Xincheng Wang

Transition from mott insulator to superconductor in GaNb4Se8 and GaTa4Se8 under high pressure

Electronic conduction in GaM4Se8 (M=Nb,Ta) compounds with the fcc GaMo4S8-type structure originates from hopping of localized unpaired electrons (S=1 / 2) among widely separated tetrahedral M4 metal clusters. We show that under pressure these systems transform from Mott insulators to a metallic and superconducting state with T(C)=2.9 and 5.8 K at 13 and 11.5 GPa for GaNb4Se8 and GaTa4Se8, respectively. The occurrence of superconductivity is shown to be connected with a pressure-induced decrease of the MSe6 octahedral distortion and simultaneous softening of the phonon associated with M-Se bonds.

Projectile coherence effects in single ionization of helium

We have measured fully differential cross sections for ionization of He by 3 MeV proton impact. A projectile beam with a coherence length larger than typical atomic scales was prepared at the Test Storage Ring taking advantage of electron cooling. Pronounced effects due to the projectile coherence are observed which are absent for an incoherent 100 MeV u−1 C6 + projectile beam and the present data are in much better agreement with theory. Thus, these results represent a major advancement in resolving the so far unexplained discrepancies between experiment and theory for the 100 MeV u−1 C6 + case.

Initial-state selective study of ionization dynamics in ion-Li collisions

Kinematically complete experiments were performed on the ionization of a laser-cooled lithium target from different initial states, Li(2s), Li(2p) and Li(1s), by 6 MeV H+ and 1.5?MeV?amu?1 O8 + impact. In the measured doubly differential cross sections as a function of electron energy and transverse momentum transfer, a significant initial state dependence is found. Furthermore, comparison to quantum mechanical theory shows surprising discrepancies for Li(2s) and Li(1s) while there is good agreement for the Li(2p) initial state.

Ion-Li collision dynamics studied with a MOTReMi

In a novel experimental approach a magneto-optical trap (MOT) is combined with a Reaction Microscope (ReMi) and implemented in an ion storage ring. Single ionization measurements were performed with 24 MeV O8+ and 6 MeV H+ projectiles and a state prepared lithium target. We obtained single-, double- and fully differential cross sections and observed features that we attribute to the structure and polarization of target initial states.

Kinematically complete measurements for electron capture in collision of keV energy ions with atomic and molecular targets

We have performed a kinematically complete experiment to obtain sub-shell resolved differential cross sections for electron capture from inert gas targets in collisions with keV energy singly and doubly charged ions. Measurements were done for single and double capture and transfer ionization using a reaction microscope.

Kinematically Complete studies on Mutual Projectile and Target Ionization

Mutual projectile and target ionizations (MPTI) of 1MeV/amu N4+ and N5+ +He collisions have been studied in kinematically complete experiments, the data is presented in four-particle (4-D) Dalitz plots. comparison to eikonal approximation (EA) calculation results shows qualitatively good agreement.

Few-Body Dynamics studied with the In-Ring Reaction Microscope at the TSR of MPIK

A Reaction Microscope was implemented into the ion storage ring TSR. Experiments have been performed studying the collision dynamics in ionization and electron loss in ion-atom collisions. An additional MCP detector was inserted, aiming to detect photons in coincidence emitted in processes such as radiative electron capture.