Safi Ullah Khan

Hybridization effects on wave packet dynamics in topological insulator thin films

Theoretical study of electron wave packet dynamics in topological insulator (TI) thin films is presented. We have investigated real space trajectories and spin dynamics of electron wave packets in TI thin films. Our focus is on the role of hybridization between the electronic states of the two surfaces. This allows us to access the crossover regime of a thick film with no hybridization to a thin film with finite hybridization. We show that the electron wave packet undergoes side-jump motion in addition to zitterbewegung. The oscillation frequency of zitterbewegung can be tuned by the strength of hybridization, which in turn can be tuned by the thickness of the film. We find that the spin expectations also exhibit zitterbewegung tunable by hybridization. We also show that it is possible to obtain persistent zitterbewegung, oscillations which do not decay, in both the real space trajectories as well as spin dynamics. The zitterbewegung oscillation frequency in TI thin films falls in a parameter regime where it might be possible to observe these effects using present day experimental techniques.

Gains and Costs Associated with Resumption of SSFs with Stringent Regulations: A Modified Approach

To curb the negative effects of Global Financial Crisis (GFC) in 2008, the regulatory bodies of Pakistan Stock Exchange (PSX) banned trading in the stock market. Trading in several financial instruments suffered due to this unavoidable situation. On the recommendations of CFS MK II review committee, trading in futures markets were also halted. As the situation got better, trading in the stock market resumed. With this, trading in Single Stock Futures (SSFs) resumed on July 27, 2009 with stringent regulatory requirements than before. This situation makes it important to investigate the role of newer SSFs with stringent regulations. This study investigates the stakeholders’ claims on destabilizing ability of futures markets in this crucial stage. This is done by examining the impact of resumption of trading in SSFs contracts with stringent regulations on the market efficiency and volatility of the stock prices of the underlying counterparts. The results of this study do not present any significant change in the market efficiency and volatility of SSFs’ underlying stocks and Non-SSFs’ stocks. This study has two implications. First, the SSFs did not play any part in destabilization of Pakistan’s Stock market during GFC. Second, the stringent regulations have helped mitigate the destabilizing ability of futures markets in Pakistan.