Condensed Matter Physics
About the Condensed Matter Physics Group
Faculty: Beach, Gladden, Ostrovskii
The research is in the field of Physics of Solids, which is a contemporary multi-area discipline. More specifically, experimental and theoretical investigations of acoustically stimulated nonlinear phenomena in real crystals are performed. So called real crystalline solids have different point and extended structural defects like interstitial atoms and vacancies, dislocations, internal boundaries, etc. When a finite amplitude acoustic wave propagates in such a medium, there is an interaction between ultrasound on one hand and crystal lattice and charge carriers on the other hand. As a result, the properties of a real crystal are altered, and new physical phenomena can occur.
Examples
1) Crystal defect manipulation – this is a new direction in physics of solids and semiconductor physics. It is frequently referred as “defect engineering”. One of the applications is to decrease a negative effect of crystal defects on some basic crystal properties, which looks like “crystal healing”.
2) Sonoluminescence of crystals (luminescence of solids induced by ultrasound) is the phenomenon of energy conversion from ultrasound to light, which takes place in real (not ideal) crystal only.
3) Acoustic memory in ferroelectric materials (like LiNbO3) is a recent discovery. The ferroelectric sample stores ultrasound about 100 μsec and then re-emits it. The physical nature of this effect is not established yet, but there is evidence that it is connected to the ferroelectric domain structure of a real piezoelectric solid.
Areas of Research in the Laboratory
Crystal defect manipulation in cesium iodide
Cesium iodide (CsI) single crystal is a basic material for the detectors of nuclear radiation. Different kinds of high-energy radiation including particles and a gamma-radiation produce intensive luminescence from the CsI single crystals. This light is then detected by silicon-based photoelectric detectors, which are placed on a top crystal surface. Intense nuclear radiation produces damage of the crystal lattice and decrease an optical transparency of CsI, which in turn affects the sensitivity and noise level of the detector as a whole. Hence, radiation-damaged scintillating CsI crystal detectors would significantly affect the accuracy, reliability, and sensitivity of High Energy Physics experiments.
What is unknown: The loss of optical transparency due to radiation defects was measured in some laboratories, mainly as the statistical data only. The physical properties of the radiation defects in CsI have not been investigated so far (atomic configurations of the defects, optical properties, mechanism of defect generation, and especially time evolution and conformational changes under various external influences).
Our research aims to explore all main physical properties of the radiation defects formation, their atomic configurations, altering of crystal optical properties, and evolution of defect structure under external influences including ultrasound and temperature. New technique of “Ultrasonic Defect Manipulation” is supposed to be developed to reduce radiation damage.
Acoustic waves in ferroelectric solids with nano-structures
The research is in the field “Structural Properties of Solids” with emphasis on nano-structures. It exploresnovel phenomena involving ultrasound propagation in real ferroelectric crystals with nano-size ferroelectric structures. The new effect of acoustic memory, consisting in storage of acoustic energy inside lithium niobate, is under investigation in detail.
By using fundamental results of this research, experimental tools to characterize and measure nano-structures in ferroelectric media will be developed.
Possible applications of nano-structured ferroelectric materials based on LiNbO3, LiTaO3, etc., comprise mobile communication (acousto-electric high-frequency filters), military applications as electronic coding-decoding devices (convolution by surface acoustic waves), telecommunications industry (ferroelectric ultrasonic RF-filters), medical therapeutic devices (ultrasonic heads), digital technologies and computers (new ferroelectric memory cells and nano-sized capacitors), next generation of mobile communication (cell phones operating at ≥2.4 GHz: RF-filters on surface acoustic waves), quantum electronics (optical harmonic generation).