatersrand, Johannesburg
Tutorial
IOP Lecture Hall
Document Date:
Hand-on introduction to Monte Carlo generators and Rivet
In search of Quantum Spin Liquid: A microscopic insight
Abstract
Competing exchange interactions in frustrated systems often responsible for a large degeneracy in the ground state and in some conditions a novel state of matter called “spin liquid” emerges where spins are highly correlated and fluctuates down to low temperatures. A very few candidate quantum spin liquid (QSL) materials proposed over the last decade bear key experimental signatures of this exotic state, including persistent spin dynamics and the absence of long-range order within the experimentally accessible temperature range. Kitaev model with anisotropic interactions on the honeycomb lattice offers an exact solution for the QSL state and expands the grounds for the QSL search from purely isotropic models to systems with strong magnetic anisotropy. There are few candidate materials where the evidence of Kitaev exchanges have been found but these materials undergoes a long range magnetic ordering because of the presence of non-negligible exchanges other than the Kitaev type exchange. Tuning the ground state of these Kitaev systems might be an ideal route to stabilize a QSL state by the application of magnetic field and external pressure. I will be discussing about my journey in the field of these Kitaev systems where we tried to stabilize a QSL state by applying magnetic field and pressure. Furthermore, we also looked for other crystallographic structure which can have QSL state with the presence of Kitaev exchange. All the evidences are mainly based on local techniques (Nuclear Magnetic Resonance (NMR) and Muon Spin Resonance (μSR)) as bulk techniques are quite inadequate in addressing the actual behavior of such complex states.
08/01/2018 at 4:00 pm
Sakshath S., TU Kaiserslautern, Germany
CMP Seminar
IOP Lecture Hall
Document Date:
Ultrafast demagnetisation dynamics in multicomponent systems
Ultrafast demagnetisation dynamics in multicomponent systems
Abstract
Excitation of multi-component materials by femtosecond laser pulses reveals interesting transient states.Using layer and element sensitive time-resolved magneto-optical Kerr effect in the pump-probe configuration,we evaluate the effect of fundamental parameters such as exchange interaction and spin currents on subpicosecond dynamics of magnetisation in exemplary systems: (i) Copper-doped ferromagnetic alloys and,(ii)Ni films deposited on gold underlayers.
In Copper-doped NiFe,we observe an anomalous speed-up of dynamics as the copper concentration is increased beyond 20%,contrary to expectations.Our analysis shows that this is due to the suppression of Nimoments stronger than Femoments in the alloy. We also show experimentally, the sudden reduction of the demagnetisation time constantat highpump fluences that was only theoretically predicted.In case of Ni films deposited on gold,we show that laser excitation of the ferromagnetic film causes a transient magnetic moment in the non-magnetic layer. We quantify the so far elusive amount of spin injection and thus the spin injection efficiency at the interface.
