# Presentation: 546442

## Carrier and Spin Dynamics in InSb- and InMnSbBased Heterostructures,  Giti Khodaparast, Virginia Tech, DMR 0507866 

**The samples for this projects are provided by groups of Prof. Furdyna****,**** University of Notre Dame and Prof.**** Santos****,**** University of Oklahoma.**

-  Recently, there has been much interest in developing and exploring spin based semiconductor devices
- and phenomena.  In the last decade, semiconductor based spintronics has achieved remarkable success
- following the trend of metal based spintronics such as giant magneto resistance (GMR) effects used in hard disks. Semiconductor spintronics has advantages, over other material systems, in logic, storage, communications, and quantum computation.
- The goals of our activities have been to characterize and manipulate spin flip, spin precession, and magnetic ordering in a series of narrow gap semiconductors using several time-resolved magneto-optical techniques.

**Spin flip**
**    ****Fast**

**Spin precession **
**   ****Long lifetime**

**Magnetic ordering**
**     ****Nonvolatile**

- As part of our activities, we have shown **(K. Nontapot *****et al., APL, 90, 143109)**** *that photo-induced carrier density
-    can be used to control the spin relaxation lifetime.

**Magneto Optical Kerr Effect (MOKE) and Differential Reflectivity (********R/R) are plotted as a function of time for one InMnSb ferromagnetic structure. MOKE signal represents spin relaxation time and ********R/R, the photo-induced carrier relaxation time. In the measurements presented in Fig. 1 the photo-induced carrier density is a factor of 100 lower than the experimental data on the same sample presented in Fig. 2. A faster relaxation is observed in the presence of large photo-induced carrier density in Fig. 2 [data is shown for room temperature (RT) and 77 K and for clarity for two different circular polarity of pump beams] . ****This effect can be important in device applications to alter spin relaxation in situ.**

**Fig. 1**

**Fig. 2**

**Notes:**
We use semiconductors in electronic or opto-electronic devices such as transistors, lasers, and computers. The functionality of current conventional semiconductor based devices is mainly on the basis of manipulating charges (positive or negative). Carriers, in addition to their charges, have another identity which is called spin (it  can be up or down); therefore, by using the spin in addition to the charge we can reach to a new level of functionality in devices with more degrees of freedom. In order to make devices on the basis of both charge and spin, it is important to understand how these two identities interact with their host materials and the external fields such as light and magnetic field.
Part of our activities is focused to understand properties of carriers and spins in “Narrow Gap Semiconductors (NGS)”. NGS have several unique properties including high carrier mobility ( important for device applications). We successfully measured the carrier and spin life times in these materials which are important parameters to develop concepts for spin based device applications. We have shown optical control of spin relaxations as a function of photo-induced carrier density using time resolved optical techniques.

## Giti Khodaparast, Virginia Tech, DMR 0507866 Group of Prof. Khodaparast at the Physics Department,Virginia Tech.

**               ****Sponsored by NSF** **DMR-0507866**
**Undergraduate summer research was supported by**
**                        ****NSF-REU supplement.**

***Educational activities:*** One post doctoral associate, two grad-students,*  *three under-grads and a high school student have been involved in different aspects of this project. One of the under-grads, Brett Spencer, has joined the University of Arizona as a grad-student. Dr. Rajeev Kini, a post doctoral associate has taken a position at the National Renewal Energy Laboratory, Golden Colorado.
***Outreach: ***Starting lectures on nano-science and nano-technology at the Roanoke Governor’s school this fall. Students from several remote districts attend this school to take their math and science classes. In concert with these lectures, internet-based tutorials** **will be developed** **that can be accessed not only by high school students but also by learners and educators who do not have access to
- the traditional university system.

- One high school student, Ashley Aissis, is setting up a photoluminescence measurement.